Surface Chemistry Of Carbon Fibers Research Articles

Surface modification of carbon fibres using ring-opening metathesis polymerization

A series of alkene bearing small molecules were electrografted to the surface of carbon fibers using the in situ generation of aryldiazonium salts. These molecules were used as an anchoring point for the use of Ring Opening Metathesis Polymerization (ROMP) in a ‘graft from’ approach to carbon fiber surface modification. After modification, evaluation of these modified fibers in an epoxy resin, using the single fiber fragmentation test, showed significant increases in interfacial shear strength (IFSS) of up to 189%, relative to untreated pristine fibers. Dilution of strained norbornene alkenes at 2:1 (alkane:alkene) had minimal effect on IFSS, while dilution at 10:1 (alkane:alkene) still resulted in improved, albeit suppressed, IFSS gains of 70% relative to pristine fibers. This study shows the potential of using ROMP as a means to tailor the surface chemistry of carbon fibers for use in advanced composites.

Effects of plasma treatment on properties of carbon fiber and its reinforced resin composites

The influence of plasma treatment on the wettability of carbon fiber was studied using the vacuum assisted resin transfer molding (VARTM) process. The influence of plasma treatment on the mechanical properties of carbon fiber-reinforced polymer (CFRP) composites, including interlaminar shear strength and tensile properties, were investigated. The carbon fiber surface chemistry analysis was carried out by Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and x-ray photoelectron spectroscopy (XPS). Results showed that low-temperature plasma treatment had little effect on the surface morphology of the carbon fiber; however, it changed the chemical surface state of the carbon fiber, which contributed to enhance the wettability of the carbon fiber by increasing the perfusion speed of the resin to be more than two times of the original speed. The fiber wettability improvements are of great significance to the preparation of the CFRP composite by the VARTM process. Compared to untreated carbon fiber, the plasma treatment caused an acceptable decrease in tensile properties and offered an increase in the interlaminar shear strength of the CFRP composite. Low-temperature plasma treatment played an important role in the effective preparation and application of the CFRP composite.

Evaluation of composite interfacial properties based on carbon fiber surface chemistry and topography: Nanometer-scale wetting analysis using molecular dynamics simulation

According to surface chemistry and topography of different high-modulus carbon fiber (HMCF), interfacial properties of various HMCF composite were evaluated, and nanoscale wetting analysis of HMCF were studied using experimental methods and molecular dynamics simulation. Hierarchical amount of active functional groups and nanoscale grooves were detected on the surface of pristine HMCF (p-HMCF), anodic oxidized HMCF (a-HMCF) and sized HMCF (s-HMCF). Remarkable enhancements in interfacial properties of a-HMCF and s-HMCF composites were obtained, which was ascribed to free-void interface from improved surface energy and wettability. Poor interfacial bonding of p-HMCF composites was due to generation of many nanobubbles with pinned contact lines during the wetting of the surface microgrooves with high aspect ratio and chemical inertness. Schematic of interfacial compatibility mechanisms was proposed to illustrate the correlation between surface features of carbon surface and interfacial properties of their composites.

Interaction between carbon fibers and polymer sizing: Influence of fiber surface chemistry and sizing reactivity

Different aspects of the interaction of carbon fibers and epoxy-based polymer sizings are investigated, e.g. the wetting behavior, the strength of adhesion between fiber and sizing, and the thermal stability of the sizing layer. The influence of carbon fiber surface chemistry and sizing reactivity is investigated using fibers of different degree of anodic oxidation and sizings with different number of reactive epoxy groups per molecule. Wetting of the carbon fibers by the sizing dispersion is found to be specified by both, the degree of fiber activation and the sizing reactivity. In contrast, adhesion strength between fibers and sizing is dominated by the surface chemistry of the carbon fibers. Here, the number of surface oxygen groups seems to be the limiting factor. We also find that the sizing and the additional functionalities induced by anodic oxidation are removed by thermal treatment at 600 °C, leaving the carbon fiber in its original state after carbonization.

Tailoring the fibre-to-matrix interface using click chemistry on carbon fibre surfaces

A convenient and effective strategy to control the surface chemistry of carbon fibres is presented, comprising electro-chemical reduction of aryl diazonium salts onto the surface, followed by ‘click chemistry’ to tether the desired surface characteristic of choice.

