Influence of the Bleaching Medium on Extraction Delignification Efficieny (I): The Role of Fiber Swelling, 1996 International Pulp Bleaching Conference Proceedings

B. N. Brogdon

T. J. McDonough

D. R. Dimmel

P. S. Bryant

Institute of Paper Science and Technology

The goal of this paper is to fundamentally examine the role of fiber de-swelling in the transport of oxidized lignin frag-ments out of the porous fiber structure during alkaline extrac-tion. It was hypothesized that abatement of pore sizes, due to decreased swelling in a de-swelling medium, would entrap lig-nin fragments and decrease delignification during alkaline ex-traction. Experiments were performed to test this hypothesis. A softwood kraft pulp was partially oxidized with C1O2 ; af-terwards, the pulp was subjected to an alkaline extraction in de-swelling media: ethanol-water or aqueous BaCl2 solutions. These media caused up to 12% fiber de-swelling as compared to an aqueous alkaline solution. High concentrations of eth-anol (>50%) or BaC12 (>0.0025 M) severely inhibited delig-nification. Additional experiments were conducted to verify the influence de-swelling on delignification. Extractions performed with a NaCl solution did not yield delig-nification levels similar to those achieved with ethanol or BaC12 solutions at a given swelling level. Additionally, the fragments’ diffusion coefficient did not differ appreciably among the various media (˜10 -11 cm 2 /s). These results suggest that fiber swelling plays a minor role in delignification during al-kaline extraction. Additional evidence for this conclusion is given from the available literature.