The influence of oxide nanaoparticles on the thermal properties of polymer matrix

Transcription

1 The influence of oxide nanaoparticles on the thermal properties of polymer matrix Branka Pilić, Oskar Bera, Mirjana Jovičić, Jelena Pavličević, Tanja Radusin International Workshop Eco-sustainable Food Packaging based on Polymers Nanomaterials: Preparation, Performance, Mechanical Characterisation and Modeling Varna, 24-25, Bulgaria September, 2013

2 Introduction Organic/inorganic composite materials combine the advantages of the inorganic materials such as a: - rigidity, hardness, durability, thermal stability and those of organic polymers: - flexibility and processability - Traditional fillers like calcium carbonate, talk, mica, alumina, silica are very well known and they require high loading amounts to achieve a significant improved performance. - Disadvantages are: Weight decrease of the final products Processability problems

3 Nanometers sized range filler, less then 100 nm can overcome this problem limitation of micro-sized filler Incorporation of nanoscale materials have provided large window of opportunity to polymer scientists and engineers in developing improved/desired properties (thermal, mechanical, optical, chemical resistance, electrical and thermal conductivity, optical clarity etc.) What are the main differences between traditional polymer composites and nanocompsites? Smaller amount of filler

4 Nanoparticles have a high specific surface advantage ultra large interfacial area per volume between the nanoelement and host polymer give high quality of materials disadvantage high surface energy between the particles caus agglomeration To take the advantage and to obtain the best properties a good disprsion of nanoparticles is necessary

5 Final properties of polymer nanocomposites depend on Uniform dispersion of nanoparticles (without agglomeration) depend on Type of nanoparticles (dimension, surface properties) Loading of nanoparticles Type of polymer matrix Interactions between nanoparticles and polymer Sample preparation

6 New class of materials introduces a new kind of problems Structuring of polymer nanocomposites with desire properties is still a challenge

7 Thermal behavior of polymer nanocomposites is consider as an important factor from the scientific and industrial point of view Glass transition temperature Tg is one of the properties which can be profoundly affected by nanoparticles Experimental results show that addition of nanoparticles in polymer cause the increase of Tg, in other cases a degrease or non changing.

8 Tg of polymer nanocomposites depends on many factors: - Degree of polymerization - Chemical structure of polymers - Nanoparticles size and loading - Dispersion conditions - Mixing method influence on Interfacial interaction between nanoparticles and polymer (adhesion) Existing and thickness of interfacial layer due to restriction of polymer mobility, that affects only the chain within few nanometerers of the particles surface

9 In this presentation will be shown how: Type of nanoparticles Nanoparticles loading Sample preparation can influence on changing of Tg in different polymer matrix and will try to give the answer to the question: Is it possible to predict the change of Tg?

10 First group of the experiments 1.1 The influence of nanosilica addition on polystyrene PS glass transition temperature, Tg Type of polymer matrix: Type of nanoparticles: Nanoparticles content: Sample preparation: polystyren (PS) silica, AEROSIL R 812, hydrophobic, 7 nm particle dimension, specific surface 260 (m 2 /g), Evonik 2, 5, 10, 15 and 30 % per weight solution casting Illustration of PS structure with dispersed silica nanoparticles O. Bera, B. Pilic at all. Thermochimica Acta, 515, 1-5 (2011)

11 DSC curves of prepared polystyrene samples with different nanosilica content With the increase of the filler content, Tg is increasing from 94 C to 99 C

12 1.2 The influence of nanosilica addition on polylactic acid PLA glass transition temperature Tg Type of polymer matrix: polylactic acid PLA Type of nanoparticles: Nanoparticles content: Sample preparation: silica, AEROSIL R 812, hydrophobic, 7 nm particle dimension, specific surface 260 (m 2 /g), Evonik 0.2, 0.5, 1, 2, 3 and 5 % per weight solution casting in chloroform DSC curves of prepared PLA samples with different nanosilica content The highest value of Tg determined for nanosilica content of 0.5% and with further increasing of silica content Tg is decreasing

13 1.3 The influence of nanosilica addition poly(methyl methacrylate) PMMA glass transition temperature, Tg Type of polymer matrix: Type of nanoparticles: Nanoparticles content: Sample preparation: PMMA (dental, Biocryl-RN, Galenika, Belgrade, Serbia) silica, AEROSIL R 812, hydrophobic, 7 nm particle dimension, specific surface 260 (m 2 /g), Evonik 0.05, 0.1, 2 % per weight polymerization in bulk First the silica dispersions were prepared by mixing silica nanoparticles with liquid monomers (MMA) as received. Stable dispersions of silica nanoparticles in MMA was formed, without phase separation and sedimentation for 24 hours. After preparation of silica nano dispersions in MMA, the common denture base material curing procedure was conducted.

14 DSC curves of prepared PMMA samples with different nanosilica content Tg of PMMA is increasing with filler loading

15 Second group of the experiments 2.1 The influence of silica content on determination of polymer layer and glass transition temperature Type of polymer matrix: Type of nanoparticles: polystyren (PS), silica, AEROSIL R 812, hydrophobic, 7 nm particle dimension, specific surface 260 (m 2 /g), Evonik A serias of nanocomposites were prepared by in situ polymerization of styrene with silica weight content: 1, 3, 5 % Sample preparation: - AIBN was dissolved in styrene (1% calculated on monomer) - Proper amount of silica was dispersed in styrene\ AIBN mixture using magnetic stirrer for 2 hours and ultrasonic bath for 15 min - Polymerization was performed under isothermal conditions at three different temperatures 70, 80, 90 C.

