Characterization on mixed-crystal structure and properties of poly(butylene adipate-co-terephthalate) biodegradable fibers

Biodegradable ideal random copolymer poly(butylene adipate-co-terephthalate) (PBAT), with 44 mol% butylene terephthalate (BT), was melt-spun into fibers with take-up velocity up to 5 km/min. The structure development and properties of the as-spun fibers were investigated through birefringence, WAXD, SAXS, DSC and tensile test. Despite of the ideal randomness and composition (1:1) of PBAT copolymer, PBAT fiber showed well-developed PBT-like crystal structure, while its melting temperature (ca. 121 °C) was over 100 °C lower than that of PBT. Based on the quantitative analyses on the lattice spacing, the crystallinity and the fraction of crystallizable BT sequences, the crystal structure of PBAT was characterized to be formed by mixed-crystallization of BT and BA units, where BA units were incorporated into BT lattice. This mixed-crystal structure was found to undergo PBT-like reversible crystal modification with the application and removal of tensile stress. This crystal modification was found to occur in a higher strain region compared with that of PBT fibers.