Identification of cellulose textile fibers.

Distinguishing different textile fibers is important for recycling waste textiles. Most studies on non-destructive optical textile identification have focused on classifying different synthetic and natural fibers but chemical recycling requires more detailed information on fiber composition and polymer properties. Here, we report the use of near infrared imaging spectroscopy and chemometrics for classifying natural and regenerated cellulose fibers. Our classifiers trained on images of consumer textiles showed 100% true positive rates based on model cross-validation and correctly identified on average 8-9 out of 10 test set pixels using images of specifically made cotton, viscose and lyocell samples of known compositions. These results are significant as they indicate the possibility to monitor and control fiber dosing and subsequent dope viscosity during chemical recycling of cellulose fibers. Our results also suggested the possibility to identify fibers purely based on polymer chain length. This finding opens the possibility to indirectly estimate dope viscosity and creates entirely new hypotheses for combining imaging spectroscopy with classification and regression methods within the broader field of cellulose modification.

Fast and quantitative compositional analysis of hybrid cellulose-based regenerated fibers using thermogravimetric analysis and chemometrics.

Cellulose can be dissolved with another biopolymer in a protic ionic liquid and spun into a bicomponent hybrid cellulose fiber using the Ioncell® technology. Inside the hybrid fibers, the biopolymers are mixed at the nanoscale, and the second biopolymer provides the produced hybrid fiber new functional properties that can be fine-tuned by controlling its share in the fiber. In the present work, we present a fast and quantitative thermoanalytical method for the compositional analysis of man-made hybrid cellulose fibers by using thermogravimetric analysis (TGA) in combination with chemometrics. First, we incorporated 0-46 wt.% of lignin or chitosan in the hybrid fibers. Then, we analyzed their thermal decomposition behavior in a TGA device following a simple, one-hour thermal treatment protocol. With an analogy to spectroscopy, we show that the derivative thermogram can be used as a predictor in a multivariate regression model for determining the share of lignin or chitosan in the cellulose hybrid fibers. The method generated cross validation errors in the range 1.5-2.1 wt.% for lignin and chitosan. In addition, we discuss how the multivariate regression outperforms more common modeling methods such as those based on thermogram deconvolution or on linear superposition of reference thermograms. Moreover, we highlight the versatility of this thermoanalytical method-which could be applied to a wide range of composite materials, provided that their components can be thermally resolved-and illustrate it with an additional example on the measurement of polyester content in cellulose and polyester fiber blends. The method could predict the polyester content in the cellulose-polyester fiber blends with a cross validation error of 1.94 wt.% in the range of 0-100 wt.%. Finally, we give a list of recommendations on good experimental and modeling practices for the readers who want to extend the application of this thermoanalytical method to other composite materials. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s10570-021-03923-6.

Close Packing of Cellulose and Chitosan in Regenerated Cellulose Fibers Improves Carbon Yield and Structural Properties of Respective Carbon Fibers.

A low carbon yield is a major limitation for the use of cellulose-based filaments as carbon fiber precursors. The present study aims to investigate the use of an abundant biopolymer chitosan as a natural charring agent particularly on enhancing the carbon yield of the cellulose-derived carbon fiber. The ionic liquid 1,5-diazabicyclo[4.3.0]non-5-enium acetate ([DBNH]OAc) was used for direct dissolution of cellulose and chitosan and to spin cellulose-chitosan composite fibers through a dry-jet wet spinning process (Ioncell). The homogenous distribution and tight packing of cellulose and chitosan revealed by X-ray scattering experiments enable a synergistic interaction between the two polymers during the pyrolysis reaction, resulting in a substantial increase of the carbon yield and preservation of mechanical properties of cellulose fiber compared to other cobiopolymers such as lignin and xylan.

Conversion of wood-biopolymers into macrofibers with tunable surface energy via dry-jet wet-spinning.

