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Abstract

Siloxane have low glass transition temperature(Tg), mechanical stability, excellent weatherability due to the high bonding strength of Si-O and hydrophobic property. Therefore, it was widely used as coating and medical application. Hydrophobic coating materials such as siloxane polymers were introduced for special purposes requiring high corrosion protection, especially as a top coating in heavy duty environments or an anti-fouling coating in shipbuilding industry. Nevertheless, the applications of Siloxane have been limited due to their bad workability during painting work, poor adhesion, poor compatibility with other coating materials and expensive material cost. A blending technology combining hydrophilic polymer with hydrophobic polymer may produce an attractive coating system having both high corrosion protection and good adhesion. In this study, Polyurethane coatings modified by hydroxyl terminated polysiloxane were prepared to improve the corrosion protection. Polyurethane coating was designed to give a hydrophobic property on its surface by modifying it with three types of hydroxyl terminated polysiloxane and then effects of the modification on the structure, surface hydrophobic tendency, water transport behavior and hence corrosion protectiveness of the modified polyurethane coating were examined using FT-IR/ATR spectroscopy, contact angle measurement, DSC analysis, pull off adhesion test and electrochemical impedance test. As results, the surface of polyurethane coating was changed from hydrophilic to hydrophobic property due primarily to a phase separation tendency between polyurethane and modifier by the modification. The phase separation tendency is more appreciable when modified by siloxane with higher content. Water transport behavior of the modified polyurethane coating decreased more in that with higher hydrophobic surface property. The decrease in the impedance modulus

Z

at low frequency region with immersion test for polyurethane coatings was associated with the initiation and growth of localized corrosion on carbon steel. The corrosion protection of the modified polyurethane coated carbon steel generally increased with an increase in the modifier content, confirming that corrosion protectiveness of the modified epoxy coating is well agree with its water transport behavior.