Cellulose Solvent Research Articles

Neutron Total Scattering Investigation of the Dissolution Mechanism of Trehalose in Alkali/Urea Aqueous Solution.

The atomic picture of cellulose dissolution in alkali/urea aqueous solution is still not clear. To reveal it, we use trehalose as the model molecule and total scattering as the main tool. Three kinds of alkali solution, i.e., LiOH, NaOH and KOH are compared. The most probable all-atom structures of the solution are thus obtained. The hydration shell of trehalose has a layered structure. The smaller alkali ions can penetrate into the glucose rings around oxygen atoms to form the first hydration layer. The larger urea molecules interact with hydroxide groups to form complexations. Then, the electronegative complexation can form the second hydration layer around alkali ions via electrostatic interaction. Therefore, the solubility of alkali aqueous solution for cellulose decreases with the alkali cation radius, i.e., LiOH > NaOH > KOH. Our findings are helpful for designing better green solvents for cellulose.

Cellulose ionic conductor with tunable Seebeck coefficient for low-grade heat harvesting

Natural polymer-based thermoelectric materials are significant for sustainable development because they can be used to directly harvest heat into electricity while avoiding the utilization of petroleum-based resources. Herein, cellulose ionic conductors were fabricated by using cellulose as the hydrogel matrix and cellulose solvents as the electrolytes. p-type and n-type thermoelectric generators (TEG) based on cellulose ionic conductor were obtained, with Seebeck coefficient of 2.61 and −1.33 mV/K, due to the different interactions between quaternary ammonium cations and cellulose. The cellulose TEG-based supercapacitor showed a high specific capacitance and the ability of charging with thermal energy and powering electronic devices with a maximum power density of 0.42 mW/m2. Moreover, a flexible module-type TE harvester with 10 pairs of p-n legs was assembled for body heat harvesting, delivering a thermovoltage of 0.42 V for a temperature gradient of 13 K, enabling waste/biological heat conversion, temperature monitoring and temperature control.

All-Cellulose Composites Properties from Pre- and Post-Consumer Denim Wastes: Comparative Study

This study reports the recycling of discarded denim textiles by the production of all-cellulose composites (ACCs). Discarded denim fabrics were shredded into fibers and then made into nonwoven fabrics by carding and needle punching. The produced nonwoven fabrics were converted to ACCs by one-step and two-step methods using an ionic liquid (IL), 1-butyl-3-methyl imidazolium acetate ([BMIM][Ac]). In this study, the effect of different ACC manufacturing methods, denim fabrics with different contents (a 100% cotton denim (CO) and a blend material (cotton, poly-ester and elastane (BCO)) and reusing of IL as a recycled cellulose solvent on the mechanical pro-perties of the formed ACCs were investigated. The ACCs were characterized according to their tensile and impact properties, as well as their void content. Microscopic analysis was carried out to study the morphology of a cross-section of the formed composites. The choice of the one-step method with recycled IL, pure IL or with a blend material (BCO) had no influence on the tensile properties. Instead, the result showed that the two-step method, with and without DMSO, will influence the E-modulus but not the tensile strength. Regarding the impact properties of the samples, the only factor likely to influence the impact energy was the one-step method with CO and BCO.

Thermo-Reversible Cellulose Micro Phase-Separation in Mixtures of Methyltributylphosphonium Acetate and γ-Valerolactone or DMSO.

We have identified cellulose solvents, comprised of binary mixtures of molecular solvents and ionic liquids that rapidly dissolve cellulose to high concentration and show upper‐critical solution temperature (UCST)‐like thermodynamic behaviour ‐ upon cooling and micro phase‐separation to roughly spherical microparticle particle‐gel mixtures. This is a result of an entropy‐dominant process, controllable by changing temperature, with an overall exothermic regeneration step. However, the initial dissolution of cellulose in this system, from the majority cellulose I allomorph upon increasing temperature, is also exothermic. The mixtures essentially act as ‘thermo‐switchable’ gels. Upon initial dissolution and cooling, micro‐scaled spherical particles are formed, the formation onset and size of which are dependent on the presence of traces of water. Wide‐angle X‐ray scattering (WAXS) and 13C cross‐polarisation magic‐angle spinning (CP‐MAS) NMR spectroscopy have identified that the cellulose micro phase‐separates with no remaining cellulose I allomorph and eventually forms a proportion of the cellulose II allomorph after water washing and drying. The rheological properties of these solutions demonstrate the possibility of a new type of cellulose processing, whereby morphology can be influenced by changing temperature.

