Quantification of cellulose nanowhiskers sulfate esterification levels

Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, combustion gas analysis and N2 adsorption were used to quantify the degree of desulfation of cellulose nanowhiskers (CNWs). CNWs were produced by hydrolyzing cotton cellulose with sulfuric acid or hydrochloric acid. Hydrochloric acid treatment did not result in any cellulose chemical modification. Hydrolysis using H2SO4 introduced sulfate groups onto the cellulose surface. Our results indicate that commercial cotton cellulose as received contained sulfur. The sulfur content of H2SO4-prepared CNWs was higher than that exhibited by the original cellulose due to the esterification process. Two desulfation methods, acid-catalyzed and solvolytic desulfation, have been explored to remove the sulfate groups. Neither desulfation method examined removed the sulfate groups from H2SO4-prepared CNWs completely. An estimation of surface sulfate esterification levels was made based on a model of the cellulose structure and available surface area of CNWs. According to these models, more than one third of hydroxyl groups on the surface were substituted by sulfate.