Synchrotron scattering and nanoindentation of heat treated high performance thermotropic polymer

A multi-scale analysis, ranging from μm → nm → Å-scaie on the influence of thermal treatment on the thermotropic copolyester based on 60 mol% (l,4)-hydroxybenzoic acid (B), 5 mol% (2,6)-hydroxynaphthoic acid (N), 17.5 mol% terephthalic acid (T) and 17.5 mol% biphenol (BP) - COTBP- was carried out. The Å and nm-scale structure was investigated by synchrotron scattering (WAXS and SAXS). Extruded tapes ca. 30 μm thick were annealed at 300 °C under air, without tension. WAXS revealed fibre-like structure with crystalline order, whereas SAXS patterns exhibited diamond-shaped diffuse scattering and discrete meridional scattering elucidating structures along the fibre axis and periodic crystallites. Heat treatment produced roughness reduction, and WAXS patterns showed reflections sharpening indicating an improvement of molecular register and packing (molecular alignment and degree of crystallinity Χ increased). Thermal treatment increased the thermal stability, melting transition and tensile Young’s modulus, E, along extrusion axis, whereas nanoindentation showed decrease of hardness and elastic modulus. Hence, a thermally-induced seif-reinforcing effect was evidenced, with microstructure reorganization correlating with improved thermo-mechanical properties.

Annealing studies on a thermotropic liquid crystalline polyester meltblown fabric

Meltblown fabrics composed of a thermotropic liquid crystalline polyester were subjected to heat conditioning at various temperatures. Physical effect of the treatment was investigated by tensile testing of the fabrics and the individual fibers. The fabrics exhibited increased tensile strength by more than 100% after the heat conditioning due to inter-fiber bonding in the fabric structure and morphological reorganization of the thermotropic polymer. The calorimetric behavior of the polymer was further investigated to obtain information about the internal structure. Structural change during the annealing was also visually observed under a polarized light microscope.