Regeneration Of Cellulose Research Articles

Phase-separation of cellulose from ionic liquid upon cooling: preparation of microsized particles

Cellulose is an historical polymer, for which its processing possibilities have been limited by the absence of a melting point and insolubility in all non-derivatizing molecular solvents. More recently, ionic liquids (ILs) have been used for cellulose dissolution and regeneration, for example, in the development of textile fiber spinning processes. In some cases, organic electrolyte solutions (OESs), that are binary mixtures of an ionic liquid and a polar aprotic co-solvent, can show even better technical dissolution capacities for cellulose than the pure ILs. Herein we use OESs consisting of two tetraalkylphosphonium acetate ILs and dimethyl sulfoxide or γ-valerolactone, as co-solvents. Cellulose can be first dissolved in these OESs at 120 °C and then regenerated, upon cooling, leading to micro and macro phase-separation. This phenomenon much resembles the upper-critical solution temperature (UCST) type thermodynamic transition. This observed UCST-like behavior of these systems allows for the controlled regeneration of cellulose into colloidal dispersions of spherical microscale particles (spherulites), with highly ordered shape and size. While this phenomenon has been reported for other IL and NMMO-based systems, the mechanisms and phase-behavior have not been well defined. The particles are obtained below the phase-separation temperature as a result of controlled multi-molecular association. The regeneration process is a consequence of multi-parameter interdependence, where the polymer characteristics, OES composition, temperature, cooling rate and time all play their roles. The influence of the experimental conditions, cellulose concentration and the effect of time on regeneration of cellulose in the form of preferential gel or particles is discussed.Graphical abstractRegular micro-sized particles regenerated from a cellulose-OES mixture of tetrabutylphosphonium acetate:DMSO (70:30 w/w) upon cooling

Facile preparation of cellulose hydrogel with Achilles tendon-like super strength through aligning hierarchical fibrous structure

The extreme mechanical strength of fibrous connective tissues in the human body, such as ligaments and tendons, has always been challenging for hydrogel scientists. Here, we created extremely strong, purely cellulose-based hydrogels (DCC-E gels). The fracture stress and Young’s modulus of the gels were improved to the level of an Achilles tendon even at their equilibrium swollen state. To make DCC-E gels, regenerated cellulose gels were first prepared with ethanol as the anti-solvent. DCC-E gels were then prepared by applying Drying in Confined Condition method, where regenerated cellulose gels were prestretched and dried while their length was fixed. Although strength improvement of materials is typically only achieved at the expense of toughness, a significant increase in strength was achieved while maintaining high levels of toughness. The high strength and toughness of the DCC-E gels were realized by optimizing the cellulose fibril arrangement from nanoscale to macroscale, which was done by selection of an appropriate solvent used for cellulose regeneration. Parallel aggregated fibrous structures observed in the DCC-E gels are thought to play a central role in the enhancement of both toughness and strength. This study can assist in expanding the application of biopolymer-based hydrogels in tissue engineering and soft electronics.

A Fast Dissolution Pretreatment to Produce Strong Regenerated Cellulose Nanofibers via Mechanical Disintegration.

This study investigates a fast dissolution and regeneration pretreatment to produce regenerated cellulose nanofibers (RCNFs) via mechanical disintegration. Two cellulose pulps, namely, birch and dissolving pulps, with degree of polymerizations of 1800 and 3600, respectively, were rapidly dissolved in dimethyl sulfoxide (DMSO) by using tetraethylammonium hydroxide (TEAOH) as aqueous electrolyte at room temperature. When TEAOH (35 wt % in water) was added to the pulp–DMSO dispersion (pulp:DMSO and TEAOH:DMSO weight ratios of 1:90 and 1:9, respectively), 95% of the dissolving pulp and 85% of the birch pulp fibers dissolved almost immediately. Addition of water caused the regeneration of cellulose without any chemical modification and only a minor decrease of DP, whereas the crystallinity structure of cellulose transformed from cellulose I to cellulose II. The regenerated cellulose could then be mechanically disintegrated into nanosized fibers with only a few passes through a microfluidizer, and RCNF showed fibrous structure. The specific tensile strength of the film produced from both RCNFs exceeded 100 kN·m/kg, and overall mechanical properties of RCNF produced from birch pulp were in line with reference CNF produced by using extensive mechanical disintegration. Although the thermal stability of RCNFs was slightly lower compared to their corresponding original cellulose pulp, the onset temperature of degradation of RCNFs was over 270 °C.

