Changes of cellulose fiber wall structure during drying investigated using NMR self-diffusion and relaxation experiments

The self-diffusion of water sorbed in cellulose fibers was investigated by means of NMR during slow drying in order to follow changes in the cellulose porous structure. In pulp fibers pores with at least one dimension on the mum scale were observed at high amounts of sorbed water and nm-scale pores at low amounts. Beating affected the mum-scale pores. Regenerated cellulose fibers had nm-scale pores up to high amounts of water. Bulk water was observed as a second component with long T-2 in a CPMG experiment. The sequence of water removal for kraft pulp fibers is: (1) bulk water, (2) water in mum-scale pores and (3) water in nm-scale pores.