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 usuallyused in the dissolution of wool fibers to regenerate keratin. In this investigation,the effect of different alkalis on the chemical composition and thesecondary structure of wool was studied. Wool was treated with equivalentamounts of alkali metal hydroxides (lithium, sodium, and potassium hydroxides)as well as alkaline earth metal hydroxides (strontium and bariumhydroxides). The effect of these alkalis on wool was monitored using aminoacid analysis, elemental analysis, carboxylic content, acid, and base combiningcapacity, 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. Scanningelectron microscopy was used to assign the alteration of the fiber morphologyof the alkali-treated wool. The results of this investigation indicate thatthe effect of the used alkalis on wool is not similar. Cystine, glycine, and thebasic amino acids are the most affected species in the treated wool. Someelimination reactions were involved during alkaline treatment of wool;namely decarboxylation, desulphydration, and deamination. The secondarystructure of wool treated with Sr(OH)2 and Ba(OH)2 was changed from the ?-helical structure into the ?-sheet form.