Interphase formation and fiber matrix adhesion in carbon fiber reinforced epoxy resin: influence of carbon fiber surface chemistry

The chemistry and morphology of the carbon fiber surface are important parameters which govern the properties of the interfacial region and the adhesion between carbon fibers and polymeric matrix in carbon fiber reinforced polymers. In the presented paper the surface chemistry of the fibers is varied while the surface morphology is left unchanged. We analyze chemical functionality and morphology of carbon fiber surfaces showing different degrees of activation, together with the adhesion of these fibers to an epoxy matrix and the width of the interfacial region between fiber and matrix. An increase of the oxygen and nitrogen concentration of the fiber surface, in particular in form of carboxyl functional groups, results in a significant increase of interfacial shear strength. Also the width of the interphase, as determined by scanning force microscopy in nanomechanical mode, depends on the activation degree of the carbon fibers. However, no direct correlation between interphase width, surface chemistry and fiber matrix adhesion is found, suggesting no direct influence of interphase width on adhesion properties.

Effect of carbon fiber surface chemistry on the interfacial properties of carbon fibers/epoxy resin composites

Polyacrylonitrile-based carbon fibers were electrochemically oxidized under a wide variety of current densities, and then surface changes in the morphological structures and the chemical compositions were characterized by scanning electron microscopy and X-ray photoelectron spectroscopy. Finally, the effects of carbon fiber surface chemistry on the interfacial properties of carbon fiber reinforced composites were researched. The results showed that surface contaminants generated during the production process were removed and the relative contents of oxygen and nitrogen elements increased by 322% and 432%, respectively, after the electrochemical oxidation. Increases in the O/C and N/C ratios resulted in the increase in the interlaminar shear strength values of composites. However, much higher O/C and N/C ratios led to decline in the interlaminar shear strength values. Carboxyl groups were responsible for strong interactions between carbon fiber surfaces and the epoxy resin. When the current densities were more than 5 A/m2, the interfacial bonding between carbon fibers and the epoxy resin became weak and the interlaminar shear strength values also decreased.

Effect of low current density electrochemical oxidation on the properties of carbon fiber‐reinforced epoxy resin composites

Changes in surface physicochemical structures of polyacrylonitrile‐based carbon fibers resulted from low current density electrochemical oxidation were monitored by scanning electron microscopy (SEM) and X‐ray photoelectron spectroscopy (XPS). The relationship between the interlaminar shear strength (ILSS) values of carbon fiber‐reinforced polymers (CFRPs) and carbon fiber surface chemistry including elemental ratios and the relative content of oxygen‐containing functional groups were researched. SEM results revealed that the electrochemical oxidation got rid of surface contaminants generated during the production process. XPS analysis showed that the relative contents of oxygen and nitrogen increased by 446% and 202%, respectively, after the electrochemical oxidation. Carbon fiber surface chemistry was of paramount importance to the interfacial properties of CFRPs. The higher the carbon fiber surface activity, the better the interfacial bonding was, and an increase in the acidic‐group contents was responsible for a higher ILSS value. However, when the current density increased to 1.0 A/m2, the interfacial bonding between carbon fiber and the epoxy resin became weak which led to the decline in ILSS values. Copyright © 2012 John Wiley & Sons, Ltd.

A Study of Atmospheric Plasma Treatment on Surface Energetics of Carbon Fibers

In this study, the atmospheric plasma treatment with <TEX>$He/O_2$</TEX> was conducted to modify the surface chemistry of carbon fibers. The effects of plasma treatment parameters on the surface energetics of carbon fibers were experimentally investigated with respect to gas flow ratio, power intensity, and treatment time. Surface characteristics of the carbon fibers were determined by X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), Fourier transform infrared (FT-IR), Zeta-potential, and contact angle measurements. The results indicated that oxygen plasma treatment led to a large amount of reactive functional groups onto the fiber surface, and these groups can form together as physical intermolecular bonding to improve the surface wettability with a hydrophilic polymer matrix.

