Acetaldehyde scavengers for poly(ethylene terephthalate) : chemistry of reactions, capacity, and modeling of interactions

Transcription

1 The University of Toledo The University of Toledo Digital Repository Theses and Dissertations 2010 Acetaldehyde scavengers for poly(ethylene terephthalate) : chemistry of reactions, capacity, and modeling of interactions Brent A. Mrozinski The University of Toledo Follow this and additional works at: Recommended Citation Mrozinski, Brent A., "Acetaldehyde scavengers for poly(ethylene terephthalate) : chemistry of reactions, capacity, and modeling of interactions" (2010). Theses and Dissertations This Dissertation is brought to you for free and open access by The University of Toledo Digital Repository. It has been accepted for inclusion in Theses and Dissertations by an authorized administrator of The University of Toledo Digital Repository. For more information, please see the repository's About page.

2 A Dissertation entitled Acetaldehyde Scavengers for Poly(ethylene terephthalate): Chemistry of Reactions, Capacity, and Modeling of Interactions by Brent A. Mrozinski Submitted to the Graduate Faculty as partial fulfillment of the requirements for the Doctor of Philosophy Degree in Engineering Dr. Saleh A. Jabarin, Committee Chair Dr. Dong-Shik Kim, Committee Member Dr. Yong-Wah Kim, Committee Member Dr. Steven E. LeBlanc, Committee Member Dr. Arunan Nadarajah, Committee Member Dr. Patricia R. Komuniecki, Dean College of Graduate Studies The University of Toledo December 2010

3 Copyright 2010, Brent A. Mrozinski This document is copyrighted material. Under copyright law, no parts of this document may be reproduced without the expressed permission of the author.

4 An Abstract of Acetaldehyde Scavengers for Poly(ethylene terephthalate): Chemistry of Reactions, Capacity, and Modeling of Interactions by Brent A. Mrozinski Submitted to the Graduate Faculty as partial fulfillment of the requirements for the Doctor of Philosophy Degree in Engineering The University of Toledo December 2010 During the melting and processing of poly(ethylene terephthalate) (PET), degradation of the material may occur. One of the more common degradation products is acetaldehyde (AA). Due to its low boiling point, 21 o C, AA is able to diffuse out of PET and into either the atmosphere or the packaged contents of the PET container. The diffusion of AA into packaged contents is of concern, because many food products have a limited threshold for the sweet, fruity taste and odor of AA. One of the ways to limit the AA affects is through the addition of AA scavenging agents. While these additives do not limit the generation of AA; they are designed to interact with and reduce the amount of AA that can be release from PET articles. The purpose of this study was not only to study these AA and AA scavenger interactions and quantify their abilities in reducing AA concentrations in PET; it was also to develop an initial model to predict effectiveness of adding AA scavengers to multi-cavity PET injection molding systems. Through this work, it was determined that anthranilamide and meta-xylenediamine (MXDA) reduce AA concentrations in PET by means of a reaction mechanism. Alpha-cyclodextrin, however, scavenges AA through a hydrogen iii

5 bonding/size-enclosing scheme. Regardless of the mechanism, it was proven that these three scavengers are capable of reducing detectable AA concentrations in PET. It was generally found that the greater the AA scavenger concentration, the great the effect. Additionally, the changes in the physical properties of PET due to AA scavenger addition were studied. It was shown that melt-blending these additives into PET could adversely affect the intrinsic viscosity (I.V.) and color of the PET blend resin and/or container. The thermal properties and oxygen permeation of PET were not affected by AA scavenger addition. The modification of an existing multi-cavity injection molding program was applied to account for the addition of AA scavengers, to PET resin, when predicting the accumulation of AA within PET preforms. The approach to modify this original program and methodologies to quantify the appropriate kinetic terms has been described in detail. Finally, the modified simulation program was then used to predict the effectiveness of various AA scavenger/pet blends in reducing detectable AA concentrations in PET preforms. While complete agreement between the modeling results and observed trends from single-cavity injection molding was not achieved, the groundwork was laid to make further improvements and advance predictability for future modeling programs. iv

6 To my wife, Whitney, you are the most important part of my life and I hope that I show you the constant and unwavering love and support that you show me everyday. I look forward to our journey together and all the joy it may bring. To my mother, Nancy, thank you for too many things to list. Your love, guidance, and friendship throughout these first 29 years of my life have been unimaginable. Thank you for the tremendous examples of how to treat and respect others, how to be a parent, and how to be a loving and selfless spouse. To my late father, Richard, who was not only a parent to me; he was also my best friend. His tireless love, support, and encouragement still lives with me to this day. We shared many great moments together: going up north to cut firewood, playing catch, watching Detroit Tigers baseball games, and trying to teach him about golf; a sport for which he had no interest except for the fact that it was important to me. His sudden passing on December 19, 2006, following a short bout with cancer, left a tremendous void in my life and heart. We were always very close, but those last 3 months were filled with moments that I will never forget: many shared laughs, tears, and short walks through the house. To quote a song from Keith Urban, I only hope when I have my own family that everyday I see a little more of my father in me.

7 Acknowledgments First and foremost, I would like to thank Dr. Saleh A. Jabarin for giving me this tremendous opportunity to learn from him and conduct this research project at the Polymer Institute, under his guidance. His knowledge, encouragement, and incredible patience have been not only appreciated, but greatly needed as well. I would like to thank Dr. Mike Cameron for his help with the computational modeling work and Mrs. Elizabeth Lofgren for her help with the various analytical experiments and for reviewing this work. The generosity of their time and effort has been immensely appreciated. Thank you to Mr. Mike Mumford for his help with the processing equipment and experiments and to Mrs. Jackie Zydorczyk for her support and help. Thank you to my fellow students at the Polymer Institute for your encouragement and suggestions throughout my project; especially to Mr. Thomas R. Matthews, Dr. Sung-Gi Kim, and Dr. Kamal Mahajan for their assistance in conducting experiments. Thank you, as well, to the PET Industrial Consortium for their financial support for this work. I would like to thank Dr. Dong-Shik Kim, Dr. Yong-Wah Kim, Dr. Steven E. LeBlanc, and Dr. Arunan Nadarajah for serving on my dissertation committee. A final thank you is extended to my wife, my mother, and my entire family for their support and encouragement throughout these years. vi

8 Contents Abstract Acknowledgments Contents List of Figures List of Tables iii vi vii xiii xxi 1 Introduction Poly(ethylene terephthalate) Overview Synthesis of PET Melt-Phase Polymerization Solid-State Polymerization Direct Melt-Phase to Higher I.V PET Copolymers Degradation of PET Hydrolytic Degradation of PET Thermal Degradation of PET Thermal-Oxidative Degradation of PET Acetaldehyde in PET Overview...11 vii

9 1.4.2 Amount of Acetaldehyde in PET PET Degradation Routes That Generate Acetaldehyde Thermal Decomposition of Hydroxyl End-Groups Breakdown of Diethylene Glycol Molecules Reactions with Vinyl Ester End-Groups Presence of Oxygen Presence of DEG Linkages within PET Chains Presence of Free Radicals Ways to Reduce the Amount of AA within PET Rationale and Objectives Literature Review Minimizing AA During PET Degradation Mechanisms Limiting Thermal Degradation Limiting Thermal-Oxidative Degradation Minimizing AA by Choice of Polymerization Catalysts Minimizing AA by Choice of PET Resins Minimizing AA by Means of Acetaldehyde (AA) Scavengers Reactive AA Scavengers Polyamides Low Molecular Weight Amides Polyamines Polyimines Polyols...37 viii

10 2.4.2 Size-Enclosing AA Scavengers Cyclodextrins Zeolites AA Scavenging Catalysts Experimental Work Materials Spectroscopic Techniques to Study Chemical Interactions Nuclear Magnetic Resonance (NMR) Spectroscopy Proton ( 1 H) NMR H- 1 H COrrelation SpectroscopY (COSY) Mass Spectrometry Twin-Screw Extrusion Preparation of Alpha-Cyclodextrin/PET Blend Samples Preparation of Anthranilamide/PET Blend Samples Preparation of MXDA/PET Blend Samples Preparation of Control PET Samples Manufacturing of PET Containers Injection Molding Stretch-Blow-Molding Gas Chromatography Acetaldehyde Generation Analysis Residual Acetaldehyde Analysis Rheological Methods...69 ix

11 3.6.1 Plate and Plate Rheometer Capillary Rheometer Color Analysis Differential Scanning Calorimetry (DSC) Analysis Oxygen Film Permeation Results and Discussion Chemical Mechanisms of AA and AA Scavenger Interactions AA and Anthranilamide AA and MXDA AA and Alpha-Cyclodextrin Effectiveness of AA Scavengers in Reducing the Amount of AA in PET AA Generation Rates Residual AA Pelletized Samples Preform Samples Comparison of Results for Pelletized Samples and Preform Samples Physical Properties of AA Scavenger/PET Blend Samples Intrinsic Viscosity (I.V.) Pelletized Samples Preform Samples Comparison of Results for Pelletized Samples and Preform Samples x

12 4.3.2 Color Color Analysis Appearance of 2-Liter Bottles Thermal Properties Glass Transition Temperature (T g ) Crystallization Behavior When Heating from the Glassy State Melting Behavior Crystallization Behavior When Cooling form the Melt Oxygen Film Permeation Optimal AA Scavenger/PET Blends Anthranilamide/PET Blends MXDA/PET Blends Alpha-Cyclodextrin/PET Blends Modeling Predictive AA Generation Program Modified AA Generation Program Numerical Analysis Determination of k 2 and a Determination of k 1, bb 1, bb 2, and b Modeling Results Conclusions and Recommendations Conclusions Chemical Mechanisms of AA and AA Scavenger Interaction xi

13 5.1.2 Effectiveness of AA Scavengers Apparent Reduction in Generated AA Physical Properties of AA Scavenger/PET Blend Samples Optimal AA Scavenger/PET Blends Modeling Recommendations References 206 A 1 H NMR Spectra of AA and Alpha-Cyclodextrin Titration Experiment 220 B Raw Data from AA Generation Experiments 228 C AA Generation Plots 248 D Arrhenius Plots 259 E Raw Data from Residual AA Experiments 259 F Raw Data from Melt Viscosity Measurements to Determine I.V. 273 G Raw Data from Color Measurements 277 H Derivation of Thermal Energy Equation 280 I AA Generation 60 Minute Curve Study Data 283 J Data Used to Determine the k 2 and a Values 287 K Data Used to Determine the k 1, bb 1, bb 2, and b Values 289 L Raw Data from Modeling Program 300 xii

14 List of Figures 1-1 The Repeating Chemical Structure of PET Reaction Scheme for TPA and EG to Produce BHET Reaction Scheme for DMT and EG to Produce BHET Reaction Scheme for the Polymerization of BHET to Produce PET and EG Chemical Structure of Cyclohexane 1,4 Dimethanol (CHDM) Chemical Structure of Isophthalic Acid (IPA) Chemical Structure of Acetaldehyde Acetaldehyde Concentration During the Lifecycle of PET Thermal Decomposition of Hydroxyl Eng-Groups to Produce AA AA Formation from Diethylene Glycol (DEG) Molecules AA Formation from Vinyl Ester End-Groups Reacting with Hydroxyl End- Groups and Carboxyl End-Groups AA Generation Due to the Presence of Oxygen AA Generation from Diethylene Glycol (DEG) Linkages AA Generation Due to the Presence of Free Radicals The Chemical Structure of MXD Acetaldehyde Scavenging Reaction Between MXD6 and AA Chemical Structure of Anthranilamide Aldehyde Scavenging Reaction Between D-Sorbitol and Valeraldehyde...39 xiii

15 2-5 Various Forms of Cyclodextrin Chemical Structure of Alpha-Cyclodextrin Proposed Fitting of Caproaldehyde and Cyclodextrin H NMR Titration Experiment of 2-TeCD and GSH Relative Location of IR Heating Zones with Respect to a Preform H NMR Spectrum of AA in CDCl H NMR Spectrum of Anthranilamide in CDCl H NMR Spectrum of the Reaction Between Anthranilamide and AA, in CDCl 3, After Heating for 2 Days at 60 o C H 1 H COSY NMR Spectrum of the Reaction Between Anthranilamide and AA, in CDCl 3, After Heating for 2 Days at 60 o C Proposed Reaction Mechanism #1 for Anthranilamide and AA Predicted 1 H NMR Spectrum for the Product Formed from the Proposed Reaction Mechanism #1 (Figure 4-5) Proposed Reaction Mechanism #2 for Anthranilamide and AA Predicted 1 H NMR Spectrum for the Product Formed from the Proposed Reaction Mechanism #2 (Figure 4-7) ESI Mass Spectrum of Anthranilamide in CDCl 3 and Methanol ESI Mass Spectrum of the Product from the Reaction Between Anthranilamide and AA in CDCl 3 and Methanol Proposed Reaction Mechanism #3 for Anthranilamide and AA Predicted 1 H NMR Spectrum for the Product Formed from the Proposed Reaction Mechanism #3 (Figure 4-11)...92 xiv

16 H NMR Spectrum of MXDA in CDCl Proposed Reaction Scheme for MXDA and AA H NMR Spectrum of the Reaction Between MXDA and AA in CDCl H NMR Spectrum of the Alpha-Cyclodextrin in D 2 O H 1 H COSY NMR Spectrum of Alpha-Cyclodextrin in D 2 O H NMR Spectrum of AA in D 2 O Equilibrium Reaction Between AA and D 2 O Predicted 1 H NMR Spectrum of AA in D 2 O Interaction Mechanism for AA and Alpha-Cyclodextrin Peak Shifting of the Protons for AA and its Equilibrium Product When Titrated with Alpha-Cyclodextrin (Solvent is D 2 O) AA Generation Plots for the 1200 ppm Anthranilamide/PET Blend AA Generation Rates as a Function of Anthranilamide Concentration AA Generation Rates as a Function of Alpha-Cyclodextrin Concentration AA Generation Rates as a Function of MXDA Concentration Arrhenius Plot of 10,000 ppm MXDA/PET Blend Sample liter Blow-Molded PET Bottles DSC Heating Curve of the 5 Weight % Alpha-Cyclodextrin/PET Blend DSC Cooling Curve of the 2.5 Weight % Alpha-Cyclodextrin/PET Blend Viscosity versus Shear Rate Curves for the Voridian CB12 PET Resin Arrhenius Plot for the Voridian CB12 PET Resin Temperature Profile as a Function of Radial Distance from the Center of a Flow Channel over a Two Second Period of Time xv

17 4-34 Distribution of AA as a Function of Radial Distance from the Center of the Flow Channel Distribution of Material to Fill Four Cavities within an Eight-Cavity Mold Temperatures for the Various Cavities as a Function of Filling Times Minute AA Generation Curve for the 10,000 ppm Anthranilamide/PET Blend Minute AA Generation Curve for the 10,000 ppm Alpha-Cyclodextrin/PET Blend Minute AA Generation Curve for the 10,000 ppm MXDA/PET Blend d[aa] 4-40 Plot of ln( R G ) Versus ln([aa]) for the 10,000 ppm dt Anthranilamide/PET Blend at 290 o C d[aa] 4-41 Plot of ln( R G ) Versus ln([aa]) for the 10,000 ppm Alphadt Cyclodextrin/PET Blend at 290 o C d[aa] 4-42 Plot of ln( R G ) Versus ln([aa]) for the 10,000 ppm MXDA/PET dt Blend at 290 o C Minute AA Generation Data for the 10,000 ppm Anthranilamide/PET Blend Fitted with Equation 22, Using a and k 2 Values Minute AA Generation Data for the 10,000 ppm Alpha-Cyclodextrin/PET Blend Fitted with Equation 22, Using a and k 2 Values Minute AA Generation Data for the 10,000 ppm MXDA/PET Blend Fitted with Equation 22, Using a and k 2 Values xvi

18 Minute AA Generation Data for the 10,000 ppm Anthranilamide/PET Blend Fitted with Equation 17; Using the a, k 1 at 290 o C, and b Values Minute AA Generation Data for the 10,000 ppm Alpha-Cyclodextrin/PET Blend Fitted with Equation 17; Using the a, k 1 at 290 o C, and b Values Minute AA Generation Data for the 10,000 ppm MXDA/PET Blend Fitted with Equation 17; Using the a, k 1 at 290 o C, and b Values Minute AA Generation Data for the 10,000 ppm Anthranilamide/PET Blend Fitted with Equation 17; Using the a, b, and bb 2 Values and the 2 nd Iteration bb 1 Value Minute AA Generation Data for the 10,000 ppm Alpha-Cyclodextrin/PET Blend Fitted with Equation 17; Using the a, b, and bb 2 Values and the 2 nd Iteration bb 1 Value Minute AA Generation Data for the 10,000 ppm MXDA/PET Blend Fitted with Equation 17; Using the a, b, and bb 2 Values and the 2 nd Iteration bb 1 Value Predicted Injection Molding Results for Various Anthranilamide/PET Blends and for Various Manifold Designs; Modeled at 280 o C Predicted Injection Molding Results for Various Alpha-Cyclodextrin/PET Blends and for Various Manifold Designs; Modeled at 280 o C Predicted Injection Molding Results for Various MXDA/PET Blends and for Various Manifold Designs; Modeled at 280 o C One Minute Simulated AA Generation at 280 o C One Minute Simulated AA Generation at 290 o C xvii

19 4-57 One Minute Simulated AA Generation at 300 o C Predicted Injection Molding Results for Various Anthranilamide/PET Blends, Studied as a Function of Temperature; Modeled for a 48 Cavity Process Predicted Injection Molding Results for Various Alpha-Cyclodextrin/PET Blends, Studied as a Function of Temperature; Modeled for a 48 Cavity Process Predicted Injection Molding Results for Various MXDA/PET Blends, Studied as a Function of Temperature; Modeled for a 48 Cavity Process A-1 AA and Alpha-Cyclodextrin, in D 2 O, Mixed in a 0.2 to 1 Ratio A-2 AA and Alpha-Cyclodextrin, in D 2 O, Mixed in a 0.4 to 1 Ratio A-3 AA and Alpha-Cyclodextrin, in D 2 O, Mixed in a 0.6 to 1 Ratio A-4 AA and Alpha-Cyclodextrin, in D 2 O, Mixed in a 0.8 to 1 Ratio A-5 AA and Alpha-Cyclodextrin, in D 2 O, Mixed in a 1 to 1 Ratio A-6 AA and Alpha-Cyclodextrin, in D 2 O, Mixed in a 2 to 1 Ratio A-7 AA and Alpha-Cyclodextrin, in D 2 O, Mixed in a 3 to 1 Ratio C-1 AA Generation Plots for the Voridian CB12 PET Resin C-2 AA Generation Plots for the One-Time Processed PET Sample C-3 AA Generation Plots for the Two-Times Processed PET Sample C-4 AA Generation Plots for the Three-Times Processed PET Sample C-5 AA Generation Plots for the 10,000 ppm Anthranilamide/PET Blend Sample C-6 AA Generation Plots for the 500 ppm Anthranilamide/PET Blend Sample C-7 AA Generation Plots for the 200 ppm Anthranilamide/PET Blend Sample xviii

20 C-8 AA Generation Plots for the 100 ppm Anthranilamide/PET Blend Sample C-9 AA Generation Plots for the 50,000 ppm Alpha-Cyclodextrin/PET Blend Sample C-10 AA Generation Plots for the 25,000 ppm Alpha-Cyclodextrin/PET Blend Sample C-11 AA Generation Plots for the 10,000 ppm Alpha-Cyclodextrin/PET Blend Sample C-12 AA Generation Plots for the 5000 ppm Alpha-Cyclodextrin/PET Blend Sample.254 C-13 AA Generation Plots for the 1200 ppm Alpha-Cyclodextrin/PET Blend Sample.254 C-14 AA Generation Plots for the 500 ppm Alpha-Cyclodextrin/PET Blend Sample C-15 AA Generation Plots for the 10,000 ppm MXDA Blend Sample C-16 AA Generation Plots for the 1200 ppm MXDA Blend Sample C-17 AA Generation Plots for the 500 ppm MXDA Blend Sample C-18 AA Generation Plots for the 200 ppm MXDA Blend Sample C-19 AA Generation Plots for the 100 ppm MXDA Blend Sample D-1 Arrhenius Plot for the One-Time Processed PET Sample D-2 Arrhenius Plot for the Two-Time Processed PET Sample D-3 Arrhenius Plot for the Three-Time Processed PET Sample D-4 Arrhenius Plot for the 10,000 ppm Anthranilamide/PET Blend Sample D-5 Arrhenius Plot for the 1200 ppm Anthranilamide/PET Blend Sample D-6 Arrhenius Plot for the 500 ppm Anthranilamide/PET Blend Sample D-7 Arrhenius Plot for the 200 ppm Anthranilamide/PET Blend Sample D-8 Arrhenius Plot for the 100 ppm Anthranilamide/PET Blend Sample xix

