From the aspects of green chemistry and sustainability, the use of green and sustainable materials and reagents for nanocellulose production is highly desirable. In this study, an acidic deep eutectic solvent (DES) pretreatment process was developed to fabricate lignin-containing cellulose nanocrystals (LCNCs) from undervalued thermomechanical pulp (TMP). LCNCs were successfully obtained using both binary DES (choline chloride:oxalic acid, 1:1 molar ratio) and ternary DES (choline chloride:oxalic acid:p-toluenesulfonic acid, 2:1:1 molar ratio) followed by a mild mechanical disintegration process. The LCNCs with a width of around 6 nm, thickness of 3.3 nm, retained cellulose I crystallinity of 57.4%, high lignin content of 47.8%, and high yield of 66% were obtained under the optimum conditions using ternary DES at 80 °C for 3 h pretreatment. Meanwhile, the LCNCs obtained from this process showed a high thermal stability (T max of 358 °C), which exhibited promising potential for further applications. The results demonstrate that the environmentally friendly DES is a promising solvent, which can provide a prospective future for both lignocellulosic material utilization and LCNCs isolation.

Acid based pretreatment efficiency frequently changes with the varying properties of raw lignocellulose feedstock and creates disturbances in industrial biorefining applications. This study revealed that high alkaline ash content in feedstocks neutralized partial acid catalyst and consequently reduced the pretreatment efficiency. The ash content varies in each batch of feedstocks by differences in growing regions, seasons, irrigation, soil, fertilizer use, harvest operation, transportation, storage, and prehandling operations. These differences lead to frequent and significant fluctuations of acid based pretreatment efficiency. The practical solution to the fluctuation should be simple and fast, preferably without performing a time-consuming pretreatment operation assay. Here we proposed a Base pH Approaching method to correct the fluctuating pretreatment efficiency by a simple titration procedure. The method contained only two simple steps in flasks. The first step is the measurement of the inherent base pH value of the thoroughly washed feedstock slurry, and the second step is the adjustment of sulfuric acid usage by titration of the feedstock slurry to the base pH value. The method is universally effective to different feedstocks (corn stover, wheat straw, or rice straw) using different strains (yeasts or bacteria) for different products (ethanol and lactic acid) and different fermentation types (SSF or SSCF).

Softwood mechanical pulps have proven to be quite recalcitrant to enzymatic hydrolysis. However, the unhydrolyzed, residual fibers might have potential as nanofibrillated cellulose feedstocks. In the work reported here, a bleached softwood chemithermomechanical pulp (CTMP) was neutrally sulfonated (S-BCTMP) in an attempt to enhance fiber accessibility and enzymatic hydrolysis. A 12 h hydrolysis at 10% solid loading with CTec3 cellulases provided optimum conditions with 22% of the pulp hydrolyzed to monosaccharides and about one-third of the original substrate remaining as lignin-containing cellulose nanofibrils (LCNFs). Prolonged hydrolysis (72 h) resulted in 42% hydrolysis of the original substrate with only 16% of the original S-BCTMP recovered as LCNFs. Although the LCNFs contained high levels of lignin (26.8%−38.5%), they were successfully used to prepare transparent films showing a high contact angle (82.8°) and strong UV-blocking properties. It was apparent that enzyme-mediated modification of CTMP has the potential to produce both fermentable sugars and higher-value LCNFs.