Deep eutectic solvent system based on choline chloride-urea as a pre-treatment for nanofibrillation of wood cellulose†
Deep eutectic solvents (DESs) are promising novel chemicals that can function as solvents, reagents, and catalysts in many applications because they are readily available, have low toxicity, are biodegradable, and exhibit negligible vapor pressure. In this study, a DES of choline chloride-urea (molar ratio of 1 : 2) was used as a non-hydrolytic pre-treatment media to promote nanofibrillation of birch cellulose pulp using a microfluidizer. The DES pre-treatment was conducted at 100 °C, and then DES was removed by washing with water. Three degrees of mechanical treatment with the microfluidizer for DES pre-treated cellulose pulp were conducted and their effects on the fiber properties were studied. Cellulose fibers were observed to disintegrate into nanofibril bundles with widths ranging from 15 to 200 nm and to individual cellulose nanofibrils with widths of 2–5 nm. Wide-angle X-ray diffraction (WAXD) and degree of polymerization analysis using the limiting viscosity method revealed that both the cellulose crystalline structure and the degree of polymerization of the cellulose remained intact after pre-treatment with DES.