Sequential Structure, Crystallization, and Properties of Biodegradable Poly(ethylene Terephthalate-Co-Ethylene Oxide-Co-Lactide) Copolyester

The sequential structure, isothermal crystallization, tensile property, and degradation behavior of poly(ethylene terephthalate-co-ethylene oxide-co-lactide) (ETOLA) copolyester based on melt transesterification of poly(ethylene terephthalate) with poly(ethylene oxide) and oligo(lactic acid) was investigated. The degree of randomness was calculated to be 0.38, showing the incorporation of poly(ethylene oxide) (PEO) blocks into the homogeneous sequences of ethylene terephthalate (ET) and lactide (LA) units. The isothermal crystallization kinetics results revealed that the crystallization activation energy of the copolyester calculated using the Arrhenius' equation was lower than that reported for poly(ethylene terephthalate) (PET), indicating that the addition of PEO and LA units into PET retarded the crystallization of PET. The copolyester exhibited the same crystal structure at different crystallization temperatures, similar to that of PET homopolymer, based on wide angle X-ray diffraction results. The size of the spherulites of ETOLA increased with crystallization temperature. The increase of crystallization temperature reduced the elongation at break of the copolyesters, as well as the enzymatic degradation.