Processing, Structure, and Properties of Nanoparticle Reinforced Nonwoven Sandwich Composites

Shockwaves produced from ballistic impacts and improvised explosive devices are capable of causing severe internal trauma to soldiers. Current antiballistic materials give adequate protection to soldiers from high velocity impacts, however they are insufficient at absorbing and dissipating shockwave energy generated by these impacts and explosive blasts. The goal of this research was to develop shockwave absorbing protective materials which can be used as liners in conjunction with current antiballistic materials by reinforcing thermoplastic polyurethane nonwovens with high modulus nanoparticles

To determine the appropriate TPU for the application, a series of TPUs of shore hardness ranging from 60D to 85A were melt blown to investigate processability, web structure, mechanical, and thermal properties. It was determined that a TPU of 90A shore hardness was most suitable and possessed a glass transition in the ideal range to exploit the transition from rubber to glass phase upon high velocity impact to allow for large amounts of energy dissipation. Nanoparticles investigated for reinforcement include: nanoclay, graphite, C60, POSS, and inorganic disulfide nanotubes. Methods used to incorporate the nanoparticles into the nonwoven web were: dip coating, ultrasonic spray coating, and melt blowing with compounded mixtures of polymer and nanoparticle blends. The loaded webs were fabricated into sandwiched nanocomposites to investigate the performance by dynamic, and high frequency testing.

The ultra-sonic spray coating method produced the most uniform dispersion of nanoparticles and greatest improvement in the dynamic mechanical properties of the reinforcement methods investigated. Of the multiple nanoparticles used for reinforcement, C60 provided the greatest improvement in damping ability. With optimized spray coating parameters, the storage and loss moduli of the C60 reinforced sandwich composite at 0.2% by weight loading were increased by 15 times over the control sample. The study showed that by proper selection of materials and processing, it is possible to develop materials for energy absorption at high strain rates.