Influence of curing agents on gelation and exotherm behaviour of an unsaturated polyester resin

A judicious choice of curing agents such as initiator and promoter and their ratio to the resin can avoid reduced gel-time and shortened exothermic reactions in applications such as liquid composite moulding processes. In this study, effects of different ratio of initiator and promoter to the unsaturated polyester resin on curing of the resin were investigated by measuring gel-time and peak exotherm using ASTM D2471 standards. Methyl ethyl ketone peroxide (MEKP) was used as an initiator and a cobalt salt was employed as an accelerator for the free radical polymerization of curing resin at ambient temperatures. It was observed that the resin gelation starts closely with the initial rise in exotherm temperature and time of gelation decreases with the increase in initiator or accelerator volume proportions. It was also found that the exotherm-peak and rate of temperature rise indicating that the curing rate increases with the initiator or accelerator proportions also increased. A nonlinear regression analysis of all gel-time and cure data were performed to quantify the dependence of curing parameters on the volume proportions of accelerator and initiator. Thus, for this polymerization initiation system, the gel-time and cure parameters can be predicted for any initiator and cobalt levels within the ranges studied.