Improving the interfacial properties of carbon fiber–epoxy resin composites with a graphene-modified sizing agent

We successfully prepared a graphene-modified carbon fiber (CF) sizing agent with good dispersity and stability by dispersing reduced graphene oxide (RGO) into an emulsion-type sizing agent. RGO was obtained by the reduction of graphene oxide (GO) with the help of gallic acid. The influence of the graphene-modified sizing agent on the interfacial properties of the CF–epoxy resin composites was investigated with microbond testing and the three-point bending method. The results show that optimized interfacial properties were achieved when the size of the modified graphene was less than 1 μm, the content of RGO was 20 ppm, and the pH value of the sizing agent was 10.5. The interfacial shear strength of the composites reached 92.3 MPa, which was 29.6% higher than that of the composites with unmodified CFs. Compared with commercial-CF-fabric-reinforced composites, the interlaminar shear strength of the composites treated with the RGO-modified sizing agent increased by 21.5%. Both the interfacial and interlaminar failure morphologies of the composites were examined with scanning electron microscopy (SEM). The results show that a large amount of residual resin adhered to the surfaces of the CFs treated with the RGO-modified sizing agent; this indicated good interfacial properties between the CFs and the resin matrix. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47122.     

Effect of carbon and oxygen on the high-temperature properties of silicon carbide–hafnium carbide nanocomposite fiber

The polymer-derived ceramics (PDCs) technique enables relatively low-temperature fabrication of Si-based ceramics, with silicon carbide fiber as a representative product. Polycarbosilane (PCS) has Si-C backbone structures and can be converted to silicon carbide. In the PDCs method, residual or excess carbon is generated from the precursor (C/Si ratio = 2 for polycarbosilane). Because of the non-stoichiometry of SiC, the physicochemical properties of polymer-derived SiC are inferior to those of conventional monolithic SiC. Herein, a silicon carbide-hafnium carbide nanocomposite fiber was optimized by crosslinking oxygen into the PCS fiber by regulating the oxidation curing time. During pyrolysis, carbothermal reduction, and sintering, carbon was removed by reaction with hydrogen and cross-linked oxygen. Non-destructive techniques (X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, and high-temperature thermomechanical analysis) were used to investigate the effects of excess carbon. The microstructure of the near-stoichiometric SiC-HfC nanocomposite fiber was more densified, with superior high-temperature properties.     

Estimate of carbon fiber’s fracture toughness based on the small angle X-ray diffraction

According to the Weibull theory, the micropore sizes were used to analyze the stress intensity factor of carbon fiber monofilament crack tip stress field. Based on the analysis of carbon fiber monofilament and multifilament tensile strength, diameter and micropore size get the relationship between carbon fiber monofilament tensile strength and the pore radius by the Guinier principle and Griffith fracture theory, thus to estimate carbon fiber fracture toughness. The results show that this method can implement the estimation of fracture toughness on the basis without destroying the structure of the carbon fibers; the fracture toughness of T300 estimated by the average pore size was 1.34 MPa·m^1/2, in accordance with data 1.25 and 1.32 MPa·m^1/2 by producing defects, errors are 7.2 and 1.5%, respectively.     

Additive manufacturing of continuous carbon fiber–reinforced silicon carbide ceramic composites

A material extrusion (MEX) technology has been developed for the additive manufacturing of continuous carbon fiber–reinforced silicon carbide ceramic (C_f/SiC) composites. By comparing and analyzing the rheological properties of the slurries with different compositions, a slurry with a high solid loading of 48.1 vol% and high viscosity was proposed. Furthermore, several complex structures of C_f/SiC ceramic composites were printed by this MEX additive manufacturing technique. Phenolic resin impregnation–carbonization process reduces the apparent porosity of the green body and protects the C_f. Finally, the reactive melting infiltration (RMI) process was used to prepare samples with different C_f contents from 0 to 2 K (a bundle of carbon fibers consisting of 1000 fibers). Samples with C_f content of 1 K show the highest bending strength (161.6 ± 10.5 MPa) and fracture toughness (3.72 ± 0.11 MPa·m^1/2) while the thermal conductivity of the samples with the C_f content of 1 K reached 11.0 W/(m·K). This study provides a strategy to prepare C_f/SiC composites via MEX additive manufacturing and RMI.     

