xtrusion of short fibre reinforced polyethylene pipes

Short fibre reinforced thermoplastic pipe was produced by an extrusion process which oriented the fibre reinforcement predominantly into the pipe hoop direction. The fibre reinforcement was thereby used to maximise the internal pressure resistance and resistance to crack propagation of the pipe in the axial direction. Careful selection of materials and development of a suitable compounding method enabled polyethylene, glass fibres and a coupling agent to be combined such that fibre length retention and effective coupling gave worthwhile improvements in the physical properties over the polyethylene matrix polymer. Extrusion configurations developed were based upon the use of motionless dies having a diverging mandrel, and other methods, to bring about melt hoop expansion. Die geometry was varied to assess the influence of such factors as melt expansion ratio, divergence angle and die land length. _ Study of the complex fibre orientation distribution produced during extrusion and the die geometry variables has led, with the application of the classical particle rotation theory proposed by Jeffrey, to the development of predictive computer software for different die configurations. Predictions have been found to agree qualitatively with measured fibre orientation ' distributions in pipes. Physical testing has enabled characterisation of a range of pipes produced under different conditions having different levels of fibre reinforcement and with different fibre orientation distributions.