Development of single‐stream resin transfer molding using in‐situ anionic polymerization of ε‐caprolactam with preprocessing on carbon fibers

Thermoplastic resin transfer molding (T‐RTM) is one of the composites manufacturing processes using anionic ring‐opening polymerization of ε‐caprolactam (CPL). Because of very fast reaction among materials, traditional T‐RTM requires two different channels before transferring resin into the mold cavity. Single‐stream method has been researched for robust and simple process, which has several advantages in aspect of manufacturing process. Carbon fibers were preprocessed including polyamide sizing, plasma treatment and activator sizing for modified single‐channel T‐RTM. Through quantitative calculation of required sizing content, concentration of sizing agent was controlled. Thermal stability of preprocessed carbon fibers during molding was measured by TGA. Crystallinity of anionic‐polyamide 6 (A‐PA6) manufactured by single‐stream T‐RTM was measured by DSC and 3.0% lower than traditional T‐RTM. Mechanical properties were measured, which are short‐beam strength and flexural strength/modulus. The short‐beam strength and flexural strength of the composites fabricated through single‐stream T‐RTM were 29.7% and 17.0% higher than those fabricated through conventional T‐RTM while strain and toughness decreased. Fracture surface of carbon fibers/A‐PA6 composites manufactured by single‐stream T‐RTM showed more adhesive bonding between carbon fiber and matrix. Highlights Surface treatment on carbon fibers to develop single‐channel T‐RTM process. Effects of surface treatment researched by thermal, quantitative, and IR analysis. Improved interfacial fracture mechanisms due to higher adhesion at the interface. Manufacturing process and mechanical property enhancements using single‐stream T‐RTM and surface treatment of carbon fibers.