Low-Cost Carbon Fibre Derived from Sustainable Coal Tar Pitch and Polyacrylonitrile: Fabrication and Characterisation

Enhancing Graphitic Carbon Precursors from Coal Pyrolysis: A Comparative Analysis of Microwave Plasma and Conventional Thermal Upgradation Methods

This study investigates and compares the efficacy of conventional thermal pyrolysis and microwave (MW) plasma pyrolysis in upgrading coal-derived precursors. Coal samples presenting a range of ranks were pyrolyzed under various reactive and nonreactive atmospheres using a pyroprobe, with the pyrolyzates analyzed by gas chromatography-mass spectrometry (GC-MS). Comparative MW plasma tests were conducted using a modified countertop MW unit, with condensed products similarly analyzed by GC-MS. A predominant coal devolatilization product-benzene was selected for analyzing the reactive MW plasma upgradation. Results demonstrate that conventional thermal pyrolysis lacks effectiveness in upgrading the precursors. To gain insight into the underlying reasons, chemical kinetic simulations were conducted. Oppositely, reactive MW plasma pyrolysis demonstrated remarkable precursor upgradation. These condensed MW plasma pyrolysis products were then subjected to a carbonization and graphitization heat-treatment with a comprehensive graphitic quality assessment conducted using X-ray diffraction and transmission electron microscopy. After graphitization, the MW plasma-upgraded precursor produced a carbon with a crystallite size several times greater than that of the initial benzene. By MW plasma processing, the poorly graphitizable benzene precursor was transformed into a highly graphitizable precursor comparable to coal tar pitch. The underlying reasons for this significant improvement were investigated by analyzing the compositional changes in the precursor under various reactive environments.

Cost-effective carbon fiber precursor selections of polyacrylonitrile-derived blend polymers: carbonization chemistry and structural characterizations

Blending polyacrylonitrile (PAN) with plastic wastes and bio-based polymers provides a convenient and inexpensive method to realize cost-effective carbon fiber (CF) precursors. In this work, PAN-based blend precursors are investigated using ReaxFF reactive molecular dynamics simulations with respect to the formation of all-carbon rings, the evolutions of oxygen-containing and nitrogen-containing species, and the migration of carbon atoms to form turbostratic graphene. From these simulations, we identify that PAN/cellulose (CL) blend manifests the highest carbon yield and the most substantial all-carbon ring formation. This ReaxFF-based finding is confirmed by Raman and TEM experiments indicating high crystallinity for PAN/CL-derived blend CFs. We trace the pathway of gasification and carbonization of PAN/CL to elaborate the mechanism of the formation of all-carbon ring networks. We discover that the acetals of CL can catalyze the cyclization of the blend precursor, allowing for the search for CL derivatives or the other kinds of bio-based polymers with similar functionalities as alternative blends. In addition, we examine the structural characteristics using the carbon-carbon (C-C) radial distribution functions, C-C bond length distributions, and sp² C atom ratios for the four representative precursors, i.e., PAN, oxidized PAN, PAN/nylon 6,6, and PAN/CL. Our simulation results show the most extensive all-carbon ring cluster and graphitic structure growths for PAN/CL. Therefore, we propose PAN/CL as a cost-effective alternative CF precursor, since (a) CL is naturally abundant and eco-friendly for production, (b) the blend precursor PAN/CL does not require oxidation treatment, (c) PAN/CL has a high carbon yield with substantial all-carbon ring formation, and (d) PAN/CL based CFs potentially provide a mechanical property enhancement.

