How to buy a quality sofa – part 4: natural fibers

10 10 2012

Since the 1960s, the use of synthetic fibers has increased dramatically,  causing the natural fiber industry to lose much of its market share. In December 2006, the United Nations General Assembly declared 2009 the International Year of Natural Fibres (IYNF); a year-long initiative focused on raising global awareness about natural fibers with specific focus on increasing market demand to help ensure the long-term sustainability for farmers who rely heavily on their production.

                       International Forum for Cotton Promotion

Natural fibers  have a history of being considered the fibers that are easiest to live with, valued for their comfort, soft hand and versatility.  They also carry a certain cachet:  cashmere, silk taffeta and 100% pure Sea Island cotton convey different images than does 100% rayon,  pure polyester or even Ultrasuede, don’t they?  And natural fibers, being a bit of an artisan product, are highly prized especially in light of campaigns by various trade associations to brand fiber:    “the fabric of our lives” from Cotton, Inc. and merino wool with the pure wool label are two examples.                                                              

Preferences for natural fibers seem to be correlated with income; in one study, people with higher incomes preferred natural fibers by a greater percentage than did those in lower income brackets.   Cotton Incorporated funded a study that demonstrated that  66% of all women with household incomes over $75,000 prefer natural fibers to synthetic.

What are the reasons, according to the United Nations, that make natural fibers so important?  The UN website, Discover Natural Fibers lists the following reasons why natural fibers are a good choice.  Please remember that this list does not include organic natural fibers, which provide even more benefits (but that’s another post):

