HIGH-SPEED PULTRUSION OF THERMOPLASTIC MATRIX COMPOSITES

The main problem with using thermoplastic matrices for composites is t he difficulty in impregnating the fibrous reinforcement with the high viscosity resin. This has led to the development of a number of differ ent manufacturing techniques, which are used to fabricate thermoplasti c 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 sam e strand, allowing a high degree of intimacy to be achieved and minimi sing the flow distance for impregnation. An alternative technique is t o impregnate the reinforcing tow with polymer powder particles and the n melt fuse the particles in place. This method, the dry powder impreg nation technique, allows for the formation of resin bridges between ad jacent fibres, and with the application of applied pressure, longitudi nal resin flow takes place. This differs from the transverse impregnat ion which occurs with the commingled fibres. These two consolidation m echanisms have been characterised and modelled using compression mould ing techniques on commingled and powder towpregs, and the results of t hese experiments have been applied to the on-line consolidation which occurs during pultrusion processing. Successful correlation was achiev ed between the experimental results and the models with commingled pol ypropylene/glass fibres and dry powder-impregnated PA12/glass fibre-re inforced towpregs. The models then enable users to produce well-impreg nated continuously reinforced composites of minimal void content at hi gh line speeds, those reported in this work are speeds up to 10 m/min. With more powerful processing equipment, even higher line speeds coul d be achieved, demonstrating the potential cost effectiveness of pultr uded thermoplastic composites. (C) 1998 Elsevier Science Ltd. All righ ts reserved.