On the crystal texture of linear polyaryls (PEEK, PEK and PPS)

Abstract

Three linear ppolyaryls, polyetheretherketone (PEEK) polyetherketone (PEK) and polyphenylenesulphide (PPS) have been examined regarding crystal morphologies as obtained from solutions and molecular orientation in melt grown spherulites, the latter involving also experiments on the carbon fibre containing polymer. In addition to the individual features observed in solution grown crystals agreeing with those being reported concurrently from elsewhere, the present coordinated results on three polymers underline the common crystallization behaviour and texture for this family of polymers. These common features comprise the existence of lamellae as symptomatic of chain folding, acicular shapes indicative of uniaxial growth (b being the growth direction in all three cases), and irregular crystal edges. The sheaf development of these crystals then leads readily to a postulated radiolb-axis orientation in spherulites, confirmed directly in melt crystallized samples possessing transcrystalline textures induced by nucleating carbon fibres. Observations on the effect of carbon fibres drew our attention to the combined influence of the crystal nucleating effect and separation distance of these fibres on the resulting crystal texture of the polymer matrix: varying the relative magnitude of the two effects, can even reverse the overall crystal orientation in the sample. Such considerations should be pertinent to crystal texture development in composites with crystaallizable thermoplastic matrices in general.