ATTEMPTS TO PHOTOSTABILIZE PAPER MADE FROM HIGH-YIELD PULP BY APPLICATION OF UV SCREENS AND CONTROL OF PH

Paper made from bleached chemithermomechanical pulp (CTMP) was treated with UV absorbers, e.g. 2,4-dihydroxybenzophenone and a 2-(2-hydroxyphenyl)benzotriazole derivative (Tinuvin 1130) to reduce the tendency of the paper to undergo photoyellowing. Whilst some of the UV absorbers offer some protection, their effect can be enhanced by use in conjunction with a reducing agent (sodium hypophosphite) and by lowering the pH of the paper by application of potassium dihydrogen phosphate. The best effect was obtained by using Tinuvin 1130 in combination with both a reducing agent and potassium dihydrogen phosphate. The use of hindered phenols in both the presence and absence of thiols offered little protection to the paper.