M. Hayward, J. Johnston, T. Dougherty, K. de Silva
Victoria University of Wellington,
New Zealand
Keywords: advanced materials, composite materials, advanced composite manufacturing, advanced materials for engineering applications, polymer composites
Summary:
The mechanical performance of a fibre-polymer composite is largely determined by the strength of the interfacial adhesion across the fibre-matrix phase boundary. Typically, inorganic fibres and organic polymers are chemically incompatible owing to surface effects. The properties of advanced fibre-polymer composite materials are, therefore, limited by the lack of strong interfacial interactions across the phase-boundaries and the subsequent formation of interfacial voids. Coupling agents can be used to treat the surface of the fibres to enhance interfacial adhesion and improve the composites’ properties. The type of coupling agent used has a significant influence on the overall performance of a composite and selecting which coupling agent to use is a critical step in the design and optimisation of novel fibre-polymer composite materials. Appropriate selection of a coupling agent which optimises interfacial adhesion and maximises composite performance is a current challenge facing the composites industry. Historically, expensive and time-consuming trial-and-error experimentation is required to find an efficient functionalisation technique best suited for a fibre-polymer composite. Our increased understanding of the interfacial processes at a molecular level within a composite has facilitated the design of a novel test method to help in the selection of a suitable coupling agent in the development of advanced composite materials. In this work, an in-depth understanding of the key processes involved in composite interfacial adhesion was developed. This knowledge was used to develop a reliable test which can be used to predict and quantify which coupling agent will onset the best interfacial adhesion in a polymer composite and maximise the composites’ mechanical performance. The key features of the developed test, which are necessary to make it applicable as an industrial standard, are that it is fast, cost-effective and accessible. The predictive test was applied to a range of silane-based coupling agents (SCAs) to determine which would onset the highest level of interfacial adhesion in Si3N4 fibres composites made with a selection of different thermoset polymer resins. The mechanical properties of the composites were tested to determine which SCA produced the composite with the highest mechanical properties for each polymer type. The results from the mechanical testing were compared with the predictions from the developed adhesion test to determine the accuracy of the new predictive method for interfacial adhesion. Using the techniques developed in this work, the mechanical properties of the fibre-polymer composites were able to be improved by up to 40 %.