Preparation of green cardanol-based epoxy and hardener as primer coatings for petroleum and gas steel in marine environment

•Sustainable coating based on cardanol epoxy and hardener system.•Moderate flexible epoxy organic coats based on bio-based material.•High salt resistance of epoxy coating system based on cardanol. New solvent-free based epoxy and polyamine hardener were prepared from renewable and sustainable materials based on cardanol derived from cashew nut shell liquid as alternative epoxy coats to protect the steel from corrosion. The epoxy resin was prepared from epoxidation of hydroxyl phenol and unsaturated double bonds of cardanol Novolac prepolymer. The polyamine cardanol based hardener was prepared by linking of triethylenetetramine with methyloyl cardanol derivatives. The chemical structures of the prepared cardanol epoxy resin and polyamine hardener were investigated by 1HNMR analysis. The physico-chemical characteristics of the cardanol based epoxy and hardener were investigated. The curing exotherms for different mixing ratios of cardanol based epoxy and hardener were determined at different temperature ranged from 35 to 55°C. The cured epoxy systems were analyzed for physical, mechanical, and salt spray resistance properties to optimize the best mixing ratio to obtain durable epoxy coat as anticorrosive coatings for steel in marine environments. The salt spray results were compared with those of the commercial cashew coating.