Investigation of progress of reactions and evolution of radial heterogeneity in the initial stage of thermal stabilization of PAN precursor fibres

The relationship between process parameters and structural transformations in the fibres at each stage of the carbon fibre manufacturing process play a crucial role in developing high performance carbon fibres. Here we report a systematic method which uses the combination of Taguchi approach and scientific evaluation techniques to establish these relationships for the initial stage of thermal stabilization. Density, cyclization index and fraction of reacted nitriles of a precursor containing acrylonitrile, methacrylate and itaconic acid (AN/MA/IA) were used to assess the progress of stabilization in the fibres with respect to various combinations of process parameters. The extent of progress of stabilization improved with increase in temperature (from 225 to 235 °C) and time (from 12 to 24 min) whereas an opposite trend was observed with increase in the tension on the fibres from (1600-2550 cN). According to optical microscopy, radial heterogeneity was observed in the fibres treated at 235 °C. Interestingly, we were able to identify the existence of heterogeneous modulus distribution from skin to core of the precursor fibres which was further transferred to treated fibres. The overall radial modulus of treated fibres was higher than the precursor fibres. In contrast to the literature, the fracture morphology of the fibre samples indicated that initiation of crack is caused by surface defects rather than radial heterogeneity.

One-step amino-functionalization of milled carbon fibre for enhancement of thermo-physical properties of epoxy composites

Development of new chemical approaches for preparation of engineered carbon-based fillers is critical for high-performance applications. Herein, an efficient method for covalent functionalization of polyacrylonitrile-based carbon fibre through azo radical addition under mild condition is demonstrated. In this way, isobutyronitrile radicals in situ produced from thermal decomposition of 2,2′-azobisisobutyronitrile (AIBN), were covalently grafted on milled carbon fibre (MCF) surface, assisted by microwave irradiation, as evidenced by FTIR, Raman, and TGA analysis. The grafted isobutyronitriles on MCF surface (n-MCF) were applied for further MCF amino-functionalization (a-MCF) via nucleophilic reaction of an amine-rich compound. Then, both pure MCF and a-MCF were incorporated into epoxy matrix; and its curing process and thermo-physical properties were investigated using DSC, rheometry, DMA, TGA, and flexural analysis. The Tg and flexural strength of epoxy/a-MCF composites, compared to epoxy/MCF, increased by ∼3.5% and ∼10.2%, resulting from good adhesion between a-MCF and epoxy matrix which confirmed by SEM observations.

A systematic investigation into a novel method for preparing carbon fibre–carbon nanotube hybrid structures

By electrospraying solvent dispersed carbon nanotubes (CNTs) with a binder onto carbon fibre (CF), hybrid structures, with an end aim to improve interfacial bonding in composites, were formed. The electrospray parameters controlling the modification of the CNT morphologies were studied. High-speed camera observations found applied voltage was critical for determining spray mode development. Electric field simulations revealed a concentrated electric field region around each fibre. Both voltage and distance played an important role in determining the CNT morphology by mediating anchoring strength and electric field force. The forming mechanism investigation of different surface morphologies suggested that binder with appropriate wetness gives freedom to the CNTs, allowing them to orientate radially from the CF surface. Linear density (LD) measurements and thermogravimetric analysis revealed that a 10 min coating increased the LD of a single CF filament by up to 31.7% while a 1 h treatment increased fibre bundle mass by 1%.

Cellulose-derived carbon fibers produced via a continuous carbonization process: investigating precursor choice and carbonization conditions

Here, the carbonization of two Lyocell type regenerated cellulose fibres is reported. Commercially available Lyocell as well as the experimental Lyocell type fibre known as Ioncell-F spun from the ionic liquid 1,5-diazabicyclo[4.3.0]non-5-ene-1-ium acetate ([DBNH]OAc) is investigated, which supports higher draw ratio and thus improves precursor mechanical properties. Lyocell fibres are known to have improved mechanical properties over other regenerated cellulose fibres and are therefore considered to be better carbon fibre precursor candidates. The Lyocell fibres used in this study are carbonized utilizing a scaled down identical replica of an in use carbon fibre line. The importance of this is the ability to assess the performance of the Lyocell fibres under more realistic continuous carbonization processing conditions. The tensile properties, morphology, and chemical composition of all fibres are determined. It is shown that by changing the carbonization temperature and atmosphere fibres with different mechanical properties and diameter can be produced. Elemental analysis confirms that each fibre has a carbon content of ≥90%.

Conducting gel-fibres based on carrageenan, chitosan and carbon nanotubes

A simple continuous flow wet-spinning method for assembling fibres consisting of two oppositely charged biopolymers (chitosan and carrageenan) and carbon nanotubes is reported. It was observed that the order in which the biopolymers are added, i.e. spinning chitosan into one of the carrageenans (or vice versa), affects the fibre composition as well as the resulting electrical and mechanical properties. The addition of carbon nanotubes into the fibres was found to improve Young's modulus values coupled with a significant improvement in the electrical conductivity by up to 6 orders of magnitude.

Carbon nanotubes reinforced electrospun polymer nanofibres

With the rapid development in nanoscience and nanotechnology, there is an ever increasing demand for polymer fibres of diameters down to a nanometre scale having multiple functionalities. Electrospinning, as a simple and efficient nanofibre-making technology, has been used to produce polymer nanofibres for diverse applications. Electrospun nanofibres
based on polymer/carbon nanotube (CNT) composites are very attractive multifunctional nanomaterials because they combine the remarkable mechanical and electronic properties of CNTs and the confinement-enhanced CNTs alignment within the nanofibre structure, which could greatly improve the fibre mechanical, electrical and thermal properties. In this chapter, we summarise recent research progress on electrospun CNTs/polymer nanofibres, with an emphasis on fibre mechanical properties and structure-property attributes. Outlook towards the challenge and future directions in this field is also presented.

