Preparation and characterization of lignin-containing cellulose nanocrystals from peanut shells using a deep eutectic solvent containing lignin-derived phenol

Abstract

In this work, a method of preparing lignin-containing cellulose nanocrystals (LCNC) from agricultural waste peanut shells by ultrasonic-assisted deep eutectic solvents (DES) was studied. The peanut shells were pretreated with binary DES ChCl-GG (choline chloride: guaiacol, 1:1 molar ratio) and ternary DES ChCl-GG-AlCl3·6 H2O (choline chloride: guaiacol: aluminum trichloride hexahydrate, 1:1:0.01, 1:1:0.03, 1:1:0.05, and 1:1:0.07 molar ratios) at 120 ℃ for 3 h, and then subjected to mild mechanical decomposition. Under the optimal DES pretreatment conditions (the molar ratio of ternary DES is 1:1:0.07), the cellulose content of peanut shell reached the highest of 59.49% (36.39% without treatment), and the removal rates of lignin and hemicellulose were 73.22% and 93.05%, respectively. At the same time, LCNC obtained by this process shows good thermal stability (Tmax = 337 ℃) and has the potential for further applications. When the conditions were optimal, the length of LCNC was about 188.94 nm, the width was about 2.60 nm, and the crystallinity of cellulose I was 69.97%. The results showed that the green and economical DES could effectively pretreat lignocellulosic materials, providing a prospect for future utilization and the separation of LCNC.