21 D-9 Arrhenius Plot for the 50,000 ppm Alpha-Cyclodextrin/PET Blend Sample D-10 Arrhenius Plot for the 25,000 ppm Alpha-Cyclodextrin/PET Blend Sample D-11 Arrhenius Plot for the 10,000 ppm Alpha-Cyclodextrin/PET Blend Sample D-12 Arrhenius Plot for the 5000 ppm Alpha-Cyclodextrin/PET Blend Sample D-13 Arrhenius Plot for the 1200 ppm Alpha-Cyclodextrin/PET Blend Sample D-14 Arrhenius Plot for the 500 ppm Alpha-Cyclodextrin/PET Blend Sample D-15 Arrhenius Plot for the 1200 ppm MXDA/PET Blend Sample D-16 Arrhenius Plot for the 500 ppm MXDA/PET Blend Sample D-17 Arrhenius Plot for the 200 ppm MXDA/PET Blend Sample D-18 Arrhenius Plot for the 100 ppm MXDA/PET Blend Sample xx

22 List of Tables 1.1 Typical I.V. Ranges for Various PET Uses The Thermal History for Each Alpha-Cyclodextrin/PET Blend The Thermal History for Each Anthranilamide/PET Blend The Thermal History for Each MXDA/PET Blend Optimized Stretch-Blow-Molding Parameters Explanation of the Variables from Equation Explanation of the Variables from Equations 2 and Melt Viscosity Testing Conditions Instrument Parameters for the Capillary Rheometry Analysis Explanation of L, a, b, and YI Values Explanation of the Variables in Equation Explanation of the Variables in Equation Explanation of the Variables in Equation Peak Assignment for the 1 H NMR Spectrum of AA in CDCl Peak Assignment for the 1 H NMR Spectrum of Anthranilamide in CDCl Peak Assignment for the 1 H NMR Spectrum of the Reaction Between Anthranilamide and AA, in CDCl 3, After Heating for 2 Days at 60 o C Peak Assignment for the 1 H NMR Spectrum of MXDA in CDCl xxi

23 4.5 Peak Assignment for the 1 H NMR Spectrum of the Reaction Between MXDA and AA, in CDCl Peak Assignment for the 1 H NMR Spectrum of Alpha-Cyclodextrin in D 2 O Peak Assignment for the 1 H NMR Spectrum of AA in D 2 O AA Generation Rates AA Generation Rates of Control Samples Activation Energies Residual AA Data for Pelletized Samples Residual AA Data for Preform Samples Comparison of the Residual AA Data for Pelletized and Preform Samples I.V. Data for Pelletized Samples I.V. Data for Preform Samples Comparison of the I.V. Data for Pelletized and Preform Samples L, a, and b Values and Yellowness Index of Pelletized Samples Glass Transition Temperature (T g ) Data Crystallization Behavior Data When Heating from the Glassy State Melting Behavior Data When Heating from the Glassy State Crystallization Behavior Data When Cooling form the Melt Oxygen Film Permeability Explanation of the Terms in Equation Explanation of the Terms in Equation Explanation of the Terms in Equations 13 and Capillary Rheometry Results Rheology Constants for the Predictive AA Generation Program Explanation of the Terms in Equation xxii

24 4.29 Explanation of the Terms in Equation Variables Needed to Run the Predictive AA Generation Program Explanation of the Terms in Equation Explanation of the Terms in Equation Explanation of the Terms in Equations 19 and Review of the Residual AA Data for Preform Samples Explanation of the Terms in Equations 22 and Variables Needed to Modify the Predictive AA Generation Program Calculated k 2, for 290 o C, and a Value for Each Scavenging Agent b, bb 1, and bb 2 Values for Each Scavenging Agent Determined Through Multiple Linear Regression Final a, b, bb 1, bb 2, and k 1 Values for Each AA Scavenging Agent A.1 Location of the AA and Alpha-Cyclodextrin Protons for each of the AA and Alpha-Cyclodextrin NMR Titration Experiments A.2 Change in Location of the Protons Representing AA and its D 2 O Equilibrium Product, Due to the Presence of Alpha-Cyclodextrin B.1 AA Generation Data for the Voridian CB12 PET Resin B.2 AA Generation Data for the One-Time Processed PET Sample B.3 AA Generation Data for the Two-Times Processed PET Sample B.4 AA Generation Data for the Three-Times Processed PET Sample B.5 AA Generation Data for the 10,000 ppm Anthranilamide/PET Blend Sample B.6 AA Generation Data for the 1200 ppm Anthranilamide/PET Blend Sample B.7 AA Generation Data for the 500 ppm Anthranilamide/PET Blend Sample B.8 AA Generation Data for the 200 ppm Anthranilamide/PET Blend Sample xxiii

25 B.9 AA Generation Data for the 100 ppm Anthranilamide/PET Blend Sample B.10 AA Generation Data for the 50,000 ppm Alpha-Cyclodextrin/PET Blend Sample B.11 AA Generation Data for the 25,000 ppm Alpha-Cyclodextrin/PET Blend Sample B.12 AA Generation Data for the 10,000 ppm Alpha-Cyclodextrin/PET Blend Sample B.13 AA Generation Data for the 5000 ppm Alpha-Cyclodextrin/PET Blend Sample.240 B.14 AA Generation Data for the 1200 ppm Alpha-Cyclodextrin/PET Blend Sample.241 B.15 AA Generation Data for the 500 ppm Alpha-Cyclodextrin/PET Blend Sample B.16 AA Generation Data for the 10,000 ppm MXDA/PET Blend Sample B.17 AA Generation Data for the 1200 ppm MXDA/PET Blend Sample B.18 AA Generation Data for the 500 ppm MXDA/PET Blend Sample B.19 AA Generation Data for the 200 ppm MXDA/PET Blend Sample B.20 AA Generation Data for the 100 ppm MXDA/PET Blend Sample E.1 Residual AA Data for the Control PET Pelletized Samples E.2 Residual AA Data for the Anthranilamide/PET Blend Pelletized Samples E.3 Residual AA Data for the Alpha-Cyclodextrin/PET Blend Pelletized Samples E.4 Residual AA Data for the MXDA/PET Blend Pelletized Samples E.5 Residual AA Data for the PET Control Preform Samples E.6 Residual AA Data for the Anthranilamide/PET Blend Preform Samples E.7 Residual AA Data for the Alpha-Cyclodextrin/PET Blend Preform Samples E.8 Residual AA Data for the MXDA/PET Blend Preform Samples xxiv

26 F.1 Melt Viscosity Data for the Control PET Pelletized Samples F.2 Melt Viscosity Data for the Anthranilamide/PET Blend Pelletized Samples F.3 Melt Viscosity Data for the Alpha-Cyclodextrin/PET Blend Pelletized Samples.274 F.4 Melt Viscosity Data for the MXDA/PET Blend Pelletized Samples F.5 Melt Viscosity Data for the Control PET Preform Samples F.6 Melt Viscosity Data for the Anthranilamide/PET Blend Preform Samples F.7 Melt Viscosity Data for the Alpha-Cyclodextrin/PET Blend Preform Samples F.8 Melt Viscosity Data for the MXDA/PET Blend Preform Samples G.1 Color Data for the Voridian CB12 PET Control Samples G.2 Color Data for the Anthranilamide/PET Blend Samples G.3 Color Data for the MXDA/PET Blend Samples G.4 Color Data for the Alpha-Cyclodextrin/PET Blend Samples H.1 Definition of Terms Listed in Equations 12 and 29 to I.1 AA Generation Data for the CB12 PET Resin I.2 AA Generation Data for the 10,000 ppm Anthranilamide/PET Blend I.3 AA Generation Data for the 10,000 ppm Alpha-Cyclodextrin/PET Blend I.4 AA Generation Data for the 10,000 ppm MXDA/PET Blend J.1 Calculated Data Based on 60 Minute AA Generation Data, at 290 o C, for the 10,000 ppm Anthranilamide/PET Blend J.2 Calculated Data Based on 60 Minute AA Generation Data, at 290 o C, for the 10,000 ppm Alpha-Cyclodextrin/PET Blend J.3 Calculated Data Based on 60 Minute AA Generation Data, at 290 o C, for the 10,000 ppm MXDA/PET Blend xxv

27 K.1 Anthranilamide/PET Blend Data, at 280 o C, Calculated for the Original ln(k 2 ) Versus ln([s 0 ]) Plot K.2 Anthranilamide/PET Blend Data, at 290 o C, Calculated for the Original ln(k 2 ) Versus ln([s 0 ]) Plot K.3 Anthranilamide/PET Blend Data, at 300 o C, Calculated for the Original ln(k 2 ) Versus ln([s 0 ]) Plot K.4 Alpha-Cyclodextrin/PET Blend Data, at 280 o C, Calculated for the Original ln(k 2 ) Versus ln([s 0 ]) Plot K.5 Alpha-Cyclodextrin/PET Blend Data, at 290 o C, Calculated for the Original ln(k 2 ) Versus ln([s 0 ]) Plot K.6 Alpha-Cyclodextrin/PET Blend Data, at 300 o C, Calculated for the Original ln(k 2 ) Versus ln([s 0 ]) Plot K.7 MXDA/PET Blend Data, at 280 o C, Calculated for the Original ln(k 2 ) Versus ln([s 0 ]) Plot K.8 MXDA/PET Blend Data, at 290 o C, Calculated for the Original ln(k 2 ) Versus ln([s 0 ]) Plot K.9 MXDA/PET Blend Data, at 300 o C, Calculated for the Original ln(k 2 ) Versus ln([s 0 ]) Plot K.10 Multiple Linear Regression Data Used to Determine the b, bb 1, and bb 2 Values for the Anthranilamide/PET Blends K.11 Multiple Linear Regression Data Used to Determine the b, bb 1, and bb 2 Values for the Alpha-Cyclodextrin/PET Blends xxvi

28 K.12 Multiple Linear Regression Data Used to Determine the b, bb 1, and bb 2 Values for the MXDA/PET Blends L.1 Predicted AA Generation Results for a 16 Cavity Injection Molding Process, Modeled at 280 o C L.2 Predicted AA Generation Results for a 24 Cavity Injection Molding Process, Modeled at 280 o C L.3 Predicted AA Generation Results for a 32 Cavity Injection Molding Process, Modeled at 280 o C L.4 Predicted AA Generation Results for a 48 Cavity Injection Molding Process, Modeled at 280 o C L.5 Predicted AA Generation Results for a 48 Cavity Injection Molding Process, Modeled at 270 o C L.6 Predicted AA Generation Results for a 48 Cavity Injection Molding Process, Modeled at 290 o C L.7 Predicted AA Generation Results for a 48 Cavity Injection Molding Process, Modeled at 300 o C xxvii

29 Chapter 1 Introduction 1.1 Poly(ethylene terephthalate) Overview Poly(ethylene terephthalate) (PET), shown in Figure 1-1, is a common polyester known for its optical, mechanical, and thermal properties. The combination of these properties makes PET applicable to many industries for a variety of uses. 1 Some of the more common applications include: synthetic fiber to manufacture both apparel and carpets for the textile industry tire cord for the transportation industry angioplasty balloons for the medical industry transparent films for the office supply industry containers for the packaging industry Figure 1-1: The repeating chemical structure of PET 1

30 For many packaging applications PET is a preferred material. When PET is properly oriented it provides good optical transparency, high impact strength, and good gas barrier properties. 1-3 PET is particularly known to be a good barrier against the permeation of carbon dioxide and water vapor. 1, 2 Over the past twenty-five years PET has become the leading packaging material for carbonated soft drinks, sports drinks, and water. Depending on the final use, the molecular weight of the PET resin may vary. It is a common practice within the industry to identify PET samples by their respective intrinsic viscosities (I.V.) rather than their molecular weights. 4 Table 1.1 shows typical I.V. ranges for a few common applications of PET. 1, 4 Table 1.1: Typical I.V. ranges for various PET uses Uses Intrinsic Viscosity (I.V.) (dl/g) Textiles 0.5 to 0.65 Film and Tape 0.65 to 0.75 Bottles 0.70 to 1.00 Tire Cord Synthesis of PET As shown in Table 1.1, the I.V., or molecular weight, of PET can vary depending on its application. Identification of the intended use is important because PET manufacturing techniques can vary depending on the I.V. that is desired. To date, there are three common processes used to manufacture PET: melt-phase polymerization, solid-state polymerization, and direct melt-phase polymerization to high I.V. material. It can be important to choose the right technique because each has its own benefits and drawbacks. 2

31 1.2.1 Melt-Phase Polymerization 1, 3, 4 PET is typically synthesized in a two-step polymerization process. The first step is known as melt-phase polymerization. During this process ethylene glycol (EG), classified as a diol, is reacted with either terephthalic acid (TPA) or dimethyl terephthalate (DMT), both can be classified as di-acids. When TPA is used, a selfcatalyzed esterification reaction occurs to produce bis-hydroxyl terephthalate (BHET) 1, 3, 4 and water; as shown in Figure 1-2. HO O O HO O HO + 2 OH O O + 2 H 2 O O OH OH TPA EG BHET Water Figure 1-2: Reaction scheme for TPA and EG to produce BHET When DMT is used, a catalyzed transesterification reaction produces BHET and acetaldehyde (AA), a byproduct. 1, 3 Some of the common catalysts used for this reaction include acetates of lithium (Li), calcium (Ca), magnesium (Mg), zinc (Zn), or lead (Pb); and oxides of Pb. This reaction scheme is shown in Figure

32 CH 3 HO O O O HO + 2 OH O O + 2 O CH 3 H O O CH 3 OH DMT EG BHET AA Figure 1-3: Reaction scheme for DMT and EG to produce BHET Once BHET is produced, either from EG and TPA or EG and DMT, it must be polymerized to form PET. PET is obtained through a catalyzed, high temperature transesterification reaction; shown in Figure , 3 This reaction is an equilibrium reaction and thus the byproduct, ethylene glycol (EG), must be removed to obtain a high yield of PET. 4 The catalysts for this reaction include acetates of antimony (Sb), Zn, or Pb; and oxides of Sb, germanium (Ge), or Pb. 1, 4 HO O O n O O HO O O O O O n H + n HO OH OH BHET PET EG Figure 1-4: Reaction scheme for the polymerization of BHET to produce PET and EG 4

33 Traditional melt-phase polymerization techniques have a limit to the molecular weight, or 1, 3, 4 I.V., that can be achieved. The constraint is due to the difficulty in removing the reaction by-products (particularly EG), BHET, and oligomers from the viscous PET melt. 1 Removal of these un-wanted by-products is needed to continually drive the equilibrium reaction forward and thus continually increase the degree of polymerization of the PET. Traditional melt-phase polymerization can be used to produce PET to be used as textile or as film or tape. 1, 4 The desired I.V. for these applications is achievable with melt-phase polymerization alone. When higher I.V. PET is needed to manufacture containers or tire cord, for example, the I.V. needs to be increased beyond what meltphase polymerization techniques can yield. While recent advancements 5-12 in melt-phase polymerization technologies have increased the achievable I.V. ranges, traditionally a second polymerization technique was required to produce higher I.V. PET. This second 1, 3, 4 step is known as solid-state polymerization (SSP) Solid-State Polymerization Similar to melt-phase polymerization, solid-state polymerization (SSP) increases molecular weight (or I.V.) by driving the various PET end-groups to react with one 1, 3, 4 another and thus increasing the length of the polymer chains. As the end-groups react with one another, by-products are formed. Removal of these by-products (water, EG, AA, etc.) is achieved by continual inert gas purging or by applying vacuum pressure. 1 As with melt-phase polymerization, by-product purging is a necessity to progress the SSP equilibrium reactions forward and ultimately reach the desired I.V. 5

34 During the SSP process, solid PET pellets are heated well above the polymer s glass transition temperature (T g ) but below its melting temperature. This temperature range is typically between 200 and 240 o C. 1 As the temperature is increased, mobility of the polymer chains also increases. This increases the likelihood/ability of the polymer chains end-groups to find and react with one another. If the temperature is excessively increased, however, thermal degradation can occur; causing random chain scission to occur. 1, 3 Random chain scission leads to the formation of low molecular weight byproducts and the loss of molecular weight from the PET chains. The thermal degradation of PET will be discussed in greater detail in Section The fundamental difference between melt-phase and solid-state polymerization is the phase of the reactants during the respective polymerization. Melt-phase polymerization is typically performed between 270 and 285 o C; which is above the melting temperature of PET, usually listed to be above 255 o C. SSP, however, is carried out at a much milder temperature range; between 200 and 240 o C. Therefore, at SSP conditions PET is in a solid, rubbery state and not the viscous liquid seen during melt-phase polymerization. This makes it much easier for a purging gas (or vacuum) to remove the volatile degradation products and reaction by-products that form during polymerization. 1 The greater ease of by-product removal allows the polymerization process to progress beyond the limitation observed during melt-phase polymerization. Additionally, the milder SSP reaction temperature causes fewer side reactions to occur. 1, 3 The combination of less side reactions and easier by-product removal create a more efficient route for the end- 6

35 groups of PET to react with one another and ultimately for the molecular weigh to increase more rapidly Direct Melt-Phase to Higher I.V. As previously mentioned, two-step polymerization (melt-phase polymerization followed by solid-state polymerization) has been the traditional method to achieve high molecular, or high I.V., PET resins. In recent years, however, new melt-phase polymerization techniques 5-12 have been developed that are now able to produce high molecular weight PET resins without the need for solid-state polymerization. This technology has especially become prevalent when producing PET resins to be used in the manufacturing of containers. These new processes use the same starting materials (EG and TPA or EG and DMT) and follow the same chemistry as the traditional two-step method (Figures 1-2 to 1-4). The appeal of these new melt-phase polymerization methods are believed to reduce the overall cost of production. Not only does SSP require additional reactors and energy to run the process, it is also a time consuming operation. Elimination of the SSP step would, in theory, allow PET producing plants to have higher throughput of resin. Elimination of the SSP step, however, may need to be carefully considered. The inherent advantages of SSP, as previously discussed, are something that could be critical to the final product. Traditional solid-state polymerized PET resins possess minimal unwanted 7

36 by-products and good thermal stability; criteria which one-step polymerization techniques may not be able to meet PET Copolymers There are applications where it is desirable to slightly alter the physical properties of poly(ethylene terephthalate) in order to better meet the needs of its end-use. To do this, 1, 3, 4 PET resins can be synthesized as copolymers instead of homopolymers. A copolymer is a polymer composed of two or more repeating monomer units. The chemistry presented up to this point details the reactions to polymerize a PET homopolymer. The synthesis of a PET copolymer is achieved by replacing a small amount of the original raw materials (EG, TPA, or DMT) with another reactant(s). The copolymer concentration in the final product is typically less than 10%. Cyclohexane dimethanol (CHDM) and isophthalic acid (IPA) are two of the more common reactants used as substitutes to create PET copolymer resins. 3, 4 When compared to EG, the increased size of CHDM alters the structured packing of the polymer chains. This phenomenon affects the resin s crystallinity and therefore lowers its melting point. 4 The carboxyl end-groups of TPA are in a 1, 4 ( para ) configuration, where as the carboxyl end-groups of IPA are in a 1, 3 ( meta ) configuration. The meta configuration gives a slight angle to the polymer chain. This again alters the resin s crystallinity and thus its melting point. 4 The chemical structures of CHDM and IPA are shown in Figure 1-5 and 1-6, respectively. 8

37 OH HO Figure 1-5: Chemical structure of cyclohexane 1, 4 dimethanol (CHDM) O OH O OH Figure 1-6: Chemical structure of isophthalic acid (IPA) 1.3 Degradation of PET The melting and processing of PET resin into manufactured articles frequently results in 1, 3, 4 at least some degradation of the material. During the extrusion or injection molding process the polymer can be subjected to moisture, oxygen, and/or elevated temperatures. Each of these can cause at least one route of degradation. There are three main degradation processes that can occur during PET processing: hydrolytic degradation, thermal degradation, and thermal-oxidative degradation. 1, Hydrolytic Degradation of PET Hydrolytic degradation occurs when of water reacts with PET at elevated temperatures. This reaction can result in the reduction of I.V. or molecular weight; resulting in the 1, 3, 13 generation of hydroxyl and carboxyl end-groups. PET is known to be a hygroscopic 9

