Fabrication of renewable myristic acid based polyurethane nano zinc phosphate hybrid coatings to mitigate corrosion of mild steel

Abstract

Purpose The present study aims to demonstrate the use of renewable source in the preparation of polyurethane (PU) coatings and mitigation of corrosion of mild steel using nano zinc phosphate. Results indicated improvement in the properties of the PU coatings, especially anticorrosive properties by the addition of nano zinc phosphate. Design/methodology/approach Renewable-source-based polyestermyristamide polyol was synthesized using myristic acid as a starting material. The synthesis of polyol was carried by amidation as well as by esterification by a one-pot route. The structure of the prepared polyestermyristamide was confirmed with the support of end-group analysis and spectral study. PU coatings were prepared from synthesized polyestermyristamide polyol and used to protect metal substrate against corrosion. Corrosion properties of the prepared PU were found to be lower; hence, to improve the performance of these coatings, nano zinc phosphate was added to the coatings. The nano zinc phosphate was synthesized in the laboratory by reported sonication method and analyzed for morphology by scanning electron microscopy. Performance of coatings was studied with respect to effect of percentage nano zinc phosphate on thermal stability, mechanical properties and chemical resistances of PU coatings. Findings The combination of zinc phosphate nano rods and particles in myristic acid-based PU coatings provided substantial corrosion barrier properties to the coatings. Different per cent of the synthesized zinc phosphate nano rods and particles were loaded into the matrix, and corresponding coatings were estimated for corrosion resistance, thermal and chemical properties. Immersion study of the coated panels in 3.5 per cent NaCl solution showed good corrosion resistance for both PU coatings containing 2 and 3 per cent nano zinc phosphate. Practical implications This paper has provided the solution to replace existing petroleum-based raw materials with myristic acid as a renewable source in preparing PU coatings. Conventional coatings act as physical barriers against aggressive species but do not have ability to perform as permanent impassable to corrosive species. Hence, nano-sized zinc phosphate is used as corrosion inhibitor in to the synthesized PU coatings for enhancing anticorrosive performance. Originality/value In the paper, polyesteramide polyol is synthesized using renewable-source-based material, i.e. myristic acid to replace existing petroleum-based acid as a greener approach. Normally, vegetable oils are preferred as they have such kinds of polyols. The polyesteramide reaction is one pot that avoids the extra steps required in the synthesis. Further, it has been found that the pristine renewable coatings are unable to fully protect subtract from corrosion, whereas an addition of the nano-size zinc phosphate has enhanced the corrosion properties of the coatings.