Adsorption of polar probe molecules on plasma-oxidised high-strength carbon fibres

The objective of this work was to examine the effect of oxygen plasma treatment on the surface chemistry of carbon fibres. Virgin, unsized high-strength carbon fibres were subjected to oxygen plasma treatments with different degrees of severity. Adsorption of probe molecules with different acid–base characteristics (acetone, carbon tetrachloride, trichloromethane, dichloromethane, diethyl ether, nitromethane, tetrahydrofurane) was measured at 303–353 K using inverse gas chromatography (IGC) at infinite dilution. Plasma treatment brings about increases in the specific free energy of adsorption of either acidic, basic or amphoteric probe molecules, indicating creation of surface functionalities with various acid–base strengths. This helps to justify the improvement in interfacial adhesion in polycarbonate matrix composites following plasma treatment of carbon fibres.

Effects of treatment on the surface composition and energy of carbon fibers

AbstractThe surface composition and energy of carbon fiber has been carefully analyzed and quantified. Untreated, AU, surface‐treated, AS, and heat‐treated AHT fibers were all studied. AS fiber was surface‐treated by an electrolytic oxidation process. AHT fiber was heat‐treated at elevated high temperatures under vacuum. X‐ray photoelectron spectroscopy (XPS or ESCA) was used to investigate the surface elemental concentration of carbon fibers. The corresponding surface free energies of these fibers were calculated from the contact angles measured by a dynamic contact angle analyzer. Results showed a strong correlation between the surface treatment and heat‐treatment history and the surface chemistry of carbon fibers. After oxidation treatment, the surface free energy was increased by adding functional group elements (oxygen and nitrogen). However, these added elements could be removed by high temperature treatment under vacuum. The diffusion of O, N, and Na was discussed. The correlation between oxygen and nitrogen concentration and carbon fiber surface free energy has been plotted. These fibers would be used to quantify the relationship between carbon fiber surface free energy and the interfacial shear strength of the fiber‐polymer interface.

The relevance of the surface structure and surface chemistry of carbon fibres in their adhesion to high temperature thermoplastics

This paper has three principle thrusts: (i) the fabrication of unidirectionally reinforced composites made from carbon fibres subjected to different surface treatments in combination with various (polycarbonate, polyethersulphone and epoxy) matrices, (ii) a study of some of the mechanical properties (that is, the interlaminar-shear strength (ILSS) and the failure behaviour) of these composites; and (iii) determination of the correlations between the adhesion of the matrix polymers as measured by the ILSS and the surface structure as well as the surface chemistry of the various fibres. It will be shown that the surface structure of the fibres has a minor effect, while the surface chemistry appears to have an extraordinarily great influence on the adhesion of the fibres to high-temperature thermoplastics

The relevance of the surface structure and surface chemistry of carbon fibres in their adhesion to high temperature thermoplastics

This paper has three principle thrusts: (i) the fabrication of unidirectionally reinforced composites made from carbon fibres subjected to different surface treatments in combination with various (polycarbonate, polyethersulphone and epoxy) matrices, (ii) a study of some of the mechanical properties (that is, the interlaminar-shear strength (ILSS) and the failure behaviour) of these composites; and (iii) determination of the correlations between the adhesion of the matrix polymers as measured by the ILSS and the surface structure as well as the surface chemistry of the various fibres. It will be shown that the surface structure of the fibres has a minor effect, while the surface chemistry appears to have an extraordinarily great influence on the adhesion of the fibres to high-temperature thermoplastics. The data clearly show that, depending on the processing temperature during the fabrication of the composites, chemical bonds can be formed at the fibre-polymer interface. This bond formation is initiated by the decomposition of carboxylic groups and, as a consequence, dangling carbon atoms are free to react with the functional groups of the polymer.