Grafting acrylate functionalities at the surface of carbon fibers to improve adhesion strength in carbon fiber–acrylate composites cured by electron beam

Acrylate functionalities were grafted at the surface of carbon fibers in order to improve the adhesion strength with an acrylate matrix cured by electron beam. An isocyanate bearing aliphatic urethane acrylate was used as a coupling agent. As revealed by X-ray photoelectron spectroscopy, the isocyanate groups reacted with carboxylic acids and hydroxyl groups located at the surface of the fiber, leading to a covalent bonding of the acrylate groups. The adhesion strength was measured by a micromechanical test derived from the pull-out test. A significant improvement of the interfacial shear strength was obtained (+91%) with an electron beam curing. For comparison, an isothermal cure by UV was also investigated and led to the same level of adhesion strength. The improvement was also proved by an increase in the 90° flexural strength of unidirectional composites (+38%). Grafting functionalities that were compatible with the radical mechanism of the polymerization of the matrix appeared to be a promising strategy for the improvement of the mechanical properties of carbon fiber–acrylate composites cured by electron beam.     

Is the structure of anisotropic pyrolytic carbon a consequence of growth by the Volmer-Weber island growth mechanism?

Pyrolytic carbon deposits, formed on flat zirconia surfaces exposed to the oxypyrolysis of CH₄ at 1673 K, were examined by SEM and found to resemble Johnson-Mehl tessellations. Carbon deposits were also observed that were isolated on the zirconia surface. These deposits were either hemispheres or resembled Johnson-Mehl tessellations with rounded edges. Examination of cross-sections and internal structures of the carbon hemispheres, produced by both FIB milling and mechanical damage, showed that the hemispheres were comprised of concentric layers of carbon. These observations are consistent with growth by the Volmer-Weber 3D island mechanism, in which isolated deposits grow and impinge upon one another, and then coalesce to eventually form a continuous film. A simple mathematical model of Volmer-Weber growth was used to demonstrate that this mechanism can produce the structures observed in this study, and more generally can provide insights into some aspects of pyrolytic carbon structure and growth. In particular, columnar structures, tessellated surfaces and growth cones, all known for anisotropic pyrolytic carbons, are consistent with growth by the Volmer-Weber 3D island mechanism.     

Determination of the optical constants of carbon black in the combustion products of a hydrogen fuel at λ=10.6 μm

Literature data on the optical constants n and of carbon black were analyzed over a wide spectral range. The values of n and at =10.6 m were determined by measuring the sizes and concentrations of carbon black particles in the combustion products of kerosene from the attenuation of the transmitted radiation in the short-wavelength range of the spectrum and from the absorption coefficient of the particles, which is proportional to their volume concentration and determined by the optical properties of carbon black.B. I. Stepanov Institute of Physics, Belarus' Academy of Sciences, 220602, Minsk. Translated form Fizika Goreniya Vzryva, No. 1, pp 70–73, January–February, 1995.     

Methanation of carbon dioxide and fluidization quality in a fluid bed reactor—the influence of a decrease in gas volume

A large decrease of fluidization quality was observed when methanation of carbon dioxide was carried out in a fluid-bed reactor even if the catalyst particles had the optimal properties for good fluidization. The cause of this phenomenon was explored by measuring pressure fluctuations, bubble frequency and extent of CO₂ conversions. The results indicated that the decrease of the fluidity was caused by a reduction in volume of reactant gases due to the reaction. The voidage in the emulsion phase is considered to be an important factor affecting the fluidity. The fluidization quality and contacting efficiency could be improved by such devices as baffle internals or two-stage spargers.     

Further studies on the use of Raman spectroscopy and X-ray diffraction for the characterisation of TiC-containing carbon–carbon composites

Raman spectroscopy and X-ray diffraction are used to study the crystalline structure of carbon–carbon and TiC-containing composites. The advantages and drawbacks of these techniques for the characterisation of carbon–carbon composites are analysed in the light of the distribution and arrangement of their components and the microstructural orientation of the supporting matrix. Analyses performed on longitudinal and transverse sections of the composites confirm that the measurements are affected by the orientation of the crystals. The overall crystalline parameters calculated by X-ray diffraction were unequivocally resolved for each single component by means of Raman spectroscopy. A significantly higher degree of order was observed in the TiC-containing matrix as a result of the catalytic graphitisation of the carbon achieved by the addition of titanium. In addition, Raman spectroscopy corroborated that the incorporation of TiC into the carbon matrix does not disrupt the orientation of the graphene planes of the matrix parallel to the fibre axis, a necessary characteristic for achieving an optimum heat transfer through the material.     

