Cotton treated with choline chloride can be dyed without electrolytes, and gives improved colour strength values with a variety of direct dyes with minor loss in tensile strength, find BH Patel, RD Pachauri and KU Desai.
Nowadays, chemical modification of textiles is the most common and convenient process to improve functional properties of textiles. In this perspective, cationisation of cotton is the most effective treatment that may help to solve the environmental problems associated with dyeing of cotton. Generally cotton is dyed with direct and reactive dyes. Direct dyes are easier to use and less expensive, but they exhibit poor fastness to washing.
In conventional dyeing of cotton with direct dye, sodium chloride or sodium sulphate has to be added in the dye bath to reduce the negative charge generated on cotton when immersed in water and thus to increase the exhaustion of dye on fibre. These electrolytes are neither exhausted nor destroyed and hence remain in the dye bath after dyeing. Direct dyes create a relatively weak hydrogen bond with fabric´s cellulose polymer, forming a semi durable attachment, even with the use of salt in the normal dyeing system.
A number of works are related to modification of cotton by substitution, cross-linking and grafting reactions. Important aspects of chemical and mechanical modification of cotton is to achieve shorter dyeing time, lower temperature of dyeing, normal salt or no salt to exhaust the bath, neutral pH fixation of modification fibre, etc. To achieve the above mentioned aspects, cotton can be modified by introduction of amino groups or quaternary ammonium group via its hydroxy group, and this process is known as ´Cationisation´. The main purpose of cationisation of cotton is to improve its dyeability towards anionic dyes particularly reactive and direct dyes. The effects of pH, electrolyte concentration and temperature on the fixation of direct and reactive dyes on cationised cotton fibre have been studied for over 50 years.
In the present work, choline chloride (COH.CH2CH2) N (CH3)3 Cl) a quaternary ammonium salt was linked to the cotton fabric on a process that can improve dyeability. Effect of this treatment on mechanical properties of cotton was measured in terms of tensile strength and % elongation of the cationised cotton compared to the untreated cotton sample. Different dyeing conditions were tested with acid dyes and direct dyes, with and without salt, at different pH levels.
Materials
Fabrics
Mill scoured and bleached pure poplin cotton fabrics purchased from local market, was used for present investigation. The plain weave cotton fabric has 90 EPI, 52 PPI and weight 0.0821 gm/sq inch. The finished fabrics, i.e., cotton purchased from market were further mild scoured with 5 gpl soap (Lissapol-D) and 2 gpl sodium carbonate at boil for 30 minutes to remove all impurities.
Dyes
The following two acid dyes and two direct dyes were selected for present study:
AD1-Commassie Brillient Blue FFS, CI Acid Blue 28 [CC No. 42645]
AD2-Commassie yellow Rs, CI Acid yellow 42 [CC No. 22910]
DD1-Direct Terquous Blue, CI No.: CI Direct Blue 86 [CC No. 42645]
DD2-Direct yellow 4A, CI Direct yellow 4G [CC No. 29000]
Chemicals
The chemicals used throughout the study are: choline chloride ([OH CH2CH2 N(CH3)2 CH3]Cl-), sodium hydroxide (NaOH), hydrochloric acid (HCl), soap, sodium carbonate (Na2CO3), hydrogen peroxide (H2O2), sodium silicate (Na2SiO2), glacial acetic acid (CH3COOH) and sodium chloride (NaCl). All dyes and chemicals were of LR grade and used without further purification.
Experimental methods
Treatment of cotton with choline chloride
The choline chloride (50<