Effect of Nanoparticles on the Thermal Stability of Polymers
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Effect of Nanoparticles on the Thermal Stability of Polymers Juan González-Irun, Ana Garcia1, Ramón Artiaga2, Luís Liz-Marzán1, David Hui, Mircea Chipara3
Department of Mechanical Engineering, University of New Orleans, LA 70148, USA. 1
Departamento de Química Física, Universidade de Vigo, Vigo, Spain
2
Departamento de Ingeniería Industrial II, Universidade da Coruña, Ferrol, Spain
3
Department of Chemistry, Indiana University, USA.
ABSTRACT The thermal stability of polymethylmethacrylate loaded with silica nnaoparticles is investigated. The temperature dependence of the mass of of polymethylmethacrylatesilica nanocomposites has been fitted accurately with a single Boltzmann-like dependence. The effect of surface functionalization, silica nanoparticles size, and silica nanoparticles concentration is reported. It was observed that the thermal stability of polymethylmethacrylate increases as the polymer matrix is filled with nanoparticles. Surface functionalization produced a modest increase in the thermal stability (compared to composites with silica nanoparticles without surface modification).
1. INTRODUCTION The use of nanoparticles as filler-reinforcement of polymer matrix is of high interest since an increase of the mechanical properties of polymeric matrices was reported for low concentrations of nanotubes. The thermal properties of the polymeric matrix (glass transition temperature, melting temperature, and crystallization temperature) are affected by the interactions between nanoparticles and macromolecular chains. For many industrial applications, where the material may be subjected to high temperatures, it is also important to know the effect of nanoparticles on the thermal stability of the polymeric matrices. It is generally accepted that an increase of the inorganic filler content results in higher thermal stability. Nevertheless, it has been also reported that at certain temperatures the nanocomposite may show higher degradation rate than the pristine polymer. The effect of nanoparticle content and nanoparticle features on the thermal stability of different polymers has been investigated by dynamic thermo-
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gravimetrical analysis. Silica nanospheres with narrow particle size distribution were dispersed in polymethyl methacrylate. The experiments were carried out both in air and inert atmosphere with pristine and filled polymers. Finally, the plots were fitted to a degradation model in order to quantify mare accurately the degradation processes.
2. EXPERIMENTAL The synthesis of colloidal silica spheres was performed by Stöber method [1]. Particles of 350
nm (diameter) have been subjected to surface modification that includes two different coatings. The first coating was performed by addition of 3-(trimethoxysilyl) propyl methacrylate3 (TPM) in excess, followed by slow distillation of ethanol and final cleaning by repeated centrifugation. For the second coating octadecyltrimethoxy silane4 (OTMS) addition was performed by adding 10% OTMS chloroform solution in the dis
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