A one‐pot biosynthesis of an aerogel composite based on attapulgite clay/bacterial cellulose to remove Pb 2+ ion

A one‐pot biosynthesis of an aerogel composite based on attapulgite clay/bacterial cellulose to remove Pb ²⁺ ion

A novel adsorbent of bentonite modified chitosan-microcrystalline cellulose aerogel prepared by bidirectional regeneration strategy for Pb(II) removal

Traditional chitosan aerogel (CSA) could be used to chelate heavy metal ions due to its large specific surface area, high porosity and rich amino groups. However, the CSA was rarely applied in practical application because of its easy hydrolysis, low mechanical strength and slow adsorption rate. In this study, we developed a novel method for increasing the anti-hydrolytic ability and mechanical strength of CSA by bidirectional regeneration of chitosan and microcrystalline cellulose to synthesize chitosan-microcrystalline cellulose aerogel (CS-MCCA). In addition, bentonite (BT) was introduced in the regeneration process to enhance the adsorption rate of CSA, and an efficient adsorbent of bentonite-chitosan-microcrystalline cellulose aerogel (BT-CS-MCCA) for Pb(II) removal was developed, and the maximum adsorption amount and adsorption equilibrium time of Pb(II) on BT-CS-MCCA were 256.24 mg g−1 and 60 min, respectively. Additionally, it was found that with the increase of Na+ or K+ concentration in the solution from 0 mol L−1 to 0.1 mol L−1, the adsorption capacity of BT-CS-MCCA was enhanced, because the Ca2+ in BT was substituted by Na+ or K+, and then the ion-exchange ability of BT-CS-MCCA was improved. Moreover, the preparation method of BT-CS-MCCA possessed merits of simple operation, low cost and hypotoxicity. Thus, the BT-CS-MCCA had a broad potential application for the purification of Pb(II) in wastewater, and the bidirectional regeneration strategy might offer a brand-new path for the utilization of biomass resources.

Regeneration and carboxymethylation of cellulose and its derivatives: application assessment for brewery wastewater treatment

Coagulation–flocculation technique is usually employed in wastewater treatment by applying conventional inorganic materials such as alum and ferric chloride. Due cost to environmental challenges associated with the use of inorganic flocculants, biopolymers are gaining ground as alternative water treatment materials. In the present study, native cellulose and hemicelluloses isolated from sugarcane bagasse were used in the removal of turbidity and biological oxygen demand from industrial wastewater. Isolated native cellulose was modified to form regenerated cellulose (RC). Also, native cellulose, hemicellulose and RC were carboxymethylated using Na-chloroacetate. Thereafter, the functional groups on the carboxymethylated biopolymers were examined using Fourier transform infrared spectroscopy and the carbon–hydrogen–nitrogen–sulfur–oxygen elemental analysis. The degree of substitution (DS) for regenerated and carboxymethylated cellulosic materials was measured using recommended standard methods. Carboxymethyl cellulose (CMC) with 1.3 DS reduced turbidity and biological oxygen demand by 62.2 and 64%, respectively. Carboxymethyl regenerated cellulose (CMC-II) at 1.1 DS reduced turbidity and by 55.6 and 60%, respectively. Carboxymethyl hemicellulose (CMH) with 1.4 DS was capable of reducing turbidity and biological oxygen demand by 45.7 and 47%, respectively. Carboxymethyl cellulose and hemicellulose have rarely been used in the treatment of brewery wastewater. In the present study, these two novel materials showed a good prospect in removing biological oxygen demand and turbidity.