16 In previous work (*) a kinetics model was developed describing two reactions observed during styrene polymerization (the first order and autoacceleration) The proposed model, based on monomer ordering and on styrene adsorption on silica particles, enabled the determination of interfacial thickness (d) a part of monomer reacted by autoacceleration fraction of order phase in monomer d p particle diameter (7 nm) y p particle volume fraction a d difference between values of parameter a and monomer with y p of nanoparticles a d = a 0 a y a 0 parameter a for pure styrene a y parameter a with y p of silica Parameter a is obtained from the measured reaction heat during monomer polymerization and decreasing of a can be connected only to the decrease of ordered monomers phases * (O. Bera at all, Polym.J. 43, 826, (2011), O.Bera, B.Pilic, at all. Polym.Composite,33, 262 (2012))

17 The thickness of interfacial layer (d ) can be found by determing a d and a y, knowing the y p and d p The values of interfacial layer thickness (d) and decrease of parameter a (a d ) for styrene free radical polymerization at different temperatures and silica content T (C) y p , , , , , , a d 0.025, 0.035, , 0.012, , 0.017, d(nm) 3.2, 1.9, , 0.9, , 1.1, 1.7 d is varied between 0.3 and 3.2 nm, and the scattering existence is explained by the accumulation of several possible errors: error of DSC measurements, signal transformation error The average value d = 1.4 nm is in a good agreement with published literature

18 DSC curves of polystyrene/silica nanocomposites polymerized at 80 C Silica content has no significant influence on Tg, it can be assumed that the interfacial layer is thin and small amount of polymer is immobilized (low a d values), no change in Tg is expected

19 2.2 The influence of the size and surface nature of nanoparticles on the interfacial layer d and glass transition temperature of PMMA hybrid materials Type of polymer matrix: poly(methyl methacrylate) (PMMA) Type of nanoparticles: Specific Diameter Surface Nanoparticles Type Chemical content d (nm) (m 2 /g) Supplier Aerosil R812 hydrophobic silica Evonik Aerosil 380 hydrophilic silica Evonik Aeroxide Alu C 805 hydrophobic alumina Evonik Aeroxide Alu C hydrophilic alumina Evonik Aeroxide T805 hydrophobic titania Evonik Aeroxide PF2 hydrophilic titania 20 57,5 Evonik Sample preparation: polymerization in situ Bera O., Jovičić M., Pavličević J., Pilić B., The influence of oxide nanoparticles on the kinetics of free radical methyl methacrylate polymerization in bulk, Polymer Composites34 (2013)

20 A series of poly(methyl methacrylate) PMMA nanocomposites were synthesized using free radical polymerization in bulk, by addition of 1 vol. % of oxide nanoparticles (silica, alumina and titania differing in nature type hydrophobic or hydrophilic. The effect of the size and surface nature of nanoparticles on the interfacial layer thickness (d), as well as the influence of (d) on Tg of PMMA was studied. Particles content Sample Nanoparticles x p* [%] y p ** [%] MMA (PMMA) + 1% v/v SiO 2 R812 Aerosil R812 2,31 1 MMA (PMMA) + 1% v/v SiO Aerosil 380 2,31 1 MMA (PMMA) + 1% v/v Al 2 O 3 AluC805 Aeroxide Alu C 805 4,11 1 MMA (PMMA) + 1% v/v Al 2 O 3 AluC Aeroxide Alu C 4,11 1 MMA (PMMA) + 1% v/v TiO 2 T805 Aeroxide T805 4,35 1 MMA (PMMA) + 1% v/v TiO 2 PF2 Aeroxide PF2 4,35 1

21 The dependence of formed polymeric interfacial layer thickness on the hydrophility and size of fillers present in PMMA nanocomposites Interfacial layer thickness (d) increases with increasing particle diameter and is thicker for the hydrophilic particles

22 The determination of Tg of pure PMMA and PMMA/TiO 2 nanocomposites obtained by polymerization at 70 C Value of Tg is higher in the presence of hydrophilic TiO 2

23 The dependence of the Tg of PMMA nanocomposites on the size and hydrophility of fillers Tg is increasing with particle diameter and are higher in the presence of hydrophilic particles The lowest Tg is for PMMA filled with SiO 2 hydrophobic nanoparticles Tg of all the samples increase with increasing the thickness of interfacial layer The existence of unique dependence of Tg on interfacial layer can be supposed, it possible to present the effect of nanoparticle type and dimension in the same graph

24 The dependence of Tg of PMMA nanocomposites on the polymeric interfacial layer thickness formed around the particles The linear increase of Tg with the increase of polymer interfacial layer was observed due to decreased mobility of polymeric chains on particle surfaces The presence of small particles sizes (smaller interfacial layer thickness) decreased Tg in regard of pure PMMA Intersection of lined assigned to the change of Tg for pure PMMA is at d=1.4 nm, and the same value was determined for PS/SiO 2 nanocomposites where the change in Tg was not found Developing this method it is possible to predict Tg of hybrid materials

25 Summary Tg of polymer nanocomposites is strongly affected by interfacial layer thickness Interfacial layer thickness depend on: 1. Type of nanoparticles surface properties and particle dimensions 2. Nanoparticles content 3. Sample preparation (good dispersion) Tg of nanaocomposites will be decreasing or not be affected by adding nanofiller if the interfacial layer is thin Tg of polymer nanocomposites increases with thickness of interfacial layer

26 I want to thank my colleagues: Dr Oskar Bera Dr Mirjana Jovičić Dr Jelena Pavličević Tanja Radusin, dipl.eng. And Finansial support: Ministry of Education and Science of the Republic of Serbia, contract grant number 45022

27 Novi Sad Thank you for your attention