DSC study of biodegradable poly(lactic acid) and poly(hydroxy ester ether) blends

DSC heating–cooling cycles (0–200 °C) were repeated on poly(lactic acid)/poly(hydroxy ester ether) (PLA/PHEE) blends to study the miscibility of the two polymers. Initial thermograms show two distinguishable Tg values corresponding to the respective neat polymers, accompanied by a crystallization and a melting peak for the PLA. Subsequent DSC runs show that the thermogram profiles depend on the number of heating–cooling cycles the blends are subjected to. As the number of cycles increases, Tg,PLA and Tg,PHEE shift toward each other and eventually merge into a single Tg, while ΔHc and ΔHm of PLA increase to maximum values then decrease to zero. It is concluded that after repeated heating–cooling cycles, PLA and PHEE achieve mixing on a molecular level, i.e. PLA and PHEE are miscible. The number of cycles needed to reach a single Tg, maximum ΔH and zero ΔH, are dependent on blend composition.