Influence of pH on fibers. Plant-derived fibres (cellulose): flax, cotton, juty, they are quite resistant to alkaline washing liquids, however, they are destroyed by a stronger acid with a pH lower than 2,5. The same fibers as a result of aging processes, degraded by oxidation and chemical agents, are already more sensitive to alkaline detergents. Unlike animal fibers (protein), e.g.. wool and natural silk, plant fibers are less sensitive to acids, and more for alkaline solutions (they tolerate pH up to 11), but already partially oxidized fibers shrink and felt even below pH 10.
Influence of pH value on dyes. Acid dyes for fibers of animal origin (wool and silk) can release color in neutral and slightly alkaline washing liquid, and in weakly acidic water or water used for rinsing, they become fixed. In the case of basic dyes, the situation is reversed, i.e.. discoloration occurs in the acid washing liquid, and in weakly alkaline fixation. Especially direct dyes (substantive) used to dye plant fibers, both in weakly acidic, alkaline and neutral washing liquids, discolor and require the addition of salt to fix.
The resistance of dyes to discoloration is checked using tissue paper or filter paper, which is placed under a piece of the test fabric impregnated with a solvent by stippling. The lack of color of the paper proves their resistance. Another very simple method is to lightly rub a white cloth over places soaked with clean water, and then with the washing liquid and on the control of the result. For very sensitive fabrics, places moistened with water, after 1 minute of operation, pressed down with a wad of cotton wool or tissue paper.
