Improvement of the chemical resistance of elastomers using organo-modified filler materials based on layered silicates Jörg G. Schauberger 1) ; Andreas Kaufmann 1) ; Rainer Puchleitner 1) ; Sandra Schlögl 2), Gisbert Riess 1,2) ; Wolfgang Kern 1,2) 1) Chair of Chemistry of Polymeric Materials, University of Leoben 2) Polymer Competence Center Leoben GmbH RubberCon 2012, Oslo, Norway
Introduction Montmorillonite - - - - - - - - H 2 O H 2 O H 2 O Na + Na + H 2 O Na + Na + H 2 O H 2 O Na + Na + H 2 O - - - - - - - - Si 200 nm Tetrahedral layer Ocathedral layer Tetrahedral layer exchangeable cations Water Oxygen Silicium Hydrogen Aluminium Layered structure - Platelets Thickness: 1 nm Length: 25-30 nm High L/D-ratio - negative surface charge - Interlayer cations to balance charges Exchangeable interlayer cations - Intercalation of organic cations i.e. amino acids, alkyl ammonium salts - Exchange of Na + with transition metals i.e. Zn 2+, Fe 3+ - Increase of layer-to-layer distance facilitate intercalation and exfoliation Improvement of dispersibility and homogenity of particle distribution
Introduction Enhancement of material behaviour using modified layered silicate filler materials - Flame retardancy prevention of dropping while burning - Enhancement of mechanical properties Impact behaviour Heat deflection temperature - Improvement of barrier properties versus gases and liquids Tortuous path diffusion barrier - Improvement of chemical resistance Good Intercalation/exfoliation Strong interactions Polymer/filler
Objectives Preparation and characterisation of modified Montmorillonites - Organo-modification with amino-acids - Interlayer cation exchange with transition metal salts Preparation of elastomer-mmt-composites - Testing of compatibility of filler materials and latex-dispersions - Thin film formation - Additional UV-crosslinking Characterisation of composite materials - Determination of filler distribution - Evaluation of resistance against crude oil
Cation-exchange organo-modified MMT Functional Fillers based on Sodium-Montmorillonite clay - Polarity tuning depending on application - Intercalation of functional groups for crosslinking reactions with polymers Intercalation of polar Amino-acids Improved hydrophilicity Biodegradeable Non-hazardous and biocompatible Covalent bonding onto functional polar polymers possible - Improved Polymer/filler interactions Intercalation of non-polar ammonia salts Combined with surface modification - Fatty acids hydrophobicity Compatibility with polyolefins - Improvement of mechanical properties - Flame retardant
Characterisation of organo-modified MMT Fourier-Transform Infrared (FTIR) Spectroscopy - Perkin-Elmer SpektrumOne - Qualitative detection of intercalated organic compounds - Wavenumber range: 4000 800 cm -1 - CaF 2 -Platelets (drop coated) Thermogravimetric Analysis - Mettler-Toledo TGA/DSC 1 STARe system - Purge gas: Nitrogen 50 ml/min - Temperature range: 50 950 C - Quantification of intercalated organic compounds
Cation-exchange anorganic Modification Na + can easily be exchanged by other metals - Resulting in i.e. Fe 3+ -MMT; Zn 2+ -MMT Cation-exchange Aqueous clay suspension Dosing of metal salt (soluble) 48 hours of dispersing Product is filtered and exchanged Nasalt is washed off EDX-measurements to prove successful cation-exchange Possible applications Radioactive waste repository Complexation reactions with heavy metal ions Reactive filler materials - Ionic crosslinking of polar polymers - Metal-ion induced decomposition (UV/thermal) - Radical generation through charge transition
Characterisation of anorganic-modified MMT-clays Thermogravimetric Analysis - Limited temperature range - Decomposition of Montmorillonite at Temperatures 900-1100 C FTIR-Spectroscopy not suitable - Metal-cations cannot be detected Scanning electron microscope (SEM) combined with - Energy dispersive X-ray spectroscopy (EDX) Zeiss Auriga 60 (Materials Center Leoben) - Detection of interlayer metal cations - Analysis of cation exchange - Visualisation of particle distribution in polymer-filler-composites
Crosslinking of XNBR I thin film preparation 1st step: ionic crosslinking by Zn 2+ -cations Thin film formation Aqueous XNBR-latex dispersion Dosing of ZnO Stirring at elevated temperature Coagulation onto porcelain forms Subsequent crosslinking via UV-irradiation and thiol-ene reaction
Thiol-Ene-reaction (NR-latex and XNBR-post curing) Accelerator free cross-linking of XNBR-Latex using UV techniques D. Lenko, S. Schlögl, R. Schaller, A. Holzner, W. Kern. Proceedings of the 7th Latex & Synthetic Polymer Dispersions, Smithers Rapra, Kuala Lumpur (2012)
Crosslinking of XNBR II 2nd step: UV-exposure of thin films crosslinking via Thiol-ene reaction
Preparation of organo-modified MMT 1st step: Acid-treatment of Na+-MMt - cation-exchange: Na+ => H+ - Activation increase of layer-to-layer distance Delamination of aggregates - Increasing amount of intercalated organic compound 2nd step: intercalation of Cysteine - Protonation of Amino-acid Low ph-value required - Possibility of crosslinking of NR by Thiol-Ene Reaction
