Kinetics and modeling of curing behavior for two different prepregs based on the same epoxy precursor: A case study for the industrial design of thick composites

The industrial production of a thick part obtained by hand lay-up of two commercial prepregs (≈35 mm) and intended for primary structural application is considered. Prepregs are made of either unidirectionally aligned fibers, PP-UD, or 2 × 2 twill woven fabric, PP-T2. While the resin is exactly the same, the prepreg production technology is different, namely, hot melt and solvent impregnation, respectively. The study shows that the prepregs age differently in the time span required for the process work up. Moreover, simulation of the independent curing process of each raw material shows unexpected differences both in the timescale (PP-UD reacts faster than PP-T2) and in the extent of reaction (PP-UD develops a higher amount of heat than PP-T2). The outlined differences require a particular care in the design of the curing cycle for production of thick composites where sequences of different prepregs alternate with no necessarily regular pattern, in order to reduce overheating, and to promote equal reaction of the two components without inducing too much residual stress between adjacent layers. This work shows that the experimental verification of raw materials and curing conditions might help identifying unforeseen industrial critical situations and avoiding the lack of performance in the final composite materials. POLYM. COMPOS., 34:1506–1514, 2013. © 2013 Society of Plastics Engineers