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The aim of the pre-treatment process is to prepare cotton fabrics for subsequent technological operations, which are, in the majority, carried out in aqueous solutions. The pre-treatment processes modify, to some extent, the properties of cotton, resulting in a significant change in their zeta potential, the amount of specific surface charge or free energy surface. This study makes an assessment of the effect of the alkali pre-treatment process on changes in the amount of negative specific charges on cotton knitted surfaces, known as cationic demand. A “back-titration” method with the use of a Muetek PCD device was adopted for these experiments. It was found that the conventional process of alkali treatment of raw cotton knitted fabrics using sodium hydroxide in the presence of non-ionic surfactant reduced by nearly 50% the amount of negative specific surface charge. Also, changes in weight loss and improvements in the whiteness index, as well as the wettability of alkali pre-treated cotton knitwear, were observed.

Modification of cotton with 3-chloro-2-hydroxypropyltrimethylammonium chloride (CHPTAC) has been studied extensively and can be operated by means of exhaustion, cold pad-batch, and continuous and pad-steam methods. Most of the research addresses the cationization of cotton fabric after bleaching or mercerization, or during the mercerization process. In our studies, we performed a comparison of the cationization effects on raw, enzymatic, and alkali-scoured cotton knitted fabrics applying CHPTAC according to the exhaustion method. The charge density of the cotton surface was measured using a Muetek Particle Charge Detector and a “back titration” method with polyelectrolytes. These results were compared with the nitrogen content in the samples, K/S measurements of tested samples after dyeing with anionic dye (Acid Yellow 194), and other physicochemical parameters such as weight loss, whiteness, and wettability.

Introducing the cellulose chain cationic groups in the modification process completely changes the charge on the cotton surface from negative to partially or totally positive. That allows the electrostatic attraction and simultaneous exhaustion and fixation of reactive dyes. This reaction can be carried out without salt and alkali at room temperature. Similarly, the reaction between reactive dye and an alone copolymer ([IME]+Cl−) with TLC chromatography was confirmed. The analysis with the use of particle optimisation with MM+ molecular mechanics and quantum-chemical calculations PM3 by the method of all valence orbitals confirmed the experimental results of the high activity of the nucleophile formed on the hydroxyl group in the chain of a modifier. It was found and experimentally confirmed that the reactive dyes during the dyeing process of the cotton cationised with copolymer (chloromethyl)oxirane -1H-imidazole ([IME]+Cl−) create covalent bonds due to a reaction with the hydroxyl group located in the modification agent instead of with the hydroxyl group in the glucopiranose ring. Although the dyeing takes place in very mild conditions, a high degree of setting is achieved, comparable to conventional methods.

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