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Dissolving pulps are used to manufacture various cellulose derived products through cellulose dissolution. Solubility of cellulose pulp has been claimed to be strongly dependent on the porosity development, the degree of polymerisation and the pulp viscosity. The removal of external cell walls has been proposed to have a key role in the pulp solubility. In this paper, the effect of the outermost surface layers on the solubility of a dissolving grade pulp was studied. Furthermore the effect of mechanical peeling and combined mechanical and enzymatic treatment on pulp solubility was compared. Based on the results combined mechanical and enzymatic treatment efficiently opens up the fibre structure and has a clear positive effect on the solubility of dissolving pulp. It seems that long fibre fraction is less accessible to solvent chemicals than the other pulp fractions. Mechanical peeling of outer fibre layers does not improve fibre dissolution to NaOH/ZnO. Thus, it seems that peeling alone is not a sufficient pre-treatment prior to dissolution. The results also revealed that the peeling treatment does not enhance the effects of enzymes as the studied mechanical treatment does. [ABSTRACT FROM AUTHOR]

Dissolving grade pulps are used as raw material for manufacture of regenerated cellulose fibres and their use is constantly growing. Despite intensive research, there is still a need to develop cellulose dissolution-regeneration processes that would be economically viable, fulfil the pre-conditions of sustainability and would be able to meet the strict product quality requirements. The basis for creation of such a process is in deep understanding of the biomass structure and factors affecting the cellulose modification and dissolution. In this paper, the effects of the mechanical and enzymatic pre-treatments on the pore structure and alkaline solubility of dissolving grade pulp are discussed. Formation of micro- and macropores in the pulp fibres during mechanical shredding was found to correlate with the susceptibility of the fibres to enzymatic hydrolysis. The fibre porosity development during the processing was studied by a modified solute exclusion approach, which revealed differences between the effect of mild enzyme or acid hydrolysis on the pore structure of fibres. The dissolution of the modified fibres in NaOH/ZnO was evaluated and found to correlate with overall pore volume and accessible surface area analysed by the modified solute exclusion method. [ABSTRACT FROM AUTHOR]

Cotton fibre dissolution has been investigated using ionic liquids having a functionalized imidazolium cation. Two ionic liquids, 3-butyric acid-1-methyl imidazolium chloride [HOOC4MIM][Cl] (IL-acid) and 3-N,N-diethyl-butyramide-1-methyl imidazolium chloride [(Et)2NOC4MIM][Cl] (IL-amide), were synthesized by passing both through the intermediate 1-(3-Ethoxycarbonyl-propyl)-1-methyl imidazolium bromide. Their chemical structures were then confirmed using NMR and FTIR. 5 wt% cotton fibers have been completely dissolved in both synthesized ionic liquids in 3 h at room temperature. The regenerated cellulose with water, as an anti-solvent, was characterized using XRD, FTIR, TGA, and degree of polymerization (DP) methods. The FTIR and XRD results showed that no other chemical reaction occurred by both synthesized ILs other than the breakage of hydrogen bonds during the dissolution and regeneration processes. In addition, the regenerated cellulose had a reduced crystallinity and a structural transition from cellulose I to cellulose II. TGA results confirmed the low crystallinity of regenerated cellulose by demonstrating its low thermal stability compared to cotton fibers. Furthermore, the DP of cotton fibers was reduced from 805 ± 15 to 737 ± 12 and 765 ± 10 after regeneration from IL-acid and IL-amide, respectively, confirming partial cellulose network degradation. The IL-acid has an oily appearance and a viscosity (44 ± 5 mPa.s at 25 °C), allowing it to dissolve 14.5 wt% cotton fibers at 25 °C, IL-amide can only dissolve 5 wt% in 5 h at 25 °C due to its viscous nature. These results imply that the produced ionic liquids can be considered as competitive solvents for dissolving cellulose. [ABSTRACT FROM AUTHOR]

