Nanocomposite coatings for healing surface defects of glass fibers and improving interfacial adhesion

Surface defects of brittle materials cause actual tensile strength much lower than the ultimate theoretical strength. Coatings can be used to 'heal' surface flaws and modify surface properties. Here, we describe an online process by which a nanometer-scale hybrid coating layer based on styrene-butadiene copolymer with single or multi-walled carbon nanotubes (SWCNTs, MWCNTs) and/or nanoclays, as mechanical enhancement and environmental barrier layer, is applied to alkali-resistant glass (ARG) and E-glass fibers. Our data indicates that the nanostructured and functionalised traditional glass fibers show significantly improved both mechanical properties and environmental corrosion resistance. With low fraction of nanotubes in sizing, the tensile and bending strength of healed glass fiber increases remarkably. No apparent strength variation appears for nanoclay coated fiber subjected to alkaline attack. We introduce a healing efficiency factor and conclude that the coating modulus, thickness and roughness are responsible for the mechanical improvement of fibers. Besides, nanocomposite coatings result in enhanced fiber/matrix interfacial adhesion, indicating nanotube related interfacial toughening mechanisms. (C) 2007 Elsevier Ltd. All rights reserved.