38 material and thus it will to absorb moisture from the atmosphere. 1, 3 To limit the effects of hydrolytic degradation, PET must be properly dried prior to processing the material. It is generally observed that PET should contain less than 50 parts per million (ppm) of water to be considered properly dried Thermal Degradation of PET Thermal degradation occurs when PET is exposed to high temperatures. This results in 13, 14 random chain scission, forming carboxyl and vinyl ester end-groups. The formation of these end-groups leads to further reduction in I.V. or molecular weight, discoloration, formation of oligomers, and formation of low molecular weight byproducts. 1, 3 Minimizing the effects of thermal degradation can be achieved by limiting the temperature, the residence time, and the shear heating that occurs during extrusion or injection molding Thermal-Oxidative Degradation of PET Thermal-oxidative degradation occurs when oxygen reacts with PET at elevated temperatures. It results in the reduction of I.V. or molecular weight, formation of carboxyl end-groups, generation of low molecular weight byproducts, discoloration, and 1, 3, 4, 16 formation of branched chains. To limit thermal-oxidative degradation, PET should be melted and/or processed under vacuum or in an inert environment. For example, the 10

39 oxygen within the headspace of an extruder can be flushed by means of a nitrogen purge or a vacuum. 1.4 Acetaldehyde in PET Overview One of the more common byproducts resulting from the degradation of PET is acetaldehyde (AA). 17 AA is commonly found as a natural component within many foods; including citrus fruits, bread, wine, and milk. 2, 18 AA is known to have a sweet, fruity 2, 18, 19 taste and odor. This small organic compound, shown in Figure 1-7, is also very volatile. The boiling point of acetaldehyde is 21 o C. 19 CH 3 O H Figure 1-7: Chemical structure of acetaldehyde The presence of acetaldehyde within PET packages has been known to result in adverse 2, 20 effects. With a boiling point that is lower than room temperature, AA is able to diffuse out of PET and into either the atmosphere or into the packaged contents. The diffusion of AA into packaged contents is a concern because many food products have a limited threshold for the taste of acetaldehyde. This is especially true when bottling 11

40 water because the taste of pure water is so sensitive that even a small amount of AA is detectable by consumers Amount of Acetaldehyde in PET The amount of acetaldehyde that is present within PET varies greatly during the polymer s lifecycle. As previously discussed in greater detail during Section 1.2, synthesis of the material begins with melt-phase polymerization. For a two-step polymerization process (Section 1.2.1), melt-phase polymerization yields an amorphous PET resin of relatively low I.V., typically around 0.60 dl/g, which possesses a high amount of AA. It is not uncommon for this resin to contain more than 20 ppm of AA. To reduce the amount of degradation byproducts and prepare the PET resin for the second polymerization step, the amorphous resin is subsequently dried and crystallized. This can reduce the amount of AA to less than 15 ppm. The second polymerization step, solid-state polymerization, is conducted to further polymerize the PET resin and increase its I.V. Inherent to the SSP process, degradation byproducts, such as AA, are removed from the polymer s matrix. SSP can reduce the AA concentration from less than 15 ppm to less than 3 ppm. Additional drying of the solidstate polymerized PET resin can ultimately yield an AA concentration of less than 1 ppm. The final step is to use this PET resin to manufacture articles for consumers to use. For instance, preforms can be injection molded. These preforms will ultimately be stretch- 12

41 blow-molded into food or beverage containers. The melting and processing that occurs during injection molding results in some PET degradation; increasing the AA content to around 10 ppm or less. It is this 10 ppm of AA that is of concern to the PET container manufacturers for foods and beverages. If an excessive amount of AA migrates from the PET container to the packaged contents, the taste of the packaged product could be undesirably altered. Figure 1-8 shows a graphical depiction of this example, showing how AA content changes throughout the lifecycle of PET. Melt-Phase Polymerization Yields Amorphous PET Pellets [>20 ppm] Crystallization Crystallized PET Pellets [<15 ppm] SSP Injection Molding Dried SSP PET Pellets [<1 ppm] Drying SSP PET Pellets [<3 ppm] [ 10 ppm] Figure 1-8: Acetaldehyde concentration during the lifecycle of PET PET Degradation Routes That Generate Acetaldehyde There are several identified PET degradation routes that result in the generation of acetaldehyde. These AA producing chemical reactions result from two of the three core degradation mechanisms of PET: thermal degradation and thermal-oxidative 13

42 degradation. 1, 3 The factors that drive these reactions are: temperature, hydroxyl endgroups, diethylene glycol (DEG) molecules, vinyl ester end-groups, oxygen, DEG linkages, and free radicals Thermal Decomposition of Hydroxyl End-Groups The chemical reaction in Figure 1-9 shows the thermal decomposition of hydroxyl end- 1, 3, 22 groups into carboxyl end-groups and AA (CH 3 CHO). The precursors to this reaction are the presence of hydroxyl end-groups and elevated temperature. Therefore, this reaction can be characterized as thermal degradation. Figure 1-9: Thermal decomposition of hydroxyl end-groups to produce AA Breakdown of Diethylene Glycol Molecules Figure 1-10 shows how acetaldehyde can be generated from diethylene glycol 1, 3, 22 molecules. In this reaction, two PET chains terminated by hydroxyl end-groups react to form a larger PET chain that is connected by an anhydride linkage. Also produced in this reaction is a DEG molecule. This DEG molecule can then undergo a dehydration reaction to produce ethylene oxide vinyl ether and water. The ethylene glycol vinyl ether molecule can subsequently decompose to produce two molecules of acetaldehyde. 14

43 Figure 1-10: AA formation from diethylene glycol (DEG) molecules Reactions with Vinyl Ester End-Groups Of all the factors that lead toward the generation of AA, researchers 3, 22, 23 have shown that the most prominent is the concentration of vinyl ester end-groups in PET. Vinyl ester end-groups typically form during a random chain scission reaction; as illustrated in Figure As previously mentioned in Section 1.3.2, this reaction is characteristic of thermal degradation. Once the vinyl ester end-group is formed, it can generate AA by two different mechanisms. The first route is by reacting with another PET chain terminated by a hydroxyl end-group. This reaction creates a larger PET chain, connected by an ethylene linkage, and a molecule of acetaldehyde. The second route occurs when the vinyl ester end-group reacts with a carboxyl end-group. This reaction ultimately yields a larger PET chain, connected by an anhydride linkage, and a molecule of AA. 15

44 Figure 1-11: AA Formation from vinyl ester end-groups reacting with hydroxyl endgroups and carboxyl end-groups Presence of Oxygen Not only can vinyl ester end-groups form by random chain scission and thermal 1, 3, 16 degradation, they can also be produced by thermal-oxidative degradation. Oxygen that is present during the melting and processing of PET can react with the ethylene linkage of a PET chain to produce a branched hydroperoxide group. This hydroperoxide group may then decompose to form free radicals. As illustrated in Figure 1-12, these free radicals will eventually yield two PET chains, one terminated by a vinyl ester end-group and one terminated by a hydroxyl end-group. As previously shown in Figure 1-11, these functional groups will react with one another to yield a larger PET chain and a molecule of acetaldehyde. 16

45 Figure 1-12: AA generation due to the presence of oxygen Presence of DEG Linkages within PET Chains The process for synthesizing PET, melt-phase polymerization, is usually carried out between 270 to 285 o C. At these elevated temperatures, it is common for a small amount of ethylene glycol (EG) to react with itself to form diethylene glycol (DEG). Since EG and DEG are both diols, it is possible for DEG to replace EG during the synthesis of the PET chains. When this occurs, a DEG linkage connects the terephthalate groups of PET 17

46 rather than an EG linkage. The disadvantage of this linkage, however, is that it is susceptible to being attacked by oxygen; as shown in Figure Figure 1-13: AA generation from diethylene glycol (DEG) linkage When oxygen attacks the DEG linkage it forms a branched hydroperoxide group; similar to the one formed in Figure With elevated temperature, this hydroperoxide group decomposes to form free radicals. In time, these free radicals lead to the formation of PET chains terminated by vinyl ester end-groups and hydroxyl end-groups. As shown in 18

47 Figures 1-11, 1-12, and 1-13; ultimately the reaction of vinyl ester end-groups and hydroxyl end-groups produces a larger PET chain and a molecule of acetaldehyde Presence of Free Radicals Figures 1-12 and 1-13 have shown how the presence of oxygen can lead to the generation of free radicals and eventually AA. 3, 4 Figure 1-14 also shows a degradation reaction scheme that results from the presence of a free radical. This time, however, the free radical is generic and could have been produced by another mechanism; such as the exposure of PET to UV light. When the free radical reacts with PET, as shown in Figure 1-14, it shifts from the generic species to the ethylene portion of the PET chain. The instability of the free radical causes the chain to split in two, forming a PET chain terminated by a vinyl ester end-group and a PET chain terminated by an unstable end-group. In either case, as illustrated by Figure 1-14, the presence of the unstable end-group and the presence of the vinyl ester endgroup will ultimately lead to the formation of acetaldehyde. 19

48 Figure 1-14: AA generation due to the presence of free radicals Ways to Reduce the Amount of AA within PET As previously mentioned in Sections and 1.4.2, the amount of AA in PET is of great concern for manufacturers of food and beverage packaging. Acetaldehyde that is generated during manufacturing can, with time, diffuse from the PET container and into the packaged contents. It is known that an excessive amount of acetaldehyde can affect 2, 20 the desired taste of many food products. The most extreme scenario exists for bottled 20

49 water distributors. The taste of pure water is very subtle and is unable to mask the taste of even a few parts per million of AA. 21 There are a few common techniques that manufacturers use to limit the generation of AA for PET packages. The first solution is to optimize the processing conditions. This includes minimizing the melt temperature, shear rate, and residence time that the polymer 13, 15 is exposed to during injection molding. Optimizing these parameters limits the temperature and amount of time the polymer is exposed to these harsh conditions. Of all the AA producing degradation mechanisms discussed in Sections 1.3 and 1.4.3, thermal degradation has the greatest impact on the generation of AA. Thermal degradation leads to random chain scission reactions, resulting in the formation of vinyl ester end-groups. As mentioned in Section , the vinyl ester end-group concentration has been shown to have the most direct influence on the amount of AA that will be generated. 23 A second solution to limiting AA formation is to use of low AA generating PET resins, sometimes referred to as water-grade resins. These are resins which have been specifically tailored to the needs of water containers. 2 One of these particular requirements is limiting the amount of AA that is generated during container manufacturing. 21

50 There are instances, however, where acetaldehyde levels are required to be lower than any optimization of conditions or resin can achieve. In these situations, compounds called AA scavengers can be melt-blended into the PET matrix. These additives do not limit the degradation of PET or the generation of AA; acetaldehyde scavengers work by 20, 24 interacting with AA to reduce the levels at which it is released from PET. 1.5 Rationale and Objectives A study by Suloff 24 examined the effectiveness of three different aldehyde scavenging agents: poly(meta-xylene adipamide) (MXD6), D-sorbitol, and alpha-cyclodextrin. He prepared his samples by dry-blending each scavenging agent with PET pellets and then thermally pressing those blends into films. Each film was stored in its own aqueous mixture, comprised of various aldehydes, for up to 14 days. He quantified the aldehyde sorption ability of each scavenger by monitoring the change in concentration of each aldehyde, within each solution, over time. Suloff 24 showed that aldehyde scavenging/pet films were more effective at reducing aldehyde concentrations than control films. He also showed that the scavenging agents preferred smaller molecular weight aldehydes to larger molecular weight aldehydes. Suloff s work 24 examined the ability of his thermally pressed scavenging agent/pet blend films to remove aldehydes from an aqueous solution. The purpose of the current research project is to expand upon Suloff s work, while focusing solely on acetaldehyde (AA) scavenging in PET. The goal is to develop a comprehensive understanding of the 22

51 overall effects of melt-blending AA scavengers into poly(ethylene terephthalate). Through this research an understanding of the influence that the AA scavengers have upon the physical properties of PET will also be developed. These physical properties include: thermal properties, thermal stability, intrinsic viscosity (I.V.), barrier properties, color, and physical appearance. Through the knowledge obtained by studying the interactions that occurs between acetaldehyde scavengers and PET, a greater understanding will be achieved and the overall benefit of adding the scavengers can be specifically evaluated. In addition, greater understanding of AA scavengers should help in the development of better sequestering systems. It is also through this research that an initial model will be developed for a multi-cavity injection molding system. This model will be used to determine the amount of AA scavengers that will be needed to melt-blend with PET in order meet desired AA concentration requirements for various packaging systems. To meet these goals, the following five objectives have been identified as the focal points of this work: 1. Determine the chemical interactions/reactions that occur between the various scavenging agents and AA. 2. Investigate the effectiveness of the AA scavengers in reducing the amounts of acetaldehyde that are present in PET. 23

52 3. Study any changes in the physical properties of PET due to the addition of the AA scavengers. 4. Determine the optimal amounts of AA scavengers to melt-blend with PET resins during injection molding. 5. Create a predictive model to quantify the overall effectiveness of the AA scavengers. 24

53 Chapter 2 Literature Review 2.1 Minimizing AA During PET Melt Processing There has been a significant amount of research focusing on reducing the presence of acetaldehyde (AA) in PET. The majority of this work has concentrated on the degradation routes that generate AA as a byproduct. As previously mentioned in Section 1.4.3, thermal degradation and thermal-oxidative degradation both lead to the generation of AA. 1, 3 Thermal degradation and thermal-oxidative degradation are two of the three main degradation routes of PET. Hydrolytic degradation, the last of the three main PET degradation routes, does not directly lead to the formation of AA. In fact, research has shown that the presence of water during PET processing actually reduces the amount of AA that is generated Limiting Thermal Degradation As previously stated in Section 1.3.2, thermal degradation of PET occurs when the polymer is exposed to excessive temperatures. Researchers have shown that exposure to these extreme conditions results in random chain scission reactions. Marshall and Todd 25 25

54 believed these reactions occurred at the end of the polymer chains. Both Goodings 17 and Ritchie 26 felt that thermal degradation reactions occur at the ester linkages. Although the true location of this degradation mechanism may be of debate, it is agreed that random chain scission reactions lead to the generation of additional carboxyl and vinyl ester endgroups. Thermal degradation is known to have several other effects upon PET besides the generation of additional carboxyl and vinyl ester end-groups. With the addition of these generated end-groups comes a reduction in the polymer s molecular weight and intrinsic viscosity (I.V.). Thermal degradation has also been known to cause discoloration within the polymer, as well as the formation of oligomers and low molecular weight byproducts. 1, 3 One of the low molecular weight byproducts that are formed through the thermal degradation of PET is acetaldehyde. AA has been shown to be the most prominent of all the byproducts generated through thermal degradation. 17 Some researchers have determined that AA comprises 80% of all the generated, gaseous byproducts. During thermal degradation, the formation of AA occurs predominantly by means of the vinyl ester end-groups. 23 As illustrated in Figure 1-11, in Section , the vinyl ester endgroup can generate AA by reacting with either a carboxyl end-group or a hydroxyl endgroup. 26

55 Shukla, et al 15 performed an exhaustive study examining the effects that various injection molding parameters can have on the degradation of PET and the generation of AA. Their work revealed that increasing the processing temperature by 10 o C will cause the AA concentration within PET to double. In addition, Shukla, et al 15 showed there exists strong relationships between an injection molder s shear rate and the generation of AA, as well as between the polymer s processing time and the amount of AA that is generated. Intuitively, to minimize the effects of thermal degradation and the amount of generated AA, a balance must be made between the processing temperature, the residence time, and the shear heating that occurs during extrusion or injection molding Limiting Thermal-Oxidative Degradation While hydrolytic degradation is reported to be the most aggressive form of PET degradation, researchers 14, 16 have shown thermal-oxidative degradation to be a more disruptive than thermal degradation. Thermal-oxidative degradation, as previously discussed in Section 1.3.3, occurs when oxygen reacts with PET at elevated temperatures. By comparing various melting environments, Jabarin and Lofgren 14 showed that thermaloxidative degradation had higher reaction rates than thermal degradation; indicating that degradation occurs more rapidly. Yoda, et al 16 found that thermal-oxidative degradation can lead to the formation of branched and cross-linked chains; and in some circumstances, thermal-oxidative degradation can even lead to gel formation. Branched/cross-linked chains and gel formation only result from thermal-oxidative degradation. 27

56 Both thermal degradation and thermal-oxidative degradation share many common traits. 1 First, both mechanisms require excessive temperature to degrade the PET chains. Second, for the most part, both degradation systems result in similar effects upon PET: reduction of I.V. or molecular weight, formation of carboxyl end-groups, discoloration, and generation of low molecular weight byproducts. Third, both degradation systems produce AA as one of their more prominent byproducts. Figure 1-12, located in Section , details the reaction scheme from which AA is produced by thermal-oxidative degradation. The exposure to elevated temperatures leaves the ethylene linkage of a PET chain susceptible to be attacked by oxygen. The formed branched hydroperoxide group will decompose and form free radicals. The formation of two free radicals causes the PET chain to split in two. One PET chain is terminated by a vinyl ester end-group and the other is terminated by a hydroxyl endgroup. These functional end-groups then react with one another to re-form a PET chain and a molecule of AA. Ideally, to minimize the chance of thermal-oxidative degradation from occurring, PET should be melted and/or processed under an inert environment. An example of this is the continual flushing of the headspace of an extruder with nitrogen gas to displace any oxygen. Vacuum pressure could also be applied in a similar manner; continually removing oxygen and any generated gaseous byproducts. 28

57 2.2 Minimizing AA by Choice of Polymerization Catalysts The manufacturing of PET requires the use of various metal acetates and/or oxides to 1, 3, 4, 27 drive both the esterification and transesterification reactions. Examples of these catalysts have been previously mentioned in Section It is well documented that catalyst systems play a critical role in the degradation of PET, and eventual generation of AA. In separate publications, Zimmermann 27, Rieckmann and Völker 4, and Jabarin 3 all provide a summary of these investigations. Zimmermann and co-workers 27 have extensively studied both the thermal and thermaloxidative degradation of PET. This work was performed by using a variety of catalyst systems. Zimmermann identifies cobalt (Co), cadmium (Cd), nickel (Ni), and zinc (Zn) as the most aggressive catalysts which lead to PET degradation. Kao, et al 28 verified Zimmermann s work, reporting that the use of Co, copper (Cu), and Zn acetates increase the rate of degradation within PET. Derivatives of antimony (Sb), meanwhile, have been acknowledged by Zimmermann and Kim 29 as catalysts that do no accelerate PET degradation. Separately, Granzow, et al 30 and Zimmermann 27 have shown that phosphorus (P) based additives are able to provide stabilization and reduce the rate of degradation. 29

58 2.3 Minimizing AA by Choice of PET Resins As previously mentioned in Section 1.4.4, one avenue toward limiting the generation of AA is through the use of specifically designed PET resins. 2 These PET resins are sometimes referred to as water-grade resins, since they have been specifically tailored to the needs of water containers. 2 Since water does not require carbonation, the strength requirements of the PET container can be lessened; compared to the strength requirements of carbonated soft drink (CSD) PET containers. The PET water bottles need only enough strength to house the packaged water and survive an impact. Fundamentally, a reduction in the strength requirements for PET packaging means that the material s molecular weight or I.V. can be reduced. Generally, water-grade PET bottles can be manufactured with resins that range in I.V. between 0.70 and 0.76 dl/g; whereas, bottles manufactured for CSD packaging require an I.V. between 0.80 and 0.84 dl/g. Some 20 believe that since these water-grade resins have lower intrinsic viscosities, they are inherently exposed to less shear heating than are CSD grade resins, during processing. Shukla, et al 15 showed that minimizing shear heating can significantly reduce the amount of AA that is generated in PET. Other researchers, 1, 31 however, feel that AA generation is unrelated to molecular weight or I.V. It is their belief that chemical composition (catalysts, monomers, etc.) is the dominant factor in whether a PET resin produces more or less AA than another resin. 30

59 2.4 Minimizing AA by Means of Acetaldehyde (AA) Scavengers Acetaldehyde (AA) scavengers are additives, which when melt-blended into PET resin 20, 24 are designed to interact with any acetaldehyde that is present in the PET matrix. There are at least three different mechanisms through which this interaction occurs. One type of scavenger is designed to react with any generated AA and the second is designed to lock AA into its structure. Both of these systems do not minimize the amount of AA that is generated during the processing of PET; they simply limit its release by interacting with generated AA and thus its effects upon the packaged contents. A third type of scavenger is a catalyst system that converts AA into another compound which possesses different migration and/or flavor threshold properties Reactive AA Scavengers Polyamides Polyamides have been identified by several researchers as possible AA scavengers for PET. Several Eastman Chemical patents describe the use of polyester/polyamide blends to improve the flavor retention for polyester packaging applications. U.S. Patent 6,042, identifies an exhaustive list of possible low molecular weight partially aromatic polyamides and low molecular weight aliphatic polyamides that can be used as AA scavengers. Of the two general classifications listed, Long, et al 32 states that aromatic polyamides are more preferable than aliphatic polyamides because the aromatic 31

