Thermoplastic Elastomer Phase Changing Materials for Stiffness Modulation

Abstract

Four natural rubber-based phase changing materials (PCMs) were synthesized and evaluated with the goal of achieving controlled stiffness modulation at elevated temperatures (∼100-120 °C). The phase changing was achieved through either the glass transition or melt transition of one of four phase changing fillers: polystyrene, poly(methyl methacrylate), low density polyethylene, and indium tin alloy. The PCM stiffness was analyzed using dynamic mechanical analysis and the results showed that all four PCMs exhibited two thermal transitions: a low temperature transition at −58 °C due to the glass transition of the natural rubber matrix and a high temperature transition at ∼100-120 °C due to the thermal transitions in the four filler materials. The degree of stiffness change of all PCMs at 100-120 °C was found to be strongly influenced by the type of the phase changing filler as well as the type of thermal transition (glass transition versus melt transition). The compatibilities of the phase changing materials were analyzed using the Flory-Huggins interaction parameter and it was shown that natural rubber and low density polyethylene had the best compatibility. All systems exhibited effective stiffness modulation with the change in temperature, enabling them to be used for applications requiring variable stiffness control.