Reinforcing and toughening of polypropylene with self-assembled low molar mass additives

This study presents a new approach to reinforce and toughen thermoplastic polymers by using a low molecular weight additive; calcium stearate (CaSt2). The method involves melt blending isotactic polypropylene (iPP) and CaSt2 at a process temperature where the CaSt2 reduces the process viscosity through its characteristic morphology. Once the mixture cools, CaSt2 coalesces and solidifies to develop reinforcing domains. Differential scanning calorimeter experiments demonstrate a significant reduction in the percent crystallinity of iPP with the addition of CaSt2. The changes in yield strength and modulus suggest a synergistic effect between the CaSt2 domains and iPP. Addition of 10% CaSt2 increases the fracture energy by almost four-fold with a simultaneous increase in the elastic modulus. The melt flow rate of the composite is dramatically increased with CaSt2 incorporation. Reduction in coefficient of thermal expansion was also observed. Simultaneous positive effects of CaSt2 filler is attributed to its rich mesomorphic structure and its interaction with the iPP matrix. POLYM. ENG. SCI., 2011. © 2010 Society of Plastics Engineers