Effects of diethylene glycol and triethylene glycol on properties of poly(ethylene terephthalate)

Abstract

Two copolyesters, poly(ethylene-co-diethylene glycol terephthalate)(PET-co-DEGT) and poly(ethylene-co-triethylene glycol terephthalate)(PET-co-TEGT), were synthesized via esterification reaction of terephthalic acid(TPA), monoethylene glycol(MEG) and two comonomers, diethylene glycol(DEG) and triethylene glycol(TEG), and then polycondensation reaction. The content of DEG and TEG were varied from 0 to 50 mol%. The chemical structures of copolyesters were analyzed by Fourier transform infrared spectroscopy and Nuclear magnetic resonance spectroscopy. The results showed that the mol% of DEG and TEG in copolyesters were higher than the feed in every case. In addition, the thermal properties of these copolyesters were measured using Differential scanning calorimeter and Thermogravimetric analysis. The results indicated that the copolyesters with increasing DEG and TEG led to the decrease in Tg and Tm of copolyesters. Moveover, all copolyesters had lower thermal decomposition than PET. The mechanical properties were also measured. It was found that percent elongation at break was higher while the tensile strength was lower when DEG and TGE content increased. In addition, the biodegradability was studied by in vitro degradation test in phosphate buffer solution during the period of 2 months. The results showed that all the copolyesters were more degradable than PET.