The effects of melt vibration blending on the subsequent crystallization and melting behavior of polypropylene/ultra-high-molecular weight polyethylene

Pure isotactic polypropylene (iPP) and 90/10 wt iPP/ultra high molecular weight polyethylene (UHMWPE) blends, prepared by a novel vibration internal mixer reformed from a conventional internal mixer via parallel superposition of an oscillatory shear on a steady shear, were investigated by differential scanning calorimetry (DSC) and wide angle X-ray diffraction. After plasticating pure iPP in the vibration field, the number of [betta] form crystals of IPP was increased. The β form exhibited a single DSC melting peak different from that of the bulk form crystals of IPP. After mixing of UHMWPE with iPP, the melting point of the UHMWPE component shifted to a lower temperature. For blends mixed at the higher-frequency and/or largeramplitude vibrations, the melting point of the UHMWPE component was further gently lowered while the bulk melting point of the iPP component was slightiy increased. The crystallization peaks of the two components overlapped into one single peak, and the total crystallinity became hi gher, together with a larger amount of the β IPP. These results showed that the two components influenced each other in blending. Hence, the resultant morphology affected the subsequent ciystallization and melting behaviors. Additionally, vibration in mixing possibly affected the conformation of some polypropylene chains to favor the subsequent packing in the β form.
Chixing Zhou (*) INTRODUCTION Blends of isotactic polypropylene (iPP) with low and high density polyethylene (LDPE and HDPE) have been widely investigated to improve the low-temperature toughness of iPP (1, [...]