Homogeneous microwave-assisted carboxymethylation from totally chlorine free bleached olive tree pruning residues pulp

This study deals with a new methodology for the production of carboxymethyl cellulose (CMC) from olive pruning residues, agricultural by-products. Cellulose was extracted by the soda?anthraquinone pulping process, and the pulp bleaching was performed using totally chlorine free (TCF) bleaching. Then, CMC microwave-assisted synthesis was performed in a homogeneous media, using DMA/LiCl as a cellulose solvent. A Box?Behnken design was applied in order to evaluate which parameters of the carboxymethylation process (viz. reaction time, reaction temperature, and amount of monochloroacetic acid) affect the degree of substitution and the yield of the synthesis reaction of this cellulose derivative. Optimized conditions to yield CMC were determined based on the desirability function approach. The prepared materials under synthesis using the optimal conditions were characterized using several analytical tools, i.e., FTIR, TGA, DSC and SEM. This cellulose derivative was successfully fabricated by a fast and efficient microwave-assisted method and thus would provide many opportunities for diverse applications.

Choline hydroxide based deep eutectic solvent for dissolving cellulose

New cellulose solvent based on choline hydroxide/urea (ChOH/Ur) deep eutectic solvent (DES) was developed.

In situ polymerization and electrical conductivity of polypyrrole/cellulose nanocomposites using Schweizer's reagent.

Cellulose-based composites have attracted interest given the shift towards ‘green’ materials, but achieving uniform dispersions of cellulose in polymer matrices and/or enhancement of interfacial interactions between components remains challenging. Herein we report the preparation of polypyrrole/cellulose nanocomposites in [Cu(NH3)4(H2O)2](OH)2 (Schweizer's reagent/cuoxam)-based reaction media via in situ polymerization. The effect of cellulose template morphology and reaction media on the microstructure, electrical conductivity, and surface wettability was studied. Aqueous reaction media favored the formation of a uniform polypyrrole coating encapsulating the cellulose fibers; concentrated cuoxam solutions promoted inhomogeneity and exhibited a progressive decline in conductivity. The maximum conductivity attained was 3.08 S cm−1 from a bacterial cellulose-templated composite prepared in aqueous reaction media and afforded an approximately threefold increase in conductivity when compared with pure PPy at 1.14 S cm−1. Generally, the composites resembled wetting surfaces – with highly concentrated cuoxam solutions yielding improved hydrophilicity, while substitution of bacterial cellulose with nanocrystalline cellulose engendered a shift towards hydrophobicity. Most composites displayed a contact angle of less than 90° suggesting PPy/cellulose composites tended towards hydrophilic behavior. This study highlights investigations into the viability of cellulose solvents as a facile means to control the structure and performance of in situ functionalized cellulose nanocomposites.

Dissolution behavior of cellulose in a novel cellulose solvent

We have found that cellulose can be dissolved rapidly in the mixed solvent of tetrabutylammonium acetate (TBAA) and a polar aprotic solvents (PAS) at 50 °C and the obtained cellulose solution could be regenerated into cellulose film and fiber. The factors affecting the dissolution behavior of cellulose were investigated and it was found that the solubility and dissolution rate of cellulose in the mixed solvent are significantly dependent on the species of PAS and the molar ratio of PAS/TBAA. The suitable PAS are dimethyl sulfoxide, pyridine, dimethylacetamide, dimethylformamide and N-Methyl-2-pyrrolidone, and dimethyl sulfoxide is the best one in regard to the solubility and dissolution rate of cellulose. The optimal molar ratio of PAS/TBAA was determined by DN of the polar aprotic solvents. The dissolution behaviour of cellulose in the mixed solvent was proposed to involve the solvent diffusion, solvation of TBA+ as well as disruption of the intermolecular or intramolecular hydrogen bonds of cellulose.