  1. Natural fibers are a healthy choice.
    1. Natural fiber textiles absorb perspiration and release it into the air, a process called “wicking” that creates natural ventilation. Because of their more compact molecular structure, synthetic fibers cannot capture air and “breathe” in the same way. That is why a cotton T-shirt is so comfortable to wear on a hot summer’s day, and why polyester and acrylic garments feel hot and clammy under the same conditions. (It also explains why sweat-suits used for weight reduction are made from 100% synthetic material.) The bends, or crimp, in wool fibers trap pockets of air which act as insulators against both cold and heat – Bedouins wear thin wool to keep them cool. Since wool can absorb liquids up to 35% of its own weight, woollen blankets efficiently absorb and disperse the cup of water lost through perspiration during sleep, leaving sheets dry and guaranteeing a much sounder slumber than synthetic blankets.
    2. The “breathability” of natural fiber textiles makes their wearers less prone to skin rashes, itching and allergies often caused by synthetics. Garments, sheets and pillowcases of organic cotton or silk are the best choice for children with sensitive skins or allergies, while hemp fabric has both a high rate of moisture dispersion and natural anti-bacterial properties.   Studies by Poland’s Institute of Natural Fibers have shown that 100% knitted linen is the most hygienic textile for bed sheets – in clinical tests, bedridden aged or ill patients did not develop bedsores. The institute is developing underwear knitted from flax which, it says, is significantly more hygienic than nylon and polyester. Chinese scientists also recommend hemp fiber for household textiles, saying it has a high capacity for absorption of toxic gases.
  2. Natural fibers are a responsible choice.
    1. Natural fibers production, processing and export are vital to the economies of many developing countries and the livelihoods of millions of small-scale farmers and low-wage workers. Today, many of those economies and livelihoods are under threat: the global financial crisis has reduced demand for natural fibers as processors, manufacturers and consumers suspend purchasing decisions or look to cheaper synthetic alternatives.
    2. Almost all natural fibers are produced by agriculture, and the major part is harvested in the developing world.
      1. For example, more than 60% of the world’s cotton is grown in China, India and Pakistan. In Asia, cotton is cultivated mainly by small farmers and the sale of cotton provides the primary source of income for some 100 million rural households.
      2. In India and Bangladesh, an estimated 4 million marginal farmers earn their living – and support 20 million dependents – from the cultivation of jute, used in sacks, carpets, rugs and curtains. Competition from synthetic fibers has eroded demand for jute over recent decades and, in the wake of recession, reduced orders from Europe and the Middle East could cut jute exports even further.
      3. Silk is another important industry in Asia. Raising silkworms generates income for some 700 000 farm households in India, while silk processing provide jobs for 20 000 weaving families in Thailand and about 1 million textile workers in China.
      4. Each year, developing countries produce around 500 000 tonnes of coconut fiber – or coir – mainly for export to developed countries for use in rope, nets, brushes, doormats, mattresses and insulation panels. In Sri Lanka, the single largest supplier of brown coir fiber to the world market, coir goods account for 6% of agricultural exports, while 500 000 people are employed in small-scale coir factories in southern India.
      5. Across the globe in Tanzania, government and private industry have been working to revive once-booming demand for sisal fiber, extracted from the sisal agave and used in twine, paper, bricks and reinforced plastic panels in automobiles. Sisal cultivation and processing in Tanzania directly employs 120 000 people and the sisal industry benefits an estimated 2.1 million people.
  3. Natural fibers are a sustainable choice.
    1. Natural fibers will play a key role in the emerging “green” economy based on energy efficiency, the use of renewable feed stocks in bio-based polymer products, industrial processes that reduce carbon emissions and recyclable materials that minimize waste.  Natural fibers are a renewable resource, par excellence – they have been renewed by nature and human ingenuity for millennia. During processing, they generate mainly organic wastes and leave residues that can be used to generate electricity or make ecological housing material. And, at the end of their life cycle, they are 100% biodegradable.
    2. An FAO study estimated that production of one ton of jute fiber requires just 10% of the energy used for the production of one ton of synthetic fibers (since jute is cultivated mainly by small-scale farmers in traditional farming systems, the main energy input is human labor, not fossil fuels).
    3. Processing of some natural fibers can lead to high levels of water pollutants, but they consist mostly of biodegradable compounds, in contrast to the persistent chemicals, including heavy metals, released in the effluent from synthetic fiber processing. More recent studies have shown that producing one ton of polypropylene – widely used in packaging, containers and cordage – emits into the atmosphere more than 3 ton of carbon dioxide, the main greenhouse gas responsible for global warming. In contrast, jute absorbs as much as 2.4 tonnes of carbon per tonne of dry fiber.
    4. The environmental benefits of natural fiber products accrue well beyond the production phase. For example, fibers such as hemp, flax and sisal are being used increasingly as reinforcing in place of glass fibers in thermoplastic panels in automobiles. Since the fibers are lighter in weight, they reduce fuel consumption and with it carbon dioxide emissions and air pollution.
