Wettability and Interfacial Properties of Carbon Fiber and Poly(ether ether ketone) Fiber Hybrid Composite.

Studies on carbon fiber (CF)/poly(ether ether ketone) (PEEK) fiber hybrid textiles were initiated several decades ago because their flexibility and conformability make them a promising alternative to traditional prepregs. The adhesion between the CFs and PEEK is mostly controlled by their inherent surface properties and mutual wettability. However, details of these properties remain largely unknown, especially those of PEEK. Therefore, to determine the surface and interfacial properties of these fibers, we performed a comprehensive study and characterized their surface topography (atomic force microscopy, scanning electron microscopy), surface chemistry [X-ray photoelectron spectrometry (XPS), acid-base titration], surface energies (wetting tests, acid-base approach), and interfacial mechanical properties [droplet test, interfacial shear strength (IFSS)]. These experiments were complemented by a theoretical approach to the prediction of the surface energy components (parachor) and contact angles of PEEK. We found good agreement between the results obtained by XPS and wetting tests (base-to-acid surface energy component ratio), as well as between the predicted and measured surface energy and contact angles. The results highlight the consistency and reliability of the proposed methodology. We found that both CFs and PEEK fibers appear to be smooth at the nanoscale and have large dispersive and basic surface energy components. The IFSS of CF/PEEK is significantly higher (44.87 ± 5.76 MPa) compared to that of other thermoplastic systems. The findings not only demonstrate the potential of CF/PEEK hybrid textiles but also emphasize the need to further increase the compatibility between CFs and PEEK fibers by increasing the acidic component of CF surfaces. Surface treatments and the design of a suitable sizing are potential methods to achieve this objective in future studies.

Enhancing the Interfacial Strength of Carbon Fiber/Poly(ether ether ketone) Hybrid Composites by Plasma Treatments.

As a promising alternative to traditional prepreg, carbon fiber/poly(ether ether ketone) (CF/PEEK) hybrid composites have attracted wide public interest for their flexibility and conformability. However, modification methods focused on the hybrid premix have not been previously studied. In the present work, the interfacial strength of the hybrid composite was improved by treating the carbon and PEEK fibers together in a radiofrequency (RF) plasma containing one of the following gases to achieve surface activation: air, Ar, or Ar-air. After plasma treatment, the increased roughness of CF and the grafted chemical groups of CFs and PEEK fibers were propitious to the mechanical interlocking and interfacial strength. Significant interfacial shear strength (IFSS) enhancement was achieved after Ar 1 min, air 1 min plasma treatment. This study offers an alternative method for improving the interfacial properties of CF/PEEK composites by focusing on the boundary layer and modifying and controlling the fiber-matrix interface.

Wet-Spinning Assembly of Continuous, Highly Stable Hyaluronic/Multiwalled Carbon Nanotube Hybrid Microfibers.

Effective multiwalled carbon nanotube (MWCNT) fiber manufacturing methods have received a substantial amount of attention due to the low cost and excellent properties of MWCNTs. Here, we fabricated hybrid microfibers composed of hyaluronic acid (HA) and multiwalled carbon nanotubes (MWCNTs) by a wet-spinning method. HA acts as a biosurfactant and an ionic crosslinker, which improves the dispersion of MWCNTs and helps MWCNT to assemble into microfibers. The effects of HA concentration, dispersion time, injection speed, and MWCNT concentration on the formation, mechanical behavior, and conductivity of the HA/MWCNT hybrid microfibers were comprehensively investigated through SEM, UV-Vis spectroscopy, tensile testing, and conductivity testing. The obtained HA/MWCNT hybrid microfibers presented excellent tensile properties in regard to Young's modulus (9.04 ± 1.13 GPa) and tensile strength (130.25 ± 10.78 MPa), and excellent flexibility and stability due to the superior mechanical and electrical properties of MWCNTs. This work presents an effective and easy-to-handle preparation method for high-performance MWCNT hybrid microfibers assembly, and the obtained HA/MWCNT hybrid microfibers have promising applications in the fields of energy storage, sensors, micro devices, intelligent materials, and high-performance fiber-reinforced composites.

