PS-TiO 2 Nanocomposites: Thermal Investigations
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PS-TiO2 Nanocomposites: Thermal Investigations Rafael Villegas1, Yun Zhai2, Hailan Xu2, Dorina Magdalena Chipara3, David Hui2, Karen Lozano1, and Mircea Chipara3 1 Mechanical Engineering, The University of Texas Pan American, Edinburg, TX, United States. 2 Mechanical Engineering, University of New Orleans, New Orleans, MO, United States. 3 Physics and Geology, The University of Texas Pan American, Edinburg, TX, United States.
ABSTRACT Nanocomposites of polystyrene loaded with various amounts of anatase (ranging between 0 % wt. and 20 % wt.) have been synthesized and investigated by thermal analysis. The research was focused on the simulation of Thermogravimetric Analysis data, aiming to a refined understanding of the interactions between of polystyrene and TiO2 nanoparticles. The dependence of the first derivative of residual mass on temperature has been used to determine more accurately the temperature at which the mass loss is maxim. Several functions have been used to simulate the dependence of the first derivative of mass loss on the temperature of the sample. The highest correlation coefficient was obtained for the asymmetric Gaussian combination, which connects two halves of a Gaussian line with different linewidth. An increase of the thermal stability of the polymeric matrix upon loading with TiO2 is reported. INTRODUCTION Thermogravimetric Analysis (TGA) examines the dependence of the mass of the sample on temperature, in a controlled atmosphere. TGA spectra of polystyrene (PS) and polystyreneTiO2 (PS-TiO2) nanocomposites in nitrogen atmosphere are single sigmoids, characterized by a single inflection point. The mass of the sample starts to decrease slowly; as the temperature is increased the mass loss rate becomes larger and larger until the inflection temperature (Ti) is reached. At the inflection point, the mass loss rate (mi) is highest. As the temperature exceeds Ti, the mass loss starts to decrease and eventually becomes zero (when all the mass of the sample is volatilized). Such dependencies have a sigmoid like character; Avrami like equation [1] can be used to describe the time evolution of the mass of a polymer or polymer-based nanocomposites.
m(T ) = m(T0 ) + Ae −C (T −T0 )
n
(1)
where m(T) is the residual mass at a temperature T, m(T0) is a fitting constant associated to the position of the zero line, A is the amplitude of the degradation process (amount of vaporized polymer), T0 represents the temperature at which degradation starts, C is a constant connected to the volatilization rate, and n a parameter. Avrami equation has been frequently used to
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investigate crystallization processes [1]. In such cases, n was ranging between 0.5 and 4and C was positive and smaller than 1. Typically, the filling of polymeric matrices by nanoparticles results in the formation of a polymer-nanoparticle interface. Due to the huge surface area of nanoparticles, the fraction of polymer belonging to this interface can be appreciable and consequently the physical properties of the polymeric matrix modified
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