STRUCTURE–PROPERTY RELATIONSHIP AND OPTIMAL FILLER CONTENT IN KAOLIN- AND GRAPHITE-FILLED EPOXY NANOCOMPOSITE COATINGS

Determining the optimal filler content is one of the central practical problems in the design of filled epoxy coatings, since the same filler can either reinforce or weaken a composite depending on its concentration and dispersity. This paper analyses the microhardness behaviour of solar-cured epoxy nanocomposite coatings filled with four industrial kaolin grades (AKF-78, AKS-30, AKT-10, AKO) and mineral graphite, at filler contents ranging from 10 to 60 parts by mass, in order to identify the concentration range at which each filler yields the best mechanical performance. The data show that microhardness does not change monotonically with filler content: each filler type reaches a distinct maximum before declining, and the position of this maximum differs by up to 20 parts by mass between filler grades. The results are interpreted in terms of particle wetting, composition viscosity, and the specific surface area of the filler, and practical recommendations are given for selecting filler content in cast composite coatings.