Monoclinic‐to‐orthorhombic transformation in polyethylene

The monoclinic‐to‐orthorhombic phase transformation induced by heat‐treatment in polyethylene was studied by x‐ray and neutron diffraction. X‐ray diffraction patterns obtained with a position‐sensitive proportional counter system showed overlaps of the several reflections of orthorhombic and monoclinic forms. Therefore, they were resolved into individual peaks by assuming the Gaussian‐Cauchy function. From the intensity distributions in reciprocal space, the geometrical relation between two forms in the transformation was clarified. Furthermore, a mechanism was proposed from the change in half‐widths. In a crystallite, the boundary between the orthorhombic and monoclinic forms, parallel to the orthorhombic (110) and monoclinic (010) planes, moves to the monoclinic side as annealing proceeds, and the transformation takes place.