Skin-core morphology ofin situ composites based on polycarbonate and a liquid crystalline polymer

Abstract

The outstanding mechanical properties of an engineering liquid crystalline polymer (LCP) can be attributed to the self-reinforcement effect due to its rigid rod-like molecular structure [1-4]. High strength and high stiffness liquid crystalline polymer fibres, e.g. Kevlar and Vectran have been developed and commercialized [5, 6]. Recently there has been increasing interest in blending thermotropic liquid crystalline polymers with conventional isotropic polymers. Liquid crystalline polymer fibre reinforcement can be formed in situ in an isotropic polymer matrix via a melt blending process [7-26]. The structure and morphology of the in situ composites may be controlled by varying the processing conditions and theological history of the blends. Blends of LCPs with conventional polyesters [7, 8], nylon [9], polycarbonate [10-13], polystyrene [11, 14], polypropylene [15, 16], polysulphone [17], poly[ether imide] [18] and poly[phenylene sulphide] [19] have been studied. For extrusion-blended materials, the structure and mechanical properties were found to be closely related to the extrusion conditions, in particular the draw-down ratio. Most researchers have attempted to explain the changes in mechanical properties in terms of the morphology of the LCP phase in the blends, with the most widely used techniques to study the morphology being scanning electron microscopy (SEM) and X-ray diffraction (XRD) [7, 12]. Transmission electron microscopy (TEM) has been widely used to study the crystalline structure of liquid crystalline fibres [4, 6, 20, 21] and the morphology of multiphase polymer systems [22]. Analysis has revealed detailed information on the crystalline structure of aramid and thermotropic liquid crystalline polyester fibres and the development of skin-core morphology of such fibres [4, 21 ]. These findings were related to the properties and sample processing conditions. The work reported in this letter is concerned with the application of the TEM technique to the analysis of blends of a liquid crystalline polymer and polycarbonate. The microstructure and morphology