Influence of nanoparticles on the shrinkage control of low profile unsaturated polyester composites

Unsaturated polyester (UP) resins are one of the most widely used materials in fabricated composites. However, a number of problems caused by their high polymerization shrinkage have limited their growth in many new markets. Our research results showed that 1-3 wt% of nanoclay can provide excellent volume shrinkage control of UP resin systems containing polyvinyl acetate (PVAc) as a low profile additive (LPA) in room temperature molding processes. Nanoclay residing in the LPA-rich phase led to a higher reaction rate and earlier onset of micro-cracking in the resin system. Consequently, an earlier volume expansion during curing was observed in the reactive dilatometry experiment, resulting in better shrinkage control.