Sized Carbon Fibers Research Articles

Interfacial property enhancement of carbon fiber/epoxy composites via constructing a gradual modulus interphase with a waterborne bio‐based spiro diacetal epoxy emulsion

AbstractIn this article, to explore the utilization of bio‐based epoxy resin in the preparation of sizing agents for carbon fibers (CFs), a bio‐based epoxy emulsion (S‐P‐S) derived from spiro diacetal epoxy (SDE) resin was prepared and compared to the traditional diglycidyl ether of bisphenol A (DGEBA) based emulsion (D‐P‐D) and a mixed emulsion of S‐P‐S and D‐P‐D (S‐P‐S&D‐P‐D). The CF sized with S‐P‐S (CF‐(S‐P‐S)) showed improved surface oxygen content (22.86%) and roughness (40.9 nm), enhancing wettability and interfacial bonding between the fiber and the matrix. Nanoindentation test and AFM results showed the enhanced interfacial stiffness and a gradual modulus interphase with a thickness of 381 nm in CF‐(S‐P‐S) reinforced epoxy resin composite (CF‐(S‐P‐S)/EP). Therefore, the resulting CF‐(S‐P‐S)/EP composite possesses the best mechanical properties, with the transverse fiber bundle tensile (TFBT) strength of 27.3 ± 1.45 MPa and the interfacial shear strength (IFSS) of 85.6 ± 8.26 MPa. These results highlight the potential of the SDE‐based emulsion (S‐P‐S) to enhance the interfacial properties and mechanical performance of CF/EP composite, offering a sustainable alternative to conventional petroleum‐based epoxy resins.Highlights Emulsion (S‐P‐S) was prepared using spiro diacetal epoxy (SDE) for carbon fiber sizing. Properties of S‐P‐S sized CF (CF‐(S‐P‐S)) and its composite were evaluated. Spiro diacetal structure created a gradual modulus interphase in CF‐(S‐P‐S)/EP. The interfacial properties of the CF‐(S‐P‐S)/EP composite were greatly improved. Bio‐based SDE resin showed promise for optimizing carbon fiber composite interphase.

Preparation of unsaturated self-emulsifying polyester sizing agents for improving interfacial and mechanical properties of carbon fiber/vinyl ester resin composites

In order to promote the interfacial adhesion between carbon fiber and vinyl ester matrix, a series of unsaturated self-emulsifying anionic polyester sizing agents were designed. The results indicated that the sizing agents exhibited a uniform particle size distribution at the nanometer level and demonstrated favorable thermal stability below 200 °C. As the content of double bonds of sizing agents increases, the glass transition temperature also increases, and the moisture absorption of sized carbon fiber decreases. The carbon fiber surface becomes smoother after sizing. Moreover, the interlaminar shear strength and interfacial shear strength increased by 18.8 % and 43.4 %, respectively, compared to the commercial carbon fiber. This is mainly due to the unsaturated bonds in the sizing agent react with the free radicals on the surface of the carbon fiber, which enhance the interface bonding strength between the sizing agent and the surface of the carbon fiber and the vinyl ester matrix.

Nanomaterial-Enhanced Sizings: Design and Optimisation of a Pilot-Scale Fibre Sizing Line

This study focuses on the development of a pilot-scale sizing line, including its initial design and installation, operational phases, and optimization of key process parameters. The primary objective is the identification of critical parameters for achieving a uniform sizing onto the fibres and the determination of optimal conditions for maximum production efficiency. This investigation focused on adjusting the furnace desizing temperature for the removal of commercial sizing, adjusting the drying temperature, as well as optimizing the corresponding residence time of carbon fibres passing through the furnaces. The highest production rate, reaching 1 m sized carbon fibres per minute, was achieved by employing a desizing temperature of 550 °C, a drying temperature of 250 °C, and a residence time of 1 min. Furthermore, a range of sizing solutions was investigated and formulated, exploring carbon-based nanomaterial types with different surface functionalizations and concentrations, to evaluate their impact on the surface morphology and mechanical properties of carbon fibres. In-depth analyses, including scanning electron microscopy and contact angle goniometry, revealed the achievement of a uniform coating on the carbon fibre surface, leading to an enhanced affinity between fibres and the polymeric epoxy matrix. The incorporation of nanomaterials, specifically N2-plasma-functionalized carbon nanotubes and few-layer graphene, demonstrated notable improvements in the interfacial shear properties (90% increase), verified by mechanical and push-out tests.

