Morphological characterization of blends of polyphenylene sulfide with a liquid crystalline polymer

Blends of polyphenylene sulfide (PPS) with a commercial, wholly aromatic, liquid crystalline polymer (LCP), Vectra-B 950, have been prepared by melt-blending in a Brabender mixer. The morphology of neat and blended PPS samples has been studied by scanning electron microscopy (SEM). The blends have been shown to be biphasic, with good contact between matrix and dispersed particles. This, as well as the observation that the LCP particles often displayed elongated shape, seems to indicate that there is good interphase adhesion between PPS and Vectra-B in these blends. The rate of PPS crystal growth was measured during isothermal crystallization of both neat and blended PPS, by optical microscopy, at different temperatures and blend compositions. It was found that the rate of crystal growth is practically unaffected by the presence of the LCP phase. On the other hand, the PPS spherulite size is considerably smaller in the blends than in the neat PPS, though being independent of LCP concentration within the investigated range (5-20%, w/w). The results, which are in a very good agreement with those of a previous calorimetric study, confirm that the observed increase of the PPS crystallization rate, caused by the LCP minor phase, can be explained in terms of an increased nucleation density of the blends; this is probably due to heterogeneous substances, initially present in the bulk of Vectra-B, which dissolve to saturation in the PPS phase, during melt-blending.