The Concept of Internal pH in Wool Fibres and the Interpretation of Data Relating to Setting

A system consisting of wool fibres immersed in a salt solution has been considered in terms of the Donnan theory and an expression obtained which relates the hydroxyl–ion concentration of the ‘internal solution’ to the pH and salt concentration in the external solution, the affinities of hydroxyl ion, cation, and anion for the fibre, and the numbers of ionisable cationic and anionic groups in the fibre. This showed that at constant external pH and ionic strength, the internal hydroxyl–ion concentration would be increased by increasing the number of ionised cationic groups on the fibre, by adsorption of cations, or by decreasing the number of ionised anionic groups on the fibre. It would be decreased by adsorption of anionic groups. The effects of several chemical modifications of wool fibres on their setting properties can be explained in terms of their effects on the internal hydroxyl–ion concentration.