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The oxygen bleaching of wood pulp takes place in a heterogeneous system involving oxygen (gas), water (liquid), and fiber (solid). Inconsistent effects of process variables (reaction temperature, alkali concentration, and oxygen pressure) on the overall oxygen delignification rate of wood pulp in various reacting systems have been reported in the literature.An apparent intrinsic reaction rate model, excluding the interphase mass transfer effects, has been developed based on oxygen bleaching experiments in an agitated and ultralow-consistency (solids content) reactor. The apparent intrinsic reaction rate model shows a faster delignification rate than those reported in the literature. The degree of inadequate delignification observed in the literature data is likely to be caused by insufficient mass transfer of bleaching chemicals to fibers.

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The fabrication of fibrillated cellulose fibers and their utilization have been of more interest recently because of their biodegradability, low cost, and mechanical and thermal properties comparable to those of glass fibers or carbon fibers. In this study, we applied the combination of a mechanical shearing process with a cooling system and an enzymatic pretreatment to produce fibrillated cellulose fibers from softwood pulps. The effects of the mechanical shearing process, the cooling system, and the enzymatic treatment on the formation of the fibrillated cellulose fibers as well as physical and mechanical properties of paper were investigated. It was indicated that the cooling system was necessary in the grinding process to prevent the adverse effect of heat generation on mechanical properties of paper sheets. It was observed that the enzyme-assisted mechanical shearing process improves the production of fibrillated cellulose fibers and results in a substantial improvement of tensile strength and elongation of paper while producing thinner and less bright paper with low water absorptiveness.