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The role of mold temperature on the morphology and properties of rotational shearing polyethylene (PE) pipes was studied via a self-developed rotational shear system (RSS). The result indicated that when the mold temperature was 150 °C, the hoop tensile strength and Vicat softening temperature were enhanced rapidly, which were 383.6% and 137.9% higher than those of the conventional PE pipes, respectively. Morphology and crystal structure studies by SEM and DSC revealed that once the rotational shear was applied, the shish-kebab structure began to appear. With the increase of the mold temperature, due to the relaxation of most of the oriented molecular chains, the preservation of shish-kebab structure became difficult. When the mold temperature was 190 °C, only the inner layer of the pipes, where the cooling rate was the largest, could preserve the shish-kebab structure. According to WAXD, there was less shish structure, and the growth of kebab was distorted in the inner layer of the pipes at 210 °C. The result of SAXS suggested that the length of shish changed most within the temperature range from 170 °C to 190 °C. The results of DSC and WAXD showed less change in crystallinity and degree of orientation between the two temperatures. It can be concluded that the reduction of shish length leads to a decrease in mechanical properties and heat-resistance.

The aim of this study is to investigate the effects of extra oscillatory shear field on morphology and mechanical properties of β-nucleated isotactic polypropylene by using a homemade vibration-assisted extrusion apparatus, in which oscillatory shear field was introduced into the extrusion head driven by crank and link mechanism. The results show that the extra oscillatory shear filed induces a significantly enhanced orientation of β-crystal besides causing a better homogeneous dispersion of β-nucleant, and the oriented β-crystal has a high ratio of daughter lamellae to parent lamellae orientation, which was rarely reported in other literatures. The vibration increased the overall crystallinity and changed the relative content of β-crystal. For the higher level nucleation agent content iPP(0.4 wt%), the relative contents of β-crystal just changed a little or basically unchanged after vibration. However, for iPP contenting 0.2 wt% nucleation agent, the content of β-crystal decreased. All the changes in the morphology, crystallinity, dispersion of β-nucleant and β-crystal content had a great influence on the mechanical properties, and that result was the improvement of yield stress and decrement of the elongation at break. POLYM. ENG. SCI., 57:838–845, 2017. © 2016 Society of Plastics Engineers