Process Optimization in Tetraacetyl Ethylenediamine Activated Sodium Perborate Bleaching of Cotton

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. t>remperature in 0c. 58 The table shows that a high degree of whiteness __ TAED,lg /L • index could be achieved at higher concentration of 56 __ TAED, 2.5g/L ~T AED,4g / L sodium perborate as expected. This may be due to the 54 liberation of more perhydroxyl ions which are mainly 52 )( responsible for bleaching at higher concentration of ill '0 .s 50 sodium perborate. Fig. 1 shows the effect of sodium II> II> ill ~ perborate and T AEO on whiteness index for a given c 48 2 temperature. It is observed that at higher E 46 concentration of T AEO, the whiteness index ~ decreases with the increase in sodium perborate 44 concentration. The maximum whiteness index is 42 obtained at higher concentration of sodium perborate 40 and lower concentration of TAEO. 10 12 14 16 [Sodium perborateJ, giL 3.1.2 Effect ofTAED Fig I-Effect of sodium perborate and TAED concentration on The concentration of T AEO present in sodium whiteness index at 50°C perborate solution determines pH of the bleach liquor. As in the case of hydrogen peroxide and concentration of T AEO. Here, it should be noted that hypochlorites, the pH also plays a major role in at lower concentration of sodium perborate (5glL), activated sodium perborate bleaching J5. Based on pH, initially the bleach bath pH was 9.5, which decreased the following two mechanisms can be proposed for to 6.5 upon the addition of T AEO. Therefore, the the bleaching action of peracetic acid formed from maximum bleaching process was carried out at pH T AEO activated sodium perborate: the liberation of 6.5. At this pH, formation of nascent oxygen would either nascent oxygen (along with acetic acid) or be more responsible for effective bleaching action perhydroxyl radical (along with carbonyl radical). The than the formation of perhydroxyl radical from liberation of nascent oxygen occurs in the acidic and peracetic acid. But, in the case of higher concentration neutral medium while that of perhydroxyl radical of sodium perborate (above 10g/L), initially the occurs in alkaline media. Table 1 shows the effect of bleach bath pH was 10.5, which decreased to 10 upon TAEO on whiteness index. It can be seen from this the addition of lower concentration of T AEO into table that with the increase in T AEO concentration, bleach bath and hence the bleaching was effectively there is an increase in whiteness index at lower performed at pH 10. This observation clearly sodium perborate concentration. However, a indicates that the maximum degree of whiteness can maximum degree of whiteness is achieved at higher be obtained when the bleaching is carried out with concentration of sodium perborate but decreased higher concentration of sodium perborate in presence 346 INDIAN J. FIBRE TEXT. RES., SEPTEMBER 2004 of lower concentration of TAED. The probable reason 75 70 for this is the formation of more perhydroxyl radical 6 5 by the dissociation of peracetic acid at pH 10. This 60 behaviour of peracetic acid in an alkaline pH is " '0'" 55 similar to the effect of pH on hydrogen peroxide .S '" 5 0 bleaching. If the pH is below 10.5, the hydrogen '"c J!! 45 peroxide decomposes very slowly and hence the ~ 4 0 formation of perhydroxyl radical would be less 16. It is 35 also reported l7 that the TAED gives maximum 30 bleaching efficiency at pH -10. At pH below 10, it is -~--,, =~:=:;==::=~ 1 .0 1 .5 2 , 0 2 . 5 3.0 3.5 4.0 found that many of the existing bleach activators lose [TAED J, giL their effectiveness and undergo competing side reactions, which produce ineffective byproducts. The Fig 2-Effect of T AEO concentration and temperature on effect of T AED and temperature on whiteness index whiteness index [sodium perborate concentration, JSg/LJ at given sodium perborate concentration is shown in Fig. 2. 80 _____ . Sod ium perb orate. 5g fL 75 _ -Sodium pe rb orate , 10gfL 3.1.3 Effect of Temperatllre 70 ~ .. Sodiu m pe rborate, 15gfL

The stability of peracetic acid also depends on the 65 temperature. At room temperature, it is relatively x 60 (1) stable and starts to decompose with the increase in "0 .s 55 II> temperature. Therefore, an increase in whiteness II> (1) 50 index with increased temperature is expected, c .'! 45 provided the decomposition rate is such that all the ~ • perhydroxyl radicals are available for bleaching. If the 40 decomposition rate is very rapid, the radicals would 35 v--- escape into the atmosphere before they could bleach, 30 as happens with a strongly alkaline pH. Preliminary 25 30 40 50 50 70 studies have indicated that for a given set of process Temperature, 'c parameters, the whiteness index is very poor if bleaching occurs either below 300 e or above 70°e. Fig 3-Effect of temperature and sodium perborate concentration The effect of temperature on whiteness index is on whiteness index [T AEO concentration, Ig/LJ shown in Table 1 and Fig. 3. At the lower concentration of sodium perborate (Sg/L), the whiteness increases considerably when the and the maximum effectiveness was thus achieved at temperature rises from 300 e to