INVESTIGATION OF THE MOISTURE ADSORPTIVITY OF POLAR AND HYDROPHILIC GROUPS IN WOOL KERATIN BY ITS CHEMICAL MODIFICATIONS

Abstract

For investigating the stoichiometry of water sorption by amino and carboxyl groups in wool keratin, two series of chemically modified specimens were prepared by partial deamination (van Slyke's reaction) and partial esterification (methylation) of a New Zealand Luster 48's wool, for which the moisture sorption isotherm and the heat of wetting were determined over the entire range of relative humidity at 30°C. Because of difficulty in preparing fully modified specimens by the chemical methods, the isotherm data were extrapolated to zero residual concentration of amino and carboxyl groups to estimate the isotherms of fully deaminated and decarboxylated specimens.
By analyzing the differences in the isotherms between the untreated/partly modified specimens and the fully modified specimen in terms of the B. E. T.'s multilayer adsorption model, the maximum number of water molecules adsorbed in monolayer per each amino or carboxyl group was estimated as 1.0mole/mole and 1.3moles/mole at low concentration of the polar groups, and 2.5moles/mole and 2.0moles/mole at high concentration of the polar groups, respectively, The values for the carboxyl group is acceptable, while the values for the amino group must be underestimated due to the effects of replaced hydroxyl groups by the deamination.
The hydration energies of the amino and carboxyl groups were evaluated as 6.7 and 9.1kcal/mole of the polar group, respectively, from the heat of wetting of the specimens at dryness. The value for the amino group must be underestimated due to the same reason as above. The differential heat of moisture sorption at dryness (hydration enthalpy) was evaluated as 4.91kcal/mole of liquid water for the untreated specimen, which was somewhat smaller than the value of 5.8kcal/mole of the alpha water proposed by Speakman.