60 polyamides tend to be more easily dispersed and produce less haze. The patent describes blends having a polyamide composition between 0.05% and 2%, by weight; the remaining balance of the blend is polyester. Long, et al 32 suggests two particular polyamides to be the most effective at AA scavenging: poly(hexamethylene adipamide) and poly(meta-xylene adipamide) (MXD6). It is recommended that the number average molecular weight for poly(hexamethylene adipamide) should be between 3,000 to 6,000 g/mol and an inherent viscosity of 0.4 to 0.9 dl/g. Long claims that MXD6 should possess a number average molecular weight between 4,000 to 7,000 g/mol and an inherent viscosity of 0.3 to 0.6 dl/g. The chemical structure for MXD6 is shown in Figure 2-1. H 2 N H 2 C CH 2 NH OOC (CH 2 ) 4 COOH Figure 2-1: The chemical structure of MXD6 Polyamides, particularly MXD6, have been added to PET to help improve its barrier properties. 47 When polyamides are melt-blended with PET a yellowing phenomenon of the polymer blend typically results. Bandi, Mehta, and Schiraldi 48 studied the mechanism from which chromophores are generated when PET is melt-blended with polyamides. Of particular interest were PET/MXD6 blends. Bandi, et al 48 linked the color generation to the formation of an imine group, which is the result of a reaction between the amine endgroup of MXD6 and the aldehyde group of AA. It is through this reaction, shown in 32

61 Figure 2-2, that MXD6 exhibits its use as an AA scavenger when melt-blended with PET. It should be noted that the reaction shown in Figure 2-2 does generate a byproduct, water (H 2 O). O H 2 N H 2 C CH 2 NH OOC (CH 2 ) 4 COOH + H 3 C CH (MXD6) (AA) H 3 C HC N H 2 C CH 2 NH OOC (CH 2 ) 4 COOH Figure 2-2: Acetaldehyde scavenging reaction between MXD6 and AA 24 Other polyamides, besides MXD6, have also been evaluated as AA scavengers for PET. In WO Patent , Turner and Nicely 44 proclaim the scavenging ability of polyester/polyesteramide blends. The addition amount of the polyesteramide ranges from 0.05% to 2% by weight. Ciba Specialty Chemicals 36, 42, 43, 45 patented polyacrylamide, polymethacrylamide, and copolymers of polyacrylamide and polymethacrylamide as AA scavengers for PET. Both polyacrylamides and polymethacrylamides possess a branched amine groups that allow the polymers to scavenge AA in a similar manner as MXD6. U.S. Patent 7,022,390 teaches that optimal polymethacrylamide concentration can vary between 0.03% to 1%, by weight, when melt-blended with PET. 33

62 Low Molecular Weight Amides U.S. Patent 7,550, lists several low molecular weight amides that can potentially be used to scavenge generated AA within PET. This list includes: anthranilamide, malonamide, salicyclamide, o-mercaptobenzamide, N-acetylglycinamide, and 2- aminobenzenesulfonamide. Of particular interest is anthranilamide, which was patented by Rule, Shi, and Huang 50 for its use as an AA scavenger. As shown in Figure 2-3, the chemical structure of anthranilamide is comprised of two functional groups, an amide group and an amine group, attached to a substituted benzene ring. According to Rule, et al 50, the reaction between anthranilamide and acetaldehyde produces water and a resulting organic compound comprising an unbridged five or six member ring including the at least two heteroatoms. The patent goes on to described two more details: one, the unbridged 5 or 6 member ring of the resulting organic compound is bonded to the aromatic ring and, two, the two heteroatoms are both nitrogen. NH 2 O NH 2 Figure 2-3: Chemical structure of anthranilamide 34

63 According to Rule, et al 50, it is the formation of this second ring structure that makes anthranilamide an appealing AA scavenger. Patent 6,274,212 claims, Unlike the prior art methods that depend on the formation of inherently colored imines, the formation of unbridged 5 or 6 member ring structures do not inherently result in color formation. It was the generation of imine functional groups that Bandi 48 suggested was the reason for color generation in PET/polyamide blend systems. In addition, Rule, et al 50 also claims that thermodynamics often favor ring formation more than imine formation; thus, significantly lower amounts of the organic additive compound of this invention can effectively decrease the AA content of melt-processed polyesters. Addition levels for anthranilamide are recommended to be between 10 and 1000 ppm Polyamines Patent literature shows that polyamines can be added to oxygen scavenging systems to react with and stabilize the byproducts that result from those reactions. In U.S. Patent 5,942,297 Speer, et al 51 identifies a list of polyamines that can react with the various aldehydes and alcohols that are formed during oxygen scavenging reactions. This list includes: polymers and copolymers of allylamine, polymers and copolymers of diallylamine, polymers and copolymers of vinyl amine, poly(d-glucosamine), silicasupported polymeric amines, and amine functionalized silicas. The scavenging reaction between terminal amines and aldehydes follow a chemistry similar to that in the reaction scheme shown in Figure 2-2. This condensation reaction generates an imine compound and water, as a byproduct. 35

64 Similar to the application depicted by Speer, et al 51, Ching, et al 52 claims a similar use for polyamines. U.S. Patent 6,057,013 describes a multi-layer oxygen scavenging system in which one of the layers is comprised of an oxygen scavenging material, a second layer is comprised of byproduct neutralizing materials, a third layer is an oxygen barrier, and a fourth layer is a polymeric selective barrier. The intent of adding these byproduct neutralizing materials is to prevent byproducts of the oxygen scavenging reactions from diffusing through the multi-layer structure and into the packaged contents. The list of neutralizing materials listed in Patent 6,057, includes low molecular weight amines, amine-containing polymers, and polyamines. The identified low molecular weight amines are: dipropylenetriamine, tris(3-aminopropylene)amine, N,N,N N -tetrakis(3- aminopropyl)ethylenediamine and 1,12 dodecanediamine. The identified aminecontaining polymers are: glycols containing amine groups such as polyethylene glycol with two amines and polypropylene glycol with two amines, and dimethylaminoethanol grafted ethylene-methyl acrylate copolymers. The identified polyamines are: pentaethylene hexamine (PEHA), triethylene tetraamine, polyvinyl oxazoline, and comparable higher molecular weight products Polyimines In U.S. Patent 5,362,784, Brodie, et al 53 teaches that a specific class of polyimines can be used to scavenge aldehydes in polyesters. The class of polyimines mentioned by Brodie, et al is known as polyalkylene imines (PAI); more specifically the authors talk of polyethylene imine (PEI). It is recommended that PEI has an average molecular weight 36

65 of at least 2500 g/mol, is not heavily branched, and has a low amount of tertiary amines. The optimal blending of PEI and PET is claimed by the authors to be between 0.01 and 10:100, by weight. It is mentioned within Patent 5,362, that the use of binding agents can be used to lock in the polyalkylene imines into the polymer matrix. It should be noted that Brodie, et al discuss the use of PAI and PEI as aldehyde scavengers in two more U.S. Patents; 5,284, and 5,413, The application of these two patents, however, concern blending the polyimines with polyolefin materials Polyols Polyols are a class of alcohols that contain multiple hydroxyl groups. The AA scavenging ability of these compounds has been claimed by several researchers in patent literature. McNeely and Woodward 56 describe a PET modified by an alkoxylated polyol; intended to enhance the material s melt-strength. The specific polyols mentioned in U.S. Patent 5,250,333 are alkoxylated trimethylolethane, alkoxylated trimethylolpropane, alkoxylated pentaerythritol, and the alkoxylated dimmer of pentaerythritol. McNeely and Woodward teach that their optimal concentration is between 100 and 50,000 ppm. While McNeely and Woodward 56 did not claim the AA scavenging ability of polyols in their patent, Al-Malaika s patents 57, 58 do state that ability. In WO Patent and U.S. Patent 6,936,204 58, Al-Malaika describes the use of polyol/pet blend systems as a way to reduce AA. These multiple hydroxylic compounds should ideally possess 37

66 between 3 to 8 hydroxyl groups and be present between and 2%, by weight. The specific polyols mentioned in these patents are triglycerin, trimethylolpropane, dipentaerythritol, tripentaerythritol, D-mannitol, xylitol, and D-sorbitol. In WO Patent , Eckert, et al 59 also describes the use of polyols as AA scavengers in PET systems. The authors of this patent claim that desired polyols have at least one primary hydroxyl group and another primary, secondary, or tertiary hydroxyl in the 2 and/or 3 position. The identified list of polyols that fit the criteria includes xylitol, mannitol, and sorbitol. To reduce AA, the concentration of these additives can range between 50 and 5000 ppm; although polyol content can be as high as 25% by weight. An example of the aldehyde scavenging ability of a polyol is shown in Figure 2-4. In this reversible reaction scheme, two molecules of D-sorbitol react with one molecule of valeraldehyde to produce a higher molecular weight acetal and a byproduct, water. A similar reaction occurs when AA is the sought after compound. This also yields water as the byproduct. Odorisio and Andrews 60 also identified a group of polyols that can be used as AA scavengers in PET. This group consists of homo- and copolymers of polyhydric alcoholcontaining polymers which are derived from 2-propenoic acid ester monomers. Within this group, the most preferable is poly(glyceryl methacrylate) homopolymer. U.S. Patent 7,138, teaches that poly(glyceryl methacrylate) homopolymer s ideal concentration can vary between 0.01 and 5%, by weight. 38

67 Figure 2-4: Aldehyde scavenging reaction between D-sorbitol and valeraldehyde Size-Enclosing AA Scavengers Cyclodextrins Cyclodextrins are cyclic oligosaccharides consisting of six, seven, or eight repeat glucopyranose units. 24 Figure 2-5 shows the how the classification of cyclodextrin changes with the number of glucopyranose repeat units; it also shows how the internal and external diameters change with the number of repeat units. 61 Figure 2-6 shows the chemical structure of alpha-cyclodextrin. 39

68 Figure 2-5: Various forms of cyclodextrin 62 Figure 2-6: Chemical structure of alpha-cyclodextrin 24 Wood, et al have several patents claiming that cyclodextrin can encapsulate AA, as wells as other permeates, into its molecular structure. An example of this interaction mechanism is shown in Figure 2-7, with caproaldehyde as the guest molecule. Cyclodextrin does not inhibit the generation of AA during the melt processing of PET. As with other AA scavengers, it merely limits the diffusion of AA out of the polymer s 40

69 matrix. 62 According to Wood, et al, the optimal amount of cyclodextrin melt-blended into PET ranges between 0.1 to 5 %, by weight. Figure 2-7: Proposed fitting of caproaldehyde and cyclodextrin 24 Several authors have shown that 1 H NMR (proton nuclear magnetic resonance spectroscopy) can be used to validate cyclodextrin s size-enclosing mechanism through NMR titration studies. NMR titration studies involve varying the concentration of the inclusion species (guest) to the concentration of cyclodextrin (host). 1 H NMR spectra are recorded for several samples of varying host to guest ratios. A plot is then made of the change in the chemical peak shift (y-axis), in ppm or δ units, versus the host to guest ratio (x-axis), in units of concentration. One such NMR titration study was performed by Hao, et al 71 who studied the complex formation of 2, 2 -ditelluro-bis(β-cyclodextrin) (2-TeCD) with glutathione (GSH). This study was performed at room temperature, using deuterium oxide (D 2 O) as the solvent. Figure 2-8 shows the change in the chemical shift ( δ) for a proton of the guest molecule 41

70 (GSH), labeled H5 proton, as the concentration of the host molecule (2-TeCD) is increased. Figure 2-8: 1 H NMR titration experiment of 2-TeCD and GSH 71 NMR measures the overall chemical environment which a particular hydrogen or carbon atom experiences; depending on the analysis method: proton ( 1 H) NMR or carbon-13 ( 13 C) NMR. It does this by averaging the chemical shift seen for each particular proton or carbon-13 atom. When the guest molecules are dissolved in a solvent, the 1 H NMR yields a standard chemical shift for each of its protons. This particular chemical shift is based on the chemical environment which those protons experience in that particular solvent. As host molecules are added, guest molecules move from the solvent to the internal structure of the host molecules. While the guest molecules are inside the internal structure of the host molecule, hydrogen bonding occurs between the protons of the guest 42

71 molecules and the protons which line the internal structure of the host molecules. The NMR instrument interprets this hydrogen bonding as a change in the chemical environment of the guest molecule s protons. The instrument responds with a different chemical shift for the guest molecules protons than previously seen when they were in solvent alone. As the concentration of the host molecules increases, the number of guest molecules which occupy the internal structure of the host molecules also increases. Since the NMR instrument averages the chemical shift for each particular proton, the change in the chemical shift changes correspondingly; as shown in Figure 2-8. The change in the chemical shift, of the guest molecules protons, occurs until a saturation point is reached. This saturation point is achieved when all of the guest molecules are occupying the internal structure of host molecules; thus changes in the chemical shift of the guest molecules protons can no longer occur. The saturation point is indicated in Figure 2-8 as the position where the slope of the graph flattens and it equals zero. Figure 2-8 shows that the saturation point for Hao s experiment 71 occurs when a 2:1 host-to-guest ratio is achieved Zeolites Zeolites 75 are a class of microporous, crystalline solids that occur both naturally and synthetically. They are generally composed of aluminum (Al), silicon (Si), and oxygen (O). The polarity of their internal pore allows cations such as sodium (Na), calcium (Ca), and potassium (K) and small molecules such as water to fill their internal cavities. 43

72 Massey and Callander 76 noted that the propensity for zeolites to absorb water, into their internal cavities, is so strong that if water is absent from the system zeolites will allow any material into their cavities as long as it is small enough to fit through the pores and enter the internal structure. This filter mechanism allows zeolites to act as molecular sieves and separate smaller molecules from larger ones. In U.S. Patent 4,391,971, Massey and Callander 76 teach of a process for reducing AA content by passing molten PET through a filter containing a molecular sieve. The described molecular sieve is a zeolite composition and is claimed to be located between an extruder outlet and a receiving mold of forming die. Massey and Callander 76 also state that their process will improve the brightness and color of the resulting PET resin. While Massey and Callander 76 pass molten PET through a zeolite based filter to reduce AA content, Mills, et al 77 teach that zeolites can also be melt-blended into the polymer s matrix to achieve the same result. The authors claim that the addition of small- or medium-pore zeolites can aid in minimizing AA concentration without reducing the clarity of the final PET article. Small-pore zeolites have an eight tetrahedral structure with an internal diameter of 4.1 angstroms (Å); while medium-pore zeolites have a tenring system with an ellipsoidal tubular diameter of 5.5 Å by 5.6 Å. WO Patent Application teaches that the optimal addition amount of these zeolites is between 100 and 1000 ppm. 44

73 2.4.3 AA Scavenging Catalysts Researchers have shown that certain catalyst systems can also act as AA scavengers. As previously discussed in Section , the catalysts used for PET polymerization include: acetates of antimony (Sb), lithium (Li), calcium (Ca), magnesium (Mg), zinc (Zn), and lead (Pb); as well as oxides of Sb, Pb, and germanium (Ge). AA scavenging catalysts are not added to assist in the polymerization of PET; there sole intent is to convert the molecular structure of AA into another product which has different migration and/or flavor threshold properties. Go and Burzynski 78 describe a method for manufacturing PET resins with enhanced thermal stability against the generation of AA. Their process incorporates an alkali metal salt of ethylenediaminetetraacetic acid (EDTA) into melt-phase polymerization. U.S. Patent 4,357, teaches that the alkali metal should be either sodium (Na) or potassium (K). The authors claim that the amount of EDTA can range between and 0.2 mol percent. They indicate that amounts above 0.5 percent can lead to discoloration. In U.S. Patent 6,569, and W.O. Patent , Rule teaches that an oxidation catalyst can be used to convert AA to acetic acid. Rule claims that the conversion of AA to acetic acid occurs as oxygen gas permeates the PET packaging. Therefore, this reaction is also capable of decreasing the migration of oxygen through PET containers. Converting AA to acetic acid is appealing because acetic acid has a taste threshold that is 45

74 more than 1000 times greater than acetaldehyde. The oxidation catalysts described in these patents are simple cobalt (Co) or manganese (Mn) salts; or Co or Mn salts comprised of an amine, phosphine, or alcohol complex. Rule 79, 80 notes that simple salts can include: cobalt acetate, cobalt octoate, cobalt naphilhenate, manganese acetate, manganese octoate, and manganese naphthenate. Examples of amine complexes include EDTA and glycine. The concentration of these catalysts should be between 1 and 500 ppm, but most preferably between 5 and 50 ppm. Rule and Shi 81 describe a PET resin comprised of a hydrogenation catalyst and at least one source of reactive hydrogen. In this application, the hydrogenation catalyst can be a Group VIII metal (zero valent nickel, palladium, or platinum) or a metal hydride (tin or titanium based complex). According to U.S. Patent 7,041,350, the catalyst s amount can range between 0.1 and 100 ppm; optimally between 5 and 50 ppm. The identified reactive hydrogen source is poly(methylhydro)siloxane (PMHSO) and its concentration should be 1 to 50 time greater than the amount of AA. 46

75 Chapter 3 Experimental Work 3.1 Materials The acetaldehyde (AA) scavenging capabilities of three materials were evaluated. Anthranilamide was purchased from Sigma-Aldrich, meta-xylenediamine (MXDA) was donated by Mitsubishi Gas Chemical America, Inc, and alpha-cyclodextrin was supplied by the Wacker Chemical Corporation. Acetaldehyde was also purchased from Sigma- Aldrich and used to spectroscopically study the chemical interactions that occur between AA and the various scavenging materials. The spectroscopic analysis, particularly NMR, was conducted in the presence of deuterated solvents. Deuterium oxide (D 2 O) and deuterated chloroform (CDCl 3 ) were both purchased from Cambridge Isotope Laboratories. The various AA scavengers were also melt-blended with a commercially available poly(ethylene terephthalate) (PET) resin. Voridian CB12, produced by Eastman Chemical, is a PET copolymer resin with an initial I.V. of 0.84 dl/g. It is designed to be used in the manufacturing of carbonated soft drink (CSD) containers. 47

76 3.2 Spectroscopic Techniques to Study Chemical Interactions AA scavengers work by interacting with the acetaldehyde that is present within PET. These chemical interactions prevent AA from diffusing from the matrix of the polymer and into either the packaged contents of the container or into the atmosphere. Studying and determining these chemicals interactions was achieved through two spectroscopic techniques: nuclear magnetic resonance (NMR) spectroscopy and mass spectroscopy. NMR provided the primary information, while mass spectroscopy was used to supplement the NMR data Nuclear Magnetic Resonance (NMR) Spectroscopy Nuclear magnetic resonance (NMR) spectroscopy is a powerful analytical tool used to perform structure elucidation and determine the identity of unknown compounds. 82 NMR works on the premises that certain nuclei ( 1 H, 13 C, etc.) have magnetic properties when in the presence of a magnetic field. 83 When an electromagnetic pulse is applied, energy is absorbed by the nuclei and then sent back out. The energy is remitted at a specific 82, 83 resonance, explicit to the studied nuclei s chemical environment. The most commonly studied nuclei in NMR are 1 H and 13 C. The appeal of studying these two nuclei is due to their relative abundance within organic compounds. Although 1 H NMR is about 5700 times more sensitive than 13 C NMR 83, both techniques are very powerful and capable of providing significant data. These NMR methods are sometimes 48

77 referred to as one-dimensional techniques. The reason for this designation is because the resulting spectrum from 1 H or 13 C NMR appears relative to only one axis or scale. In addition to one-dimensional NMR, there also exists a family of two-dimensional NMR techniques. Two-dimensional NMR yields spectra that are shown relative to two scales; one scale is on the x-axis and the other scale is on the y-axis. The data can be correlated between these two axes to show which nuclei are coupled or connected to oneanother 83 ; information that one-dimensional techniques may not be able provide. Two-dimensional NMR techniques enhance the information that one-dimensional methods provide, making it possible to decipher the chemical structure of compounds too difficult with only one-dimensional NMR spectra Proton ( 1 H) NMR In order to properly identify the interaction mechanisms between the various AA scavengers and acetaldehyde, proton nuclear magnetic resonance ( 1 H NMR) was used. 1 H NMR was chosen over 13 C NMR for two reasons: one, 1 H NMR is approximately 5700 times more sensitive than 13 C NMR and two, 1 H NMR is able to provide quantitative data; something 13 C NMR cannot always provide. 82 For this project, the NMR Varian Inova 600 MHz spectrometer, located in the University of Toledo s Instrumentation Center, was used. 49

