Toughened polypropylene with balanced rigidity. IV. Morphology, crystallization behavior, and thermal properties

The morphology of toughened polypropylene with balanced rigidity (TRPP) was characterized by using transmission electron microscopy and polarizing lig ht microscopy. The crystallization behavior and thermal properties were inv estigated by differential thermal analysis and thermogravimetric analysis. The PP component in the polymer blend was realized as the continuous phase and the elastomer component as the dispersed phase with a cellular structur e (salami structure) containing some PP. The particles of the dispersed pha se were small and regular. The cellular structure of the TRPPs resulted fro m the introduction of toughening master batches and was similar to the morp hology of acrylonitrile-butadiene-styrene and high-impact polystyrene synth esized by graft copolymerization. By gradually cooling from the melt, cryst allization of TRPPs was nucleated heterogeneously and the crystallization t emperature was slightly higher than that of PP whereas the crystallite size was remarkably reduced. For the samples with different compositions, the n umber, shape, and size of the cellular dispersed particles and the crystall ite size were different. Considering the toughening theories and our experi mental data, it was concluded that the samples with more regular and small cellular dispersed particles generally had better mechanical properties and the remarkably reduced crystallite size of PP was favorable for toughness improvement. The melting point, thermal oxidation temperature, and thermal oxidation onset temperature of the TRPPs were all a little lower than those of PP and the processability remained good. (C) 2000 John Wiley & Sons, In c.