Textile impregnation with thermoplastic resin - models and application

One of the key issues of the development of cost-effective thermoplastic composites for the aerospace industry is the process quality control. A complete, void free impregnation of the textile reinforcement by the thermoplastic resin is an important measure of the quality of composites. The introduction of new, more thermal resistant and tougher polymers is accompanied by a large number of trial and error cycli to optimise the production process, since the polymer grade strongly influences the processing conditions. Therefore, a study on the impregnation is performed. Thermoplastic manufacturing processes are often based on pressure driven, transverse impregnation, that can be described as a transient, non-isothermal flow of a non-Newtonian fluid, where a dual scale porosity is assumed for the reinforcement's internal geometry. Meso- and micro scale models of isothermal flow revealed a limited sensitivity to the process conditions at the bundle scale for high pressure processes such as plate pressing, with an increasing sensitivity for lower pressures as apply for autoclave processes. The process conditions are significant for the quality of impregnation at filament scale. Specific combinations of pressure, viscosity and bundle compressibility can lead to void formation inside the bundles, as confirmed by microscopic analysis. The methodology developed has been translated to a ready-to-use design tool for the implementation of new polymers.