Microcellular injection molded lightweight, strong and thermally insulating PP/fibrillated-PTFE composite foams with enhanced surface appearance

Abstract

Microcellular polymer foams are a kind of advanced polymeric foams that show light weight and enhanced thermally insulating performance compared with traditional polymer foams. Microcellular injection molding (MIM) has emerged as a pollution-free technique to efficiently prepare microcellular polymer components. However, MIM products surfer from the problems including poor surface appearance, limited weight loss, and deteriorated mechanical properties, which seriously limit the application of this technology. Herein, we reported an approach to fabricate ultra-lightweight, high strength, surface quality and thermal insulation in-situ polytetrafluoroethylene (PTFE) microfibrils reinforced polypropylene (PP) foams using mold opening microcellular injection molding (MOMIM). Firstly, different morphology PP/PTFE composites were prepared by melt blending, and subsequently their crystallization behavior and rheological properties were further investigated. Afterwards, both MIM and MOMIM were conducted to produce PP and PP/PTFE microcellular parts. The results showed that the in-situ fibrillated PTFE benefit to accelerate crystallization, refine crystals and enhance viscoelasticity of PP compared with spherical PTFE. Both fibrillated and spherical PTFE led to greatly refined cellular morphology although the former is more effective. Compared with pristine PP foams, the tensile and impact strength of PP/fibrillated-PTFE foams could be enhanced by 21% and 133%, respectively. Meanwhile, the thermal conductivity of PP/fibrillated-PTFE foams could be reduced by 32% compared with the pristine PP foams. Moreover, MOMIM-fabricated parts exhibited better surface quality compared with MIM-fabricated ones.