Some issues on impregnation in manufacturing of thermoplastic composites by using a double belt press

Abstract

AbstractThe manufacturing of thermoplastic composite intermediates by a continuously running double belt press (System of Held Comp., Germany) has become one of the most effective techniques for high quantity production. The process of combining thermoplastic materials and reinforcing fabrics during the manufacturing results in impregnation phenomena of the reinforcing layers distinct from one in resin transfer molding (RTM). Here, the work is focused on the clarification of the impregnation process that occurred in such a continuous manufacturing process. A composite intermediate of 50 wt% fibers consisting of E‐glass fabrics and nylon 66 films (Zytel, DuPont) was produced at different processing conditions to exhibit the influence of the degree of impregnation on mechanical properties and damage patterns of thermoplastic composites. It can be proved that because of strong inhomogeneity in the fabric concerning the permeability of the yarns and the weaving structure, respectively, the time required to impregnate the fabrics is governed by transversal micro‐flow into the fiber bundles rather than macro‐infiltration of the polymer into the fabric structure. Imperfect impregnation resulted in specific damage pattern in the center of the compressed yarns after flexural loading. The results are to be applied to guide the optimization of the manufacturing process with respect to material selection and preselection of processing conditions.