L‐Cysteine‐Encapsulated MXene Nanosheet Possessing Ultra‐Antioxidation in Aqueous Suspension for Electrophoretic Deposition Assisted Carbon‐Fiber‐Surface Modification

AbstractWith recent progress in 2D materials, Ti3C2Tx MXene featured high metallic electrical conductivity, high electromagnetic interference shielding effectiveness, and super in‐plane stiffness, exhibits unique advantages in many fields, but is rarely applied as a sizing agent in long‐time continuous processing of carbon fiber sizing because of its poor ambient stability in aqueous suspension. Herein, a new strategy to chemically encapsulate the reactive sites of MXene nanosheet with l‐cysteine for restricting the attacking of water and/or oxygen in aqueous suspension is proposed. Based on the ultra‐antioxidation, polarity, and electrical properties of l‐cysteine‐encapsulated Ti3C2Tx MXene (LC‐MX) nanosheet, the LC‐MX, even if aging for weeks in aqueous suspension, can be deposited on the surface of high‐modulus carbon fiber (HMCF) uniformly via the electrophoretic deposition assisted sizing. Benefiting from the enhanced surface energy, wettability, and roughness of LC‐MX‐sized HMCF (HMCF‐LCMX) relative to that of unsized one (U‐HMCF), the interfacial property of HMCF‐LCMX/epoxy (EP) composites is also improved, for which the interlayer shear strength (ILSS) of the composite reached 88.5 MPa, 52.8% higher than that of U‐HMCF/EP composite (57.9 MPa). This work makes an essential step toward the application of ultra‐stable MXene nanosheet suspension in large‐scale continuous carbon fiber sizing.

Novel stable aqueous emulsion of vinyl sizing agents for strong adhesion force between carbon fiber and vinyl resin

The sizing process is the best surface modification method to improve the interfacial properties of carbon fiber reinforced resin composites. In order to reinforce the interfacial adhesion of carbon fiber(CF)/vinyl resin (VE) composites, one novel emulsifying main slurry (NYDA) and resin (NE) were designed and synthesized from the view of the covalent bond between the CF and VE. The slurry NY-NE (2 wt% emulsion) exhibited excellent storage stability for three months. For introducing abundant active functional groups (C=C) to the NY-NE sized carbon fibers (NCF) surface, the interlaminar shear strength (ILSS) of NCF/VE composites (62.44 MPa) has increased by 69.31 % compared with unsizing carbon fiber (UCF)/VE composites (36.88 MPa). Moreover, the interfacial adhesion between CF and VE was also enhanced by the formation of C=C groups on the CFs surface to react with the VE effectively, which reinforced the interfacial layer to well transfer the load among the composite resin.

Effects on the Thermo-Mechanical and Interfacial Performance of Newly Developed PI-Sized Carbon Fiber-Polyether Ether Ketone Composites: Experiments and Molecular Dynamics Simulations.

