Evaluation of Low-profile Additives in the Curing of Unsaturated Polyester Resins at Low Temperatures

The effects of four low-profile additives (LPAs) namely poly (vinyl acetate) (PVAc), poly (methyl methacrylate) (PMMA), general purpose polystyrene (PS), and a high density polyethylene (HDPE) on the volume shrinkage of two series of unsaturated polyester (UP) resins with different chemical composition or structure have been investigated by volume shrinkage method. Different low cure temperatures from 25 to 70oC have been used to cure the specimens. Within limits of this study, it was found that shrinkageincreases as the curing temperature increases. In addition, our studies show thatthere are two phase transitions for UP resins containing PVAc and PMMA cured at lowtemperatures. Adding LPAs to the neat UP resins can decrease the volume shrinkage todifferent extents, depending on the types of LPAs added and the kind of UP resin used.Results show that the nature of UP resin has a significant effect on the amount of volumeshrinkage but, the trend is similar for each kind of LPAs. In both unsaturated polyesterresins the best, second best, and worst shrinkage control obtained by adding PVAc,PMMA, and PS, respectively. But, surprisingly HDPE has a good shrinkage control effectat 70oC.