Synthesis of water soluble full biobased cellulose levulinate ester through the reaction of cellulose and alpha-Angelica lactone in the DBU/CO2/DMSO solvent system
Cellulose esters is one kinds of important cellulose derivatives with good processing ability and material properties, and the design and sustainable synthesis of cellulose esters is prime research topic. Herein, cellulose levulinate esters (CLEs) with degree of substitution (DS) ranging from 0.15 to 2.04 could be prepared simply through an atom economic reaction between cellulose dissolved in newly developed 1.8- diazabicyclo [5.4.0] undec-7-ene (DBU)/DMSO/CO2 solvent system and alpha-angelica lactone, a biomass-derived and commercial available platform chemical, without adding any external catalyst and condensation reagents. The reaction conditions were optimized to 120 oC, 0.5 h, 5/1 molar ratio of alpha-Angelica lactone to the hydroxyl groups in cellulose in order to get CLEs with appropriate DS and satisfactory materials properties. Their structures and thermal properties had been characterized by various analytic techniques such as NMR, FT-IR, DSC and TGA towards an in-depth understanding of the correlations among of their chemical structure, thermal properties and mechanical properties. The solubility study of CLEs in conventional solvents indicated that CLEs with appropriate DS were soluble in water, which provided a green solvent processing strategy to prepare CLEs films with a tensile strength up to 72 MPa and an elongation at break up to 26.7%. The morphology of the films were characterized by SEM and AFM. The cytotoxicity of the water soluble cellulose levulinate ester was also primary evaluated on Vaginal Epithelial Cells (VK2/E6E7) with a cell-counting kit-8 assay in order to identify its potential in biomedical application.