STUDIES ON MELT-SPINNING OF POLYPROPYLENE/POLYSTYRENE BLENDS

Abstract

Melt-spinning experiments were carried out to investigate the effect of blend ratio and take-up velocity on the mechanical properties of the polymer blends. Ultra-fine fibrils having several hundred A in diameter and ca. 105 in aspect ratio are oriented along the extrusion axis and dispersed uniformly in the cross section of the blend filaments.The following results were obtained.1) Birefringence and Young's modulus of each component polymer in the resultant blend filaments were estimated on the basis of the linear relationship between birefringence and Young's modulus for each homopolymer of the filaments obtained by the melt-spinning of PP and PS.2) Orientation of PP component decreases with an increase in PS content. Orientation of PS component is independent of the composition where PS component is formed as a continuous phase and shows the same orientation as that of pure PS filament obtained at the same take-up speed. In the range of the composition where PS is formed as a dispersion phase, orientation of PS increases drastically with a decrease in PS content.3) For the tenacity of the blend filaments, the transition of ductile to brittle is clearly observed at the critical PS composition V*PS The relationship between the tenacity and the blend ratio can be expressed by means of two straight lines, which lines cross with each other at the V*PS where a fracture mechanism of the blend filament is changed.4) In order to discuss the relationship between the tenacity and the blend ratio, the effect of the blend ratio on orientation properties of each component of PP and PS must be taken into account. Such a treatment is actually valid in explaining the fracture mechanism of the blend filaments on the basis of the simple composite model, namely parallel model.