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

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.

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.

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

Carbon fibers, 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 fiber, to elucidate the influence of precursor fabrication parameters (draw ratio and lignin content) on the efficiency of stabilization and carbonization, 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 fibers production, was also observed. Finally, the carbonization of incompletely stabilized fibers is shown to produce hollow carbon fibers, which have potential application in batteries or membranes.

Exfoliating B. mori silk into high aspect ratio nanofibrils facilitated by response surface methodology.

Silk fiber is formed by an assembly of fibrils. The fibrils can be isolated by a top-down mechanical process called microfibrillation and the fibrils are known as microfibrillated silk (MFS). The process involves chopping, milling, enzyme treatment and high-pressure homogenization. The milling is an important manufacturing step and to optimize the milling step, a response surface methodology was used in this work where the influence of fiber content in milled suspension, milling time and alkaline concentration were investigated. Output responses for the optimization were diameter distribution of fibrils, size and percentage of different diameter fractions, and the aspect ratio. The main and interaction effects of the milling parameters on these responses were statistically analysed. Milling time was the most significant factor for producing finer fibrils while the fiber content in milling had the maximum impact in reducing the number of large fibrils. Milling time had a positive correlation with the aspect ratio. The optimized milling resulted in MFS with an average diameter of 55.35 nm and 90% of MFS less than 100 nm based on high-magnification SEM image analysis. The aspect ratio of the MFS was 137. The MFS suspension was stable over the pH range 3-11.

Cellulose Beads Derived from Waste Textiles for Drug Delivery.

Cellulose beads were successfully prepared from waste denim using a dissolution-regeneration approach with ionic liquids as the dissolving solvent. Cellulose beads with different morphologies were achieved by altering the dissolving and coagulating solvents. The morphological differences were quantified by N2 physisorption. The impact of morphology on the cellulose beads' potential application was investigated in the context of drug loading and release. The results show that the fibrous morphology showed a better loading capacity than the globular analogue due to its higher surface area and pore volume.

Converting waste textiles into highly effective sorbent materials.

Activated carbon fibres with a tubular structure and exfoliated surface were produced utilizing cotton textile waste as the precursor. The synthesized carbon fibres were freeze dried resulting in a tubular structure and large pore size distribution. The absorption properties against various oils and organic solvents were accessed, these fibres showed some of the highest absorption capabilities reported for cellulose based carbons, in particular for olive oil, gasoline and chloroform.

Development of cellulose based aerogel utilizing waste denim-A Morphology study.

Cellulose aerogels with orientated micron-sized pore structure were obtained from denim waste utilizing ionic liquid solvents through dissolution, regeneration and drying. The pore structure of denim-derived aerogels was comprised of a mixture of micron-sized vertically aligned pores and a nanoporous fibrous network. The size and distribution of vertically aligned pores and the nanopores were influenced by the choice of ionic liquid solvent, amount of denim used and drying method employed. A detailed study on the morphology of the cellulose aerogels produced from waste denim is provided.

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.

Utilization of cotton waste for regenerated cellulose fibres: Influence of degree of polymerization on mechanical properties.

Cotton accounts for 30% of total fibre production worldwide with over 50% of cotton being used for apparel. In the process from cotton bud to finished textile product many steps are required, and significant cotton waste is generated. Typically only 30% of pre consumer cotton is recycled. Here we use cotton waste lint to produce regenerated cellulose fibres (RCF). We find the RCF from waste cotton lint had increased mechanical properties compared to RCF produced from wood pulp. We show that this is likely linked to the higher degree of polymerization (DP) of waste cotton lint. An ionic liquid is used to dissolve the cotton lint and the rheology of the spinning is measured. The properties of the RCF are characterized and compared to wood pulp RCF.

Development of a novel cellulose/duck feather composite fibre regenerated in ionic liquid.

By blending cellulose and duck feather in the common solvent 1-allyl-3-methylimidazoloium chloride, a regenerated composite fibre has been developed with improved fibres over regenerated cellulose fibres (RCF). The mechanical properties of composite fibre was shown to be better than RCF with a 63.7% improvement in tensile strain. Here, we thoroughly characterise the composite fibre and show that the composite fibre has many advantages over RCFs both from a spinning perspective and as a regenerated fibre.

Characterization of the phase behaviour of a novel polymerizable lyotropic ionic liquid crystal.

The development of new polymerizable lyotropic liquid crystals (LLCs) utilizing charged amphiphilic molecules such as those based on long chain imidazolium compounds, is a relatively new design direction for producing robust membranes with controllable nano-structures. Here we have developed a novel polymerizable ionic liquid based LLC, 1-hexadecyl-3-methylimidazolium acrylate (C16mimAcr), where the acrylate anion acts as the polymerizable moiety. The phase behaviour of the C16mimAcr upon the addition of water was characterized using small and wide angle X-ray scatterings, differential scanning calorimetry and polarized optical microscopy. We compare the phase behaviour of this new polymerizable LLC to that of the well known LLC chloride analogue, 1-hexadecyl-3-methylimidazolium chloride (C16mimCl). We find that the C16mimAcr system has a more complex phase behaviour compared to the C16mimCl system. Additional lyotropic liquid crystalline mesophases such as hexagonal phase (H1) and discontinuous cubic phase (I1) are observed at 20 °C for the acrylate system at 50 and 65 wt% water respectively. The appearance of the hexagonal phase (H1) and discontinuous cubic phase (I1) for the acrylate system is likely due to the strong hydrating nature of the acrylate anion, which increases the head group area. The formation of these additional mesophases seen for the acrylate system, especially the hexagonal phase (H1), coupled with the polymerization functionality offers great potential in the design of advanced membrane materials with selective and anisotropic transport properties.

