New development for combined bioscouring and bleaching of cotton-based fabrics
Introduction
Cotton cellulose has excellent properties such as higher water absorbency and moisture, being comfortable to wear and easily to dye. For these reasons, the apparel industry is predominantly cotton based, and the share of cotton in total fibre consumption is about 50% (Carr, 1995, Karmakar, 1999).
Cotton is composed almost entirely of cellulose (88.0–96% based on weight of fibres (owf)). The impurities in cotton fibre range from 4 to 12% and include protein (1.0–1.9%), wax (0.4–1.2%), ash (inorganic salts) (0.7–1.6%), pectin (0.4–1.2%) and others (resins, pigments, hemi-cellulose) (0.5–0.8%) (Lewin and Mark, 2007, Segal and Wakelyn, 1988).
With the exception of natural coloring matters that may be removed by bleaching using certain oxidants, many other impurities are removed by alkali treatment in scouring stage. The latter in common practice involves boiling the cotton in sodium hydroxide (2–5%) for 30–60 min, which means that a higher energy is consumed. Because of the high pH values, the treatment should be followed by intensive rinsing and neutralizing, which means that large amount of water is also consumed. Moreover, the aggressive scouring treatment conditions frequently damage the fibre (Hashem, 2007, Lewin and Sello, 1984).
The aforementioned disadvantages of scouring with sodium hydroxide have motivated the textile industry to introduce more enhanced biological agents, which would be as effective in removing non-cellulose substances but would not have damaging effects and would be less energy and water consuming. Pectinases or pectinolytic enzymes are the enzymes that catalyze the hydrolysis of pectin substances. Three main types of enzymes are used to break down pectin substances namely, pectin esterases, polygalacturonases and pectin lyases (Hashem, 2007). After breaking down and removing pectin, which binds, as a natural binder, non-cellulose substances with the fibre cellulose core, other non-cellulose substances can be removed from cotton by using hot washing with surfactant.
Over the last two decades, chlorine-containing bleaching compounds have been withdrawn from the market and their usage become limited. This is due to the formation of highly toxic chlorinated organic by-products (AOX) during the bleaching process as well as effluents discharged therefrom. Moreover, the legal regulations have stipulated very limiting values for (AOX) in the textile effluent. Nowadays textile industries are obliged to bleach without using chlorine-containing compounds. Peracetic acid is environmentally safe alternative bleaching agent, since it decomposes to acetic acid and oxygen. The decomposition products are biodegradable and do not form any toxic by-products (Boesinga et al., 1999, Krizman et al., 2005, Reinhardt, 2006).
Peracetic acid as an industrial chemical agent is easily available and can be safely introduced into an existing process design. An important advantage of peracetic acid, which contain –COOH groups, is that they are fast acting, non foaming, water soluble liquids and break down to innocuous decomposition products that are environmentally acceptable (Guersoy and Dayioglu, 2000, Hashem, 1999).
Recent research has shown that tetraacetylethylenediamine (TAED) activated peroxide system has potential in bleaching of cotton-based textiles with improved bleaching effectiveness under mild conditions. Both TAED and reaction by-product (diacetylethylenediamine) as well as peracetic acid are nontoxic and biodegrade to give carbon dioxide, water, nitrate and ammonia as end product. Therefore, TAED provides totally environment friendly bleaching agent (Hashem, El-Bisi, & Hebeish, 2003).
As scouring with pectinases and bleaching with PAA are carried out at the same temperature, a similar pH value and a similar time, it is so feasible that, both processes could be joined into a single combined process. In this way, consumption of water, energy, time and auxiliary agents would be lowered. Prior to combining both processes, we wanted to find out whether pectinases retained their activity in the presence of PAA.
The present work was essentially aimed at:
(i) Discovering the proper conditions for the enzymatic scouring of cotton and cotton/polyester fabrics, (ii) comparing the alkaline scouring of cotton and cotton/polyester fabrics with enzymatic scouring of the latter using pectinases and mixtures of pectinase and cellulase enzymes, (iii) studying the influence of EDTA and β-cyclodextrin independently when used at different concentrations as a pretreatment for bioscouring on the efficiency of the latter and (iv) investigating the effects of EDTA and β-cyclodextrin on the efficiency of bioscouring using alkaline pectinase enzyme in single use or in admixtures with cellulase enzyme. (v) The optimization of bleaching process parameters including TAED and H2O2 concentrations, pH, temperature and time and; vi) comparing the single use of bleaching process using TAED and H2O2 with the combined use of TAED, H2O2 and alkaline pectinase in one bath. Quality of bleached cotton-based fabric was measured in terms of weight loss, whiteness index, tensile strength, fabric absorbency and carboxyl content.
Section snippets
Materials
Four different types of cotton-based fabrics were used. These comprised grey 100% cotton fabric (160 g/m2), grey mercerized cotton fabric (160 g/m2), grey cotton/polyester (50/50) blended fabric (160 g/m2) and grey cotton/polyester (35/65) blended fabric (224 g/m2). These four cotton-based fabrics will be referred to as substrates I–IV for convenience. All substrates (fabrics) were sized using the same sizing recipe based on starch. The cotton/polyester blend fabrics were sized using a size base
Effect of pectinase concentration
The four substrates under investigation were treated with alkaline pectinase enzyme at different conditions and the technical properties of the resultant bioscoured substrates were determined; these properties are summarized in Table 1. Results of Table 1 signify that with all substrates, increasing the alkaline pectinase concentration from 0.5 to 2 g/L acts in favor of loss in fabric weight, however, type and nature of the substrate determine the magnitude of the loss in fabric weight. As the
Conclusion
Four cotton-based substrates in the fabric form were subjected to bioscouring by single use of alkaline pectinase enzymes or by using binary mixtures of alkaline pectinase and cellulase enzymes. Substrates under investigation comprised: (a) desized cotton fabric (substrate I), (b) desized mercerized cotton fabric (substrate II), (c) desized cotton/polyester (50/50) blend fabric (substrate III) and (d) desized cotton/polyester (35/65) blend fabric (substrate IV). The aforementioned
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