S03 AFTEX 1 2013 Dyes and Chemicals_Layout 1 08/03/2013 09:57 Page 13
TEXTILE PRE-TREATMENT fabric demonstrated that the Sera Zyme C-PE process offered significant savings in process time (7.3 per cent), water (15.9 per cent), electricity (11.3 per cent) and steam (19.6 per cent). Another enzyme for bio-scouring is Novozymes' Scourzyme 300L, which is a pectate lyase enzyme that degrades the pectin in cotton into soluble compounds. Applied at 60°C, Scourzyme 300L requires no rinsing or neutralising steps prior to dyeing and cotton yarn can be scoured in half the time required for traditional alkaline scouring. Importantly, the yarn weight loss was only 3.3 per cent compared with 5.7 per cent for alkaline scouring. In addition, the carbon footprint is improved with CO2 emissions being decreased by around 1,000kg per ton of yarn. Prima Green Ecoscour is a novel enzyme for bio-scouring from Genencor which is claimed to yield 30 per cent savings in water and 60 per cent savings in energy compared with standard cotton scouring treatments. This pectate lyase enzyme treatment utilises milder processing conditions resulting in improved fabric quality and better absorbency. Another important factor for fashion apparel is that Prima Green is claimed to enhance the colour brightness after dyeing.
Bleaching systems Traditional chlorine-based bleaching systems, based on sodium hypochlorite and sodium chlorite, have been in decline over the last two decades because these lead to the production of AOX (absorbable organo-halides) in the waste water, and chlorine-based bleaching systems are regarded as less eco-friendly. While alkaline hydrogen peroxide bleaching is the main chemical bleaching method currently in use, the enzyme producers are starting to introduce alternative enzyme-based bio-bleaching systems that offer some significant advantages. A major innovation is Huntsman Textile Effects’ (Singapore) novel Gentle Power Bleach system. This is based upon the latest breakthrough in enzyme technology by Genencor and the Gentle Power Bleach system was awarded the prestigious German ‘Industriepreis 2010’ in the biotechnology category. This highly-rated bio-bleaching system is based upon the use of four components that enable bio-bleaching to be conducted at 65°C and under near neutral pH conditions. The products used for bio-bleaching in the Gentle Power Bleach system comprise: ● Invazyme LTE - the enzyme used to catalyse the hydrogen peroxide bleach ● Invatex LTA - an agent that assists and boosts the action of the peroxide ● Clarite LTC - an agent with combined excellent wetting detergent and dispersing properties ● Invatex LAB - a liquid buffer used for maintaining an optimum pH The Gentle Power Bleach system results in a lower weight loss, a softer handle and leads to improved fabric strength retention after chemical cross-linking finishes have been applied and cured.
Over the last two decades there has been a progressive shift away from the harsh chemical pre-treatments to a softer handle
This bio-bleaching system is claimed to be a more sustainable, eco-friendly enzyme-based pretreatment system that can provide a 25 per cent lower climate change impact compared with traditional hydrogen peroxide bleaching. The Gentle Power Bleach system is applicable to all types of closed equipment. Fabrics may be bio-bleached in jet, overflow and jig machines while yarns may be treated in package dyeing machines. Recipes appropriate for bio-bleaching have been formulated for both low liquor ratio processing at 1:4-1:6 and for high liquor ratio (1:81:12) processing. Bio-bleaching is normally carried out at 65°C for 50 minutes, followed by draining and rinsing twice in separate baths for 10 minutes at 50°C. Where woven fabrics and terry towelling fabrics are to be pre-treated, Huntsman Textile Effects have recommended the addition of an enzyme, Invazyme ADC, which promotes the enzymatic desizing of starch-based sizing materials. An important aspect of peroxide bleaching treatments is the use of catalase enzymes that are used to decompose any residual peroxide remaining in the fibres, because these can lead to undesirable shade changes if the fabric is subsequently dyed with reactive dyes. Two types of catalase enzymes are generally in use. Those based upon bacterium micrococcus luteus are generally applied at pH 5-11 and temperatures of 20-50°C. These catalases are highly efficient in decomposing peroxide residues but at high peroxide levels they can be inactivated. Catalases based upon fungal Aspergillus niger normally operate in the pH range 3-10 and in the temperature range 20-70°C. This type of catalase is more resistant to oxidation by peroxide and therefore can be used where high-levels of residual peroxide are present. The catalase enzyme used with Huntsman's Gentle Power Bleach system is a stabilised liquid catalase, namely Invazyme CAT. Prochimica Novarese SpA (Italy) showcased its novel EASYWHITE eco-friendly bleaching
AFRICA AND MIDDLE EAST TEXTILES ISSUE FOUR 2012 / ONE 2013
system at ITMA 2011, Barcelona. This chemical bleaching system uses a wetting/detergent/sequestering auxiliary EASYWHITE AC/JET and a peroxide activator EASYWHITE ACTIV-N. In this bleaching system, the hydrogen peroxide bonds with the EASYWHITE ACTIV-N to form a new and complex molecule, capable of reaction with the fabric at a lower temperature under moderate pH conditions e.g. pH 9.5-12. Bleaching trials on raw cotton have demonstrated that bleaching can be carried out at 80°C, some 15-20°C lower than traditionally used. Viscose/elastane fabrics could be bleached at 60-70°C compared with 80-90°C conventionally. With the EASYWHITE bleaching process, Prochimica Novarese claim a reduction of 20 per cent in bleaching time as well as saving in water costs of 5-10 per cent and in energy of 10-20 per cent. Cotton fabrics bleached using the EASYWHITE system have a softer handle enabling less fabric softener to be required in subsequent finishing. There is less fibre damage and reduced pilling. It is clear from all these developments that pretreatment systems for cotton and polyester/cotton fabrics are moving into a transitional phase whereby bio-based pre-treatments are being introduced that could ultimately replace the harsher chemical pre-treatments using strongly alkaline conditions. The fabric weight loss with bio-based pre-treatment is lower and the cellulosic fibre degradation is less. In addition the milder temperature/pH conditions are more sustainable, requiring less rinsing and neutralisation with acid. The enzymes are also biodegradable in waste water treatment systems, and there are cost savings in terms of water, energy and water treatment costs. Further progress in enzyme technology may yet lead to a new generation of enzymes for more sustainable desizing, bio-scouring and biobleaching processes that enable even lower and milder treatment conditions to be used. ❑
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