Hydration and swelling of pulp fibers measured with differential scanning calorimetry

This study describes a new differential scanning calorimetry (DSC) method, based on the isothermal melting of water, which may be used to measure hydration and swelling phenomena in pulp fibers. Nonfreezing and melting temperature depressed water (freezing bound water) are considered. Nonfreezing water is probably related to the number and type of accessible hydration sites. Both solution and pore effects may cause; the melting temperature of water in the cell wall to be depressed. Experiments with xylans with differing charge and drying history indicate that the isothermal melting technique can be used to measure the swelling of the gel phase in heterogeneous hydrated systems, such as pulp fibers. In previously-dried cotton it is found that the sum of nonfreezing and freezing bound water is equal to the fiber saturation point measured with solute exclusion. For never-dried unbleached kraft pulp a significant part of the water within the cell wall melts at the same temperature as bulk water. A likely interpretation is that such water is located within macropores, formed when lignin is dissolved in pulping.