Receiving considerable interest in recent years, the reducing ends of cellulose nanocrystals (CNCs) with heterogeneous groups and different reactivity from surface chemistry contribute to the development of new strategies for regioselective modification and performance tailoring for this building block of natural biomass. However, the understanding of the phenomena involved at the reducing end is still at the research stage for cellulose chains, usually in dissolved form in a solvent, but lacks extensive investigation for nanocrystals, existing in the form of suspensions. Two issues are explored in this study. The first one concerns the comprehensive analysis of various conditions and parameters for the introduction of aldehyde groups at the reducing end of CNCs. The second investigates the influence of end-modified species on the crystalline reconfiguration of nanocrystals during mercerization. Quantitative measurements of the content of reducing end aldehyde groups are carried out for nine nanocellulose samples, offering scientific evidence to obtain more aldehyde groups available at the reducing end of CNCs for future studies. Furthermore, four species of CNCs with various chemical structures and macroscopic properties are modified at the reducing ends, and their reorganization as type-II nanocrystals during mercerization is investigated. The results indicate a critical effect of the steric hindrance of end species on the crystalline reconfiguration of nanocrystals, providing inspiration for a possible molecular structure and asymmetric modification for this ageless nanomaterial.
Cao Liming,Zhu Jiatian,Deng Baojuan,Zeng Fanyan,Wang Shanshan,Ma Yun,Qin Chengrong,Yao Shuangquan
The mercerization of fiber is an important method for the high-value utilization of cellulose. In this study, the bagasse fiber was mercerized by freeze–thaw-assisted alkali treatment (FT/AT). The effects of freezing temperature, freezing time, alkali concentration, and thawing temperature on cellulose and hemicellulose removal were studied. The optimal freezing temperature was −40°C, freezing time was 8.0 h, alkali concentration was 5.0%, and thawing temperature was 30°C. The highest removal rate of hemicellulose was 75.64%. It was 5.80% higher than that of alkali treatment (AT). The alkaline degradation of cellulose was inhibited. The penetration of alkaline solution to fiber was promoted by the assistance of freeze-thaw pretreatment. The effective alkali concentration (5.0%) of cellulose I completely transformed into cellulose II decreased by 66.67% compared with traditional alkaline mercerization (15.0%). The high-efficiency mercerization of fiber was achieved by FT/AT. It provides theoretical support for promoting the high-value utilization of lignocellulosic biomass.
危险品化学品经营许可证（带存储）