Aqueous N,N-dimethylmorpholinium hydroxide as a novel solvent for cellulose

• NDMM-OH(aq) was used for the first time to dissolve cellulose. • MCC 3 wt% could be dissolved in 1-2M NDMM-OH(aq) with maximum dissolution of 7 wt%. • Two different pulps showed clear microscopy images with traces of fiber ballooning. • SEC and NMR showed high stability of cellulose solutions over refrigeratin. • DLS indicated molecular dissolution of majority of cellulose. N,N -dimethylmorpholinium hydroxide was synthesized and its ability to dissolve microcrystalline cellulose and pulp was assessed for the first time. Microscopy and UV–Vis measurements showed that dissolution occurred over a range of 1–2 M concentration of the solvent and a maximum solubility of 7 wt% microcrystalline cellulose could be achieved. The stability of cellulose solutions was evaluated by size exclusion chromatography, which did not detect degradation to any noticeable extent. This observation was further confirmed by 13 C NMR measurements. Finally, DLS studies confirmed that most of the cellulose was molecularly dissolved, with intrinsic viscosity values indicating cellulose chains expansion in this solvent.

Electrospun cellulose fiber-reinforced UV-curable composites with tunable properties

The goal of a carbon-neutral economy urges the search for unconventional eco-friendly methods of manufacturing conventional materials, including functional composites. This study combines the best practices of cellulose dissolution, fiber production through electrospinning, and composite preparation to develop a facile method for preparing lightweight fiber-reinforced composites. The challenge in solution electrospinning is that the solvent must be immediately removed. We demonstrated an electrospinning method using the nonvolatile cellulose solvent ionic liquid 1-butyl-3-methylimidazolium acetate (BMIMAc). Fiber fusion was effectively prevented through the rapid removal of the solvent. The overall process resulted in micro-sized fibers and a porous cellulose matrix, which was further impregnated to prepare polymer composites. The removal of ionic liquid (IL) and the grafting of Si for reducing the hydrophilicity were confirmed by solid-state nuclear magnetic resonance, Fourier-transform infrared, and water contact angle analyses. Finally, strong, tough fiber-reinforced composites were fabricated through impregnation using UV-curable acrylic resin. The composite samples containing 10 wt% of cellulose fibers had a 10% higher Young’s modulus, 50% greater tensile strength, and an almost 100% higher strain at break compared with neat acrylic resin. All in all it was shown that pure cellulose fiber can be readily produced in controlled environment and used for effective reinforcement of polymer matrix.

High-tensile regenerated cellulose films enabled by unexpected enhancement of cellulose dissolution in cryogenic aqueous phosphoric acid

We have demonstrated, for the first time, high-efficient non-destructive and non-derivative dissolution of cellulose could be achieved in cryogenic aqueous phosphoric acid. Cellulose from different sources and of varying degree of polymerization from 200 (MCC) to 2200 (cotton fabric) could be dissolved completely to afford solutions containing 5 wt%–18 wt% cellulose, from which ultra-strong and tough cellulose films of tensile strength as high as 707 MPa could be obtained using water as the coagulant. These solutions can be stored at −18 °C for extended time without noticeable degradation while desired degree of polymerization is also attainable by tuning the storage conditions. The findings of this work call for renewal attention on phosphoric acid as a promising cellulose solvent for being non-toxic, non-volatile, easy to handle, and cost-effective.

Fivefold Helical Cellulose Trapped in a Sulfuric Acid Framework

A sulfuric acid aqueous solution effectively dissolves cellulose at a concentration of 64 wt % when it is precooled at −20 °C. Although this low-temperature acid solution has a high potential as an aqueous cellulose solvent, the molecular detail of its swelling and dissolution mechanism is not known. In this study, we followed the swelling behavior of cellulose in sulfuric acid using X-ray diffraction and found a crystalline complex of cellulose and sulfuric acid at −20 °C. In this structure, the sulfuric acid molecules are organized in a similar manner to those in its tetrahydrate crystal. Cellulose molecules adopt a rare fivefold helical conformation, and their hydroxyl groups participate in the hydration of sulfuric acid. This complexation is acid-concentration dependent and occurs only above 62 wt %, indicating that the deficiency of the number of water molecules around sulfuric acid drives the sulfuric acid to recruit cellulose hydroxyl groups to form a stable tetrahydrate-like hydration state. It swells and opens the cellulose structure without completely destroying the crystalline order, as can be confirmed by the partial reversibility to regenerate cellulose I.

