Wenshuai Chen

Ultralight and highly flexible aerogels with long cellulose I nanofibers

Ultralight and highly flexible aerogels with long cellulose I nanofibers (CNFs) were produced viapurification and defibrillation of wood fibers into CNF hydrogels, followed by freeze-drying. The aerogels had a web-like entangled structure, low density, and high water uptake capability. With the increase of CNF content in hydrogels from 0.1 to 1.5%, the bulk density of the aerogels increased from 1.3 × 10−3 to 17.0 × 10−3 g cm−3, whereas the water uptake ratio (WUR) decreased from 155 to 54. The microstructure of the aerogels can be transformed from open 3D porous nanofibrillar network to 2D sheet-like skeletons by adjusting the CNF content of the hydrogels. A possible assembly mechanism was proposed based on this transformation. When the transparent supernatant fraction, which has ∼0.018% solid content obtained viacentrifugation of the hydrogels, was subjected to freeze-drying, ultra-low density aerogels (0.2 × 10−3 g cm−3) consisting of nanofibers with lengths above 1 mm and a width range of 40–180 nm, were successfully produced due to the self-assembled of the tiny CNFs and their bundles along the longitudinal direction.

Comparative Study of Aerogels Obtained from Differently Prepared Nanocellulose Fibers

This article describes the fabrication of nanocellulose fibers (NCFs) with different morphologies and surface properties from biomass resources as well as their self-aggregation into lightweight aerogels. By carefully modulating the nanofibrillation process, four types of NCFs could be readily fabricated, including long aggregated nanofiber bundles, long individualized nanofibers with surface C6 -carboxylate groups, short aggregated nanofibers, and short individualized nanofibers with surface sulfate groups. Free-standing lightweight aerogels were obtained from the corresponding aqueous NCF suspensions through freeze-drying. The structure of the aerogels could be controlled by manipulating the type of NCFs and the concentration of their suspensions. A possible mechanism for the self-aggregation of NCFs into two- or three-dimensional aerogel nanostructures was further proposed. Owing to web-like structure, high porosity, and high surface reactivity, the NCF aerogels exhibited high mechanical flexibility and ductility, and excellent properties for water uptake, removal of dye pollutants, and the use as thermal insulation materials. The aerogels also displayed sound-adsorption capability at high frequencies.

Concentration effects on the isolation and dynamic rheological behavior of cellulose nanofibers via ultrasonic processing

Chemical pretreatment combined with high-intensity ultrasonication was performed to disintegrate cellulose nanofibers from poplar wood powders. The cellulose content in each suspension was treated as the control variable because the suspension concentration significantly influences the properties of the resultant cellulose nanofibers via ultrasonic processing. The as-obtained cellulose nanofibers were characterized by fiber diameter distribution, crystal structure, and rheological analysis. An increase of not more than 1.2 % of the cellulose content resulted in finer nanofibers. Both storage modulus and loss modulus of cellulose nanofiber suspensions rapidly increased with increasing concentration because of the gradual formation of a stronger network structure. In addition, the dynamic mechanical behavior of suspensions with fiber contents lower than 0.8 % was affected by the frequency and temperature alteration in contrast with the suspension with higher fiber contents. The sol–gel transformation and the visco-elastic transition depend on the hydroxyl bonding and the cross-linking extent of cellulose nanofibers in various concentration environments.

Facile extraction of cellulose nanocrystals from wood using ethanol and peroxide solvothermal pretreatment followed by ultrasonic nanofibrillation

Cellulose nanocrystals (CNCs) were successfully extracted from wood flour by a two-step process that comprised ethanol and peroxide solvothermal pretreatment and an ultrasonic disintegration process. Characterization results showed that 97% of the total lignin and 70% of the hemicellulose could be fractionated in a single ethanosolv pretreatment step. Additional treatment with alkaline hydrogen peroxide removed the residual lignin and hemicellulose and resulted in high purity cellulose. The CNCs obtained after ultrasonication displayed a similar yield, size, morphology, and crystallinity but had better thermal stability and film forming properties than those produced by concentrated acid hydrolysis. Overall, the solvothermal treatment using ethanol and its combination with peroxide is an ideal substitute method for pretreatment of lignocellulose. Further integration of such pretreatments with ultrasonication provides a promising efficient process with low environmental impact for production of CNCs.

Highly Flexible and Conductive Cellulose-Mediated PEDOT:PSS/MWCNT Composite Films for Supercapacitor Electrodes

Recent improvements in flexible electronics have increased the need to develop flexible and lightweight power sources. However, current flexible electrodes are limited by low capacitance, poor mechanical properties, and lack of cycling stability. In this article, we describe an ionic liquid-processed supramolecular assembly of cellulose and 3,4-ethylenedioxythiophene for the formation of a flexible and conductive cellulose/poly(3,4-ethylenedioxythiophene) PEDOT:poly(styrene sulfonate) (PSS) composite matrix. On this base, multiwalled carbon nanotubes (MWCNTs) were incorporated into the matrix to fabricate an MWCNT-reinforced cellulose/PEDOT:PSS film (MCPP), which exhibited favorable flexibility and conductivity. The MCPP-based electrode displayed comprehensively excellent electrochemical properties, such as a low resistance of 0.45 Ω, a high specific capacitance of 485 F g-1 at 1 A g-1, and good cycling stability, with a capacity retention of 95% after 2000 cycles at 2 A g-1. An MCPP-based symmetric solid-state supercapacitor with Ni foam as the current collector and PVA/KOH gel as the electrolyte exhibited a specific capacitance of 380 F g-1 at 0.25 A g-1 and achieved a maximum energy density of 13.2 Wh kg-1 (0.25 A g-1) with a power density of 0.126 kW kg-1 or an energy density of 4.86 Wh kg-1 at 10 A g-1, corresponding to a high power density of 4.99 kW kg-1. Another kind of MCPP-based solid-state supercapacitor without the Ni foam showed excellent flexibility and a high volumetric capacitance of 50.4 F cm-3 at 0.05 A cm-3. Both the electrodes and the supercapacitors were environmentally stable and could be operated under remarkable deformation or high temperature without damage to their structural integrity or a significant decrease in capacitive performance. Overall, this work provides a strategy for the fabrication of flexible and conductive energy-storage films with ionic liquid-processed cellulose as a medium.

