**2.1 Materials**

78 Textile Dyeing

Sawada et al., 1998, Buschle-Diller et al., 1998) or alkaline (Etters, 1999; Durden et al., 2001; Lenting & Warmoeskerken, 2004) medium and is dependent on the type of pectinase. Pectin acts as a sort of cement or matrix that stabilizes the primary cell wall of cotton fibres. Pectinases decompose insoluble pectin into smaller particles thereby destabilizing the structure in the outer layers. The weakened outer layers can be removed in a subsequent wash process to such extent that following finishing processes and dyeing can be easily preformed (Etters, 1999; Losconzi et al., 2004; Cavaco-Paulo & Gubitz, 2003). It has been established that agitation of the treatment bath is very important for pectinase to function efficiently (Anis & Eren, 2002; Li & Hardin, 1998) and that selected sequestering agents can improve their effectiveness (Losonczi, 2005). Since enzymes act selectively, no damage to fibres occur during treatment. Also, it has been observed that after enzymatic treatment, baths are less polluted than baths after scouring with sodium hydroxide (Losonczi et al.,

Bleaching with peracetic acid (PAA) is an alternative to bleaching with hydrogen peroxide (Tavčer, 2010). It is a powerful oxidizing agent (redox potential: 1.81 eV) (Preša & Tavčer, 2009) with excellent antimicrobial and bleaching properties. It is efficient at low concentrations, temperatures and in neutral to slightly alkaline medium. Its products of decomposition are biologically degradable. In the past, it was prepared in situ from acetic acid anhydride and hydrogen peroxide (Rucker, 1989; Wurster, 1992). However, the risk of explosion during the synthesis reaction prevented affirmation of peracetic acid as a bleaching agent in industry. In recent years, peracetic acid has become interesting (Hickman, 2002; Križman et al., 2005; Križman Lavrič et al., 2007). Several commercial products are available as balanced mixtures of peracetic acid, acetic acid and hydrogen peroxide (Equation 1). They are stabilized with a minimum amount of sequestering agent. Today, peracetic acid products available in the market are safe, simple to use, and priceeffective. Equation 2 shows the reaction that occurs when peracetic acid is used for

+ OO H H CH3 C

stabilizer

Both processes, scouring with pectinases and bleaching with peracetic acid, are conducted at temperatures of 50–60 °C for 40–60 minutes and pH 5–8. If both processes could be combined into one process, huge amounts of water, energy, time, and auxiliary agents can be saved. In a recent study (Preša & Tavčer, 2008b), it was confirmed using a viscosimetric method that pectinases retain their activity in the presence of peracetic acid and that

The objective of our work was to compare the properties of enzymatically-scoured and peracetic acid-bleached cotton fabrics treated by two-bath and one-bath scouring/bleaching methods, with respect to conventionally-treated fabrics (alkaline scoured and bleached with hydrogen peroxide) with emphasis on their degree of

CH3COOOH + impurities CH3COOH + oxidised impurities (2)

<sup>O</sup> catalyst

O

+

H2O

(1)

O H

2005; Choe et al., 2004).

bleaching.

CH3 C

O

OH

combined processes are feasible.

whiteness and dyeability.

Desized cotton fabric, 100 g/m2, was obtained from Tekstina, Slovenia. Acid pectinase Forylase KL (AP) was supplied from Cognis, Germany, and alkaline pectinase Bioprep 3000L (BP) from Novozymes, Denmark. Cotoblanc HTD-N (anionic wetting and dispersing agent, alkansulphonate with chelator) was supplied from CHT, Germany. H2O2 35% (HP) and peracetic acid (PAA) as a 15% equilibrium solution in the commercial bleaching agent Persan S15 were obtained from Belinka, Slovenia. Foryl JA (nonionic wetting agent) and Locanit S (ionic-nonionic dispersing agent) were obtained from Cognis, Germany and Lawotan RWS (nonionic wetting agent) was obtained from CHT, Germany. Sodium hydroxide was supplied from Šampionka, Slovenia, and acetic acid and sodium carbonate were supplied from Riedel-de Haen, Germany.

