Changes in pore size distribution during the drying of cellulose fibers as measured by differential scanning calorimetry

Changes in pore size distribution during the drying of cellulose fibers were determined using differential scanning calorimetry (DSC) with an isothermal step melting procedure. Softwood bleached kraft pulp at various moisture ratios were generated from partial drying in a thermogravimetric analyzer and then analyzed in a DSC. The pore size distribution was calculated using the Gibbs–Thomson equation and specific melting point depression of water detected by DSC. It was observed that larger pores collapse first followed by the sequential collapse of smaller pores. It is suggested that pore wall collapse resistance is the primary factor that determines which size pores close. The average measured pore size in the fiber wall of the never dried fiber was calculated to be about 80 nm and reduced with drying of the fibers. A constant pore size of about 20 nm was observed at moisture ratios below 0.3 g/g, which corresponds to one-to-two layers of non-freezing bound water tightly bound to the surface.