Wool

9 06 2010

When we talk about wool, we almost always mean the fiber from sheep, although the term “wool” can be applied to the hair of other mammals including cashmere and mohair from goats, vicuna, alpaca and camel from animals in the camel family and angora from rabbits.

As with many discoveries of early man, anthropologists believe the use of wool came out of the challenge to survive – Neolithic man used pelts from animals to keep warm.

Sheep (Ovis aries) were first domesticated 10 000 years ago.  The British sought to protect their own wool industry during the eighteenth century, and passed laws requiring native English wool be used – for example, judges, professors, and students were required to  wear robes made of English wool. Another law required that the dead be buried in native wool. When the American colonies began to compete with the motherland, the English passed a series of laws in an attempt to protect their “golden fleece.” One law even threatened the amputation of the hand of any colonist caught trying to improve the blood line of American sheep.

Today, wool is a global industry, with Australia, Argentina, the United States, and New Zealand serving as the major suppliers of raw wool – but wool is produced worldwide in about 100 countries on half a million farms.   Wool producers range from small farmers to large scale grazing operations.  While the United States is the largest consumer of wool fabric, Australia is the leading supplier. Australian wool accounts for approximately one-fourth of the world’s production.

The annual global output is now estimated at 2.2 billion pounds, yet wool represents less than 5 percent of the world consumption of fibers. Wool is an expensive fiber to produce and process.  Though cotton is the number one plant used for fabrics and the number one natural fiber overall, the number one source for animal fiber is still wool.

Two terms one often sees are Merino and worsted.  The main difference between them is that Merino pertains to the type of fiber while worsted pertains to the process the fibers go through:

Merino is a term used in the textile industry which has varied meanings:  originally it meant wool made from a specific breed of sheep:  the Merino.  Merino sheep are regarded as having some of the finest and softest wool of any sheep: it is finely crimped and soft, fibers are commonly 65 – 100 mm (2.5 – 4 inches) long and generally less than 24 microns in diameter.

But now the term has broader use and may pertain to an article which just contains some percentage of wool from Merino sheep – or even just a fine wool and cotton yarn!  The Australian Wool Testing Authority Ltd is trying to institute a definition for Merino wool, citing fiber diameter and comfort factors.

The essential feature of a worsted yarn is its long, straight fibers which lie parallel to each other, the result of having been both carded AND combed.

So yes, you can have Merino worsted wools!

THE FIBER:

In scientific terms, wool is considered to be a protein called keratin. Its length usually ranges from 1.5 to 15 inches (3.8 to 38 centimeters) depending on the breed of sheep. Fiber diameter ranges from 16 microns in superfine merino wool (similar to cashmere) to more than 40 microns in coarse hairy wools.  Wool has several qualities that distinguish it from hair or fur: it is crimped (meaning it has waves),  it has a different texture or handle, it is  elastic, and it grows in staples (clusters).

Each wool fiber is made up of three essential components: the cuticle, the cortex, and the medulla.

  • The cuticle is the outer layer. It is a protective layer of scales arranged like shingles or fish scales.   They are sometimes described as little “barbs” because it’s the points of the scales that give wool the reputation for being prickly.
    • When two fibers come in contact with each other, these scales tend to cling and stick to each other. It’s this physical clinging and sticking that allows wool fibers to be spun into thread so easily.  And it’s also what causes the fiber to interlock – or felt.   See below for more information on this.

    Scales on a wool fiber under electron microscope

  • The cortex is the inner structure made up of millions of cigar-shaped cortical cells. The arrangement of these cells is responsible for the natural crimp unique to wool fiber.  The amount of crimp corresponds to the fineness of the wool fibers.  A fine wool like Merino may have up to 100 crimps per inch, while the coarser wools may have as few as 1 to 2. Hair, by contrast, has little if any scales and no crimp, and little ability to bind into yarn.  Its wool’s scaling and crimp that make it easier to spin into yarn, because the individual fibers attach to each other, so they stay together.
  • Rarely found in fine wools, the medulla comprises a series of cells (similar to honeycombs) that provide air spaces, giving wool its thermal insulation value.

The Manufacturing Process

The major steps necessary to process wool from the sheep into yarns are:  shearing, cleaning and scouring, grading and sorting, carding.

SHEARING:

Sheep are usually sheared once a year—usually in the springtime. The fleece recovered from a sheep can weigh between 6 and 18 pounds (2.7 and 8.1 kilograms); as much as possible, the fleece is kept in one piece. While most sheep are still sheared by hand, new technologies have been developed that use computers and sensitive, robot-controlled arms to do the clipping.

GRADING AND SORTING:

Grading is the breaking up of the fleece based on overall quality. Wool fibers are judged not only on the basis of their strength but also by their fineness (diameter), length, crimp (waviness) and color.  In wool grading, high quality does not always mean high durability.

In sorting, the wool is broken up into sections of different quality fibers, from different parts of the body. The best quality of wool comes from the shoulders and sides of the sheep and is used for clothing; the lesser quality comes from the lower legs and is used to make rugs.

CLEANING AND SCOURING:

Scouring in the true sense of the word in the textile industry means simply removing any foreign material from the fabric; the term scour grew up around the washing of cottons and linens.