Electronic, Structural, and Magnetic Upgrading of Coal-Based Products through Laser Annealing

Most coal-to-product routes require complex thermal treatment to carbonize the raw materials. However, the lack of unified comparison of products made from different kinds of coals downplays the role of initial coal chemistry in high-temperature reactions. Here, we used a CO₂ laser to investigate the roles that aromatic content and maturity play in the structural evolution and doping of coals during annealing. Results show that a bituminous coal (DECS 19) with aromatic content and maturity in between higher rank, more mature anthracite (DECS 21) and lower rank, lower maturity lignite (DECS 25) leads to more graphite-like structure observed from the highest 2D peak on the Raman spectrum and conductivity (sheet resistance ∼30 ohm sq^-1) after lasing. When nitrogen dopants are incorporated with saturated urea dopants into coals through laser ablation, nitrogen preferentially incorporates at the edge sites of graphitic grains. Furthermore, oxide nanoparticles can be incorporated into the graphitic backbone of coal to modify their electronic and magnetic properties through laser annealing. Leveraging tunable magnetic behavior, we demonstrate a soft actuator using both conductive and magnetic coal-Fe/Co oxide. Through laser annealing, we propose a paradigm to understand and control coal chemistry toward flexible and tunable doping and magnetism.

Effects of Bromination-Dehydrobromination on the Microstructure of Isotropic Pitch Precursors for Carbon Fibers

In this work, isotropic pitch precursors are synthesized by the bromination-debromination method with ethylene bottom oil (EO) as the raw material and bromine as the initiator for pitch formation and condensation reactions. The aggregation structure, molecular weight distribution, and molecular structure of isotropic pitch precursors are characterized by thermal mechanical analyzer (TMA), MALDI TOF-MS, and ¹³C NMR, respectively, for revealing the mechanism of synthesis of isotropic pitch precursors. The results show that at low bromine concentrations, polycyclic aromatic hydrocarbons (PAHs) were mainly ordered in cross-linked structures by bromination-debromination through substitution reactions of side chains. The condensed reactivity can be improved by the effect of bromine, meaning that condensation reaction was aggravated by the method of bromination-dehydrobromination. In the presence of excess bromine, the cross-linked stereo structure of PAHs changed to the planar structure of condensed PAHs, which was not conducive to the subsequent spinning and preparation of carbon fibers.

A Sustainable Approach to the Low-Cost Recycling of Waste Glass Fibres Composites towards Circular Economy

For practical applications, both environmental and economic aspects are highly required to consider in the development of recycling of fibre reinforced polymers (FRPs) encountering their end-of-life. Here, a sustainable, low cost, and efficient approach for the recycling of the glass fibre (GF) from GF reinforced epoxy polymer (GFRP) waste is introduced, based on a microwave-assisted chemical oxidation method. It was found that in a one-step process using microwave irradiation, a mixture of hydrogen peroxide (H2O2) as a green oxidiser and tartaric acid (TA) as a natural organic acid could be used to decompose the epoxy matrix of a waste GFRP up to 90% yield. The recycled GFs with ~92.7% tensile strength, ~99.0% Young’s modulus, and ~96.2% strain-to-failure retentions were obtained when compared to virgin GFs (VGFs). This short microwave irradiation time using these green and sustainable recycling solvents makes this a significantly low energy consumption approach for the recycling of end-of-life GFRPs.

Structural Characterisation and Chemical Stability of Commercial Fibrous Carbons in Molten Lithium Salts

The growing trend towards sustainable energy production, while intermittent, can meet all the criteria of energy demand through the use and development of high-performance thermal energy storage (TES). In this context, high-temperature hybrid TES systems, based upon the combination of fibrous carbon hosts and peritectic phase change materials (PCMs), are seen as promising solutions. One of the main conditions for the operational viability of hybrid TES is the chemical inertness between the components of the system. Thus, the chemical stability and compatibility of several commercial carbon felts (CFs) and molten lithium salts are discussed in the present study. Commercial CFs were characterised by elemental analysis, X-ray diffraction (XRD) and Raman spectroscopy before being tested in molten lithium salts: LiOH, LiBr, and the LiOH/LiBr peritectic mixture defined as our PCM of interest. The chemical stability was evaluated by gravimetry, gas adsorption and scanning electron microscopy (SEM). Among the studied CFs, the materials with the highest carbon purity and the most graphitic structure showed improved stability in contact with molten lithium salts, even under the most severe test conditions (750 °C). The application of the Arrhenius law allowed calculating the activation energy (in the range of 116 to 165 kJ mol^-1), and estimating the potential stability of CFs at actual application temperatures. These results confirmed the applicability of CFs as porous hosts for stabilising peritectic PCMs based on molten lithium salts.