Accessibility of swollen cellulosic fibers

The present study concerns the changes of the porous structure of fibers and fiber surface modifications related to the treatment of wood chips with different swelling agents (amines, carbonates, chlorides), prior to high-yield pulping at high temperature. Several techniques, such as water retention, nitrogen adsorption, mercury porosimetry, solute exclusion method, light scattering and enzymatic hydrolysis were used to analyse the accessibility of fiber surface, structural characteristics and bonding ability of fibers. It was shown that pulps prepared with carbonates of univalent cations and amines have the highest ability to retain water and exhibit a higher fiber saturation point than pulps swollen in LiCl or pulps prepared without a swelling agent. These pulps show the highest specific surface, measured by nitrogen adsorption as well as by mercury porosimetry. Also, an excellent correlation of these results was found with those of enzymatic hydrolysis using cellulases and xylanases. Pulps with the highest specific surfaces which were preliminarly swollen in powerful swelling agents were more accessible to both cellulases or xylanases during enzymatic hydrolysis, than pulps prepared with LiCl or without a swelling agent. Better enzymatic accessibility is provided not only by higher porosity and specific surface, but also by positive chemical changes on the fiber surface. In other words, well-swollen fibers are able to create more interfiber bonds because more polysaccharides are present on the fiber surface.