Preparation and Properties of Carbon Fiber/Carbon Nanotube Wet-Laid Composites

Smart Cementitious Sensors with Nano-, Micro-, and Hybrid-Modified Reinforcement: Mechanical and Electrical Properties

The current paper presents the results of an experimental study of carbon nano-, micro-, and hybrid-modified cementitious mortar to evaluate mechanical performance, energy absorption, electrical conductivity, and piezoresistive sensibility. Three amounts of single-walled carbon nanotubes (SWCNTs), namely 0.05 wt.%, 0.1 wt.%, 0.2 wt.%, and 0.3 wt.% of the cement mass, were used to prepare nano-modified cement-based specimens. In the microscale modification, 0.05 wt.%, 0.5 wt.%, 1.0 wt.% carbon fibers (CFs) were incorporated in the matrix. The hybrid-modified cementitious specimens were enhanced by adding optimized amounts of CFs and SWCNTs. The smartness of modified mortars, indicated by their piezoresistive behavior, was investigated by measuring the changes in electrical resistivity. The effective parameters that enhance the composites' mechanical and electrical performance are the different concentrations of reinforcement and the synergistic effect between the types of reinforcement used in the hybrid structure. Results reveal that all the strengthening types improved flexural strength, toughness, and electrical conductivity by about an order of magnitude compared to the reference specimens. Specifically, the hybrid-modified mortars presented a marginal reduction of 1.5% in compressive strength and an increase in flexural strength of 21%. The hybrid-modified mortar absorbed the most energy, 1509%, 921%, and 544% more than the reference mortar, nano-modified mortar, and micro-modified mortar, respectively. The change rate of impedance, capacitance, and resistivity in piezoresistive 28-day hybrid mortars improved the tree ratios by 289%, 324%, and 576%, respectively, for nano-modified mortars and by 64%, 93%, and 234%, respectively, for micro-modified mortars.

Green and Low-Cost Natural Lignocellulosic Biomass-Based Carbon Fibers—Processing, Properties, and Applications in Sports Equipment: A Review

At present, high-performance carbon fibers (CFs) are mainly produced from petroleum-based materials. However, the high costs and environmental problems of the production process prompted the development of new precursors from natural biopolymers. This review focuses on the latest research on the conversion of natural lignocellulosic biomass into precursor fibers and CFs. The influence of the properties, advantages, separation, and extraction of lignin and cellulose (the most abundant natural biopolymers), as well as the spinning process on the final CF performance are detailed. Recent strategies to further improve the quality of such CFs are discussed. The importance and application of CFs in sports equipment manufacturing are briefly summarized. While the large-scale production of CFs from natural lignocellulosic biomass and their applications in sports equipment have not yet been realized, CFs still provide a promising market prospect as green and low-cost materials. Further research is needed to ensure the market entry of lignocellulosic biomass-based CFs.

Process Optimization for Manufacturing PAN-Based Conductive Yarn with Carbon Nanomaterials through Wet Spinning

This study aimed to manufacture PAN-based conductive yarn using a wet-spinning process. Two types of carbon nanomaterials, multiwall carbon nanotubes (MWCNT) and carbon nanofiber (CNF), were used alone or in a mixture. First, to derive the optimal composite solution condition for the wet spinning process, a composite solution was prepared with carbon nanomaterials of the same total mass weight (%) and three types of mechanical stirring were performed: mechanical stirring, ultra-sonication, and ball milling. A ball milling process was finally selected by analyzing the viscosity. Based on the above results, 8, 16, 24, and 32 wt% carbon nanomaterial/PAN composite solutions were prepared to produce wet spinning-based composite films before preparing a conductive yarn, and their physical and electrical properties were examined. By measuring the viscosity of the composite solution and the surface resistance of the composite film according to the type and content of carbon nanomaterials, a suitable range of viscosity was found from 10³ cP to 10⁵ cP, and the electrical percolation threshold was from 16 wt% carbon nanomaterial/PAN, which showed a surface resistance of 10⁶ Ω/sq or less. Wet spinning was possible with a PAN-based composite solution with a high content of carbon nanomaterials. The crystallinity, crystal orientation, tenacity, and thermal properties were improved when CNF was added up to 24 wt%. On the other hand, the properties deteriorated when CNTs were added alone due to aggregation. Mixing CNT and CNF resulted in poorer properties than with CNF alone, but superior properties to CNT alone. In particular, the electrical properties after incorporating 8 wt% CNT/16 wt% CNF into the PAN, 10⁶ Ω/cm was similar to the PAN-based conductive yarn containing 32 wt% CNF. Therefore, this yarn is expected to be applicable to various smart textiles and wearable devices because of its improved physical properties such as strength and conductivity.

