Cellulose最新文献

Numerous studies have investigated the use of cellulose hydrogels produced via the dissolution–regeneration method. However, using different cellulose solvents, a comprehensive comparison of their structures and properties has yet to be reported. In this study, we prepared cellulose hydrogels using six different solvents: LiCl/N,N-dimethylacetamide (DMAc), 1-butyl-3-methylimidazolium chloride, NaOH/urea, ZnCl₂/AlCl₃, LiBr, and Ca(SCN)₂ solutions with the same cellulose concentration and evaluated their structure, transparency, and mechanical properties. Depending on the cellulose solvent used, significant differences in volume shrinkage were observed during regeneration and washing with water. The cellulose hydrogels prepared from LiCl/DMAc and NaOH/urea solutions showed the most significant volume shrinkage during regeneration and washing. Greater volume shrinkage resulted in a higher solid cellulose content in the hydrogel. A positive correlation exists between solid content and both elastic modulus and strength. The cellulose hydrogel prepared from LiCl/DMAc showed excellent mechanical properties: compressive modulus of 332 kPa, tensile modulus of almost 1000 kPa, and ultimate tensile strength of 523 kPa. The cellulose hydrogels prepared from LiBr and Ca(SCN)₂ solutions showed negligible volume shrinkage and lower solid content. However, the elastic modulus and strength of the hydrogels were relatively high despite their solid content due to the three-dimensional network structure composed of nanofibers. Moreover, the transparency was higher for the hydrogels prepared from LiCl/DMAc with amorphous cellulose and a uniform internal structure. These findings could assist in customizing the material properties of cellulose hydrogels.

Separating emulsified oil/water mixture is full of challenges. Special permeable wetted surfaces can separate emulsions but usually require modification by fluorine or silicon based chemicals, which can cause second pollution after use. Carbon aerogels are porous hydrophobic materials, which provide a promising approach to selectively adsorb oil from oil water mixture. However, during the course of the fabrication of carbon cryogels, freeze drying is essential, which is time-consuming and energy-intensive process. In this article, we introduced wet papermaking technology manufacturing base paper to replace freeze drying, followed by carbonization in N₂ at 800 ºC, hydrophobic carbon paper with a porosity of 90.22% was obtained when the content of micro glass fiber was 70%. The resulting carbon paper not only separates oil slick but also separates water-in-oil emulsion with an efficiency of 98.5% and flux of 1200 L/m²·h.

Comprehending how raw materials, pretreatments, and treatments affect the properties of cellulose nanofibrils (CNFs) is crucial for their use. This study aims to understand the effect that alkaline treatment has on the characteristics of pulps, the mechanical processes of CNF production, and the characteristics of CNFs from Pinus radiata and Eucalyptus nitens pulps with native and oxidized lignin. For this purpose, Pinus radiata and Eucalyptus nitens pulps with different lignin contents produced by oxidative pretreatment were used as raw material. From these, pulps with different hemicellulose and lignin contents were produced by alkaline treatment. Furthermore, CNFs were prepared by refining and homogenization processes. The chemical composition analysis of pulps containing native lignin, before and after alkaline treatment, revealed distinct behaviors of hemicellulose. In Pinus radiata pulp, hemicellulose remained insoluble under alkaline conditions. In contrast, the hemicellulose from Eucalyptus nitens pulp was partially soluble. Morphological characteristics of CNFs revealed that removing 41.8% of total hemicellulose by alkaline treatment promoted the mechanical fibrillation of Eucalyptus nitens pulp with native lignin, decreasing the average width by 30%. Furthermore, a very low lignin content in this species (~ 1.3%) hindered the mechanical fibrillation of fibers. Finally, the dielectric spectra of CNFs showed that the alkaline treatment increased the activation energies of the relaxations associated with the molecular motions of the hemicellulose and lignin groups, evidencing changes in their structures. These changes were related to the deacetylation of hemicellulose, and the deprotonation of hydroxy groups and the formation of carboxyl groups in lignin.