    5. But where natural fibers really excel is in the disposal stage of their life cycle. Since they absorb water, natural fibers decay through the action of fungi and bacteria – this releases the fixed CO2 in the fibers and closes the cycle; it also improves soil structure.  Synthetics present society with a range of disposal problems. In land fills they release heavy metals and other additives into soil and groundwater. Recycling requires costly separation, while incineration produces pollutants and, in the case of high-density polyethylene, 3 tonnes of carbon dioxide emissions for every tonne of material burnt. Left in the environment, synthetic fibers contribute, for example, to the estimated 640 000 tonnes of abandoned fishing nets and gear in the world’s oceans.
  4. Natural fibers are a high-tech choice.
    1. Natural fibers have intrinsic properties – mechanical strength, low weight and low cost – that have made them particularly attractive to the automobile industry.
      1. In Europe, car makers are using mats made from abaca, flax and hemp in press-molded      thermoplastic panels for door liners, parcel shelves, seat backs, engine shields and headrests.
        1. For consumers, natural fiber composites in automobiles provide better thermal and acoustic insulation than fiberglass, and reduce irritation of the skin and respiratory system. The low density of plant fibers also reduces vehicle weight, which cuts fuel consumption.
        2. For car manufacturers, the moulding process consumes less energy than that of fibreglass and produces less wear and tear on machinery, cutting production costs by up to 30%. The use of natural fibres by Europe’s car industry is projected to reach 100 000 tonnes by 2010. German companies lead the way. Daimler-Chrysler has developed a flax-reinforced polyester composite, and in 2005 produced an award-winning spare wheel well cover that incorporated abaca yarn from the Philippines. Vehicles in some BMW series contain up to 24 kg of flax and sisal. Released in July 2008, the Lotus Eco Elise (pictured above) features body panels made with hemp, along with sisal carpets and seats upholstered with hemp fabric. Japan’s carmakers, too, are “going green”. In Indonesia, Toyota manufactures door trims made from kenaf and polypropylene, and Mazda is using a bioplastic made with kenaf for car interiors.
    1. Worldwide, the construction industry is moving to natural fibres for a range of products, including light structural walls, insulation materials, floor and wall coverings, and roofing. Among recent innovations are cement blocks reinforced with sisal fibre, now being manufactured in Tanzania and Brazil. In India, a growing shortage of timber for the construction industry has spurred development of composite board made from jute veneer and coir ply – studies show that coir’s high lignin content makes it both stronger and more resistant to rotting than teak. In Europe, hemp hurd and fibres are being used in cement and to make particle boards half the weight of wood-based boards. Geotextiles are another promising new outlet for natural fibre producers. Originally developed in the Netherlands for the construction of dykes, geotextile nets made from hard natural fibres strengthen earthworks and encourage the growth of plants and trees, which provide further reinforcement. Unlike plastic textiles used for the same purpose, natural fibre nets – particularly those made from coir – decay over time as the earthworks stabilize.
  1. Natural fibers are a fashionable choice.
    John Patrick Organic Fall/Winter 2010
    1. Natural fibers are at the heart of a fashion movement that goes by various names: sustainable, green, uncycled, ethical, eco-, even eco-environmental. It focuses fashion on concern for the environment, the well-being of fiber producers and consumers, and the conditions of workers in the textile industry. Young designers now offer “100% carbon neutral” collections that strive for sustainability at every stage of their garments’ life cycle – from production, processing and packaging to transportation, retailing and ultimate disposal. Preferred raw materials include age-old fibres such as flax and hemp, which can be grown without agrochemicals and produce garments that are durable, recyclable and biodegradable. Fashion collections also feature organic wool, produced by sheep that have not been exposed to pesticide dips, and “cruelty-free” wild silk, which is harvested – unlike most silk – after the moths have left their cocoons.
    2. The Global Organic Textile Standard (GOTS)   sets strict standards on chemicals permitted in processing, on waste water treatment, packaging material and technical quality parameters, on factory working conditions and on residue testing.
    3. Sustainable fashion intersects with the “fair trade” movement, which offers producers in developing countries higher prices for their natural fibres and promotes social and environmental standards in fibre processing. Fair trade fashion pioneers are working with organic cotton producers’ cooperatives in Mali, hand-weavers groups in Bangladesh and Nepal, and alpaca producers in Peru. A major UK chain store launched in 2007 a fair trade range of clothing that uses cotton “ethically sourced” from farmers in the Gujarat region of India. It has since sold almost 5 million garments and doubled sales in the first six months of 2008.
    4. Another dimension of sustainable fashion is concern for the working conditions of employees in textile and garment factories, which are often associated with long working hours, exposure to hazardous chemicals used in bleaching and dyeing, and the scourge of child labor. The  Global Organic Textile Standard (GOTS), widely accepted by manufacturers, retailers and brand dealers, includes a series of “minimum social criteria” for textile processing, including a prohibition on the use of child labor, workers’ freedom of association and right to collective bargaining, safe and hygienic working conditions, and “living wages”.
Advertisements




