Homogeneous grafting of cellulose with polycaprolactone using quaternary ammonium salt systems and its application for ultraviolet-shielding composite films.

Microcrystalline cellulose grafted polycaprolactone (MCC--PCL) was successfully synthesized by ring-opening copolymerization catalyzed by 4-dimethylaminopyridine in a dual tetrabutylammonium acetate/dimethyl sulfoxide solvent system. A novel ultraviolet-shielding film based on MCC--PCL was prepared by introducing graphene oxide (GO). The results obtained showed that the introduction of GO not only obviously influenced the inherent structure of the MCC--PCL but remarkably changed the surface morphology of the composite film. Moreover, the GO/MCC--PCL composite showed a significant improvement in tensile strength, from 2.63 to 4.55 MPa, as well as elongation-at-break, from 6.4% to 15.5%, compared with the pure MCC--PCL film, owing to the strong hydrogen-bonding interaction that physically crosslinked GO with MCC--PCL. Importantly, GO/MCC--PCL composite films offered an effective high-energy light-shielding capacity; in particular MCC--PCL film containing 1.0 wt% GO possessed good absorbance between 200 nm and 300 nm. This study provides a framework for developing cellulose-based ultraviolet-shielding polymers and better understanding the ultraviolet-shielding mechanism.