ABSTRACT: Surface chemistry of regenerated all-wood-biopolymer fibers that are fine-tuned by composition of cellulose, lignin and xylan is elucidated via revealing their surface energy and adhesion. Xylan additive resulted in thin fibers and decreased surface energy of the fiber outer surfaces compared to the cellulose fibers, or when lignin was used as an additive. Lignin increased the water contact angle on the fiber surface and decreased adhesion force between the fiber cross section and a hydrophilic probe, confirming that lignin reduced fiber surface affinity to water. Lignin and xylan enabled fiber decoration with charged groups that could tune the adhesion force between the fiber and an AFM probe. The fibers swelled in water: the neat cellulose fiber cross section area increased 9.2%, the fibers with lignin as the main additive 9.1%, with xylan 6.8%, and the 3-component fibers 5.5%. This indicates that dimensional stability in elevated humidity is improved in the case of 3-component fiber compared to 2-component fibers. Xylan or lignin as an additive neither improved strength nor elongation at break. However, improved deformability was achieved when all the three components were incorporated into the fibers.

Enhanced stabilization of cellulose-lignin hybrid filaments for carbon fiber production.

Herein we investigate the stabilization behavior of a cellulose-lignin composite fibre towards application as a new bio derived precursor for carbon fibres. Carbon fibre materials are in high demand as we move towards a lower emission high-efficiency society. However, the most prominent current carbon fibre precursor is an expensive fossil-based polymer. Over the past decade significant research has focused on using renewable and bio derived alternatives. By blending cellulose and lignin and spinning a fibre with a continuous bi-component matrix a new approach to overcome the current limitations of both these precursors is proposed. A thorough study is conducted here on understanding the stabilization of the new precursors which is a critical step in the carbon fibre process. We show that stabilization times of the composite fibre are significantly reduced in comparison to pure lignin and improvements in mass yield compared to pure cellulose fibres are observed.

Correction: Cellulose regeneration and spinnability from ionic liquids.

Correction for 'Cellulose regeneration and spinnability from ionic liquids' by Lauri K. J. Hauru et al., Soft Matter, 2016, 12, 1487-1495.

High stability and low competitive inhibition of thermophilic Thermopolyspora flexuosa GH10 xylanase in biomass-dissolving ionic liquids.

Thermophilic Thermopolyspora flexuosa GH10 xylanase (TfXYN10A) was studied in the presence of biomass-dissolving hydrophilic ionic liquids (ILs) [EMIM]OAc, [EMIM]DMP and [DBNH]OAc. The temperature optimum of TfXYN10A with insoluble xylan in the pulp was at 65-70 °C, with solubilised 1 % xylan at 70-75 °C and with 3 % xylan at 75-80 °C. Therefore, the amount of soluble substrate affects the enzyme activity at high temperatures. The experiments with ILs were done with 1 % substrate. TfXYN10A can partially hydrolyse soluble xylan even in the presence of 40 % (v/v) ILs. Although ILs decrease the apparent temperature optimum, a surprising finding was that at the inactivating temperatures (80-90 °C), especially [EMIM]OAc increases the stability of TfXYN10A indicating that the binding of IL molecules strengthens the protein structure. Earlier kinetic studies showed an increased K m with ILs, indicating that ILs function as competitive inhibitors. TfXYN10A showed low increase of K m, which was 2-, 3- and 4-fold with 15 % [EMIM]OAc, [DBNH]OAc and [EMIM]DMP, respectively. One reason for the low competitive inhibition could be the high affinity to the substrate (low K m). Xylanases with low K m (~1 mg/mL) appear to show higher tolerance to ILs than xylanases with higher K m (~2 mg/mL). Capillary electrophoresis showed that TfXYN10A hydrolyses xylan to the end-products in 15-35 % ILs practically as completely as without IL, also indicating good binding of the short substrate molecules by TfXYN10A despite of major apparent IL binding sites above the catalytic residues. Substrate binding interactions in the active site appear to explain the high tolerance of TfXYN10A to ILs.

Hyperthermostable Thermotoga maritima xylanase XYN10B shows high activity at high temperatures in the presence of biomass-dissolving hydrophilic ionic liquids.

