Structure and mechanical properties of blends of two thermotropic copolyesters

Blends of two thermotropic copolyesters, poly(ethylene terephthalate/p‐hydroxy benzoic acid) (20/80), EB, and poly(p‐hydroxy benzoic acid/2,6‐hydroxy naphthoic acid) (73/27), BN, were obtained in the melt state by direct mixing in an injection machine throughout the full composition range. They comprised an almost pure EB phase and a BN‐rich phase that contained some reacted EB. Important synergisms with most of the values above those of the two pure blend components were found at most compositions in the modulus of elasticity and the tensile strength. The synergisms appeared to be due to the concomitant effect mainly of an orientation of the components higher in the blends than in the pure components, and to a lesser extent, of a blending‐induced specific volume decrease.