Investigating the influence of polyvinylidene fluoride (PVDF) on the crystallization behavior and rheological properties of syndiotactic polypropylene (sPP)

Abstract

Aiming at the performance deficiencies of syndiotactic polypropylene (sPP), specifically its low crystallization temperature and slow crystallization rate, this study innovatively selected polar polymer polyvinylidene fluoride (PVDF) as a crystallization-promoting component. The findings demonstrated that when the PVDF content exceeded 2 wt%, the crystallization temperature of the blends increased by over 10 °C compared to pure sPP. The crystallization rate underwent significant enhancement across all blending ratios. However, this crystallisation performance enhancement did not exhibit concentration-dependent characteristics. Furthermore, PVDF significantly reduced the energy barrier to be overcome in the nucleation stage of the system, as well as the crystal growth activation energy. While maintaining the limited disordered Form I crystal structure of sPP unchanged, PVDF altered the one-dimensional needle-like crystalline morphology of sPP, shifting the dominant crystal growth mechanism to two-dimensional lamellar growth. The distinct thermodynamic incompatibility between PVDF and sPP resulted in spherical PVDF particles uniformly dispersed within the sPP continuous phase, forming clear phase interfaces. Combined crystallization behavior and rheological analyses demonstrated that the high-density nucleation sites created by the PVDF phase, through interface-induced crystallization effects, effectively enhanced the crystallization performance of sPP. Simultaneously, the restricted mobility characteristics of PVDF minimized interference with macromolecular chain relaxation dynamics of the matrix, thereby achieving dual functionality of promoting the crystallization and maintaining the matrix’s rheological properties.