Crystallization, structures and properties of biodegradable poly (butylene succinate-co-butylene terephthalate) with a symmetric composition

The crystallization, crystalline structure, morphology and properties of poly (butylene succinate-co-butylene terephthalate) random copolymer (PBST) with 50 mol% of PBT, a very promising biodegradable polymer, was studied with a focus on understanding the structure property relationship. PBT spherulites are formed with an average diameter of ~11 μm, also implying a good crystal packing structure at lamellar level. The modulus and hardness of the copolymer are mainly contributed by the PBT crystals. It is known that no PBS crystal structure can be detected by X-ray diffraction; however, based on our FTIR and DSC studies, immature PBS crystals can be formed slowly (in days and months) at room temperature under no strain or quickly when stretched. These PBS aggregates contribute significantly to the mechanical properties of the copolymer, such as, mechanical strength, a good elongation to break and a permanent set at 80%. This biodegradable copolymer with a melting point (132 °C) close to HDPE, a modulus about 59 MPa, an elongation to break at 1300% and a shore D hardness of 42 can have many potential industrial applications.