Aromatic Polyesters and Copolyesters
2024-05-16 16:06As an engineering thermoplastic, poly(trimethylene terephthalate) (PTT) has a very desirable property set, combining the rigidity, strength, and heat resistance of PET with the good processability of poly(butylene terephthalate) (PBT). PTT is crystalline, hard, strong, and extremely tough. The density of PTT is slightly lower than PET and similar to PBT. The tensile strength and flexural modulus decrease between PET, PTT, and PBT, respectively. The thermal and relaxation characteristics of PTT are intermediate to the properties of PET and PBT, and are typical of those encountered with semiflexible polymers of low to medium crystallinity. The reported equilibrium melting temperature for PTT is approximately 237 C, with a corresponding 100% crystalline heat of fusion estimated to be 30 kJ/mol. To improve the thermal and mechanical properties of biodegradable aliphatic polyesters, introducing aromatic terephthalate units into the main chain of aliphatic polyesters has been considered to produce aliphatic aromatic copolyesters with better physical properties as well as still having biodegradability. The solid-state microstructures and thermal properties of aliphatic aromatic copolyesters of poly were investigated by wide-angle X-ray, solid-state 13C nuclear magnetic resonance, DSC, and atomic force microscopy. Both the melting temperature and crystallinity of copolyesters showed minimum values at around 25 mol% butylene terephthalate content, which is the transition point from PBA crystal structure to PBT crystal structure. It was reported that introducing 40 mol% or more butylene adipate units could reduce the glass transition temperature (Tg) of the copolyesters from 66 C to below 210 C, and reduce the melting temperature Tm from above 200 C to about 100 C. Biodegradable ideal random copolymer poly(butylene adipate-co-terephthalate) (PBAT) was melt-spun into fibers with a take-up velocity up to 5 km/min. Despite the ideal randomness and composition (1:1) of PBAT copolymers, the PBAT fiber showed a well-developed PBT-like crystal structure, while its melting temperature was over 100 C lower than that of PBT. Ecoflex (PBAT), a commercialized aliphatic aromatic copolyester from BASF, was characterized to be an ideal random copolymer with 44 mol% of BT units. The glass transition occurs at 230 C, and the melting point is 110 115 C . The physical and mechanical properties of this soft thermoplastic are similar to those of LDPE, and it can be processed on conventional equipment for LDPE. Ecoflex complies with food safety requirements, is water- and tear-resistant, elastic, printable, and weldable.