RISM-assisted analysis of role of alkali metal hydroxides in the solvation of cellulose in alkali/urea aqueous solutions

The three-dimensional reference interaction site model theory with the Kovalenko–Hirata closure (3D-RISM–KH) combined with the Kirkwood–Buff integral (KBI) was used to clarify the role of alkali metal hydroxides (MOHs) in cellulose solvation in alkali/urea aqueous solutions. Pair distribution functions, KBI, and the excess number of MOHs showed that M+ hydrates were formed close to cellulose and that their distance was the same as the distance between M+ ions and water molecules in the hydrates. The most stable Li+ hydrate due to the highest Li+ charge density was the closest to the cellulose resulting in the most electrostatic interaction and possibly hydrogen bonding with the cellulose. However, K+ had the lowest charge density, formed the least stable hydrate, and had the least interaction with the cellulose. Hence, the direct solvation energy, which is part of the cellulose solvation energy and accounts for the solute–solvent interaction, was the most negative in the LiOH/urea solution. The solvent reorganization energy—which is another part of the cellulose solvation energy and arises from the clustering of urea, water, and MOH (i.e., ion hydrates) around cellulose—was the most negative in the LiOH/urea solution because of the highest probability and the closest positioning of the Li+ hydrate to the cellulose. Therefore, the calculation results obtained using 3D-RISM–KH and KBI explained the difference among the cellulose solubilities in the LiOH/urea, NaOH/urea, and KOH/urea aqueous solutions.

Fabricating Sustainable All-Cellulose Composites

Climate change, waste disposal challenges, and emissions generated by the manufacture of non-renewable materials are driving forces behind the production of more sustainable composite materials. All-cellulose composites (ACCs) originate from renewable biomass, such as trees and other plants, and are considered fully biodegradable. Dissolving cellulose is a common part of manufacturing ACCs, and currently there is a lot of research focused on effective, but also more environmentally friendly cellulose solvents. There are several beneficial properties of ACC materials that make them competitive: light weight, recyclability, low toxicity, good optical, mechanical, and gas barrier properties, and abundance of renewable plant-based raw material. The most prominent ACC applications are currently found in the food packing, medical, technical and vehicle industries. All-cellulose nanocomposites (ACNCs) expand the current research field and can offer a variety of more specific and functional applications. This review provides an overview of the manufacture of sustainable ACCs from lignocellulose, purified cellulose, and cellulosic textiles. There is an introduction of the cellulose dissolution practices of creating ACCs that are currently researched, the structure of cellulose during complete or partial dissolution is discussed, and a brief overview of factors which influence composite properties is presented.

DMSO/IL solvent systems for cellulose dissolution: Binary or ternary mixtures?

The mechanism of cellulose dissolution in ionic liquid (IL)/dimethyl sulfoxide (DMSO) solvent systems has attracted much attention due to the possible replacement of synthetic materials. However, the solvent behaviour is not completely understood. This work has found an explanation for the solvent behaviour in cellulose dissolution, considering the almost unavoidable presence of the water. Ternary [C4mim]Cl/DMSO/H2O mixtures were studied with Nuclear Magnetic Resonance experiments and molecular dynamics simulations to explore IL/molecular solvents interactions and disclose the water interactions in these complex media. Titration of binary and ternary solvent systems with water and DMSO disclosed a relation between water’s proton chemical shift and the molar fraction of the mixture components, creating an unprecedent theory to predict the cellulose solvation ability. A “working range” for IL/DMSO/H2O ratio was observed, tested in cellulose dissolution, and rationalized using cellobiose interaction. Within this solvent ratio, the interactions between components are maximized, being switched on, while out of the range, the interactions are no longer detected.

Comparison of Cellulose Dissolution Behavior by Alkaline and Sulfuric Acid Solvents and Their Films' Physical Properties.

