Differential scanning calorimetry as an aid for investigating the wet state of pulp

The melting behaviour of water in wet pulp webs at different water contents has been investigated by differential scanning calorimetry (DSC) within the temperature range from -50°C to 20°C for bleached hardwood kraft and synthetic pulps. Compared with the DSC heating curve of pure water, those of wet pulp webs were clearly broadened toward the low temperature side. The relationship between water content and the heat of fusion for the pulps was well represented by two straight lines. The slopes and intercepts of the lines were interpreted in terms of the coexistence of three states of water in wet pulp, i.e. bulk water, non-freezing water and capillary water.