Rheological characterization of unsaturated polyester resin used in resin transfer molding

Liquid Composite Moulding process (LCM) such as Resin Transfer Moulding (RTM) generally produces polymer matrix composites by pressurizing precatalyzed resin into mould cavities that contains reinforcement fibers. Reinforcement performing, mould filling and curing are the steps involved in the LCM process. Complete filling of the mould with adequate wetting of the fibrous media is the primary objective in resin transfer moulding (RTM). Incomplete impregnation of the reinforcement preform results in expensive defective parts, which must be scrapped. Therefore, the simulation of the resin flow through the preform is an important step in modeling RTM manufacturing process. RTM involves a large number of variables related to process and product performance. Among them, rheology of the resin is the governing factor for the mould filling and the flow front progression, which directly influences the process efficiency. The resin viscosity during mould filling implicitly depends on the precatalyzed curing reaction and the process temperature. Hence, the evolution of the resin cure viscosity during mould filling can be correlated to the degree of cure and temperature. In this study, the rheological characterization of an medium reactive Unsaturated Polyester (UP) resin which is commonly used in RTM process has been quantified with varying proportions of accelerator and catalyst and temperature effects. The viscosity measurement has been performed using Bohlin Viscometer under constant shear rate conditions. The viscosity has been recorded as the function of elapsed cure time until the onset of resin gelation, where the resin loses its mobility.  The extent of cure reaction data has been obtained for the unsaturated polyester resin from the literature and it has been correlated with the experimental measure rheological data.