Preparation and Properties of Superhydrophobic Coatings Based on Cardanol Polybenzoxazine

Cardanol-based benzoxazine (C-a) was synthesized from cardanol, paraformaldehyde and aniline, and then superhydrophobic coating combined with cardanol-based polybenzoxazine. Silica nanoparticles (SiO₂ NPs) were produced through spinning coating technique and thermal curing method. The chemical structure of C-a benzoxazine monomer was characterized by Fourier transform infrared (FT-IR) spectroscopy and nuclear magnetic resonance (NMR). Then, the polybenzoxazine coating (PC-a) was fabricated through thermal curing method and exhibited surface free energy of 22.5 mJ/m² after thermal curing at 200℃ for 1 h. The wettability properties of PC-a/SiO₂ coating were characterized by optical contact angle (OCA) meter. As a result, the water contact angle of pure PC-a coating was (104±2)°, showing a hydrophobic property. By incorporating different contents of SiO₂ NPs, a "lotus effect" superhydrophobic PC-a/SiO₂ coating with water contact angle of (166±4)° and water sliding angle of 6°, a "petal effect" superhydrophobic PC-a/SiO₂ coating with water contact angle of (151±3)° could be both developed. After thermal treatment at 200℃ for 1 h, the water contact angle and sliding angle of PC-a/SiO₂70 coating were (163±4)° and 7°, respectively. Therefore, the superhydrophobic PC-a/SiO₂70 coating could keep its stable superhydrophobicity with a wide range temperature. Moreover, the as-prepared hydrophobic PC-a coating still had hydrophobicity with a water contact angle of (97±1)°. Superhydrophobic PC-a/SiO₂70 coating could both keep stable after UV exposure for 8 h. So the hydrophobic PC-a coating and superhydrophobic PC-a/SiO₂70 coating had UV resistant property. In conclusion, this superhydrophobic coating based on cardanol polybenzoxazine shows excellent thermal stability and UV resistant property, which show broad application in the fields of oil-water separation and anti-corrosion.