IONIC LIQUID-MEDIATED SYNTHESIS OF CELLULOSE/MONTMORILLONITE NANOCOMPOSITE

Cellulose regeneration is a facile approach to produce biopolymer/clay composites with improved physical properties. In this study, a cellulose/montmorillonite nanocomposite was prepared using a novel ionic liquid, 1-butyl-3-ethylimidazolium bromide ([BEIm]Br). Montmorillonite clay was modified using cetyltrimethylammonium bromide (CTAB) and was characterized using X-ray diffraction (XRD) analysis, which revealed the substitution of cetyltrimethylammonium (CTA+) cations in the clay gallery. The exfoliation-adsorption method was used to prepare the cellulose/montmorillonite nanocomposites, and scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD) analyses confirmed the successful dispersion of cellulose into the clay matrix. Thermogravimetric analysis (TGA) further revealed the optimum thermal stability of the nanocomposite was achieved with 4 wt% montmorillonite, which provided a white cellulose/montmorillonite nanocomposite.

Education for Sustainable Development: An Undergraduate Chemistry Project on Cellulose Dissolution, Regeneration, and Chemical Recycling of Polycotton

We introduced an undergraduate chemistry project within the framework of education for sustainable development (ESD). The objective of the first part was to demonstrate the efficiency of an ionic liquid (IL)- 1-(n-butyl)-3-methylimidazolium acetate (BuMeImAcO)- as solvent for the dissolution, and subsequent regeneration of cellulose as fiber. Under mechanical stirring, the students dissolved microcrystalline cellulose in a mixture of BuMeImAcO-dimethyl sulfoxide (DMSO) at 80°C. Subsequently, they dyed the dissolved cellulose with a reactive dye, and regenerated (pink) colored fibers by injecting the resulting biopolymer solution into water (a non-solvent for cellulose). The objective of the second experiment was to show the potential application of BuMeImAcO-DMSO for the chemical recycling of the cellulosic component of polycotton (cellulose: polyethylene terephthalate; PET). Cellulose dissolves under the above-mentioned experimental conditions, leaving a mat of PET. The students dyed the dissolved cellulose, and then regenerated the biopolymer as fiber. This project fits the following aspects of ESD: fiber production from renewable sources other than cotton (wood-based cellulose); recycling of cellulose from its blends with synthetic polymers, when their reuse is not feasible. We recommend this project for senior science students of, e.g., chemistry, engineering and pharmacy, because of its simplicity, safety and socioeconomic relevance.

Effect of regeneration solvent on the characteristics of regenerated cellulose from lithium bromide trihydrate molten salt

Dissolution and regeneration of cellulose is of vital importance for its end use. In the present work, the effect of different regeneration solvents (i.e. water, ethanol, and N, N-dimethylacetamide (DMAc)) on the characteristics of the regenerated cellulose from lithium bromide trihydrate (LBTH) molten salt was comprehensively investigated. It was found that the regenerated celluloses displayed obvious changes in macro- and micro-morphologies compared with the original microcrystalline cellulose (MCC). Furthermore, after the dissolution and regeneration process, the crystalline structure of cellulose was changed from cellulose I to cellulose II or amorphous structure, and the crystallinity of cellulose clearly decreased due to the deconstruction and rearrangement of cellulose chains. Moreover, the regenerated cellulose with ethanol had a relatively higher degree of crystallinity (70.2%) than that with water (42.3%) and DMAc (33.2%). Both X-ray Diffraction (XRD) and Attenuated Total Reflection Flourier transformed Infrared Spectroscopy (ATR-FTIR) analysis results indicated that ethanol as a regeneration solvent could be more beneficial to rearrange cellulose molecular chains and rebuild a more ordered structure compared to water and DMAc. In addition, thermogravimetric analysis showed that regenerated cellulose from LBTH exhibited a lower decomposition onset temperature and a higher char yield (over 17.8%) compared with the raw MCC (2.8%). The obtained results verified that regeneration solvents could substantially affect the reconstitution of cellulose molecule chains during regeneration as well as the multiscale structures and properties of the regenerated cellulose.