Characterisation of organo-modified MMT Two-step preparation of organo-modified MMT Interlayer and surface water - OH-stretching vib. at 3650 cm -1 - Structural OH at 917 cm -1 Si-O absorption - 1114 and 1040 cm -1 No difference between pristine and activated MMT - Only changes of anorganic interlayer cations and purification of product Organic content - C=O at 1750-1700 cm -1 - -NH 3 + at 1515 cm -1
Characterisation of organo-modified MMT Two-step preparation of organo-modified MMT region I (up to 200 C) - Evaporation of surface and interlayer water Cysteine represses water region II (200-500 C) - Decomposition of AlCl 3 Byproduct of activation - Decomposition of Cysteine 10,9 wt.-% intercalated organic compound region III and IV - Dehydroxylation reactions - Changes in morphology
Preparation of cation-exchanged MMT Preparation of metal-cation-exchanged clay Characterisation via EDX-measurements Dispersing of Na + -MMT and ZnCl 2-48 hours at RT Purification - Filtration and washing with distilled water Dilution to 1 wt.-% - Improved miscibility with latex dispersion Si Si Na +, Ca 2+ -cations are exchanged by Zn 2+
Preparation of NR-latex films Dispersing of Cysteine-modified Montmorillonite into NR-latex - Instant coagulation of NR-latex Destabilisation by the acidic MMT - Alternatively: Dispersing of Na + -MMT into Latex No significant effect on chemical resistance versus crude oil Degree of Swelling > 400 wt.-% Adaptation of concept: crosslinking of XNBR using metal cation-exchanged MMTs
XNBR Methods of sample preparation Method I - Conventional ZnO-crosslinking of XNBR-latex - Reference Material Method II - ZnO-Crosslinking of XNBR-latex - Zn 2+ -MMT acts as passive filler material Method III - Crosslinking of XNBR-Latex using Zn 2+ -MMT Modified montmorillonite acts as Zn 2+ -ion donor Improved incorporation of filler into elastomer Addon: Subsequent UV-crosslinking - Thiol-Ene reaction (Thiole + Photoinitiator) - Influence on the resistance versus crude oil and chloroform
Preparation of XNBR-MMT- composite materials Method II 5 wt.-% Zn 2+ -MMT Method II 10 wt.-% Zn 2+ -MMT 1 µm 1 µm Method III 2 wt.-% Zn 2+ -MMT Method III 7 wt.-% Zn 2+ -MMT 1 µm 1 µm
Mechanical properties Method I (reference) - High elongation and stress at break Method II - Improved stiffness, reduced elongation and stress - 10 wt.-% filler material lead to very brittle films Method Sample E t ε B σ B [Mpa] [%] [Mpa] I ZnO 1,78 690 43,75 II III ZnO/ 5 wt.-% Zn 2+ - MMT ZnO/ 10 wt.-% Zn 2+ - MMT 2,82 428 15,33 Films too brittle for die cutting of samples 2 wt.-% Zn 2+ -MMT 0,91 732 17,75 7 wt.-% Zn 2+ -MMT 1,89 470 12,67 Method III - 2 wt.-% Zn 2+ -MMT Improved elongation at break Reduced stiffness - 7 wt.-% Zn 2+ -MMT Improved stiffness, Reduction of stress and strain at break
Swelling behaviour I Method I (reference) - Degree of swelling: 140 wt.-% Method III 2 wt.-% Zn 2+ -MMT - Lowest degree of swelling - Crosslinking Zn 2+ -ion release or: ionic-bonding of filler particles onto XNBR Method II - Decrease of swelling - Degradation of mechanical properties At higher filler contents Too brittle for sealent purpose 7 wt.-% Zn 2+ -MMT - Increased oil-absorption Microcracks? Porosity?
Swelling behaviour II XNBR - 2 wt.-% Zn 2+ -MMT - Thiol and Photoinitiator Additional crosslinking via Thiol-Ene- Reaction - Irradiation with Ga-doped Hg-Lamp Effect of UV-irradiation - Degree of Swelling in CHCl 3 observed - Formation of covalent bonds Resistance vs. crude oil - Slight effect on degree of swelling - Decrease of about 10 wt.-%
Conclusions Amino-acid modified Montmorillonite / NR-latex - Compatibility with other polymers (PVA, EVOH) - Coagulation of NR-latex due to destabilisation Cation-exchanged Montmorillonite (Zn 2+ -MMT)/XNBR-latex - Good compatility - Increased resistance versus crude oil - Improved elasticity, but reduced stress at break - Low filler content required to enhance XNBR Subsequent UV-exposure - Additional crosslinking improved resistance versus CHCl 3 - First results -> additional work on this topic variation of crosslinking agents (Photoinitiator / Thiol)
Outlook / ongoing work New approach to Cysteine-modified MMT - Decreased acidity - No coagulation of NR-latex Mechanical Testing of UV-exposed XNBR-samples Investigations on gas-barrier properties of XNBR-MMT-composites - GC-MS-technique - Different volatile test fluids Octane/Decane Toluene - Determination of occurrrence of microcracking Preparation and testing of sealants/couplings
Acknowledgement The author wants to thank Gisbert Riess and his collegues of the application engineering group for their input and advice. Also I want to thank Sandra Schlögl and Dietmar Lenko for their effort and for sharing their expertise concerning latices and rubber chemistry. Further thanks goes to Professor Wolfgang Kern and my collegues on the Chair of chemistry of polymeric materials.