Deaggregation of cellulose macrofibrils and its effect on bound water

The purpose of this study was to determine how to control and measure the hierarchical swelling in pulp fibers via electrostatic interactions and localized osmotic pressure. A eutectic solvent system was used to systematically increase phosphate groups in the cell wall. Increase in fiber charge led to an increase in swelling properties, as expected. At a charge value around 180–200 μmol/g the macrofibrils were found to deaggregate. This led to a large jump in mesoscale swelling, from 0.9 to 2.5 mL/g, and surface area, from 400 to 1000 m²/g. This deaggregation was confirmed with X-ray scattering and solute exclusion. A novel thermoporosimetry method was used in the study. This involved splitting the nonfreezing water into two subfractions, thus allowing a more complete analysis of pore structure and surface area. The hydrated surface area for the samples was in the range 1200–1400 m²/g, which agreed well with simulations of aggregated microfibrils. Adding charge to the pulp fibers had a nonlinear effect on handsheet strength properties. This suggests that hierarchical control of fiber swelling may be a useful approach to improve important property pairs such as strength/density in packaging and other commercially important fiber products.