Surface treatment of chemithermomechanical pulp (CTMP) to prevent brightness reversion

The photostabilizing effects of sodium borohydride (SB) and dimethyl sulfate (DS) chemical modification; thioglycerol (TG), 2.2?-oxydiethanethiol (OD), and 1-dodecanethiol (DC), as free radical scavengers; and benzophenone (BF), 2,4-dihydroxybenzophenone (DHBF)), and 2,2?,4,4?-tetrahydroxybenzophenone (THBF) as UV-absorbers. were investigated for bleached chemithermomechanical pulps. All chemicals were applied by spraying on the surface of paper, in a sequential treatment of chemical modification, free radical scavengers and UV-absorbers. Certain additive combinations, such as SB-DS-TG-DHBF, exhibited a synergistic interaction effect that assured substantial brightness stabilization to light and heat treatment. Sequential treatment is somewhat better than when the additives are mixed before spraying on paper. Chemical modification treatment (SB + DS) on the surface of paper contributed only with 0.6% of the total brightness stabilization, whereas the free radical scavenger, TG, contributed with 25.1% and the UV absorber, DHBF, with the remaining 74.3%