Phase segregation in blends of linear with branched polyethylene: the effect of varying the molecular weight of the linear polymer

Abstract

This paper reports investigations into the phase behaviour of six blend systems containing linear with branched polyethylenes. Five systems used linear polyethylenes of differing molecular weight blended with the same branched polyethylene. The sixth system involved a branched polyethylene of lower branch content and shorter branches. The main experimental methods used were differential scanning calorimetry and transmission electron microscopy. Very good agreement was found between results obtained from both experimental methods. The phase diagrams deduced are of the same general form, all but one showing liquid-liquid phase separation in the melt with both upper and lower critical temperatures. This phase separation is most extensive where the molecular weight of the linear polymer is highest. At the other extreme, for a linear component of molecular weight of 2155, no liquid-liquid phase separation is observed. Of the two branched polyethylenes, that with the higher branch content is more prone to phase separation. These results lead us to conclude that the phase diagram found previously for a similar blend pair is not unique since the various systems studied here all give similar thermal results, morphologies and phase diagrams.