Biodegradable polyester blend and copolyesters studied by positron annihilation and other methods

Two polyesters, i.e. an aromatic one: poly(butylene terephthalate) – PBT and an aliphatic one: poly(ĺ- -caprolactone) – PCL were mixed in melt to obtain a biodegradable product. DSC, 1H NMR, SEM, WAXS, SAXS, BOD and PALS measurements were performed to study the homopolymers as well as their physical blend and copolyesters. The latter were obtained due to the transesterification reaction. Ortho-positronium (o-Ps) annihilation lifetimes were used to create the distributions of free volume. The progressive changes in probability density function of free volume, i.e. increase in large free volume holes contribution to the total free volume, appearing when going from the homopolymers to the blend and then to the copolyesters reflect the influence of: the addition of aliphatic polyester, the weight fraction of it in the composition and transesterification. The higher contribution of larger free volume holes corresponds well with the reduced crystallinity of compositions revealed in X-ray diffraction and the worsening of the regularity of structure of the macromolecules involved in formation of crystals, deduced from the 1H NMR.