Indian Journal of Fibre & Textile Research Vol 29, September 2004, pp. 343-349 Process optimization in tetraacetyl ethylenediamine activated sodium perborate bleaching of cotton M Prabaharan" & L Almeida Centre for Science and Textile Technology, University of Minho, Guimaraes 4800, Portugal Received 17 March 2003; revised received 28 July 2003; accepted 24 September 2003 Cotton fabric has been bleached with tetraacetyl ethylenediamine (TAED) activated sodium perborate by varying sodium perborate concentration, TAED concentration and temperature. The effect of these process parameters on the quality of the bleached cotton has been studied and compared with the conventionally bleached cotton. Improved whiteness with minimum fibre damage can be obtained by activated sodium perborate bleaching at lower temperature and for shorter exposure duration. The process is found to reduce energy cost and effluent load on environment. Keywords: Bleaching, Cotton, Desizing, Scouring, Whiteness index IPC Code: Int. CI. 7 D06L 3/00, D06B 3/00 1 Introduction that by incorporating TAED, a bleach activator, into The impurities present in grey cotton fabric are the bleach bath containing hydrogen peroxide or sizing ingredients, fat, waxes, pectins and natural persalts, bleaching can be performed at both lower colouring matter. Efficient removal of these temperature and alkalinity with significant benefits in impurities during grey preparation is essential to terms of retained fibre quality. Recently, the guarantee proper dyeing, printing and finishing. Till application of T AED in industrial textile bleaching, today, the most commonly accepted sequence of particularly for cotton/wool blends, has been 4 7 operations for cotton grey preparation is acid or reported . In the detergent industry, the bleach enzyme desizing, alkali scouring and hypochlorite or activator TAED has been used for many years in hydrogen peroxide bleaching. Recently, the use of combination with a persalt to provide effective hypochlorites has been discouraged due to the bleaching by the production of peracetic anion at low 8 liberation of harmful chlorinated organic compounds temperature and residence time . T AED is colourless, in the bleach plant effluents. Bleaching with hydrogen odourless, storage stable, safe and easy to handle. It peroxide is a well-established process in textile has been established as a non-toxic, non-sensitizing industry. However, optimized bleaching is often and non-mutagenic product which readily biodegrades dependent on processing conditions that can to form carbon dioxide, water, ammonia and nitrate. sometimes be detrimental to fibre quality, specially Sodium perborate is primarily used as a bleaching through the use of high temperatures, high pH values agent in detergent powders. It is used as a bleaching or extended reaction duration. The increasing demand agent at 15-30% by weight of the total detergent for the conservation of natural resources, composition. It is a crystalline compound formed by environmental protection and reducing energy cost reaction between sodium borate and hydrogen has now forced researchers to look for the processes peroxide. When dissolved in water, sodium perborate which can be carried out at a low temperature in a releases back hydrogen peroxide; its aqueous solution short duration without the use of harmful chemicals practically performs like a solution of hydrogen such as hypochlorite. Now, the textile industry is peroxide. Therefore, in this study, an attempt has been becoming increasingly aware of the potential benefits made to bleach cotton fabric with sodium perborate in of using peroxide acti vated systems. It is reported 1·3 presence of T AEJ. To optimize the process parameters, such as sodium perborate concentration, "To whom all the correspondence should be addressed. TAED concentration and temperature, the quality of Phone: 510280; Fax: +351-253-510293; E-mail: [email protected] the bleached fabric was assessed for the degree of 344 INDIAN J. FIBRE TEXT. RES., SEPTEMBER 2004 whiteness, per cent strength loss and cellulose 3 Results and Discussion degradation in terms of carboxyl group content and In the standard sodium perborate bleaching copper number. The properties of T AEO bleached method, the fabric should be bleached at high fabrics were compared with the properties of temperatures and high pH over a prolonged period in hydrogen peroxide bleached fabrics. order to achieve a satisfactory whiteness. This operation is time consuming and needs a large 2 Materials and Methods quantity of energy. It is possible to