Revealing the structures of cellulose nanofiber bundles obtained by mechanical nanofibrillation via TEM observation.

To reveal the structures of cellulose naonfiber bundles extracted from lignocellulosic pulps and prepared by mechanical nanofibrillation methods, the samples were systematically investigated by transmission electron microscopy (TEM) observation. First, high magnification and high resolution TEM images were obtained starting from one end of the bundles. The imaging position was then carefully shifted along the length of the bundles until the other end was reached. Finally, a series of TEM images were integrated through image processing and analyzed. The cellulose nanofiber bundles displayed ribbon-like structures, which were organized with parallel aligned cellulose nanofibers 2-5 nm in width. The length of the bundles was >11 μm. The bundles were interconnected with other nanofibers and nanofiber bundles, forming entangled, web-like networks in suspension. Evidence demonstrating the existence of twisted bundle morphologies was also presented.

Efficient Cleavage of Lignin–Carbohydrate Complexes and Ultrafast Extraction of Lignin Oligomers from Wood Biomass by Microwave-Assisted Treatment with Deep Eutectic Solvent

Abstract Lignocellulosic biomass is an abundant and renewable resource for the production of biobased value‐added fuels, chemicals, and materials, but its effective exploitation by an energy‐efficient and environmentally friendly strategy remains a challenge. Herein, a facile approach for efficiently cleaving lignin–carbohydrate complexes and ultrafast fractionation of components from wood by microwave‐assisted treatment with deep eutectic solvent is reported. The solvent was composed of sustainable choline chloride and oxalic acid dihydrate, and showed a hydrogen‐bond acidity of 1.31. Efficient fractionation of lignocellulose with the solvent was realized by heating at 80 °C under 800 W microwave irradiation for 3 min. The extracted lignin showed a low molecular weight of 913, a low polydispersity of 1.25, and consisted of lignin oligomers with high purity (ca. 96 %), and thus shows potential in downstream production of aromatic chemicals. The other dissolved matter mainly comprised glucose, xylose, and hydroxymethylfurfural. The undissolved material was cellulose with crystal I structure and a crystallinity of approximately 75 %, which can be used for fabricating nanocellulose. Therefore, this work promotes an ultrafast lignin‐first biorefinery approach while simultaneously keeping the undissolved cellulose available for further utilization. This work is expected to contribute to improving the economics of overall biorefining of lignocellulosic biomass.

Nanocellulose: a promising nanomaterial for advanced electrochemical energy storage

Nanocellulose has emerged as a sustainable and promising nanomaterial owing to its unique structures, superb properties, and natural abundance. Here, we present a comprehensive review of the current research activities that center on the development of nanocellulose for advanced electrochemical energy storage. We begin with a brief introduction of the structural features of cellulose nanofibers within the cell walls of cellulose resources. We then focus on a variety of processes that have been explored to fabricate nanocellulose with various structures and surface chemical properties. Next, we highlight a number of energy storage systems that utilize nanocellulose-derived materials, including supercapacitors, lithium-ion batteries, lithium-sulfur batteries, and sodium-ion batteries. In this section, the main focus is on the integration of nanocellulose with other active materials, developing films/aerogel as flexible substrates, and the pyrolyzation of nanocellulose to carbon materials and their functionalization by activation, heteroatom-doping, and hybridization with other active materials. Finally, we present our perspectives on several issues that need further exploration in this active research field in the future.

A process of converting cellulosic fibers to a superhydrophobic fiber product by internal and surface applications of calcium carbonate in combination with bio-wax post-treatment

To convert cellulosic fibers to a superhydrophobic fiber product (i.e., cellulosic paper), the simple concept involving wet-end and surface applications of calcium carbonate in combination with bio-wax post-treatment was proposed and demonstrated.

Multiple hydrogen bond coordination in three-constituent deep eutectic solvents enhances lignin fractionation from biomass

As an emerging generation of green solvents, deep eutectic solvents (DESs) are promising for the pretreatment of lignocellulose and the production of biochemicals. However, not all DESs are effective for the cleavage of lignin–carbohydrate complexes (LCCs) in lignocellulose and the fractionation of lignin. In this study, we analyzed the nature of complex molecular interactions between choline chloride (ChCl) and glycerol in ChCl/glycerol (1 : 2) DES using density functional theory and the Kamlet–Taft solvatochromic method. The ChCl–glycerol DES exhibited weak competing interactions towards the linkages in the LCC network because the intramolecular hydrogen bonds (H-bonds) in ChCl–glycerol were constrained by mutually anionic H-bonds ([Cl(glycerol)]−) and cationic H-bonds ([Ch(glycerol)]+). Furthermore, because of the absence of active protons and acidic sites, the DES was unable to cleave ether bond linkages in the LCCs. Accordingly, we designed a three-constituent DES (3c-DES) by coordinating AlCl3·6H2O in ChCl/glycerol DES based on an acidic multisite coordination theory. The competition of anionic H-bonds and unidentate aluminum ligands was synchronized to form supramolecular complexes, allowing the multisite bridging ligands to cleave both the H-bonds and ether bonds in LCCs. Consequently, the lignin fractionation efficiency was significantly improved from 3.61% to 95.46%, and the lignin purity reached 94 ± 0.45%.