Integrated analysis of unsaturated polyester and vinylester resins in vacuum-assisted resin transfer molding (SCRIMP)

Seemann Composites Resin Infusion Molding Process (SCRIMP) has already been used for marine, civil infrastructure, transportation and defense applications to produce large composite parts because of its low cost, processing flexibility, high fiber-to-resin ratio, and near-zero emission of volatile organic chemicals. The process, however, is not thoroughly understood, and most technologies developed to date are based on experience or trial-and-error approaches. Therefore, there is considerable potential for improving the process through greater technical understanding.; A systematic study of reaction kinetics and rheological behaviors of two widely used SCRIMP resins (e.g., unsaturated polyester and vinylester resins) cured at low temperatures is conducted. A differential scanning calorimeter (DSC), a Fourier transform infrared spectrometer (FTIR), and a rheometrics dynamic analyzer (RDA) are used to study the reaction kinetics and rheological behaviors. The effects of curing agents including initiator, promoter, inhibitor and retarder on the low temperature polymerization are investigated. A model is developed to quantify the effects of temperature and various curing agents on the gel time. The effects of styrene concentration on curing kinetics of styrene/vinylester systems are also studied. The microstructure formation in the primary polymer is studied based on the analysis of particle size distribution. An atomic force microscopy (AFM) is used to investigate the micrographs and topologies of the cured resins, and an electron spin resonance (ESR) spectroscope is used to track the behavior of free radicals during curing. A series of well-defined unsaturated polyester resins are used to further study the effects of resin chemistry on the reaction kinetics and rheological behaviors.; Considering the diffusion-controlled propagation reaction, a mechanistic kinetic model is proposed to predict the reaction rate and conversion profiles of various resins cured at different temperatures. The developed kinetic model in conjunction with a heat transfer model is used to simulate the mold curing process. The results of this research provide a comprehensive analysis tool for optimizing SCRIMP.