SELF-ADHESIVE HONEYCOMB PREPREG SYSTEMS FOR SECONDARY STRUCTURAL APPLICATIONS

Porosity in cured honeycomb parts was investigated using model prepreg systems and compared with a commercial solvent produced prepreg. Wove n glass fabric was used as the reinforcement in both of the systems. T hree main solvents were identified in the commercial prepreg. These so lvents were found to cause porosity or reduce thermal properties in mo del solvent prepreg based laminates when used either separately or in combination. Lowering the solvent content reduced the porosity in the prepreg but was limited by resin staging. The high level of porosity, resulting from solvents, found in these commercial prepreg systems mot ivated the investigation of the feasibility of changing the method of impregnation from solvent to hot-melt. Hot-melt model prepreg produced essentially void-free laminates as well as honeycomb parts. Model pre preg produced by hot-melt impregnation was found to be more robust, pr oviding the capability of changing the degree of resin impregnation in the fiber bed. A low level of impregnation resulted in the best fille ts to the honeycomb core, while still producing essentially void free parts. The use of both solid and liquid carboxyl-functional elastomers was incorporated in the epoxy based resin to provide flow control and self-adhesive characteristics. Mechanical properties of both the mode l hot-melt and commercial prepreg based honeycomb structures and lamin ates were compared. The model hot-melt prepreg was found to have bette r cured properties along with the necessary prepreg characteristics pr oviding an optimized self-adhesive controlled flow prepreg system.