FRONTAL POLYMERIZATION OF THERMOSET COMPOSITES: A PROSPECTIVE ROUTE FOR ADDITIVE MANUFACTURING

Abstract

cracks due to residual thermal stresses developed during curing. Excitation temperature shows some effects on the exothermic reaction temperature and frontal velocity. The exothermic reaction temperatures range between 110 0C and 147 0C, whereas the initial excitation temperature varies from 150 0C to 270 0C. The FP velocities are seen to be 0.65 mm/sec for neat resin and 0.63 mm/sec, 0.62 mm/sec, and 0.57 mm/sec for 1%, 2%, and 3% SCF-reinforced composites, respectively. The result shows an FP velocity of 0.72 mm/sec for unidirectional continuous fiber reinforcement composites. This velocity is seen to be 28% higher in comparison to the neat resin. This is due to continuous carbon fiber-reinforced composites' faster heat flow rate. Failure strength is observed to be increased with enhanced initial excitation temperature. This is possibly due to enhanced reaction temperature, which resulted in a higher degree of cure. Finally, FP is seen to be a promising route for additive manufacturing of thermoset composites which emphasizes further studies to overcome shortcomings of the process.In this paper, frontal polymerization (FP) of carbon/epoxy (C/E) composites is investigated, considering FP as a promising route for additive manufacturing (AM) of thermoset composites. It is a fast and self-propagating polymerization process activated by thermal and cationic initiators. This study uses FP for neat epoxy resin, short carbon fiber (SCF), and continuous carbon fiber (CCF) reinforced composites. The evolution of exothermic reaction temperature, polymerization frontal velocity, degree of cure, and fracture surface are experimentally determined for different thermoset composites. As the FP continued, the temperature distribution and the FP path were monitored using a thermally activated infrared (IR) camera. The differential scanning calorimeter (DSC) is used to measure the degree of cure of the polymerized samples. The effects of excitation temperature and fiber contents in self-propagating reaction temperature and FP velocity are studied. FP-based thermoset composites' void contents and tensile properties are determined and compared with those manufactured through conventional methods with long-duration cure cycles. The results show increased cure time and decreased average frontal velocity with increased fiber contents in SCF-reinforced composites. This occurs because, at higher fiber contents, the resin percentage (heat source) is reduced, which primarily drives the exothermic reaction. Such a trend is primarily observed in low filler loading of SCF (1% to 3%). The FP velocity varied at different sample regions during polymerization, possibly due to the non-uniform distribution of short fiber contents. Increased tensile strength is observed in SCF-based composite in comparison to neat resin. The void contents in the 8% and 12% range were observed in neat resin and short fiber composites, respectively. The microstructure of the specimens shows large