A novel chemical approach for the development of thioesterified cellulose derivatives

Abstract

In this study, thioesterified cellulose was synthesized by grafting thiol moiety onto α-cellulose, which was first oxidized with different reactive oxygen species such as H2O2, Fenton reagent (FR), and peroxyacetic acid in aqueous solution. The thioesterification was done by refluxing oxidized cellulose with ethanedithiol in a mixture of toluene and water (4:1) at 85°C for 6 h. The modification of cellulose was evidenced by FTIR, Raman, solid-state 13C CP MAS NMR spectroscopy, conductometric titration, thermogravimetric analysis, X-ray diffraction, zeta potential measurement, molecular weight determination, and SEM analysis. The characteristic absorption bands for −C=O and −C(=O)−S− bonds in FTIR and Raman spectra were suggestive of the modification of cellulose. 20 % FR was the most efficient in introducing the highest amount (158.93 μmol g−1) of the -COOH groups, while cleavage of cellulose backbone was found to take place as evidenced by the result of the degree of polymerization. The presence of new peaks in 13C CP MAS NMR spectra of thiol-functionalized cellulose ascertained the anchoring of thiol onto oxidized cellulose. Additionally, the significant decrease in the C6 signals for the amorphous region of thiol-modified cellulose provided information about successful modification. In addition, the degree of substitution was determined to be about 0.025. The efficacious functionalization was further supported by the measurement of zeta potential, wherein thioesterified cellulose exhibited the highest negative zeta potential due to increased hydrophobicity. This study would open up a new route for the development of important derivatives of cellulose, including cellulose dimer, containing the thioester group which is the backbone of many antibiotics and natural products.

Keywords

• Cellulose
• Oxidation
• Dithiols
• Thioesterified
• Derivatives
• Characterization