Cellulose is a readily available, renewable, and natural biomaterial that has the potential to replace synthetic fibres. However, their processing to shaped materials such as fibre or film is still complex and restricted due to its insolubility in most conventional solvents. Herein, we present the synthesis and cellulose dissolution characteristics of a new class of recyclable zwitterions composed of tethered N-oxyethylene substituted imidazolium cation and alkyl carboxylate anion. Investigations on cellulose dissolution showed that increasing the alkyl chain length of carboxylate anion and introduction of oxyethylene unit on imidazolium ring led to better cellulose dissolution ability, and up to 12% (w/w) cellulose could be dissolved in aqueous zwitterions at 105 °C. The thermal behavior of zwitterions and their cellulose solutions was characterized by TGA and found to be more stable than the NMMO and Lyocell solutions. Rheological characterization of cellulose solutions revealed viscoelastic behavior and zero shear viscosity of 6–12% (w/w) cellulose solution in hexanoate containing aqueous zwitterion was 555 to 5900 Pa.s at 120 °C. The characteristics of cellulose solution indicate its potential for processing to cellulose fibre by extrusion through a tiny spinneret. Physico-chemical analysis of regenerated cellulose indicates that zwitterions cause no adverse effect on cellulose structure and morphology during dissolution. The zwitterions are recovered after the cellulose regeneration process, and the recovery was found to be 99.6% after purification using the ion-exchange method. [ABSTRACT FROM AUTHOR]

The dissolution of cellulose is a critical step for the efficient utilization of this renewable resource as a starting material for high value-added chemical and biofuel production. In this study, three aprotic solvents were chosen to couple with three ionic liquids (ILs) as binary solvent systems for cellulose dissolution. The percentage of dissolved cellulose of each IL/co-solvent was evaluated and the crystallinity index (CrI) of the undissolved cellulose residues after dissolution were investigated by XRD. Dimethyl sulfoxide exhibited the most effective synergistic interaction with the ILs among three co-solvents for cellulose dissolution. In general, the higher percentage of dissolved cellulose of the IL/co-solvent binary system, the lower CrI value of the undissolved cellulose residue after dissolution. In addition, the dissolution of cellulosic materials with different crystallinity and degree of polymerization indicated that the crystallinity of a cellulosic material played a more dominating role than degree of polymerization in its dissolution process. The hydrogen bond basicity (β value) of selected IL/co-solvent binary system was also calculated. The results showed that the β value of a binary IL/co-solvent system exhibited different trend than neat IL in terms of the cellulose dissolution ability, which should be attributed to the co-solvent effect. [ABSTRACT FROM AUTHOR]

Lyocell fibers have received increased attention during the recent years. This is due to their high potential to satisfy the rising market demand for cellulose-based textiles in a sustainable way. Typically, this technology adopts a dry-jet wet spinning process, which offers regenerated cellulose fibers of excellent mechanical properties. Compared to the widely exploited viscose process, the lyocell technology fosters an eco-friendly process employing green direct solvents that can be fully recovered with low environmental impact. N-methylmorpholine N-oxide (NMMO) is a widely known direct solvent that has proven its success in commercializing the lyocell process. Its regenerated cellulose fibers exhibit higher tenacities and chain orientation compared to viscose fibers. Recently, protic superbase-based ionic liquids (ILs) have also been found to be suitable solvents for lyocell-type fiber spinning. Similar to NMMO, fibers of high mechanical properties can be spun from the cellulose-IL solutions at lower spinning temperatures. In this article, we study the different aspects of producing regenerated cellulose fibers using NMMO and relevant superbase-based ILs. The selected ILs are 1,5-diazabicyclo[4.3.0]non-5-ene-1-ium acetate ([DBNH]OAc), 7-methyl-1,5,7-triazabicyclo[4.4.0] dec-5-enium acetate ([mTBDH]OAc) and 1,8-diazabicyclo[5.4.0]undec-7-enium acetate ([DBUH]OAc). All ILs were used to dissolve a 13 wt% (PHK) cellulose pulp. The study covers the fiber spinning process, including the rheological characterization of the various cellulose solutions. Moreover, we discuss the properties of the produced fibers such as mechanical performance, macromolecular properties and morphology. [ABSTRACT FROM AUTHOR]

It is essential for textile manufacturing industries to invent new resources, composites and industrial technologies, which are environmentally acceptable and can fulfill the consumer necessities. Therefore, in the recent years, large number of research is focused on optimizing and modifying the fibre manufacturing processes. The recent advances in technology have allowed modifying these processes through various techniques and novel raw materials/additives to manufacture the fibres. Among the various fibre regeneration processes, the NMMO based lyocell process has numerous advantages over conventional rayon fibres and it has great potential to fulfil the environmental and customer requirements. The present review delivers a complete account of all the six types of cellulose regeneration processes namely viscose, cellulose acetate, cuprammonium, LiCl/DMAc as well as lyocell processes based on ionic liquid or NMMO. Additionally, the review considers latest developments with process technology, cellulose swelling and dissolution phenomena, factors affecting the lyocell process and future prospects of the lyocell fibres. [ABSTRACT FROM AUTHOR]

