Strengthening of Polyolefins by Bottom-up Self-assemlby of POSS Nanoparticles

It is known that molecules of polyhedral oligomeric silsesquioxane (POSS) can self-assemble into spherical, fibrillar, or lamellar nanoparticles by bottom-up self assembly process while mixing with a host polymer. This study capitalizes on such nanoparticle formation to increase the melt strength and tensile properties of polyolefins and polyolefin fibers. We found that melt-mixing of POSS with polyolefins does not produce desired results due to poor compatibility between most POSS molecules and polyolefins. Therefore, a novel method was developed whereby mixtures of nucleating agents and POSS were mixed with polyolefins. Nucleating agents having higher compatibility with POSS aid its dispersion and provide templates for self-assembly of POSS molecules into nanoparticles of 25-200 nm. A typical polypropylene (PP) formulation contains 0.3 wt% clarifying agent and 5-10 wt% POSS. These materials can be spun into fibers with close to 68% reduction in diameter and offer 40- 50% increase in modulus and 45-55% increase in tensile strength compared to unfilled PP.