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

DSC heating-cooling cycles (0-200 degreesC) 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 T-g 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, T-g.PLA and T-g.PHEE shift toward each other and eventually merge into a single T-g, while DeltaH(c) and DeltaH(m) 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 T-g, maximum DeltaH and zero DeltaH, are dependent on blend composition. Published by Elsevier B.V.