Structural,mechanical, and thermal properties of extruded sheets of a liquid crystalline copolyester

Structural, Mechanical, and thermal properties of extruded sheets of a liquid crystalline copolyester containing p-hydroxybenzoic acid and 2-hydroxynaphthoic acid were investigated using X-ray diffraction measurements, differential scanning calorimetry, rheovibron measurements, and scanning electron microscopic observation. The extruded sheets of the thermotropic copolyester are composed of layered structures containing skin and core layers. A skin layer comprises fine fibrils oriented almost parallel to the extrusion direction. A core layer contains poorly oriented thicker fibrils or platelike structures. The orientation function of sheets and their tensile dynamic modulus parallel to the extrusion direction increase with increasing draw-down ratio of the sheet. Annealing of the sheet caused the increases in the temperature and the heat of crystal—mesophase transition, the heat-resistance to the mechanical tensiles properties, and the inherent viscosity of the polymer. The effect of annealing on the structural properties of the extruded sheet was discussed. © 1993 John Wiley & Sons, Inc.