On the macromolecular cellulosic network of paper: changes induced by acid hydrolysis studied by NMR diffusometry and relaxometry

The cellulosic network of artificially acidified paper has been studied by 2D NMR relaxometry, NMR diffusometry and NMR diffusion-diffraction. Results show that the acidifying treatment enlarges the macropore structure of paper increasing the pore connectivity and modifying the exchange between water populations localized in amorphous cellulose. Acidification damage suggests that simple breaking of the amorphous portion of fibrils occurs. Nevertheless, under a specific acidifying condition, a rearrangement in the cellulose network seems to take place, with a reduction of the average macropore size and a loss of pore connectivity. The identification of water populations by 2D relaxation maps allows for monitoring the changes in cellulose water mobility due to the depolymerization process. In general the relaxation and self-diffusion results confirm that water mobility increases with acidification.