Cellulose dissolution and regeneration using a non-aqueous, non-stoichiometric protic ionic liquid system

The solubility of cellulose has been studied as a function of composition in the binary mixture of 1,1,3,3-tetramethylguanidine and propionic acid. In amine-rich compositions, greater quantities of cellulose can be dissolved than in the equimolar composition, a.k.a. the protic ionic liquid [TMGH][OPr]. By applying a methodology of a short period of heating followed by cooling, similar concentrations of cellulose can be achieved in a much shorter time period. Finally, regeneration of cellulose from solution can be achieved by altering the acid:amine molar ratio. In comparison to cellulose regenerated from these solutions using water as an antisolvent, cellulose regenerated with propionic acid exhibit a lower crystallinity as inferred from x-ray diffractometry, but a greater average molecular weight as inferred from gel permeation chromatography.

3D printing of lightweight, super-strong yet flexible all-cellulose structure

Lightweight yet strong cellular structural materials have long been sought for varied engineering applications due to the outstanding performance, and have been existing in numerous nature’s designs such as wood, bone, and honeycomb. Cellulose is considered an ideal building block for such structure due to its natural abundance, low density, and high mechanical properties derived from the hydrogen bonded crystalline structure. However, restructuring pristine cellulose into 3D architectures with outstanding mechanical properties has always been a challenge. Here, a lightweight (∼90 mg/cm3) and super-strong (16.6 MPa compressive Young’s modulus) honeycomb structure is constructed by 3D printing of all-cellulose ink. The 3D printed all-cellulose structure demonstrates switchable high elasticity (to withstand varied repetitive elastic deformation) at the wet state and high rigidity (to support over 15,800 of its own weight) at dry state. Such superb printing and mechanical properties can be ascribed to the controlled dissolution and regeneration of cellulose, as well as shear induced cellulose alignment during printing. In addition, the 3D printed all-cellulose honeycomb structure demonstrates good thermal insulation properties after filling with cellulose nanofibrils aerogel.

Natural Celluloses as Catalysts in Dehydrogenation of NaBH4 in Methanol for H2 Production.

Cellulose, the most abundant renewable biopolymer, exists in many forms, such as microgranular cellulose (MGCell), sigmacell cellulose (SCell), cellulose fibers (FCell), and α-cellulose (AlfaCell). Several of these cellulose forms were protonated with an amine-containing agent polyethyleneimine (PEI), and the modified celluloses (XCell-PEI+) were studied as catalysts in methanolysis of NaBH4 for hydrogen (H2) generation. It was found that the SCell-PEI+-catalyzed reaction is the fastest one among the modified celluloses with a hydrogen generation rate of 5520 ± 119 mL H2/(g of catalyst × min). The activation energies of MGCell-PEI+, SCell-PEI+, FCell-PEI+, and AlfaCell-PEI+ were determined as +21.7, +23.4, +24.8, and + 21.8 kJ/mol, respectively. Reusability of catalysts was investigated, and regeneration of cellulose based catalysts after the fifth cycle could be readily achieved by HCl treatment to completely recover its activity. Therefore, PEI-modified-protonated cellulose forms constitute sustainable, re-generable, and renewable catalysts for production of H2, an environmentally benign green energy carrier.

In-situ fabrication of dynamic and recyclable TiO2 coated bacterial cellulose membranes as an efficient hybrid absorbent for tellurium extraction

Tellurium, a rare element with special properties, has practical industrial application value, but the extensive utilization of tellurium has caused irreparable damage to the ecological environment and human health. Meanwhile, the toxicity of Te(IV) is higher than that of Te(VI), thus it is crucial to develop an environmentally friendly material for removing Te(IV). In this work, bacterial cellulose membrane (BCM) was prepared by dissolution and regeneration of bacterial cellulose (BC), and then a novel TiO2 coated BCM (TiO2@BCM) was prepared by in-situ growth of TiO2 on the surface of BCM by hydrothermal method, which can be used for tellurium adsorption from tellurium-containing contaminants with maximum adsorption capacity of 103.64 mg/g. Importantly, BC is a sustainable, degradable and renewable material that is widely used worldwide. It also can be used as a novel support for TiO2 with the advantages of enhanced adsorption recycling. Besides, kinetics and thermodynamics studies show that tellurium was adsorbed onto TiO2@BCM by chemical interactions through the monolayer. Furthermore, the possible adsorption mechanism is also proposed, which was achieved by ion exchange between -OH on the surface of TiO2@BCM and TeO32− in aqueous solution. Additionally, TiO2@BCM has excellent regenerability and still achieve 50% removal efficiency after the ninth cycle. Therefore, these unique advantages of TiO2@BCM make it as a potential candidate for practical application in tellurium separation. Adsorption process of tellurium by TiO2@BCM with good cycle and high adsorption capacity.

