Effect of titanium dioxide and silicon dioxide on the thermal stability of isotactic polypropylene deformed via solvent-crazing mechanism
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The effect of a finely divided structure created via the mechanism of delocalized crazing on the processes of thermo-oxidative degradation of isotactic polypropylene has been studied. It has been shown that the thermal stability of porous films is reduced at relatively low temperatures (up to 155°C) and they become brittle. In contrast, their degradation rate at temperatures above 400°C is two times below that for the original, nonporous films because of the formation of crosslinked network structures and carbonization. The formation of titania and silica nanoparticles via hydrolytic decomposition of the respective alkoxides directly in the pore space of the polypropylene matrix substantially alters its thermal stability, depending on the precursor concentration, the extent of hydrolysis, and the composite structure. The greatest increases in the mass-loss-onset temperature and the temperature of the maximum mass-loss rate (by 80–100°C) have been observed for the composites with 40 wt % titanium dioxide. It has been assumed that the enhancement of thermal stability is due to the significant concentration of the products of incomplete hydrolysis of titanium alkoxy derivatives. The silica particles, in contrast, exert a signification influence on the thermo-oxidative-degradation processes in polypropylene at their low concentration (up to 5 wt %), a result that is associated with the structural features of such composites.
KeywordsPolymer Science Series Mass Loss Rate Scan Ning Electron Microscopy Isotactic Polypropylene Titanium Dioxide Phase
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