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Dyeing, Finishing & Printing Sustainability

Ethanol a cost effective eco-friendly alternative of toxic non-biodegradable auxiliaries in cotton dyeing

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A dyeing process for cotton fabric with reactive dye has been developed to substitute harmful chemical auxiliaries with low volume of ethanol (1gm/L-3gm/L). The results were studied in comparison with the standard conventional recipe and satisfactory exhaustion rate with better washing & rubbing fastness including acceptable uniformity of dyeing was achieved in laboratory scale. Ethanol alone served the function of both wetting and leveling agent successfully where it is readily biodegradable and hence this process becomes eco-friendly. The alternative process gives better environmental effects due to the chemical substitution of toxic auxiliaries with ethanol. Cost comparison with the traditional dyeing process shows a great advantage for the ethanol process.

Keywords: Ethanol, chemical substitution, toxic auxiliaries, eco-friendly, cost effective

1. Introduction

Replacement of toxic chemicals having high polluting strength with others that have less impact on water quality or that are more amenable to wastewater treatment is known as chemical substitution (Kwok et al., 1999). Textile industries emit a large amount of toxic water especially in dyeing step (Vandevivere et al., 1998). The toxicity is due to the chemical complexities of different organic and inorganic chemical agents (e.g. wetting & leveling agents) which are non-biodegradable. Non-biodegradability of such chemicals leads them to remain in dissolved or suspended state in water and thus increases B.O.D resulting in catastrophic imbalance on the ecology (Ratna et al., 2012). On the contrary these chemicals perform very significant role to ensure quality dyeing and so they cannot be eliminated. But, newer processes are being developed which are ecologically advanced and can replace dyeing auxiliaries in some extent (Savarino et al., 2009). Wool dyeing in water-alcohol solution was proposed almost four decade ago in literature (Bird, 1975; Peters, 1975). Some elaborated experiments were taken out using different alcohols on wool, cotton, nylon, polyester with wide range of dyes in hank form. Cotton hanks dyed with reactive dye established ethanol as a wetting agent; but further experimentation to replace other auxiliaries were not taken out (Franco Ferrero et al., 2011).

The idea is to replace these toxic non-biodegradable compounds with low molecular weight organic substance like alcohol; more specifically ethanol (46.06844 g/mol) which is eco-friendly and biodegradable (D R Shelton and J M Tiedje, 1984). It has the ability to reduce surface tension and can assure level dyeing by disaggregating the dyes (Yakubu et al., 2006). The boiling point (78.37 °C) of ethanol ensures its application with monofluorochlorotriazine, dichlorotriazine, difluorochloro pyrimidine, dichloroquinoxaline, vinyl sulfone, vinyl amide with some other  dyes. Another important parameter is the price of industrial ethanol which makes it cost effective comparing to the commonly used auxiliaries. Use of ethanol can also reduce the load on E.T.P. as it is readily absorbed by soil (Mackay, 1996).

Reactive dyes are invariably used in cotton dyeing worldwide which makes them suitable candidate for this experiment (Kris Kolonko).  The objective of this experiment is to establish ethanol as a substitute for leveling and wetting agent with acceptable fastness property for fabric specimen.

2. Experimental

2.1 Materials

Fully bleached single jersey fabric of 100% cotton was supplied by a local textile industry in Bangladesh. DyStar provided reactive dye with leveling and wetting agent where all these chemicals are of commercial grade. Ethanol and alkalis were of laboratory grade bought from chemical store and used as received. Specifications of the chemicals are shown in Table 1.  All the dyeing were carried out in Ahiba IR dyeing equipment (Data color ltd. NJ, USA) where r.p.m. (revolution per minute) 20 was kept constant for each dyeing.

2.2 Measurements

The extinction co-efficient of the dye (Remazol Red RR) was measured by Data Color-650 spectrophotometer (Data color ltd. NJ, USA). It was determined from absorbance value of the dye using equation 1 known as The Beer-Lambert law.

ε = A/lc                                                    (1)


ε = the extinction coefficient of the substance, has units of M-1 × cm-1

l = the sample path length measured in centimeters (the width of the cuvette is 1 cm)

c = the molarconcentration of the solution.

To determine extinction coefficient (ε) different solutions of known concentrations were made and absorbance value of those solutions were measured. When studying Remazol Red RR dye solution by spectrophotometry, the solutions were put in a sample holder called a cuvette and it was placed in the spectrophotometer. Light was passed through the solution inside the cuvette and the amount of light transmitted (passed through the solution—Transmittance) or absorbed (Absorbance) by the solution is measured by a light meter. While a spectrophotometer can display measurements as either transmittance or absorbance, in practical applications we used the absorbance of the given sample. All of the values showed highest absorbency for 510 nm wavelength which will be same at any degree of concentration for this particular dye.

1Figure 1: Determination of extinction co-efficient (ε).

