Detecting crystallization structure evolution of polypropylene injection-molded bar induced by nucleating agent

The crystallization structures of Polypropylene (PP) injection-molded bars nucleated by nucleating agent were detected from the skin layer to the core zone, layer by layer. alpha-phase nucleating agent 1,3:2,4-bis (3,4-dimethylbenzylidene) sorbitol (DMDBS, Millad 3988), beta-phase nucleating agent aryl amides compounds (TMB-5), and their compounds were introduced into PP matrix, respectively. The relative content of beta-phase PP in the different zones of an injection-molded bar was characterized and calculated by Wide angle X-ray diffraction (WAXD) and Differential scanning calorimetry (DSC). The results show that, whether in pure PP or in nucleated PP, both beta-phase PP and alpha-phase PP grow in the skin layer of the injection-molded bar. However, in the intermediate layers and the core zone, the crystallization structures of PP are dependent on the used nucleating agent. beta-phase is the main crystallization structure of TMB-5 (0.1 and 0.2 wt%) nucleated PP, and alpha-phase in DMDBS (0.1 and 0.2 wt%) nucleated PP. Compounding nucleating agents with 0.1 wt% DMDBS and 0.1 wt% TMB-5 induces PP crystallization almost in beta-phase; however, PP nucleated by 0.2 wt% DMDBS and 0.2 wt% TMB-5 crystallizes exclusively in alpha-phase. The crystallization mechanism of PP nucleated by compounding nucleating agents was further studied in this work.