Silk

16 06 2010

Silk has set the standard in luxury fabrics for several millennia. Silk is highly valued because it possesses many excellent properties. Not only does it look lustrous and feel luxurious, but it is also lightweight, resilient, and extremely strong— the strongest natural fiber known to man, one filament of silk is stronger then a comparable filament of steel! Although fabric manufacturers have created less costly alternatives to silk, such as nylon and polyester, silk is still in a class by itself.

The origins of silk date back to ancient China. Legend has it that a Chinese princess was sipping tea in her garden when a cocoon fell into her cup, and the hot tea loosened the long strand of silk. Ancient literature, however, attributes the popularization of silk to the Chinese Empress Si-Ling, to around 2600 B.C. Called the Goddess of the Silkworm, Si-Ling apparently raised silkworms and designed a loom for making silk fabrics. Silk was originally reserved exclusively for the use of the emperor; gradually silk came into more general use.   Silk, indeed, rapidly became one of the principal elements of the Chinese economy. Silk was used for musical instruments, fishing-lines, bowstrings, bonds of all kinds, and even rag paper, the word’s first luxury paper. Eventually even the common people were able to wear garments of silk.

During the Han Dynasty, silk ceased to be a mere industrial material and became an absolute value in itself. Farmers paid their taxes in grain and silk. Silk began to be used for paying civil servants and rewarding subjects for outstanding services. Values were calculated in lengths of silk as they had been calculated in pounds of gold. Before long it was to become a currency used in trade with foreign countries.

For more than two thousand years the Chinese kept the secret of silk altogether to themselves. It was the most zealously guarded secret in history. Indeed, the reigning powers decreed death by torture to anyone who divulged the secret of the silk-worm. Eventually, the mystery of the silk-making process was smuggled into neighboring regions, reaching Japan about A.D. 300 and India around A.D. 400.

The first country to apply scientific techniques to raising silkworms was Japan, which produces some of the world’s finest silk fabrics. Other countries that also produce quality silks are China, Italy, India, Spain, and France. China was the largest exporter of raw silk in the early 1990s, accounting for about 85% of the world’s raw silk, worth about $800 million. Exports of China’s finished silk products were about half of the world’s total at about $3 billion.

Silk has a miniscule percentage of the global textile fibre market—less than 0.2%. This figure, however, is misleading, since the actual trading value of silk and silk products is much more impressive. This is a multibillion dollar trade, with a unit price for raw silk roughly twenty times that of raw cotton. (The precise global value is difficult to assess, since reliable data on finished silk products is lacking in most importing countries.)

“With time and patience the mulberry leaf becomes a silk gown”

Ancient Chinese Proverb.

The finest, most desirable silk comes from the mulberry silkworm, which is actually a caterpillar and not a worm. Blind and flightless, it feeds solely on the leaves of mulberry trees.  Known as the Bombyx mori, the mulberry silk worm is a fascinating but tragic bundle of insect life. Raised by professional keepers in China on trays of mulberry leaves a thousand years before the Roman Empire when wild tribes were roaming Europe living in stick and mud huts, the mulberry silkworm has been totally domesticated and can not live without humans for their care and feeding. There are no wild silkworms or Bombyx mori moths that roam and feed in the wild.

The cultivation of silkworms for the purpose of producing silk is called sericulture.  Over the centuries, sericulture has been developed and refined to a precise science. Today, a hugely developed industry has developed around the raising of silkworms for the production of silk. Silk worms are raised by large corporate silk worm farmers and hobbyists all over the world. Sericulture companies sell and ship all that the silk grower enthusiast needs from Bombyx mori ova (silkworm eggs) in an incubation dish to handling tools.

One acre of mulberry trees produces enough foliage to feed silkworms that create 178 pounds of cocoons which can be unraveled into 35 pounds of raw silk. The mulberry leaves are a renewable and sustainable crop as the trees produce year after year. One mature mulberry tree will produce enough foliage for 100 silkworms. Generally, one cocoon produces between 1,000 and 2,000 feet of silk filament, made essentially of two elements: a substance, called fibroin, makes up between 75 and 90% of the filament, and sericin, the gum secreted by the caterpillar to glue the fiber into a cocoon, comprises about 10-25%. Other elements include fats, salts, and wax. One silkworm produces very little useable silk.  To make one yard of silk material, about 3,000 cocoons are used.

The natural course in the cycle of worm to moth would be for the chrysalis to break through the protective cocoon and emerge as a moth. But by breaking its way out, it cuts this fiber off in many places, thus largely decreasing its value;  So, sericulturists must destroy the chrysalis so that it does not break the silk filament. This is done by stoving, or stifling, the chrysalis with heat.  The usual method is that of immersing the cocoons in steam for a few minutes. Another method, that of placing the cocoons in boiling water, serves a double purpose. Not only does it kill the chrysalides, but it also softens the seracin, the “gum”  that sticks the threads together, so that they can be unreeled from the cocoon.  Although silk is about 20% seracin, only about 1% is removed at this point.

