(80c) High Temperature Mechanical Properties of Thermoplastic Polyurethane Nanocomposites
Incorporation of nanoparticles into a polymer can result in enhancement of electrical, thermal and mechanical properties. It also leads to improvement in flammability of polymers. This high flame retardant property of polymers nanocomposites are due for specific materials to the enhancement of char produced at the surface. If a significant amount of char is produced which consists of carbon formed from resin, one effect is that the amount of evolved gas (fuel) is reduced either by the barrier effect of the formed char or ultimately by mass balance considerations. The reduction in fuel supply reduces heat release rate, an important contributor to fire risk. The heat shielding capacity of the char (barrier property) is one desirable property, but if the char so formed is mechanically weak its failure could result in breach of the heat shield and loss of any benefit in the energy balance that the nanomaterial was designed for. This work describes the modulus enhancement of thermoplastic polyurethane (TPU) nanocomposite chars at high temperature (up to 300o C) using Dynamic Mechanical Analysis. Different compositions of TPU nanocomposites were prepared on a pilot scale twin-screw extruder using a Montmorillonite organo-clay, carbon nanofiber and multiwall carbon nanotubes. The dynamic mechanical properties of different TPU nanocomposite chars have been correlated with their fire retardance properties, including UL-94. The onset of softening was found to increase with loading at 1 Hz for all nanocomposites, and overall MWNT were found to produce the optimal reinforcement response in the char for TPU-based nanocomposites heated to 3000C.