Studies on Curing Kinetics and Tensile Properties of Silica-Filled Phenolic Amine/Epoxy Resin Nanocomposite.

In this study, the curing kinetics of the phenolic amine/epoxy resin system were investigated by nonisothermal differential scanning calorimetry (DSC). The model-free isoconversional method of Ozawa-Flynn-Wall reveals a dependence of Eα (activation energy) on conversion (α), which interprets the autocatalytic curing reaction mechanism of the phenolic amine/epoxy resin system. Studies on the effects of nano-SiO2 particles on the tensile properties and tensile fracture face morphology of nanocomposites show that the uniform dispersion of SiO2 nanoparticles plays an important role in promoting the tensile performance of nanocomposites. Additionally, increases of 184.1% and 217.2% were achieved by adding 1.5% weight parts of nano-SiO2 in composites for the tensile strength and tensile modulus, respectively.

Preparation and Properties of Highly Electroconductive and Heat-Resistant CMC/Buckypaper/Epoxy Nanocomposites.

Self-assembled buckypapers have been successfully prepared using sodium carboxyl methyl cellulose (CMC) as a binder. The lowest resistivity that was reached was 0.43 ± 0.03 Ω·m, when the buckypapers were prepared by the same mass of CMC and carboxy-modified carbon nanotubes (CNTs). A heat-resistant electroconductive nanocomposite with epoxy resin as the matrix and CMC/buckypapers as the reinforcement was fabricated by a resin impregnation molding technique. The effects of CMC/buckypaper layers on the conductivity, thermal stability, and mechanical and dynamic mechanical performance of the epoxy resin polymer nanocomposites were investigated. It was found that CMC/buckypapers hold great promise for improving the properties of nanocomposites, and the buckypapers' performance can be enhanced by using modified CNTs to prepare them. The obtained nanocomposites showed an approximate 71.23% bending strength improvement (125.04 ± 5.62 MPa) and a 30.71% bending modulus improvement (5.83 ± 0.68 GPa), with an increased number of CMC/buckypaper layers. An enhanced degradation temperature and residual mass were also achieved for the nanocomposites when compared with a pure polymer. The nanocomposites with four CMC/buckypaper layers possessed the highest storage modulus (1934 MPa), which was approximately 60% higher than that of a neat polymer (1185 MPa). Therefore, CMC/buckypapers could be effectively used to manufacture heat-resistant electroconductive polymer nanocomposites with improved properties.

The Optimization of Process Parameters and Characterization of High-Performance CF/PEEK Composites Prepared by Flexible CF/PEEK Plain Weave Fabrics.

Continuous carbon fiber (CF)-reinforced poly (ether ether ketone) (PEEK) composites have excellent mechanical properties, but their processing techniques are limited. Therefore, we promoted a braiding method based on the hybrid fiber method by hot-compacting CF/PEEK plain weave fabrics to solve the problem of difficult wetting between CF and PEEK. Four parameters-melting temperature, molding pressure, crystallization temperature and the resin contents-were investigated for optimized fabrication. After studying the melting range, thermal stability and the contact angle of PEEK under different temperatures, the melting temperature was set at 370 °C. An ultra-depth-of-field 3D microscope was adopted to investigate the effects of molding pressure in the melting stage. The tensile strength or modulus along and perpendicular to the carbon fiber direction and crystallinity under different crystallization temperatures were analyzed. As a result, the sample crystalized at 300 °C showed an excellent tensile properties and crystallinity. The increased mass ratio of PEEK ranging from 50.45% to 59.07% allowed for much stronger interfacial strength; however, the higher resin content can lead to the dispersion of CFs, loss of resin and the formation of defects during processing. Finally, the optimal resin mass content was 59.07%, with a tensile strength of 738.36 ± 14.49 MPa and a flexural strength of 659.68 ± 57.53 MPa. This paper studied the optimized processing parameters to obtain better properties from CF/PEEK plain weave fabrics and to further broaden the specific applications of CF/PEEK composites, demonstrating a new direction for its fabrication.