The gene of Thermotoga maritima GH10 xylanase (TmXYN10B) was synthesised to study the extreme limits of this hyperthermostable enzyme at high temperatures in the presence of biomass-dissolving hydrophilic ionic liquids (ILs). TmXYN10B expressed from Pichia pastoris showed maximal activity at 100 °C and retained 92 % of maximal activity at 105 °C in a 30-min assay. Although the temperature optimum of activity was lowered by 1-ethyl-3-methylimidazolium acetate ([EMIM]OAc), TmXYN10B retained partial activity in 15-35 % hydrophilic ILs, even at 75-90 °C. TmXYN10B retained over 80 % of its activity at 90 °C in 15 % [EMIM]OAc and 15-25 % 1-ethyl-3-methylimidazolium dimethylphosphate ([EMIM]DMP) during 22-h reactions. [EMIM]OAc may rigidify the enzyme and lower V max. However, only minor changes in kinetic parameter K m showed that competitive inhibition by [EMIM]OAc of TmXYN10B is minimal. In conclusion, when extended enzymatic reactions under extreme conditions are required, TmXYN10B shows extraordinary potential.

Cellulose regeneration and spinnability from ionic liquids.

Ionic liquid solutions of cellulose or dopes can be spun into Lyocell-type textile fibers by dry-jet wet spinning. An extruded dope is drawn over an air gap into water, where the water hydrates the ionic liquid and cellulose is regenerated. Spinnability studies have concentrated on the deformation and failure modes in the air gap and thus the rheology of the unhydrated spinning dope. Herein, a breach in the bath, another failure mode, is discussed. Dopes are prepared from the good spinning solvents NMMO·H2O and [DBNH]OAc and the poor spinning solvents [emim]OAc and [TMGH]OAc. The diffusion constants for water diffusing inwards and for ionic liquid diffusing outwards the emerging filament are measured offline. The resiliences and strengths of cellulose-ionic liquid solutions with different hydration stoichiometries are measured by means of rheometry. By calculating the diffusion dynamics, the resilience distribution of the forming filament is simulated. Gel strength distribution accounts for the tendency of [emim]OAc dopes to undergo a telescope-type breach, whereas the gelatinous solution state of [TMGH]OAc dopes accounts for their poor spinnability.

Degradation and Crystallization of Cellulose in Hydrogen Chloride Vapor for High-Yield Isolation of Cellulose Nanocrystals.

Despite the structural, load-bearing role of cellulose in the plant kingdom, countless efforts have been devoted to degrading this recalcitrant polysaccharide, particularly in the context of biofuels and renewable nanomaterials. Herein, we show how the exposure of plant-based fibers to HCl vapor results in rapid degradation with simultaneous crystallization. Because of the unchanged sample texture and the lack of mass transfer out of the substrate in the gas/solid system, the changes in the crystallinity could be reliably monitored. Furthermore, we describe the preparation of cellulose nanocrystals in high yields and with minimal water consumption. The study serves as a starting point for the solid-state tuning of the supramolecular properties of morphologically heterogeneous biological materials.

Thermal behaviour and tolerance to ionic liquid [emim]OAc in GH10 xylanase from Thermoascus aurantiacus SL16W.

GH10 xylanase from Thermoascus aurantiacus strain SL16W (TasXyn10A) showed high stability and activity up to 70-75 °C. The enzyme's half-lives were 101 h, 65 h, 63 min and 6 min at 60, 70, 75 and 80 °C, respectively. The melting point (T m), as measured by DSC, was 78.5 °C, which is in line with a strong activity decrease at 75-80 °C. The biomass-dissolving ionic liquid 1-ethyl-3-methylimidazolium acetate ([emim]OAc) in 30 % concentration had a small effect on the stability of TasXyn10A; T m decreased by only 5 °C. It was also observed that [emim]OAc inhibited much less GH10 xylanase (TasXyn10A) than the studied GH11 xylanases. The K m of TasXyn10A increased 3.5-fold in 15 % [emim]OAc with xylan as the substrate, whereas the approximate level of V max was not altered. The inhibition of enzyme activity by [emim]OAc was lesser at higher substrate concentrations. Therefore, high solid concentrations in industrial conditions may mitigate the inhibition of enzyme activity by ionic liquids. Molecular docking experiments indicated that the [emim] cation has major binding sites near the catalytic residues but in lower amounts in GH10 than in GH11 xylanases. Therefore, [emim] cation likely competes with the substrate when binding to the active site. The docking results indicated why the effect is lower in GH10.

Scanning WAXS microscopy of regenerated cellulose fibers at mesoscopic resolution.

