Silk is a protein fibre produced by silkworms. As a silkworm develops into an adult it feeds on leaves and then spins a cocoon from one continuous silk strand or filament, approximately 914 meters yards long. Inside the cocoon the worm changes into a chrysalis, then into a moth, which then seeks to leave the chrysalis.1 The moth achieves an escape path by secreting a liquid, which dissolves a hole in the cocoon through which the moth can then escape.[2] Heat is used to soften the hardened filaments so they can be unwound. Single filaments are then combined with a slight twist into one strand, a process known as filature or "silk reeling."
Benefits
Silk is a renewable natural resource and biodegradable in 100% form. Since the silk filament is a continuous thread it has great tensile strength. In woven fabrics, silk’s triangular structure acts as a prism that refracts light, giving silk cloth its highly prized "natural shimmer."[2] Silk has good absorbency, low conductivity and dyes easily.[2] Being a natural fibre, silk is readily biodegradable after its useful life, though absolute biodegradability depends on the dyes and trims used, and route of disposal. The silkworms used for wild or “tussah,” or “tasar” feed on leaves, not necessarily mulberry, and does not harm the chrysalis. Tussah silk is derived from cocoons collected after the moth has emerged naturally in the field. Because the continuous silk fibre is broken into smaller pieces as the moth leaves the cocoon, wild silk has a rougher and slubbier surface than cultivated silk.[3] Sericulture (silk farming) is labor-intensive. About 1 million workers are employed in the silk sector in China. Sericulture provides income for 700,000 households in India, and 20,000 weaving families in Thailand. Wild silk can provide a year round income for tribal people in India and some areas of China.[4]
Potential impacts
Animal welfare
On domesticated silk farms the chrysalis is killed to prevent the moth from making a hole in the cocoon. The reason for this is that the hole breaks the highly prized long silk filament into thousands of short lengths, which are useless for higher quality spinning.
Processing
Cocoons are soaked in sodium carbonate to soften in preparation for reeling (unwinding the filament from the cocoon). Silk fabric is then woven with the natural gum or sericin still on the yarn, acting as a natural sizing agent. After weaving, the gum is removed by boiling the fabric in alkali. This can result in a 20% reduction of the harvested weight of the silk. Some of this lost weight is added back by saturating the silk fabric in a bath of tin-phosphate-silicate salts. These processes can create a high biological load on the water, and deplete available oxygen for aquatic species if left untreated. Exposure to tin through breathing and skin contact can have acute and long-term effects on worker health if proper equipment is not used.[6]
Lightweight silk fabrics (fine gauge silk) are prone to wear and are degraded by exposure to sunlight and hot temperatures. They can also be susceptible to abrasion and twisting in laundering.[7]
Dyeing
The dyeing processes for silk involve standard industry chemicals and water use. Certain types of dyes are suspected carcinogens and mutagens, and untreated dye water can negatively impact receiving water bodies and harm aquatic ecosystems if left untreated before its release.
Consumer care/washing
Due to the delicacy of the fabric, silk products are typically handwashed or dry-cleaned. Washing and caring for any product can cause significant environmental impacts due to chemicals used in cleaning products. Certain chemicals used in dry-cleaning and at-home products have been reported to have detrimental affects on humans and the environment, contribute to ozone depletion and can pollute wastewater.
Silk tends to crush and wrinkle easily. This wrinkling creates a need to increase the frequency of ironing. This can use significant amounts of electrical energy over the long term.
End of use
Although 100% silk fibre is biodegradable, the amount of time it could take for a silk product to decompose naturally and in a short period of time is dependent upon a number of conditions—including how much air, temperature and sunlight the fibre is exposed to. If the waste is buried in a landfill, it can take even longer for it to break down.[8]
Optimize sustainability benefits
| OPPORTUNITY | BENEFITS | CONSIDERATIONS |
|---|---|---|
| Promote the use of wild or “Tussah” silk. | • Wild silk doesn’t require the chrysalis to be killed. • Wild silk provides a year round income for tribal people in India and some areas of China.[4] |
• Due to the shorter (less prized) fibre length, wild/Tussah silk is less expensive than domesticated silk. • Tussah silk fabrics have a coarser texture and are typically stiffer and heavier than domesticated silk. Wild/Tussah silk is available in small quantities. |
| Promote the use of Ahimsa silk.[9] | • Cultivated in India and doesn’t require the chrysalis to be killed. • The fibres are spun into “slubby threads” instead of reeled. • The quality of Ahimsa silk is softer and finer in comparison to regular silk and has a pearl matte natural finish. |
• More costly than regular silk due to its laborious process of spinning the many pieces of yarn into one continuous thread. • Not all slubby silks are Ahimsa silk. • Manufacturers often label these slubby silks as Dupioni or shantung, and claim they are Ahimsa silk. This should be substantiated with documentation. |
| Promote the use of Organic silk. | • Since pesticides are rarely used on silk fibre production (this would kill the silk worm), the main benefit of organic certification is using organically cultivated mulberry bushes. • Organic cultivation has wide ranging benefits for the surrounding ecosystem. |
• Organic silk is available in small quantities and carries a price premium. • Certification of organic silk must be in place by an internationally recognized certification agency accredited by International Federation of Agriculture Movements (IFOAM). |
| Promote the use of Fairtrade silk. | Ensures the proper treatment of workers. | Fairtrade silk products are less available then conventional silk. Does not necessarily mean “organic.” |
| Blend silk with organic cotton, organic wool, organic linen, etc. | • Brings a “luxury” element to the product and commands a higher retail price. • Blending with a washable fibre reduces the impact of consumer care/dry-cleaning |
Availability
China produces about 70% of the world's silk, followed by Brazil, India, Thailand and Vietnam, with minor production in Turkmenistan and Uzbekistan. India, Italy and Japan are the main importers of raw silk for processing.[2] Organic silk is available in small quantities at premium prices. Certification of organic silk must be in place by an internationally recognized certification agency accredited by IFOAM. Most wild silk is cultivated in China, India and Japan.[3] Verification of the source of the wild silk must be provided. Ahimsa silk is cultivated in India.
