Effect of surface pretreatment on water absorption and wet adhesion of organic coatings

A study has been conducted on the effects of surface pretreatment with 3-aminopropyltriethoxysilane (3-APS) on the water absorption and adhesion behaviour on mild steel and glass substrates of two commercial organic coatings, one an alkyd coating and the other a two pack epoxypolyamide coating. The results have shown that using 3-APS for surface pretreatment before coating results in a significant reduction of total water absorption for both coating systems on a glass substrate. However, for the mild steel substrate, treatment with 3-APS reduces water absorption using an alkyd system, but increases it in the epoxy system. The results also indicate that using 3-APS for pretreatment enhances the overall wet adhesion performance for alkyd coatings on steel and epoxy and alkyd coatings on glass substrates but not for epoxy on steel. These data are consistent with the known adsorption behaviour of 3-APS on steel, i.e. as an easily hydrolysed hydrogen bond to the amine group, rather than as the more stable metal–oxide–silicon bond.