Study for prevention of photo yellowing occurring at TMP

Abstract

Light-induced, yellowing of mechanical pulps proceeds through photooxidative discoloration of lignin in fibers. Lignin absorbs near UV light, which creates short-lived, high-energy excited molecules generating free radicals. Free radicals reacts in the presence of oxygen to form yellow chromophores. Several different strategies have been applied to inhibit photoyellowing of thermomechanical pulps (TMP). Even though the initial brightness of TMP bleached by sodium borohydride was lower than that of TMP done by hydrogen peroxide, sodium borohydride decreased the rate of photoyellowing more than did hydrogen peroxide. UV-light absorbers treated on BTMP adsorbed UV radiation more strongly than untreated pulp. Hardwood bleached kraft pulp (Hw-BKP) mixed with BTMP contributed to the decrease in the rate of photoyellowing. When oxidized starch adding UV absorbers coated paper containing BTMP, the UV absorbers had a meaningful effect on the inhibition of photoyellowing.