Synthesis of thermoplastic cellulose grafted polyurethane from regenerated cellulose

Due to the fact that natural cellulose cannot be melted, it is still challenging to process this biopolymer via thermoplastic processing methods. Herein, polycaprolactone diol was grafted onto regenerated cellulose (RC) via hydroxyl/isocyanate chemistry in dimethyl sulfoxide to endow cellulose with thermoplasticity. By adjusting the reaction parameters including the feeding ratios of reactants and reaction time, several homogeneous cellulose grafted polyurethanes (RC-g-PU) with the degree of substitution (DS) ranging from 0.49 to 1.48 and degree of polymerization ranging from 1.84 to 3.3 were synthesized. The thermoplasticity of the obtained RC-g-PU was well characterized by differential scanning calorimetry and optical microscope. The results revealed that the prepared RC-g-PU with DS values ranging from 1.01 to 1.48 can be melted at above 168.4 °C because PU side chains can serve as internal plasticizers and prevent the restacking of cellulose chains. Eventually, the synthesized thermoplastic RC-g-PU can be processed into transparent films by hot-pressing at 170 °C. Therefore, this research constructs a melt-processable cellulose derivative by a simple and engineering method.