78 The 1 H NMR work began by analyzing the various AA scavengers and acetaldehyde independently. Each material was dissolved in an NMR tube using an appropriate deuterated solvent. Its spectrum was then obtained and analyzed to characterize each 1 H NMR peak for the given compound. After obtaining the spectrum for each respective component, the next step was to mix acetaldehyde with each scavenger and study any changes in the resulting 1 H NMR spectrum. Both acetaldehyde and an AA scavenger were separately dissolved using the same deuterated solvent. The weights of each component were recorded so that the proper stoichiometric ratio was achieved. These solutions were then mixed together in an NMR tube and analyzed H- 1 H COrrelation SpectroscopY (COSY) Proton Proton ( 1 H- 1 H) COrrelation SpectroscopY (COSY) is a common twodimensional NMR technique. This experiment reveals the coupling/connection pattern of the protons that compose the studied chemical compound 83 ; helping to map-out the chemical structure. The output of this experiment is the sample s 1 H NMR spectrum on both the y- and x-axes. Since these spectra are obtained by the same magnetization, there is a symmetry that yields diagonal peaks. The off diagonal peaks or cross peaks are what indicate the coupled protons of the analyzed sample. 50

79 1 H- 1 H COSY NMR was used to help decipher those 1 H NMR spectra that were, alone, too hard to interpret. The sample preparation for this experiment was the same as for 1 H NMR. Separately, acetaldehyde and an AA scavenger were dissolved using the same deuterated solvent. These two solutions were stoichiometrically mixed together and then analyzed. Analysis was conducted via the NMR Varian Inova 600 MHz spectrometer, located in the University of Toledo s Instrumentation Center Mass Spectrometry Mass spectrometry is a versatile, analytical tool that can be used to both qualitatively and 82, 83 quantitatively determine an unknown analyte based upon its mass. Upon entering a mass spectrometer, a chemical compound is ionized by some ionization method incumbent within the machine. These generated ions are then separated, by the instrument s separations method, based upon their mass to charge ratio. 82 The spectrometer s detector subsequently quantifies the amount of ions at each mass to charge ratio, yielding a chart illustrating the abundance of each ion at the various ratios. 83 There are various types of mass spectrometers, each possessing a different ionization 82, 83 method and a different mass analyzer. For this project, the Esquire liquid chromatograph/mass spectrometer (LC-MS), located in the University of Toledo s Instrumentation Center, was used. This mass spectrometer possesses electrospray ionization, as its ionization source, and an ion trap, as its mass analyzer. The intent of the 51

80 mass spectrometry experiments was to compliment and validate the results seen from the NMR work. The preparation of each sample was as follows. A small amount of the sample, typically between 10 to 15 milligrams, was dissolved in a solvent; usually chloroform. Next, to aid with the ionization process, a very small aliquot of methanol was added to the dissolved sample. Prior to analysis, the mass spectrometer was purged with pure solvent, in order to clean the instrument of any residual impurities. Experimental samples were then directly injected into the mass spectrometer. The resulting spectrum was recorded and analyzed. 3.3 Twin-Screw Extrusion The melt-blending of AA scavengers into PET resin was performed by means of a Werner and Pfleiderer ZSK-30 twin-screw extruder; operating at 300 revolutions per minute (rpms) and 280 o C. Attached to this extruder are a nitrogen tank and a vacuum pump. Nitrogen gas is fed into the throat of the extruder to displace any oxygen, creating an inert environment for PET melting and processing. The vacuum pump is attached to the barrel of the extruder and is used to remove any volatile chemicals that are generated during PET processing. Experimental samples were prepared by melt-blending each of the three scavenging agents with the CSD PET resin. For each AA scavenger, a master-batch AA 52

81 scavenger/pet blend sample was initially extruded. Further concentrations of each AA scavenger/pet blend system were made by diluting the appropriate master-batch blend. A determined amount of the master-batch sample was re-extruded with a known amount of virgin PET. For comparative purposes, control samples were also extruded under similar conditions. These samples were the same CSD PET resin, however, without the addition of any AA scavenging agents. Prior to extrusion, all PET samples were dried overnight at 150 o C and under vacuum; in either a Conair Franklin desiccant hopper/dryer or a small vacuum oven. This step was taken to limit the presence of moisture and thus minimize the effect of hydrolytic degradation during extrusion Preparation of Alpha-Cyclodextrin/PET Blend Samples To prepare the alpha-cyclodextrin/pet master-batch sample, determined amounts of pure resin and the AA scavenger were weighed and then placed in separate vacuum ovens. The virgin PET sample was dried overnight at 150 o C, while alpha-cyclodextrin was dried at 80 o C. After drying, the alpha-cyclodextrin and PET samples were removed from their respective ovens and dry-mixed in a small metal bucket. The mixing was done as quickly as possible to minimize the resin s absorption of moisture from the atmosphere. This PET blend was then extruded, pelletized, and collected. The concentration of alphacyclodextrin within this master-batch sample was 5 % by weight. 53

82 Through the dilution of this 5 weight % alpha-cyclodextrin/pet master-batch sample, further blend concentrations were obtained. A 2.5 weight % blend was produced by melt-blending equal parts, by weight, of the 5 weight % master-batch sample with the virgin, CSD PET resin. Each of these components was weighed and placed in a metal bucket that was dried overnight in a small vacuum oven, at 150 o C. The next morning this sample was extruded, pelletized, and collected. A similar process was followed to yield 1 weight % (or 10,000 ppm) and 0.5 weight % (or 5000 ppm) alpha-cyclodextrin/pet blend samples. To obtain the least concentrated alpha-cyclodextrin/pet samples, the 1 weight % sample was used as the concentrate instead of the 5 weight % master-batch sample. The thought was that by using a more diluted blend the AA scavenger would have a better chance of being uniformly dispersed, within the PET resin, during the extrusion process. A better distribution of the AA scavenger should provide a more homogeneous blend, limiting variability within the pellets. This methodology may have increased the possibility of acquiring more uniform AA scavenger dispersions, at the lowest concentrations; however, it also increased the thermal histories of these PET blends. As an example, portions of the 500 ppm alphacyclodextrin/pet blend sample have been processed up to three times: Extruded once: the virgin PET resin added to dilute the 1 weight % blend to the desired 500 ppm concentration 54

83 Extruded twice: the virgin resin melt-blended with the 5 weight % master-batch sample to yield an overall alpha-cyclodextrin concentration of 1 weight % Extruded three times: the 5 weight % master-batch sample that was extruded with virgin resin to dilute the blend s alpha-cyclodextrin concentration to 1 weight % blend Table 3.1 breaks down the thermal histories of the various alpha-cyclodextrin/pet blend samples. This table shows how much of each sample was extruded once, twice, and even three times to achieve the final, desired AA scavenger concentration. Table 3.1: The thermal history for each alpha-cyclodextrin/pet blend Scavenger Concentration Percentage of Processed Material weight % ppm 1x 2x 3x , , , Preparation of Anthranilamide/PET Blend Samples The preparation of the anthranilamide/pet blend samples was very similar to the procedure used to prepare the alpha-cyclodextrin/pet blend samples. The anthranilamide/pet master-batch sample was prepared by weighing determined amounts of the AA scavenger and pure resin. Each sample was place in its own vacuum oven and dried overnight; virgin PET at 150 o C and anthranilamide at 80 o C. The next morning, these two components were dry-mixed in a small metal bucket and then extruded and 55

84 pelletized. The anthranilamide concentration of this master-batch sample was 1 weight %. Similar to the process described in Section 3.3.1, the anthranilamide/pet master-batch sample was further diluted to make additional blend samples. The 1 weight % (or 10,000 ppm) anthranilamide/pet master-batch blend was reprocessed and diluted to produce a 1200 ppm blend and a 500 ppm blend. The lowest anthranilamide/pet blend samples, the 200 ppm and the 100 ppm blends, were prepared from the 1200 ppm concentrate. As discussed in Section 3.3.1, a more diluted blend was used with the hope that it would produce less variability and more homogeneity among these samples. Table 3.2 has been prepared to show the amount of each anthranilamide/pet blend that has been extruded once, twice, and even three times. Table 3.2: The thermal history for each anthranilamide/pet blend Scavenger Concentration Percentage of Processed Material weight % ppm 1x 2x 3x , Preparation of MXDA/PET Blend Samples The process to produce the MXDA/PET blends varied slightly in comparison to the methods discussed in Sections (alpha-cyclodextrin/pet blends) and (anthranilamide/pet blends). The change in preparation methods was because at room 56

85 temperature MXDA is a liquid 84 ; while alpha-cyclodextrin 85 and anthranilamide 86 are crystalline materials. To blend this scavenger with PET, MXDA was pumped into the throat of the extruder at a desired rate; through the use of a pump. Prior to extrusion, the virgin PET resin was dried overnight at 150 o C in a Conair Franklin hopper/dryer to eliminate moisture. The next morning, the process began by extruding PET resin until a steady-state was established. Once steady-state was achieved, the pump was turned on, blending MXDA with the molten polymer. Collection of the pelletized MXDA/PET blend sample began three minutes after the pump was initially turned on. As with the previous processes, a vacuum pump and nitrogen gas were used to limit the degradation of the material during extrusion. Since MXDA is known to be very reactive, a plastic tarp was used to create a tent that surrounded the twin-screw extruder. This precaution was used to direct any volatiles toward the lab hood that was located above the extruder. The resulting MXDA/PET master-batch sample had an AA scavenger concentration of 1 weight %. It should be noted that this sample had a slight greenish tint to its appearance. The various MXDA/PET blend samples were produced by the same manner as described (Section 3.3.2) for the range of anthranilamide/pet blends. The 1 weight % (or 10,000 ppm) master-batch blend was used to make a 1200 ppm blend and a 500 ppm blend. The 200 ppm and 100 ppm blend were created from the 1200 ppm MXDA/PET concentrate. Table 3.3 shows the amount of each MXDA/PET blend that has been extruded once, twice, and even three times. Since the MXDA/PET blend samples were prepared in the 57

86 same manner as the anthranilamide/pet blend samples, the thermal histories shown in Tables 3.2 and 3.3 are identical to one another. Table 3.3: The thermal history for each MXDA/PET blend Scavenger Concentration Percentage of Processed Material weight % ppm 1x 2x 3x , Preparation of Control PET Samples A pure PET resin, without the addition of any AA scavenging agent, was extruded under conditions equivalent to those experienced during the melt-blending process of the various AA scavenger/pet blends. The resin used to establish this control sample was the same CSD PET resin which was melt-blended to make each of the various AA scavenger/pet blend samples. To simulate the sample blending methods discussed in Sections 3.3.1, 3.3.2, and 3.3.3, a total of three control samples were prepared. Prior to processing, all of these samples were dried overnight at 150 o C in a Conair Franklin hopper/dryer to eliminate moisture. The process to prepare these three control samples began by initially extruding, pelletizing, and collecting a large amount of the CSD PET resin. About one-half of this one-time processed control sample was set aside for analysis. The other half of this sample was re-extruded to establish the two-times processed control sample. Again, 58

87 about one-half of this two-times processed sample was set aside for analysis and the other half was re-extruded to create the three-times processed control sample. While this approach does not replicate the exact blend ratios established in Sections 3.3.1, 3.3.2, and 3.3.3; it does allow for comparisons to be made. For any analytical method, the evaluation of each control sample produces data which can be proportioned with the data from the other two control samples. This method creates theoretical values that can be compared to any AA scavenger/pet blend sample as long as the thermal histories of these two samples match. Matching the thermal histories is achieved by proportioning the correct amount of the one-time processed, two-times processed, and three-times processed control samples to equal the ratio for any particular AA scavenger/pet blend sample shown in Tables 3.1, 3.2, and Manufacturing PET Containers Producing PET containers is generally performed by means of a two stage process. The first step is known as injection molding, a process that melts PET resin and pushes the viscous polymer to fill a mold. For container manufacturing, the article that is produced is known as a preform. Transforming these performs into containers is achieved by a separate process known as stretch-blow-molding. This second and final step of the container manufacturing progression heats the PET preforms to temperatures that are slightly above the glass transition temperature (T g ) of 59

88 the material, but below its crystallization temperature. When a polymer is heated above its T g, it transitions from a glassy state into a rubbery state. These rubbery preforms are then mechanically stretched, by a rod, and blown to fill another mold. The result of the stretch-blow-molding process is a final PET container of a desired volume and design Injection Molding The Arburg 320S machine was used to injection mold preforms. This is a single cavity injection molder that has a 55-ton capacity and a reciprocating screw. The processing temperature was controlled to be 280 o C, with a nozzle temperature of 290 o C. The injection pressure was set at 1500 bar and the cooling time was 10 seconds. The mold used this work produces preforms specifically designed for 2-liter bottle manufacturing. In preparation for injection molding, two concentrations of each AA scavenger were prepared. A determined amount of an already extruded and melt-blended AA scavenger/pet blend was dry-blended with a determined amount of virgin PET. Each dry-blended sample was then dried overnight, at 150 o C, in a Conair Franklin hopper/drier. After drying, a transfer pipe from the Conair Franklin drier was attached to the throat of the injection molder for automated resin loading. A pure PET resin sample was also prepared by a similar process. This control sample provided a benchmark, to be compared against, for analytical testing. 60

89 For each sample set, the first ten preforms were discarded; allowing the machine to reach a steady-state until sample collecting began. Once the machine reached steady-state, twenty samples were collected and immediately placed in a freezer. This was to prevent any acetaldehyde from diffusing from the PET preforms and into the atmosphere; a vital step toward assuring accurate results when analyzing the residual AA content of those samples. The remaining preforms were set aside to be stretch-blow-molded into 2-liter bottles Stretch-Blow-Molding Transforming the prepared preforms into 2-liter bottles was achieved through a stretchblow-molding process. This process begins by heating a PET preform above its T g, as a result of exposure to infrared radiation (IR). The IR heating system consists of twelve quartz lamps, each rated at 1600 watts; with peak filament temperatures of 2200K at 240 volts. These twelve zones can be adjusted to alter the temperature profile. Figure 3-1 shows a drawing of a preform and approximately where the twelve zones are located Figure 3-1: Relative location of IR heating zones with respect to a perform 61

90 After loading a preform onto a rotating mandrel, the IR heater box passes the PET preform twice; returning to its starting position. The speed at which the heater box passes the preform and the voltages of the twelve IR heaters were optimized yield the best possible bottles. Additionally, the stretch rod pressure and the blow pressures were optimized to yield the best bottle appearance. Table 3.4 shows the optimized stretchblow-molding conditions for Voridian CB12 PET based samples. Table 3.4: Optimized stretch-blow-molding parameters Stretch Rod Pressure 100 psi Low Blow Pressure 60 psi High Blow Pressure 200 psi Heater Box Speed 230 Heating Settings -- Zone volts Zone volts Zone volts Zone volts Zone volts Zone volts Zone volts Zone volts Zone volts Zone volts Zone volts Zone volts 3.5 Gas Chromatography (GC) Chromatography is a common family of analytical techniques used as separation methods and used to quantify analytes. Chromatography methods are defined by their respective stationary and mobile phases. 82 Gas chromatography (GC), for example, uses a carrier gas as the mobile phase and a solid column as the stationary phase. 62

91 During GC, an inert carrier gas moves the gaseous sample through a long column, which is stored within an oven, and eventually to the instrument s detector where it will be quantified. As the sample moves through the column, it separates into its individual chemical species based on the affinity that each individual chemical species has toward interacting with the column (stationary phase). 82 If the strength of non-covalent interactions is strong between the chemical compound and the stationary phase, then it will have a longer retention time within the column than a chemical that does not interact as well with the material composing the stationary phase. 82 Gas chromatography is commonly used to analyze the presence of acetaldehyde in PET by two different techniques. The first method determines the rate at which AA is generated during the processing of PET resin. The second technique, known as headspace analysis, is used to determine the amount of AA that remains trapped within PET following processing Acetaldehyde Generation Analysis To quantify how much acetaldehyde is generated during processing, the AA generation rates were studied by a method described by Kim and Jabarin 23. This technique simulates the heating conditions that are needed to process PET. Measurements are made through the use of a Perkin-Elmer Automatic Thermal Desorption System (ATD 400) coupled to a Perkin-Elmer AutoSystem XL Gas Chromatograph. The gas chromatograph contains a Stabilwax -DA column, measuring 30 meters in length and has an internal diameter of 63

92 0.32 mm. The column temperature was 60 o C and used a helium gas purge. The GC uses a flame ionization detector (FID) to sense the amount of analtyes that have passed through the system. Perkin-Elmer s TurboChrom software then interprets the FID s response into the quantified peak areas of each analyte. Samples for this measurement are PET pellets, virgin or with AA scavengers, which have been dried and crystallized overnight, at 120 o C, in a vacuum oven. For each sample, two PET pellets are weighed using a five decimal place analytical balance; the combined target weight for these pellets is 0.03 ± 0.01 grams. These two pellets are placed in a cylindrical Teflon sample chamber, separated by quartz wool. This packed sample chamber is placed into a metal sample tube. Each sample tube that is placed in the ATD 400 is melted for a specified residence time and at a specified temperature; establishing only one data point along the AA generation curve. Multiple samples, measured at varying residence times, are therefore required to create an AA generation curve. The slope of this curve is the AA generation rate for the studied PET sample, at the evaluated temperature. The instrument is calibrated by injecting ten microliters (µl) of a µg/µl concentrated standard into a metal sample tube, containing a Teflon sample chamber packed with Tenax ; an analyte absorbing agent. This standard is purged into this sample tube for five minutes at a pressure of 0.5 pounds per square inch (psi). This process was repeated at least three times in order to obtain an averaged peak area. These prepared standards are placed in the ATD 400 and heated for 10 minutes at 250 o C. The 64

93 instrument s response is determined by dividing the averaged peak area, for the AA standards, by the amount of sample injected. A typical value for the GC s instrument response for this set-up is in the vicinity of 50,000 µ Volts sec onds ; µ means micro. µ grams AA Equation 1 shows the equation used to calculate the amount of AA for each sample. Table 3.5 provides an explanation of the variables in Equation 1. AA E E PA = (Equation 1) SW 1 S IR Table 3.5: Explanation of the variables from Equation 1 Variable Meaning Units AA Amount of acetaldehyde µgrams AA gramspet or ppm AA E PA Peak area of the experimental sample µ Volts seconds E SW Weight of the experimental PET sample grams PET S IR Instrument response obtained from the µ Volts sec onds standardized sample µ grams AA AA generation rates were established at three different temperatures (280, 290, and 300 o C) so that the activation energy (E A ) could be determined by means of the Arrhenius equation. Equation 1 shows the Arrhenius equation in its most common form. Table 3.6 provides an explanation of the variables displayed in Equations 2 and 3. Equation 3 shows the Arrhenius equation in a derived form. Using this equation, the activation energy can be determined graphically by plotting the natural log of the rate versus the inverse of the temperature, in degrees Kelvin. The slope of this plot is the activation 65

94 energy divided by the gas constant, and the y-intercept is the natural log of the preexponential factor. E A RT k = A e (Equation 2) Table 3.6: Explanation of the variables in Equations 2 and 3 Variable Meaning Units k Rate ppm min. A Pre-exponential factor ppm min. E A Activation energy Joules mole R Gas constant Joules mole Kelvin T Temperature Kelvin ( k) = ln( A) E ln (Equation 3) R A 1 T Residual Acetaldehyde Analysis As AA is generated through the degradation of PET it has the ability to diffuse out of the polymer s matrix; due to AA s low boiling point of 21 o C. 19 A portion of the generated AA, however, usually remains trapped within the manufactured PET article as residual AA. Quantifying the concentration of residual AA in PET packages is a critical aspect for many packaging applications because many foods and beverages have a limited 2, 20 threshold for AA. 66

95 For this work, the quantification of residual AA was performed by a headspace analysis technique. This technique coupled a Perkin-Elmer TurboMatrix 40 (TM 40) Headspace Sampler with a Perkin-Elmer AutoSystem XL Gas Chromatograph. The GC s settings for headspace analysis are identical to the parameters that were previously mentioned in Section For this measurement, processed samples (either melt-blended by twin screw extrusion or injection molded into preforms) were immediately collected and placed in a freezer to prevent the AA from volatilizing out of the PET matrix. Each sample, in its amorphous state, was ground by means of a small grinder made by the Tekmar Company. The amorphous PET sample was placed in the grinder and then saturated with liquid nitrogen to keep the polymer cold. The resulting ground powder was then separated using a sieve combination of 20 mesh, 40 mesh, and solid bottom. Only the 20 mesh sample was collected and used for this analysis. This is done in order to maximize surface area and increase amount of AA that can diffuse from PET. The ground PET samples were, again, immediately placed back into the freezer to prevent the diffusion of AA. Prior to analysis, the PET powder samples were removed from the freezer and then weighed on a five decimal place analytical balance. The samples are weighed within a glass sample vial which is capped and sealed immediately after weighing. During analysis, each sample is heated for 60 minutes at 150 o C and at 18 psi. This temperature does not melt the PET, it simply volatizes the residual amount of AA that is trapped within the PET into the headspace of the glass vial. Once the sixty minutes has lapsed, 67

