NIHR Royal Brompton Respiratory Biomedical Research Unit

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 200 °C, screw speed of 12.5 rpm and take‐up speed of either 1.5 or 3.5 rpm 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.