Voids formation characteristics in typical epoxy-based CFRP laminates during low-temperature annealing in the air or N2 atmosphere

The feedstock recycling of carbon fiber reinforced plastics (CFRPs) is typically conducted by either thermal decomposition or dissolution methods for resin separation. A common issue in the recycling processes is that neither oxygen nor solvents can easily penetrate dense CFRP; therefore, penetrating diffusion paths such as voids is expected to improve the separation efficiency. This study presents voids formation characteristics by low-temperature annealing as pre-treatment in typical epoxy-based cross-ply CFRP laminates. The void characteristics were evaluated by electrical treatment and observations after the annealing in the air or N2 atmosphere. Annealing in air resulted primarily in ply delamination and matrix cracking through slight oxidative reactions. By contrast, annealing in the N2 atmosphere denatured the epoxy resin, resulting in the formation of voids and swelling that reached the interior of the specimens. The void characteristics could be controlled by the atmosphere in the low-temperature annealing, leading to the penetrating diffusion paths.