Enzymes in textile processing

2 12 2011

Humankind has used enzymes for thousands of years to carry out important chemical reactions for making products such as cheese, beer, and wine. Bread and yogurt also owe their flavor and texture to a range of enzyme producing organisms that were domesticated many years ago.

In the textile industry, one of the first areas which enzyme research opened up was the field of desizing of textiles.  A size is a substance that coats and strengthens the fibers to prevent damage during the weaving process. Size is usually applied to the warp yarn, since this is particularly prone to mechanical strain during weaving.   The size must be removed before a fabric can be bleached and dyed, since it affects the uniformity of wet processing. Previously, in order to remove the size, textiles were treated with acid, alkali or oxidising agents, or soaked in water for several days so that naturally occurring microorganisms could break down the starch. However, both of these methods were difficult to control and sometimes damaged or discoloured the material. But by using enzymes, which are specific for starch, the size can be removed without damaging the fibers.

Enzymes used in textile processing - photo from Novozymes

It represented great progress, therefore, when crude enzyme extracts in the form of malt extract, or later, in the form of pancreas extract, were first used to carry out desizing.  Bacterial amylase derived from Bacillus subtilis  was used for desizing  as early as 1917. Amylase is a hydrolytic enzyme which catalyses the breakdown of dietary starch to short chain sugars, dextrose  and maltose.

Enzymes have been used increasingly in the textile industry since the late 1980s. Many of the enzymes developed in the last 20 years are able to replace chemicals used by mills. The first major breakthrough was when enzymes were introduced for stonewashing jeans in 1987 – because more than one billion pairs of denim jeans require some sort of pre-wash treatment every year. Within a few years, the majority of denim finishing laundries had switched from pumice stones to enzymes.

Today, enzymes are used to  treat and modify fibers, particularly during textile processing and in caring for textiles afterwards.  They are used to enhance the preparation of cotton for weaving, reduce impurities, minimize “pulls” in fabric, or as pre-treatment before dying to reduce rinsing time and improve color quality.  New processing applications have been developed for:

  • Scouring (the process of removing natural waxes, pectins, fats and other impurities from the surface of fibers), which gives a fabric a high and even wet ability so that it can be bleached and dyed successfully. Today, highly alkaline chemicals (such as caustic soda) are used for scouring. These chemicals not only remove the non-cellulosic impurities from the cotton, but also attack the cellulose leading to heavy strength loss and weight loss in the fabric. Furthermore, using these hazardous chemicals result in high COD (chemical oxygen demand) and BOD (biological oxygen demand)  in the waste water. Recently a new enzymatic scouring process known as ‘Bio-Scouring’ is being used in textile wet-processing with which all non-cellulosic components from native cotton are completely or partially removed. After this Bio-Scouring process, the cotton has an intact cellulose structure, with lower weight loss and strength loss. The fabric gives better wetting and penetration properties, making the subsequent bleach process easy and  giving much better dye uptake.
    • One of the newest products, PrimaGreen® EcoScour from Genencor, offers sustainability advantages for eco-scouring in cotton pretreatment, including 30 percent water savings and 60 percent energy savings compared to standard processing. In addition, the mild processing conditions result in improved fabric quality and enhanced color brightness after dyeing.
  • Bleaching – When bleaching cotton, a lot of chemicals, energy and water are part of the process. The company Huntsman has developed a wetter/stabilizer that maximizes the wetting and detergency of the bleaching process and a one-bath caustic neutralizer and peroxide remover in order to shorten the bleaching cycle, reduce energy and water required and deliver more consistent bleaching results. They have developed surfactants that are environmentally friendly (in that they do not contain Alkylphenol ethoxylates), and the system is both Oeko-Tex and GOTS approved.  After fabric or yarn bleaching, residues of hydrogen peroxide are left in the bath, and need to be completely removed prior to the dyeingprocess, using a step called bleach cleanup.  The traditional method is to neutralize the bleach with a reducing agent, but the dose has to be controlled precisely. Incomplete peroxide removal results in poor dyeing with distinct change of color shade and intensity, as well as patchy, inconsistent dye distribution. Enzymes used for bleach clean-up ensure that residual hydrogen peroxide from the bleaching process is removed efficiently – a small dose of catalase breaks hydrogen peroxide into water and oxygen.  This results in cleaner waste water and reduced water consumption.
    • In 2010, a life-cycle assessment was completed comparing PrimaGreen enzymatic bleaching to conventional textile bleaching methods. According to this LCA, if the enzymatic system were to see wide scale global adoption, the potential savings in freshwater consumption could be up to 10 trillion liters of water annually, and greenhouse gas reductions could range from 10-30 million metric tons. (1)
  • Biofinishing or biopolishing (removing fiber fuzz and pills from fabric surface) –  enzymatic biofinishing yields a cleaner surface, softer handfeel, reduces pilling and increases luster;
  • Denim finishing – In the traditional stonewashing process, the blue denim was faded by the abrasive action of pumice stones on the garment surface. Nowadays, denim finishers are using a special cellulase.  Cellulase works by loosening the indigo dye on the denim in a process known as ‘Bio-Stonewashing’. A small dose of enzyme can replace several kilograms of pumice stones. The use of less pumice stones results in less damage to garment, machine and less pumice dust in the laundry environment; in addition, it’s possible to fade denim without risk of damaging the garment.
  • European scientists have just announced a new and environmentally friendly way to produce textile dyes using enzymes from fungi. (2)

