Chemical Mechanism of Permanent Set

Abstract

SOME years ago¹ it was argued that the permanent set which strained wool fibres acquire in steam is due to two consecutive intramolecular reactions, namely, disulphide bond breakdown, which leads to the dissipation of stress, and linkage rebuilding, which stabilizes the relaxed structure. Indirect evidence of many kinds led to the conclusion that the reactions take place according to the following scheme: Following a suggestion of Phillips², evidence was afterwards obtained³ that, when alkalis are used as setting assistants, —CH=N— as well as sulphenamide linkages are formed: The above conception of the chemical mechanism of permanent set has, however, failed to command general acceptance, because Cuthbertson and Phillips⁴ and Lindley and Phillips⁵ found little or no fall in free amino-nitrogen, as estimated by the van Slyke reagent, after wool had been boiled for 1 hr. with borate buffers at pH 8 or pH 10, nor was there any rise in the content of cysteine. Direct evidence that the lysine side-chains of wool take part in the linkage-rebuilding reaction has now been obtained in the following way.