Multiscale interfacial correlation of plasma polymer coated E-glass fibre composites

• Main Author: Liu, Zheng
• Published: University of Sheffield 2007
• Subjects: 666
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.485890

Glass fibres are usually coated with a complex mixture of an adhesion promoter and film former in an emulsion. The former is usually a silane which enhances adhesion to the matrix while the latter protects the fibres from damage during handling and ma'nufacture. Chemical vapour deposition (CVD) which introduces a function alised coating'specific to the matrix has much potential as a gas phase environmentally friendly technique. One such technique is low power (cold) plasma polymerisation, which can deposit a conformal molecularly thin coating with expected functional chemistry. In this work, plasma polymerization was used to modify the interfacial adhesion between the fibres and epoxy resin, to improve the interfacial properties, provide a correlation between single filament and high volume fraction adhesion tests for composites, and ultimately demonstrate the value of plasma polymerization as a functional coating for fibre reinforcements. Specifically, uncoated E-glass fibre tows were continuously coated with acrylic acid / 1, 7octadiene or allylamine 11, 7-octadiene plasma copolymers in the plasma reactor to optimize the bond with matrix resin. The surface chemistry of the coated fibres was characterised using X-ray photoelectron spectroscopy (XPS) and trifluoroethanol derivatisation (TFE). The concentration of the functional group (COOH), which can react with epoxy groups in the matrix, in the deposit increased with the acrylic acid content in the monomer feed. The similarly reactive amine (NH2) group exhibited the same trend as allylamine concentration in the monomer feed. The results of single fibre tensile tests show that the plasma polymer coating did not affect the fibre tensile strength, but reduced the variability within the statistics of the data. The interlaminar shear properties of high glass fibre volume fraction (Vj) composite were measured and correlated with interfacial properties determined by the single fibre fragmentation test. The thickness of the plasma polymer coating was varied using the residence time in the reactor. It was shown that at a thickness < 5 nm the interfacial stress transfer at a fibrebreak, in a composite, was greatest. This was attributed to the formation of an interphase through diffusion of the matrix into the crosslink coating on the fibre surface.