Tensile creep and deformation mechanisms in oriented low-density polyethylene

Low density polyethylene (LDPE) which had been uniaxially oriented by cold drawing was stressed parallel to the fibre axis at 20? C. In most of the experiments static tensile loads were applied. Changes in the internal texture and molecular orientation during tensile deformation and recovery were determined by low- and wide-angle X-ray diffraction. Instantaneous elasticity, both in tension and recovery, occurred by extension of the macrolattice formed of layered crystalline and amorphous regions, of which the volume of the material was found to be mainly comprised. Tensile creep was observed having a retardation time for the main process of about 70 h, and was not produced by simple changes in the geometry of the macrolattice. Relaxation mechanisms which could account for slow viscoelasticity in this fibrous material are discussed, and the results are analysed with reference to earlier work on these subjects.