By plotting the values of absorbency and concentration in Figure 1 the extinction co-efficient was determined as,   ε = 20.21; with R2 = 0.996

2.3 Dyeing process

Dyeing was carried out with 2% shade following the recipe shown in Table 1 for both standard and ethanol included dyeing. Several combinations of auxiliaries with ethanol were tested.

2Figure 2: Dyeing flow chart.

A combination of Only ethanol, Only leveling agent and Only wetting agent for each 1 gm/L, 2 gm/L, and 3 gm/L ethanol (99.5%) with other required chemicals as given in the standard recipe in Table 1 were taken into account, resulting in 12 individual variation of dyeing sample.  Fabric samples were weighed out 5 gm each for all dyeing. All the dyeing was executed using Figure 2 sequence.

Table 1: Chemicals and standard recipe.

table-12.4 Fastness Tests

Washing fastness was determined using ISO 105-C03 .The effect on staining and shade change measured by Grey Scale is given in Table 2.

Rubbing fastness for all the samples was determined using Crock Meter following ISO 105 X12. Table 3 shows the effects of both dry and wet rubbing.

3.  Results and Discussion

3.1 Exhaustion Rate

Exhaustion percentage was determined using equation 2 from absorbency value of subsequent samples.

formula-1Chart 1: Comparison of exhaustion rate of only ethanol and standard recipe.

chart-1A little rise in the exhaustion rate has been observed with the addition of ethanol. Clearly, the use of ethanol in an optimum quantity has positive effect on exhaustion rate. Comparing the exhaustion rate of standard recipe with that of no auxiliaries (only ethanol) it can be easily found that ethanol alone can achieve more or equal exhaustion than the standard one.

But use of more ethanol reduced the exhaustion rate resulting in increase of dyeing time as shown in Chart 1. The reduction of exhaustion may be explained as the use of more ethanol probably makes stable disaggregate phase in the dyeing medium unwilling to leave the solution.

Color yield of dyed fabrics

Dyed textile samples were analyzed by measuring the reflectance curve between 400 and 700 nm with a spectrophotometer with illuminant D65 for 100 observer. The reflectance value (R) of dyed sample was used to determine the ratio of light absorption (K) and scatter (S) via the Kubelka-Munk function showed in equation (3).

formula-23.2 Uniformity of Dyeing:

Color uniformity was calculated by measuring K/S values using spectrophotometer on 20 random sample spots at maximum absorption wave length using following equation number 4, 5 & 6.

   formula-3formual-textShade uniformity is shown in chart 2, where ethanol assisted samples show low variance than the conventionally dyed (standard) sample which indicates that ethanol has the ability to substitute leveling agent even with better performance.

Chart 2: Uniformity of shade.

chart-23.3 Fastness Property:

Reactive dyes usually show excellent dry rubbing fastness with varying degree of wet rubbing fastness depending on dye properties.  Laboratory results shows that use of ethanol provides same fastness to rubbing as provided by the standard one.

Table 2: Staining and shade change assessment.

table-2Samples dyed with ethanol shows good resistance to staining than the standard sample and a negligible change in shade was obtained by washing fastness tests carried out in laboratory.

Table 3: Rubbing fastness assessment.

table-33.4 Cost Analysis:

Using ethanol in dye house as a substitute of leveling and wetting agent can save significant amount of money.  1-2 gm/L of ethanol can easily replace the functions of both wetting and leveling agent successfully as previously discussed.

Table 4: Cost analysis.

table-4An example of typically used wetting agent, leveling agent and industrial ethanol is given in Table 4 with respective price and cost analysis. Industrial ethanol can be found with a wide range of strength, but our desired strength for ethanol incorporated dyeing is around 95%-99.5% (Alibaba.com); whilst the price may vary from $0.4-$1.5 depending on strength and manufacturer. Owing to the ability of ethanol to replace both of these auxiliaries, almost $3-$4.1 per kg can be saved if 1 gm/L ethanol is used as a substitute of them.

3.5 Biodegradability

In aerobic conditions using adapted wastewater from domestic sewage, degradation was 74% after 5 days while rising to 95% by day 15 and in similar conditions in synthetic seawater, ethanol was 45% degraded after 5 days rising to 75% by day 20 (Price, 1974). Biodegradation in a study to a MITI protocol showed degradation of 89% after 14 days (>70% after 10 days, CERI, 2004) and >90% within 10 days (Birch, 1991). Activated domestic sludge was capable of aerobically oxidizing ethanol, as measured by BOD, which was 37.3% of maximum after 1 day (Gerhold, 1966). The rate of biodegradation in anaerobic conditions was calculated to be 17.9 ppm ethanol per day with a total methane recovery of 91% of the theoretical limit (Suflita, 1993).

Biodegradation is the main method of removal of ethanol from water. Ethanol is stable to hydrolysis. Reaction with hydroxyl radicals in aquatic media will not likely be a significant process (Anbar, 1969).

