Preparation and properties of silane-modified cardanol–benzoxazine for hydrophobic coating

Cardanol is a kind of green industrial raw material, refined from cashew nut shell oil by advanced technology, which has shown potential for anticorrosion coating application. A new cardanol-based benzoxazine monomer (CB) was synthesized by Mannich condensation of a cardanol, paraformaldehyde, and cardanol aldehyde amine (Carala), which was prepared based on cardanol, paraformaldehyde, and triethylenetetramine, and finally, the cardanol-based benzoxazines containing amino group were modified by silane (CBSi). Cardanol, Carala, and CB were characterized by Fourier transform infrared spectroscopy and proton nuclear magnetic resonance spectroscopy. Furthermore, the cured films have been evaluated by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), respectively. The result of DSC of CB and CBSi showed that curing behavior of CBSi was similar to that of CB; however, the enthalpy of polymerization reaction corresponding to CB and CBSi is 84.7 J g−1 and 91.3 J g−1, respectively, and exothermic enthalpy of CBSi is slightly higher than that of CB. TGA results illuminated that the thermal stability and char yield of cardanol-based polybenzoxazine could be enhanced due to increment of silane, and residual char yield at 700°C of CBSi30 is 13%. Especially, incorporation of silane could improve the water contact angle, which can increase from 78.7° to 98.9° when the ratio of γ-(2,3-epoxypropoxy) propytrimethoxysilane to CB increases from 0% to 30%.