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.

Dynamic Nanohybrid-Polysaccharide Hydrogels for Soft Wearable Strain Sensing.

Electroconductive hydrogels with stimuli-free self-healing and self-recovery (SELF) properties and high mechanical strength for wearable strain sensors is an area of intensive research activity at the moment. Most electroconductive hydrogels, however, consist of static bonds for mechanical strength and dynamic bonds for SELF performance, presenting a challenge to improve both properties into one single hydrogel. An alternative strategy to successfully incorporate both properties into one system is via the use of stiff or rigid, yet dynamic nano-materials. In this work, a nano-hybrid modifier derived from nano-chitin coated with ferric ions and tannic acid (TA/Fe@ChNFs) is blended into a starch/polyvinyl alcohol/polyacrylic acid (St/PVA/PAA) hydrogel. It is hypothesized that the TA/Fe@ChNFs nanohybrid imparts both mechanical strength and stimuli-free SELF properties to the hydrogel via dynamic catecholato-metal coordination bonds. Additionally, the catechol groups of TA provide mussel-inspired adhesion properties to the hydrogel. Due to its electroconductivity, toughness, stimuli-free SELF properties, and self-adhesiveness, a prototype soft wearable strain sensor is created using this hydrogel and subsequently tested.

Rational Design of Mussel-Inspired Hydrogels with Dynamic Catecholato-Metal Coordination Bonds.

Nature has often been the main source of inspiration for designing smart functional materials. As an example, mussels can attach to almost any wet surfaces, for example, wood, rocks, metal, etc., due to the presence of catechols containing amino acid 3,4-dihydroxyphenyl-l-alanine (DOPA). Fabrication of mussel-inspired hydrogels using dynamic catecholato-metal coordination bonds has recently been in the limelight because of the hydrogels' ease of gelation, interesting self-healing, self-recovery, adhesiveness, and pH-responsiveness, as well as shear-thinning and mechanical properties. Mussel inspired hydrogels take advantage of catechols, for example, DOPA in the blue mussel, to undergo catecholatometal gelation through coordination chemistry. This review explores the latest developments in the fabrication of such hydrogels using catecholato-metal coordination bonds, and discusses their potential applications in sensors, flexible electronics, tissue engineering, and wound dressing. Moreover, current challenges and prospects of such hydrogels are discussed. The main focus of this paper is on providing a deeper understanding of this growing field in terms of chemistry, physics, and associated properties.

High Performance Carbon Fiber Structural Batteries Using Cellulose Nanocrystal Reinforced Polymer Electrolyte.

In recent years, structural batteries have received great attention for future automotive application in which a load-bearing car panel is used as an energy storage. However, based on the current advances, achieving both high ionic conductivity and mechanical performance has remained a challenge. To address this challenge, this study introduces a cellulose nanocrystal (CNC) reinforced structural battery electrolyte (CSBE) consisting of CNC, triethylene glycol dimethyl ether (TriG) electrolyte containing a quasi-solid additive, e.g., cyclohexanedimethanol (CHDM), in a vinyl ester polymer. This green and renewable CSBE electrolyte system was in situ polymerized via reaction induced phase transition to form a high performance multidimensional channel electrolyte to be used in structural carbon fiber-based battery fabrication. The effect of various concentrations of CNC on the electrolyte ionic conductivity and mechanical properties was obtained in their relation to intermolecular interactions, interpreted by FTIR, Raman, Li NMR results. Compared to the neat SBE system, the optimized CSBE nanocomposite containing 2 wt % CNC shows a remarkable ionic conductivity of 1.1 × 10-3 S cm-1 at 30 °C, which reveals ∼300% improvement, alongside higher thermal stability. Based on the FTIR, Raman, Li NMR results, the content of CNC in the CSBE structure plays a crucial role not only in the formation of cellulose network skeleton but also in physical interaction with polymer matrix, providing an efficient Li+ pathway through the electrolyte matrix. The carbon fiber composite was fabricated by 2 wt % CNC reinforced SBE electrolyte to evaluate as a battery half-cell. The results demonstrated that by addition of 2 wt % CNC into SBE system, 7.6% and 33.9% improvements were achieved in specific capacity at 0.33 C and tensile strength, respectively, implying outstanding potential of ion conduction and mechanical load transfer between the carbon fibers and the electrolyte.

Dynamic nanocellulose hydrogels: Recent advancements and future outlook.

Nanocellulose is of great interest in material science nowadays mainly because of its hydrophilic, renewable, biodegradable, and biocompatible nature, as well as its excellent mechanical strength and tailorable surface ready for modification. Currently, nanocellulose is attracting attention to overcome the current challenges of dynamic hydrogels: robustness, autonomous self-healing, and self-recovery (SELF) properties simultaneously occurring in one system. In this regard, this review aims to explore current advances in design and fabrication of dynamic nanocellulose hydrogels and elucidate how incorporating nanocellulose with dynamic motifs simultaneously improves both SELF and robustness of hydrogels. Finally, current challenges and prospects of dynamic nanocellulose hydrogels are discussed.

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.

Time Dependent Structure and Property Evolution in Fibres during Continuous Carbon Fibre Manufacturing.

Here we report on how residence time influences the evolution of the structure and properties through each stage of the carbon fibre manufacturing process. The chemical structural transformations and density variations in stabilized fibres were monitored by Fourier Transform Infrared Spectroscopy and density column studies. The microstructural evolution and property variation in subsequent carbon fibres were studied by X-ray diffraction and monofilament tensile testing methods, which indicated that the fibres thermally stabilized at longer residence times showed higher degrees of structural conversion and attained higher densities. Overall, the density of stabilized fibres was maintained in the optimal range of 1.33 to 1.37 g/cm³. Interestingly, carbon fibres manufactured from higher density stabilized fibres possessed lower apparent crystallite size (1.599 nm). Moreover, the tensile strength of carbon fibres obtained from stabilized fibres at the high end of the observed range (density: 1.37 g/cm³) was at least 20% higher than the carbon fibres manufactured from low density (1.33 g/cm³) stabilized fibres. Conversely, the tensile modulus of carbon fibres produced from low density stabilized fibres was at least 17 GPa higher than those from high density stabilized fibres. Finally, it was shown that there is potential to customize the required properties of resultant carbon fibres suiting specific applications via careful control of residence time during the stabilization stage.

Biocompatibility and modification of the protein-based adhesive secreted by the Australian frog Notaden bennetti.

When provoked, Notaden bennetti frogs secrete a proteinaceous exudate, which rapidly forms a tacky and elastic glue. This material has potential in biomedical applications. Cultured cells attached and proliferated well on glue-coated tissue culture polystyrene, but migrated somewhat slower than on uncoated surfaces. In organ culture, dissolved glue successfully adhered collagen-coated perfluoropolyether lenses to debrided bovine corneas and supported epithelial regrowth. Small pellets of glue implanted subcutaneously into mice were resorbed by surrounding tissues, and all of the animals made a full recovery. An initial but transient skin necrosis at the implant site was probably caused by some of the potentially toxic metabolites present in the frog secretion; these include sterols and carotenoids, as well as fatty alcohols, aldehydes, ketones, acids, and aromatic compounds. Removal of the carotenoid pigments did not significantly alter the glue's material properties. In contrast, peroxidase treatment of dissolved glue introduced unnatural crosslinks between molecules of the major protein (Nb-1R) and resulted in the formation of a soft hydrogel, which was very different to the original material.