Anthraquinone (AQ) is used in the pulp and paper industries as a cooking catalyst. However, because AQ is "possibly carcinogenic", it is no longer approved in Germany for the manufacture of paper and paperboard that contact food. To address this problem, we examined 2-methylanthraquinone (2-MAQ) , a natural anthraquinone from teak (Tectona grandis) wood. Eucalyptus globulus wood was subjected to kraft cooking at 145℃ for 3 h with 0.03% 2-MAQ and 15-19% active alkali to provide pulp in 55.5-58.1% yield. Kraft cooking with the acetone extract of Myanmar teak wood increased pulp yield by 1.6% but decreased kappa number by two points compared to that with only 2-MAQ. Ames testing suggests that 2-MAQ is not mutagenic. Unbleached and oxygen-bleached pulp contained 0.40-2.90 ppm and 0.21-0.39 ppm residual 2-MAQ, respectively, while 2-MAQ was not detected in fully bleached pulp; therefore, this pulp should be safe for food-packaging use.
Considering the toxicity of the impurities of synthesized anthraquinone, this study clarified new catalytic compounds for kraft cooking with improved carbohydrate yield and delignification and less mutagenicity, which are important for ensuring the safety of paper products in contact with food. The 2-methylanthraquinone contents of teak (Tectona grandis) woods were 0.18–0.21%. Acetone extracts containing 2-methylanthraquinone from Myanmar and Indonesia teak woods as additives improved lignin removal during kraft cooking of eucalyptus wood, which resulted in kappa numbers that were 2.2–6.0 points lower than the absence of additive. Myanmar extracts and 2-methylanthraquinone improved carbohydrate yield in pulps with 1.7–2.2% yield gains. Indonesia extracts contained more deoxylapachol and its isomer than 2-methylanthraquinone. The residual content of 2-methylanthraquinone in the kraft pulp was trace. Although Ames tests showed that the Indonesia and Myanmar extracts were mutagenic to Salmonella typhimurium, 2-methylanthraquinone was not. The kraft pulp obtained with the additives should be safe for food-packaging applications, and the addition of 0.03% 2-methylanthraquinone to kraft cooking saves forest resources and fossil energy in industries requiring increased pulp yield.
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