Thermophysical properties of carbon fiber reinforced multilayered (PyC–SiC)n matrix composites

Three kinds of carbon fiber reinforced multilayered (PyC–SiC)_n matrix (C/(PyC–SiC)_n) composites (n = 1, 2 and 4) were prepared by means of layer-by-layer deposition of PyC and SiC via chemical vapor infiltration. Thermal expansion behaviors in the temperature range of 800–2500 °C and thermal conductivity from room temperature to 1900 °C of C/(PyC–SiC)_n composites with various microstructures were investigated. The results show that with increasing PyC–SiC sequences number (n), the coefficients of thermal expansion of the composites decrease due to the increase of interfacial delamination, providing room for thermal expansion. The thermal diffusivity and thermal conductivity also decrease with the increase of sequences number, which are attributed to the enhancement of phonon-interface scattering resulted from the increasing number of interfaces. Modified parallel and series models considering the interfacial thermal resistance are proposed to elaborate thermal conductivity of the composites, which is in accordance with the experimental results.     

The effect of metal–solvent properties on the alteration of specific zones on a carbon phase diagram

In this work Fe–Sb and Fe–Ge alloys (up to 10 wt.% Sb, Ge) were used as a solvent-catalyst for diamond synthesis at pressures of 5–6 GPa and temperatures of 1800–1900 K. Carbon solubility, capillary properties and synthesis performance of alloys were investigated. When using alloys with additive content up to 10 wt.%, rapid graphite to diamond transformation was observed. In spite of identical P,T-conditions and identical composition of a solvent–catalyst, different crystal morphology on the top and on the bottom sides of a diamond polycrystalline layer was formed, although their habit type {111} was identical. Thermodynamic and kinetic aspects of these phenomena are discussed.     

Supplementation of the diet with the functional fiber PolyGlycoplex® is well tolerated by healthy subjects in a clinical trial

Background

This study was designed to evaluate the safety of PolyGlycopleX^® (PGX^®), a novel viscous dietary polysaccharide (fiber), when administered to Sprague Dawley^® rats in the diet for 90 days.

Methods

Groups of ten male and ten female rats each consumed PGX mixed in the diet at levels of 0, 1.25, 2.5 or 5.0% for 90 days, then evaluated for toxicological effects on parameters that included neuromotor activity, body weight, clinical chemistry, urinalysis, hematology, and histopathology.

Results

Mean body weight, mean feed consumption and food efficiency in the treated groups were generally comparable to controls for both male and female rats. No changes were noted in neuromotor behavior, and histopathological analysis revealed no significant changes between treated and control animals. There were no differences in mean organ weight, organ-to-body weight or organ-to-brain weight values between controls and treated animals. Decreased red blood cell count occurred in the high dose males and increases in aspartate and alanine aminotransferase enzyme levels and triglycerides, while significant decreases in serum sodium, potassium and chloride concentrations were observed in the females fed 5.0% PGX. However, the decreased mineral concentrations may be the result of significantly increased urinary volume in both males and females at the high dose, with a concomitant decrease in urinary specific gravity (males and females) and protein concentration (females). These results were within historical control values, did not correlate with any histopathological changes, and were not considered adverse.

Conclusion

The results indicate a no observed adverse effect level (NOAEL) for PGX at 5.0% of the diet, corresponding to an average daily intake of 3219 and 3799 mg/kg bw/day in male and female rats, respectively.     

Study of the release kinetics of (−) epicatechin: Effect of its location within the fiber or sphere

The (−) epicatechin (Epi) is a flavonoid with antioxidant and regenerative properties for cardiac tissue. In this work, a study of release assays and their corresponding adjustments to models was performed to determine the mechanism of (−) Epi release in the cellulose acetate (CA)–polyvinylpyrrolidone (PVP) system. The morphology of the material was considered, fibers, or spheres, as well as the possible chemical interactions between Epi, PVP, and CA. It was observed that in the systems in which the PVP is present, a high release is observed in comparison with those that only contained CA and (−) Epi, which showed very low release. This difference can be explained considering the possible hydrogen bond interaction between CA and (−) Epi, as well as the insolubility of the CA, in the release medium. The factors that have an important effect on the release of (−) Epi in the different systems are: the morphology, a faster release in morphologies with greater surface area, and the chemical interactions that can be formed among the (−) Epi and the components of the matrix. Another factor is the solubility of the components in the release medium, which allows the diffusion and drag phenomena to be observed simultaneously. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47166.     

