Dyeing Effects of Cationized Cotton

Cotton fibers, like most textile fibers, are negative charged (zeta potential) in neutral and alkali aqueous solutions. It is important to consider that dyestuffs, optical brighteners and finishing agents in aqueous solution have the same electrical sign as cotton. In this case difficulties in adsorption processes arise from existing repulsion forces between the particles of the same electrical sign. It is well known that for overcome these forces in dyeing processes, a large amounts of electrolyte is needed, what is economically and ecologically unfavorable. The aim of present paper was to study the cotton modification for achieving its electropositive charge and better dyeing properties. Modification of cotton yarns was carried out with quarternary ammonium compound in different stages of pretreatment for the purpose of lowering the zeta potential of cotton. It is one of alternative method to low the high electrolyte amount in dyeing bath. For this purpose, raw and bleached cotton yarns were cationized with 3-chloro-2-hydroxypropyl-trimethyl ammonium chloride (CHPTAC) before and during the mercerization process. Untreated and mercerized cotton samples are electronegative having the zeta potential, from x = - 15 mV to x= - 20 mV. According to zeta potential results (measured on Electro-kinetic Analyzer-EKA, A. Paar) it was shown that electrical charge of all cationized cotton yarns was noticeable changed, from negative to positive values by 10 to 15 mV. Bleached cationized yarns are electropositive in whole applied pH range (pH 2 to pH 10) while raw cotton yarns are little negative (x = - 5 mV). Such electropositive cottons show the better attracts of electronegative dyestuffs and finishing agents. Breaking force and elongation were measured on Tenso Lab Strength Tester. Although expected the negative mechanical changes, modified cotton showed better properties then untreated one and almost the same properties as well-known positive mechanical changes in mercerization process. Dyeing processes were presumed using direct dyestuff, Tubantin Green GL (Bezema) by an exhaustion method. The samples selected for dyeing were the next: row and bleached cottons separately untreated, mercerized and cationized (before and during the mercerization process). All the yarns were dyed with and without electrolyte (10g/l NaCl), in AHIBA Turbomat (Datacolor) with constant bath flow, in one depth of shade (3% owf), using liquor ration 30:1, at 100 °C, for 90 min. Spectral characteristics were measured on remission spectrophotometer Spectraflash 600 plus-CT (Datacolor). It was shown very high dyeing effect for mercerized and cationized cottons, incomparable with untreated cottons. It is to notice that these cottons dyed in baths without electrolyte content could show better dyeing effects than when electrolyte was added. Electrolyte addition in these cases is unfavorable. Bleached cotton yarns are more hydrophilic than raw ones, so they have stronger reaction with 3-chloro-2-hydroxypropyl-trimethyl ammonium chloride. Due to their hydrophilicity, they have better dye uptake as well. Dyeing effects of mercerized cotton are well known in practice, but cationization during the mercerization process gives a new dimension of cotton pretreatment, as well as the quality assurance of cotton in the future.