Nanoscale Dispersion of POSS in PP Assisted by Sorbitol Nucleating Agents

The study developed fundamental understanding of nanocomposite formation by “bottom-up” self-assembly of inorganic-organic hybrid molecules, such as polyhedral oligomeric silsesquioxane (POSS) in polypropylene (PP) matrix. A nucleating agent compatible with POSS was used to promote dispersion of POSS molecules and to provide templates for self-assembly of POSS molecules into spherical and cylindrical nanoparticles of 25-200 nm diameter. Typical formulations containing 0.3-0.7 wt% nucleating agent and 0-30 wt% POSS were spun into fibers and converted into films and their mechanical properties studied. It was found that the addition of POSS helped increase the draw-down ratio substantially. The maximum tensile properties of spun fibers were obtained with 10 wt% POSS. Microscopic POSS particles formed at POSS concentration higher than 10 wt%. The optimum formulation resulted in a 50% reduction in fiber diameter, 70% increase in tensile modulus, and 30% increase in tensile strength compared to unfilled PP. The interactions between POSS and nucleating agents were studied using infra-red spectroscopy, differential scanning calorimetry, and oscillatory shear rheology. It was found that fibrillation of nucleating agent was subdued due to hydrogen bonding interactions with POSS.