Crystallization behavior and properties of polypropylene and its copolymers modified with sorbitol nucleating agents
Based on the polypropylene(PP)homopolymer and its copolymers with different ethylene contents,the effects of the contents of sorbitol nucleating agents and ethylene units on the crystallization kinetics,crystalline structure,crystalline morphology,transparency and mechanical property were systematically investigated.The self-organization behavior of the nucleating agent upon cooling was also analyzed through rheological behavior.The results show that,the crystallization,transparency and mechanical property of PP were dependent on the contents of nucleating agents and ethylene units.When the nucleating agent content increased to 0.1％(mass),the crystallization rates of PP and its copolymers were significantly accelerated,and their crystallinities were enhanced,resulting in the improvement of the rigidity of PP and its copolymers.However,the increase in ethylene unit content slows down the crystallization rate of PP,reduces the crystallinity and the rigidity of the material.The incorporations of ethylene units and nucleating agents facilitated the formation of γ crystals of PP.The relative fraction of γcrystals increased with increasing the contents of ethylene units and nucleating agents.As the contents of ethylene units and nucleating agents increased,the transparency of PP was also improved.
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