Characterization on mixed-crystal structure of poly(butylene terephthalate/succinate/adipate) biodegradable copolymer fibers

Biodegradable poly(butylene terephthalate/succinate/adipate) (PBTSA) pellet, an ideal random copolymer characterized by 1H solution NMR, was melt-spun into fibers. The crystal structure and physical properties of the as-spun fibers were investigated by WAXD, solid-state 13C NMR, DSC and tensile test measurements. Only poly(butylene terephthalate) (PBT)-like diffraction pattern was observed in WAXD; however, two different 13C spin-lattice relaxation time (T1C) components were observed for aliphatic units, in which the longer and the shorter T1C components correspond to the crystalline and the amorphous domains, respectively. Therefore the crystal structure of PBTSA was concluded to be formed by mixed crystallization of its comonomers. Such crystallization behavior enabled the PBTSA fibers to have well developed PBT-like crystal structure despite of its ideal randomness. Furthermore, due to the introduction of soft segments (BA and BS) into BT crystal lattice, melting temperature of PBTSA fibers (115 °C) was over 100 °C lower than that of PBT.