Examination of self-healing properties of chitosan-polyurethane based compounds on steel and aluminium substrates

Self-healing features of the materials are repair of the damage caused by scratching, abrasion or rupture, in other words return to a structure similar to the pre-damage situation. Benefiting from this feature, coatings have been developed to protect metallic surfaces against external enviromental effects and preserve the aesthetic appearance of the material. In case of scratching the coatings, exposed metal surface continues to be protected by self-reapair of the coatings by means of a catalyst such as heat, light and temperature. The purpose of this study, to prepare different compostions using the chitosan-polyurethane based coatings known to be self-healing feature and to observe and determine the self-healing feature by applying these compostions to the surfaces of steel (AISI 1040) and aluminum (AA 7178) substrates. In accordance wth this purpose, three different mixtures were prepared and first, their featrures of coatings metal surface have been examined. Since homogeneous thickness can not be obtained in coatings prepared by dip coating method, the spin coating method also been tried. Thickness measurement, visual inspection and electrochemical experiments were used in the characterizastion studies of coatings. In order to determine the self-healing features of the coatings, the coatings surface is cross-scratched in such a way that it touches the metal sample with a sharp tip, then immediately after scratched, after waiting for a certain period of time, visual and optical microscope examination, salt water immersion and electrochemical experiments were performed. Experimental results have shown that some compositions are not suitable for steel surface. Corrosion products were found after coating on steel surface Since there is no significant change in aluminum samples, electrochemical experiments were performed in these samples. It showed that the scratched coatings do not protect the metal surface due to the corrosion potentials in the polarization curves go into active directions after scratching and remain at these values at different times. This shows that compostion of the coating can not heal itself during the experiment. In order to provide support to experimental data, CorrosionX Heavy Duty commercial product known to be self-healing purchased and then applied to steel and aluminum substrates by spraying. Characterization studies have been performed in the same way as chitosan-polyurethane coatings. Experimental results with this product show that CorrosionX Heavy Duty protects metal surfaces and heals after scratching.