#### **2.2 Treatment methods**

The cotton fabric was scoured according to three different procedures using sodium hydroxide, acid pectinase or alkaline pectinase. The scoured fabrics were bleached with two bleaching agents: hydrogen peroxide and Persan S15. The abbreviation of processes and treatment conditions are displayed in Table 1. Enzymatic scouring and one-step treatments were performed 60 minutes at 55 °C, than the temperature of the bath was increased to 80 °C for 10 minutes to deactivate the enzymes. To activate peracetic acid in AP/PAA treatment, the pH was adjusted to 8 after 30 minutes. Demineralised water was used in all processes. The treatments were performed on the Jet JFL apparatus manufactured by Werner Mathis AG loaded with 50 g of fabric at a liquor ratio of 1:20. After all treatments, the bath was discharged and the jet was filled sequentially with fresh water heated to 80 °C, 60 °C and 25 °C to rinse the fabric. After alkaline scouring and peroxide bleaching, the fabrics were additionally neutralized with a neutralizing bath containing acetic acid and rinsed with cold water.

Dyeing of Environmentaly Friendly Pretreated Cotton Fabric 81

the fibres swelled, became smoother and clean of non-cellulose impurities and the degree of whiteness increased to 19.5. However, after scouring with acidic and alkaline pectinases, both samples had lower degrees of whiteness relative to the desized sample, i.e. the sample treated with acidic pectinases (AP) had a whiteness degree of 8.2, and the sample treated with alkaline pectinases (BP) had a whiteness degree of 8.4. Negative TV values demonstrated that all scoured and desized samples had a red shade. After alkaline scouring,

The degree of whiteness of all scoured samples increased significantly after hydrogen peroxide bleaching. The differences in whiteness from previous scouring disappeared. Alkaline and bioscoured samples have a whiteness values above 84 and the red shade

With peracetic acid bleaching, a high degree of whiteness was not achieved and the differences in whiteness from the previous scouring remained visible. The sample, which was alkaline scoured prior to bleaching (AS+PAA), had the highest degree of whiteness (72.7), whereas both bioscoured samples had lower degrees of whiteness (57.7 AP+PAA and 57.3 AP+PAA). The red shade was visible on all peracetic acid bleached samples and was more on bioscoured than on alkaline scoured fabrics, which suggests that bleaching with peracetic acid is not as effective as bleaching with hydrogen peroxide. This occurs because bleaching with peracetic acid proceeds at a low temperature and pH, where the impurities remaining after scouring could not be fully oxidised. Bioscoured fibres contained also more waxes and other impurities that hindered the successful oxidation with peracetic acid at mild conditions. Bleaching the alkaline scoured fabrics with peracetic acid is more effective since the impurities were removed from cotton fibres to a higher extent in the previous process and the pigments within fibres were more exposed to the oxidant's influence. This is

The degrees of whiteness after a one-bath treatment (68.7 AP/PAA and 69.6 BP/PAA) were higher than those after two-bath bioscouring and bleaching with peracetic acid and close to the whiteness achieved after alkaline scouring and bleaching with peracetic acid. This can be explained by the fact that at the bleaching conditions of peracetic acid (55 °C, pH 8), hydrogen peroxide, which was present in the balanced mixture with peracetic acid, was not consumed, whereas at temperature 80 °C, which was the finite temperature of the one-bath process, hydrogen peroxide was activated, which further increased the degree of whiteness.

Scouring HP PAA Scouring/PAA

W TV W TV W TV W TV

D 11.1 -9.1 - - - - - -

AS 19.5 -7.6 84.12 -0.45 72.7 -0.95 - -

AP 8.2 -9.73 85.59 -0.37 57.7 -2.05 68.7 -1.3

BP 8.4 -9.6 85.07 -0.36 57.3 -1.9 69.6 -1.2

Table 2. Whiteness (W) and tint values (TV).

the red shade decreased, whereas after both bioscourings, the red shade increased.

confirmed by comparing data of the mass loss during treatments (Table 3).

almost disappeared.


Table 1. The abbreviation of processes and treatment conditions

#### **2.3 Dyeing procedure**

Dyeing the pre-treated fabrics was performed at 60 °C for 90 minutes with 0.5% and 2% Cibacron rot F-B. 30 g/L Na2SO4 and 8 g/L Na2CO3 was used for pale shade and 50 g/L Na2SO4 and 11 g/L Na2CO3 for medium shade. The weight of the dyed samples was 5 g. Finally, the cotton was soaped, washed and air dried. Dyeing was performed in closed beakers on an Launder-Ometer (Atlas).
