Equal channel angular extrusion of polyalkenes

The deformation of both high density polyethylene and polypropylene undergoing equal channel angular extrusion (ECAE) has been investigated, and the resultant molecular orientation characterised by X-ray diffraction. The ECAE process using a 45° extrusion angle is found to result in permanent deformation only when a considerable backpressure is applied, whereas 90° extrusion results in plastic strain without backpressure, albeit requiring lubrication. The extent of the shear strain acquired is generally less than the theoretical maximum, indicating that elastic bending plays a significant role in the angular extrusion of these polymers. The crystalline orientation is found to be similar to the orientation caused by simple shear, where two different preferred molecular orientations are found, and which can be attributed to two different slip systems operating. In addition, a partial change in crystalline form is observed, with the appearance of a monoclinic crystalline fraction after deformation.