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  • 1. 1 A Comparison of Peracetic Acid and Hydrogen Peroxide Bleaching on Cotton Fabric By: Dr. A. Farhan Khan Department of Textile Science, Textile Institute of Pakistan, Karachi Abstract Bleaching tests were conducted to study the efficacy of peracetic acid as a replacement of hydrogen peroxide in bleaching processes of 100% cotton fabric. The criteria chosen for assessing bleaching performances of peracetic acid and hydrogen peroxide were whiteness index, tensile strength, absorbency and fluidity values. The CIE whiteness index value of fabrics was measured by a spectrophotometer using appropriate computer software. Universal Strength Tester (Titan) was used to measure tensile strength. Ostwald – Fenske Cuen viscosimeter was used to determine chemical degradation of cotton fabric by measurement of its fluidity and embroidery hoop was used to determine absorbency. The results of this research showed that the peracetic acid is more effective as a bleaching agent than hydrogen peroxide. An acceptable degree of whiteness (CIE whiteness index 80) can be obtained with minimum loss of tensile strength. This study has also provided valuable information for industrial application of the developed bleaching systems. Key words: Cotton, Bleaching, Peracetic acid, Hydrogen peroxide 1
  • 2. 2 Introduction: The art of bleaching has been practiced since beginning of civilization [1,2]. Bleaching is the process of removing colored impurities from the griege fabric as efficiently as possible, with minimum or no damage to the fiber and leaving in a perfect white state [3,4]. Nowadays, consumers increasingly demand more environmentally friendly products. This also effect the textile industry, and thus, aspects such as control of water, energy and chemicals consumption should be taken into account in wet textile processes. Hydrogen peroxide (H2O2) is the most widely used bleaching agent for textiles and came into use around 1878 [1]. Hydrogen peroxide is suitable for most fibers and it can be used in a wide range of machines under different conditions. Reaction products are non-toxic and non-dangerous but hydrogen peroxide is a highly corrosive compound and degrades to oxygen and water. Hydrogen peroxide is however, damaging to fiber, because it is applicable in strongly alkaline medium and it requires a high temperature to give the most effective bleaching [5,6 ]. Paracetic Acid (PAA) as a bleaching agent has many advantages compared to hydrogen peroxide. It does not produce any toxic by product in bleach reaction, it is less corrosive, it is biologically totally degradable and it causes no AOX (absorbable halogenated organic compounds) load in the waste water [7]. Paracetic acid can be prepared in situ in solution from hydrogen peroxide and acetic anhydride. 2
  • 3. 3 H2O2 + (CH3CO)2O → CH3COOOH + CH3COOH Commercial peracetic acid, which is available, for example, in 5% and 15% solutions, is a colorless liquid with a pungent smell & both solutions are water soluble [8]. Experimental: Materials: Fabric: The characteristic parameters of the 100% pure scoured cotton fabric used for all the experiments, purchased from the market are presented in Table-1. Table-1: Basic characteristics of 100% cotton scoured fabric Area Warp Weft CIE Tensile Fabric Weave Weight Yarn Yarn Whiteness Strength Absorbency Fluidity Composition Count count Index (N) (g/m2) (tex) (tex) (WI) Warp Weft (Sec) (Rhe) Scoured Taffeta 100% Cotton weave 168.5 40 31 26.9 542.0 240.4 4.2 1.3 Water: The water used during all bleaching and washing operations had the following qualities. Table-2: The Quality of Water pH Total Hardness Total Dissolve Solids (ppm) (ppm) 7.8 42.0 145 3
