24—STOICHIOMETRIC ANALYSIS OF THE WOOL-WATER ISOTHERM

Abstract

Determination of the amount of absorbed water attributable to the various types of side-chain polar groups in wool keratin at humidities of up to 80% r.h. enables a stoichiometric analysis of the wool-water isotherm to be made. The amount absorbed by the aromatic (tyrosine) hydroxyl and aliphatic (serine and threonine) hydroxyl groups was estimated from the change in the water-absorption isotherm after separate chemical modification of these groups. The reduction in water content was much less than that for either amino-group or carboxyl-group modification, the data for these having been reported previously for wool from the same source examined under identical conditions. The difference between the sum of the water attributable to the side-chain basic, carboxyl, and hydroxyl groups, and the water content of unmodified wool has been designated as water attached to peptide and amide groups. The water-sorbing power of these groups is in good agreement with experimental data for peptide groups in polyglycine. It thus appears that all peptide groups are accessible to water vapour. A change in properties of the wool-water system at 75–80% r.h. is attributed to the formation of a hydrogen-bonded network. The water involved is termed ‘network’ water.