Three alkaline mixtures (NaOH/thiourea, NaOH/urea/thiourea, NaOH/urea/ZnO) and sulfuric acid were used at low temperatures as cellulose solvents, and their cellulose solubility and films’ physical properties for bleached chemical wood pulps and cotton linter were compared. Their degree of polymerization (DP) was controlled to 600–800 before dissolution. Among the alkaline solvents, NaOH/urea/ZnO gave the film the highest tensile strength and stretch. When compared to sulfuric acid, NaOH/urea/ZnO gave lower strength properties but higher crystallinity indices in the films. While alkaline solvents could not dissolve the high DP cellulose (DP ~ 2000), sulfuric acid could dissolve the high DP cellulose at below zero Celsius temperature, and the strength properties of the films were not much different from that of the low DP one. It appeared that the low-temperature sulfuric acid treatment did away with the cellulose’s DP controlling stage; it decreased cellulose DP very quickly for the high-DP cellulose at the initial stage, and as soon as the cellulose DP reached a DP low enough for dissolution, it began to dissolve the cellulose to result in stable cellulose solution.

Applications of the Hansen solubility parameter for cellulose

Based on the solubility parameter theory, the Hansen solubility parameters of various solvents were calculated and compared to predict the solubility of cellulose in various solvents, which illustrates the feasibility of Hansen solubility parameters to predict the solubility of cellulose in solvents. This paper aims to make a more accurate prediction in advance when finding suitable cellulose solvent system, and then to reduce the burden of cellulose solvent selection.

Dedicate to commemorate of Prof. Lina Zhang

Dedicate to commemorate of Prof. Lina Zhang

A review on the properties and applications of chitosan, cellulose and deep eutectic solvent in green chemistry

The concept of green chemistry has attracted attention due to the green synthesis and ecofriendly nature of the compounds leading to the green and sustainable chemical industries and processes. Chitosan is an ecofriendly material, which is biodegradable, non-toxic, and biocompatible. It has the potential to be modified into biofilms for various applications such as biomedical, packaging, and pharmaceutical fields. Nevertheless, some poor properties of chitosan restrict its wide applications. The incorporation of nanocellulose fillers into chitosan matrix can enhance the mechanical and thermal properties of chitosan. Cellulose nanomaterials can be achieved through chemical and mechanical modifications. The common type of nanocellulose are cellulose nanofibers (CNFs), cellulose nano-whiskers (CNWs), tunicate CNCs (t-CNCs), algae cellulose particles (AC) and bacterial cellulose particles (BC). Nanocellulose are applied as the reinforcement fillers in various polymer matrices such as polysaccharides, proteins, lipids, polylactic acid etc. Deep eutectic solvents (DES) are relatively novel green solvents, which can be applied in various fields. DES are widely applied in metal processing, polymer processing and synthesis. Even though there are not much studies available on DES for synthesis of nanocomposite films; however they are used as eco-friendly solvents in manufacturing processes. This study reviews the discovery, structure, properties of chitosan and cellulose, their derivatives and applications. In addition, the paper also discusses the properties of DES and their applications.

Molecular level insight into the solvation of cellulose in deep eutectic solvents.

Deep eutectic solvents as sustainable and new-generation solvents show potential in the field of cellulose dissolution. Although these novel materials are tested for numerous industrial, environmental, and medical applications, little is known about the structural features of cellulose interacting with deep eutectic solvents. In this work, the interplay of cellulose is studied in two deep eutectic solvents: choline acetate mixed with urea and choline chloride mixed with urea using classical molecular dynamics simulations. Dissolution of cellulose in the studied liquids was not observed to be in agreement with experimental work from the literature. However, a slight swelling in the chloride, as compared to the acetate-based solvent, is apparent. A possible rationale might be found in the stronger hydrogen bonding of the chloride anion compared to the acetate anion with the hydrogen atoms of the cellulose. Moreover, chloride approaches the outer glucose units comparatively more, which could be interpreted as the onset of entering and thus dissolving the cellulose as was previously observed. Specific hydrogen bonds between all units are analyzed and discussed in detail.