Design and synthesis of bio-based epoxidized alkyd resin for anti-corrosive coating application

Abstract

Alkyd resins with long aliphatic chain in their backbone are not suitable for high-performance applications. To overcome this limitation of alkyd resins, their backbone structure is usually chemically modified. In this study, an alkyd resin was successfully synthesized from renewable resources, including itaconic acid and linseed oil. Subsequently, the unsaturated backbone of the alkyd resin was converted to oxirane ring through epoxidation reaction in the presence of hydrogen peroxide and acetic acid. The epoxidized alkyd (EA) resin backbone was modified with various amounts of 3-amino propyltrimethoxysilane (APTMS) from 10 to 40 mol percent to enhance the anti-corrosive properties of coatings prepared from the alkyd resins. The structural elucidation of synthesized resins was described by physicochemical analysis and Fourier transform infrared and 1H nuclear magnetic resonance spectroscopies. The EA resin and APTMS-modified EA resin were cured by itaconic acid in 1:1 stoichiometric ratio on the equivalent weight basis. The differential scanning calorimetric and thermogravimetric analysis results showed that thermal properties improved with increasing APTMS content. The cured coatings were characterized for their mechanical properties, chemical and solvent resistance, gel content, and water absorption. The corrosion-resistance performance of coatings was evaluated by electrochemical impedance spectroscopy and salt-spray test. It was observed that the highly cross-linked structure of the APTMS-modified EA coatings enhanced the corrosion protective property of coating films.