Dual-Cure Frontal Polymerization for Rapid Manufacturing of Fiber Reinforced Composites

This article presents a dual-cure frontal polymerization approach for processing composites with high fiber volume fraction. The proposed strategy combines a partial cure phase via low-intensity radical-induced cationic polymerization with a subsequent frontal cure driven by radical-induced cationic frontal polymerization. Experiments show that about 50% bulk polymerization can be achieved by regulating the activation of thermal initiator during the partial-cure stage, after which on-demand frontal initiation can generate a thermally stable, bubble-free reaction front. A distributed reaction initiation strategy is introduced on composites with high fiber volume fraction (~58%) replacing single-point-initiation, resulting in a stable through-thickness propagation. The effect of ply number and ply dimension was also studied on the composite samples. Results show that both the reaction initiation time and initiation temperature are affected by the ply count and dimensions. However, once initiated, the dual-cure resin demonstrates consistent front generation and propagation through the thickness direction with slight variations in maximum reaction zone temperature. To complement the experiments, a thermo-chemical finite element model was developed to study how the partial cure and fiber volume fraction influence temperature evolution, reaction kinetics, front velocity during the merging of polymerization fronts. The model demonstrated that increasing the initial degree of cure and fiber volume fraction reduces the peak temperature and local reaction rate at the merging point. The numerical results along with the experiments demonstrate partial curing as an effective strategy for stabilizing frontal polymerization. These results aims to establish the dual-cure RICFP process as a promising pathway for rapid, energy-efficient manufacturing of high-performance composite structures.