Photo-oxidation initiated by ultraviolet ray (UV) is a pivotal factor which affects degradation of the coatings.Quartz crystal
microbalance (QCM) testing results show that the absorbance of water and SO 2 in the coatings
increases remarkably after exposure to UV.Changes in porosity after exposure were determined by means of electrochemical impedance spectroscopy (EIS),and the results show that the porosity increases with the increase of exposure time.Fourier transform infrared spectroscopy (FTIR) analysis shows that breakdown occurs in the C-chain of the coatings after exposure to UV,which occurs at C-O bond of aromatic ester for the alkyd resin and at C-O bond of aromatic ester and C-N bond of urethane for the polyurethane resin.Some
hydrophilic groups may be formed simultaneously.Scanning electron microscope (SEM) was employed to analyze the morphology of the coatings and the results show that many pores and holes were formed after exposure to UV.It was suggested that the increase of water is the cooperation of the increases both of the amount of hydrophilic groups and of the porosity of the coatings,but the contribution of the increase of porosity may be greater.The increase of absorbance of SO 2 is the cooperation of the increase of α -H peroxide and the increase of porosity,but the contribution of the increase of α-H peroxide may be higher.