Surface chemistry of PAN carbon fibres in relation to ILSS in epoxy-resin composites

In the manufacture of high performance carbon fibre re-inforced plastics (CFRP) good adhesion between fibre and matrix is essential in order to ensure optimum stress transfer across the resulting interfaces. The overall interfacial interaction is due to specific (chemical) and non-specific Van de Waals interactions between fibre surface atoms and matrix materials. Fibre surface topography, roughness and porosity, are also likely to contribute to interracial bonding by the mechanical keying together of the two components. In order to enhance the surface reactivity of carbon fibres the concentration of oxygen functionality is often increased by an oxidation step during manufacture. The process may also remove loosely bound, low molecular weight, carbon species from the fibl-e surfaces leaving a mechanically more suitable surface for adhesion. Detailed studies of the factors which determine interracial interactions are essential to the understanding of mechanical properties and modes of failure of composiite materials. We are engaged in a long-term investigation of how the surface chemistry of carbon fibre, and other fibre and particulate reinforcing materials, influences interface formation and the resulting mechanical properties of composites. In this communication we discuss the changes in surface chemistry, brought about by commercial anodic oxidation treatment, of PAN fibres and their effect on apparent interlaminar shear strength (1LSS) data for an epoxy composite. Batches of Akzo HTA polyacrylonitrile (PAN)based carbon fibres have been studied. Surface chemistry and contact angle data are compared for 0% and 100% (HTA 500X and 5001, Lots 11019 and 11011 respectively). Unoxidized fibres have quoted tensile strengths of 4012 (+1.5)MPa and tensile moduli of 239 (_+1.5) GPa. Oxidized materials have tensile strength of 3900 (+124)GPa and tensile moduli of 245.7 (+4.0)GPa. Unidirectional fibre test pieces have been produced from both fibre types after application of a bis-phenyl A size (HTA 5130 and 5131 same strength and modulus as above). A standard toughened epoxy (Ciba-Geigy F914) has been used as matrix. Apparent ILSS data have been calculated using the three-point bend test, short beam, method according to ASTM D2344-84. X-ray photoelectron spectroscopy (XPS) measurements have been carried out on a VG MK 1 Escalab using A1 K1 X-rays (energy 1486.6 eV) at a power of 200W in a residual vacuum of 1.333 × 10 -6 Pa. Binding energy resolution has been increased by removal of the X-ray line shape using in-house software on an IBM-AT computer, for functional group identification. Full experimental details have been published elsewhere [1]. Oxidation leads to a factor of 2 increase in measured surface oxygen (Table I). High energy resolution carbon ls spectra (not shown) show this to be distributed as hydroxyl/ether (C-O), carbonyl (C~---O) and carboxylic acid/ester(COOH/COOR). As expected both fibre types have very similar surface compositions after application of size (Table I). However, the oxygen levels recorded are slightly higher than those expected from a stoichiometric bisphenyl A layer (-11%). The 0% oxidized fibres generally have surface nitrogen levels of 2-3 at % which, after this method of oxidation, does not change significantly. In previous studies we have found that anodic oxidation in ammonium bicarbonate solution gives a similar increase in surface

The relevance of the surface structure and surface chemistry of carbon fibres in their adhesion to high-temperature thermoplastics

The surface structure and morphology of several high strength polyacrylonitrile (PAN) based carbon fibres was studied with the scanning electron microscope (SEM) on the micrometre scale and the scanning tunnelling microscope (STM) down to the atomic scale. In addition, active surface area measurements were made to determine the number of bonding sites/unit area. Prior to the observations, the surfaces of some of the samples were subjected to either the commercial surface treatment or to oxidation in air or ozone in our laboratory. The roughness and number of bonding sites on each fibre surface was determined. These values will be correlated with the mechanical properties of composites made with these fibres and thermoplastic polymers in Part III of this study

The use of XPS and labelling techniques to study the surface chemistry of carbon fibres

A technique has been developed for the chemical analysis of carbon-fibre surfaces. This is based upon the labelling of acidic COOH groups, with barium Ba2+ for X-ray photo-electron spectroscopy (XPS). The technique provides a quantification of the surface concentrations of oxygen atoms and acid groups and has demonstrated the general chemisorptive ability of the fibre surface. It is shown that a saturation level exists for oxygen present as functional groups, which is approximately equal to 6000 atoms per (10 nm)2 unit surface area, for both Type I and II fibres. However, the maximum unit area concentrations of acid groups are 550 (Type I) and 1900 (Type II), as a result of oxidative surface treatments. Oxidation of Type I samples results in an approximately threefold increase in chemisorptive power. The overall picture of surface chemistry which emerges is important to an understanding of the true and complex nature of the adhesive interfacial bond, between the fibre and resin matrix, in a composite material.