The effects of lignocellulosic fiber surface area on the dynamics of lignin oxidation and diffusion

摘要

A novel preliminary experimental approach was developed to determine the effect of maximizing pulp fiber surface area for the regulation of the oxidation and diffusion of lignin through the carbohydrate matrix. The approach entailed liquid nitrogen freezing of mature black spruce kraft pulp fibers and subsequent mechanical grinding to a fine powder to test the effect of enhanced pulp fiber surface area on the efficiencies of lignin oxidation and lignin diffusion. It was found that the liquid nitrogen ground pulp samples provided higher optical reflectance (brightness) after both oxygen and hydrogen peroxide oxidation, which appears to be from chromophoric (chemical) differences and not light scattering differences as supported by UV/Vis spectroscopy. BET (absorption) experiments indicated a dramatic difference in the surface area of the pulp as a result of the grinding, although no differences existed among the pore sizes between the samples, as determined from SEM experiments. Lignin diffusion experiments demonstrated that differences did exist in the kinetics of lignin diffusion into a bulk solution between a control and liquid nitrogen ground samples. Lignin uptake into bulk solutions was enhanced by the liquid nitrogen/pulp-grinding technique albeit not from chemical changes in the lignin because the subsequent NMR spectra did not point to any major chemical differences as a result of liquid nitrogen freezing and grinding. (C) 2004 Wiley Periodicals, Inc.