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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

Foaming behavior of thermoplastic polyurethane (TPU) is extremely difficult to be regulated due to the special microphase-separation structure. Therefore, organic montmorillonite (O-MMT) was applied in TPU foaming to regulate cell nucleation, growth and stabilization simultaneously: (1) strong interfacial interaction between O-MMT with TPU could not only facilitate O-MMTs’ nanoscale dispersion but also ensure a similar cell nucleation at various O-MMT loading, which effectively decoupled the complicated influences of cell nucleation and growth on TPU foam's shrinkage; (2) TPU/O-MMT topological network was constructed by O-MMT loading, regulating cell growth and corresponding decreasing cell size; (3) -OH group on O-MMT surface could hydrogen bond with TPU molecular chains in soft/hard segments, stabilizing TPU molecular chains and finally reducing foams' shrinkage. Combining hydrogen bonding and topological network resulted from O-MMT, it enables us to optimize TPU foam structure by controlling cell nucleation, growth and stabilization simultaneously, the optimal O-MMT loading was 1 wt%.

Properties of plastic products depend on their microstructure and morphology. To improve the pressure rating (maximum pressure) of plastic pipes, a novel rotational shear system (RSS) was developed in this study to fabricate plastic pipes with enhanced hoop tensile strength through applying hoop shear on the pipes using a rotational mandrel. Morphology study results showed that different morphologies of the HDPE pipes were produced when the mandrel rotated at 5 rpm, 7.5 rpm, 10 rpm, 12.5 rpm and 15 rpm. The hoop tensile strength and heat resistance of the pipes were found to increase rapidly with the rotation speed and the properties peaked at 7.5 rpm. At this speed, the hoop tensile strength and Vicat softening temperature (VST) increased by about 338% and 26.8 °C, respectively. The axial tensile strength of the pipe was also slightly improved under this condition. The high mechanical and thermal performance of the pipe produced at 7.5 rpm was attributed to homogeneously distributed shish-kebab structures throughout the pipe wall.