The Application of Differential Scanning Calorimetry (DSC) to Pulp Evaluation

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The melting phenomena of water in the wet pulp sheets at different water contents have been investigated by DSC within the temperature range from -50ﾟC to 20ﾟC for the various pulps in order to develop the pulp evaluation method. The concluding remarks are as follows.1. Comparing with the melting DSC curve of pure water, the DSC curve of wet pulp sheet clearly broadened toward the lower temperature side. The shape of DSC melting curve at lower temperature side may therefore characterize pulps provided a comparable heat of fusion.2. With decreasing water contents of the wet pulp sheet, the heat of fusion at lower temperature side of DSC melting curve increased for the less hydrophilic pulp, but decreased for the more hydrophilic pulp.3. The relationship between water contents and the heat of fusion is well represented by two straight lines. The slope of the line at the higher water contents gave a value of 334 J/g for the heat of fusion of bulk water. At the lower water contents, the slope of the straight line is smaller than that at the higher water contents.4. Although nonfreezing water increased with increasing the beating degree, the increase of nonfreezing water is too small to employ for pulp evaluation. On the other hand, the electrical conductivity measurement must be more practical to evaluate the pulp for papermaking.5. The existence of two straight lines in the relationship between water contents and the heat of fusion and the broadened DSC curve toward lower temperature side indicated three states of water in the wet pulp sheets, i.e., nonfreezing, freezable bulk, and freezable but different from bulk water.