96 the TM 40 injects a needle and extracts a sample of the gaseous headspace. This sample is sent through the GC column to be quantified. Calibration for this technique is similar to the procedure that is followed to perform experimental measurements. 2, 4, 6, 8, and 10 µl aliquots of standardized AA solution are respectively injected, by means of a syringe, into a glass sample vial. The standardized sample has a typical concentration of around µg/µl. Each of these five samples is heated for 15 minutes at 150 o C and at 18 psi. The instrument s response factor is determined by plotting the resulting peak areas against the respective AA concentrations; the origin is also used as a data point. The instrument s response factor is the slope of this linear line. Typical instrument response values for headspace determination vary between 600 and 900 µ Volts sec onds. µ grams AA Determining AA content within PET samples is calculated by means of Equation 1; previously shown in Section Equation 1 uses the experimental sample s weight (E SW ), the experimental sample s resulting peak area (E PA ), and the instrument s response factor (S IR ) from the calibration standards to tabulate the AA content within the PET sample. Table 3.5, also located within Section 3.5.1, provides further explanation of the variables in Equation 1. 68

97 3.6 Rheological Methods Plate and Plate Rheometer Determination of a PET sample s intrinsic viscosity (I.V.) was performed by measuring its melt viscosity. Conversion from melt viscosity to intrinsic viscosity was made by evaluating the melt viscosities of standardized samples that possess precisely known I.V.s. The solvent used to measure the intrinsic viscosities of standard PET samples was composed of 60% phenol and 40% tetrachloroethane. Melt viscosity measurements were made by a RDA III viscoelastic tester from Rheometric Scientific. Measurements were made at using parallel plate and plate geometry. Before making any measurements, the PET samples were crystallized and dried, at 140 o C, overnight. Table 3.7 summarizes the test conditions for the melt viscosity measurements. Table 3.7: Melt viscosity testing conditions Temperature 280 o C Motor Dynamic Test Delay 120 seconds Gap 1 mm Strain 15% Environment Nitrogen Shear Rate 10 radians/second 69

98 3.6.2 Capillary Rheometer An Instron Capillary Rheometer was used to study the viscosity of PET resin as a function of varying shear rates. Pelletized, virgin PET resin was dried overnight, at 140 o C, prior to analysis. Measurements were made at three different temperatures (260, 270, and 280 o C) so that the data could be extrapolated to predict the material behavior for an even wider range of temperatures. The resin samples were melted under an inert, nitrogen environment. Once the samples were completely melted within the capillary column, a desired crosshead speed was set and the force was measured; this was varied over a range of crosshead speeds. Using this data, along with instrumentation parameters, the apparent shear rates, shear stresses, and apparent viscosities were tabulated. Plots of viscosity versus shear rate yielded the desired rheology curves. Mathematical constants were determined from these plots and were used to predict the resin s rheology behavior within the multi-cavity injection molding modeling program. Table 3.8 lists the instrumentation parameters for this analysis. Table 3.8: Instrument parameters for the capillary rheometry analysis Capillary Diameter inches Capillary Length inches Barrel Diameter inches 3.7 Color Analysis Changes in color, due to the processing and/or addition of additives melt-blended into PET, were analyzed by means of a Hunter Lab Color/Difference Meter D25-2. The 70

99 instrument was initially calibrated using the standard colored plates supplied the company. Experimental measurements were made on crystallized PET pellets, at room temperature. Response from the instrument yields L, a, and b values for each sample. These values were then converted to Y, X%, and Z% values; according to Equations 5, 6, and 7, respectively. Ultimately, the Y, X%, and Z% values were used to calculate a yellowness index (YI). The yellowness index was calculated according to ASTM D , which is described by Equation 4. YI ( 125 ( X % Z% )) = (Equation 4) Y Where: Y 2 = 0.01 L (Equation 5) 2 a L ( 0.01 L ) + X % = (Equation 6) b L ( 0.01 L ) Z % = (Equation 7) 70 Table 3.9 gives an explanation of the L, a, b, and YI values that are obtained from the instrument or calculated using above equations. Table 3.9: Explanation of L, a, b, and YI values Variable Meaning L Measures lightness and varies from 100, for perfect white, to 0, for black; approximately as the eye would evaluate it a Measures redness when plus, gray when zero, and greenness when minus b Measures yellowness when plus, gray when zero, and blueness when minus YI Yellowness index of nearly white plastic samples; positive values indicate increase yellowness, while negative values indicate decreased yellowness or increased blueness 71

100 3.8 Differential Scanning Calorimetry (DSC) Analysis Differential scanning calorimetry (DSC) is a common technique used to analyze the thermal properties of polymeric materials. DSC analysis was performed to see if any changes in the thermal properties of the PET resin resulted from the melt blending of AA scavenging agents into PET. Measurements were made by means of a Perkin-Elmer DSC 7; with an attached nitrogen purge to prevent oxidative degradation from occurring during melting of the samples. Prior to analysis, samples were vacuum dried overnight at 120 o C. Each sample was heated to 300 o C, held for 5 minutes to remove all of its inherent crystallinity, and then rapidly quenched to 40 o C creating a completely amorphous sample. The sample was then reheated at 10 o C per minute to give the melting behavior, the crystallization behavior, as well as a value for the glass transition temperature (T g ). Cooling the sample at a rate of 10 o C per minute also indicated its crystallization behavior when cooled from the melt. 3.9 Oxygen Film Permeation Understanding the oxygen permeation rate for a given polymeric material is vital information when packaging oxygen-sensitive food or beverages. Oxygen from the atmosphere permeates through the plastic wall of the package, interacting with the packaged contents. Depending on the sensitivity of the contents, this interaction can alter the shelf-life of the packaged material. Studying the oxygen film permeation was 72

101 conducted to determine if the addition of AA scavengers would have any affect upon the oxygen barrier properties of PET. In order to understand the oxygen permeation rate a coulometric method was used, similar to the one described in ASTM Procedure D This procedure involves the use of the MoCon OxTran 1050 Oxygen Permeation Analyzer. This instrument uses a single coulometric detector that is switched by a valve to any of the 10 samples cells contained on the apparatus. Samples from sidewalls of stretch blow molded bottles were cut into four inch squares; two samples of each material were analyzed. For each sample, the average thickness was calculated after measuring the sample s thickness at nine evenly distributed points using a Magna-Mike With the sensor turned off, the samples were placed in the respective chambers of the analyzer and sealed in place. Initially, baseline measurements were made by purging the instrument of any oxygen with nitrogen gas. Once a baseline for each chamber was established, the purging gas was changed to oxygen. Over time the oxygen permeates from one side of the chamber, through the polymeric samples, and to the other side of the chamber where the oxygen purge is detected. The instrument output is an electrical current that corresponds to the amount of oxygen present. This current increases with time, until steady state is reached. Equation 8 shows the calculation used to determine the oxygen gas transmission rate (GTR). Table 3.10 gives an explanation of the variables used in Equation 8. 73

102 ( AV BV ) IF GTR = (Equation 8) Table 3.10: Explanation of the variables in Equation 8 Variable Meaning Units GTR gas transmission rate cc STP 2 100in day AV voltage for oxygen permeation mv BV base voltage mv IF instrument factor, which accounts for the cell area and the conversion factor for the detector cc STP 2 mv 100in day It should be noted that the baseline voltage is an averaged value, based upon two measurements. The voltage for oxygen permeation is the actual daily value; therefore, the oxygen gas transmission rate is calculated each day and not an averaged value. This value is not averaged is due daily fluctuations in barometric pressure. As shown in Equation 9, the oxygen permeance is inversely proportional to the barometric pressure. Table 3.11 gives an explanation of the variables used in Equation 9. GTR OP = (Equation 9) P Table 3.11: Explanation of the variables in Equation 9 Variable Meaning Units OP oxygen permeance cc STP 2 100in day atmospheres GTR gas transmission rate cc STP 2 100in day P change in pressure atmospheres 74

103 Since the fluctuations in barometric pressure are accounted for, the oxygen permeance may be averaged over the time of analysis. This averaged value for oxygen permeance can now be used, along with the average thickness of the sample, to determine the oxygen permeability, shown below in Equation 10. Table 3.12 gives an explanation of the variables used in Equation 10. P = OP AT (Equation 10) Table 3.12: Explanation of the variables in Equation 10 Variable Meaning Units P oxygen permeability cc STP mil 2 100in day atmospheres OP oxygen permeance cc STP 2 100in day atmospheres AT average sample thickness mils 75

104 Chapter 4 Results and Discussion 4.1 Chemical Mechanisms of AA and AA Scavenger Interactions The acetaldehyde (AA) scavenging interactions of anthranilamide, meta-xylenediamine (MXDA), and alpha-cyclodextrin were studied by various nuclear magnetic resonance (NMR) and mass spectrometry experiments. Proper determination of these chemical interactions/reactions involved the identification by which these three scavenging agents sequester AA and the exact stoichiometry for each of these mechanisms. For each experiment, the AA scavenging mechanism was studied under the most ideal circumstances. Most notably, the presence of PET was omitted from each system; eliminating diffusion as a controlling step. Each reactant was dissolved in an appropriate solvent and mixed only with the other, respective reactant and solvent solution AA and Anthranilamide The investigation into the AA scavenging reaction between anthranilamide and acetaldehyde began by obtaining the individual 1 H NMR spectra of these two components. Figure 4-1 shows the 1 H NMR spectrum of AA, dissolved in deuterated 76

105 chloroform (CDCl 3 ). Under each prominent signal there is an integration factor, indicating the number of protons which are represented by that particular peak. From left to right, the 1 to 3 ratio shown in Figure 4-1 correlates the one hydrogen atom in AA s aldehyde (O=CH) group to the three hydrogen atoms located in its methyl (CH 3 ) group. The scale on the x-axis is in ppm or δ units. Table 4.1 provides a list of the assigned peaks for Figure Figure 4-1: 1 H NMR spectrum of AA in CDCl 3 Table 4.1: Peak assignment for the 1 H NMR spectrum of AA in CDCl 3 Peak Location (ppm) Peak Type Integration Factor Peak Assignment Chemical Compound Functional Group 2.07 Doublet 3 AA CH Singlet - Chloroform-d 9.65 Quartet 1 AA O=CH 77

106 The 1 H NMR spectrum of anthranilamide, also dissolved in deuterated chloroform, is shown in Figure 4-2. A prominent feature of this spectrum is the broad singlet that appears at 5.67 ppm. The peak s broadness is due to the fact that it represents exchangeable protons, which are rapidly traded when in an appropriate solution. 83 Generally, these protons are present on heteroatoms such as oxygen (O), sulfur (S), and nitrogen (N). The peak at 5.67 ppm represents the four protons which comprise both the amide (O=CNH 2 ) and the amine (NH 2 ) groups of anthranilamide. Also shown in Figure 4-2, a number is adjacent to each of anthranilamide s four methine (CH) groups; all are located within the ring formation. This numbering system corresponds to Table 4.2 and is used to ease the identification of these CH groups which are represented by the peaks centered at 6.63, 6.665, 7.20, and 7.34 ppm Figure 4-2: 1 H NMR spectrum of anthranilamide in CDCl 3 78

107 Table 4.2: Peak assignment for the 1 H NMR spectrum of anthranilamide in CDCl 3 Peak Peak Integration Peak Assignment Location (ppm) Type Factor Chemical Compound Functional Group Ring Position 5.67 Singlet 4.5 Anthranilamide NH 2 and - O=CNH Triplet 1 Anthranilamide CH Doublet 1 Anthranilamide CH Triplet 1 Anthranilamide CH Singlet - Chloroform-d Doublet 1 Anthranilamide CH 1 Anthranilamide and AA were each dissolved in deuterated chloroform, in separate NMR tubes. These two solutions were combined into one tube, at room temperature, and then analyzed by 1 H NMR. The resulting spectrum, however, showed no evidence that a reaction between anthranilamide and AA took place. This spectrum was simply a combination of the 1 H NMR spectra of AA (Figure 4-1) and anthranilamide (Figure 4-2). The conclusion from this experiment was that energy must be added to this system to initiate a reaction. A second attempt to analyze the AA scavenging reaction between anthranilamide and acetaldehyde was made by again dissolving each component in deuterated chloroform. These two solutions, in separate NMR tubes, were then combined into one NMR tube that was subsequently was sealed. To seal this glass NMR tube, the contents (AA, anthranilamide, and deuterated chloroform solution) and the bottom of the tube were frozen in liquid nitrogen. Throughout this process, vacuum pressure was applied to continually remove air from the system. The neck of the NMR tube was then heated with a gas flame to melt the glass. When the glass reached a sufficient temperature, the tube 79

108 was twisted and a seal was created. The creation of this seal ensured that this solution could be heated without the risk of volatilizing and losing any of the components. Figure 4-3 shows the 1 H NMR spectrum that resulted after heating the anthranilamide and AA solution, in the sealed tube, for two days at 60 o C. This sample was kept just under the boiling point deuterated chloroform, which is 62 o C. Interpretation of Figure 4-3 indicates that two compounds still remain in this solution, and one of these components is still acetaldehyde. The presence of AA is confirmed by the doublet at 2.21 ppm and the quartet at 9.80 ppm. These peaks closely mirror the location of AA s peaks in Figure 4-1; the integration factors are close matches as well. There are two pieces of evidence within Figure 4-3 that indication the second component is a product generated by a reaction between anthranilamide and AA. The first bit of evidence is the appearance of a new peak (doublet) at 1.50 ppm, and has an integration factor of three. The location and integration factor indicate this peak represents a methyl group (CH 3 ). The fact that this peak is a doublet means that it is coupled to another functional group comprised of only one proton. The second piece of evidence confirming a reaction between anthranilamide and AA is the formation of a quartet peak at 5.06 ppm. This peak s integration factor equals one, indicating it corresponds to one proton. Additionally, the peak is a quartet; meaning it is coupled to three other protons. Previously stated, the methyl group at 1.50 ppm was 80

109 coupled to an unknown peak representing one proton. The combination of these two pieces of information points toward the formation of a HC-CH 3 linkage. Figure 4-3: 1 H NMR spectrum of the reaction between anthranilamide and AA, in CDCl 3, after heating for 2 days at 60 o C A peak assignment list for the 1 H NMR spectrum shown in Figure 4-3 is provided in Table 4.3. Within this list, there is a broad singlet at 6.24 ppm that has yet to be determined. The broadness of the peak and integration factor indicates that it correlates to an exchangeable proton bonded to a heteroatom (oxygen, nitrogen, sulfur, etc.). While in solution, however, these protons exchange so rapidly that it is not always possible to correlate the integration factor with the number of protons for which peak truly represents. 81

110 Table 4.3: Peak assignment for the 1 H NMR spectrum of the reaction between anthranilamide and AA, in CDCl 3, after heating for 2 days at 60 o C Peak Peak Integration Peak Assignment Location (ppm) Type Factor Chemical Compound Functional Group 1.50 Doublet 3 Reaction Product CH Doublet 15.5 AA CH Quartet 1 Reaction Product Undetermined 6.24 Singlet 1 Reaction Product Undetermined 6.68 Doublet 1 Reaction Product CH 6.87 Triplet 1 Reaction Product CH 7.27 Singlet - Chloroform-d 7.31 Triplet 1 Reaction Product CH 7.89 Doublet 1 Reaction Product CH 9.80 Quartet 4 AA O=CH To provide further clarity and proof of a reaction between anthranilamide and AA, a 1 H- 1 H COSY (COrrelation SpectroscopY) NMR experiment was conducted. The scale of the peak intensities, as seen in Figure 4-4, is very difficult to read because of the dominant size of AA s methyl group peak at 2.21 ppm. Figure 4-4 validates the earlier hypothesis that the quartet peak at 5.06 ppm is coupled with the doublet at 1.50 ppm. This spectrum, however, shows no other evidence of this peak at 5.06 ppm being coupled to any other protons. This means one of two things: either this group is not bonded to any other group, besides the methyl group, or it is bonded to a heteroatom(s). 82

111 Figure 4-4: 1 H 1 H COSY NMR spectrum of the reaction between anthranilamide and AA, in CDCl 3, after heating for 2 days at 60 o C Analysis of the previous two NMR spectra can lead to the prediction of at least two different mechanisms which are able to describe the reaction that occurs between anthranilamide and AA. The first proposed reaction mechanism is shown in Figure 4-5. In this reaction, anthranilamide and AA react to produce a larger organic compound. 83

112 This compound has a terminal methyl group (CH 3 ) and a CH group which is attached to two heteroatoms; oxygen and nitrogen. O O O OH NH 2 + NH 2 NH 2 C H 3 H NH CH 3 (Anthranilamide) (AA) Figure 4-5: Proposed reaction mechanism #1 for anthranilamide and AA As a way to help confirm reaction mechanism #1, shown in Figure 4-5, the ChemSketch software package was used to predict the 1 H NMR spectrum for the reaction product. The predicted 1 H NMR spectrum, shown in Figure 4-6, shows a similar pattern to the actual spectrum, shown in Figure 4-3; with one exception. In Figure 4-3 the quartet appears at 5.06 ppm, while in Figure 4-6 that peaks appears at about 5.53 ppm. Further analysis was needed to prove if this 0.5 ppm difference is significant or if this value lies within the error of the predictive software program. 84

113 [13] O NH 7 CH 3 12 NH OH [12] 1.32[12] 7 6 Molecular Weight = g/mol [3] 8.07[3] 5.51[8] 5.53[8] 7.24[5] 7.22[5] 7.12[4] 5.54[8] 5.49[8] 0.20[7,9] Figure 4-6: Predicted 1 H NMR spectrum for the product formed from the proposed reaction mechanism #1 (Figure 4.5) A second proposed reaction mechanism for anthranilamide and AA is shown in Figure 4-7. This reaction results in the formation of water and a two ring structured, organic compound. Similar to the reaction product formed in proposed reaction mechanism #1, shown in Figure 4-5, this compound has a terminal methyl group (CH 3 ) and a CH group which is attached to two heteroatoms. This time, however, the CH group bonds to two nitrogen atoms instead; of a nitrogen atom and an oxygen atom. 85

114 O O O NH 2 NH 2 + C H 3 H H 2 O + NH H N H CH 3 (Anthranilamide) (AA) Figure 4-7: Proposed reaction mechanism #2 for anthranilamide and AA ChemSketch was again used to help evaluate the reaction products from another proposed reaction mechanism between anthranilamide and AA. Previously it was shown that the only significant difference between the predicted 1 H NMR spectrum from the first proposed reaction mechanism (Figure 4-6) and the actual spectrum (Figure 4-3) was the location of the CH quartet peak; 5.53 and 5.06 ppm respectively. This time, however, the predicted 1 H NMR spectrum, shown in Figure 4-8, of the reaction product shown in Figure 4-7 closely matches the actual spectrum shown in Figure 4-3. The location of the predicted quartet peak, representing the CH group, is 4.98 ppm; very close to the actual location of 5.06 ppm. 86

115 [11] 1.47[11] O 12 6 NH N H 3 2 CH Molecular Weight = g/mol 4.08[1] [10] 7.66[10] 7.16[8] 7.14[8] 7.06[9] 6.40[7] 4.98[2] [2] Figure 4-8: Predicted 1 H NMR spectrum for the product formed from the proposed reaction mechanism #2 (Figure 4-7) Based on the data presented up to this point, it is difficult to truly distinguish between these two proposed reaction mechanisms. Even though the 1 H NMR spectra for proposed reaction mechanism #1 (Figure 4-6) and proposed reaction mechanism #2 (Figure 4-8) are very similar, there is one drastic difference. The reaction product for proposed reaction mechanism #1 has a molecular weight of grams/mol; while, the reaction product for proposed reaction mechanism #2 has a molecular weight of grams/mol. One way to distinguish between the two mechanisms would be through the use of mass spectrometry. 87

