Characterization of chitin, chitosan and their carboxymethyl derivatives by differential scanning calorimetry

Chitin, chitosan and their O,N-carboxymethyl derivatives were characterized by differential scanning calorimetry (DSC) mainly focusing on changes in physical and chemical structures at different levels of acetyl and carboxymethyl contents. The thermograms were characterized by endo- and exotherms corresponding to water evaporation and decomposition of the polymer, respectively. However, each endo- or exothermic peak temperature and area changed as a function of primary and higher order structures of the macromolecule. It was found that the enthalpy value for endotherm increased with increase in amino and carboxymethyl contents. Further, in the case of carboxymethyl derivatives, no glass transition was observed despite the presence of substantial amount of amorphous content. During decomposition, the decomposition peak temperature and area changed as a function of molecular weight (MW), acetyl and carboxymethyl contents. A theoretical basis was adopted to correlate the heat of the reaction, ΔH, to the degree of deacetylation (%DD) and carboxymethylation (DS). A good correlation was obtained when the corresponding peak area and peak height were plotted against %DD and DS.