In this study, polyether ether ketone (PEEK) composites reinforced with newly developed water-dispersible polyimide (PI)-sized carbon fibers (CFs) were developed to enhance the effects of the interfacial interaction between PI-sized CFs and a PEEK polymer on their thermo-mechanical properties. The PI sizing layers on these CFs may be induced to interact vigorously with the p-phenylene groups of PEEK polymer chains because of increased electron affinity. Therefore, these PI-sized CFs are effective for improving the interfacial adhesion of PEEK composites. PEEK composites were reinforced with C-CFs, de-CFs, and PI-sized CFs. The PI-sized CFs were prepared by spin-coating a water-dispersible PAS suspension onto the de-CFs, followed by heat treatment for imidization. The composites were cured using a compression molding machine at a constant temperature and pressure. Atomic force and scanning electron microscopy observations of the structures and morphologies of the carbon fiber surfaces verified the improvement of their thermo-mechanical properties. Molecular dynamics simulations were used to investigate the effects of PI sizing agents on the stronger interfacial interaction energy between the PI-sized CFs and the PEEK polymer. These results suggest that optimal amounts of PI sizing agents increased the interfacial properties between the CFs and the PEEK polymer.

Exploration of the Effect of Carbon Fiber Ratio and Dimensions on Electrical Conductivity in Mortars

This study was carried out on Class F and C fly ash reinforced, carbon fiber added mortar samples as a substitute for PÇ42,5 cement. Carbon fiber was added in different sizes at rates of 0.5%, 1%, and 3% in order to investigate the effects of the size and ratio of carbon fiber on electrical conductivity. 33 different series were formed such as obtained Class F; without fly ash 10%, 20% and Class C; without fly ash, 10%, 20% with samples without carbon fiber and with carbon fiber having dimensions 5 mm and 10 mm. The water/cement ratio was prepared to take the value of 22-23cm in the flow table test.,A viscosity regulator of 0.1% of the fine material was used in order to ensure homogeneous distribution of carbon fiber in the mortar. 3 samples were prepared for each series in order to reduce the margin of error. Electrical conductivity, compressive and tensile strength tests were applied to the oven dry and naturally moist conditions of the samples that completed their 7, 28 and 56 days curing periods. Increasing the carbon fiber size increased the tensile strengths and increasing the carbon fiber ratio increased the tensile strengths. It has been observed that carbon fiber increases the electrical conductivity, but the conductivity decreases depending on time, and as the sizes and proportions of the carbon fiber fibers increase, the compressive strength decreases due to the void effect in the mortar, while the compressive strength increases with the increase in the fly ash ratio. The microstructure and carbon fiber distribution of the samples were examined using SEM (Scanning Electron Microscopy) and it was seen that the carbon fiber distribution was in a way that supports the electrical conductivity measurement. The study allowed the size and proportion effect of carbon fiber in mortars to be compared with C and Class F reinforced mortar samples.

Using a carbon fiber sizing to tailor the interface-interphase of a carbon nanotube-polymer system

The primary goal of this work is to integrate a critical step (sizing application to fiber) of conventional carbon fiber-reinforced composite (CFRPs) manufacturing to carbon nanotube composite fabrication. A polyimide-based (Hydrosize HP 1632) sizing agent was used in studying the effect of sizing on interface-interphase properties of the CNT-BMI composite system. The effect of CNT and degree of functionalization and defects (DOFD) of CNTs in the cure kinetics and reaction of polyimide-based sizing was investigated via DSC and XPS analysis. The DSC results showed that the presence of CNTs changes the cure kinetics of the sizing agent, and functionalized CNTs have the most prominent effect compared to unfunctionalized CNTs as it changes the endothermic curing of pristine sizing to exothermic curing by addition of 25 wt% functionalized CNTs. Then the effect of sizing in CNT on the CNT/BMI composite interface-interphase was investigated by studying the cure kinetics of the high strength BMI matrix. Thermomechanical properties, molecular heterogeneity, and molecular hierarchy of the nanocomposite were studied and presented. The outcome of this study demonstrates the CNTs with sizing can significantly alter the cure reactions of the resin as well as the structure and thermo-mechanical properties of the CNT polymer nanocomposites.

