Wool Setting: The Effect of Esterification

Abstract

Esterification of wool fabrics with methanol, ethanol, n-propanol or n-butanol (containing 0.1 M HCl as catalyst) has been found to modify both amide and carboxyl side chains. Modification of amide groups is especially marked with the higher alcohols. The esterified fabrics set more readily than untreated fabric when steam-pressed in the presence of 0.05 M buffer (pH 7), but not when M potassium chloride is added to the buffer. The effect of esterification in enhancing the settability of wool can be explained in terms of the Donnan effect. In solutions of low ionic strength, the internal pH of a wool fiber differs from that of the external solution and this effect is accentuated on esterification. As a result, the internal pH of esterified wool is much higher than that of untreated wool. Since wool sets more readily in alkaline than in neutral solution, esterification enhances settability. At high ionic strengths, however, the Donnan effect is suppressed. The internal and external pH values are the same for both untreated and esterified fabrics, which therefore set at the same rate.