Freezing bound water

As shown in Figure 4.68, the first-order phase transition is not detected until a critical amount of water is added to a polymer (curve I). The amount of water is defined as non-freezing water content (W f) [89-92]. The maximum depends on the hydrophlylicity of the polymer. When the water content in the polymer exceeds a critical amount, a small peak (peak II) is observed at a lower temperature than the crystallization peak of bulk water. The amount of water is categorized as freezing bound water content (Wf,). 

Figure 4.68 Schematic DSC cooling curves of water sorbed on hydrophilic polymers I, Non-freezing water (W,) II, W + freezing bound water (IV ). HI + free water...

Non-freezing water is observed for the sample with W = 0.21 gg". On the crystallization curves, freezing bound water is observed at a temperature lower than the melting temperature of free water (Nos 2 and 3). The melting peak of freezing bound water merges into that of of free water (Nos 6 and 7). 

Free water is located inside the lumen, large pores and between fibers in papermaking pulps. This water is kept by surface tension forces. This water can be removed using pressing operation, vacuum suction, or centrifugation. Freezing bound water is located in... 

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