PROCESSING FOCUS
METHODS Preparation of mordant
Determination of antimicrobial activities of dyed fabrics The antibacterial activity of the dyed fabrics was estimated by AATCC Test Method 100-2004 [13]. The reduction in number of bacterial colonies formed with respect to the untreated control sample was estimated by using following equation,
The 1% stock solution of metal mordants (alum and CuSO4) was made by dissolving 1 gm of mordant powder in 100 ml water. The stock solutions were used for mordanting of wool fabric as per the concentration required (on the weight of fabric). Extraction of dye
R =
B where, R = reduction in bacterial count (%), A = the number of bacterial colonies recovered from the inoculated treated test specimen swatches in the jar incubated for 24 hr contact period;
The 1% stock solu on of the green tea was prepared by boiling 10 g of dry tea powder in 1000 ml water for 1 h. The extract was filtered and made to 1000 ml and used for dyeing. Mordanting and dyeing of wool
B = the number of bacterial colonies recovered from the inoculated untreated control test specimen swatches in the jar immediately after inoculation (at “0” contact time).
The mordanting of wool fabric was carried out in rota dyer (Rota Dyer machine, Rossari® Labtech, Mumbai) keeping the liquor to material ratio of 30:1.The fabrics were introduced into the mordant solution at room temperature and slowly the temperature was raised to 95oC. The mordanting was continued at this temperature for 30 min. After mordanting, the fabric was squeezed and dyed using green tea extract as a dye. The mordanted fabrics were introduced in dyebath and dyeing was continued at 900C for 1h. After dyeing, the fabrics were squeezed and washed with cold water.
RESULTS AND DISCUSSION Optimization of mordant and dye concentrations The dyeing of wool using metal mordant alum and CuSO4 was attempted and results are summarized in Tables 1 and 2. The wool fabrics were dyed using different mordant and dye concentrations. At the constant dye concentration, the increase in concentration of alum resulted in increase in colour values of wool till 20%. Hence 20% alum concentration was taken as an optimum concentration. For a constant alum concentration, K/S values were found to be increasing with green tea dye concentration from 5% to 20%. The colour value thus obtained, in the case of natural dyes is a combined contribution of the effect of mordant and the dye. Hence the K/S was improved with mordant and dye concentration initially till the equilibrium was reached. The increase in concentrations of either mordant or dye beyond optimum concentrations did not signicantly contribute in the improvement of the depth of dyeing which is reected in K/S values. Hence 20% dye concentration was taken as optimum.
Colour value by reectance method The dyed samples were evaluated for the depth of colour by reectance method using 10 degree observer and Spectraash K/S =
(1-R) 2 2R
SF 300 (Datacolor International, U.S.A.) equipped with reectance accessories. The K/S values were determined using expression; where, R is the reectance at complete opacity, K is the Absorption coefcient & S is the Scattering coefcient Dyed fabrics were simultaneously evaluated in terms of CIELAB colour space (L*, a* and b*) values using the Spectraash SF300. In general, the higher the K/S value, the higher the depth of the colour on the fabric. L* corresponding to the brightness (100= white, 0= black), a* to the red–green coordinate (+ve= red, ve =green) and b* to the yellow–blue coordinate (+ve =yellow, -ve =blue). As a whole, a combination of all these enables one to understand the tonal variations.
Table 1: Effect of alum and Green tea concentration on colour values of Wool fabrics Alum (%)
Washing fastness Evaluation of colour fastness to washing was carried out using ISO II methods [11]. Rubbing fastness Evaluation of colour fastness to rubbing (dry and wet) was carried out using “crock-meter” with 10 strokes of rubbing. Light fastness Dyed fabric was tested for colourfastness to light according to ISO 105/B02 [12]. The light fastness was estimated using articial illumination with Xenon arc light source, Q-Sun Xenon Testing Chamber with black standard temperature 65 0C with relative humidity of the air in the testing chamber as 40% and daylight lter, wavelength, k= 420 nm. The samples were compared with the standard scale of blue wool ratings. TEXTILE VALUE CHAIN | Oct -Dec 2013
100 (B – A)
58
5 5 5 5 10 10 10 10 15 15 15 15 20 20 20 20
Green Tea(%) 5 10 15 20 5 10 15 20 5 10 15 20 5 10 15 20
K/S
L*
0.2716 0.2957 0.3171 0.3691 0.2809 0.3158 0.3277 0.3354 0.3426 0.3431 0.351 0.4081 0.292 0.3871 0.3769 0.5662
31.764 31.827 30.807 30.199 31.713 30.933 30.729 30.431 31.119 30.364 29.616 29.912 31.414 30.66 30.203 31.603
a* 4.558 4.491 5.444 6.041 4.695 5.179 5.649 6.004 4.968 5.6 6.143 6.313 4.513 5.66 5.957 4.331
b* 19.095 18.505 20.188 21.532 18.472 19.914 20.401 21.611 19.515 20.755 21.805 21.355 17.756 20.682 21.415 20.358