Fabrication and characterisation of carbon nanofibres from cellulose nanofibres

Carbon nanofibers were fabricated by pyrolysis of plant-based cellulose nanofibers. The findings demonstrate the possibility of obtaining strong and commercially competitive carbon nanofibers that are used in many industries including aerospace, automobile and electronics.

The surface finish of thermally aged carbon fibre reinforced composites using E-glass as a surface barrier

This work investigated the effect of woven E-glass mass (25 g/m2, 50 g/m2, 85 g/m2, 135 g/m2) on the painted surface finish of various thermoset (EPIKOTETM RIM935, EPIKOTETM 04434, Ultratec LpTM ES300, Ultratec LpTM SPV6035) carbon fibre composite laminates, before and after aging at 95 °C for 168 h. The as-moulded laminate surfaces were evaluated using surface profilometry techniques and the painted and aged surfaces were evaluated using a wave-scan distinctness of image (DOI) instrument. It was found that the 25 g/m2 E-glass surface layer assisted with reducing the roughness of the as-moulded surfaces and the long-term waviness of the painted surfaces due to the increase in resin-richness at the surface. The EPIKOTETM 04434 resin system that contained diglycidyl ether of bisphenol F (DGEBF) epoxy had the least change in long-term waviness with thermal aging due to the rigid fluorene-based backbone in comparison to the diglycidyl ether of bisphenol A (DGEBA) systems.

A novel approach to functionalise pristine unsized carbon fibre using in situ generated diazonium species to enhance interfacial shear strength

Complex molecules have been successfully grafted onto the surface of unsized carbon fibre, a heterogeneous material which is a challenge to functionalise. The in situ generation of highly reactive phenyldiazo-species from their corresponding anilines was employed to achieve this task. The success of an initial proof-of-concept study (bearing a nitro moiety) supported by X-ray Photoelectron Spectroscopy (XPS) and physical characterisation, led to the design and synthesis of a more complex compound possessing a pendant amine moiety which could theoretically react with an epoxide based resin. After attachment to unsized oxidised fibres, analysis by XPS of the resulting fibres (fluorine used as an XPS tag) indicated a marked difference in functionalisation success which was attributed to steric factors, shown to be critical in influencing the attachment of the phenyldiazo-intermediate to the carbon fibre surface. Analysis of key fibre performance parameters of these fibres showed no change in elastic modulus, strength, surface topography or microscopic roughness when compared to the control unsized oxidised fibres. The functionalised fibres did however show a large increase in coefficient of friction. Single fibre fragmentation tests indicated a marked increase in interfacial shear strength, which was attributed to the pendent amine functionalities interacting with the epoxy resin.

Continuous polyacrylonitrile nanofiber yarns: Preparation and dry-drawing treatment for carbon nanofiber production

Precursor fibers with diameters in nanometer scale and highly aligned polymer chains in fibers are highly promising for the preparation of high-performance carbon nanofibers, but are challenging to make. In this study, we demonstrate for the first time that a carbon nanofiber precursor can be prepared by the electrospinning of polyacrylonitrile into a nanofiber yarn and by the subsequent drawing treatment of the yarn in dry conditions. The yarn shows excellent drawing performance, which can be drawn evenly up to 6 times of its original length without breaking. The drawing treatment improves the yarn and fiber uniformity, polymer chain orientation within the fibers, as well as yarn tension and modules, but shows decreased yarn and fiber diameter and elongation at break. The drawing temperature and force show influences on the drawing behavior. The highest strength and modules (362 ± 37 MPa and 9.2 ± 1.4 GPa, respectively) are found on the yarn drawn by 5 times its length, which increased by 800% and 1800% when compared to the as-spun yarn. Through un-optimized stabilization and carbonization treatments, we further demonstrate that the carbonized nanofiber yarn shows comparable tensile properties as the commercial carbon fibers. Electrospun nanofiber yarns may form next generation precursors for making high performance carbon fibers. This journal is

A facile approach to spinning multifunctional conductive elastomer fibres with nanocarbon fillers

Electrically conductive elastomeric fibres prepared using a wet-spinning process are promising materials for intelligent textiles, in particular as a strain sensing component of the fabric. However, these fibres, when reinforced with conducting fillers, typically result in a compromise between mechanical and electrical properties and, ultimately, in the strain sensing functionality. Here we investigate the wet-spinning of polyurethane (PU) fibres with a range of conducting fillers such as carbon black (CB), single-walled carbon nanotubes (SWCNTs), and chemically converted graphene. We show that the electrical and mechanical properties of the composite fibres were strongly dependent on the aspect ratio of the filler and the interaction between the filler and the elastomer. The high aspect ratio SWCNT filler resulted in fibres with the highest electrical properties and reinforcement, while the fibres produced from the low aspect ratio CB had the highest stretchability. Furthermore, PU/SWCNT fibres presented the largest sensing range (up to 60% applied strain) and the most consistent and stable cyclic sensing behaviour. This work provides an understanding of the important factors that influence the production of conductive elastomer fibres by wet-spinning, which can be woven or knitted into textiles for the development of wearable strain sensors.