| Many composite manufacturing processes are carried out at room temperature, which require the resins to be cured at low temperatures. Examples are Seemann Composite Resin Infusion Molding Process (SCRIMP)---a vacuum assisted resin transfer molding (VARTM) process, hand lay-up and spray-up. In these methods, chemical reactions occur throughout the mold filling and curing step, and resin cure can not be controlled by external heating sources. Various kinds of curing agents have to be added in the resin in order to adjust the resin gelation and curing, and hence achieve a desirable mold-ability. This makes the polymerization kinetics much more complicated than that in high temperature processes. Most previous studies on resin reactions have focused on high temperature applications, and very little effort has been devoted to the polymerization of resins at low temperatures. The purpose of this research is two-fold: (1) to provide a fundamental understanding of the reaction kinetics and rheological changes of styrenic/polyester resins in low temperature molding processes in the presence of complicated curing agent systems, including initiators, promoters, inhibitors, and retarders; and (2) to develop a new curing system which can provide long mold filling time (e.g., long gel time), but short cure time and high resin conversion for composites manufactured at room temperatures. The reaction kinetics and rheological changes are investigated using an integrated experimental technique, including differential scanning calorimetry (DSC), Fourier transform infrared (FTIR) spectroscopy, rheometry and ultraviolet spectroscopy (UV). Based on the reaction kinetics, a diffusion-limitation kinetic model was developed, which was applied for the simulation of temperature and resin cure profiles in the molding processes. |
