Eco-friendly protective coatings based on poly(urethane sulfone amide) dispersions for carbon steel

Abstract

Eight eco-friendly protective coatings (PU, PUA1, PUA3, PUA5, T30PUA5, T60PUA5, T90PUA5, and T120PUA5), were formulated based on series of laboratory-synthesized poly(urethane co-sulfone amide) copolymer dispersions (CPDs) as binders. The first four formulations were based on CPDs prepared by the copolymerization reaction of PU based on castor oil (CO) with aromatic polyamide sulfone (APAS) in four different concentrations (0%, 1%, 3%, and 5% solid to solid). The other four formulations were based on CPDs synthesized by the copolymerization reaction of PU based on transesterified CO with triethanolamine (CON) at different time intervals (30, 60, 90, and 120 min) with APAS at only one concentration. The effect of the degree of copolymerization and transesterification reactions on the physical, chemical, and mechanical properties of the formulated coatings was studied. The results showed that the copolymerization and transesterification reactions led to an increase in the density and viscosity of the coating formulations. Additionally, the hardness of the dried films increased with copolymerization and transesterification reactions. The transesterification reaction decreased the adhesion force of the coated films. The copolymerization process caused a decrease in the water uptake of the coated films. However, the transesterification reaction increased the water uptake. The prepared formulations were applied on carbon steel substrates to estimate their efficiency as eco-friendly protective coatings for steel. The weight loss of the coated steel panels decreased with an increase in the amount of the copolymerized APAS within the PU chains, while it increased with an increase in the transesterification time of the CON used in the preparation of the coated copolymers. From the corrosion test results, PUA5 and T30PUA5 showed the best anticorrosive performance as estimated from the degree of rusting, weight loss measurements, and failure at scribe.