Steel protective coatings of cottonseed oil alkyd modified urethane/mercapto methyl tetrazole adduct

Author(s): Heba A.Mohamed, Badran M.Badran

The growing interest toward energy conservation and green environment driven the coating technologists to replace petroleumbased polymeric binders with renewable sources. Cottonseed oil alkyd (CSA) was prepared in the laboratory by alcoholysis of cottonseed oil with glycerol followed by esterification with phthalic anhydride and an excess of pentaerythritol to obtain the polymer with excess hydroxyl value. The structure of CSA polymer was confirmed by FTIR spectral analysis and its molecular weight was investigated by gel permeation chromatography (GPC). Instantly before coating steel surface, CSAwasmodified by reactionwith TDI at roomtemperature to introduce polyurethane linkage and got modified cottonseed alkyd modified urethane (CSAU) coat. Thermo gravimetric analysis (TGA) was used to investigate the thermal stability and curing behavior of the modified CSAU coating. The modified CSAU paints were formulated and prepared. The performance of high molecular weight heterocyclic 5-mercapto-1-methyl tetrazole adduct (MMT) in the modified paint (CSAU/MMT) was studied. Drying time tests, crosscut adhesion test, impact strength, pencil hardness, chemical and water resistance were used to evaluate the modified CSAU and CSAU/MMT paints. Corrosion resistance tests, including blistering, scribing and unscribing area of metal surface in 5% NaCl solution in addition to the weight loss determination of steel are specialized corrosion tests to evaluate CSAU and CSAU/MMT as anticorrosive paints. It was found that cottonseed oil could be modified successfully and replace petroleum raw materials in anticorrosive coatings and paint industries. It exhibited good physical, mechanical performances and chemical resistance. It’s characterized by high thermal stability. Incorporation of only 0.02% MMT adduct to CSAU paint, increased the corrosion inhibition efficiency to a higher extent.

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