A novel biodegradable polyurethane based on hydroxylated polylactic acid and tung oil mixtures. I. Synthesis,physicochemical and biodegradability characterization

A novel biodegradable polylactic acid-based polyurethane (PU) was synthesized via a chain extension reaction between hydroxylated polylactic acid (PLA-OH) and hydroxylated tung oil (HTO) using 1,6-hexamethylene diisocyanate (HDI) to link the two polyols and dibutyltin dilaurate (DBTDL) as a catalyst. Both PLA-OH and HTO, as polyols, were separately synthesized in our laboratory. Three different molecular weights of PLA-OH prepolymers were used, and the molar ratio of PLA-OH to HTO was also changed to investigate the effect of these two parameters on the structure and properties of the final PUs. Chemical structures of PLA-OH, HTO, and final PUs were investigated by Fourier transform infrared (FTIR) and Hydrogen-1 nuclear magnetic resonance (¹HNMR) spectroscopies. Thermal transitions and thermal stability of the final PUs were, respectively, studied by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The FTIR and ¹HNMR results showed that the chain-extension reaction of the two polyols with HDI was sufficiently achieved. The TGA results showed that the polyurethanes based on the lower molecular weight PLA segments were more thermally stable; it was not degraded up to 270 °C. DSC results showed that incorporating HTO in the PU chains led to formation of more flexible PU chains, while the glass transition temperatures of the PUs of higher PLA-OH molecular weights were higher than those of lower ones.