Tuning the properties of regenerated cellulose: Effects of polarity and water solubility of the coagulation medium

In this study, the effect of different alcohols and esters as a coagulation medium in the regeneration of cellulose dissolved in an aqueous LiOH-urea-based solvent was thoroughly investigated using various methods such as solid state NMR, X-ray diffraction, water contact angle, oxygen gas permeability, mechanical testing, and scanning electron microscopy. It was observed that several material properties of the regenerated cellulose films follow trends that correlate to the degree of cellulose II crystallinity, which is determined to be set by the miscibility of the coagulant medium (nonsolvent) and the aqueous alkali cellulose solvent rather than the nonsolvents’ polarity. This article provides an insight, thus creating a possibility to carefully tune and control the cellulose material properties when tailor-made for different applications. [Display omitted] [Display omitted]

Effect of antisolvents on the structure of regenerated cellulose: development of an efficient regeneration process

Abstract In this study, the effect of antisolvents on the structure of regenerated microcrystalline cellulose (MCC) obtained from the extraction of 1-butyl-3-methylimidazolium chloride (BmimCl) was investigated; further, the usage of the aqueous N,N-dimethylmethanamide (DMF) solution was proposed as an effective antisolvent for cellulose regeneration. The results denoted that regeneration after dissolution resulted in a looser cellulose texture with a high specific surface area, low degree of polymerization (DP), low crystallinity index (CrI), and decreased thermostability, which are favorable for its downstream processing. Among the studied antisolvents, the DMF solution was superior in cellulose regeneration from BmimCl, as demonstrated by the kinetics of enzymatic hydrolysis. The improved ability of the DMF solution with respect to cellulose regeneration can be attributed to the effective dispersion of H-bonds and the inductive hydrophobic orientation of cellulose chains; correspondingly, a looser H-bond network was observed in the regenerated cellulose. The DMF solution as an antisolvent offers an effective cellulose regeneration method and an optimal structure for subsequent processing and applications.

Cellulose in Ionic Liquids and Alkaline Solutions: Advances in the Mechanisms of Biopolymer Dissolution and Regeneration.

This review is focused on assessment of solvents for cellulose dissolution and the mechanism of regeneration of the dissolved biopolymer. The solvents of interest are imidazole-based ionic liquids, quaternary ammonium electrolytes, salts of super-bases, and their binary mixtures with molecular solvents. We briefly discuss the mechanism of cellulose dissolution and address the strategies for assessing solvent efficiency, as inferred from its physico-chemical properties. In addition to the favorable effect of lower cellulose solution rheology, microscopic solvent/solution properties, including empirical polarity, Lewis acidity, Lewis basicity, and dipolarity/polarizability are determinants of cellulose dissolution. We discuss how these microscopic properties are calculated from the UV-Vis spectra of solvatochromic probes, and their use to explain the observed solvent efficiency order. We dwell briefly on use of other techniques, in particular NMR and theoretical calculations for the same purpose. Once dissolved, cellulose is either regenerated in different physical shapes, or derivatized under homogeneous conditions. We discuss the mechanism of, and the steps involved in cellulose regeneration, via formation of mini-sheets, association into “mini-crystals”, and convergence into larger crystalline and amorphous regions. We discuss the use of different techniques, including FTIR, X-ray diffraction, and theoretical calculations to probe the forces involved in cellulose regeneration.

