退火对PP/PTFE发泡材料力学性能和微结构的影响

通过二次开模微孔发泡注塑工艺制备不同聚四氟乙烯(PTFE)含量的聚丙烯(PP)微孔发泡材料,对比常规注塑成型的 PP 未发泡材料,研究不同退火温度对材料微结构及冲击强度的影响规律。结果表明,经二次开模微孔发泡注塑成型,再经退火处理能有效提高微孔发泡材料的冲击强度,达到退火前材料的 1.45 倍,而退火工艺对微孔发泡材料的微结构影响与对未发泡材料的影响基本相似。退火处理时PP材料结构中软无定型区的分子链进一步松弛,使材料更易于塑性变形,而其它软无定型区分子链易于规整重排,转变为硬无定型区,原硬无定型区的分子链同样进一步规整重排,甚至转变为结晶区,变得更硬,从而提高材料软硬兼具的抗冲击性能。

Effects of Annealing on Mechanical Properties and Microstructure of PP/PTFE Foams

Polypropylene (PP) microcellular foaming materials with different polytetrafluoroethylene (PTFE) content were fabricated using core-back foam injection molding,and the corresponding unfoamed samples were prepared via ordinary injection molding as a control group. The effects of various annealing temperature on the microstructure and the impact strength of PP/PTFE foams was studied. The results showed that annealing was a good method to improve the impact property of foams,and the impact strength could be increased to 1.45 times as compared with that of the foams before annealing. The evolution of microstructure during annealing process was similar in both of foam and unfoamed samples. During the annealing treatment,amorphous chain segments of mobile amorphous fraction (MAF) was further relaxed,which made the deformation of materials easy to occur. The other amorphous chain segments of MAF rearranged into the rigid amorphous fraction (RAF),leading to the formation of more orderly RAF. Partial molecular chains of the original RAF even rearranged into a crystalline region,and became harder. Those changes of RAF and MAF improved the impact strength of materials.