The Effect of Low Power Ammonia and Nitrogen Plasmas on Carbon Fibre Surfaces
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THE EFFECT OF LOW POWER AMMONIA AND NITROGEN PLASMAS ON CARBON FIBRE SURFACES **C.JONES AND *E.SAMMANN National Centre for Composite Materials Research, University of Illinois, Urbana, 111.61801;*Materials Research Laboratory, University of Illinois.(**Now at Liverpool University, England) ABSTRACT The effect of low power nitrogen and ammonia plasmas on carbon fibre surfaces has been studied using X-ray photoelectron spectroscopy(XPS) and scanning electron microscopy (SEM). A comparison is made between two polyacrylonitrile based fibres and a pitch based fibre. Grazing angle techniques have been exploited to probe only the first 12-15A of the fibre surface. Plasma treatments were carried out in an insitu plasma treatment cell which was attached to a PHI 5400 X-ray photoelectron spectrometer enabling the immediate effects of the plasma to be studied before the treated surface was exposed to air. INTRODUCTION The properties of composite materials are not only governed by the properties of the individual components but also by the interface between them. Successful reinforcement of composite materials is only achieved by obtaining sufficient stress transfer between fibre and matrix. This can be realised by physical and/or chemical adhesion between the two. However, for recent applications an extremely strong interface is not always desirable. It would be ideal to be able to design the interfacial properties to suit a particular application for example increase stiffness or promote toughness at the interface. One method of achieving this would be to chemically graft a monomer with a suitable backbone onto the fibre surface. It would also be necessary for this monomer to be fully compatible with the resin. An ideal example would be another epoxy with the desired backbone. Some of the most common curing agents for epoxy resins are amines. These allow curing of the resin at room temperature. It would therefore seem beneficial to introduce amines onto the fibre surface which would certainly have the potential to react with the epoxy coating at room temperature. The effect of ammonia plasmas on fibre reinforcement has been examined by several research groups[I-51, however, a thorough understanding of the chemical changes induced on fibre surfaces and whether or not they play a a role in fibre resin adhesion is yet to be determined. A method of selectively introducing amines onto the surface would be a great advantage. Introducing the desired fibre surface chemistry without destroying the mechanical properties of the fibre itself would also prove very useful. Most of the plasma treatments used to date however, remove a substantial amount of material causing pits to form in the fibre surface [e.g.2,3]. This has led the authors to develop a low power plasma (
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