Chain orientation in melt-extruded samples of vectra A, vectra B, and blends in relation to the mechanical properties

Abstract

ABSTRACT:The profile of molecular orientation within injection-molded tensile bars of the liquid crystalline copolyesters Vectra A, Vectra B, and Vectra C, as well as blends of these polymers, was investigated by means of wide-angle X-ray scattering (WAXS) using synchrotron radiation (HASYLAB, Hamburg). The local variation of chain orientation was resolved into steps of 100 mm. An even higher resolution was obtained by using the microfocus camera (focal spot 2 mm) at the European Synchrotron Radiation Facility (ESRF) in Grenoble. In Vectra A and in the blend of Vectra A and Vectra B, a smooth variation of the orientation was found being almost zero at the surface and showing its maximum at a distance of 0.6 mm from the surface. The orientation in Vectra B was rather fluctuating. The average chain orientation in the blend samples processed under the same conditions was higher than in samples of the pure liquid crystalline copolyesters. The mechanical properties of the different layers within the injection moldings were determined by cutting the samples into slices and measuring the stress-strain curves. For specimens of comparable orientation, it turned out that the blend samples had the largest values of Young's modulus and tensile strength. The synergism of orientation and mechanical strength was also found for different blend compositions, as well as in blends of Vectra B and Vectra C. Annealing the injection moldings above the melting point resulted in a rapid relaxation of the orientation, whereas the chain alignment persisted at lower temperatures.

Effect of complex flow kinematics on the molecular orientation distribution in injection molding of liquid crystalline copolyesters

“…We postulate that the 'skin' found in morphological studies is a very thin sub-region of a thicker region near the mold surface in which shear kinematics still create a reasonable degree of molecular orientation, and that the two orientation populations revealed by X-ray scattering should not be assumed to uniquely correspond to 'skin' and 'core' as traditionally defined. This issue could be more satisfactorily addressed using characterization methods that are uniquely sensitive to molecular orientation at the surface [39,40].…”

Phase Structure, Processability, and Mechanical Properties of Rodrun Liquid Crystalline 5000/Rodrun Liquid Crystalline 3000 Blends

“…These differences are slight and do not agree with the observed modulus behavior. However, discarded specific volume effects, the orientation should be the main parameter that controls the modulus of elasticity, and synergistic modulus are often seen 5 6. ------------------------------------- is not explained; but, despite the X-Ray results, the possibility of an orientation effect cannot be fully discarded.…”

Simulation of mechanical properties of oriented glassy polystyrene

“…In such cases, the simulated homogeneous systems should be viewed as representative volume elements (RVEs) of the larger, spatially heterogeneous system. Such an approach can be readily used to investigate the spatial variation in, e.g., the orientation of injection-molded parts [6].…”