In this work, regenerated cellulose textile fibers, Ioncell-F, dry-wet spun with different draw ratios, have been investigated by scanning wide-angle X-ray scattering (WAXS) using a mesoscopic X-ray beam. The fibers were found to be homogeneous on the 500 nm length scale. Analysis of the azimuthal angular dependence of a crystalline Bragg spot intensity revealed a radial dependence of the degree of orientation of crystallites that was found to increase with the distance from the center of the fiber. We attribute this to radial velocity gradients during the extrusion of the spin dope and the early stage of drawing. On the other hand, the fiber crystallinity was found to be essentially homogeneous over the fiber cross section.

Separation of hemicellulose and cellulose from wood pulp by means of ionic liquid/cosolvent systems.

Pulp of high cellulose content, also known as dissolving pulp, is needed for many purposes, including the production of cellulosic fibers and films. Paper-grade pulp, which is rich in hemicellulose, could be a cheap source but must be refined. Hitherto, hemicellulose extraction procedures suffered from a loss of cellulose and the non-recoverability of unaltered hemicelluloses. Herein, an environmentally benign fractionation concept is presented, using mixtures of a cosolvent (water, ethanol, or acetone) and the cellulose dissolving ionic liquid 1-ethyl-3-methylimidazolium acetate (EMIM OAc). This cosolvent addition was monitored using Kamlet-Taft parameters, and appropriate stirring conditions (3 h at 60 °C) were maintained. This allowed the fractionation of a paper-grade kraft pulp into a separated cellulose and a regenerated hemicellulose fraction. Both of these exhibited high levels of purity, without any yield losses or depolymerization. Thus, this process represents an ecologically and economically efficient alternative in producing dissolving pulp of highest purity.

Optimization of Dry-Jet Wet Spinning of Regenerated Cellulose Fibers Using [mTBDH][OAc] as a Solvent.

Superbase-based ionic liquids (ILs) have demonstrated excellent dissolution capability for cellulose, and employing the dry-jet wet spinning process, high-tenacity regenerated textile fibers have been made. Among a range of superbase-based ILs, [mTBDH][OAc] exhibited not only good spinnability but also exceptional recyclability, making it highly suitable for a closed-loop production of regenerated cellulose fibers. To further optimize the spinning process, we investigated the influence of the cellulosic raw materials and the IL with residual water on spinnability and fiber properties. In addition, single-filament spinning and multifilament spinning using spinnerets with different hole densities were investigated to reveal the upscaling challenges of the dry-jet wet spinning process. The air gap conditions, for example, temperature and moisture concentration were simulated using COMSOL multiphysics. The results indicate that the presence of a small amount of water (3 wt%) in the IL has a positive effect on spinnability, while the mechanical properties of the fibers remain unchanged.

Gamma-valerolactone biorefinery: Catalyzed birch fractionation and valorization of pulping streams with solvent recovery.

In this study, we propose a full gamma-valerolactone (GVL) organosolv biorefinery concept including the utilization of all pulping streams, solvent recovery, and preliminary material and energy balances. GVL is a renewable and non-toxic solvent that fractionates woody biomass. The silver birch chips were pulped (45-65 wt% GVL, 150 °C, 2 h) under a series of acid-catalyzed conditions (5-12 kg H2SO4/t), and the fully bleached pulp was spun into fibers by the IONCELL® process and knitted into the fabric. The dissolved lignin was precipitated by water from spent liquor (1:1) and processed into polyhydroxyurethane. Most of the dissolved hemicelluloses were in the form of xylose, therefore, the crystallization efficiency of xylose from spent liquor in the presence of residual GVL was studied. The GVL recovery rate in the lab column was 66%, however by increasing the number of equilibrium stages, 99% recovery could be achieved.

Pulp properties and their influence on enzymatic degradability.

Endoglucanase treatment of pulp for the adjustment of viscosity and the increase in pulp reactivity is a promising step in the concept for the beneficial production of dissolving pulps from paper grade pulps. To promote the commercial applicability of these enzymes, the influence of pulp properties such as carbohydrate composition, pulp type and cellulose morphology on the enzymatic degradability of a pulp was examined. High contents of hemicelluloses and lignin were shown to impair the accessibility of the cellulose to the enzymes. Due to the elevated swelling capacity of cellulose II, conversion of the cellulose morphology from I to II upon alkaline treatments showed a large increasing effect on the cellulose accessibility, and enzymatic degradability. Reactivity measurements of softwood sulfite pulps after enzymatic degradation and acid-catalyzed hydrolysis, respectively, revealed elevated reactivity for the pulp after acid treatment. This is in contrast to effects of enzyme treatments reported for CCE treated kraft pulps.

