Self-toughening and self-reinforcing of polypropylene via melt-volume-pulsation-induced crystalline network

Abstract

To achieve low-cost self-toughening and self-reinforcing is highly desired for the application and recycling of polypropylene (PP) but remains unresolved. This work reports the construction of a robust crystalline network via a volume pulsation injection molding (VPIM) process to meet the challenge. In particular, it is found that melt volume pulsation under a normal packing pressure can induce the formation of high-content γ-lamellae in PP. These γ-lamellae can effectively connect α-lamellae to construct the robust crystalline network, which imparts PP with greatly enhanced mechanical properties. Moreover, the robustness of the crystalline network and the mechanical properties of PP can be easily regulated by tuning the pulsatile frequency. Compared with those of conventional injection-molded samples, impact strength, yield strength, and tensile modulus of VPIM samples can be enhanced by 584.70 %, 13.96 %, and 29.84 %, respectively. To reveal the processing-structure-properties relationships, the microstructure and mechanical properties of PP under different processing conditions were discussed in detail. Furthermore, a theoretical analysis of the mechanical energy of polymer melt during volume pulsation process was conducted. The results disclose that the frequency-dependent microstructure and properties of PP are closely related to the frequency-dependent mechanical energy gained by melt. Hence, this paper paves a new avenue toward the low-cost self-toughening and self-reinforcing of PP for value-added application.