Unique Slow Crack Growth Behavior of Isotactic Polypropylene: The Role of Shear Layer-Spherulites Layer Alternated Structure

Abstract

With the development of polymer science, more attention is being paid to the longevity of polymer products. Slow crack growth (SCG), one of the most important factors that reveal the service life of the products, has been investigated widely in the past decades. Here, we manufactured an isotactic polypropylene (iPP) sample with a novel shear layer–spherulites layer alternated structure using multiflow vibration injection molding (MFVIM). However, the effect of the alternated structure on the SCG behavior has never been reported before. Surprisingly, the results showed that the resistivity of polymer to SCG can be enhanced remarkably due to the special alternated structure. Moreover, this sample shows unique slow crack propagation behavior in contrast to the sample with the same thickness of shear layer, presenting multiple microcracks in the spherulites layer, which can explain the reason of the resistivity improvement of polymer to SCG.

Further improved mechanical properties of polypropylene by shish‐kebab structure and high‐temperature annealing

“…The oriented structure like shish-kebab shows ultra-high strength, stiffness, thermal stability, and high tribological performance [5][6][7][8] , and has been used in reinforced parts in various industrial processing methods, such as compression molding [9] , injection molding [10,11] , microinjection molding [12] , intermittent injection molding [13] , Ultrasonic vibration injection molding [14] , rotation extrusion [15] , expansion extrusion [16,17] , and three-dimensional (3D) printing [18] . Using these methods, ordered structures like shish-kebabs are formed during polymer processing and can manufacture self-toughening and self-reinforcing polymer products at a low cost [9,19] . Furthermore, considering recycling at the beginning of the manufacturing process and integrating shish-kebab into the design stage of a product can reduce the amount of plastic that would otherwise end up in landfills or are burnt, thus causing pollution.…”