(713a) Effect of Wettability on the Void Formation during Liquid Infusion into Fibers

Void formation during liquid composite molding (LCM) is perhaps the most significant roadblock to the incorporation of LCM as a lower cost manufacturing option compared to traditional prepreg-autoclave methods. Void formation is thought to primarily arise from mechanical entrapment of bubbles during the resin wet-out of the reinforcement. Such bubble formation is thought to be dependent upon interfacial interactions between the solid (composite), liquid (resin), and vapor (air / bubble) phases, and the role of capillary flow in this mechanism has been documented in previous studies. However, the relation between the bubble formation and contact angle has not been empirically quantified previously. In this article, the hypothesis that higher wettability, i.e. lower contact angles of liquid on solids, would lead to lower void content is tested. First, a theory that can calculate the energy required to form a bubble as a function of contact angle is formulated by accounting for the interfacial energy differences at a thermodynamic equilibrium state with a bubble and without. To experimentally prove this hypothesis, several fabric samples were prepared with each of six different fiber surface treatments, to provide the fabrics with different contact angles. The wettability from the surface treatments was evaluated with contact angle measurements based on capillary rise between two fiber yarns from a carbon satin yarn. Void formation in situ during infusion was evaluated by a series of 1D infusion experiments using canola oil as a simulant for infusing polymeric liquid into carbon satin weave samples made with each of the same six surface modifications. Of six samples, the fabrics coated with fluorinated alkane and APTES showed the highest wettability and lowest void content, suggesting that a lower contact angle can reduce the formation of voids during the infusion process.