Structure and Property Relationship of Oriented Polymers by Solid- State Cross-Rolling

Orientation from either the molten state or solid-state has been widely used to improve the strength and toughness of polymers. Compared to orientation in molten state, orientation in solid-state has the advantage of being able to freeze in the overall orientation as molecular chains in the solid-state have lower mobility. In orienting polymers, the macromolecular chains, segments of the macromolecular chains, or the crystalline regions in the polymers will gradually become preferentially aligned along the orientation direction. This study investigates the morphology change of amorphous and crystalline polymers with orientation by solid-state cross-rolling and its effect on the macro-mechanical properties in both uniaxial tension and indentation conditions and on the failure mechanisms in puncture condition. In Part 1of this thesis, the effect of biaxial orientation by solid state cross-rolling on the morphology of an amorphous polyamide and three crystalline polymers polypropylene (PP), high density polyethylene (HDPE) and Nylon 6/6 was investigated with polarized optical microscopy, atomic force microscopy, wide-angle X-ray scattering, small-angle X-ray scattering and dynamic mechanical analysis techniques. The effect of microstructure change on the macromechanical properties was then studied in uniaxial tension at both ambient temperature and a low temperature of -40°C.

In Part 2, the effect of orientation on the indentation hardness and energy absorption of an amorphous TROGAMID polyamide and three crystalline polymers was investigated with a spherical indentation methodology. From the indentation hardness measurement, the mechanical properties were derived from both the elastic and plastic regions of the indentation load–displacement curves. The mechanical properties from indentation measurements were then compared to values obtained from uniaxial tension test. In Part 3, the effect of orientation by solid-state cross-rolling on the puncture performance and fracture mechanism was investigated for an amorphous TROGAMID material and three semi-crystalline polymers: high density polyethylene (HDPE), polypropylene (PP) and Nylon 6/6. The brittle-to-ductile transition of PP and Nylon 6/6 in low temperature puncture test was explained from the oriented morphology of these materials.