Effect of oxalate unit on polycarbonate-based polyurethane and biodegradation by fungi

A series of aliphatic oxalate-polycarbonate polyols (AOPC) was synthesized from dimethyl carbonate, 1,6-hexanediol, and diethyl oxalate, made from oxalic acid that is a kind of bio-based material, via melting polycondensation. The aliphatic polycarbonate-based polyurethanes with oxalate units (AOPCUs) were successfully prepared using the AOPCs and hexamethylene diisocyanate (HDI) with 1,4-butanediol (1,4-BD) as the chain extender. The results of the 1H NMR analysis showed that the Mn of AOPCs was approximately 2900. Whereas, the Mw of the AOPCUs was ca. 48,200–53,000 from the gel permeation chromatography (GPC) measurement. The oxalate unit effectively impeded the crystallization of the AOPCUs as shown in the Differential scanning calorimetry (DSC) analysis. Based on the stress-strain curves, the AOPCUs with 10 M ratio of oxalate unit had best strength and elongation at break; however, their Young's modulus decreased from 130 MPa to 26 MPa. In addition, the biodegradation of the AOPCUs was studied using the fungi, Aspergillus sp. and Fusarium sp. The more oxalate units in the AOPCUs, the better biodegradability they presented after the 84-day degradation test. The characteristics of the biodegradation analysis for the AOPCUs presented the bulk erosion, and the oxalate unit played an important role in their biodegradability.