Carbonaceous Materials Coated Carbon Fibre Reinforced Polymer Matrix Composites

Carbon fibre reinforced polymer composites have high mechanical properties that make them exemplary engineered materials to carry loads and stresses. Coupling fibre and matrix together require good understanding of not only fibre morphology but also matrix rheology. One way of having a strongly coupled fibre and matrix interface is to size the reinforcing fibres by means of micro- or nanocarbon materials coating on the fibre surface. Common coating materials used are carbon nanotubes and nanofibres and graphene, and more recently carbon black (colloidal particles of virtually pure elemental carbon) and graphite. There are several chemical, thermal, and electrochemical processes that are used for coating the carbonous materials onto a carbon fibre surface. Sizing of fibres provides higher interfacial adhesion between fibre and matrix and allows better fibre wetting by the surrounded matrix material. This review paper goes over numerous techniques that are used for engineering the interface between both fibre and matrix systems, which is eventually the key to better mechanical properties of the composite systems.

Enhanced Surface Energetics of CNT-Grafted Carbon Fibers for Superior Electrical and Mechanical Properties in CFRPs

Surface enhancement of components is vital for achieving superior properties in a composite system. In this study, carbon nanotubes (CNTs) were grown on carbon fiber (CF) substrates to improve the surface area and, in turn, increase the adhesion between epoxy-resin and CFs. Nickel (Ni) was used as the catalyst in CNT growth, and was coated on CF sheets via the electroplating method. Surface energetics of CNT-grown CFs and their work of adhesion with epoxy resin were measured. SEM and TEM were used to analyze the morphology of the samples. After the optimization of surface energetics by catalyst weight ratio (15 wt.% Ni), CF-reinforced plastic (CFRP) samples were prepared using the hand lay-up method. To validate the effect of chemical vapor deposition (CVD)-grown CNTs on CFRP properties, samples were also prepared where CNT powder was added to epoxy prior to reinforcement with Ni-coated CFs. CFRP specimens were tested to determine their electrical resistivity, flexural strength, and ductility index. The electrical resistivity of CNT-grown CFRP was found to be about 9 and 2.3 times lower than those of as-received CFRP and CNT-added Ni-CFRP, respectively. Flexural strength of CNT-grown Ni-CFRP was enhanced by 52.9% of that of as-received CFRP. Interestingly, the ductility index in CNT-grown Ni-CFRP was 40% lower than that of CNT-added Ni-CFRP. This was attributed to the tip-growth formation of CNTs and the breakage of Ni coating.

Synthesis, Characterization, and Analysis of Hybrid Carbon Nanotubes by Chemical Vapor Deposition: Application for Aluminum Removal

Hybrid carbon nanotubes (CNTs) are grown on biomass powder-activated carbon (bio-PAC) by loading iron nanoparticles (Fe) as catalyst templates using chemical vapor deposition (CVD) and using acetylene as carbon source, under specific conditions as reaction temperature, time, and gas ratio that are 550 °C, 47 min, and 1, respectively. Specifications of hybrid CNTs were analyzed and characterized using field emission scanning electron microscope (FESEM) with energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopic (TEM), Fourier-transform infrared (FTIR), X-ray diffraction (XRD), thermogravimetric analysis (TGA), surface area Brunauer-Emmett-Teller (BET), and zeta potential. The results revealed the high quality and unique morphologies of hybrid CNTs. Furthermore, removal and capacity of Al3+ were optimized by response surface methodology (RSM). However, the results revealed that the pseudo-second-order model well represented adsorption kinetic data, while the isotherm data were effectively fitted using a Freundlich model. The maximum adsorption capacity was 347.88 mg/g. It could be concluded that synthesized hybrid CNTs are a new cost-effective and promising adsorbent for removing Al3+ ion from wastewater.

Polyamide 6/Poly(vinylidene fluoride) Blend-Based Nanocomposites with Enhanced Rigidity: Selective Localization of Carbon Nanotube and Organoclay

Polyamide 6 (PA6)/poly(vinylidene fluoride) (PVDF) blend-based nanocomposites were successfully prepared using a twin screw extruder. Carbon nanotube (CNT) and organo-montmorillonite (30B) were used individually and simultaneously as reinforcing nanofillers for the immiscible PA6/PVDF blend. Scanning electron micrographs showed that adding 30B reduced the dispersed domain size of PVDF in the blend, and CNT played a vital role in the formation of a quasi-co-continuous PA6-PVDF morphology. Transmission electron microscopy observation revealed that both fillers were mainly located in the PA6 matrix phase. X-ray diffraction patterns showed that the presence of 30B facilitated the formation of γ-form PA6 crystals in the composites. Differential scanning calorimetry results indicated that the crystallization temperature of PA6 increased after adding CNT into the blend. The inclusion of 30B retarded PA6 nucleation (γ-form crystals growth) upon crystallization. The Young's and flexural moduli of the blend increased after adding CNT and/or 30B. 30B exhibited higher enhancing efficiency compared with CNT. The composite with 2 phr 30B exhibited 21% higher Young's modulus than the blend. Measurements of the rheological properties confirmed the development of a pseudo-network structure in the CNT-loaded composites. Double percolation morphology in the PA6/PVDF blend was achieved with the addition of CNT.