Heterogeneous enantioselective carbon–carbon bond formation: role of the inorganic support in the synthesis and activity of supported chiral auxiliaries

Heterogeneous enantioselective alkylation of benzaldehyde with diethylzinc was performed using (-)-ephedrine grafted on mesoporous micelle templated aluminosilicates or silicates, as chiral auxiliary. Supports were characterized by a regular mesoporosity and a same initial pore diameter. Immobilization of the chiral aminoalcohol was performed through covalent anchoring of 3-halogenopropyltrimethoxysilane (XPTMS) and substitution of the halogen by (-)-ephedrine. Comparison of the efficiency of the catalysts was carried out. Results were analyzed taking into account the accessibility to the catalytic sites by changing their density (decrease of XPTMS concentration, spacing of the sites by alkyl goups) and the effect of the uncovered mineral surface on activities and enantioselectivities. This revised version was published online in June 2006 with corrections to the Cover Date.     

Adsorption of carbon dioxide at high temperature—a review

In this review, the adsorption of carbon dioxide on adsorbent materials at high temperature is examined critically. Adsorbent materials including carbon-based adsorbents, metal oxide sorbents, zeolites and hydrotalcite-like compounds (HTlcs) for carbon dioxide at high temperature are discussed. Research areas, which may make a significant impact in future are put forward.     

Organic–inorganic interface enhancement for boosting mechanical and tribological performances of carbon fiber reinforced composites

The limitation in the poor interface would severely affect the further development and application of carbon fiber reinforced composites (CFRP). Unique organic–inorganic hybrid architectures of MOF-5-NH₂ and carboxymethyl cellulose (CMC) were established on the fiber/matrix interphase for promoting mechanical and tribological performances of the composites. The existence of above interfacial reinforced structure was in favor of generating abundant micromechanical interaction sites for enhancing mechanical interlocking. Meanwhile, high-density chemical crosslinking networks played a positive role in elevating interfacial adhesion, further relieving stress concentration and hindering crack propagation. The tensile strength of CFRP-2, CFRP-3, CFRP-4, and CFRP-5 exhibited a significant rising of 27.18%, 30.64%, 27.75%, and 36.88%, respectively. The friction coefficient of MOF-5-NH₂/CMC modified sample increased from 0.0953 to 0.1219, while the drop in the wear rate of the composites achieved 68.51%. This work provides an effective method for achieving the structure–function integrated design of composite materials according to the organic–inorganic interface enhancement of MOF-5-NH₂/CMC.     

Synthesis and properties of electrical conductive and antibacterial siloxane-modified carbon fiber–silver–acrylate nanocomposites

First, silanized carbon fiber (SCF) was synthesized, then silanized carbon fiber–silver (SCF-S) was obtained. Finally, silanized carbon fiber–silver–acrylate (SCF-S-A) electrical conductive and antibacterial composites were prepared. The structures of CF, SCF, SCF-S, and SCF-S-A were characterized by X-ray photoelectron spectroscopy, FTIR, scanning electron microscopy, X-ray diffraction, Raman spectroscopy, and UV spectra. The electrical conductive and antibacterial properties of SCF-S-A nanocomposites were studied. The results showed that electrical conductive and antibacterial activity properties of SCF-S-A nanocomposites were improved. When the content of SCF-S was 50%, the conductivity of SCF-S-A nanocomposites was maximum. The SCF-S-A nanocomposites will have promising application in high-performance electrical conductive and antibacterial materials.     

Growth of carbon nanotube forests between a bi-metallic catalyst layer and a SiO2 substrate to form a self-assembled carbon–metal heterostructure

A special nanostructure was formed by the growth of carbon nanotubes (CNTs) between a substrate and a thin bi-metallic catalyst layer using a thermal chemical vapor deposition process. The catalyst layer is composed of adjacently disposed Cr and Ni phases formed prior to CNT growth. The Cr/Ni layer serves as a bi-metallic catalyst layer, which is pushed away from the substrate as a thin and continuous nanomembrane with the growth of CNTs. The self-assembled CNT–catalyst heterostructure possesses a smooth surface (RMS = 2.9 nm) with a metallic shine. Directly interlinked to the Cr/Ni layer, dense and vertically aligned multi-walled CNTs are found. Compared to conventional CNT films, the structure has significant advantages for CNT integration. From technology point of view, the structure allows further processing without impact on the CNTs as well as transfer of pristine vertically aligned CNTs to arbitrary substrates. Moreover, the as-grown CNT films provide an interface ideal for further electrical, thermal and mechanical contacting of CNT films. We present structural investigations of this special CNT–metal heterostructure. Furthermore, we discuss possible interface mechanisms during catalyst layer formation and CNT growth.