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 (W-nf) of the complexes was measured by differential scanning calorimetry (DSC). W-nf of NaCMC increased with increasing DS, since hydrophilic groups restrict water molecules. W-nf of CMC-PLys complexes decreased with increasing PLys/CMC ratio due to cross-linking formation. It was found that the amounts of Wn(f) calculated from melting enthalpies (W-nfm) were larger than those calculated from crystallization enthalpies (W-nfc). The difference between W-nf and W-nfc (Delta W-nf = W-nf c = W-nfm) of CMC-PLys increased with increasing DS and PLys/CMC ratio. It was concluded that W-nf 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 DeltaW(nf) (C) 2003 Elsevier B.V. All rights reserved.