Deformation of high density polyethylene by dynamic equal-channel-angular pressing.

The effect of high strain rate and large shear deformation on the orientation of crystallites in high density polyethylene (HDPE) was investigated with dynamic equal-channel-angular pressing (D-ECAP). The HDPE samples were processed by two loading routes, route A and route C. Grid lines were used to obtain macroscopic strain distributions, which were substantiated by finite element modeling. Owing to the strain rate effect, the number of D-ECAP processing passes has a minor effect on the shear strain accumulations compared to ECAP. D-ECAP leads to a decrease in the thickness of the crystalline stem, and the crystallinity. After route-A or route-C D-ECAP processing, a new monoclinic phase emerges, and two types of crystallographic -axis orientations appear: the crystallographic -axis is approximately parallel to the flow direction (FD), or is tilted at approximately 55° clockwise away from FD. However, only one type of crystallographic -axis orientation is detected after 2 passes of route-C D-ECAP. It is viable to utilize D-ECAP to control the structure and orientation of crystalline polymers, as a complement to ECAP and other processing techniques.