Abstract: The transesterification reaction between cellulose and vinyl esters is regarded as a clean and facile strategy for the tunable synthesis of cellulose esters. In this study, a series of cellulose esters with degrees of substitution from 0.58 to 3.0 have been prepared successfully under mild conditions without adding any external catalysts when cellulose was dissolved in the 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU)/DMSO/CO2 solvent system and then followed by adding equimolar amounts of long chain fatty, aromatic, branched and steric vinyl esters. The optimization study of different reaction parameters like reaction time, temperature and amounts of substrates demonstrates that the reaction can proceed smoothly even at room temperature. This is evidenced by a cellulose benzoate with a DS of 2.6 obtained when the reaction is performed at 25 °C in 4 h. The as-prepared cellulose esters structure has been confirmed by 1H NMR, 13C NMR and FTIR, and material thermal properties were evaluated by DSC and TGA for an in-depth understanding the relationship between the cellulose esters structure and properties. It is believed that the DBU not only acts as a reagent for the CO2-derivative dissolution of cellulose in DMSO, but also acts as an in situ organocatalyst for the subsequent transesterification reaction.Graphical abstract: Cellulose esters have been prepared successfully at low temperature using long chain fatty acids, aromatic, branched and steric vinyl esters as acyl donors in the DMSO/DBU/CO2 solvents system, and the DBU not only acts as reagents for the CO2-derivative dissolution of cellulose in DMSO, acts as an organocatalyst for the subsequent derivatisation. [ABSTRACT FROM AUTHOR]

High cellulose solubility is an essential to successful production of regenerated cellulose, from which hydrogels can be produced. Additionally, some pretreatment usually facilitates cellulose solubility. Bleached cellulose pulp from kenaf core (BK), consisting of lignin (0.3%), hemicellulose (5.2%) and ash (0%), was treated with an electron beam irradiation (EBI) at 10, 30, 50 and 70 kGy. The BK and irradiated bleached cellulose pulp (IK) were then dissolved in either sodium hydroxide/urea or lithium hydroxide/urea solvents which subsequently crosslinked with epichlorohydrin (ECH) solution to stabilize the formation of regenerated cellulose hydrogels. The amount of α-cellulose component in IK samples decreased as much as 38% and caused the viscosity average molecular weight (Mv) and degree of polymerization of IK samples to be reduced significantly by 84 and 87%, respectively. This resulted in an increase in cellulose solubility (up to 30%) for the IK samples in both solvent systems. However, this treatment resulted in a reduction in the overall cellulose fibre strength. X-ray diffraction of the hydrogels showed a transformation from cellulose I to amorphous cellulose. These hydrogels exhibited a higher degree of swelling, transparency and porosity compared to hydrogels prepared from non-irradiated pulp. [ABSTRACT FROM AUTHOR]

Cellulose is the most abundant natural polymer on the earth, and effective solvents are essential for its wide application. Among various solvents such as alkali/urea or ionic liquids, cations all play a very important role on the cellulose dissolution. In this work, the influence of cation on the cellulose dissolution in alkali/urea via a cooling process was investigated with a combination of MD simulation and experiments, including differential scanning calorimetry (DSC) and NMR diffusometry (PFG-SE NMR). The results of DSC proved that the dissolution of cellulose in both solvents was a process within a temperature range, starting at above 0 °C and completing at low temperature (−5 °C for LiOH/urea and −20 °C for NaOH/urea), indicating the necessity of low temperature for the cellulose dissolution. Molecular dynamic (MD) simulation suggested that the electrostatic force between OH and cellulose dominated the inter-molecular interactions. In our findings, Li could penetrate closer to cellulose, and displayed stronger electrostatic interaction with the biomacromolecule than Na, thus possessed a greater 'stabilizing' effect on the OH/cellulose interaction. PFG-SE NMR demonstrated a more significant binding fraction of Li than Na to cellulose, which was consistent with MD. These results indicated that the direct interactions existed between the cations and cellulose, and Li exhibited stronger interaction with cellulose, leading to stronger dissolving power. [ABSTRACT FROM AUTHOR]

