Effect of Shear Stress during Processing on Structure, Morphology, and Properties of Isotactic Polypropylene Nucleated with Silsesquioxane-Based β-Nucleating Agent

The study aimed to determine the influence of shear stress during real-life industrial processes such as compression molding and injection molding to different cavities on the crystallization of the isotactic polypropylene nucleated with a novel silsesquioxane-based beta-nucleating agent. Octakis(N-2,N-6-dicyclohexyl-4-(3-(dimethylsiloxy)propyl)naphthalene-2,6-dicarboxamido) octasilsesquioxane (SF-B01) is a highly effective nucleating agent (NA) based on the hybrid organicinorganic silsesquioxane cage. The samples containing various amounts of the silsesquioxane-based and commercial iPP beta-nucleants (0.01-0.5 wt%) were prepared by compression molding and injection molding, including forming in the cavities with different thicknesses.The study of the thermal properties, morphology, and mechanical properties of iPP samples allows for obtaining comprehensive information about the efficiency of silsesquioxane-based NA in shearing conditions during the forming. As a reference sample, iPP nucleated by commercial beta-NA (namely N-2,N(6)dicyclohexylnaphthalene-2,6-dicarboxamide, NU-100) was used. The static tensile test assessed the mechanical properties of pure and nucleated iPP samples formed in different shearing conditions. Variations of the beta-nucleation efficiency of the silsesquioxane-based and commercial nucleating agents caused by shear forces accompanying the crystallization process during forming were evaluated by differential scanning calorimetry (DSC) and wide-angle X-ray scattering (WAXS). The investigations of changes in the mechanism of interactions between silsesquioxane and commercial nucleating agents were supplemented by rheological analysis of crystallization. It was found that despite the differences in the chemical structure and solubility of the two nucleating agents, they influence the formation of the hexagonal iPP phase in a similar way, taking into consideration the shearing and cooling conditions.

Automated summary

This study aimed to investigate the influence of shear stress during real-life industrial processes on the crystallization of isotactic polypropylene nucleated with a silsesquioxane-based beta-nucleating agent. The samples were prepared by compression molding and injection molding, and the thermal, morphological, and mechanical properties were studied to evaluate the efficiency of the nucleating agents under shearing conditions. The results showed that both the silsesquioxane-based and commercial nucleating agents have similar effects on the formation of the hexagonal iPP phase, considering the shearing and cooling conditions.