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.

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.

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.

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.

Cellulose-lignin composite fibres as precursors for carbon fibres. Part 1 - Manufacturing and properties of precursor fibres.

Cellulose-lignin composite fibres were spun from ionic liquid (IL) solutions by dry-jet wet spinning. Birch pre-hydrolysed Kraft (PHK) pulp and organosolv beech (BL) or spruce lignin (SL) were dissolved in the IL 1,5-diazabicyclo[4.3.0]non-5-enium acetate ([DBNH]OAc) to prepare spinning dopes. Fibres with lignin concentrations of up to 50 % were spun successfully. The fibres were analysed focusing on important properties for the production of carbon fibres (CF). Due to the higher molar mass of the SL compared to the BL, SL showed higher stability in the spinning process, giving higher lignin content in the final fibres. The CF yield after carbonization increased with increasing lignin content. The higher carbon content of SL compared to BL, resulted in moderately higher CF yield of the SL fibres, compared to fibres with BL. Overall, the produced cellulose-lignin composite fibres show great potential as precursors for CF production.

Green Conducting Cellulose Yarns for Machine-Sewn Electronic Textiles.

The emergence of "green" electronics is a response to the pressing global situation where conventional electronics contribute to resource depletion and a global build-up of waste. For wearable applications, green electronic textile (e-textile) materials present an opportunity to unobtrusively incorporate sensing, energy harvesting, and other functionality into the clothes we wear. Here, we demonstrate electrically conducting wood-based yarns produced by a roll-to-roll coating process with an ink based on the biocompatible polymer:polyelectrolyte complex poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS). The developed e-textile yarns display a, for cellulose yarns, record-high bulk conductivity of 36 Scm-1, which could be further increased to 181 Scm-1 by adding silver nanowires. The PEDOT:PSS-coated yarn could be machine washed at least five times without loss in conductivity. We demonstrate the electrochemical functionality of the yarn through incorporation into organic electrochemical transistors (OECTs). Moreover, by using a household sewing machine, we have manufactured an out-of-plane thermoelectric textile device, which can produce 0.2 µW at a temperature gradient of 37 K.

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.

Exploring Large Ductility in Cellulose Nanopaper Combining High Toughness and Strength.

Cellulose nanopaper is a strong lightweight material made from renewable resources with a wide range of potential applications, from membranes to electronic displays. Most studies on nanopaper target high mechanical strength, which compromises ductility and toughness. Herein, we demonstrate the fabrication of highly ductile and tough cellulose nanopaper via mechanical fibrillation of hemicellulose-rich wood fibers and dispersion of the obtained cellulose nanofibrils (CNFs) in an ionic liquid (IL)-water mixture. This treatment allows hemicellulose swelling, which leads to dissociation of CNF bundles into highly disordered long flexible fibrils and the formation of a nanonetwork as supported by cryogenic transmission electron microscopy (cryo-TEM) imaging. Rheology of the suspensions shows a 300-fold increase in storage and loss moduli of CNF-IL-water suspensions, compared to their CNF-water counterparts. The nanopaper prepared by removing the IL-water shows a combination of large elongation (up to 35%), high strength (260 MPa), and toughness as high as 51 MJ/m3, because of efficient interfibrillar slippage and energy dissipation in the highly disordered isotropic structure. This work provides a nanostructure-engineered strategy of making ductile and tough cellulose nanopaper.

Unidirectional All-Cellulose Composites from Flax via Controlled Impregnation with Ionic Liquid.

Mechanically strong all-cellulose composites are very attractive in the terms of fully bio-based and bio-degradable materials. Unidirectional flax-based all-cellulose composites are prepared via facile room-temperature impregnation with an ionic liquid, 1-ethyl-3-methyl imidazolium acetate. To determine the optimal processing conditions, the kinetics of flax dissolution in this solvent is first studied using optical microscopy. Composite morphology, crystallinity, density, the volume fraction of cellulose II and tensile properties are investigated, indicating that flax dissolution should be within certain limits. On the one hand, the amount of cellulose II formed through dissolution and coagulation should be high enough to "fuse" flax fibers, resulting in a density increase. On the other hand, only the surface layer of the fibers should be dissolved to maintain the strength provided by the inner secondary layer and avoid a detrimental decrease in crystallinity. The highest Young's modulus and strength, 10.1 GPa and 151.3 MPa, respectively, are obtained with a crystallinity of 43% and 20 vol% of cellulose II.

