Paper documents experience severe acidification and embrittlement. Nanocellulose is an excellent reinforcement material for paper documents owing to its compatibility and excellent mechanical strength. However, little research has been conducted on the aging resistance of nanocellulose-reinforced paper. In this study, six types of nanocelluloses were used to reinforce aged paper. The reinforcement and anti-aging performances were evaluated, and the anti-aging mechanism was further clarified. Nanocellulose with a high degree of polymerization can better enhance aged paper, and non-chemical nanocellulose also shows better anti-aging performance, such as nanocellulose prepared by mechanical or biological methods. However, nanocellulose prepared using chemical methods exhibits poor reinforcement and anti-aging performance. This is because it has a small particle size that is not beneficial for physical crosslinking with paper fibers. More importantly, the introduction of acidic or oxidizing groups on nanocellulose accelerates the acid hydrolysis and oxidation rate of paper fibers, especially nanocellulose prepared by 2,2,6,6-tetramethylpiperidine-1-oxyl oxidation, which should not be used to protect paper documents.

Isomerization of glucose derived from lignocellulosic biomass is an important step in biorefinery. Fructose isomerized from glucose, is used as a highly attractive sweetener in the food and beverages industries. However, the prevalence of side reactions at high glucose concentrations is a serious issue, leading to a significant reduction in the fructose yield, especially in the aqueous phase. In this study, an efficient method for the conversion of highly concentrated glucose into fructose under low temperature conditions using triethylamine as the catalyst was developed. It was demonstrated that high fructose yield could be maintained at high glucose concentration. At 60℃, fructose yield of 38.7% and fructose selectivity of 80.6% were achieved in 1 mol/L (approximately 17 wt%) glucose. When glucose concentration was increased to 2 mol/L (approximately 31 wt%), the fructose yield and selectivity were maintained at 34.7% and 77.4%, respectively. ¹³C nuclear magnetic resonance (NMR) spectrometer was used to examine the glucose isomerization reaction. Compared to the NaOH catalytic system, triethylamine acted as a buffer to provide a stable alkaline environment for the catalytic system, further maintaining a high level of catalytic efficiency for the isomerization of glucose to fructose.

Recently, increasing interest has been focused on the hydrolysis of carbohydrates to monosaccharides, among which, glucose and xylose as typical platform sugars can be used to produce chemicals and biofuels. As heterogeneous catalysts, solid acids have gained extensive attention for biomass biorefinery and could replace the conventional process owing to their excellent properties, including acceptable acidity and easy separation. In particular, biochar-based solid acids derived from biomass are promising for biomass conversion owing to the low-cost of feedstocks and the simple preparation procedure. Herein, we attempt to provide a critical overview of biochar-based solid acids for hydrolysis of carbohydrates into glucose and xylose. The preparation methods and properties of biochar-based catalysts as well as the influence of their properties on catalytic performance were discussed in detail. We also highlight the major challenges facing the use of biochar-based solid acids for carbohydrate hydrolysis.