PROCESSING EFFECTS IN PRODUCTION OF COMPOSITE PREPREG BY HOT-MELT IMPREGNATION

The hot melt impregnation process for producing composite prepreg has been studied. The role of the exit die is highlighted by operating wit hout impregnation bars. Experimental results show that when a fiber to w is pulled through a resin bath and then through a wedge shaped die, the total resin mass fraction and the extent of resin impregnation in the tow increase with the processing viscosity. The penetration of res in into a fiber bundle is greater when the resin viscosity is higher. This trend is unchanged over a range of tow speeds up to the breaking point. A theoretical model is developed to describe the effect of proc essing conditions and die geometry on the degree of impregnation. Calc ulations with this model indicate that for a given die geometry, the d egree of impregnation increases from 58% to 90% as the ratio of the cl earance between the tow and the die wall, to the total die gap is decr eased from 0.15 to 0.05. Physical arguments related to the effective v iscosity of the prepreg show that the clearance ratio is independent o f the tow speed, but decreases as the ratio of the effective shear vis cosity of the prepreg to the resin viscosity increases. This provides a connection between the experimental results obtained with varying re sin viscosity and the computational results obtained with varying clea rance values at the die inlet.