Development of a novel regenerated cellulose composite material.

We report for the first time on a new natural composite material achieved by blending cotton and duck feather using an ionic liquid. The addition of duck feather was found to improve the elasticity, strain at break, by 50% when compared to regenerated cellulose alone. This is a significant finding since regenerated cotton using ionic liquids often suffers from poor elasticity. The improved elasticity is likely due to the regenerated duck feather maintaining its helical structure. The new regenerated cellulose composites were characterized using a combination of dynamic mechanical analysis, Fourier transform infrared spectroscopy, thermal gravimetric analysis, contact angle measurements and scanning electron microscopy.

What Happens during Natural Protein Fibre Dissolution in Ionic Liquids.

Here, we monitor the dissolution of several natural protein fibres such as wool, human hair and silk, in various ionic liquids (ILs). The dissolution of protein-based materials using ILs is an emerging area exploring the production of new materials from waste products. Wool is a keratin fibre, which is extensively used in the textiles industry and as a result has considerable amounts of waste produced each year. Wool, along with human hair, has a unique morphology whereby the outer layer, the cuticle, is heavily cross linked with disulphide bonds, whereas silk does not have this outer layer. Here we show how ILs dissolve natural protein fibres and how the mechanism of dissolution is directly related to the structure and morphology of the wool fibre.

Inducing alignment of cyclic peptide nanotubes through the use of structured ionic liquids.

We describe a convenient route to the alignment of cyclic peptide nanotubes (CPNs). The key lies in the use of nanostructured ionic liquids. An ionic liquid supported membrane with orientated domains is demonstrated, leading to aligned CPNs within a solid membrane.

Phase transition of poly(N-isopropylacrylamide) in aqueous protic ionic liquids: kosmotropic versus chaotropic anions and their interaction with water.

We have investigated the influence of a series of triethylammonium-based protic ionic liquid-water solutions on the lower critical solution temperature (LCST) of poly(N-isopropylacrylamide) (PNIPAM). We find that kosmotropic anions lower the LCST of PNIPAM more dramatically when compared with chaotropic anions. In addition, we have probed the solvent properties of the hydrated protic ionic liquid solutions using (1)H NMR, polarity measurements, and solvatochromic analysis of the Kamlet-Taft parameters, ß and π*. We find that the hydrogen bond character--more specifically, the interactions between water and pIL--is the dominant parameter responsible for lowering the LCST of PNIPAM. We have added choline dihydrogen phosphate (choline dhp) into this study on the basis of positive results from previously reported protein folding studies using this ionic liquid.

Enhanced stabilization of the Tobacco mosaic virus using protic ionic liquids.

We report on the use of protic ionic liquids, pILs, as solvents for the solubilisation and stabilization of viruses. We show that the shelf life of the pIL stabilized tobacco mosaic virus is significantly enhanced when compared to traditional phosphate buffer. This has new opportunities for the preparation, characterization and storage of viruses and virus based technologies.

Regenerated silk fibroin using protic ionic liquids solvents: towards an all-ionic-liquid process for producing silk with tunable properties.

We have shown that protic ionic liquids, pILs, are effective coagulation solvents for the regenerated of silk fibroin, RSF. We show that the choice of pIL has a dramatic effect on the composition of the RSF. Additionally the use of pILs as the coagulator eliminates the need for volatile organic solvents in silk processing.

A protic ionic liquid attenuates the deleterious actions of urea on α-chymotrypsin.

We present a biocompatible ionic liquid, triethyl ammonium acetate (TEAA), that attenuates the denaturation action of a non-ionic chaotrope, urea, on the industrially relevant proteolytic enzyme α-chymotrypsin.

The impact of ionic liquids on amyloid fibrilization of Aß16-22: tuning the rate of fibrilization using a reverse Hofmeister strategy.

We have shown that the amyloid fibrilization of Aß16-22 follows a reverse hofmeister trend in pILs. Fast fibrilization rates of seconds can be achieved.

Structure inducing ionic liquids-enhancement of alpha helicity in the Abeta(1-40) peptide from Alzheimer's disease.

We have studied the impact of ionic liquid solvents on the structure of the Abeta(1-40) peptide from Alzheimer's disease and found that ionic liquid solvents were able to induce a conformational change in the structure of the Abeta(1-40) peptide. This conformational change impacts the self-assembly of the peptide into amyloid fibrils.