Interface Properties of Epoxy and Polyurethane Mutually Sized Carbon Fiber Reinforced Composites

Interface Properties of Epoxy and Polyurethane Mutually Sized Carbon Fiber Reinforced Composites

Fiber-matrix adhesion between high-density polyethylene and carbon fiber

Carbon fiber reinforced polyethylene composites have garnered recent interest in many industrial fields owing to their inherent benefits of excellent chemical and corrosion resistance, and processing ease. The interfacial strength between polyethylene and carbon fiber has been understudied to this point but it is critical to the performance of these new composite parts. In this study the apparent interfacial shear strength between three differently sized carbon fibers and high-density polyethylene containing various levels of maleic anhydride grafted polyethylene coupling agent has been evaluated. Overall, the compatibilizer content plays a more significant role than the fiber sizing but it was found that there are competing and complementary effects between them. Additionally, based on examination of the post debonding frictional forces, the mechanics of the pullout test are changed even with a small content of maleic anhydride even where the magnitude of the interfacial shear strength is unchanged.

Soluble semi-aliphatic polyimide sizing in CF/PEI composites for improving mechanical performance and hydrothermal aging resistance

Carbon fiber reinforced thermoplastics (CFRTP) inherited special advantages from the thermoplastics, which caused the demand for soaring. However, due to its high molding temperature and the absence of reactive groups, traditional carbon fiber sizing needs to be redesigned. Herein, a suspension formulated from a soluble semi-aliphatic polyimide (S-SA-PI) was used for CF sizing. The effective replacement of the sizing layer on the surface of T300 was clarified by microscopic morphology and surface element content of CFs. The mechanical performance of CF/PEI composites was measured, and the effects of annealing and hydrothermal aging on the mechanical performance were observed. The results show that S-SA-PI sizing can simply improve mechanical performance and hydrothermal aging resistance of CF/PEI. Combining the characteristics of S-SA-PI sizing layer, the mechanism by which S-SA-PI sizing improves the CF/PEI interface was analyzed.

The Impact of Carbon Nanofibres on the Interfacial Properties of CFRPs Produced with Sized Carbon Fibres.

In this work, different amounts of CNFs were added into a complex formulation to coat the CFs surfaces via sizing in order to enhance the bonding between the fibre and the resin in the CF-reinforced polymer composites. The sized CFs bundles were characterised by SEM and Raman. The nanomechanical properties of the composite materials produced were assessed by the nanoindentation test. The interfacial properties of the fibre and resin were evaluated by a push-out method developed on nanoindentation. The average interfacial shear strength of the fibre/matrix interface could be calculated by the critical load, sheet thickness and fibre diameter. The contact angle measurements and resin spreadability were performed prior to nanoindentation to investigate the wetting properties of the fibre. After the push-out tests, the characterisation via optical microscopy/SEM was carried out to ratify the results. It was found the CFs sizing with CNFs (1 to 10 wt%) could generally increase the interfacial shear strength but it was more cost-effective with a small amount of evenly distributed CNFs on CFs.

Improving interfacial properties and thermal conductivity of carbon fiber/epoxy composites via the solvent-free GO@Fe3O4 nanofluid modified water-based sizing agent

In order to address the less-than-satisfactory interfacial properties and thermal conductivity of carbon fiber reinforced polymers (CFRPs), a general solvent-free GO@Fe3O4 nanofluid (GFNF) hybrid water-based sizing agent was prepared and applied for carbon fiber (CF) sizing. A discussion was conducted about the effects of different GFNF contents on the CF/epoxy composites (CF/EP) for their interfacial properties and thermal conductivity. In comparison with the composites made up of commercial CF and epoxy, the interfacial and thermal conductivities of the GFNFCF/EP composites were significantly improved. Notably, the increase in 2.5-GFNFCF/EP was most noticeable, with ILSS and flexural strength improved by 15% and 43.6%, respectively. This is attributed to the uniform adhesion of GFNF to the CF surface, which enhances the physical-chemical interaction of fiber with matrix, promotes the dispersion of stress, and prevents cracking from spreading. Also, the thermal conductivity was improved by 128.9% due to the formation of continuous thermal conduction pathways at the interface. The mechanism behind interface and thermal conductivity enhancement of the composites was proposed. This hybrid sizing agent contributed a different solution to improving the interfacial properties and thermal conductivity of CFRPs at the same time.