Ethanol is stable to hydrolysis but is readily biodegradable (74% after 5 days) and is not likely to bio-accumulate (calculated log BCF=0.5). Ethanol is not persistent in the environment. Fugacity-based modelling shows that ethanol released into the environment will become distributed mainly into air, water and soil as shown in Table 5

Table 5: Distributions of ethanol in nature.

table-5The aquatic toxicity data in fish, invertebrates, and algae indicate a low order of acute toxicity with LC50/EC50 values greater than 1000 mg/L. The most sensitive species were algae Chlorella vulgaris with a 96hr EC50 of 1000 mg/L and the invertebrate Artemia Salina with a 24hr LC50 of 1833 mg/L. Valid chronic toxicity data are available for two trophic levels. The lowest reported NOEC for invertebrates is 9.6 mg/l (10 day reproduction) whilst for plants it is 280mg/l (7 day study).

Ethanol has a low order of acute toxicity by all routes of exposure. Lowest robust reported values are an inhalation LC50 of >60,000ppm (114,000 mg/m3, 1 hour, mouse), and an oral LD50 of 8300mg/kg.bw (mouse). Ethanol is a moderate eye irritant but is neither a skin irritant nor a sensitizer (SIDS, 2004).As a result no chances of threat to the worker involved in dyeing step with ethanol which makes its use more effective for dyeing industries.

4. Conclusion:

Wetting agent and leveling agent have been successfully substituted by low amount of ethanol in laboratory for 100% cotton fabric in a greener way. In consideration with the industrial aspect the results may vary to some extent with the change in chemicals and their concentration. Similar performance can be achieved in dyeing factories with little improvisation in process if needed. Future trend of this process may therefore have many more opportunities to improve dyeing process with ethanol not only for reactive dyes but for mostly used dyes in the textile industry.

5. References:

  1. W.Y. Kwok, J.H. Xin, T.F. Chong, “Environmental compliance for Hong Kong textile dyeing industry”, Research Journal of Textile and Apparel (RJTA), 3, 9-15, 1999.
  2. P.C. Vandevivere, Bianchi, R., Verstraete, “Treatment and reuse of wastewater from the textile wet-processing industry: review of emerging technologies”, Journal of Chemical Technology and Biotechnology, 72, 289-302, 1998.
  3. Ratna, B.S. Padhi. “Pollution due to synthetic dyes toxicity & carcinogenicity studies and remediation”, International Journal of Environmental Sciences, 3, No 3, 2012.
  4. S.B. Moore, L.W. Ausley, “Systems thinking and green chemistry in the textile industry: concepts, technologies and benefits”, Journal of Cleaner Production, 12, 585-601, 2004.
  5. C.L. Bird, W.S. Boston, “The Theory of Coloration of Textiles”, Bradford: Dyers Company Publications Trust, England, 310-312, 1975.
  6. R.H. Peters, “Textile Chemistry”, Elsevier, 3, 741-753, 1975.
  7. Franco Ferrero, Monica Periolatto, Giorgio Rovero, Mirco Giansetti, “Alcohol-assisted dyeing processes: a chemical substitution study”,Journal of Cleaner Production, 1377, 2011.
  8. D R Shelton and J M Tiedje, “General method for determining anaerobic biodegradation          potential”, Applied and Environmental Microbiology, 47, 850-857, 1984.
  9. M.K. Yakubu, S.M. Gumel, L.O. Ogbose and A.T. Adekunle, “Pretreatment of cotton fibres with alcohols to optimize dye uptake”, Caspian Journal of Environmental Sciences, 4, 39-44, 2006.
  10.  Mackay, D. DiGuardo, A. Paterson, S. Cowan, “Evaluating the environmental fate of a variety of types of chemicals using the EQC model”, Environmental Toxicology and Chemistry, 15, 1627-1637, (1996.
  11.  Kris Kolonko, Reich group, November 3, 2005.
  12.  http://www.alibaba.com/showroom/industrial-ethanol-price.html (accessed on May 18, 2014).
  13.  Price and K. S. et al., “Brine shrimp bioassay and seawater BOD of petrochemicals”, Journal of the Water Pollution Control Federation, 46, 63 – 77, 1974.
  14.  R.R. Birch, R.J. Fletcher, “The application of dissolved inorganic carbon measurements to the study of aerobic biodegradability”, Chemosphere, 23, 855-872, 1991.
  15.  R. Gerhold and G. Malaney, “Structural determinants in the oxidation of aliphatic compounds by activated sludge”, Journal of Water Pollution Control Federation, 38,562-579, 1966.
  16.  J. Suflita, and M. Mormile, “Anaerobic biodegradation of known and potential gasoline oxygenates in the terrestrial subsurface”, Environmental Science and Technology, 27, 976-978, 1993.
  17. M. Anbar and P. Netta, “Antioxidants and protein oxidation”, The International Journal of Applied Radiation & Isotopes, 18, 493 – 523, 1967.
  18. P Howard, “Handbook of Environmental Fate and Exposure Data for Organic Chemicals”, Lewis Publishers: Chelsea, 2, 1990.
  19. SIDS Initial Assessment Report For SIAM 19 Berlin, Germany, 19 – 22 October 2004.
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