Countries are duly focusing more on biomass resources because of the increasing oil crisis. Owing to their excellent properties, such as natural characteristics, good mechanical performance, and outstanding chemical properties, cellulose-based materials are highly valued as promising bio-derived nanomaterials, especially bacterial cellulose (BC). The main advantage lies in eliminating the problem of removing lignin and hemicellulose from woody cellulose. Moreover, the use of BC reduces the consumption of wood, the excessive use of which aggravates global warming. Herein, we summarize the applications of BC composites in filter, medical, and conductive materials, and other fields. This review contributes to further expand the applications of this renewable polymer.

Pretreatment is important for achieving high-value utilization of biomass. This study is conducted to evaluate the destruction of the Moso bamboo cell wall via hydrothermal pretreatment at different temperatures and pH values. Compositional and morphological analyses and subsequent enzymatic hydrolysis of the solid fractions indicate that the destruction of the cell wall, instead of the degradation or removal of hemicellulose and lignin, or the configuration transition of the cellulose crystal structure, is the most critical aspect for improving bioconversion efficiency. Although only an 8%-10% weight loss is incurred and similar crystalline indexes are achieved after mild hydrothermal treatments, the recovery of glucose is doubled, whereas the recovery of xylose from pretreated samples is approximately 35%.

Recalcitrance of lignocellulosic biomass is closely related to the presence of lignin in secondary cell walls, which has a negative effect on enzyme digestibility, biomass-to-biofuels conversion, and chemical pulping. The lignification process and structural heterogeneity of the cell wall for various parts of moso bamboo were investigated. There were slight differences among three different column parts of moso bamboo in terms of chemical compositions, including cellulose, hemicelluloses, and lignin. However, the detailed analysis of the fractionated lignin indicated that the acid-soluble lignin was first biosynthesized, and the largest molecular weight value was detected from the bottom part of the moso bamboo, as well as the highest syringyl-to-guaiacyl ratio. Although the main β-O-4 aryl ethers and resinol structures were clearly present in all lignin samples examined by NMR analysis, the relatively small lignin biomacromolecule in the top part of the moso bamboo lead to poor thermal stability. For the bioconversion process, no significant difference was found among all the moso bamboo samples, and the relatively higher hydrolysis efficiency was largely dependent on the low crystallinity of cellulose rather than the degree of lignin biosynthesis.

The conversion of lignocellulose to value-added products is normally focused on fuel production; however, large-scale biorefineries require a cost-effective pretreatment process that can effectively fractionate the three main constituents of lignocellulose for the production of chemicals, fuels, and materials. In this study, a hemicellulosic biopolymer from poplar was fractionated by a mild organosolv process and the effects of various chemicals (sodium hydroxide, triethylamine, and formic acid) and alcohols on the fractionation efficiency and structural variation of hemicellulose were examined. Comparative studies indicated that an acidic catalyst decreased the purity of hemicelluloses by partial degradation of cellulose, and the core of the hemicellulosic biomacromolecule could be released and dissolved under alkaline conditions with 5.8%~19.0% yields. In addition, the use of alcohol with longer alkyl chains facilitated the release of the hemicellulosic biomacromolecule by partially cleaving the ether bonds in the lignin-carbohydrate complex (LCC); this is probably due to steric hindrance. The thermal degradation behavior showed that complete pyrolysis was easily achieved for the hemicellulosic polymer with minimal branches irrespective of its molecular weight.

With the continued depletion of non-renewable energy resources, it is essential to seek new methods of harnessing clean and renewable energy. In this regard, second-generation bioethanol derived from lignocellulosic biomass has attracted increasing attention in recent years. The choice of the pretreatment method of lignocellulose is critical to the subsequent bioconversion processes. Compared with other conventional chemical pretreatment methods, hydrothermal pretreatment is a simple, low-cost, and economically feasible process that requires water as the only reagent. This paper reviews the research efforts that have been made toward hydrothermal pretreatment of lignocellulosic biomass and focuses on the transformations involving cellulose, hemicellulose, and lignin during this process.