We have found that the dissolution of cellulose in the binary mixed solvent tetrabutylammonium acetate/dimethyl sulfoxide follows a previously overlooked near-stoichiometric relationship such that one dissolved acetate ion is able to dissolve an amount of cellulose corresponding to about one glucose residue. The structure and dynamics of the resulting cellulose solutions were investigated using small-angle X-ray scattering (SAXS) and nuclear magnetic resonance techniques as well as molecular dynamics simulation. This yielded a detailed picture of the dissolution mechanism in which acetate ions form hydrogen bonds to cellulose and causes a diffuse solvation sheath of bulky tetrabutylammonium counterions to form. In turn, this leads to a steric repulsion that helps to keep the cellulose chains apart. Structural similarities to previously investigated cellulose solutions in aqueous tetrabutylammonium hydroxide were revealed by SAXS measurement. To what extent this corresponds to similarities in dissolution mechanism is discussed. [ABSTRACT FROM AUTHOR]

The amphiphilicity of solvent systems is realized for adjusting the dissolution of natural cellulose by making use of tetra-butylammonium hydroxide (TBAH) as an example. TBAH aqueous solution is found to have an obvious effect on adjusting its amphiphilicity, along with a flexible concentration ranging from 40 to 60 wt% for dissolving cellulose. With a suitable amphiphilic property, cellulose can be dissolved by a TBAH aqueous system . The experimental results demonstrate that with the introduction of urea (more than 0.2:1, w:v) into a TBAH aqueous system, the dissolution process of cellulose can be dramatically promoted, leading to a transparent solution of cellulose. Herein, a complex solvent of TBAH/urea has been proposed for mild and effective dissolution of cellulose under ambient conditions. In the TBAH/urea complex solvent, the structure of the hybrid hydrate of TBAH and urea formed. Urea served as a hydrophobic contributor adjusting the amphiphilicity of the solvent system, allowing interfacial resistance between the amphiphilic crystal surfaces of the natural cellulose and solvent to be reduced. After that, the crystal of natural cellulose could be fully infiltrated and subsequently dissolved by the TBAH/urea aqueous solvent. The performances of the aqueous solvent and ambient temperature dissolution make aqueous TBAH/urea a potential and green solvent of cellulose for broad applications, such as composites, films or wet spinning of cellulose, in laboratories or industries. [ABSTRACT FROM AUTHOR]

Chitosan is a widely used biopolymer with very attractive properties. However, to compensate for the deficiencies in the application of this bio-macromolecule, many studies have been performed on the preparation of chitosan blends with various polymers, such as cellulose, which is abundant and unique with a tough bio-structure. Because of the different dissolution conditions of chitosan and cellulose, an acceptable industrial and environmentally friendly process to prepare a monotonous cellulose-chitosan composite film has not been achieved yet. Therefore, as an alternative approach, nanochitosan (Nano-CS) particles were synthesized and blended with a cellulose matrix, which was dissolved using ionic liquid. Atomic force microscope and field emission scanning electron microscope (FESEM) images demonstrated that the most frequent size of Nano-CS particles was in the 10-60 nm range. FESEM nano-graphs evidenced monotonous distribution of Nano-CS particles through the produced nano-biocomposite films. X-ray diffractograms indicated that following the dissolution process of cellulose a less ordered cellulose matrix or one with less crystallite sizes was formed. Meanwhile, following the addition of certain amounts of Nano-CS, the mechanical properties were improved. Also, optical analysis exhibited proper transparency of the biocomposite films (≈80 %) in the range of visible wavelengths (400-700 nm). [ABSTRACT FROM AUTHOR]

