Structure and mechanical anisotropy of cold‐rolled ultrahigh molecular weight polypropylene

Wide angle X‐ray diffraction pole figure, small angle X‐ray scattering (SAXS), and refractive index techniques have been employed to investigate structure and deformation mechanisms in unidirectionally cold‐rolled ultrahigh molecular weight polypropylene (UHMWPP) films. All reciprocal lattice vectors (plane normals) of (110), (040), and (130) were found to populate in the film normal (thickness) direction, suggesting that more than one orientation process must be involved in the deformation. SAXS studies on the cold‐rolled UHMWPP reveal an oriented lamellar structure with its long axis perpendicular to the rolled direction, however, the lamellae are somewhat tilted. Refractive index and tensile measurements were undertaken to determine the optical and mechanical anisotropy of the cold‐rolled UHMWPP films. A similar study was undertaken of unidirectionally rolled conventional polypropylene (PP) for comparison.