Large-scale extrusion of auxetic polypropylene fibre

Auxetic polyproplyene fibres have been produced on a large-scale industrial extruder for the first time. A first batch of tests identified a coarse processing window which was then more closely defined by subsequent tests. The effects of barrel temperature, screw speed, take-up speed and quenching (through the parameters of air gap and bath temperature) on the Poisson’s ratio and Young’s modulus of the fibres were examined. It was found that a temperature of 200ºC, screw speed of 12.5rpm and take-up speed of either 1.5 or 3.5rpm produced fibres with a high degree of auxeticity up to 5% strain – significantly increasing the auxetic strain range previously reported for lab-scale extrusions at lower extruder temperatures. Quenching with a water bath reduced the auxeticity, so was not employed as a processing parameter. Keywords: auxetic, negative Poisson’s ratio, melt extrusion, polypropylene fibre