Upcycling corn straw into nanocelluloses via enzyme-assisted homogenization: Application as building blocks for high-performance films

In this study, corn straw skin (CSS) and core (CSC) are separated and nanofibrillated into cellulose nanofibers (CNF) respectively for the first time via a sequential strategy involving enzymatic pretreatment and high-pressure homogenization. Based on CNF obtained from CSS and CSC, CNF films with excellent mechanical and optical properties are successfully fabricated. The synergy of cellulase and xylanase at relatively low total content is effective on pretreatment of cellulose from CSS and CSC. With increase of enzyme activity from 0 to 18 U/mL, CNF shows much more uniform size distribution, better thixotropy, and higher thermal stability. Under the same pretreatment condition, CNF obtained from CSS shows more uniform size distribution, but lower thermal stability than those of CNF obtained from CSC. The as-prepared CNF films exhibit enhanced mechanical and optical properties with the tensile strength being up to 223 MPa, the light transmittance being more than 85%, and the haze being regulated between 18% and 90%. The CNF films made from CSC displays higher haze, while the ones from CSS show higher tensile strength. This work provides a green and efficient strategy for upcycling corn straw into high value-added CNF that can be used for various applications.