The 3D printing technique for the fabrication of composite components appears to be an emerging and revolutionary method in the manufacturing sector. The present work is dedicated to analyse the effect of varying weight percentages of crystalline nanocellulose (i.e., 0, 1, 3, and 5) on the morphology, crystallinity, and mechanical and dynamical mechanical properties of 3D-printed PLA-based bionanocomposites. The crystalline behaviour and mechanical and dynamical mechanical properties of the bionanocomposites were seen to be significantly improved by the incorporation of cellulose nanocrystals (CNCs). The highest tensile strength and modulus were achieved at 1 wt% CNC reinforcement showing increases of 22.3% and 64.17%, respectively over neat PLA. Similarly, the maximum flexural strength and modulus were also observed at 1 wt% CNC reinforcement. The impact strength of the bionanocomposites was consistently increased with CNC reinforcement and its maximum value (16.92 kJ/m²) was seen for bionanocomposite with 5 wt% CNC reinforcement, which was 53.95% higher than that of neat PLA. A statistical analysis was also performed to analyse significant differences in the mechanical properties among the 3D printed bionanocomposites. DMA analysis revealed significant changes in storage and loss modulus and their highest values were observed at 5 wt% of CNC reinforcement, which was more than the neat PLA by 34.50% and 53.95%, respectively. However, the glass transition temperature of the bionanocomposites remained largely unaffected by the addition of CNCs.

Coating a paperboard is the most important finishing process to achieve a good barrier against oxygen, water vapor and grease, which are typically obtained with fossil-based plastics. In this study, three different cellulose-based coating components—methyl nanocellulose (MeNC), microfibrillated cellulose (MFC) and hydrophobically modified ethyl(hydroxyethyl) cellulose (HM-EHEC)—were investigated. One to five coating layers were applied to the paperboard using spray and rod coating. Combinations of different coating components, coat weights, and barrier properties at different temperatures and relative humidities were studied. Scanning electron microscopy, air permeance and contact angle measurements using water and oil were used to characterize the uncoated and coated surfaces. It was shown that the MeNC and MFC layers increased the surface wettability. On contrary, HM-EHEC coating provided surface hydrophobicity, but reduced oil repellence. According to oxygen barrier measurements, HM-EHEC seemed to provide resistance at high humidities. In addition, a coating with a low weight could not close the surface completely and resulted in a poor grease barrier. However, high-weight coatings with MFC and HM-EHEC layers were greaseproof, even at elevated temperature and humidities.

Plants have been essential to human technological development since the beginning of time. Today, due to their structural diversity and adaptability, they continue to hold a great potential for addressing modern energy and material challenges. Plant glycans, as central components of the plant cell wall, play a crucial role in defining many of the wall’s unique mechanical and chemical characteristics. A deep understanding of the structure and chemical properties of these biopolymers can help optimize the use of plant resources. Here, we discuss fundamental aspects of the primary structure, conformation, and reactivity of plant glycans, focusing on the ubiquitous β-1,4-linked plant glycans (cellulose, xylans, glucomannans, xyloglucans) and the glycosyl residues that constitute their backbones: glucosyl, xylosyl, and mannosyl residues. In the discussion, the higher rate of acidic hydrolysis in aqueous solution observed for xylans in comparison to cellulose is attributed to the lower electron deficiency and greater conformational freedom of xylosyl rings, with both factors resulting from the absence of the hydroxymethyl (CH₂OH) group in these rings. In furanosides, the higher rate of acidic hydrolysis when compared to their pyranosyl counterparts is explained by the greater similarity between the conformations of furanosides in the ground state and those in the oxocarbenium ion-like transition state upon glycosidic bond cleavage. These phenomena, alongside other factors such as steric interactions, offer an effective explanation for the rates of acidic hydrolysis in solution observed for plant glycans.

