PU-coating performance of bio-based hyperbranched alkyd resin on mild steel and wood substrate

In the present research article, a hyperbranched alkyd resin was synthesized by using bio-based material (castor oil based fatty amide) and pyromellitic dianhydride. The synthesized hyperbranched alkyd resin was characterized by nuclear magnetic resonance (NMR) and Fourier transform infrared (FTIR) spectroscopy. The polyurethanes (PMFAI and PMFAM) were prepared from hyperbranched alkyd resin and diisocyanates [isophorone diisocyanates (IPDI) and methylene diphenyl diisocyanate (MDI)] maintaining the OH:NCO ratio of 1:1.2. These polyurethanes were used in coating applications on mild steel and wood panels. The performance of cured polyurethane coatings was studied in terms of crosscut adhesion, impact resistance, gloss, scratch hardness, and chemical resistance. The chemical resistance test was performed by immersion method in 2 N HCl, 2 N NaOH, 3.5% NaCl solution, xylene, and water. The corrosion rate and anticorrosion efficiency of the coating panels were determined by a potentiostat. From a study of coating properties, it was found that the PMFAI and PMFAM exhibited better coating properties as compared to reported linear alkyd polyurethanes. The stain test of coatings was performed on wood panels. The thermal behavior of the coatings was determined by thermogravimetric analyzer. The surface morphology of coating films was examined by scanning electron microscopy and atomic force microscopy. It was found that the coating properties of hyperbranched alkyd resin were excellent as compared to linear alkyd resin polyurethanes.