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Clay such as kaolinite, is commonly used as an additive to modify the thermal properties of polymer. In thispaper, the morphology, composition, shape and structure of kaolinite was characterized by various advancedtechniques. The TEM/ EDX data showed that the kaolinite had a larger particle size and a Si/Al ratio of 1.8. Theindividual particle of kaolinite was a single crystalline. TEM also showed that these particles were always stackedtogether due to the presence of electrostatic cohesive energy and hydrogen bond between plaletes. The PAS-FTIRspectra showed that no absorbance of hydroxyl group for hydration water in hydrogen bond region or at 1650cm-1was observed at room temperature. It meant a little ability to adsorb water for kaolinite particle. Kaolinite clay alsoshowed no change for its PAS-FTIR spectra with increasing temperature. The TGA results revealed that kaolinitealmost doesn′t lose weight at 60℃ due to loss of dehydration of absorbed water, however, it will decomposed around510℃ and lose its hydroxyl functional group in the form of water (dehydroxylation). The result is consistent withthat of PAS-FTIR analysis. This suggests that the structural hydroxyl group on the surface of individual kaoliniteclay particle is very stable below 500℃, and the kaolinite composed polymer could be got by the reaction of itsstable structural hydroxyl group with isocynate group of polyurethane prepolymer.