116 Electrospray ionization (ESI) mass spectrometry was used to analyze both a sample of anthranilamide dissolved in deuterated chloroform and a solution of anthranilamide and AA dissolved in deuterated chloroform. A small aliquot of methanol was added to both samples to aid with the ionization process. The mass spectrum of the anthranilamide solution is shown in Figure 4-9. Within this figure, it can be seen that the molecular ion peak is located at m/z (mass to charge ratio). The molecular weight of anthranilamide, however, is known to be grams/mol. The difference between these two masses is 23 grams/mol, the molecular weight of sodium (Na). Sodium is a major component of glass containers, which happens to be what the sample was stored in prior to analysis. Intens. x10 4 All, min (#1-#10) (molecular ion peak) (molecular weight of anthranilamide) = 23 (molecular weight of sodium ion) m/z Figure 4-9: ESI mass spectrum of anthranilamide in CDCl 3 and methanol

117 Figure 4-10 shows the mass spectrum of the product from the reaction between anthranilamide and AA. The molecular ion peak for this product is m/z. As previously mentioned, this sample was also stored in glass. Therefore, it is assumed that Na is the ion which is attached to the product. Subtracting the mass of sodium from the molecular ion peak yields a mass of grams/mol. This molecular weight (162.5 grams/mol) corresponds very well with the product which is formed from the proposed reaction mechanism #2 (162.2 grams/mol); shown in Figure 4-7. The molecular weight of the product formed in proposed reaction mechanism #1, shown in Figure 4-5, is grams/mol. The use of both the mass spectrum and the 1 H NMR spectral data confirm that proposed reaction mechanism #2 is the reaction scheme by which anthranilamide acts as an AA scavenger. Further examination of the patent by Rule, et al 50 also indicates that proposed mechanism #2 is the correct reaction scheme. U.S. Patent 7,550,203 describes the interaction of anthranilamide and AA, in the presence of PET, as: combining with polyester an organic additive compound comprising at least two hydrogen-substituted heteroatoms bonded to carbons of the organic additive compounds, the organic additive compound being reactive with acetaldehyde in the polyester to form water and a resulting organic compound comprising an unbridged 5- or 6-member ring including at least two heteroatoms. Further on in the patent 50, the authors state that the two heteroatoms are both nitrogen. 89

118 The mass spectrum shown in Figure 4-10 produces one more peak of interest; the peak at m/z (mass to charge ratio). ESI mass spectrometry ionizes a compound by adding an ion such as hydrogen (H), sodium (Na), etc. While ESI does not typically knock off a hydrogen atom, if it did the peak at m/z would correlate very well with the mass of the product from reaction mechanism #2 (162.2 grams/mol). As just mentioned, this phenomenon does not typically occur. In essence, a compound which has a molecular weight of about 160 grams/mol, ionized with a hydrogen atom, would correspond with the secondary molecular ion peak shown in Figure Intens. x10 4 All, min (#1-#26) (molecular ion peak) 23 (molecular weight of sodium ion) = (molecular weight of product) m/z Figure 4-10: ESI mass spectrum of the product from the reaction between anthranilamide and AA in CDCl 3 and methanol

119 Figure 4-11 shows a proposed reaction mechanism for anthranilamide and AA in which the final product possesses a molecular weight of grams/mol. Proposed reaction mechanism #3, Figure 4-11, starts with proposed reaction mechanism #2 (Figure 4-7) but adds one more step to the reaction. In this de-saturation reaction, the organic product formed in reaction mechanism #2 gives off a di-hydrogen molecule that yields a similar two-ring structured organic compound, now with a double bond in its second ring. The formation of this final product, shown in Figure 4-11, has been observed by several authors Abdel-Jalil, et al 89 showed that this product can be produced through the addition of time, energy, and a catalyst. O O O NH 2 NH 2 + C H 3 H H 2 O + NH H N H CH 3 (Anthranilamide) (AA) O H 2 + N NH CH 3 Figure 4-11: Proposed reaction mechanism #3 for anthranilamide and AA Beyond what was previously stated, Rule, et al 50 give no further indication of the exact composition for the resulting organic compound that is formed. Further experiments were required to determine if proposed mechanism #3 (Figure 4-11) is more correct than proposed mechanism #2 (Figure 4-7). This entailed periodic 1 H NMR analysis to study 91

120 the possible double bond formation in the second ring of the organic compound produced by the anthranilamide and AA reaction. To begin this work, ChemSketch was used to predict a 1 H NMR spectrum of the final reaction product that is shown in Figure Figure 4-12 shows this predicted spectrum. Next, the sealed NMR tube which contained the dissolved mixture of anthranilamide and AA was heated over a four week period, at 60 o C. Throughout this time, periodic 1 H NMR spectra were obtained and analyzed [12] O 11 2 N 5 NH 1 6 CH Molecular Weight = g/mol [8] 7.71[10] 7.64[9] 7.73[10] Figure 4-12: Predicted 1 H NMR spectrum for the product formed from the proposed reaction mechanism #3 (Figure 4-11) 92

121 While each 1 H NMR spectra confirmed the final product in proposed mechanism #2 (Figure 4-7), there proved to be no tangible evidence of the double bond formation on the second ring. Never was there a spectrum that resembled the appearance of Figure It is important to note, however, that this experiment was conducted without the presence of a catalyst; which was used in the experiments performed by Abdel-Jalil, et al 89. It is therefore possible that the formation of the final product in proposed reaction mechanism #3 could be obtained when anthranilamide is added to PET. All PET resins contain a small amount of residual catalyst within their matrix. When anthranilamide is added, to act as an AA scavenger, this residual amount of catalyst could drive the reaction to form the final product shown in proposed reaction scheme #3 (Figure 4-11) AA and MXDA The investigation into the AA scavenging reaction between meta-xylenediamine (MXDA) and acetaldehyde began in the same manner as previously discussed in Section The initial step was to obtain the individual 1 H NMR spectra for AA and MXDA. Previously shown and discussed, Figure 4-1 shows the 1 H NMR spectrum of AA dissolved in deuterated chloroform (CDCl 3 ). Similarly, MXDA was also dissolved in CDCl 3 and analyzed by means of 1 H NMR. Figure 4-13 shows the 1 H NMR spectrum for MXDA in the presence of deuterated chloroform. The peaks appearing between 7.0 and 7.3 ppm are enhanced for detailed viewing; making it easier to see the multiplicity and integration factors. It can be seen 93

122 that the ratio of integration factors, from left to right, is 1:1:2:4:4. Similar to anthranilamide, MXDA s 1 H NMR spectrum contains a very broad peak. As previously mentioned, this broad peak indicates the presence of exchangeable protons. These protons are from MXDA s two primary amine groups (NH 2 ) and are represented by the peak located at 1.35 ppm. Table 4.4 provides a list of the assigned peaks for Figure Figure 4-13: 1 H NMR spectrum of MXDA in CDCl 3 Table 4.4: Peak assignment for the 1 H NMR spectrum of MXDA in CDCl 3 Peak Peak Integration Peak Assignment Location (ppm) Type Factor Chemical Compound Functional Group Ring Position 1.35 Singlet 4 MXDA Two NH Singlet 4 MXDA Two CH Doublet 2 MXDA Two CH Singlet 1 MXDA CH Triplet 1 MXDA CH 3 94

123 Similar to the mixing procedure for anthranilamide and AA, MXDA and AA were each dissolved in separate NMR tubes using deuterated chloroform. These two individual solutions were then combined into one tube. The mixing of the two solutions resulted in an instantaneous reaction that occurred at room temperature; forming a solid, orange product. Further dilution of the resulting product altered its color from orange to a dark yellow, slight greenish appearance. The appearance of this sample was similar to that of the 1 weight % MXDA/PET blend sample; following twin-screw extrusion. The reason for this color formation was documented by Bandi, et al. 48 Through the study of polyamide/pet blends, the authors proved that this color generation was the result of a reaction between the amine group, from MXD6, and generated AA, from PET. This reaction results in the formation of imine (N=CH) groups; which Bandi, et al 48 proved to be the chromophores. MXDA is the monomer from which MXD6 is manufactured. MXDA has two primary amines, while MXD6 has only one. A reaction scheme between MXD6 and AA has been previously presented in Figure 2-2. Using this as a guide, a proposed reaction mechanism for MXDA and AA is shown in Figure Similar to the reaction for MXD6 and AA, the aldehyde group (O=CH) of AA reacts with a primary amine group from MXDA. Since MXDA has two primary amine groups, one molecule of MXDA can react with up to two molecules of AA. The result of this reaction can therefore generate up to two imine groups and up to two molecules of water, as a byproduct. 95

124 H 2 N H 2 C CH 2 NH 2 O + 2 H 3 C CH (MXDA) (AA) H 3 C HC N H 2 C CH 2 N CH CH H 2O Figure 4-14: Proposed reaction scheme for MXDA and AA The 1 H NMR spectrum representing the reaction between MXDA and AA is shown in Figure This spectrum contains two pieces of evidence that verify the reaction scheme shown in Figure First, it can be seen that the reaction forms water, evident by the singlet at 1.90 ppm. Second, a new peak is formed at 7.80 ppm. This peak is a quartet and represents the two imine (HC=N) groups that were the result of the reactions between the two amine groups from MXDA and the aldehyde group from AA. Table 4.5 provides a complete list of the identified peaks that are shown in Figure The 1 H NMR spectrum of the reaction between MXDA and AA, Figure 4-15, also shows another interesting fact. Analysis of this spectrum shows that only two components are present: AA and the resulting product. This indicates that any MXDA that was originally present has since completely reacted. This is validated by the fact that the singlet at 1.35 ppm, present in Figure 4-13, is absent in the 1 H NMR spectrum shown in Figure This singlet represented the two primary amines of MXDA, and the absence of this peak indicates that no MXDA is present in this system. 96

125 Figure 4-15: 1 H NMR spectrum of the reaction between MXDA and AA in CDCl 3 Table 4.5: Peak assignment for the 1 H NMR spectrum of the reaction between MXDA and AA in CDCl 3 Peak Peak Integration Peak Assignment Location (ppm) Type Factor Chemical Compound Functional Group Ring Position 1.90 Singlet - H Doublet 4.5 AA CH Doublet 6 Reaction Product Two CH Singlet 4 Reaction Product Two CH Doublet 2 Reaction Product Two CH Singlet 1 Reaction Product CH Singlet - Chloroform-d Triplet 1 Reaction Product CH Quartet 2 Reaction Product Two HC=N Quartet 1.5 AA O=CH - 97

126 4.1.3 AA and Alpha-Cyclodextrin The previously presented 1 H NMR spectra for the anthranilamide and the MXDA scavenging reactions have all used deuterated chloroform (CDCl 3 ) as the solvent. Deuterated chloroform is a very common solvent because it has a low boiling point, is relatively inexpensive, and dissolves a plethora of organic compounds. The solubility of cyclodextrins in deuterated chloroform, however, is very low. Alpha-cyclodextrin contains hydroxyl groups that make it a polar molecule; while CDCl 3 is non-polar. The general rule for solubility states that like dissolves like. In other words, alphacyclodextrin will be more soluble in a polar solvent like deuterium oxide (D 2 O). Studying the AA scavenging mechanism between alpha-cyclodextrin and acetaldehyde was initially similar to the approach discussed in Sections and This process began by obtaining the individual 1 H NMR spectra for alpha-cyclodextrin and AA. Figure 4-16 shows the 1 H NMR spectrum of alpha-cyclodextrin in deuterium oxide; also shown is alpha-cyclodextrin s repeat unit. The peaks shown in this spectrum correspond only to the hydrogen atoms which are bonded to carbon atoms (CH groups). Not seen in this spectrum are the hydrogen atoms bonded to oxygen atoms; hydroxyl groups. This phenomenon is a result of the chosen solvent. The hydrogen atoms of the hydroxyl groups are rapidly exchanged with the deuterium atoms in deuterium oxide. This exchange causes these hydrogen atoms to be grouped into the water peak at 4.8 ppm. 98

127 O H O 2 H OH OH H 3 5H H H 6 6 OH H 4 O n Figure 4-16: 1 H NMR spectrum of alpha-cyclodextrin in D 2 O In order to aid in the peak assignment for Figure 4-16, a 1 H- 1 H NMR COSY experiment was conducted. The resulting 1 H- 1 H COSY spectrum of alpha-cyclodextrin, dissolved in deuterium oxide, is shown in Figure Due to the dominant size of the water peak at 4.80 ppm, the scale of the peak intensities is very difficult to read. The coupling pattern of this spectrum was used to assign the various peaks to their proper CH protons, within alpha-cyclodextrin s repeat unit. The complete peak assignment list is shown in Table

128 Figure 4-17: 1 H 1 H COSY NMR spectrum of alpha-cyclodextrin in D 2 O Table 4.6: Peak assignment for the 1 H NMR spectrum of alpha-cyclodextrin in D 2 O Peak Peak Integration Peak Assignment Location (ppm) Type Factor Chemical Compound Functional Group Ring Position 3.60 Triplet 1 α-cyclodextrin CH Doublet of 1 α-cyclodextrin CH 2 Doublets 3.83 Triplet 1 α-cyclodextrin CH Triplet 2 α-cyclodextrin CH Triplet 1 α-cyclodextrin CH Singlet - D 2 O Doublet 1 α-cyclodextrin CH 1 100

129 The 1 H NMR spectrum of AA that is dissolved in deuterated chloroform has been previously discussed and shown, in Figure 4-1. For this part of the study, however, alpha-cyclodextrin was dissolved in deuterium oxide; not deuterated chloroform. The 1 H NMR spectrum of AA was therefore re-obtained using deuterium oxide as the solvent. This spectrum is shown in Figure Figure 4-18: 1 H NMR spectrum of AA in D 2 O Comparing Figures 4-1 and 4-18, it can be seen that there is a dramatic difference between the 1 H NMR spectra of AA. The reason for this disparity is the result of the solvent that is used to dissolve AA. In the presence of deuterium oxide, which is slightly acidic, AA reacts with D 2 O to form an equilibrium product; as illustrated in Figure ChemSketch was used to predict the 1 H NMR spectrum of a solution containing AA and 101

130 the acetal-based equilibrium product shown in Figure This proposed equilibrium reaction is confirmed through the comparison of the predicted 1 H NMR spectrum, Figure 4-20, and the actual spectrum, Figure The spectral patterns of these two spectra are very similar; within the error of the software program. 2 O D O O D D 3 H 3 C 4 1 H 3 C O D Figure 4-19: Equilibrium reaction between AA and D 2 O [9] 1.31[6] O 7 H 8a 8 CH 3 9 D2O H 3 C O O 4 D 2 D [8a] 5.78[3] 5.79[3] [3] 5.77[3] Figure 4-20: Predicted 1 H NMR spectrum of AA in D 2 O 102

131 The peak assignment list, shown in Table 4.7, corresponds to the 1 H NMR spectrum of AA in deuterium oxide, shown in Figure 4-18 shows the approximate ratio of integration factors, from left to right, is 1:2:3:6. Looking back at Figure 4-1, the 1 H NMR spectrum of AA in deuterated chloroform, the ratio of integration factors is 1:3. Looking at the peak assignment in Table 4.7, the ratio of AA s protons, within its two functional groups, is still 1:3. The ratio for the acetal-based equilibrium product is 2:6; simplified to be 1:3. The doubling phenomenon indicates that the equilibrium product is twice as prominent as AA, within this solution. Table 4.7: Peak assignment for the 1 H NMR spectrum of AA in D 2 O Peak Peak Integration Peak Assignment Location Type Factor Chemical Functional Group (ppm) Compound Group Number 1.12 Doublet 6 Equilibrium Product CH Doublet 3 AA CH Singlet - D 2 O Quartet 2 Equilibrium Product CH Quartet 1 AA O=CH 2 According to the literature 24, cyclodextrins act as AA scavengers by a size-enclosing mechanism. Cyclodextrins have hydrophilic exterior structures and lipophilic internal structures. 24 This hydrophilic exterior makes water, or deuterium oxide, the solvent of choice to dissolve cyclodextrins. The lipophilic interior makes it favorable for aldehydes and other organics to enter its internal cavity. 24, 62 As depicted in Figure 4-21, alphacyclodextrin encapsulates AA into its cyclical structure without the need for a chemical reaction. The force by which AA is held inside of alpha-cyclodextrin is hydrogen bonding. 103

132 Figure 4-21: Interaction mechanism for AA and alpha-cyclodextrin Several authors have shown that 1 H NMR can be used to validate cyclodextrin s sizeenclosing mechanism through NMR titration studies; as discussed in Section A similar experimental procedure was followed in an attempt to reproduce the results, seen in Figure 2-8. In this experiment, however, alpha-cyclodextrin is the host molecule and AA is the guest molecule. Samples were prepared by separately weighing and then dissolving each component in D 2 O. These two solutions, in separate vessels, were then combined into one NMR tube to achieve the desired molar ratios. Nine samples were prepared in all: Pure alpha-cyclodextrin Pure AA 0.2 to 1 (AA to alpha-cyclodextrin) 0.4 to 1 (AA to alpha-cyclodextrin) 0.6 to 1 (AA to alpha-cyclodextrin) 0.8 to 1 (AA to alpha-cyclodextrin) 104

133 1 to 1 (AA to alpha-cyclodextrin) 2 to 1 (AA to alpha-cyclodextrin) 3 to 1 (AA to alpha-cyclodextrin) The protons that were monitored during this NMR titration study were previously identified in Figure 4-19 and Table 4.7. For AA there are two sets of protons which can be monitored: the aldehyde proton (group 2) and the methyl protons (group 1). For the acetal-based equilibrium product, the methyl protons (group 3) and the CH proton (group 4) were also monitored. Figure 4-22 shows the comprehensive results from the NMR titration experiment that was conducted to study alpha-cyclodextrin s AA scavenging mechanism; Appendix A contains the individual spectra from this study. This plot shows that as the concentration of AA increases, relative to that of alpha-cyclodextrin, the chemical shift of protons for AA and its equilibrium product also increase until a saturation point is reached. The saturation point for the AA and alpha-cyclodextrin complex occurs at a one to one ratio. This implies that every molecule of alpha-cyclodextrin can sequester only one molecule of AA. Figure 4-22 provides the experimental proof to confirm the interaction mechanism between AA and alpha-cyclodextrin, which has been reported for other 61, 71-74, 93 host/guest complexes. 105

134 Peak Shifting (ppm) Methyl Protons (AA) Aldehyde Proton (AA) Methyl Protons (AA's Equilibrium Product) CH Proton (AA's Equilibrium Product) Guest to Host Ratio Figure 4-22: Peak shifting of the protons for AA and its equilibrium product when titrated with alpha-cyclodextrin (solvent is D 2 O) 4.2 Effectiveness of AA Scavengers in Reducing the Amount of AA in PET The second objective of this work was to investigate the efficiency of these three scavenging agents (anthranilamide, MXDA, and alpha-cyclodextrin) in reducing the amount of AA that is present in PET. The intent of these scavenging agents is not to limit PET degradation and reduce the amount of generated AA. The purpose of adding AA scavengers to PET is to interact with generated AA, reducing the amount that is able to migrate and affect the packaged food or beverage. 106

135 Acetaldehyde concentrations in PET have been studied through two gas chromatography methods. The first method quantifies the rate at which AA is generated during the processing of PET. The second technique, known as headspace analysis, is used to determine the amount of AA that remains residually trapped within PET AA Generation Rates To quantify how much AA is created during processing, the AA generation rates of each sample were established. These measurements were made using a Perkin-Elmer Automatic Thermal Desorption System (ATD-400) and AutoSystem XL Gas Chromatograph. Details of the gas chromatograph column and testing conditions for these experiments were previously discussed in Section Under isothermal conditions, the establishment of AA generation rates were achieved by varying the sample s heating time between 9 and 17 minutes. For each sample, rates were established at three different temperatures: 280, 290, and 300 o C. This allowed for the determination of a sample s activation energy (E A ) through the derived Arrhenius equation; Equation 3 (Section 3.5.1). Compilations of raw data from these AA generation experiments are shown in Appendix B. As an example, Figure 4-23 shows the AA generations rates that were determined for the 1200 ppm anthranilamide/pet blend sample. It can be seen from this figure that the AA generation of this sample at 280 o C is around 1.0 ppm/minute. Increasing the temperature 107

136 by 10 o C raises the rate to about 1.9 ppm/minute. At 300 o C, the AA generation rate for the 1200 ppm anthranilamide/pet blend sample is 3.0 ppm/minute. This trend exemplifies the fact that increasing the melting/processing temperature of PET also increases the rate of degradation within the polymer Acetaldehyde (ppm) C 290 C 300 C y = x R 2 = y = x R 2 = y = x R 2 = Time (minutes) Figure 4-23: AA generation plots for the 1200 ppm anthranilamide/pet blend Plots like Figure 4-23 were prepared for each sample analyzed throughout this work: the virgin PET sample, the extruded PET control sample, and the various AA scavenger/pet blend samples; they are located within Appendix C. Table 4.8 lists the AA generation rates at 280 o C, 290 o C, and 300 o C for each sample. The general trend is that as AA scavenger concentration increases, the AA generation rate decreases. This is better illustrated by Figures 4-24, 4-25, and Respectively, these plots show the AA 108

