Y. Wang, A. Tarafdar
Syracuse University,
United States
Keywords: frontal polymerization, tensile properties, traditional thermal curing
Summary:
The aerospace industry’s reliance on thermoset carbon fiber composites has been rapidly increasing, however, thermoset composites require cross linking for curing and consolidation, which is time consuming and can often take several hours. For example, the complete cure cycle of the Solvay CYCOM 977-2 epoxy resin will take about 10 hours in an autoclave. Such a long curing time significantly hinders the additive manufacturing/repair of such composites. Additionally, a large autoclave is a major capital investment for any composite structure manufacturers, e.g., a 14-meter diameter by 27-meter-long autoclave could cost on the order of $40 million to build and $60 million to install, not to mention the high cost of operation (nitrogen and power). Meanwhile, the energy consumption will lead to associated environmental impacts. The major challenge in the additive manufacturing and repair of thermoset-matrix fiber composites is an issue with the in-situ curing. To address this challenge, the emergent frontal polymerization technique can be used to significantly reduce the manufacturing and repair time of the thermoset-matrix fiber composite materials from several hours to only a few seconds, without compromising the mechanical properties. This technique features the creation of a self-sustained polymerization front which propagates through the thermoset resin due to the generation of the exothermic heating. Before this promising frontal polymerization technique can be scaled up to manufacture thermoset-based fiber composites, it is crucial to examine (i) how the mechanical properties of the thermoset resin, such as epoxy resin, cured using the frontal polymerization, compare with those cured using the traditional thermal curing method and (ii) how can we control the frontal polymerization process to achieve optimum mechanical properties. This talk will present our research on the frontal polymerization of epoxy resin monomer, where the front was initiated using a photoinitiator (TPP+) and a thermal co-initiator (H2O2). The monomer’s, photoinitiator’s, and thermal/co initiator’s reaction together will be characterized and the resulting cured epoxy resin’s material properties will be compared to the same epoxy resin cured using the traditional oven curing method. Experimental results on the frontal polymerization of epoxy resin, including the optical temperature measurements, SEM images with corresponding porosity percentages of the cured epoxy resin specimens, and the tensile properties of the dog-bone cured epoxy resin, at varying weight percentages of the photoinitiator and thermal co-initiators, will be presented and compared with the same epoxy resin system cured using the traditional oven curing method.