Fungal Treatment Modifies Kraft Lignin for Lignin- and Cellulose-Based Carbon Fiber Precursors

The kraft lignin's low molecular weight and too high hydroxyl content hinder its application in bio-based carbon fibers. In this study, we were able to polymerize kraft lignin and reduce the amount of hydroxyl groups by incubating it with the white-rot fungus Obba rivulosa. Enzymatic radical oxidation reactions were hypothesized to induce condensation of lignin, which increased the amount of aromatic rings connected by carbon-carbon bonds. This modification is assumed to be beneficial when aiming for graphite materials such as carbon fibers. Furthermore, the ratio of remaining aliphatic hydroxyls to phenolic hydroxyls was increased, making the structure more favorable for carbon fiber production. When the modified lignin was mixed together with cellulose, the mixture could be spun into intact precursor fibers by using dry-jet wet spinning. The modified lignin leaked less to the spin bath compared with the unmodified lignin starting material, making the recycling of spin-bath solvents easier. The stronger incorporation of modified lignin in the precursor fibers was confirmed by composition analysis, thermogravimetry, and mechanical testing. This work shows how white-rot fungal treatment can be used to modify the structure of lignin to be more favorable for the production of bio-based fiber materials.Peer reviewe

Autohydrolysis of softwood prior to alkaline pulping

This work focused on auto hydrolysis followed by alkaline pulping of softwood. As raw material pine (pinus sylvestris) and spruce (picea abies) were used. The influence of different hydrolysis and cooking conditions was investigated. The objectives of the thesis were:. 1. To find the optimal hydrolysis conditions in order to extract as much hemicelluloses as possible, while avoiding unfavourable side reactions (for instance lignin condensation reactions). 2. To find the optimal cooking conditions for the pre-hydrolysed wood chips in order to maintain good pulp yield and properties. 3. To investigate the influence of anthraquinone on the pulping of pre-hydrolysed wood chips. 4. Lower the sulphidity level in the cooking process. The results showed that pre-hydrolysed pulps reached lower kappa numbers at the same H-factor compared to the reference pulps (kraft). Pre-hydrolysed pulps also responded better to oxygen delignification. Due to this, the cooking process could be interrupted at higher kappa numbers compared to the reference pulps. The zero span tensile strength was slightly lower for the pre-hydrolysed pulps compared to the reference. When using anthraquinone (0.1 %) and a sulphidity level of 20%, the screened yield at a certain kappa number was slightly higher than those of normal kraft pulp (sulphidity 40 %)

Chemically Accelerated Stabilization of a Cellulose-Lignin Precursor as a Route to High Yield Carbon Fiber Production

| openaire: EC/H2020/715788/EU//WoCaFi Funding Information: M.T. and M.H. have received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement no. 715788). Publisher Copyright: © 2022 American Chemical Society.The production of carbon fiber from bio-based or renewable resources has gained considerable attention in recent years with much of the focus upon cellulose, lignin, and cellulose-lignin composite precursor fibers. A critical step in optimizing the manufacture of carbon fiber is the stabilization process, through which the chemical and physical structure of the precursor fiber is transformed, allowing it to withstand very high temperatures. In this work, thermogravimetric analysis (TGA) is used to explore and optimize stabilization by simulating different stabilization profiles. Using this approach, we explore the influence of atmosphere (nitrogen or air), cellulose-lignin composition, and alternative catalysts on the carbon yield, efficiency, and rate of stabilization. Carbon dioxide and water vapor released during stabilization are analyzed by Fourier transform infrared (FTIR) spectroscopy, providing further information about the stabilization mechanism and the accelerating effect of oxygen and increased char yield (carbon content), especially for lignin. A range of different catalysts are evaluated for their ability to enhance the char yield, and a phosphorus-based flame retardant (H3PO4) proved to be the most effective; in fact, a doubling of the char yield was observed.Peer reviewe

Interdependent factors influencing the carbon yield, structure, and CO2 adsorption capacity of lignocellulose-derived carbon fibers using multiple linear regression

| openaire: EC/H2020/715788/EU//WoCaFi Funding Information: Open Access funding provided by Aalto University. The research was supported by European Union’s Horizon 2020 research and innovation programme [715788] and the Academy of Finland (Elucidation of the structural development during cellulose carbonization for advanced carbon materials) [348354]. Publisher Copyright: © 2023, The Author(s).Cellulose has experienced a renaissance as a precursor for carbon fibers (CFs). However, cellulose possesses intrinsic challenges as precursor substrate such as typically low carbon yield. This study examines the interplay of strategies to increase the carbonization yield of (ligno-) cellulosic fibers manufactured via a coagulation process. Using Design of Experiments, this article assesses the individual and combined effects of diammonium hydrogen phosphate (DAP), lignin, and CO2 activation on the carbonization yield and properties of cellulose-based carbon fibers. Synergistic effects are identified using the response surface methodology. This paper evidences that DAP and lignin could affect cellulose pyrolysis positively in terms of carbonization yield. Nevertheless, DAP and lignin do not have an additive effect on increasing the yield. In fact, combined DAP and lignin can affect negatively the carbonization yield within a certain composition range. Further, the thermogravimetric CO2 adsorption of the respective CFs was measured, showing relatively high values (ca. 2 mmol/g) at unsaturated pressure conditions. The CFs were microporous materials with potential applications in gas separation membranes and CO2 storage systems. Peer reviewe

