Kinetic study on the sunlight-induced degradation of acid azo dyes on silk

The effects of solar irradiation on the two azo dyes CI Acid Red 1 and CI A cid Orange 8 were investigated both on dyed silk and in aqueous solution at pH 2-4.5. When absorbed on silk, the dyes were more photoreactive, both un dergoing photodegradation, though at different rates, and displaying a prot ective action towards the fibre substrate, as evidenced by viscosimetric an alysis. In aqueous solution CI Acid Orange 8 underwent photodegradation, wi th a quantum yield around 10(-3) mol einstein(-1), while the predominant re action occurring from CI Acid Red 1 was photocyclization, especially at low pH. (C) 1998 Elsevier Science Ltd. All rights reserved.