Full bio-based phenalkamine prepared by one-pot process used for preparing solvent-free protective coating

The utilization and conversion of renewable biomass is a promising strategy to attain sustainable society. Herein, full bio-based phenalkamine (FBA) was prepared using three bio-based raw materials, which were cardanol, furfural and 1,5-pentanediamine, by one-pot process based on Mannich reaction without catalyst and solvent. Then, FBA was used to cure epoxy under the condition of solvent-free, which can eliminate the negative effect of volatile organic solvents (VOCs). Attributed to the long chain, large steric hindrance and strong hydrophobicity of FBA, solvent-free FBA/epoxy coating had appropriate curing speed, non-defects morphologies, high flexibility (impact resistance height: 100 cm, bending resistant shaft diameter: 2 mm), low water absorption (0.65 wt%), and long-term protective performance (|Z|0.01Hz = 1.23 × 109 Ω·cm2 after 100 d immersion under harsh environment). Compared with partial bio-based phenalkamine (MD1041)/epoxy coating and petroleum-based phenalkamine (T31)/epoxy coating, FBA/epoxy coating had satisfactory underwater-cured protective properties (|Z|0.01Hz>106 Ω·cm2 after directly cured and immersed for 100 d in 5 wt% NaCl solution) based on the strong hydrophobicity and dense crosslink networks. Notably, FBA/epoxy coating had improved performance compared with purified FBA (PFBA)/epoxy coating, which was related to the high crosslink density coming from the residual 1,5-pentanediamine. This work provided some enlightenment to prepare solvent-free coating using full bio-based materials.