SO°e. But when the sooe, o temperature further increases to 70 e, the whiteness 3.2 Effect of Process Parameters on Strenglth Loss index either remains constant or decreases marginally. The major drawback of bleaching cellulose with However, at >Sg/L sodium perborate concentration, oxidizing agents is the loss in tensile strength. This is the whiteness increases with the increase 111 due to the cellulose degradation owing to the drop in 0 0 temperature from 30 e to 70 e and is maximum at cellulose chai n length and conversion of hydroxyl l8 about 70°e. Rucker established a relationship groups into aldehyde and carboxyl groups. It is between temperature and per cent peracetic acid always expected that a high degree of whiteness is decomposition and claimed that at pH 7 when the accompanied by a high strength loss. Therefore, to temperature increases from 200 e to 60oe, the per cent establish commercial acceptability of the bleaching decomposition increases from 5.7 to 81 but the process, it is ecessary to study the tensile properties whiteness index increases up to sooe, and then of bleached samples. Table 1 shows the effect of all decreases slightly. He also found that the increased the process parameters on per cent strength loss. It bleaching effectiveness with temperature was can be seen from this table that with the increase in counteracted by decrease in peracetic acid stability whiteness index, the per cent strength loss also PRABAHARAN & ALMEIDA: TAED ACTIVATED SODIUM PERBORATE BLEACHING OF COTTON 347 increases. It also shows that v,u'ious combinations of Table 2- Optimum process conditions process parameters can achieve a desired whiteness Whiteness Sodium TAED Temperature Strength index, for example at a particular T AED index perborate giL °C loss, % giL concentration with either a low temperature and a 40 15 35 5.0 high concentration of sodium perborate or a high 44 15 39 6.5 temperature and a low concentration of sodium 48 15 42 7.5 perborate. In such situations, it is found that the per 52 15 45 8.0 15 49 8.5 cent strength loss need not be same for these two 56 60 15 54 10.0 samples. Therefore, it is worthwhile to determine 64 15 58 10.5 which process parameter has a more detrimental 68 15 62 11.5 effect on tensile properties. Also, to get a desired 72 15 65 12.5 whiteness index, how can the per cent strength loss be minimized by changing the processing condition? The mlnllTIlZe the objective function while ensuring that study of the regression equation, as shown below, for none of the constraints is violated. This is an iterative per cent strength loss clearly shows that it is most search and stops when successive iterations show only markedly influenced by changes in temperature than an insignificant improvement in the value of the in T AED concentration: objective function. Table 2 shows the optimized processing conditions for obtaining various whiteness Stren~th loss (%) = 7.967 - 0.15XI + 0.888 X2 + 2.0875 XJ + 2 levels with minimum per cent strength loss. These 0.929 X - + 0.904 x/ - 0.746 + 0.05 XI X) - 2.575 X2 X). I xJ predicted processing conditions have been experimentally verified and found to be con·ect. The R2 value = 0.9724 results show that for a desired whiteness, minimum The negative coefficient of sodium perborate per cent strength loss can be achieved when the concentration indicates that a high concentration bleaching is carried out with higher concentration of results in less strength loss than a lower one. From the sodium perborate, keeping T AED concentration and regression equation for whiteness index, it is observed temperature low. that the coefficient for sodium perborate concentration is positive, which means that as the 3.3 Effect on Extent of Chemical Damage sodium perborate concentration increases, the The measure of the presence of carboxyl and whiteness index also increases. Thus, there is little aldehyde groups in cellulose is an indication of the incentive to bleach in a low sodium perborate extent of damage during bleaching. The presence of concentration as it not only increases the per cent these groups reduces reactive dye uptake. It is strength loss but also reduces the whiteness index normally accepted that among conventional bleaching achieved. agents, hypochlorites give a higher degree of Since three process parameters are involved, the chemical damage than hydrogen peroxide, and hence optimum process conditions to achieve a desired lesser reactive dye uptake for the samples bleached whiteness with minimum per cent strength loss cannot with the former than with the latter. While assessing be determined by manual examination of relevant chemical damage, it is observed that on several graphs. Therefore, the regress ion equations obtained occasions the carboxyl group content is less than that are optimized by the "complex search" method of of the control sample. Similar observations are l9 Box using non-linear response surface equations. For reported in the literature • The reason for such this purpose, four constraints are set: three are implicit observation is the removal of residual size materials constraints (process parameters) limiting the