Production of cellulose nanofibers using phenolic enhanced surface oxidation

Dissolution behavior of ionic liquids for different ratios of lignin and cellulose in the preparation of nanocellulose/lignin blends

Lignin is regarded as a potential solution for boosting the strength of cellulose-based products. However, the mechanism of co-solubilization for lignin and cellulose has not been investigated. In this study, the effect of lignin content on the interaction between lignin and nanocellulose during lignin/cellulose co-dissolution was examined. The results revealed that lignin binds to nanocellulose throughout the dissolution process to limit the degradation of cellulose and to prepare nanocellulose/lignin composites. Moreover, the S units in lignin were more likely to interact with cellulose during the dissolution process, whereas the G units were more likely to condense. However, when the lignin content exceeded 30 wt%, the excess lignin created a severe condensation reaction, which led to a decrease in the lignin content bound to cellulose, resulting in an unequal dissolution of cellulose. Thus, a small amount of lignin attached to cellulose during the co-dissolution of lignin and cellulose inhibits cellulose degradation and can be utilized to create nanocellulose/lignin to extend the potential applications of nanocellulosic materials.

Nanocellulose-based composite aerogels toward the environmental protection: Preparation, modification and applications

Nanocellulose aerogel has the advantages of porosity, low density and high specific surface area, which can effectively realize the adsorption and treatment of wastewater waste gas. The methods of preparing nanocellulose mainly include mechanical, chemical and biological methods. Nanocellulose is formed into nanocellulose aerogel after gelation, solvent replacement and drying processes. Based on the advantages of easy modification of nanocellulose aerogels, nanocellulose aerogels can be functionalized with conductive fillers, reinforcing fillers and other materials to give nanocellulose aerogels in electrical, mechanical and other properties. Through functionalization, the properties of nanocellulose composite aerogel such as hydrophobicity and adsorption are improved, and the aerogel is endowed with the ability of electrical conductivity and electromagnetic shielding. Through functionalization, the applicability and general applicability of nanocellulose composite aerogel in the field of environmental protection are improved. In this paper, the preparation and functional modification methods of nanocellulose aerogels are reviewed, and the application prospects of nanocellulose composite aerogels in common environmental protection fields such as dye adsorption, heavy metal ion adsorption, gas adsorption, electromagnetic shielding, and oil-water separation are specifically reviewed, and new solutions are proposed.

Recent Advances in Cellulose Nanofibers Preparation through Energy-Efficient Approaches: A Review

Cellulose nanofibers (CNFs) and their applications have recently gained significant attention due to the attractive and unique combination of their properties including excellent mechanical properties, surface chemistry, biocompatibility, and most importantly, their abundance from sustainable and renewable resources. Although there are some commercial production plants, mostly in developed countries, the optimum CNF production is still restricted due to the expensive initial investment, high mechanical energy demand, and high relevant production cost. This paper discusses the development of the current trend and most applied methods to introduce energy-efficient approaches for the preparation of CNFs. The production of cost-effective CNFs represents a critical step for introducing bio-based materials to industrial markets and provides a platform for the development of novel high value applications. The key factor remains within the process and feedstock optimization of the production conditions to achieve high yields and quality with consistent production aimed at cost effective CNFs from different feedstock.

Iso- and Anisotropic Etching of Micro Nanofibrillated Cellulose Films by Sequential Oxygen and Nitrogen Gas Plasma Exposure for Tunable Wettability on Crystalline and Amorphous Regions

The surface of cellulose films, obtained from micro nanofibrillated cellulose produced with different enzymatic pretreatment digestion times of refined pulp, was exposed to gas plasma, resulting in a range of surface chemical and morphological changes affecting the mechanical and surface interactional properties. The action of separate and dual exposure to oxygen and nitrogen cold dielectric barrier discharge plasma was studied with respect to the generation of roughness (confocal laser and atomic force microscopy), nanostructural and chemical changes on the cellulose film surface, and their combined effect on wettability. Elemental analysis showed that with longer enzymatic pretreatment time the wetting response was sensitive to the chemical and morphological changes induced by both plasma gases, but distinctly oxygen plasma was seen to induce much greater morphological change while nitrogen plasma contributed more to chemical modification of the film surface. In this novel study, it is shown that exposure to oxygen plasma, subsequently followed by exposure to nitrogen plasma, leads first to an increase in wetting, and second to more hydrophobic behaviour, thus improving, for example, suitability for printing using polar functional inks or providing film barrier properties, respectively.