Differences in surface chemistry of regenerated lignocellulose fibers determined by chemically sensitive scanning probe microscopy.

Tuning the composition of regenerated lignocellulosic fibers in the production process enables targeting of specific material properties. In composite materials, such properties could be manipulated by controlled heterogeneous distribution of chemical components of regenerated fibers. This attribute requires a visualization method to show their inherent chemical characteristics. We compared complementary microscopic techniques to analyze the surface chemistry of four differently tuned regenerated lignocellulosic fibers. Adhesion properties were visualized with chemical force microscopy and showed contrasts towards hydrophilic and hydrophobic atomic force microscopy tips. Fibers containing xylan showed heterogeneous adhesion properties within the fiber structure towards hydrophilic tips. Additionally, peak force infrared microscopy mapped spectroscopic contrasts with nanometer resolution and provided point infrared spectra, which were consistent to classical infrared microscopy data. With this setup, infrared signals with a spatial resolution below 20 nm reveal chemical gradients in specific fiber types.

Upcycling of cotton polyester blended textile waste to new man-made cellulose fibers.

The creation of a circular economy for cellulose based textile waste is supported by the development of an upcycling method for cotton polyester blended waste garments. We present a separation procedure for cotton and polyester using [DBNH] [OAc], a superbase based ionic liquid, which allows the selective dissolution of the cellulose component. After the removal of PET, the resulting solution could be employed to dry-jet wet spin textile grade cellulose fibers down to the microfiber range (0.75-2.95 dtex) with breaking tenacities (27-48 cN/tex) and elongations (7-9%) comparable to commercial Lyocell fibers made from high-purity dissolving pulp. The treatment time in [DBNH] [OAc] was found to reduce the tensile properties (<52%) and the molar mass distribution (<51%) of PET under certain processing conditions.

Binary mixtures of ionic liquids-DMSO as solvents for the dissolution and derivatization of cellulose: Effects of alkyl and alkoxy side chains.

The efficiency of mixtures of ionic liquids (ILs) and molecular solvents in cellulose dissolution and derivatization depends on the structures of both components. We investigated the ILs 1-(1-butyl)-3-methylimidazolium acetate (C4MeImAc) and 1-(2-methoxyethyl)-3-methylimidazolium acetate (C3OMeImAc) and their solutions in dimethyl sulfoxide, DMSO, to assess the effect of presence of an ether linkage in the IL side-chain. Surprisingly, C4MeImAc-DMSO was more efficient than C3OMeImAc-DMSO for the dissolution and acylation of cellulose. We investigated both solvents using rheology, NMR spectroscopy, and solvatochromism. Mixtures of C3OMeImAc-DMSO are more viscous, less basic, and form weaker hydrogen bonds with cellobiose than C4MeImAc-DMSO. We attribute the lower efficiency of C3OMeImAc to "deactivation" of the ether oxygen and C2H of the imidazolium ring due to intramolecular hydrogen bonding. Using the corresponding ILs with C2CH3 instead of C2H, namely, 1-butyl-2,3-dimethylimidazolium acetate (C4Me2ImAc) and 1-(2-methoxyethyl)-2,3-dimethylimidazolium acetate (C3OMe2ImAc) increased the concentration of dissolved cellulose; without noticeable effect on biopolymer reactivity.

Solid-state NMR method for the quantification of cellulose and polyester in textile blends.

The valorization of cellulose rich textile waste is promoted by the development of a novel solid-state NMR method for the quantification of cellulose and polyester in textile blends. We applied 13C CP-MAS NMR as a tool for the quantification and structural characterization of cellulose in cotton polyester blends. Gaussian functions were used to integrate the spectra obtained from a set of calibration standards in order to calculate a sigmoidal calibration curve. Acid hydrolysis was chosen as a reference method. The results demonstrated that solid-state NMR enables a reliable determination of cellulose and polyester in both preconsumer and postconsumer waste textiles and suggests a possible extension of the concept to blends of man-made cellulose fibers (MMCFs) and polyester.

Chemical Recovery of γ-Valerolactone/Water Biorefinery.

