An infra-red spectroscopic and X-ray diffraction study of cold-drawn high density polyethylene samples

Three samples of high-density polyethylene, one linear, the second with one ethyl branch per thousand carbon atoms and the third with a comparable concentration of butyl branches, cold drawn at 60° C to elongations of 300, 800 and 1600%, have been examined by infra-red spectroscopy and wide- and small-angle X-ray diffraction. The results are consistent with, and give additional information about, the Peterlin model of plastic deformation. The change in crystallinity with draw ratio has been measured by infra-red spectroscopy and a wide-angle transmission X-ray diffraction method that minimizes the effect of the uniaxial orientation of the drawn specimens. Wide-angle measurements by reflection proved to be unreliable. Changes in the relative concentrations of methylene groups in crystalline regions, in gauche conformations and in tie chains in amorphous regions, and the alignment of tie molecules, have been followed by unpolarized and polarized infra-red spectroscopy. Small-angle X-ray diffraction measurements show that microvoids, with average dimensions of 250 and 80 Å parallel to and perpendicular to the draw direction respectively, are formed during the transition from the lamellar to the fibrillar structure.