137 generation rate as a function of scavenger concentration and temperature for the anthranilamide, alpha-cyclodextrin, and MXDA blend samples. Table 4.8: AA generation rates Scavenger Type / Sample Concentration AA Generation Rate (ppm/min) (ppm) 280 o C 290 o C 300 o C Virgin PET resin Extruded PET (Control) Anthranilamide , Alpha-Cyclodextrin , , , MXDA ,

138 9.0 Generation Rate of AA (ppm/min.) C 290 C 300 C AA Scavenger Concentration (ppm) Figure 4-24: AA generation rate as a function of anthranilamide concentration 9.0 Generation Rate of AA (ppm/min.) C 290 C 300 C AA Scavenger Concentration (ppm) Figure 4-25: AA generation rate as a function of alpha-cyclodextrin concentration 110

139 9.0 Generation Rate of AA (ppm/min.) C 290 C 300 C AA Scavenger Concentration (ppm) Figure 4-26: AA generation rate as a function of MXDA concentration There are two common behaviors that are observed in each of these plots (Figures 4-24, 4-25, and 4-26). The first familiar feature among these figures is that eventually the AA generation rate becomes independent of concentration; the slope of the plot nears zero. For MXDA this appears to happen around 1200 ppm, for anthranilamide this phenomenon seems to occur between 1200 ppm and 10,000 ppm, and for alphacyclodextrin the slope looks to flatten in the region of 10,000 ppm (or 1 weight %). The difference between these values has to do with the molecular structure and interaction mechanism of these scavenging agents. As shown in Section 4.1, a molecule of both anthranilamide and alpha-cyclodextrin can only interact with one molecule of AA. MXDA, however, can scavenge up to two molecules of AA. 111

140 The second common feature among Figures 4-24, 4-25, and 4-26, is that at 280 and 290 o C there is an initial increase in the AA generation rate for each scavenging agent. This deviation from the previously mentioned general trend is observed for the anthranilamide concentrations between 0 and 500 ppm, the alpha-cyclodextrin concentrations between 0 and 1200 ppm, and the MXDA concentrations between 0 and 200 ppm. Initially, this phenomenon was attributed to experimental error in the preparation and/or AA generation measurement of the processed PET control sample. To investigate this idea, a second control sample was produced and subsequently analyzed. The AA generation results from this second sample upheld those from the first control sample. Discussed in Section 3.3 are the twin-screw extrusion experiments that melt-blended the various scavenging agents with PET resin. Respectively, Sections 3.3.1, 3.3.2, and 3.3.3, describe in detail how each of the various AA scavenger/pet blend samples was prepared. Within these sections, Tables 3.1, 3.2, and 3.3 show the proportions of each sample that was extruded once, twice, and up to three times; this general concept is labeled as a sample s thermal history. It is known that increasing a PET sample s thermal history will also increase its amount of degradation and consequently the AA concentration. To simulate this effect, a portion of the one-time processed PET control sample was re-extruded to establish a two-time processed control sample. A portion of this two-time processed PET sample was then 112

141 extruded again to produce the three-time processed control sample. A more detailed explanation is provided in Section The AA generation rates of the one-time processed, two-times processed, and threetimes processed control samples were analyzed and are reported in Table 4.9. It can be seen from this data that as the thermal history of the PET sample increases, so does its AA generation rate. This information shows that the initial increase in the AA generation rates of the lowest concentrated samples was the result of the sample preparation methodology. Table 4.9: AA generation rates of control samples Sample Number of AA Generation Rate (ppm/min) Processing Times 280 o C 290 o C 300 o C Extruded PET As previously mentioned, the intent of establishing AA generation rates at three different temperatures was to allow for the determination of each sample s activation energy (E A ). Activation energy is obtained by means of the Arrhenius plot; which is derived from the Arrhenius equation (Equation 2). The slope of this graph is the activation energy divided by the gas constant; the y-intercept is the natural log of pre-exponential factor. Figure 4-27 shows the Arrhenius plot for the 10,000 ppm (or 1 weight %) MXDA/PET blend sample. Similar plots were prepared for each sample and are located within Appendix D. The comprehensive results from these individual graphs are shown in Table

142 ln Rate y = x R 2 = /Temperature (1/K) Figure 4-27: Arrhenius plot of 10,000 ppm MXDA/PET blend sample According to the data in Table 4.10, the respective anthranilamide and MXDA blend samples possess similar activation energies; the lone exception being the 100 ppm samples. The similarity in values is attributed to the fact that anthranilamide and MXDA scavenge AA by similar mechanisms. In comparison, Table 4.10 shows that similarly concentrated alpha-cyclodextrin samples have higher activation energies. As previously shown, alpha-cyclodextrin sequesters AA by a mechanism that is completely different to those of anthranilamide and MXDA. This indicates that the activation energy, which corresponds to the generation of AA, is a function of the interaction method by which AA is scavenged. 114

143 Table 4.10 shows that four of the six evaluated alpha-cyclodextrin/pet blend samples have higher activation energies than any other sample. This demonstrates that it takes more energy to remove AA from the internal molecular structure of alpha-cyclodextrin than it is does to break the bonds that were formed by the reaction between AA and anthranilamide, or between AA and MXDA. Since these samples have higher activation energies than the virgin, unprocessed PET resin the data indicates that it requires more energy to remove AA from alpha-cyclodextrin s structure than it does to generate AA during PET degradation. Table 4.10: Activation energies Scavenger Type / Number of Sample Processing Times Concentration (ppm) Activation Energy (kj/mol) Virgin PET resin Extruded PET (Control) Anthranilamide Alpha- Cyclodextrin MXDA , , , , ,

144 Examination of the data in Table 4.10 indicates that generally activation energy increases with increasing scavenger concentration. In other words, the greater the concentration of the scavenging agent, in a PET blend system, the more likely generated AA will be sequestered and not allowed to diffuse from the polymer. Traditionally, activation energies for PET resins have been shown to decrease with I.V. A comparison between Tables 4.10 and 4.14, which will be discussed in Section , show that this is still true for the virgin PET and the three extruded PET control samples. The opposite, however, appears to be true for the various AA scavenger/pet blend samples. In this case, activation energy appears to increase with decreasing I.V. This phenomenon is assumed to be the combined result of both the sample blending method and the addition of AA scavenging agents, rather than a deviation from what has been previously observed Residual AA As AA is generated, through the degradation of PET, it has the ability to diffuse out of the polymer. A portion of the generated AA, however, usually remains residually trapped within the matrix of PET. Since AA is able to diffuse out of PET, even at temperatures as low as 21 o C, 19 quantifying its residual concentration is important because many foods 2, 20 and beverages have a limited threshold for AA. Residual AA was quantified by means of a procedure known as headspace analysis. This technique uses a Perkin-Elmer TurboMatrix 40 Headspace Sampler (TM-40) coupled to a Perkin-Elmer AutoSystem XL Gas Chromatograph. Amorphous PET pellets or preform 116

145 samples are ground, in a liquid nitrogen environment, and then sieved to obtain a powder that increases the diffusion ability of AA. Samples are heated at an elevated temperature, not to melt the polymer but to volatize the residual AA that is trapped within the PET matrix. Details of the gas chromatograph column and testing conditions for these experiments were previously discussed in Section Appendix E provides the comprehensive results for the residual AA experiments, for both the pelletized samples and preform samples Pelletized Samples During each AA scavenger/pet melt-blending process, a portion of the extruded, pelletized sample was collected for headspace analysis. Immediately upon collection, this sample was place in a freezer to prevent the AA, within this PET sample, from volatilizing. At a later point in time this sample was further prepared to be analyzed. Table 4.11 shows the residual AA results for the various pelletized AA scavenger/pet blend and control samples. Within this table, the effectiveness of each AA scavenger/pet blend sample s ability to reduce the amount of residual AA has been quantified relative to the one-time processed control sample. It should also be noted that no data is reported for the 10,000 ppm (1 weight %) anthranilamide/pet blend sample because the entire allotment of sample was dried and crystallized prior to headspace analysis. It was assumed that the drying and crystallization processes removed much of the residual AA from this sample. 117

146 Table 4.11: Residual AA data for pelletized samples Scavenger / Sample Number of Processing Times Concentration (ppm) Residual AA (ppm) Amount of Reduction (%) PET resin Extruded PET (control) Anthranilamide Alpha- Cyclodextrin MXDA , , , , , It can be seen that the results shown in Table 4.11 corroborate with the general trend that was observed for the previously discussed AA generation rate results. Generally, as the concentration of AA scavenging agent increases, the percent reduction of AA also increases. These results also indicate, as did Table 4.9, that the amount of AA (generated or residual) increases with increasing thermal histories. The virgin PET resin, that was not processed, has an initial residual AA concentration that is less than 1 ppm. Processing this resin one time increases its residual AA content up to 8.9 ppm. Processing this resin a second and then third time, increases the residual AA concentration to 13.5 and 14.5, respectively. 118

147 Preform Samples Six of the AA scavenger/pet blend samples, along with a control sample, were chosen to be injection molded into preform samples for two reasons. The first reason was to blowmold a portion of these preforms in to 2-liter bottles for further analysis. The second reason was to analyze the residual AA content, of these samples, that resulted from an injection molding process. Table 4.12 shows the results of this work. Table 4.12: Residual AA data for preform samples Scavenger / Sample Concentration (ppm) Residual AA (ppm) Amount of Reduction (%) PET Anthranilamide Alpha Cyclodextrin MXDA The results shown in Table 4.12 clearly reveal two points. The first is that the addition of scavenging agents is successful in reducing the amount of detectable residual AA within PET preforms. The second point confirms the previously observed results; the greater the amount of scavenging agent, the greater the reduction in AA. As with Table 4.11, the effectiveness of each AA scavenger/pet blend sample has been quantified relative to a PET control sample. 119

148 Comparison of Results for Pelletized Samples and Preform Samples Table 4.13 was prepared to compare the residual AA results for similar AA scavenger/pet blend pellet and preform samples. The sample blending process for the preform samples varied in comparison to the blending of the pelletized samples. The preform samples were produced by melt-blending virgin PET resin with a master-batch sample that was passed through the twin-screw extruder only once. In the end, these preform samples were composed of a portion that was processed once and the remaining amount was processed twice; twin-screw extruded once and injection molded once. As discussed in greater detail in Section 3.3, similarly concentrated pelletized samples contained portions that were extruded once, twice and three times. Table 4.13: Comparison of the residual AA data for pelletized and preform samples Scavenger / Concentration Residual AA (ppm) Sample (ppm) Pellets Preforms PET Anthranilamide Cyclodextrin MXDA Since the scavenger concentrations for each of these sets of samples are assumed to be the same, the comparison of their residual AA content can be made; even though their overall thermal histories may differ. Table 4.13 shows that in most every case the residual AA concentration is fairly similar for each respective pelletized and preform 120

149 sample. The one common trend in both circumstances is that the more scavenging agent, the lower the residual AA content. 4.3 Physical Properties of AA Scavenger/PET Blend Samples For sensitive PET packaging applications, reducing the amount of detectable AA can be an immense concern. This enhancement, however, is not acceptable if it comes at the cost of sacrificing the overall appearance and physical properties of PET. Studying changes in the physical properties of PET was a vital step in determining the overall benefit of adding AA scavenging agents. The properties that were analyzed to complete this objective are: intrinsic viscosity (I.V.), color, thermal properties, and oxygen permeability. For each type of analysis, the results for the various AA scavenger/pet blend samples were compared to those of an appropriate PET control sample Intrinsic Viscosity (I.V.) The intrinsic viscosities (I.V.) of the various AA scavenger/pet blend and PET control samples were obtained by measuring their respective melt viscosities. Measurements were made by means of a RDA III viscoelastic tester, using parallel plate and plate geometry. For each sample, a conversion of melt viscosity to I.V. was made through the use of a calibration curve; established from the measurements of standardized samples possessing precisely known I.V.s. Further details of this experimental setup and testing conditions were discussed in greater detail in Section All of the data from the melt 121

150 viscosity measurements, for both the pelletized samples and preform samples, are shown in Appendix F Pelletized Samples Each AA scavenger/pet blend sample was prepared via twin-screw extrusion. During these melt-blending procedures, a portion of each blend was set aside for melt viscosity analysis. Prior to their evaluation, these samples were dried and crystallized overnight in a vacuum oven, at a temperature of 140 o C. Table 4.14 shows the I.V. for each sample and its change in comparison to that of virgin PET resin. The general trend that is shown in this table indicates that increasing scavenger concentration results in decreasing I.V. It is believed, however, that increasing scavenger concentration is not the only reason for reductions in viscosity. As previously mentioned, these AA scavenger/pet blend samples are composed of portions that have been extruded once, twice, and up to three times. It can be seen that one pass through the twin-screw extruded degrades the PET resin enough to reduce the I.V. by 2.5%. A second and then third time through the extruder reduces the I.V. by 13.8% and 18.8%, respectively. This sample blending method, however, does not completely explain the loss in I.V. for each sample. If that were the case, the three times processed sample should have the 122

151 lowest I.V. The I.V. of that sample is 0.65 dl/g; yet, the lowest I.V. (0.34 dl/g) belongs to the 1 weight % (or 10,000 ppm) MXDA/PET blend sample. This implies that the loss in each sample s I.V. is due to a combination of both the addition of scavenging agents and the sample blending method used in this work. Table 4.14: I.V. data for pelletized samples Scavenger / Sample Number of Processing Times Concentration (ppm) I.V. (dl/g) Amount of Reduction (%) PET resin Extruded PET Anthranilamide , Alpha Cyclodextrin - 10, , , MXDA , Preform Samples As previously mentioned in Section , seven PET blends were injection molded into preforms: six AA scavenger/pet blends and one control sample. Preforms of each sample type were put aside for melt viscosity measurements. The purpose of this work 123

152 was to isolate the effect of AA scavenger addition on I.V.; by keeping the thermal histories for the various AA scavenger/pet blend samples as much the same as possible. Table 4.15 shows the results from these measurements. Table 4.15: I.V. data for preform samples Scavenger / Sample Concentration (ppm) I.V. (dl/g) PET Anthranilamide Alpha-Cyclodextrin MXDA The data in Table 4.15 shows that the anthranilamide and MXDA samples show no reduction in I.V.; relative to the control sample (pure PET preforms). The alphacyclodextrin samples, however, did show a reduction in the viscosity. The 500 ppm alpha-cyclodextrin samples showed a 4% reduction and the 1200 ppm samples showed an 8% reduction; compared to the pure PET samples. This implies that it may be possible to add a small amount of AA scavenging agents, less than 500 ppm, and not affect the final I.V. of the preform. The reason the alpha-cyclodextrin/pet blend samples have a lower I.V. than the other samples is due to the addition levels of this scavenger. As an example, as shown in Table 4.14, when 500 ppm and 1200 ppm of anthranilamide or MXDA are melt-blended into PET, the resulting viscosities of these AA scavenger/pet blend samples are lower than those of the 500 ppm and 1200 ppm alpha-cyclodextrin/pet blend samples. 124

153 Comparison of Results for Pelletized Samples and Preform Samples As previously discussed, the blending process for the preform samples varied in comparison to the blending for the pelletized samples; in terms of each respective sample s overall thermal history. Since the concentrations are assumed to be the same, a comparison of their intrinsic viscosity values can be made among these sets of samples. Table 4.16 shows the comparison between the I.V. of the pelletized samples and preform samples. Table 4.16: Comparison of the I.V. data for pelletized and preform samples Scavenger / Concentration I.V. (dl/g) Sample (ppm) Pellets Preforms PET Anthranilamide Alpha Cyclodextrin MXDA While, the results for the alpha-cyclodextrin samples shows no change between the pelletized samples and the preform samples; changes in I.V. become apparent for the anthranilamide and MXDA samples. For both of the anthranilamide samples, the preform I.V. is 0.10 dl/g greater than the I.V. of the pellets. The same trend is true for the two MXDA samples; this time, however, the difference in I.V. is 0.09 dl/g. There are two reasons for the disparities seen between pelletized and preform samples for both anthranilamide and the MXDA. The first reason, as previously mentioned, is that 125

154 the preform samples have less thermal history than the pelletized samples. The second reason is due to the mechanisms by which anthranilamide and MXDA each scavenger AA. In each of these reactions, between anthranilamide and AA (Figure 4-7 or 4-11) or between MXDA and AA (Figure 4-14), water forms as a byproduct. It is well known that the presence of water decreases the I.V. Since the pelletized samples have a greater thermal history than the preform samples, there is a greater chance for more reactions with AA and a greater chance that residual water still exists in these samples Color Part of PET s appeal to the food and beverage industry is the combination of its excellent clarity and lack of color. This makes studying color generation in PET a vital step. As previously mentioned, the goal of adding AA scavengers to PET is to reduce the AA concentration without disturbing any of its desirable properties. If the addition of AA scavenging agents were to generate an undesirable color within PET, it could negatively affect the final appearance of the container and its attractiveness to the customer. The color of PET samples can be studied by both the human eye and by analytical techniques. ASTM D describes a process by which the yellowness of white plastics can be quantified. In this method a meter is utilized, similar to the one used in this work, to measure the L, a, and b values of a crystallized polymer at room temperature. The meaning of each of these three variables (L, a, and b) is described in Table 3.8. Through a series of calculations these three values are then converted into Y, X%, and 126

155 Z%; as respectively shown in Equations 5, 6, and 7. Ultimately, the results of these conversions are used to calculate a yellowness index (YI) for each PET sample; as shown in Equation 4. Further information concerning this analytical procedure, the calibration of the instrument, and the equations used to tabulate the results can be found in Section Color Analysis The determination of any color changes due to processing and/or AA scavenger additive addition, were made through the use of the Hunter Lab Color/Difference Meter D25-2. The instrument was used to analyze the crystallized PET pellets of each blend; ultimately determining a yellowness index (YI) for each sample. Table 4.17 shows the L, a, and b values and the calculated yellowness index for each sample. Table 4.17: L, a, and b values and yellowness index of pelletized samples Scavenger / Sample Number of Concentration (ppm) Averaged Values Processing Times L a b Yellowness Index PET resin Extruded PET Anthranilamide MXDA - 10, ,

156 The results for all of the PET samples containing alpha-cyclodextrin have been omitted from Table 4.17 because every sample had some brownness in its appearance. The relative prominence of this color altered the L, a, and b values and inherently yielded a false yellowness index for each alpha-cyclodextrin/pet blend sample. It can also be seen, in Table 4.17, that processing alone affects the b value and the yellowness index. As the number of passes through the twin-screw extruded increases, these two values also increase. The virgin PET resin, which had not been processed, has a b value of -2.3 and a YI of -7.2; while, the values for the one-time processed sample are 0.7 and 1.4, respectively. A second and then third pass through the extruder further increases these values. In terms of the anthranilamide/pet blends and the MXDA/PET blends, the general trend in Table 4.17 shows that both the b value and yellowness index increase with scavenging concentration. Reasonable yellowness indexes, for both anthranilamide and MXDA, were achieved when the scavenger concentration was decreased below 500 ppm. While their b values are higher, the yellowness indexes at the 100 and 200 ppm level for both of these scavengers are lower than that of the PET control sample that was only extruded once. The raw data from this analysis are shown in Appendix G Appearance of 2-Liter Bottles As previously mentioned, one PET control sample and six AA scavenger/pet blend samples were injection molded into preforms. These preforms were then stretch-blow- 128

157 molded into 2-liter bottles. Figure 4-28 shows a representative sample for each of the seven concentrations that were produced: 1200 ppm alpha-cyclodextrin/pet blend, 500 ppm alpha-cyclodextrin/pet blend, 200 ppm MXDA/PET blend, 100 ppm MXDA/PET blend, 200 ppm anthranilamide/pet blend, 100 ppm anthranilamide/pet blend, and pure PET resin. As mentioned in Section , the bottles containing alpha-cyclodextrin have a brownish tint. The two MXDA/PET blends and the two anthranilamide/pet blends all have an appearance that is indistinguishable from that of the pure PET bottle. The similar appearance of these five bottles confirms the color results seen in Table Figure 4-28: 2-liter blow-molded PET bottles (from left to right: 1200 ppm alphacyclodextrin, 500 ppm alpha-cyclodextrin, 200 ppm MXDA, 100 ppm MXDA, 200 ppm anthranilamide, 100 ppm anthranilamide, pure PET) Thermal Properties A polymer s thermal properties are important characteristics that can be critical in dictating its end uses. These properties also determine how the material should be 129