  • 4. 4 The Total Hardness was measured in terms of calcium carbonate. The pH, Total Hardness and Total Dissolve Solids (TDS) of water suitable for all textile processing are 6.5-7.5, 0-50 ppm and 65-150 ppm respectively [9]. Equipments/ Methods: Bleaching Machine: Bleaching runs were carried out in an SDL ‘ECO’ Infra Red Lab Bleaching/Dyeing machine with automatic temperature programming and agitation. Digital pH Meter: A digital pH/Temperature meter was used with a combination of glass electrode. Whiteness Measurement: The CIE Whiteness Index value (CIE WI) was determined for the bleached fabric using AATCC Test method (110–1995) [10]. The whiteness was measured using a DataColorSpectra flash SF 600X with the following setting; illuminants D-65, large area view, specular included and CIE 1964 supplemental standard observer (100 observer). Each sample was folded twice to give an opaque sample with four piles and the whiteness was measured four times at different fabric surface. The average value of (CIE WI) was recorded. Absorbency: Absorbency was determined as per AATCC Test Method (79-1986) [11]. Absorbency is one of the several factors that determine the suitability of a fabric for 4
  • 5. 5 a particular use wet ability or absorbency of textiles or fabric can be determined by the this test method. Fluidity: Ostwald Cannon-Fenske (Cuen) (Cupriethylene Diamine Hydroxide) viscosimeter was used to determine the chemical degradation of cotton by measurement of their fluidity as per AATCC Test Method (82-1989) [11]. Tensile Strength: The tensile strength was measured by Universal Strength Tester (Titan) according to EN (ISO. 13934-1: 1999) [12]. Chemicals: Hydrogen Peroxide: Hydrogen Peroxide (35% wt/wt) supplied by MERCK (Germany). Wetting Agent: Sandozin liq (non ionic) wetting agent supplied by Clariant (Pakistan). Sodium Hydroxide: Sodium Hydroxide (NaOH) pellets supplied by MERCK (Germany). Peracetic Acid: Peracetic acid supplied by Tianjin Xinyuan Chemical, CO., Ltd (China). Stabilizer EDTA: Stabilizer EDTA supplied by MERCK (Germany). For comparing the hydrogen peroxide and peraectic acid bleaching effects, the recipes used are shown in Table-3. 5
  • 6. 6 Table-3: Bleaching recipes of hydrogen peroxide and peracetic acid Hydrogen peroxide Bleaching Peracetic acid Bleaching H2O2 35% (wt/wt) 5% (owf) PAA (8% solution) 10g/l NaOH 100% 2.5% (owf) for pH 10-10.5 Wetting agent 1.5% (owf) Pellets (non ionic) Wetting agent 1.5% (owf) Stabilizer EDTA 2% (owf) (nonionic) Stabilizer EDTA 2% (owf) Treatment 65°C temperature Treatment temperature 95°C Treatment time 45 min Treatment time 60 min pH 6.5-7.0 Fabric Scoured Cotton Fabric Scoured Cotton Liquor to fabric ratio 15:01 Liquor to fabric 15:01 ratio *owf: On the weight of fabric The hydrogen peroxide and peracetic acid bleached samples were then hot washed at 95°C for 15 minutes followed by cold wash and air dried. Results and Discussion: The purpose of this comparative study was to explore the possibility of bleaching cotton fabric by peracetic acid and to achieve an acceptable degree of whiteness (CIE whiteness index 80) with minimum loss of tensile strength and maximum absorbency. The results of CIE whiteness index, tensile strength, absorbency and fluidity are shown in Table- 4. 6
  • 7. 7 Table-4: Comparison of properties of cotton fabric bleached by hydrogen peroxide and peracetic acid Kind of treatment CIE whiteness index Tensile strength Absorbency Fluidity (WI) (N) (Sec) (Rhe) Warp Weft H2O2 81.1 435.1 198.9 1.0 2.3 PAA 83.6 450.7 205.1 1.0 2.1 The colouring matter present in cotton is characterized by the presence of conjugated double bonds and these double bonds are attacked by the oxidizing species during bleaching [13,14]. Bleaching was carried out with PAA (10g/l) on scoured cotton fabric at pH- 6.5-7 for 45 minutes. The PAA bleached sample was compared with sample bleached by hydrogen peroxide. It was observed that PAA bleaching increased the CIE whiteness index from 26.9 (non bleached cotton fabric) to 83.6, this whiteness index was about 3% higher than of hydrogen peroxide bleaching. Which is considered as acceptable whiteness index, so that the material would be ready for dyeing/printing. This acceptable degree of whiteness was decided in consultation with processing mills. The same results are shown in graphical form in Fig. 1. 7
