DSC studies on bound water in carboxymethylcellulose–polylysine complexes

Sodium carboxymethylcellulose (NaCMC) with various degrees of substitution (carboxymethylation, DS=0.72–2.38) was mixed with polylysine (PLys) in aqueous media and water insoluble sheets of carboxymethylcellulose–polylysine (CMC–PLys) molecular complexes were prepared. CMC–PLys molecular complexes form three-dimensional network structures. Non-freezing water content (Wnf) of the complexes was measured by differential scanning calorimetry (DSC). Wnf of NaCMC increased with increasing DS, since hydrophilic groups restrict water molecules. Wnf of CMC–PLys complexes decreased with increasing PLys/CMC ratio due to cross-linking formation. It was found that the amounts of Wnf calculated from melting enthalpies (Wnfm) were larger than those calculated from crystallization enthalpies (Wnfc). The difference between Wnfm and Wnfc (ΔWnf=Wnfc−Wnfm) of CMC–PLys increased with increasing DS and PLys/CMC ratio. It was concluded that Wnf is markedly affected by DS and cross-linking density. The amount of super-cooled water in CMC–PLys complexes is the same as that in ΔWnf.