reduce the bleach 2.1 Materials temperature to less than 60°C by adding organic The commercial medium quality desized cotton activators into sodium perborate bleach solution. fabric having the following specifications was used TAEO reacts with hydrogen peroxide formed in the for the study: solution of sodium perborate to generate peracetic Weave, plain; ends/cm, 34; picks/cm, 26; warp acid and peracetate anion ill situ that are stronger count, 16.7 tex; weft count, 21 tex; and fabric weight, 2 bleaching agents than peroxide or perborate at low 120.8 g/m • temperatures. The T AEO activated sodium perborate All the chemicals used were of analytical grade. rapidly generates peracetic acid over a wide temperature range, which improves the bleaching 2.2 Methods 2.2.1 Experimental Design efficiency at both cold and medium temperatures. It is The experiments were conducted using Box­ reported 13.14 that peracetic acid, unlike hypochlorite, Behnken second order composite design for three gives satisfactory bleaching results with overall variables. The variables were selected at three levels improved substrate whiteness, improved cotton seed­ (-1,0, +1) and the response was given by a second­ coat removal and reduced fibre damage at low order polynomial. To test the estimated regression temperatures. However, a contm lled reaction equation for tl.e goodness of fit, Fisher F-test was condition must be required to ensure maximum employed and the multiple correlation coefficient R2 perhydrolysis of T AEO to maintain bleach was calculated. If the R2 value lies between 0.75 and performance at low temperature and to minimize side 1, the fitted regression equation is considered to be a reactions such as nucleophilic attack of peracetic acid good fit of the model. anion on unreacted TAEO molecule to form diacetyl peroxide, and the hydrolysis of T AED. Therefore, an 2.2.2 Bleachillg attempt has been made to optimize the process The samples were bleached with sodium perborate variables to achieve a maximum whiteness with less and T AEO solution for I h using the material-to­ fibre damage. The following limits for the process liquor ratio of I: lO. Bleaching with hydrogen variables were fixed based on a preliminary study: peroxide involved the standard procedures. sodi um perborate concentration (XI)' 5 - 15 gil; T AEO concentration (X2), 1 - 4g/L; and temperature 2.2.3 Test Methods (X3 ), 30 - 70°C. To establish the relationship between The bleached samples were tested for whiteness the process variables, regression analysis was index using the CIE formula for illuminant 0 65 and performed using the regression coefficients in the 9 1964 10° observer • quadratic equation. Whiteness index = Y + 800 (0.3138 - x) + 1700 (0.3310 - y) 3.1 Effect of Process Parameters on Whiteness Index where Y, x and y represent the chromaticity 3.1.1 Effect ofSodillm Perborate coordinates of the specimen; and 0.3138 and 0.3310 The effect of process parameters on whiteness represent the x, y chromaticity coordinates for the index is shown in Table 1. The result:s were obtained perfect diffuser respectively. Tensile strength was from the following response surface equation of determined according to Indian standards whiteness index: specification 10, and from this the per cent strength loss was determined after bleaching. The extent of Whiteness index = 44.9 + 1.75 XI - 0.75 X2 + 9.75 X3 + 2. 175 2 chemical modification was measured in terms of XI + 1.675 x/ - 4.325 x/ - 5.75 XI X2 + 5.25 XI X) - 4.75 Xl X3. carboxyl groups II and aldehyde groups (copper number)12. R2 value = 0.9204 PRABAHARAN & ALMEIDA: T AED ACTIVATED SODIUM PERBORATE BLEACHING OF COTTON 345 Table 1 - Effect of process parameters on fabric propertiesa Sodium TAED Whiteness index Strength loss, % Carboxyl content)milli- Copper number perborate gIL eguiv.l100g b b b gIL 30b SOb 70b 30b SOb 70b 30b SOb 70 30 SOb 70 5 1 28.4 42 42.2 3.7 9. 1 12.9 5.31 4.99 5.17 0.056 0.047 0.053 2.5 36.5 45.3 45.5 6.3 9.0 10.3 5.47 5.58 6.18 0.052 0.040 0.044 4 47.9 52 47.4 10.6 10.8 9.6 5.10 5.63 6.67 0.052 0.039 0.040 10 1 28.5 47.3 57.5 2.6 8.0 11.9 5.49 4.63 4.28 0.048 0.038 0.043 2.5 30.8 44.9 50.3 5.1 8.0 9.3 5.86 5.44 5.51 0.047 0.035 0.037 4 36.5 45.8 46.5 9.5 9.8 8.5 5.70 5.70 6.20 0.052 0.037 0.037 15 1 32.9 57 72.4 3.3 8.8 12.7 6.12 4.73 3.84 0.051 0.040 0.044 2.5 29.5 48.8 59.5 5.9 8.7 10.1 6.71 5.74 5.28 0.053 0.040 0.041 4 29.4 44 49.9 10.2 10.5 9.4 6.76 6.22 6.18 0.061 0.046 0.045 aDesized fabric - whiteness index, 22; maximum load at break, 539.5 N; carboxyl content, 5.93 milli equiv.l100g; and copper number, 0.051.