High-performance anti-corrosion polybenzoxazine nanocomposite coatings containing functional SiO2-BNNS nano-hybrid fillers based on double-layer structure: Design, preparation and performance

To fabricate high-performance anti-corrosion double-layer structure polybenzoxazine (PBZ) nanocomposite coating, herein, the main-chain benzoxazine (BA-ddm) and diamine benzoxazine (Ph-hda) were first synthesized and then compounded to produce PBZ copolymer matrix (PB5). Simultaneously, NH 2 -BNNS and Epoxy-SiO 2 were obtained through the surface decoration by APTS and GPTS to the surfaces of BNNS and SiO 2 , respectively. Then, a series of nano-hybrid fillers (SiO 2 -BNNS) were prepared by hybridizing NH 2 -BNNS and Epoxy-SiO 2 at various mass ratios, and finally incorporated into the PBZ matrix to investigate the optimal hybridization ratios and the optimal addition contents of the nano-hybrid fillers. The results showed that the addition of SiO 2 -BNNS (with mass ration of 1:2) nano-hybrid filler into PBZ matrix significantly enhanced the corrosion resistance of the PBZ nanocomposite coating. When the SiO 2 -BNNS(1:2) content reached 3 wt%, the |Z| 0.01 Hz value of the PBZ nanocomposite coating reached 1.06 × 10 11 Ω·cm 2 . To further improve the comprehensive properties of the PBZ coating, a double-layer structure PBZ nanocomposite coating was fabricated through a layer-by-layer coating and layer-by-layer curing approach. The bottom layer consisted of a 3 % SiO 2 -BNNS(1:2)/PBZ coating, while the top layer was composed of a SiO 2 -BNNS(1:2) nano-hybrid particle layer. The results indicated that when the number of top SiO 2 -BNNS(1:2) layers was 4, the water contact angle (WCA) of the coating increased to 126.9°, the thermal decomposition temperature ( T d ) reached 446.8 °C, and the impedance modulus increased to 1.43 × 10 11 Ω·cm 2 . Compared with the 3 % SiO 2 -BNNS(1:2)/PBZ coating, the double-layer structure PBZ nanocomposite coating exhibited excellent hydrophobicity, thermal stability, and corrosion resistance.