Synthesis, characterization and biodegradability of the biodegradable aliphatic–aromatic random copolyesters

Two series of biodegradable aliphatic–aromatic random copolyesters (PBCSTs) were synthesized by polycondensation. Specifically, we controlled the molar ratio of diols (1.4-butane diol, 1.4-cyclohexane dimethanol:CHDM) as well as that of diacids (succinic acid, dimethyl terephthalate:DMT) in order to investigate both the degradation behavior and the light transparency improvement of the final products. According to DSC observation, the melting temperature decreased gradually as more CHDM was added, and no melting temperature was observed when more than 20% of CHDM was used. Using 500 Mhz 1H NMR, we noticed that succinic acid has the same reactivity as DMT. However, in diols, the composition of CHDM was richer than its feed. We also observed that the introduction of CHDM improved the transparency of the samples even though it deteriorated the mechanical properties slightly. In the hydrolytic degradation, the S70 series samples of which have more succinic units in their main chain, showed better degradability than S50 series samples at pH 10 and pH 7. Furthermore, S70C40 and S50C40 which contain much CHDM showed faster hydrolytic degradation than other samples because of their rich amorphous phase. In the composting experiment, in all samples, we found stains, which were the trace of growing microorganisms, on the their surfaces. Even S50C20 samples, which showed the lowest weight loss, showed severe surface degradation by the attack of microorganisms. Using simple empirical degradation models, we evaluated the effect of the crystallinity and the hydrophilicity.