Fundamental insights into the oxidation of lignocellulosics obtained from singlet oxygen photochemistry

A photochemical approach for the delignification of lignocellulosics, specifically Southern kraft softwood pulp, was adopted to provide insight into the nature of the general oxidative chemistry leading to lignin removal and carbohydrate (cellulose) degradation. This is the first paper that primarily provides a systematic investigation of the singlet oxygen photochemistry of kraft pulp, in which Rose Bengal (RB) was employed as the photosensitizer to degrade lignin, and secondarily describes the resultant properties of the pulp. The oxidative chemistry was efficient until approximately 50% of the native lignin polymer remained, at which point the carbohydrate component was not exempt from depolymerization reactions. This study examined the influence of lignin chemical characteristics and a general metal-based radical inhibitor on the reactivity of singlet oxygen. In general, the oxidative chemistry obtained in this study from singlet oxygen was not unlike what has been observed in ground state oxygen reactions.