Regenerated Cellulose Films Obtained via Ball Milling with Dry Ice

Owing to the limited solubility of cellulose in conventional solvents, the development of efficient solvent systems to dissolve cellulose is necessary for its subsequent processing into value-added cellulose-based materials. In recent years, a green, low-cost, and sustainable CO2-based reversible solvent system (CO2/DMSO/DBU) has been developed. In this system, dimethyl sulfoxide (DMSO) facilitates the swelling of cellulose, and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) provides a strong alkaline environment, enabling the derivatization of cellulose with CO2 to form cellulose carbonate, which is soluble in the solvent. Nevertheless, these systems have drawbacks, including high temperature (>50 °C) and inadequate mechanical properties of the regenerated cellulose films. In this study, ball milling was used to lower the dissolution temperature of cellulose and further improve the mechanical properties of regenerated cellulose films. To do this, dry ice as a source of CO2 and DMSO/DBU as mixed solvents, together with cellulose, were ball-milled at room temperature. A series of regenerated cellulose films were prepared at different dry ice contents and ball milling times. The results demonstrate that the cellulose can be readily dissolved within 0.5 h at room temperature, resulting in a stable cellulose solution (4.48 wt%), thanks to the mechanochemistry provided by ball milling. The prepared regenerated cellulose films exhibit satisfactory mechanical properties with a tensile strength of up to 77.3 MPa and a tensile strain of 8.6%, which are among the highest values reported for regenerated cellulose films. This work illustrates a simple, mild, and efficient method for green cellulose processing.