Effect of boric acid on the stabilisation of cellulose-lignin filaments as precursors for carbon fibres

| openaire: EC/H2020/715788/EU//WoCaFiThe increasing demand for a low-cost and renewable carbon fibre precursor has driven the focus on bio-based precursors. Cellulose-lignin composite fibres are a new approach toward this direction. The combination of cellulose and lignin into a composite fibre could solve some of the current limitations for pure cellulose and lignin fibres. This study investigated the treatment of the composite fibres with boric acid with focus on carbon yield, stabilisation rate and fibre fusion, which is a typical defect in carbon fibre production. The influence of boric acid on the mechanism of stabilisation was studied. The stabilisation time was reduced by 25% through treatment with the reduction of fibre fusion, while the carbon yield increased significantly in comparison to the untreated fibres.Peer reviewe

Cellulose-lignin composite fibres as precursors for carbon fibres. Part 2 - The impact of precursor properties on carbon fibres

| openaire: EC/H2020/715788/EU//WoCaFiCarbon fibres, despite being responsible lightweight structures that improve sustainability through fuel efficiency and occupational safety, remain largely derived from fossil fuels. Alternative precursors such as cellulose and lignin (bio-derived and low cost) are rapidly gaining attention as replacements for polyacrylonitrile (PAN, an oil-based and costly precursor). This study uses a cellulose-lignin composite fibre, to elucidate the influence of precursor fabrication parameters (draw ratio and lignin content) on the efficiency of stabilisation and carbonisation, from the perspective of the chemical, morphological and mechanical changes. The degradation of cellulose chains was the primary contributor to the decrease in mechanical properties during stabilization, but is slowed by the incorporation of lignin. The skin-core phenomenon, a typical effect in PAN-based carbon fibres production, was also observed. Finally, the carbonization of incompletely stabilized fibres is shown to produce hollow carbon fibres, which have potential application in batteries or membranes.Peer reviewe

Understanding the influence of key parameters on the stabilisation of cellulose-lignin composite fibres

| openaire: EC/H2020/715788/EU//WoCaFiThe high cost of carbon fibre continues to limit its use in industries like automotive, construction and energy. Since the cost is closely linked to the precursor, considerable research has focussed on the use of low-cost alternatives. A promising candidate is a composite fibre consisting of blended cellulose and lignin, which has the added benefit of being derived from sustainable resources. The benefits of blending cellulose and lignin reduce some of the negative aspects of converting single component cellulose and lignin fibres to carbon fibre, although the production from such a blend, remains largely underdeveloped. In this study, the effects of stabilisation temperature and the stabilisation process of the blended fibres are explored. Moreover, the viscoelastic properties of the cellulose-lignin fibre are investigated by DMA for the first time. Finally, the cause of fusion in the stabilisation is adressed and solved by applying a spin finish.Peer reviewe

Process-dependent nanostructures of regenerated cellulose fibres revealed by small angle neutron scattering

| openaire: EC/H2020/715788/EU//WoCaFiThe nanometric internal structure of polymeric fibres is fundamental for their mechanical properties. Two-dimensional small angle neutron scattering patterns were collected to obtain structural parameters of the elementary fibrils in regenerated cellulose fibres prepared by various fibre spinning technologies. Scattering features were fitted to model functions to derive parameters such as elementary fibril radius, long period of the repeating units of crystal and amorphous phase along the fibre axis, degree of orientation, and ellipticity. The correlation between structural parameters and the mechanical properties was studied for the fibres of different existing spinning processes and for the high-strength fibres. Former group showed high correlation with mechanical properties. The latter group showed generally lower correlation, but showed relatively high correlation with the long period. These structural parameters provide a basis for understanding the structure-property relationship of regenerated cellulose fibres as function of spinning types and conditions for further optimization.Peer reviewe

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

| openaire: EC/H2020/715788/EU//WoCaFi Funding Information: This project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation program (Grant Agreement No 715788). Publisher Copyright: © 2021, The Author(s).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.Peer reviewe

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

| openaire: EC/H2020/715788/EU//WoCaFiCellulose-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.Peer reviewe