ON MOLECULAR AND TEXTURAL REORIENTATIONS IN POLYETHYLENE CAUSED BY APPLIED STRESS

Biaxially oriented branched polyethylene was used as a model material for an investigation of crystalline polymer structure and deformation mechanisms. Within the prepared form of this material were regions with a morphology consisting of alternate crystalline lamellae and amorphous layers. X-ray methods were used to assess the reorientations of the crystalline texture, and also of the chains of which the crystals were composed, when a uniaxial stress was applied at constant temperature. The initial orientation and the compressive stress system were such that rotation of undeformed lamellae took place, in accordance with an interlamellar slip mechanism, as previously observed. A transition to an intralamellar slip mode occurred when the lamellae became normal to the stress axis, and the X-ray long spacing then decreased with further compression. With simple geometric assumptions the angular rotation of chain directions is related to the above change in interlamellar separation; a quantitative explanation of the total deformation, however, requires the existence of amorphous polymer other than that between the lamellae, a finding which supports a structural suggestion made earlier. © 1969 Chapman and Hall Ltd.