Surface properties of epoxy clay nanocomposite coating

Epoxy clay nanocomposite coating was evaluated for its surface hardness, surface roughness, surface morphology and topography. Full factorial design consisting of 3 input factors (nanoclay loading, sonication amplitude and sonication time) and one output response (hardness) was applied in order to optimize hardness as well as to evaluate the effect of input factors and their interactions on the hardness of epoxy clay nanocomposite coating. Three levels were chosen for all the factors and hence 27 experimental trials were conducted. It was found out that all the three factors are significant; however the contribution of nanoclay loading and sonication time is very high compared to sonication amplitude. Nanoclay loading has negative influence on hardness whereas the other two factors have positive influence. The maximum hardness is obtained when nanoclay loading was 1 wt%, sonication time was 20 min and sonication amplitude was 100%. Scanning electron microscope (SEM) and atomic force microscope (AFM) was used to evaluate the morphology and topography of the coating. The reasons for minimum and maximum hardness in the full factorial experimentation is explained using SEM and AFM images. It was observed that at nanoclay loading of 1 wt%, there is better dispersion of nanoclay with smaller cluster size. Increase in nanoclay increases the cluster size and surface roughness but due to reduced hardening effect decreases the hardness of the coating. (C) 2020 The Authors. Published by Elsevier Ltd.