End use
Silk's natural beauty and other properties—such as comfort in warm weather and warmth during colder months— have made it sought after for use in high-fashion clothes, lingerie and underwear.[2] Due to its coarseness, wild silk is largely used in furnishings and interiors.3
Marketing opportunities
fairtrade/artisan wild silk When developed through a nonprofit organization and source is verified.
wild silk With verification of source in place.
ahimsa silk With verification of source in place.
renewable natural resource
biodegradable All fibres, yarns, trims and dyes used to manufacture the product or garment must also be biodegradable, or disassembled before disposal. This should be substantiated with documentation that the product can completely break down into non-toxic material by being processed in a facility where compost is accepted. Secondary label or marketing material should be provided to instruct customer.
organic If organic silk is used.
alternative dyes If used.
handwash in cold water or spot clean instead of dry-clean Can save significant amounts of electrical energy over time.
Innovation opportunities
1. Encourage handwashing or spot cleaning on the hangtag and labeling/POS to influence the consumer to take an active role in reducing environmental impacts of silk garment care.
2. Wild silk is an important peasant industry in India, and areas of China. An artisan project would bring an additional
social/fairtrade element to a sustainable fabric program.
3. Blending with another fibre that is washable, such as cotton, reduces the impact of consumer care/dry-cleaning.
4. Design garments that utlilize the natural wrinkling of silk as a design feature to influence the customer to reduce ironing of the final product and the energy it uses.
5. Create a silk garment that is 100% biodegradable: the product is either undyed or natural-dyed, with biodegradable trims and thread, and is equipped with secondary label or marketing material that instructs the customer on how to dispose.
Sources
- http://www.textileexchange.org/node/1096
- http://www.naturalfibres2009.org/en/fibres/silk.html
- http://www.thehindubusinessline.com/industry-and-economy/agri-biz/govt-may-use-wastelands-for-tasar-silk-cultivation/ article4479274.ece
- Slater, K. (2003), Environmental impact of textiles: production, processes and protection. Cambridge: Woodhead Publishing, p27
- Slater, K. (2003), Environmental impact of textiles: production, processes and protection. Cambridge: Woodhead Publishing, p27
- http://www.lenntech.com/periodic/elements/sn.htm
- http://www.treehugger.com/culture/qa-is-silk-green.html
- http://www.greenlivingtips.com/articles/waste-decomposition-rates.html
- http://hwww.theethicalsilkco.com/eco-friendly-silk/
Other:
http://www.bacsa-silk.org/en/the-prospects-of-the-european-sericulture-within-the-frame-of-the-eu-common-agricultural-policy/
ec.europa.eu/agriculture/quality/schemes/index_en.htm
http://www.cdfd.org.in/wildsilkbase/info_moths.php
greenopedia.com/article/cruelty-free-silk-fact-or-fiction
Silk is a small but exclusive protein fiber where one have the make distinguishes between cultivated silk (Silk) and wild silk (tussah silk). Silk consists of a double filament that is incorporated with a low molecular weight protein called sericin. This, together with naturally occurring oils and organic impurities, is removed in hot water at the unwinding of the cocoon. Sericin, which represents 20-25% of raw silk is allergenic, which has caused problems in the use of silk waste as cushioning material. China is currently the largest silk grower.
Environmental aspects
Waste water from boiling silk contains a high concentration of nitrogen, organic compounds that may have bad environmental impacts. Silk was earlier sold by weight instead of per unit area and it was allowed to increase the weight by impregnation with metal salts. This " allowed cheating " still occur. The process is very energy and water consuming and provides a high concentration of metal salts in the waste water. There are several reported cases of allergies to silk, although these have been traced to the remnants of sericin in the finished product. There is Öko-Tex 100 certified silk products in the market which can ensure that no residues of sericin is still present.