Effect of Different Shear Modes on Morphology and Mechanical Properties of Polypropylene Pipes Produced by Rotational Sh
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ARTICLE
POLYMER SCIENCE
https://doi.org/10.1007/s10118-020-2477-8 Chinese J. Polym. Sci.
Effect of Different Shear Modes on Morphology and Mechanical Properties of Polypropylene Pipes Produced by Rotational Shear Wei-Chen Zhou, Zu-Chen Du, Hao Yang, Jun-Jie Li, Ying Zhang, Xue-Qin Gao*, and Qiang Fu* College of Polymer Science and Engineering, Sichuan University, Chengdu 610065, China
Abstract Oriented “shish-kebab” structures could be obtained by shearing to enhance the mechanical properties of polymer samples markedly. However, the effect of shear mode on mechanical properties is still uncertain. The study of stepped hoop shear field on the isotactic polypropylene (iPP) pipe was developed through applying a self-designed rotational shear system (RSS). The effect of stepped shear field on the microstructure and comprehensive properties of iPP pipe was investigated by the comparison with continuous shear. It could be found that the loosely-assembled shish-kebabs with the larger size were formed in the continuous shear pipes, but the smaller and tightly-stacked ones existed in the pipes with stepped shear. Surprisingly, due to differential morphologies under different shear modes, better comprehensive mechanical properties were obtained in the pipes with stepped shear. Keywords iPP pipe; Shish-kebab; Rotational Shear; Shear mode Citation: Zhou, W. C.; Du, Z. C.; Yang, H.; Li, J. J.; Zhang, Y.; Gao, X. Q.; Fu, Q. Effect of different shear modes on morphology and mechanical properties of polypropylene pipes produced by rotational shear. Chinese J. Polym. Sci. https://doi.org/10.1007/s10118-020-2477-8
INTRODUCTION Isotactic polypropylene (iPP) pipes have been widely used in indoor cold and hot water supply and heating systems because of its excellent characteristics, such as corrosion resistance, lightweight, non-toxic and environmental protection.[1−3] However, in practical use, the hoop stress of iPP pipes is twice as much as its axial stress, and the main failure form in iPP pipes for fluid transportation is hoop fracture.[4−6] This phenomenon can be explained by the thermodynamically stable α-spherulite and the molecular chains oriented along the direction of melt flowing in iPP pipes produced by the conventional extrusion.[7−9] The morphology results in excellent axial strength but poor hoop strength of iPP pipes. How to improve the hoop strength of iPP pipes by polymer processing has been paid considerable attention. To enhance the performance of iPP pipes, blending,[10,11] adding fillers[12,13] and fiber winding reinforcement[1,14] have been carried out in the past period. However, high processing costs and difficulty in recycling waste are regarded as the most common problems in processing methods mentioned previously. Obviously, it is feasible to enhance mechanical properties via varying morphologies of polymer. A massive number of researches have shown that the specific structure of crystals (e.g. shish-kebab) in polymer can be ob
* Corresponding authors, E-mail: [email protected] (X.Q.G
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