High-Temperature Flammability and Mechanical Properties of Thermoplastic Polyurethane Nanocomposites

Abstract

Incorporation of nanoparticles into a polymer can result in enhancement of electrical, thermal and mechanical properties, particularly at high temperatures where the polymer alone might exhibit softening or degradation. The nanocomposite softening temperature may or may not coincide with the temperature at which the nanoparticle enhances char formation. This work describes the modulus enhancement of thermoplastic polyurethane (TPU) nanocomposites at high temperature (up to 300 °C) using dynamic mechanical analysis (DMA). Different compositions of TPU nanocomposites were prepared on a commercial scale twin-screw extruder using a montmorillonite organo-clay, carbon nanofibers and multiwall carbon nanotubes (MWNT). The onset of softening was found to increase with nanoparticle loading (tested at 1 Hz). Overall MWNT were found to produce the optimal reinforcement response in the char for TPU-based nanocomposites heated to 300°C. A gap in reinforcement was noted at certain temperatures as the samples developed char. A correlation can be drawn between crossover of dissipative versus elastic behavior (dominance of loss modulus versus storage modulus) and dripping in UL 94 tests.