We introduce the optimization of the pulping conditions and propose different chemical recovery options for a proven biorefinery concept based on γ-valerolactone (GVL)/water fractionation. The pulping process has been optimized whereby the liquor-to-wood (L:W) ratio could be reduced to 3 L/kg without compromising the pulp properties as raw material for textile fibers production. The recovery of the pulping solvent was performed through combinations of lignin precipitation by water addition, distillation at reduced pressure, and liquid CO2 extraction. With a two-step lignin precipitation coupled with vacuum distillation, more than 90% of lignin and GVL could be recovered from the spent liquor. However, a significant part of GVL remained unrecoverable in the residue, which was a highly viscous liquid with complicated phase behavior. The recovery by lignin precipitation combined with liquid CO2 extraction could recover more than 85% GVL and 90% lignin without forming any problematic residue as in the distillation process. The remaining GVL remained in the raffinate containing a low amount of lignin and other compounds, which can be further processed to isolate the GVL and improve the recovery rate.

High-Performance Acetylated Ioncell-F Fibers with Low Degree of Substitution.

Cellulose acetate is one of the most important cellulose derivatives. Herein we present a method to access cellulose acetate with a low degree of substitution through a homogeneous reaction in the ionic liquid 1,5-diazabicyclo[4.3.0]non-5-enium acetate ([DBNH][OAc]). This ionic liquid has also been identified as an excellent cellulose solvent for dry-jet wet fiber spinning. Cellulose was dissolved in [DBNH][OAc] and esterified in situ to be immediately spun into modified cellulose filaments with a degree of substitution (DS) value of 0.05-0.75. The structural properties of the resulting fibers, which are characterized by particularly high tensile strength values (525-750 MPa conditioned and 315-615 MPa wet) and elastic moduli between 10-26 GPa, were investigated by birefringence measurements, wide-angle X-ray scattering, and molar mass distribution techniques while their unique interactions with water have been studied through dynamic vapor sorption. Thus, an understanding of the novel process is gained, and the advantages are demonstrated for producing high-value products such as textiles, biocomposites, filters, and membranes.

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.

Adhesion properties of regenerated lignocellulosic fibres towards poly(lactic acid) microspheres assessed by colloidal probe technique.

In the field of polymer reinforcement, it is important to understand the interactions involved between the polymer matrix and the reinforcing component. This paper is a contribution to the fundamental understanding of the adhesion mechanisms involved in natural fibre reinforced composites. We report on the use of the colloidal probe technique for the assessment of the adhesion behaviour between poly(lactic acid) microspheres and embedded cross-sections of regenerated lignocellulosic fibres. These fibres consisted of tailored mixtures of cellulose, lignin and xylan, the amount of which was determined beforehand. The influence of the chemical composition of the fibres on the adhesion behaviour was studied in ambient air and in dry atmosphere. In ambient air, capillary forces resulted in larger adhesion between the sphere and the fibres. Changing the ambient medium to a dry nitrogen atmosphere allowed reducing the capillary forces, leading to a drop in the adhesion forces. Differences between fibres of distinct chemical compositions could be measured only on freshly cut surfaces. Moreover, the surface energy of the fibres was assessed by inverse gas chromatography. Compared to fibres containing solely cellulose, the presence of lignin and/or hemicellulose led to higher adhesion and lower surface energy, suggesting that these chemicals could serve as natural coupling agents between hydrophobic and hydrophilic components.

Birch wood pre-hydrolysis vs pulp post-hydrolysis for the production of xylan-based compounds and cellulose for viscose application.

Hydrothermal treatments of birch wood and kraft pulp were compared for their ability to extract the xylan and produce viscose-grade pulp. Water post-hydrolysis of kraft pulp produced a high-purity cellulosic pulp with lower viscosity but higher cellulose yield than traditional pre-hydrolysis kraft pulping of wood. Post-hydrolysis of pulp also increased the crystallite dimensions and degree of crystallinity in cellulose, and promoted a higher extent of fibril aggregation. The lower specific surface area in post-hydrolyzed pulps, derived from their larger fibril aggregates, decreased the accessibility of OH groups. However, this lower accessibility did not seem to decrease the pulp reactivity to derivatizing chemicals. In the aqueous side-stream, the xylose yield was similar in both pre- and post-hydrolysates, although conducting post-hydrolysis of pulp in a flow-through system enabled the recovery of high purity and molar mass (∼10 kDa) xylan for high-value applications.