Strong PP/PTFE microfibril reinforced composites achieved by enhanced crystallization under CO2 environment

Abstract

In-situ polypropylene/polytetrafluoroethylene (PP/PTFE) composites are amazing and promising materials because continuous PTFE fibrils can be dispersed in polymer matrix randomly and uniformly, and meanwhile, PTFE microfibrils can greatly enhance the melt strength and thereby foaming ability of PP. It's worth noting that the crystallization, double influenced by fibrils and carbon dioxide (CO2) environment, plays a very important role in determining the mechanical performance of the composites. In this study, the crystallization kinetics of in-situ PTFE microfibril reinforced PP composites, spherical PTFE particle reinforced PP composites and pristine PP were compared. Furthermore, the crystallization behavior of composites under high-pressure CO2 environment and its influence on the mechanical properties of the material were studied. The crystallization kinetics calculation showed PTFE fibrils have more pronounced heterogeneous nucleation effect than PTFE particles, and yet PTFE fibrils restrict the growth of crystals compared with PTFE particles under atmosphere. Visual observations of crystallization further confirmed that PTFE fibrils led to nucleation-dominated crystallization behavior of PP/PTFE microfibril reinforced composites (MFC) especially under CO2 environment. The refined crystals by PTFE fibrils and further enhanced crystallization by CO2 treatment contributed to remarkably enhanced strength and modulus of PP/PTFE microfibril reinforced composites.