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Oriented structure, mainly controlled by processing conditions, is another efficient method of reinforcing polymer materials in addition to compounding with rigid inorganic fillers such as carbon nanotubes (CNTs). The mechanical properties of oriented polypropylene (PP)/multiwalled CNT (MWCNT) composites, which are vital to their application fields, are investigated extensively in this paper, with an aim to distinguish the contribution of MWCNTs contents from that of the oriented structure to the final performance of the composite. The results indicate that MWCNTs mainly increase the modulus of the composites by approximately 140%. The oriented structure formed during the die-drawing process contributes more to the enhancement of tensile strength, increasing up to 550%. The modulus and tensile strength can be further improved by increasing the drawing speed. Moreover, the tensile stress field in the die-drawing process can vastly improve the dispersion of the MWCNTs in the matrix, thus providing a new idea for improving the dispersion of nanofillers in the polymer matrix. • Die-drawing process contributes more to increase tensile strength. • MWCNTs mainly increase modulus rather than tensile strength. • Tensile strength and modulus can be further improved by increasing the drawing rate. • The die-drawing process can vastly improve the dispersion of MWCNTs in the PP matrix. • MWCNTs can hinder the molecular chain orientation. [ABSTRACT FROM AUTHOR]

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. Image 1 • A systematic processing-morphology-property relationship study of HDPE pipes under shear field is reported. • There are the most uniform shish-kebab structures along the thickness of the pipes at 7.5 rpm. • The significant enhanced hoop strength and heat resistance have been confirmed. [ABSTRACT FROM AUTHOR]

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%. Image 1 • Strong interfacial interaction facilitated O-MMTs' nanoscale dispersion in TPU. • TPU/O-MMT topological network has been constructed to well regulate cell growth. • Hydrogen bonding between TPU and O-MMT is beneficial to foams' cell stabilization. • O-MMT regulated foams' cell growth/stabilization without affecting cell nucleation. [ABSTRACT FROM AUTHOR]