Rheo-Raman Spectroscopic Study of Microscopic Deformation Behavior of Low- and High-Density Polyethylene Solids under Uniaxial Deformation

The microscopic deformation behaviors of high-density polyethylene (HDPE) and low-density polyethylene (LDPE) under uniaxial stretching were investigated using rheo-Raman spectroscopy. The crystalline chains of LDPE were oriented uniaxially into the stretching direction beyond the first yielding point, which was accompanied by applying stretching load to the crystalline chains. In contrast, at the first yielding point of HDPE, the orientation of crystalline chains was suppressed and compression load was applied to the amorphous and crystalline chains owing to lateral shrinkage of the specimen. Additionally, the orthorhombic crystalline regularity was significantly disordered at the first yielding point for HDPE, concomitant with the fragmentation of the rigid lamellar crystals. In comparison, the disordering of the crystalline regularity of LDPE was induced at the second yielding point, when the orientation of the crystalline chains was nearly complete, owing to the application of a strong stretching load to the highly oriented crystalline chains.