Microstructure in injection molded samples of liquid crystalline poly(P‐hydroxy‐benzoic acid‐Co‐ethylene terephthalate)

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Abstract
The microstructure of injection molded bars (2.9 and 5.8 mm thick) of thermotropic liquid crystalline poly(p‐hydroxy‐benzoic acid‐co‐ethylene terephthalate) has been studied by SEM on samples etched with n‐propylamine, SEM fractography, DSC, IR, ESCA, WAXS and polarized microscopy. The 2.9 mm bar consists of three different layers: a highly oriented surface skin, an oriented intermediate layer and a non‐oriented core. The 5.8 mm bar has a more complex microstructure and is composed of five different layers: a highly oriented surface skin, an oriented layer just beneath, a non‐oriented layer, another oriented layer and a non‐oriented core. The thicknesses of the different layers vary, significantly, with distance from the mold gate. The thickness of the core increases, significantly, with increasing distance from the mold gate at the expense of the oriented layers. The structure within the different morphological layers is not perfectly uniform. Tensile testing demonstrated the mechanical anisotropy of the surface material (a ratio of almost 20 between the longitudinal and transverse moduli) and the isotropy of the central core material.