Efective Impregnation of ε‑Caprolactam with Polyamide 6 Oligomer in Thermoplastic Resin Transfer Molding

Abstract

The low-viscosity ε-caprolactam resin exhibits rapid infltration in thermoplastic resin transfer molding (T-RTM), causing an unstable fow front at a macroscopic level and uneven impregnation between inter-/intra-tows. Uneven impregnation arises when there is a substantial diference between external and capillary pressures, resulting in the formation of micro-/ macrovoids in the fber preform. To address this issue, we propose to minimize total void content by regulating key parameters (contact angle between resin and carbon fber, surface tension, viscosity, and resin infltration viscosity) related to capillary pressure. Unlike previous studies focused on optimizing impregnation velocity through external pressure control, our approach employs polyamide 6 oligomers to enhance the compatibility between ε-caprolactam resin and carbon fber, reducing the contact angle and minimizing void content by managing capillary pressure.