Effect of pressure on the impregnation of thermoplastic resin into a unidirectional fiber bundle

Impregnation of molten thermoplastic resin into continuous unidirectional fiber tows was investigated. The degree of impregnation is defined as the ratio between the number of impregnated fibers and the total number of fibers of a tow. The degree of impregnation was modeled as a function of time, impregnation pressure, impregnation temperature, and tow size, assuming that the radial inward flow of resin through the fiber tow is governed by Darcy's law. The effect of the impregnation pressure on the permeability was studied. Experiments were performed to evaluate the validity of the model. Toray T300 graphite fiber bundles and Polyetheretherketone (PEEK) resin were used. Pressure and temperature were applied to fiber tows surrounded with resin powder in a mold. After a predetermined time, the sample was taken out and the degree of impregnation was measured from the microphotographs of the cross sections of samples. Experiments were performed for different impregnation conditions such as impregnation time, pressure, temperature, and tow size. Good agreement was found between the model and the experimental data.