Improvements of Hydrophobicity and Toughness of Epoxy Coatings Modified with Hydroxyl-terminated Fluororubber

To address the brittleness of epoxy resin (EP) caused by high crosslinking density, the modification of epoxy resin with flexible rubber segments was proposed in this work. Bisphenol A-type epoxy resin (E51) was reacted with isocyanate-terminated groups via an addition reaction to prepare a prepolymer (E51-TDI). Subsequently, E51-TDI was grafted with hydroxyl-terminated fluororubber (HTFR) to synthesize a high-toughness fluorinated epoxy resin (E51-TDI-HTFR) with side chains. A mixture of E51-TDI-HTFR and curing agent (D230) was used to fabricate the coating. The chemical structure of the modified epoxy resin and the thermal, hydrophobic, mechanical, and cavitation erosion resistance of the coatings were investigated. When the HTFR concentration was 25%, the epoxy coating exhibited the best hydrophobicity, mechanical properties, and cavitation resistance. The contact angle of the modified epoxy resin was increased to 110°. Meanwhile, the elongation at break increased to 46.40%, which was approximately four times that of the unmodified coatings. The fracture surface gradually became rougher as the HTFR content increased, indicating a ductile fracture characteristic. Although the addition of HTFR slightly reduced the glass transition temperature, it maintained good thermal stability. In addition, the cavitation erosion resistance of the epoxy coatings was enhanced. This study provides theoretical support for the development of high-toughness and hydrophobic epoxy coatings.