Volume shrinkage characteristics in the cure of low-shrink unsaturated polyester resins

Abstract

The effects of four low-profile additives (LPA), namely poly(vinyl acetate) (PVAc), poly(methyl methacrylate) (PMMA), thermoplastic polyurethane (PU), and polystyrene (PS), on volume shrinkage in the cure of unsaturated polyester (UP) resins at 110°C were investigated by the linear shrinkage method, density measurements, and dilatometry. Experimental results showed that, for the finally cured samples, the fractional volume shrinkage would generally decrease linearly with increasing LPA concentration. Also, the effectiveness of volume shrinkage control was the best for PVAc, followed by PMMA and PS, while the shrinkage control behavior of PU depends on its concentration. Based on an integrated approach of measurements for volume change—microvoid formation—morphology—static phase characteristics for styrene/UP/LPA systems at 25°C, the mechanism of shrinkage control in UP resins containing LPA during cure and factors which affect overall volume change after cure have been explored.