Wool taken directly from the sheep is called “raw” or “greasy”  wool.  It contains a substantial amount of natural contaminants, such as  sand, dirt, grease, and dried sweat (called suint) as well as pesticide residues from the treatment of sheep to prevent disease; the weight of contaminants accounts for about 30 to 70%  of the total weight of the fleece.

To clean the wool, the fiber is washed in a series of alkaline baths containing water, soap, and soda ash or a similar alkali. The scouring effluent contains these impurities, which has high levels of COD (chemical oxygen demand) and BOD (biochemical oxygen demand), suspended solids, organic matter and sheep dip chemicals.  These levels represent a significant pollution load:   the organic effluent from a typical wool-scouring plant is approximately equal to the sewage from a town of 50,000 people.[1]

The effluent is separated into three categories:

  1. grease – when refined, this is known as lanolin, which is saved and sold for a variety of consumer products.
  2. liquor (water) – discharged to sewage works or open waters
  3. sludge – this needs to be disposed of too:   The sludge contains high levels of organic materials such as the potentially toxic sheep dip pesticides (such as organochlorines, organophosphates and synthetic prethroids).   In the EU, landfills will now only accept non-recoverable and inert waste.  Since the global production of wool sludge is over 930,000 tons, research is being done on the feasibility of disposing of scouring waste by composting, incineration and other methods.

The processing stages to this point cause the natural fiber alignment of the scales (or “barbs” as mentioned above) to be completely disrupted; the scales no longer line up “tip to base” as they would in the fleece. Those scales make raw wool itchy and also cause the fiber to shrink when wet.

In order to prevent this shrinkage (also called felting), and to make the wool more comfortable when worn next to the skin, many producers use chlorine to “burn” off the scales…this doesn’t entirely remove them, but it does lessen their profile, and then the fibers are coated with a synthetic polymer resin, which essentially glues down the scales. This allows the wool to be machine washed without felting, and gets rid of the shrinkage of the fabric associated with felting.  This is the chemistry behind Superwash wool.  The tradeoff, of course, is that this chlorination process is highly toxic.

See our blog post on Organic Wool to read about the environmental effects of wool scouring and chlorination.  It’s not pretty.

CARDING:

Next, the fibers are passed through a series of metal teeth.  The teeth untangle the fibers and arrange them into a flat sheet called a web. The web is then formed into narrow ropes known as silvers.   Carding  is one of the processes that untangles the wool fibers and lays them straight; it also removes residual dirt and other matter left in the fibers.  Combing is the next process, which removes shorter length fibers and helps to further straighten the fibers and lay them parallel.  Combing also helps to clean more debris from the fibers.

  • Carding only produces woolenyarn.   Woolen yarns:
    • Have a short staple (1-4 inch long fibers).
    • Are carded ONLY
    • Have a slack twist
    • Are weaker, softer and bulkier than worsted
  • Carding and Combing produces worsted yarn.Worsted yarns:
    • Have a long staple (4 inch and longer)
    • Have a tight twist in spinning
    • Are stronger, finer, smoother and harder than woolen yarns.

CHARACTERISTICS of WOOL:

Wool is highly regarded as one of the most lavish natural fibers in the world.  Lightweight, versatile, resistant to dirt and considered somewhat water repellant, non wrinkling, and durable, wool:

  • Can absorb almost 30% of its own weight in water – and it can also release it.  This makes it breathable and extremely comfortable next to the skin.  It can absorb sweat and release it as vapor, keeping you cool and dry.  It prevents the clammy, cold feeling you may experience when wearing some types of synthetic clothing and sweating.
  • Is resistant to static electricity,  because the moisture retained within the fabric conducts electricity. This is why wool garments are much less likely to spark or cling to the body. The use of wool car seat covers or carpets reduces the risk of a shock when a person touches a grounded object.
  • fabrics have a greater bulk than other textiles because of the crimp, and retain air, which is a great insulation.  It keeps you warm when you’re cold, but insulation also works both ways – Bedouins and Tuaregs use wool clothes to keep the heat out.  And it does not cling to the skin, allowing for air circulation next to the skin.
  • fibers can be bent 20,000 times without breaking (compared to cotton, which breaks after 3,000 bends or rayon, which can be bent only 75 times without breaking), and have the power to elongate (it can be stretched 25 – 30% before breaking), stretch and recover. This natural elasticity and memory  returns to its natural shape
  • doesn’t readily catch fire – its ignition point is higher than cotton and some synthetics.  Even if it does burn, it burns slowly (not melting or dripping as in synthetics) and self-extinguishes when the source of the flame is removed.  It contributes less to toxic gases and smoke than synthetics, and is therefore often specified for high safety environments such as trains and aircraft.
  • has a naturally high UV protection, which is much higher than most synthetics and cotton.
  • is considered by the medical profession to be hypoallergenic.
  • is hydrophilic—it has a strong affinity for water—and therefore is easily dyed.

[1] Christoe, Jock; The treatment of wool scouring effluents in Australia, China and India”,  project # AS1/1997/069; http://aciar.gov.au/system/files/node/9074/AS%2003-04%20AS1-1997-069.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








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