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

Multiflow injection molding is used to prepare a highly oriented shish‐kebab structure, and the mechanical properties of Polypropylene in the weak direction (WD) and strong direction (SD) are analyzed in this work. The oriented structure shows strong anisotropy. For example, the impact strength in SD is 6 times that of WD. One or three minutes of high‐temperature‐annealing (HTA, 30°C higher than Tm) has been proven to be an effective method to trigger the partial melting and re‐crystallization process, which in turn, can improve the shish‐kebab structure and greatly improve yield and impact strength in both WD and SD. Furthermore, results confirm that the chains in the amorphous region play a key role in the mechanical properties in the WD, while the shish‐kebab crystal structure determines the properties in the SD. Using shish‐kebab structure and HTA to improve mechanical properties in both SD and WD directions will be helpful to avoid generating fiber composites that create recycling difficulties and loss of properties with cycle times. [ABSTRACT FROM AUTHOR]