Stabilization of Mechanical Pulp Against Color Reversion

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ABSTRACT Arthur J. Ragauskas CTS-9414695 This is a study of the chemical pathways by which mercapto-derived antioxidants photostabilize mechanical pulps. The principal factor limiting use of mechanical pulp is its tendency to undergo color reversion. All types of mechanical pulp suffer from surface discoloration induced thermally or photonically. The processes causing surface discoloration also cause oxidative degradation of the carbohydrate and lignin components of wood fibers. The accepted mechanism for this process involves photoexcitation of extended conjugated structures in lignin; this initiates a free-radical process either by intramolecular bond cleavage, by intermolecular abstraction of phenolic hydrogen, or by generation of singlet oxygen. Although the mechanisms of photoyellowing have received substantial attention, the ways in which antioxidants could retard this process are not well understood. In this work, the mechanisms by which thiol groups can inhibit these processes are examined. Mechanical pulp for papermaking is a more efficient intermediate than chemical pulp. Generally, chemical pulp uses only the cellulose in wood, while mechanical pulp contains 85% of the original wood mass including cellulose hemicellulose, and lignin. However, mechanical pulp is more difficult to stabilize chemically, and this limits its use for most paper products. This is the issue addressed in this project. This award is part of the Special Initiative in Environmentally Benign Chemical Synthesis and Processing.