Engineered nanocellulose-based hydrogels for smart drug delivery applications

Nanocellulose is a promising "green" nanomaterial that has recently gained scientific interest because of its excellent characteristics, such as less risks of toxicity, biocompatibility, biodegradability, recyclability, and tunable surface features. Initially, three nanocellulose types (i.e., bacterial nanocellulose, nanocrystals, and nanofibers) and their potential biotechnological production routes have been discussed in detail. Contemporary studies are discussed in the development of nanocellulose aerogels, responsive hydrogels, injectable hydrogels/implants, and magnetic nanocellulose. Moreover, the development of hydrogels and potential crosslinking agents for the induction of desired properties has been described. Studies have revealed that the release kinetics of nanocellulosic gels/hydrogels varies from few minutes to several days depending on the given physicochemical conditions. However, such systems provide sustained drug release properties, so they are considered "smart" systems. Recent studies on controlled drug delivery systems have demonstrated their considerable potential for the next-generation transport of therapeutic drugs to target sites via various administration routes. This review presents the selection of appropriate sources and processing methodologies for the development of target nanocellulose types. It explains the potential challenges and opportunities and recommends future research directions about the smart delivery of therapeutic drugs.

Green synthesis of aluminum-hydrochar for the selective isomerization of glucose to fructose

Hydrochar microspheres supported Al catalysts with hierarchically porous structure (Al/HPHMs) for glucose to fructose isomerization were fabricated. Superior catalytic selectivity (93.3%) and fructose yield (32.6%) were achieved in aqueous under 160 °C for 20 min. Hierarchically porous structure was formed after KHCO₃ and K₂CO₃ activation and the roles of KHCO₃ and K₂CO₃ in controlling the Al phase and tailoring morphology of hydrochar supported Al were evaluated. The major active sites were characterized as Al hydroxides including β-Al(OH)₃, γ-Al(OH)₃, γ-AlO(OH), Al-C-O linkages. Active sites by KHCO₃ activation with high contents of Al-C-O and Al(OH)₃ have better selectivity. Oxygen-containing functional groups including aluminum‑oxygen groups on the hydrochar microspheres have contributed to the formation of hydrogen bond and π-π interactions between glucose and Al species. Green process synthesized aluminum-hydrochars have potential for their application as a variety of stable, recyclable, and efficient catalysts for lignocellulosic biorefining.

Ozone Oxidation of Kraft Bamboo Pulp for Preparation of Nanofibrillated Cellulose

The influence of ozonation on the homogenization of Kraft bamboo pulp (KBP) for the production of nanofibrillated cellulose (NFC) was studied. Using optimized conditions for ozonation, that is, pulp consistency 35%, ozone dosage 0.87% (v/w), and pH=2.5, the kappa number and viscosity of KBP decreased from 10.8 to 2.8 and from 1024 mL∙g−1 to 258 mL∙g−1, respectively, while the crystallinity and carboxylate content increased from 36.2% to 48% and 0.93 mmol/g to 1.26 mmol/g, respectively. The ozonation-treated KPB was used as the substrate for NFC preparation through homogenization. With a width of 10–20 nm and length≥250 nm, the prepared NFC had a high aspect ratio of length versus width. Ozonation can be used as an alternative approach to promote the efficient production of NFC from KBP.

Recent Strategies in Preparation of Cellulose Nanocrystals and Cellulose Nanofibrils Derived from Raw Cellulose Materials

The recent strategies in preparation of cellulose nanocrystals (CNCs) and cellulose nanofibrils (CNFs) were described. CNCs and CNFs are two types of nanocelluloses (NCs), and they possess various superior properties, such as large specific surface area, high tensile strength and stiffness, low density, and low thermal expansion coefficient. Due to various applications in biomedical engineering, food, sensor, packaging, and so on, there are many studies conducted on CNCs and CNFs. In this review, various methods of preparation of CNCs and CNFs are summarized, including mechanical, chemical, and biological methods. The methods of pretreatment of cellulose are described in view of the benefits to fibrillation.