values to and impurities (bearing acidic and reducing groups) the ranges used in the experimental design, and the from the fabric during bleaching treatment. It seems fourth constraint is whiteness index which is set to be that the removal of acidic and reducing contents of greater than or equal to successively higher values of these non-cellulose materials exceeds those created as 40 - 72 in steps of 4. The per cent strength loss a result of the chemical degradation of cotton equation is used as the objective function. The cellulose. That is why the carboxyl group content of "complex search" method uses a hill climb technique the treated fabric is less than that of the control similar to the concept of "simplex search" to sample. Table 1 shows the effect of process 348 INDIAN J. FIBRE TEXT. RES., SEPTEMBER 2004 parameters on extent of chemical degradation. The Table 3 - Comparison of properties of fabrics bleached with results were obtained from th e following response activated sodium perborate and hydrogen peroxide surface equations of carboxyl and aldehyde group Bleaching Whiteness Strength Carboxyl Copper contents: agent index loss content number % milii equi '/./IOOg Carboxyl group content = 5.439 + 0.083 1 XI + 0.532 Xl - 2 Activated 44 6.5 5.43 0.045 0.178 X, + 0.226 XI - 0.269 X/ + 0.247 X/ + 0.211 XI X2 - sodium 48 7.5 5. 34 0.043 0.537 XI X.1 + 0.427 X2 X,. perborate 52 8.0 5. 13 0.04 1 u ~ va lue = 0.9684 56 8.5 4.72 0.040 60 10.0 4.5 1 0.041 Aldehyde group content = 0.0347 - 0.0002 XI - 0.000725 X2 - Hydrogen 44 7.0 5.52 0.047 2 0.004925 X.1 + 0.005296 XI + 0.002896 X/ + 0.007396 X/ + peroxide 48 7.8 5.33 0.044 0.003625 XI Xl - 0.000975 XI X, - 0.002325 X X.1. 2 52 8.5 5.24 0.04 1 56 9.0 4.92 0.043 u2 va lue = 0.8920 60 10.0 4.4 1 0.044 temperatures and for shorter exposure duration. The It can be clearly observed from the table th at the quality of activated sodium perborate bleached fabric formation of carboxyl groups during bl eaching was also compared with that of sodium perborate depends on the process parameters. From th e (without T AEO) bleached fabri c un der the identical regression equation of carboxyl group content, it is bleaching conditions. The results are fo und to be less observed th at the carboxyl groups of the treated fabric satisfactory for the fabrics bleached with sodium decrease by increasing the temperature and decreasin g perborate without activator. the concentration of T AEO. The carboxyl group is also fo und to be hi gh at low or hi gh concentrati on of 4 Conclusions sodium perborate. Equation of aldehyde group content Bleaching of cotton using T AEO activated sodium shows that aldehyde group content is most markedly perborate is environment-friendl y, energy savin g and in fluenced by the changes in temperature, followed by low-temperature process and is a good repl acement of T AEO concentration and sodium perborate conventional bl eaching processes. Bleaching can be concentration. It is generall y found th at the values of done with 15 giL of sodium perborate and I giL of carboxyl group and aldehyde group contents are more T AEO at 50 - 60°C fo r 1 h in order to achi eve an at both low and high levels of process parameters. acceptable degree of whiteness (ready for dyeing) The probable reason for thi s is that at low levels of with minimum cellulose degradation. For the process parameters, th e presence of impuriti es materials that undergo subsequent optical brightening markedly influences the determination of carboxyl agent treatment, the bleaching process can be done for and aldehyde group contents. At high levels of about 90 min or so at 60 - 70°C. The quality of the process parameters, the impurities are not present and bleached material is marginally better than that of so the increase in carboxyl and aldehyde group hydrogen peroxide bleached material since the contents may be attributed to the increase in cellulose process is carried out at lower temperature and for degradation. shorter exposure duration. The process would also seem to be highl y suitable fo r fi bres, uch as linen, 3.4 Comparison with Conventional Process linen blends and wool blends, which cannot withstand An attempt has also been made to compare the traditional severe bleaching condition. quality of T AEO activated sodium perborate bleached material with that of hydrogen peroxide bleached Acknowledgement material (Table 3). For a given whiteness index, the The authors are thankful to the Foundation of per cent strength loss and extent of chemi cal damage Science and Technology, Government of Portugal, for measured in terms of carboxyl and aldehyde group providing the financial assistance. contents for the activated sodium perborate bleaching References process are marginally better than that of hydrogen I Mathews J, J Soc Dyers Colour, 115 (1999) 154. peroxide bleaching. These benefici al properties are 2 Milne J N & Watkins J M, US Pal 5,840,667 (to Warwick due to bleaching under milder conditions at lower International Group Ltd.), 24 November 1998; PRABAHARAN & ALMEIDA: TAED ACTIVATED SODIUM PERBORATE BLEACHING OF COTTON 349

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