Because of the properties of enzymes, they make the textile manufacturing process much more  environmentally benign. (3)   Generally, they:

  1. operate under milder conditions (temperature and pH) than conventional process chemicals – this results in lower energy costs ( up to 120 kg CO2 savings per ton of textile produced) (4) ;
  2. save water – reduction of water usage up to 19,000 liters per ton of textiles bleached;
  3. are an alternative for toxic chemicals, making wastewater easier and cheaper to treat.
  4.  are easy to control;  do not attack the fiber structure with resulting loss of weight, resulting in better quality of material;
  5. better and more uniform affinity for dyes;
  6. contribute to safer working conditions through elimination of chemical treatments during production processes;
  7. are fully biodegradable.

So why is there a ruckus about enzymes being used in textile processing by GOTS and other organic certifying agencies?

(1)   http://primagreen.genencor.com/sustainability/lca_results/

(2)   http://www.just-style.com/news/eco-friendly-textile-dyes-use-enzymes-from-fungi_id112195.aspx

(3)   http://www.textiletodaybd.com/index.php?pid=magazine&id=52

(4)  http://www.europabio.org/sites/default/files/pages/lutz-walter-benefits-from-white-biotechnology-applications-in-the-european-textile-and-clothing-industry.pdf

What does organic wool mean?

11 08 2009

Last week we talked about the importance of livestock management in the battle against climate change.  It came as a real revelation to this city girl that large grazing animals are a vital and necessary part of the solution to climate change.   Sheep can actually help to improve soils, which improves the soil’s ability to absorb water and maintain its original nutrient balance – and most importantly, by increasing the organic matter in the soil, it makes the soil a highly effective carbon bank.

many sheep

So the management of the livestock can be beneficial – but it’s a long way from a sheep in the pasture to a wool fabric.  So let’s look at the wool produced by these sheep and examine  what “organic wool” means.

In order for wool to be certified organic in the U.S., it must be produced in accordance with federal standards for organic livestock production, which are:

  • Feed and forage used for the sheep from the last third of gestation must be certified organic.
  • Synthetic hormones and genetic engineering of the sheep is prohibited.
  • Use of synthetic pesticides on pastureland is prohibited and the sheep cannot be treated with parasiticides, which can be toxic to both the sheep and the people exposed to them.
  • Good cultural and management practices of livestock must be used.

A key point to remember about the USDA and OTA organic wool designations:  the organic certification extends only to livestock – it doesn’t  cover the  further processing of the raw wool. Should that be a concern?

Wool as shorn from the sheep is known as greasy (or raw) wool. Before it is suitable for further processing it must be washed to remove dirt, water soluble contaminants (called suint), and woolgrease – and there are a lot of these contaminants.  On average, each ton of greasy wool contains:

  • 150 KG woolgrease (when refined this is known as lanolin)
  • 40 KG suint
  • 150 KG dirt
  • 20 KG vegetable matter
  • 640 KG wool fiber

This process of washing the wool is known as scouring.  Scouring uses lots of water and  energy :

  • water for washing:  The traditional method of wool scouring uses large amounts of water to wash the wool – the wool is passed through a series of 4 – 8 wash tanks (bowls), each followed by a squeeze to remove excess water.   Typical scouring plants can consume up to half a million litres of water per day.
  • pollution: The scouring water uses detergents and other chemicals in order to remove contaminants in the greasy wool,  which creates the problem of disposing of the waste water without contaminating the environment.  In unmodified plants, a single scouring line produces a pollution load equivalent to the pollution produced by 30,000 people.[1]
  • energy: to power the scouring line.

wool scour diagram

What about the chemicals used?

