In the quest of finding new alternatives to natural processes and to tame the entire working methodology, humankind has perhaps gone too far and now the time has come when it must return to nature, there’s no other resort left. This ideology is termed ‘Sustainability’.
Wet processing of textiles being one of the most polluting industries yet one of the most necessary fields; requires tremendous changes to include sustainability in the work processes. Now, among the various wet processes, dyeing is perhaps the largest evil due to the discharge containing a high amount of color, acids, alkalis, salts, and many a times metal ions too. There is a dire need to substitute synthetic colors with natural ones without compromising on essential qualities of dyed materials like shade, depth, and fastness properties.
Natural dyes; obtained from different sources such as plants, animals, and minerals, are renewable and sustainable bio-resource products with minimum environmental impact and known since antiquity for their use not only in coloration of textiles but also as food ingredients and cosmetics. The natural colorants are obtained directly from nature and are extremely environmentally friendly. Unlike chemical colorants, natural dyes cause no or very little pollution.
In this literature, dyeing from the waste of tea shops has been reported. The point to be noted here is that, in this paper, waste obtained from black tea (no milk or sugar) was used as raw materials since there is a huge shift in the masses towards a healthy lifestyle and hence, more and more people are opting black tea instead of the regular one with milk and sugar in it to cut down on carbs
Tea is a mixture of variously processed leaves of one of the varieties of an evergreen shrub, Camellia sinensis, which is the most popular non-alcoholic beverage in the world. Flavonoids, flavanols, and PHenolic acids make up approximately 30% of dried Camellia Sinensis by weight.
A commercial tea brand was used for this research. First of all, the raw material was procured. It was obtained by adding fresh tea leaves to boiling water in MLR (Material to Liquor Ratio) of 1:50 for 5 minutes (the usual parameters observed for preparing black tea). This liquor (black tea) was then, discarded and the residue was left to dry under shade over a synthetic fabric so that no color gets wasted during drying. Next, this dried residue was taken and used as the raw materials for further proceedings.
A handloom prepared 100% cotton fabric of plain weave was used. The fabric was cut into samples having dimensions of 10cm X 10cm measuring 1.2g each.
Glacial Acetic Acid was used to maintain the PH of the dye extract in acidic dyeing. Another chemical used was Common Salt; used as an exhausting agent.
The extraction of the natural colorants from the raw material (waste/ spent tea leaves) was done by adding the raw material in boiling water for 10 minutes under MLR (Material to Liquor Ratio) of 1:50.
PH of the dye liquor thus obtained was found to be lying between 9 – 9.5 (alkaline). So, dyeing on the cotton substrate (fabric form) was carried out only in neutral (i.e., no external agent was added to alter the PH of the dyeing liquor) and acidic conditions. Also, it was observed that if the raw material was left for a few days, the color of the dye extract then obtained was lighter than that obtained from the freshly obtained raw material.
5g of the raw material (waste/ spent tea leaves) was added to 250mL of water (MLR = 1:50) at 100°C and was left to brew at the same temperature for 10 minutes. Next, this solution was filtered and this liquor was used to dye a single sample of 10cm X 10cm (weighing 1.2g). 2% common salt owf (of the weight of the fabric) was used as an exhausting agent and this exhausting agent was added in two instalments to minimize the chances of uneven dyeing.
Two parameters; temperature and time were varied. Dyeing in the similar manner was carried out at 70°C, 90°C and 110°C while time duration for dyeing to take place was 30 min, 45 min and 60 min.
Dyeing was carried out in similar manner as that in the neutral dyeing except for the fact that to maintain the PH during dyeing, Glacial Acetic Acid was added. PH of the dye liquor in this method was maintained at 3-4. Temperature and time parameters were also kept same as that in the neutral dyeing procedure.
The dye was extracted similarly to that in the exhaust method. The only difference here is that the samples were dyed in an Infra-Red (IR) dyeing machine. In the heating cycle, temperature increases at the gradient of 2°C/min, followed by dyeing at the set temperature, and then, finally the cooling cycle where the system was cooled at the gradient of 2°C/min.
Dyeing in a similar manner was carried out at 70°C, 90°C, and 110°C for 30 minutes each.
Washing Fastness Testing was done as per ISO 2. Washing fastness determines the bleeding of color on washing. All 18 samples were tested and the results were checked against Gray Scale.
Rubbing Fastness (both dry and wet) Testing was done as per ISO 105- C06: 2016-A/ B/ C. Rubbing fastness determines the extent to which the color fades upon prolonged rubbing action. All 18 samples were tested and the results were checked against Gray Scale.
For measuring the color strength of the dyed samples, spectroPHotometer with model no. Premier Colors can SS 5100 was used.
RESULTS AND DISCUSSIONS
The color obtained on the cotton samples by dyeing of the above stated dye extract ranges from beige to pink. The dyed samples have been observed to have good washing fastness properties. Also, the rubbing fastness was found to be moderate for all the samples.
The differences in the properties of varying the time and PH for exhaust dyeing are as recorded in the following table:
The graphical representation of this data can be as shown below:
The color strength seemed to increase for both increase in temperature at which dyeing occurs and the duration for which the dyeing is done. Also, the dyeing done in acidic medium (PH 3 – 4) yielded lighter and duller shades than that done in the neutral medium for the same temperature and time parameters. This is probably due to the fact that cotton has more endurance for alkaline medium than acidic medium, so, the dye uptake is greater in the neutral dyeing (PH of dye extract is 9 – 9.5). The dyed samples had overall good wash and rubbing fastness properties.
Next, Exhaust and Infra Red dyeing methods were compared. The following table shows the comparison between the samples obtained from Exhaust Dyeing (Aqueous Medium) and Infra Red Dyeing:
The graphical representation of the above data is as shown below:
The color strength seemed to increase with increase in temperature for both the dyeing techniques, i.e., exhaust method and infra red dyeing. However, there was a stark difference in the color strength values obtained through the two methods as seen in the graph. Also, infra red dyeing yielded duller shades than the dyeing by the exhaust method for the same temperature and time parameters. The dyed samples had overall good wash. Not much difference was seen in the wash fastness of the samples dyed by the two above stated methods, it’s the color strength which varies largely.
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