VOLUME SHRINKAGE CHARACTERISTICS IN THE CURE OF LOW-SHRINK UNSATURATED POLYESTER RESINS

The effects of four low-profile additives (LPA), namely poly(vinyl ace tate) (PVAc), poly(methyl methacrylate) (PMMA), thermoplastic polyuret hane (PU), and polystyrene (PS), on volume shrinkage in the cure of un saturated polyester (UP) resins at 110 degrees C were investigated by the linear shrinkage method, density measurements, and dilatometry. Ex perimental results showed that, for the finally cured samples, the fra ctional volume shrinkage would generally decrease linearly with increa sing LPA concentration. Also, the effectiveness of volume shrinkage co ntrol was the best for PVAc, followed by PMMA and PS, while the shrink age control behavior of PU depends on its concentration. Based on an i ntegrated approach of measurements for volume change-microvoid formati on-morphology-static phase characteristics for styrene/UP/LPA systems at 25 degrees C, the mechanism of shrinkage control in UP resins conta ining LPA during cure and factors which affect overall volume change a fter cure have been explored.