Reeling the filament

  • Reeling may be achieved manually or automatically. The cocoon is brushed to locate the end of the fiber. The method is as simple as it is laborious.  It is threaded through a porcelain eyelet, and the fiber is reeled onto a wheel. Meanwhile, diligent operators check for flaws in the filaments as they are being reeled.
  • As each filament is nearly finished being reeled, a new fiber is twisted onto it, thereby forming one long, continuous thread. Sericin contributes to the adhesion of the fibers to each other. s. The average cocoon reels off about three hundred yards in a single thread.

Packaging the skeins

This is raw silk, just pure silk fibers without any chemicals or treatments added, although sometimes the raw silk fibers will be soaked in a 1% hydrogen peroxide solution for a few hours to refine the creamy color. Organic and sustainable certification organizations are working on standards for organic silk but they have not yet been finalized and adopted.

Degumming

The remaining sericin, or silk “gum”,  must be removed from the yarn by soaking it in warm soapy water.  This is called degumming, and it improves the sheen, color, hand and texture of the silk.  Because the gum can serve as a protective layer, it is usually left on the silk until it’s ready to dye.  But the degumming process,  which enables the silk to accept dyes readily and which contributes  to its high gloss,  also causes the silk to lose about 25% of its weight and not a little strength. If the scouring and bleaching are not well and carefully done, the reduction in strength may be serious indeed.

Finishing silk fabrics

  • After degumming, the silk yarn is a creamy white color. It may next be dyed as yarn, or after the yarn has been woven into fabric.   After dyeing, the skeins are again dried, run through an equalizing machine similar to a stretcher, and then rewound into the form in which they are wanted by consumers and the trade, such as spools, bobbins, skeins, etc.
  • This completes the process of silk throwing. The silk is now ready for the weaver, the knitter, the lace maker, or the embroidery maker.

After the raw silk has been reeled into skeins or hanks, the most laborious parts of silk production are completed; that is, most of the work done on the fiber thereafter is done by machine processes instead of by hand. The amount of hand labor that it takes to produce raw silk is almost incredible, and the amount of labor taken after the machine processes begin is no less than for other textiles. It has been said that it takes more human labor to produce a lady’s silk dress, from the mulberry leaves into the finished product ready for wear, than it takes to produce and build a locomotive out of the raw ores in the ground. More hours are expended, and more people have something to do with the work.  If the laborers employed in the production of silk were paid as high wages as are commonly paid in the iron and steel industry the silk dress would cost almost as much as that locomotive. As it is, raw silk production is carried on chiefly in countries where wages are very low. At the present prices of silk, the most efficient workmen doing their very best could not earn more than fifteen cents per day at this kind of work.

WEIGHTED SILK:

Silk is sold by weight.  “Weighting” is a textile manufacturing practice peculiar to silk manufacturing and involves the application of metallic salts to add body, luster and physical weight to silk fabric. The reason for adding metals to silk fabric is to increase the weight of the fabric and, because silk fabric sells by the pound, the extra weight increases the selling price of the fabric. Generally, only the finer and more expensive reeled silks are weighted rather than the less costly spun silks By means of weighting the manufacturer can increase the weight of silk by 3 to 4 times.

Weighting is done by immersing the silk  in a solution rich in tannin, then transferred to iron or tin baths, then washed.   Weighting causes the fabric to lose its strength as soon as the weighting is applied. Heavily weighted silk must be made into garments as soon as it is made. Spots develop in the dyes. Saltwater, perspiration and tears cause spots to be formed which seems as if the silk is eaten by acids. Sunlight also attacks weighted silk and can cause silk to fall to pieces.

