Plasma polymerised coatings for engineered interfaces for enhanced composite performance

Abstract

Abstract Uncoupled unsized glass fibers were subjected to a continuous treatment to coat the tows with an acrylic acid/octadiene plasma copolymer. The fibres were separated prior to coating in order to minimise shadowing effects associated with the coating of fibre bundles. The plasma polymer coating was analysed for composition and coating uniformity using high resolution XPS, which confirmed that increasing acrylic acid content in the plasma copolymer led to an increase in retained surface carboxylic acid groups (confirmed by trifluoroethanol derivatisation). The concentration of hydroxyl or ether groups in the plasma polymer was higher than expected, which affected the retained COOH functionality. The single filament strengths of the coated and uncoated, separated control fibres were comparable. However, for the plasma polymer coated fibers, there was less variability (assessed using Weibull modulus), in comparison to the separated unsized fibres. Single fibre fragmentation testing was used to identify the change in the interfacial response as a function of the fibre coating. It was noted that the presence of the plasma polymer coating altered the interfacial properties (which were assessed using the Kelly–Tyson model, and the CSTF and STE methodologies). A functionalised plasma polymer with high acrylic acid content gave rise to a strong interfacial bond, with little debonding. The unfunctionalised octadiene plasma polymer coated fibres, exhibited a poor interfacial strength, with significant levels of debonding. It is concluded that glass fiber tows can be continuously coated with plasma copolymers, leading to uniform levels of coating throughout the fibre tow, thus giving the ability to tailor the interfacial response of the composite.