Manufacturing and characterisation of microfibrillar reinforced composites from liquid crystalline polymers and poly(phenylene ether)

Abstract

The purpose of the present study was to investigate the fibrillisation process of liquid crystalline polymers (LCPs) in an amorphous poly(phenylene ether) (PPE) matrix during melt blending and a subsequent drawing operation, as well as to analyse the relationship between morphology and mechanical properties of the fibrillar reinforced LCP/PPE blends. In order to understand the effect of the compatibility between the blend partners, an additional set of LCP/PEE blends, containing different amounts of a compatibiliser, was studied too. The processing steps included: (i) melt extrusion and continuous hot stretching for fibrillisation of the LCP component in the different LCP/PPE blends, and (ii) compression (CM) or injection moulding (IM) of the drawn blends at temperatures below the melting temperature (Tm) of the LCPs. Samples from each processing stage were characterised by means of scanning electron microscopy (SEM), wide and small angle X-ray scattering (WAXS and SAXS), and mechanical testing. SEM and WAXS showed that the as extruded blends were isotropic, but after hot stretching the LCP components became highly oriented, with a high aspect ratio and a diameter of the fibrils between 0·4 and 3 μm. The fibrillated structure of the LCPs in the blends could be preserved after the compression and injection moulding only at temperatures below Tm of the LCPs. Addition of a compatibiliser to the LCP/PPE blend did not remarkably improve the adhesion between the components, as a result of the large difference between the coefficients of thermal expansion of the blend partners, which leads to different shrinkage conditions of the LCP fibrils and the PPE matrix. The flexural modulus (E) of all IM blends increased stepwise with an increase in the weight (wt) fraction of the LCP. At the same time, the highest values for the flexural strength (σ) were obtained for the LCP/PPE blends containing 5 wt-% LCP.