Rapid multiple-front polymerization of fiber-reinforced polymer composites

Frontal polymerization (FP) is an out-of-autoclave, self-sustaining cure process that enables rapid and energy efficient manufacturing of composites compared to conventional processes. Prior FP demonstrations for both polymer and composite materials rely on one polymerization front to achieve full cure. In this work, we investigate the effect of multiple polymerization fronts on the composite cure time, quality, and mechanical performance. Localized void formation, panel thickness increase, and thermal spike are measured between two merging fronts and observed to have a detrimental impact on composite performance. Numerical simulations guide the mitigation of the thermal spike by modifying the layup from thermally insulated boundaries (TIB) to thermally conductive boundaries (TCB). Panels manufactured with TCB successfully mitigate all adverse phenomena at the merging fronts, leading to improved composite mechanical properties. A 5-fold reduction in cure time from ca. 5 min for one-front TIB panels to ca. 1 min for two-front TCB panels is achieved.