Dramatic influence of compatibility on crystallization behavior and morphology of polypropylene in NBR/PP thermoplastic vulcanizates

In this study, the isothermal/nonisothermal crystallization behavior of polypropylene (PP) in acrylonitrile butadiene rubber (NBR)/PP thermoplastic vulcanizates (TPVs) prepared with three different processing methods, the compatibility effect therein, and the mechanism involved were studied. We concluded that the vulcanized NBR particles in TPVs act as heterogeneous nucleation centers and increase the number of nuclei. The crystallization rate of PP thereby increases and the growth of PP spherulites is restrained because of the isolation of vulcanized NBR particles. Since the addition of compatibilizer improves the compatibility of NBR and PP, the smaller and uniformly dispersed NBR particles are obtained, resulting in more and smaller PP crystals as well as higher crystallization rate, compared with Ultra-fine fully vulcanized NBR particles (UFNBR)/PP TPV and NBR/PP TPV without compatibilization. The isothermal crystallization kinetics of PP in TPVs obeys the Avrami equation, whereas the nonisothermal crystallization kinetics is well described by the equation of Mo et al.