Fabrication and characterization of porous cellulose beads with high strength and specific surface area via preliminary chemical cross-linking reaction for protein separation

Porous cellulose beads are widely used in the adsorption field, in which enhancing the structure stability and enlarging the specific surface area are the ways to improve the adsorption efficiency. Here, a preliminary chemical cross-linking (PCC) strategy is explored to construct the tough and highly porous cellulose beads as high efficient adsorbent. Especially, the customized cellulose solution is preliminarily mixed with a cross-linking agent for emulsification and followed by cellulose regeneration. The entrapped cross-linking agent creates the inner covalent linkages between the neighboring long cellulose chains, which accounts for strong mechanical strength of cellulose framework. Meanwhile, the entrapped covalent bonds disrupt the normal growth of cellulose crystalline and lead to more amorphousness, which conduces to high specific surface area. Finally, the proposed cellulose beads, after being modified by DEAE, were evaluated for protein adsorption. As a result, the obtained porous cellulose beads exhibits high adsorption capacities (BSA: 204.58 mg g−1; BHb: 144.78 mg g−1) and excellent structure stability. Taken together these properties, the porous cellulose beads developed here enjoy great potential for separation application.

Fabrication and Mechanistic Study of Aerogels Directly from Whole Biomass

Lignocellulosic aerogels were prepared directly from whole biomass Douglas fir wood without prior removal of hemicellulose and lignin using lithium bromide (LiBr) molten salt hydrate (lithium bromide trihydrate, LBTH) as a cellulose solvent via a procedure of cellulose dissolution, gelation, and regeneration. The fabricated aerogels had a homogeneous and continuous porous structure, extremely high porosity, large surface area, and very low density. The lignin-excluding aerogel had a density as low as 4.6 mg/cm3 and a porosity larger than 99%, while the lignin-including whole biomass aerogel retained almost all lignin and more than 90% of the starting biomass and had 24.9 mg/cm3 density and 98.3% porosity. A mechanistic study revealed that different from that in other cellulose solvent systems, cellulose gelation and regeneration occurred in two independent steps in the LBTH system. The weak cross-linking through a coordination effect between a cellulose hydroxyl group and Li+ cation when cooling the cellulose solution in the LBTH led to gelation, while cellulose regeneration via precipitation/aggregation due to the exchange of solvent LBTH with nonsolvent water during washing resulted in the formation of a 3D fibrous network of cellulose skeleton.

A New Approach to Development of Photochromic Composites Based on Hydrated Tungsten(VI) Oxide Particles and Cellulose Matrix

Abstract—The synthesis strategy for the photochromic material containing the ultrafine dispersions of orthotungstic acid embedded in a hydrated cellulose matrix was proposed. The composite was obtained from solution of cellulose in Schweizer’s reagent with addition of a tungstate containing agent (sodium tungstate dehydrate) by acid regeneration of cellulose and hydrated tungstic(VI). The structure and phase composition were determined for substances obtained in the course of synthesis. In addition, the photochromic properties were investigated by the screen printing technique of the coating: spectral dependences of the reflection factor for the chromatic and bleached states, kinetics of the photochromic transformations, and the dependence of the coloration efficiency on the length of the radiation mode.

Impact of non‐solvent on regeneration of cellulose dissolved in 1‐(carboxymethyl)pyridinium chloride ionic liquid

AbstractCellulose dissolved in ionic liquid (1‐(carboxymethyl)pyridinium chloride)/water (60/40 w/w) mixture is regenerated in various non‐solvents, namely water, ethanol, methanol and acetone, to gain more insight into the contribution of non‐solvent medium to the morphology of regenerated cellulose. To this end, the initial and regenerated celluloses were characterized with respect to crystallinity, thermal stability, chemical structure and surface morphology using wide‐angle X‐ray diffraction, thermogravimetric analysis, Fourier transform infrared spectroscopy and scanning electron microscopy. According to the results, regardless of non‐solvent type, all regenerated samples have the same chemical structure and lower crystallinity in comparison to the initial cellulose, making them a promising candidate for efficient biofuel production based on enzymatic hydrolysis of cellulose. The reduction in crystallinity of regenerated samples is explained based on the potential of the non‐solvent to break the hydrogen bonds between cellulose chains and ionic liquid molecules as well as the affinity of water and non‐solvent which can be evaluated based on Hansen solubility parameter. The latter also determines the phase‐separation mechanism during the regeneration process, which in turn affects surface morphology of the regenerated cellulose. The pivotal effect of regenerated cellulose crystallinity on its thermal stability is also demonstrated. Regenerated cellulose with lower crystallinity is more susceptible to molecular rearrangement during heating and hence exhibits enhanced thermal stability. © 2019 Society of Chemical Industry