The silk industry makes a distinction between pure-dye silk and  weighted silk. In the pure-dye process, the silk is colored with dye, and may be finished with water-soluble substances such as starch, glue, sugar, or gelatin.  But it is not weighted.    If weighting is not executed properly, it can decrease the longevity of the fabric by causing it to lose much of its strength and durability, so pure-dye silk is considered the superior product.  Also, the metallic salts used to weight silk can cause health risks and problems for some people.

After dyeing, silk fabric may be finished by additional processes, such as bleaching, embossing, steaming, or stiffening.

WILD SILKS:

The wild silks are gathered principally in Japan, China; and India. There are several varieties of wild silk cocoons, each with qualities somewhat different from the rest. The principal variety of Japan is the Yamai-mai, and the chief varieties of India are the tusser, or tussah, and the ailanthus. Most of these silks are much darker in color than the domesticated silk, the Bombyx mori, probably because of the difference in feed. Wild silkworms do not always have mulberry leaves to eat. Great numbers feed on oak leaves and in some cases on other plants.

In  general,  it may be said that wild silks are in most respects of poorer quality than domesticated silk. They are harder to bleach, and do not take dyes so well. They are generally very uneven in texture, but when made up into fabrics are often more durable than common silks. Wild silks are used principally in the manufacture of pile fabrics such as velvet, plush, and imitation sealskin, and in heavy or rough cloths such as pongees and shantungs. While the silkworms of the wild varieties take care of themselves, and therefore do not require the constant labor that must be given to domesticated silk, the expense of gathering is nevertheless high. The wild cocoons must be hunted, trees must be climbed to gather them, and much time may be consumed in collecting comparatively few. On the whole, however, because of the poorer qualities, wild silks are worth considerably less than “tame” silks.

CHARACTERISTICS OF SILK:

Silk, a protein fiber like wool, with a smooth hand, is very lustrous and retains its shape well. Silk can take on many different appearances. A raw silk fabric may fool you into thinking that it is cotton or synthetic. The more refined the silk and the smaller the yarn, the more it resembles the look and feel that we know as silky.

Silk is the strongest natural fiber and  is very strong in terms of tensile strength, meaning it can withstand a lot of pulling type pressure without breaking. This should not, however, be confused with wear ability or abrasion resistance. Silk will not stand up to the heavy wear that other fibers will.

Because of it’s good absorbency, fabrics made from silk are comfortable in summer and warm in winter.

Silk creases and wrinkles easily, especially when damp or wet. Some silk clothing manufacturers apply softeners, elastomers, and synthetic resins such as EPSIA – a silicone-containing epoxy crosslinking agent – to increase the dry and wet anti-wrinkling and crease-resistance performance of silk garments. With the family of silicone epoxy crosslinking agents (EPSIA, EPSIB and EPTA) this crease resistance occurs because chemical cross links occur between the silk fibroin strand and the epoxy groups. Research by Zaisheng Cai and Yiping Qiu in the Textile Research Journal (January 2003) reported “in conventional epoxide finishing of silk, organic solvents have to be used, which may be hazardous to the health of the exposed workers as well as the environment.”

Chemical treatments are also added to silk to improve anti-static, water and oil repellency, flame retardant, dimensional stability and other wash-and-wear properties that our easy-care culture seems to expect. Textile chemicals have become an integral and important component of conventional textile and clothing manufacturing. Textile chemicals, also know as textile auxiliaries, have two primary purposes: to increase the efficiency and lower the costs of conventional textile manufacturing; and to create special finishing effects and properties for the clothing.

Silk fabrics have  poor resistance to sunlight and UV exposure and must be protected from the sun. Draperies should be lined and even interlining may be desirable. Colors can fade by oxidation, called “gas fading”, if unaired in storage for a period of time. Impurities in the air may cause as much fading as the direct rays of the sun. Avoid storing silk fabric in a basement or attic near a furnace. Furnaces not only give off fumes but also pull fumes and impurities from other parts of the home.  Silk will become brittle with age and exposure to sunlight.

The silk fibroin from the silkworm is an ideal biomaterial (biocompatibility, biodegradation, non-toxicity, absorption properties, etc.) and has been widely used for sutures and other medical applications.