Processing and Mechanical Properties of Strands of Liquid Crystalline Copolyester and Copolyesteramide

Abstract

Extrusion moulding behaviour, mechanical and morphological properties of thermotropic liquid crystalline copolyester (LCP-A) and copolyesteramide (LCP-B) strands were investigated using a co-rotating twin-screw extruder, tensile testing, x-ray diffraction measurements, and scanning electron microscopic observation. Extrusion pressure and torque of LCP-B strands were larger than those of LCP-A strands under the same extrusion conditions, reflecting a difference in the apparent melt viscosity of the two polymers. The LCP-B strands obtained in this study had more homogeneous diameters, as compared with the LCP-A strands. The irregularity in diameter of the LCP-A strands tended to become smaller with increasing the length-to-diameter ratio (l/D) and output flow rate. The molecular orientation of LCP-B strands rose rapidly with draw ratio and reached almost a plateau at a much lower one, whilst that of the LCP-A strands became slowly higher with draw ratio. The tensile modulus and strength of LCP-B strands increased gradually with a draw ratio, even after the molecular orientation of the strands levelled off. The effect of the draw ratio on the molecular orientation and the mechanical properties of the strands was discussed from a morphological point of view.