An investigation of UV photo-degradation on acrylic polyurethane varnish coatings

Acrylic polyurethane varnish coatings were exposed to artificial weathering test (UVB radiation/condensation) for different periods of time. The changes of properties and barrier protection property were monitored by adhesion tester, glossmeter, spectrophotometer, Fourier transform infrared spectroscopy (FTIR) and electrochemical impedance spectroscopy (EIS). The results showed that the adhesion strength and low frequency impedance |Z|_f at a fixed frequency from EIS spectra decreased, while gloss loss and yellow index increased with increasing aging time. FTIR results showed that the increase of adhesion strength or |Z|_f at 12 days exposure may be attributed to the re-association of scission molecular segments. The low frequency impedance of intact coatings for different exposure time correlated with other physical and chemical properties.