The effect of hydrophobic coating applied to mica reinforced epoxy matrix composites on the water absorption properties of the composite

In this study, epoxy matrix composites containing mica with different particle sizes (40 and 80 µm) and quantities (0, 10, 20, 40 wt.%) were produced by the casting method. Composites were coated with a commercial agent imparting hydrophobicity in order to decrease water absorption. The bulk density and % open porosity values of the finished composites were determined by Archimedes' principle, and detailed microstructural analysis was carried out with scanning electron microscopy (SEM). The surfaces were characterized by the contact angle and roughness measurements. The durability and protective performance of the coating were quantified by the water absorption tests for various immersion times and temperatures (ASTM D570-98) and salt water resistance tests. Microstructure analysis showed that for all filler ratios and particle sizes, mica particles were homogeneously dispersed in the epoxy matrix and the mica–polymer interface was well bonded. It has been observed that the % theoretical density values of the composite products vary between 91.1 and 98.6%, and the total porosity varies between 1.4 and 8.87%. As the amount of mica increased, the total porosity also increased, regardless of the size of the mica particles. The neat epoxy matrix absorbed a higher quantity of water than composites in almost all cases, and the water absorption of the composites decreased with the increasing mica quantities and the decreasing particle size. The hydrophobic coating definitely caused the water absorption rates of the composite samples to decrease and the salt water resistance to increase, rendering them a convenient moisture- and corrosion-resistant composite material.