Cellulose Levulinate and Its Mixed Esters: One Pot Synthesis and Properties

Due to the depletion of petroleum resources and the development of the emerging bioeconomy, the conversion of biomass into renewable chemicals for the preparation of advanced materials is believed to reduce modern society's dependence on fossil resources. The abundant hydroxyl groups on cellulose make it easy to modify, and it has the advantages of wide source, renewable, biodegradable and excellent bio-co MPatibility. Therefore, the preparation of novel cellulose-based functional materials based on cellulose skeleton has broad application prospects. In 1,8-diazabicyclo[5.4.0]undec-7-ene/dimethyl sulfoxide/CO2 (DBU/DMSO/CO2) solvent system, the transesterification between the hydroxyl groups of cellulose and a- angelicolactone (a- AL) were processed catalyzed by DBU. During this solvent system, the organic base DBU acted as solvent component and catalyst, the cellulose levulinate with high substitution degree (DS) and water solubility could be prepared successfully. In this study, cellulose, a-AL and acid anhydride are used as raw materials to prepare cellulose levulinic acid mixed ester by one-pot method in the same solvent system. The effects of reaction time, temperature and molar ratio of a-AL/anhydride/-OH on monomer conversion rate and DS were studied systematically. The results showed that cellulose levulinic acid mixed ester with DS of 3.0 could be obtained after reaction at 80. for 3 h. The structure and thermal properties of cellulose levulinic acid mixed ester were studied by magnetic resonance spectroscopy (1H-NMR, 13C-NMR), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). And the relationship between structure and properties of cellulose levulinic acid mixed ester was studied in depth. The results showed that the material had good thermal stability and the glass transition temperature decreased with the extension of side chain alkyl. The mechanical properties of cellulose levulinic acid mixed ester films were investigated by stress-strain experiments. And the results showed that the maximum tensile strength of the CLE-A film reached 32.02 MPa, the elongation at break of CLE-B was 65.83% showing strong and tough characteristics.