Fibre-matrix adhesion -carbon fibres

The TEM in its various forms is widely used in materials science, and some of its applications are studies of adhesion. It has helped to elucidate failure and bonding mechanisms in composites (see Fibre matrix adhesion - carbon fibres). An important use is in the examination of the structure of surface oxides. Several techniques have been employed. 

Carbon fibres are frequently subjected to an oxidative etching process to improve adhesion, but a size is sometimes used (see Fibre-matrix adhesion - carbon fibres). Sizing is generally ineffective with aramid fibres because of lack of susceptible sites, but plasma deposition of amine groups is said to improve adhesion. 

As with glass, a range of cloth constructions is available. Further details of the fibres and their surface treatment are discussed under Fibre-matrix adhesion - carbon fibres. 

There is a related article on Fibre-matrix adhesion - carbon fibres. 

King JA, Buttry DA, Adams DF, Development and evaluation of surface treatments to enhance the fibre matrix adhesion in PAN based carbon fibre liquid crystal polymer composites 2. Electrochemical treatments, Polym Composites, 14(4), 301-307, 1993. 

SURFACE TREATMENT OF CARBON FIBERS TO OPTIMIZE FIBRE-MATRIX ADHESION... 

Nanofillers are increasingly being used as high-performance additives for plastics and Finegan et / [ 51 ] have used DMA to qualitatively and quantitatively study the fibre-matrix adhesion of various carbon nanofibres that had been subjected to several different types of surface treatments in a polypropylene matrix. Lee, Hsieh and McKinley [52] have characterised a nanocomposite of poly(methylmethacrylate) containing 1-7.5% of modified montmorillonite clay. They established a number of relationships, which included that the storage and loss moduli were strongly dependent upon the clay content, and that the presence of the clay increased the distortion temperature of the plastic. 

In previous work (30-321. it has been suggested that the adhesion between a carbon fibre and an epoxy matrix is essentially the result of physical bonds, either dispersive or polar. It is clear from the results in the last column of Table VI that there is no correlation between x and the reversible energy of adhesion WA, calculated as the sum of the dispersive and polar interactions at the fibre-matrix interface. 

Inverse gas chromatography at infinite dilution appears to be a powerful tool for studying the surface properties of carbon fibres and polymer matrices. The use of alkane probes and acid/base probes allows the characterization of the surfaces in terms of their London dispersive component of surface energy and their acid/base or acceptor/donor characteristics. A strong correlation was obtained between fibre-matrix adhesion, measured by a destructive fragmentation technique, and the level of acid base interactions calculated from the chromatographic analysis. 

If concrete removal is not required or supplementary reinforcing bars cannot be used, external reinforcement can be applied. For instance, steel bars may be encased in a shotcrete layer or steel plates may be bonded onto the concrete surface. Recently, the use of steel plates has been substituted by fibre-reinforced plastics (F. R.P.), that are composite materials with glass, aramide or carbon fibres embedded in a polymeric matrix (usually an epoxy system). F. R.P. are available in the form of laminates or sheets that are bonded to the concrete surface using an epoxy adhesive [11]. They are typically used to improve the flexural and shear strength or to provide confinement to concrete subjected to compression. The... 

One of the first applications for the adhesive grade of PES is as a structural adhesive to upgrade the temperature performance of epoxy resins (17). Mixtures of PES with epoxy resin are used to stick the aluminium outer skin on to aluminium honeycomb and such structures are designed for a 10,000 hr lifetime at 300°F whioh is typical of idle performance requirements of some supersonic aircraft. This adhesive grade can also be used as a matrix for making carbon fibre composites which show hi ... 

Feih S, Schwartz P, Modification of the carbon fibre matrix interface using gas plasma treatment with acetylene and oxygen, J Adhesion Sci Technol, 12(5), 523-539, 1998. 

Yumitori S, Nakanishi Y, Effect of anodic oxidation of coal tar pitch based carbon fibre on adhesion in epoxy matrix. 2. Comparitive study of three alkaline solutions. Composites Part A—Appl Sci Manuf, 27(11), 1059-1066, 1996. 

For systems involving, on the one hand, poorly polar matrices, such as polyethylene, polyvinylchloride and polyurethane and, on the other hand, untreated and surface treated glass or carbon fibres, it has been shown in our laboratory [12,13] that a linear relationship can be established to a first approximation between t and the reversible work of adhesion W defined by equation (5). However for more polar matrices, like epoxy resin for example, such a relationship is no longer valid, since strong specific interactions are now established at the fibre-matrix interface. 

A tentative model has been proposed to relate the interfacial shear strength at the fibre-matrix interface, measured by a fragmentation test on single fibre composites, to the level of adhesion between both materials. This last quantity has been estimated from the surface properties of both the fibre and the matrix and was defined as the sum of dispersive and acid-base interactions. This new model clearly indicates that the micromechanical properties of a composites are mainly determined by the level of physical interactions established at the fibre-matrix interface and, in particular, by electron acceptor-donor interactions. Moreover, to a first approximation, our model is able to explain the stress transfer phenomenon through interfacial layers, such as crystalline interphases in semi-crystalline matrices and interphases of reduced mobility in elastomeric matrices. An estimation of the elastic moduli of these interphases can also be proposed. Furthermore, recent work [21] has shown that the level of interfacial adhesion plays a major role on the final performances (tensile, transverse and compressive strengths and strains) of unidirectional carbon fibre-PEEK composites. 

To investigate the adhesion between fibres and matrix, composites containing 60 vol. % of coated Hercules AS4 and Grafil XAS carbon fibres in a matrix of epoxy resin were manufactured. 

Further investigations should be realized in plasma treatment of carbon fibres in relation to acidic surface groups. An acidic surface could be produced in a benzene/ argon/sulphur dioxide plasma. Because of the rather basic matrix of the polycarbonate, an acidic fibre surface should improve the adhesion to a basic matrix due to acid-base interactions. 

The performance of all Composite materials is dependent on the adhesion between the different phases. In this article, aspects relevant to carbon-fibre reinforced plastics are discussed. There is a parallel article on Fibre-matrix adhesion - glass fibres. A discussion of the fibre-matrix interface can be found in Fibre composites - introduction. 

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