Effect of Alkali Metals and Alkaline Earth Metals Hydroxides on the Structure of Wool Fibers

Wool is sensitive toward the effect of alkaline solutions which are usually used in the dissolution of wool fibers to regenerate keratin. In this investigation, the effect of different alkalis on the chemical composition and the secondary structure of wool was studied. Wool was treated with equivalent amounts of alkali metal hydroxides (lithium, sodium, and potassium hydroxides) as well as alkaline earth metal hydroxides (strontium and barium hydroxides). The effect of these alkalis on wool was monitored using amino acid analysis, elemental analysis, carboxylic content, acid, and base combining capacity, urea-bisulfite and alkali solubility, and FTIR spectroscopy. Further structure elucidation was conducted by thermo-gravimetric analysis, differential scanning calorimetry, and X-ray diffraction pattern. Scanning electron microscopy was used to assign the alteration of the fiber morphology of the alkali-treated wool. The results of this investigation indicate that the effect of the used alkalis on wool is not similar. Cystine, glycine, and the basic amino acids are the most affected species in the treated wool. Some elimination reactions were involved during alkaline treatment of wool; namely decarboxylation, desulphydration, and deamination. The secondary structure of wool treated with Sr(OH)2 and Ba(OH)2 was changed from the α-helical structure into the β-sheet form.