Photostabilization of Bagasse Chemimechanical Pulp through Acetylation in Liquid Phase

Papers made from bagasse chemimechanical pulp were chemically modified by acetylation. A combination of sodium borohydride reduction and acetylation was also tested. Efficient inhibition of photo-yellowing of papers made from bagasse CMP was achieved by acetylation. The acetylated unbleached CMP was noticeably photo-bleached during irradiation. Sodium borohydride reduction followed by acetylation had the same effect as acetylation alone at the same degree of reaction time. The prereduced, acetylated unbleached papers were, however, not brightened during irradiation. The reductive treatment had little effect in reducing the photo-yellowing of paper made from CMP pulp; a small stabilization effect was observed in the case of bleached CMP, while unbleached CMP was slightly more prone to discolour in the later phase of photoreversion. The improved stability towards light was closely related to the decrease in the phenolic hydroxyl content as a result of blocking by acetyl groups during treatment with acetic anhydride. The results support the hypothesis that phenolic hydroxyl has an important role in the process of photo-reversion of high-yield pulps.