  • 8. 8 Fig.1: Comparison of degree of whiteness for samples bleached by Hydrogen peroxide & Peracetic acid. 90 80 70 CIE Whiteness Index (WI) 60 50 40 30 20 10 0 Non bleached H2O2 PAA On the other hand when the tensile strength and fluidity values of hydrogen peroxide and peracetic acid bleached samples were examined, it was noticed that the tensile strength of PAA bleached sample was (3.5% warp direction; 3.1% weft direction) higher than hydrogen peroxide, also the fluidity values were changed from 1.3rhes (non bleached) to 2.1rhes in the case of PAA bleached sample and 2.3rhes in the case of hydrogen peroxide bleached samples. The fluidity value of PAA 2.1rhes shows the marginal degradation of cellulose than those of bleached sample by hydrogen peroxide. A report by Hickman.W.S and Andrianjafy.H showed that the value of fluidity below 5rhes is considered acceptable for bleached fabric and Vaeck showed direct relationship between fluidity values and loss of tensile strength [15,16]. The results of tensile strength and fluidity are also exhibited in graphical form. Fig.2,3. 8
  • 9. 9 Fig.2: Comparison of tensile strength for samples bleached by Hydrogen peroxide & Peracetic acid. 600 500 Tensile strength (N) 400 300 200 100 0 (warp)(weft)non bleached (warp)(weft)H2O2 (warp)(weft)PAA Fig.3: Comparison of fluidity for samples bleached by Hydrogen peroxide & Peracetic acid. 3.5 3 2.5 Fluidity (Rhe) 2 1.5 1 0.5 0 Non bleached H2O2 PAA 9
  • 10. 10 A big improvement in the absorbency (time required for the specular reflection of the water drop to disappear) (4.2sec to 1.0sec) were also observed in all cases of bleaching. The results of these figures are represented in Fig.4. Fig.4: Comparison of absorbency for samples bleached by Hydrogen peroxide & Peracetic acid. 4.5 4 3.5 Absorbency (sec) 3 2.5 2 1.5 1 0.5 0 Non bleached H2O2 PAA All the above results of CIE whiteness index, tensile strength, fluidity and absorbency obtained by PAA bleaching indicate that the main advantage of bleaching with PAA instead of peroxide is that a satisfactory degree of whiteness can be obtained at 65ºC in 45 minutes at neutral pH. This results in lower energy and water consumption in both during bleaching and rinsing of the fabric. Neutralization of the fabric after bleaching is not required, unlike bleaching with hydrogen peroxide, where large amount of alkali must be removed before dyeing. This is also much less damaging to the cotton fabric when PAA is used. 10
  • 11. 11 Conclusion: In this study PAA has been studied as an alternative to hydrogen peroxide for the bleaching of cotton. It has been demonstrated in this work that scoured cotton fabric can be bleached by PAA and it is possible to achieve an acceptable degree of whiteness in a shorter time than is required for hydrogen peroxide bleaching process. Furthermore, bleaching can be carried out at 65ºC with neutral pH without producing any harmful chemicals. PAA, as an industrial chemical is easily available and can be safely introduce to an existing process design. References: 1) Peters,R.H., Textile Chemistry, Elsevier Publ., 1967,vol.2. 2) Easton,B.K., Ciba Geigy Rev., 1971, 3, 3. 3) Shenai,V. A., Technology of Bleaching and Mercerizing, Sevak Publications., New Dehli, 1991, p.10-60. 4) Cates, D.M; Cranor,W.H., Textile Res. J, 1960, 30, 848. 5) Conzelmann, F; Wurster, P; Zahn, A., Textil Praxis International, 1989, p.644. 6) Schulz, G., Textil Praxis International, 1990, p.40. 7) Parch, al., Fette Wachse, 1990, 77. 8) John, Shore., Colorant & Auxiliaries, Hobbs The printers., Hampshire, UK,2002, vol.2, p.602-607. 11
  • 12. 12 9) Athur,D. Broadbent., Basic Principles of Textile Coloration., Society of Dyers & Colourists, UK, 2001, p.132. 10) AATCC Technical Manual, Vol.75, Research Triangle Park: AATCC, 2000. 11) AATCC Technical Manual, Vol.66, Research Triangle Park: AATCC, 1991 12) British Standard, BS EN ISO 13934-1: 1999. 13) Jones,B.M; Langlois,G.W; Sakaji,R.H., Environ. Prog., 1985, 4, 252. 14) Rounsaville, J; Rice,R.G,. Ozone.sci.eng., 1997, 18, 549. 15) Hickman,W.S; Andrianjafy,H., J.S.D.C., 1983, 99, 88. 16) Vaeck., J.S.D.C.,1966, 82, 374. 12