Investigation on the interfacial properties of CNTs sized carbon fibres in epoxy resin using push-out method via nano-indentation technique

In this work, the carbon fibres (CFs) surfaces were modified via sizing and coated with a very thin layer of a complex formulation including carbon nanotubes (CNTs). A push-out method was developed based on nanoindentation to assess the interfacial shear strength of the fibre/matrix. The mechanical properties such as indentation hardness, reduced modulus, indentation displacement and indentation creep of the composite were evaluated by means of the Oliver-Pharr method. The critical load of different composites was measured and the interfacial shear strength (IFSS) was calculated to compare the effect of the CNTs concentration in the sizing solution. Wettability evaluation of the sized fibres was performed prior to nanoindentation to investigate the adhesion of the resin. After push-out testing, characterisation by optical microscopy/SEM was carried out to ratify the results. It was found sizing with a small amount of evenly distributed nano-inclusion on CFs can increase the interfacial shear strength but large amount of sizing could lead to a decrease of the interfacial bonding due to the agglomeration of CNTs on CFs.

Preparation of semi-aliphatic polyimide for organic-solvent-free sizing agent in CF/PEEK composites

The inert structure and high molding temperature of thermoplastic resin bring new challenges to carbon fiber (CF) sizing agents. Herein, an easily purified semi-aliphatic polyimide (SA-PI) was synthesized as CF sizing agent. The SA-PI has no significant decomposition before 300 °C and a 5% decomposition temperature of 442 °C. Based on the solubility of its polyamic acid ammonium salt, the SA-PI is configured as an aqueous solution for CF sizing. The results show the surface of sized carbon fiber (SCF) is covered with a sizing coating. At the same time, the polar group of the sizing coating increases the surface energy by 28.45%. Compared with bare CF, the tensile strength of SCF is increased by 11.43%, the ILSS and flexural strength of SCF/PEEK increased from 55.71 MPa and 485.34 MPa to68.98 MPa and 523.33 MPa, respectively. In addition, the micro-morphology at the fracture of the composite clearly proves that the sizing agent improves the interface performance of the composites effectively.

A novel use of twisted continuous carbon fibers in additive manufacturing of composites

3D printing of composites is one of the trending topics in the field of additive manufacturing. Several research papers on carbon fiber reinforced composites, used carbon fiber tows directly or sized carbon fibers as reinforcement for the composite, which is time consuming and not reliable as frequent clogging occurs. This paper presents a simple method by introducing the novel use of twisted carbon fiber filament and analyze its effect on the additive manufactured composites. The matrix material used is PLA. The commercially available 3D printers for printing continuous fibers, use double nozzle setups for printing the matrix and reinforcement separately in a layer by layer manner. However, there are no reports on the use of twisted continuous carbon fiber as filament and its effect on the printed parts. This paper uses twisted carbon fibers with single nozzle setup such that the material coming out of the nozzle will be ready to use CCF-PLA composite. Thus, the need of separate stacking of each layer of the matrix and fiber can be avoided. A separate path process planning has been done for printing the twisted carbon fibers in consideration of its continuity and the anisotropy. Standard mechanical tests are conducted, and the morphological study of the composite is done.

Rational Modulation of Carbon Fibers for High‐Performance Zinc–Iodine Batteries

AbstractZinc–iodine batteries (ZIBs) are regarded as promising energy storage devices due to their high performance and low cost. Nevertheless, their wide application is mainly limited by the preparation of iodine‐based cathode and dendrite‐free zinc anode. Flexible carbon fibers have attracted tremendous attention, due to their iodine encapsulation properties. This characteristic is a result of their porous structure, large surface area, and excellent intrinsic properties. With the development of carbon fibers for loading iodine, the surface properties can be rationally modulated via heteroatom doping and combination with various polymers can enhance battery performance. In this review, recent research advances on the functionalization of carbon fibers for ZIBs are summarized, with special focus on the pore size of carbon fibers, the species, and content of doping elements, and the selection of targeted polymers toward the loading of iodine. Finally, the prospects and future challenges of ZIBs based on carbon fibers are presented. The review aims to provide the basic guides for designing advanced iodine‐based electrode materials on the basis of carbon fibers with both compositional advantages and microporous structure to achieve high‐performance ZIBs.

