High speed pultrusion of thermoplastic matrix composites

Abstract

The main problem with using thermoplastic matrices for composites is the difficulty in impregnating the fibrous reinforcement with the high viscosity resin. This has led to the development of a number of different manufacturing techniques, which are used to fabricate thermoplastic matrix composites. One method is to provide the matrix in fibre form and intermingle, or co-weave, the polymer fibres with the reinforcing fibres. These commingled fibres should ideally be combined in the same strand, allowing a high degree of intimacy to be achieved and minimising the flow distance for impregnation. An alternative technique is to impregnate the reinforcing tow with polymer powder particles and then melt fuse the particles in place. This method, the dry powder impregnation technique, allows for the formation of resin bridges between adjacent fibres, and with the application of applied pressure, longitudinal resin flow takes place. This differs from the transverse impregnation which occurs with the commingled fibres.These two consolidation mechanisms have been characterised and modelled using compression moulding techniques on commingled and powder towpregs, and the results of these experiments have been applied to the on-line consolidation which occurs during pultrusion processing. Successful correlation was achieved between the experimental results and the models with commingled polypropylene/glass fibres and dry powder-impregnated PA12/glass fibre-reinforced towpregs. The models then enable users to produce well-impregnated continuously reinforced composites of minimal void content at high line speeds, those reported in this work are speeds up to 10 m/min. With more powerful processing equipment, even higher line speeds could be achieved, demonstrating the potential cost effectiveness of pultruded thermoplastic composites.