Role of solvent parameters in the regeneration of cellulose from ionic liquid solutions.

The ionic liquids 1-ethyl-3-methylimidazolium acetate [emim]OAc, N,N,N,N-tetramethylguanidium propionate [TMGH]EtCO(2), and N,N,N,N-tetramethylguanidium acetate [TMGH]OAc, and the traditional cellulose solvent N-methylmorpholine N-oxide NMMO were characterized for their Kamlet-Taft (KT) values at several water contents and temperatures. For the ionic liquids and NMMO, thresholds of regeneration of cellulose solutions by water were determined using nephelometry and rheometry. Regeneration from wet IL was found to be asymmetric compared to dissolution into wet IL. KT parameters were found to remain almost constant at temperatures, between 20-100 °C, even at different water contents. Among the KT parameters, the ß value was found to change most drastically, with an almost linear decrease upon addition of water. The ability of the mixtures to dissolve cellulose was best explained by the difference ß-α (net basicity), rather than ß alone. Regeneration of cellulose starts at thresholds values of approximately ß < 0.8 (ß-α < 0.35) and displayed four phases.

Dialkyl phosphate-related ionic liquids as selective solvents for xylan.

Herein we describe a possibility of selective dissolution of xylan, the most important type of hemicellulose, from Eucalyptus globulus kraft pulp using ionic liquids (ILs). On the basis of the IL 1-butyl-3-methylimidazolium dimethyl phosphate, which is well-known to dissolve pulp, the phosphate anion was modified by substituting one oxygen atom for sulfur and selenium, respectively. This alteration reduces the hydrogen bond basicity of the IL and therefore prevents dissolution of cellulose fibers, whereas the less ordered xylan is still dissolved. (1)H NMR spectra of model solutions and Kamlet-Taft parameters were used to quantify the solvent polarity and hydrogen bond acceptor properties of the ILs. These parameters have been correlated to their ability to dissolve xylan and cellulose, which was monitored by (13)C NMR spectroscopy. It was found that the selectivity for xylan dissolution increases to a certain extent with decreasing hydrogen-bond-accepting ability of anions of the ILs.

A novel X-ray diffraction approach to assess the crystallinity of regenerated cellulose fibers.

Here, a new accurate approach is presented to quantify the degree of crystallinity of regenerated cellulose textile fibers using wide-angle X-ray scattering. The approach is based on the observation that the contributions to the scattering from crystalline and amorphous domains of the fibers can be separated due to their different degree of orientation with respect to the fiber direction. The method is tested on Ioncell-F fibers, dry jet wet spun with different draw ratios from an ionic liquid solution. The analysis output includes, apart from an accurate estimate of the fiber crystallinity, the degrees of orientation of the cellulose nanocrystals and the cellulose chains in the amorphous domains.

High-purity cellulose production from birch wood by γ-valerolactone/water fractionation and IONCELL-P process.

This study presents an environmentally friendly process to produce high-purity cellulose (dissolving pulp) from birch wood by combining γ-valerolactone (GVL)/water fractionation and ionic liquid treatment of pulp, IONCELL-P (IP). A paper grade pulp was produced from optimal GVL cook with a similar composition to birch kraft pulp and was bleached with ECF sequence before the hemicelluloses were removed using the IONCELL-P process. The purity of the GVL-IP pulp significantly exceeded that of commercial prehydrolysis kraft (PHK) and prehydrolysis soda-anthraquinone (PH-Soda-AQ) pulps. IONCELL-P extraction removed more than 90% of the hemicelluloses, resulting in a dissolving pulp with a purity of 96% and a high molecular mass fraction, 2.3 times higher than that of a conventional PHK pulp. GVL-IP pulps are suitable not only for regenerated cellulose fibers or films, but also for high-purity, high-viscosity cellulose acetate and ethers, which cannot be produced in an environmentally friendly way by conventional processes.