Detergents used in wool scouring include alkylphenol ethoxylates (APEOs) or fatty alcohol ethoxylates (more benign); sodium carbonate (soda ash), sodium chloride and sodium sulphate.  APEOs are among those chemicals known as endocrine disruptors – they interfere with the body’s endocrine system   They’re known to be very toxic for aquatic life – they cause feminization of male fish, for example.  (Click here to see what happened to alligators in Florida’s Lake Apopka as a result of endocrine disruptors traced to effluents from a textile mill. )  More importantly they break down in the environment into other substances which are much more potent than the parent compound.  They’re banned in Europe.

The surface of wool fibers are covered by small barbed scales. These are the reason that untreated wool itches when worn next to skin.  So the next step is to remove the scales, which also shrinkproofs the wool.  Shrinking/descaling is done using a chlorine pretreatment sometimes combined with  a thin polymer coating.  (Fleece is soaked in tertiary amyl or butyl hypochlorite in solution and heated to 104° for one hour.   The wool absorbs 1.5% of the chlorine. [2] )   These treatments make wool fibers smooth and allow them to slide against each other without interlocking. This also makes the wool feel comfortable and not itchy.

Unfortunately, this process results in wastewater with unacceptably high levels of adsorbable organohalogens (AOX) – toxins created when chlorine reacts with available carbon-based compounds. Dioxins, a group of AOX, are one of the most toxic known substances. They can be deadly to humans at levels below 1 part per trillion. Because the wastewater from the wool chlorination process contains chemicals of environmental concern, it is not accepted by water treatment facilities in the United States. Therefore all chlorinated wool is processed in other countries, then imported.[3] (For more about chlorine, go to the nonprofit research group Environmental Working Groups report about chlorine, http://www.ewg.org/reports/considerthesource.)  There are new chlorine free shrink/descaling processes coming on the market, but they’re still rare.

Finally, there is the weaving of the yarn into fabric – and all the environmental problems associated with conventional weaving and finishing.  In addition to the environmental concerns associated with conventional weaving, dyeing, and finishing (see some of our earlier blog posts), wool is often treated for moth and beetle protection, using pyrethroids, chlorinated sulphonamide derivatives, biphenyl ether or urea derivatives, which cause neutrotoxic effects in humans.

In the last 10 years, the textile industry,  along with animal ethics groups like People for the Ethical Treatment of Animals,  have lobbied against the wool industry, taking a stand against unethical treatment of sheep. In 2004, U.S. retailer Abercrombie and Fitch became the first to sign on to an animal rights campaign boycott of Australian wool that stood firmly against the typical practices of mulesing (where folds of skin around the sheep’s anus are cut off with shears during the wool shearing) and live export of sheep to halal butchers when their wool production becomes minimal.  Other companies such as H&M,  Marks & Spencer,  Nike, Gap,  Timberland, and Adidas (among others) have since joined, sourcing wool from South Africa or South America (where mulesing is not done).  The result of this outcry has led to the increased production of both organic and ethical wool, though it is still relatively minor when compared to the overall global wool production.

To complicate things a bit more, each country maintains their own standards for “organic wool” – Australia, for instance, has no equivalence or agreement with US organic standards.  The International Wool Textile Organization (IWTO) has adopted a new organic wool standard (closely aligned with GOTS) which they hope will be accepted by its members.  In addition, many companies use the term “eco wool”, which means the wool is sheared from free range roaming sheep that have not been subjected to toxic flea dipping, and the fleece was not treated with chemicals, dyes or bleaches – but this is wide open to interpretation and exploitation.  According to the IWTO, “Eco wool” must meet the standards set by the EU Eco-label.

Wool is a fabulous fiber – in addition to its many other attributes, it smolders rather than burns, and tends to be self-extinguishing.  (Read what The Commonwealth Scientific and Industrial Research Organisation (CISRO), Australia’s national science agency,  has to say about the flame resistance of wool by clicking here:   http://www.csiro.au/files/files/p9z9.pdf )  So if you can find organic wool  – making sure, of course, that the term “organic” covers:

  • management of the livestock according to organic or holistic management principles
  • processing of the raw wool,  using newer, more benign processes rather than harmful scouring and descaling chemicals; and wastewater  treatment from scouring and processing
  • weaving according to Global Organic Textile Standards (GOTS).  Read more about GOTS here.

…then go for it!  Nothing is quite like it in terms of comfort, resilience, versatility and durability.

But first you have to find it.  And that means you’ll have to ask lots of questions because there are lots of certifications to hide behind.

[1]The Cleanier Production Case Studies Directory EnviroNET Australia, Environment Protection Group, November 1998

[2] “Textiles: Shrink-proof wool”, Time, October 17, 1938

[3] “Fabric: Chlorine Free Wool”,  Patagonia website, http://www.patagonia.com/web/us/patagonia.go?slc=en_US&sct=US&assetid=8516