As a result of the constantly growing demand for textile fibres interest in utilising cellulose pulps for manufacturing regenerated cellulose fibres is growing. One promising water-based process for the manufacture of regenerated cellulosic products is the Biocelsol process based on an NaOH/ZnO solvent system. The drawback of the Biocelsol process is the need for pre-treatment of the pulp, i.e. long mechanical pre-treatment (up to 5 h) followed by a 2-3-h enzymatic hydrolysis utilising a rather high amount of cellulolytic enzymes. In this work more efficient conditions to carry out the pre-treatment of cellulose pulp prior to dissolution into NaOH/ZnO are presented. Based on the results, cellulase treatment, when carried out in an extruder, can be used to effectively open up and fibrillate the fibres without completely destroying the fibre structure. The molar mass of the pulp treated enzymatically in an extruder was 14 % lower as compared to the state-of-the-art-treated cellulose. As a consequence, the alkaline solutions prepared from the pulp treated enzymatically in an extruder had clearly lower dope viscosities regarding the cellulose content than the solutions prepared from the state-of-the-art-treated pulp. This enabled increasing the cellulose content in the dope up to 7 % (w/w) without increasing the dope viscosity. [ABSTRACT FROM AUTHOR]

Subcritical and supercritical water are known to dissolve crystalline cellulose, offering a simple way to produce low molar mass cellulose which precipitates at ambient temperatures. However, the yield of precipitate is limited by concomitant degradation reactions. In this study, the formation of cellulose precipitate from six different microcrystalline celluloses (MCC) was investigated in 0.2 s treatments at 250-380 °C. The results were elucidated with a simple two-step kinetic model. The maximum yield of cellulose precipitate depended on the choice of starting material, which had a more important role than the optimized treatment time or temperature. Wood-derived MCCs dissolved faster and resulted in a higher yield of precipitate than those prepared from cotton linter. The highest yield of precipitate, 68 %, was recovered from a MCC prepared from mercerized prehydrolysis hardwood Kraft pulp. The high yield of precipitate could not be attributed to any single factor but in general the wood-derived MCCs had a smaller particle size, smaller crystallite dimensions, and lower molar mass than their cotton-derived equivalents. The analysis of molar mass distributions indicated heterogeneous dissolution mechanism at 250 and 320 °C whereas at 380 °C the cellulose crystallites were subjected to random chain cleavage. [ABSTRACT FROM AUTHOR]

The rapid coagulation of NaOH-based cellulose solution during the wet spinning process leads to a low stretching ratio and, consequently, the low mechanical properties of the fibres. The aim of this work was to slow down the coagulation by replacing the sulphuric acid spin bath with an acetic acid bath. The spin dope was prepared by dissolving the enzyme-treated dissolving pulp in aqueous sodium zincate using a freezing-thawing method. The optimal zinc oxide and sodium hydroxide concentrations were studied first. The most thermally stable cellulose solution contained 6.5 wt% NaOH and 1.3 wt% ZnO with 6 wt% enzyme-treated dissolving pulp. The spin dope was prepared accordingly. Coagulation of the cellulose solution slowed down in the acetic acid bath, resulting in a significantly higher stretching ratio for the fibres than with the sulphuric acid bath. However, the acetic acid spun fibres shrunk strongly during drying, and the possibly aligned order of the molecular chains due to the high stretch was partly lost. As a consequence, the high stretch was not transferred to high tenacity of the fibres in this study. However, the result suggests attractive potential to develop processing conditions to increase fibre tenacity. [ABSTRACT FROM AUTHOR]

The dissolution of different cellulose pulps from different sources such as wood, bamboo and ramie pulp in 7 wt% NaOH/12 wt% urea aqueous solution was investigated in the present article, as well as the structure and properties of the resultant regenerated films. All of the cellulose samples with molecular weight below 1.2 × 10 could be quickly and completely dissolved in NaOH/urea aqueous solution precooled to −12.5 °C in 2 min, regardless of the cellulose source, indicating the universality of cellulose dissolution in NaOH/urea solvent. The resultant cellulose solutions exhibited similar rheological behaviors, indicating a similar solution procedure of cellulose in NaOH/urea. These regenerated cellulose films exhibited similar structures and morphologies according to the results of the scanning electron microscope, X-ray diffraction and Fourier transform infrared spectroscopy analyses, indicating a microporous structure with a pore diameter ranging from 100 to 300 nm, as well as a complete transition from cellulose I to cellulose II after the dissolution and regeneration process. Furthermore, all of the films had good mechanical properties and light transmittance as a result of the homogeneous structure. In view of the results mentioned above, the NaOH/urea solvent system displayed a strong cellulose dissolving capacity, exhibiting great potential for the further development and comprehensive utilization of cellulose from agricultural and forestry wastes. It is capable of increasing the applications of cellulose and has potential for further development. [ABSTRACT FROM AUTHOR]