Maleic acid grafted low density polyethylene for thermally sprayable anticorrosive coatings

Low density polyethylene (LDPE) coatings are being used in an ever growing range of applications. However, non-polar characteristics of LDPE make its adhesion poor to metal substrate and so become less suitable for anticorrosive coating application. An anticorrosive coating can therefore be developed if LDPE is modified with requisite polar groups. In the present work, a polar group has been introduced in polyethylene matrix by grafting maleic acid. Grafted LDPE was characterized by chemical method, Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), thermo-gravimetric analysis (TGA), melt flow index (MFI), particle size analysis and hot stage optical microscopy. The presence of carbonyl peak of high intensity, high acid value and low melt flow index value confirmed grafting of maleic acid on LDPE. Change in crystallization behaviour of LDPE has been noticed after grafting. Grafted LDPE was applied on grit blasted mild steel surface by flame spray technique and adhesion study showed improved adhesion of grafted LDPE than LDPE. The coated panels were evaluated for resistance to corrosion in salt spray, humidity cabinet and seawater. The corrosion resistance of modified LDPE was also studied by AC Impedance technique. Grafted LDPE showed satisfactory corrosion resistance. Grafted LDPE was pigmented with red iron oxide and pigmented composition has shown improved resistance to corrosion in laboratory tests.