Molecular dynamics simulation of the influence of sizing agent on the interfacial properties of sized carbon fiber/vinyl ester resin composite modified by self-migration method

ABSTRACT The interfacial property of sized carbon fiber reinforced vinyl ester resin (SCF/VE) composite was improved by a self-migration method using acrylamide (AM) as a modifier. A molecular dynamics simulation was performed to study the influence of sizing agent on the interphase formation and the interfacial modification effect. After the system equilibrium, the analysis of monomer distribution shows that an interphase region with thickness of ~2.0–2.5 nm was formed surrounding the fiber surface and the interaction energy was increased obviously. The thickness of this interphase region is obviously larger than that of unsized carbon-reinforced composite (~0.5–1.0 nm). This is mainly due to the sizing agent diffusion to the resin and the strong polar interaction between the sizing agent and AM molecule. As a consequence, the interfacial strength and toughness of the composite were enhanced jointly, which was confirmed by the test of interface shear strength and interlaminar shear strength.

The effect of aqueous polyimide sizing agent on PEEK based carbon fiber composites using experimental techniques and molecular dynamics simulations

In this paper, we proposed an efficient method for manufacturing water-soluble polyimide (PI)- sized carbon fiber (CF) reinforced poly (ether ether ketone) (PEEK) composites with excellent mechanical and thermal properties. The PI sizing agent used in this study was synthesized by thermal imidization of prepared poly (amic acid) salt solution. The PI-sized CFs were fabricated by an optimized process that included a sizing treatment and a spreading process using a specially customized equipment. Composites containing PI-sized CFs were characterized by interfacial shear strength and glass-transition temperature according to the PI concentration on the CF surfaces. Molecular dynamics simulations show that the presence of an appropriate amount of PI sizing agent on the CF surface significantly enhances the interface compatibility of the CF/PEEK polymer composites.

Impact of Microstructure on the Electrochemical Performance of Round-Shaped Pitch-Based Graphite Fibers

In this study, three kinds of round-shaped pitch-based graphite fiber with different microstructural features (crystallinity and carbon layer orientation) were fabricated by melt-spinning, preoxidation, carbonization and graphitization. The morphology, crystalline size and carbon layer orientation of carbon fibers from different pitch precursors and spinning rates were characterized through X-ray diffraction, scanning electron microscopy and transmission electron analyses. The correlation of the electrochemical performance and microstructure of graphite fibers as anode materials for lithium-ion batteries was investigated. The results suggest that large-diameter anisotropic graphite fibers (L-AF3000) with a radial texture of the transverse section are more favorable for lithium intercalation storage. The discharge capacity of L-AF3000 is 319.1 mAh∙g−1 at 0.1 C (current density). Nevertheless, the capacity drops to 209.9 mAh∙g−1 at a high current density of 1 C, and the capacity retention is only 82.2% over 100 cycles at 0.1 C. Small-diameter anisotropic graphite fibers (S-AF3000) with a spiral-shaped wrinkle texture of the transverse section possess discharge capacities of 284.1 mAh∙g−1 at 0.1 C and 260.2 mAh∙g−1 at a high current density of 1 C. Meanwhile, the best capacity retention of the fibers is 101.6% over 100 cycles at 0.1 C. The results suggest that the disordered carbon layers in S-AF3000 can retain the structural integrity of fibers as anode material for lithium-ion batteries and thus obtain excellent cycle stability. In addition, larger crystalline sizes of fibers correspond to higher discharge capacity, and a smaller diameter is beneficial to the fast insertion and extraction of lithium-ion in fibers.