Natural cellulose fibers have a unique hierarchical structure, starting from nanofibers, to microfiber bundles, and consequent to large scale fibers. This work wants to utilize this characteristic to tailor the surface morphology of plant-based fabrics in situ, avoiding complex separate washing process, and explore their functional applications. Specifically, ramie fabric was moderately oxidated using the 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)/NaClO₂/NaClO system. The scanning electron microscopy results show that a large number of cellulose micro-nanofibers can protrude from the fiber surface on the TEMPO-mediated oxidized ramie fabric (TORF) by controlling the reagent additions, which enlarges the specific surface area of the fabric. Subsequently, the crystal structure, chemical structure, carboxylate content and mechanical properties of the fabrics with different degrees of oxidation were determined in detail. In addition, the TORF was successfully modified by carbon nanotubes (CNTs) through simple physical adsorption. The electrical conductivity of the CNT-modified TORF increases with the oxidation degree of the fabric. Moreover, it shows application potential in fields such as electric heating. Based on the natural hierarchical structure, this work provides new ideas for the surface structure tailoring of natural plant fabrics and fibers, and also provides a platform for fabric functionalization.

Graphical abstract

Cellulose scaffolds have been widely used for biomedical applications. The character and functionalities of these porous materials are mainly dependent on their porous structure and chemical composition. The possibility of customizing the porous structure of scaffolds, which arises from the manufacturing process used, allows the use of these materials as support to mimic cellular matrix native building blocks and, combined with the introduction of functional groups, it can facilitate the adhesion and cultivation of different types of cells. Obtaining a balance between structural mechanical properties, porous architecture, and chemical composition in scaffolds for cell placement is a key challenge for the development of an optimum porous scaffold. In this sense, this review manuscript presents an approach to the main methods of production and drying techniques of cellulose and nanocellulose scaffolds, as well as possible chemical functionalizations for application in biomaterials, mainly as 3D cell culture. Moreover, a revision of the state of the art for cellulose and nanocellulose-based porous materials (aerogels and foams) for cell culture in recent years has been included in the manuscript.

Balancing the adsorption rate and efficiency is crucial for the removal of hazardous chemicals such as Cr(VI) in water, especially when the adsorbent could be easily separated from system. To address this challenge, polyethyleneimine (PEI) modified cellulose nanofiber (CNF) microgels (PCM) were prepared using an emulsion template method, where glutaraldehyde (GA) served as the crosslinking agent between the amino group in PEI and hydroxyl group in CNFs. The resulting PCM materials exhibited an ellipsoidal shape with an average size of approximately 500 μm, which allowed these adsorbents to be easily separated by Nylon filter mesh. Furthermore, the optimal sample PCM3 reached adsorption equilibrium within 20–240 min, which was shorter than most cellulose based aerogels or bead adsorbents. This sample also demonstrated a high adsorption capacity for Cr(VI) (410.0 mg g⁻¹), higher than the macroscopic PEI/CNF aerogel (16.9 mg g⁻¹). After five recycling cycles, the removal quantity remained at 122.9 mg g⁻¹, indicating good reusability. The adsorption of Cr(VI) in aqueous solution was primarily driven by electrostatic interactions, due to the protonation of amino group, and some Cr(VI) ions were reduced into Cr(III) by amino group during the adsorption process. This study provides a novel strategy for developing CNF-based microgels that can efficiently and rapidly adsorb Cr(VI).

Transparent flexible heaters attract great attention due to their potential applications in smart windows, wearable electronics, hand warmers, etc. Here, we present a highly flexible cellulose/zinc oxide/indium tin oxide (CZI) film heater, which was prepared by spinning coating of zinc oxide (ZnO) solution on cellulose film followed by magnetron sputtering of indium tin oxide (ITO). The CZI film exhibits a high visible light transmittance (80.3%), low resistance (7.3 Ω·sq⁻¹), and good thermostability. As connected to the circuit, the CZI film showed an excellent Joule heating performance even after multiple repeated bending tests. The temperature of the CZI film could increase from room temperature to 89 ℃ within 2 min under the working voltage of 6 V. Prompted by these versatile properties, and we demoed the application scenarios of this CZI film heater in thermochromism, deicing, and defogging to enlighten for the application of this film material in sensors or smart windows.