Silk production process steps

Introduction

The word silk comes from ancient English: sioloc, from ancient Greek: σηρικός, Romanized: serikos, "silken", finally compare from Asian sources Mandarin s ī "silk". Silk is a natural protein fiber that we get from insects that can be woven into textiles. Silk protein fibers are composed primarily of fibroin and are produced by insect larvae specific to cocoon formation. The most well-known silk captive mulberry silkworm Bombyx is found in Mori's larvae cocoon.

The shiny appearance of silk is due to the triangular prism structure of silk fiber that allows the silk fabric to reflect the light coming from different angles and produce different colors. Silk is produced by several insects but moth caterpillar silks are used to make textiles. There have been some studies on other types of silk, which differ at the molecular level. Silk is mainly produced by the larvae of fully transformed insects, but some insects, such as web spinners and raspy cricket, produce lifelong silk.

Silk is also produced by Hymenoptera (bees, seeds, and ants), Silverfish, Mayflies, Thrips, Leafhoppers, Beetles, Lacewings, Flies, Flies, and Midge. Other types of arthropods produce silk, especially arachnids like spiders.

Silk production process steps-

Wild silk

Wild silks have been known and used in many countries in the early stages, although the amount of production is much lower than the cultivation of silkworms. Silk cocoons and nests are often similar to paper or cloth and their use has appeared independently in many societies. Wild silks tend to be more difficult to dye than silkworms from cultivated silkworms. A technique known as demineralizing allows the removal of the mineral layer around the cocoons of wild silkworms that hinder the sole variability of color as a way to create a commercial silk industry based on wild silk in different parts of the world, such as Africa and South America. The word ‘Vanya’ is a Sanskrit source, meaning unfamiliar, wild, or forest-based. Muga, Tasar, and Eri silkworms are not completely hegemonic and the world affectionately calls the silk they produce 'Wild Silks'. India produces four types of silk: Mulberry, Tassar, Muga, and Eri. The silkworms are fed on mulberry leaves grown in the orchard of the Bombyx mori tree. Silkworms are also found wild in forest trees like Antheraea paphia produces Tasar silk. Antheraea paphia feeds on a variety of plants such as Anogeissuslatifolia, Terminaliatomentosa, T. arjuna, Lagerstroemia parviflora, and Madhuca Indica. The wild silkworm Antheraea assamensis produces Muga silk and another wild silkworm Philosamia Synthia ricini eri silk. 

History of Silk Fiber

1st Neolithic A silk production in China. During the last half of the first millennium BC, the Silk was confined to China until the Silk Road reached some stage. China has maintained a virtual monopoly on silk production for thousands of years. Not limited to clothing, silk was also used for many more applications, including writing, and the color of the silk worn was an important guide to social class during the Tang Dynasty. Silk cultivation spread to Japan around 300 AD and during Byzantine time’s silkworm eggs were able to hatch and silkworm farming was started. The Arabs also started producing silk at the same time. As a result of silk cultivation, Chinese silk exports became less important even though they still dominated the luxury silk market. The Crusades brought silk production to Western Europe, especially to many Italian states, which saw the rest of Europe export silk economically. In Europe, the silk industry was very much industrial changed at the time of the revolution. Due to the innovation in spin cotton, cotton became much cheaper to make and as a result, more expensive silk production became less mainstream. New weaving technologies, however, have increased production efficiency. Among these was the Jacquard loom, which was made for silk embroidery. Epidemic production of several silkworm diseases declined, especially in France, where the industry never recovered. In the twentieth century, Japan and China regained their former role in silk production, and China is now again the world's largest silk producer. The emergence of new fabrics like nylon has reduced the prevalence of silk around the world and silk is now again a rare luxury, much less important than its legacy.

Physical properties of Silk

1.  Silk fiber's cross-sectional view is triangular with rounded corners, 5–10 μm wide.

2.  It has a smooth, soft texture that is not slippery.

3.  It is one of the strongest natural fibers, but it loses up to 20% of its strength when wet.

4.  It has a good moisture regain of 11%.

5. Its elasticity is moderate to poor: if elongated even a small amount, it remains stretched.

6. It can be weakened if exposed to too much sunlight.

7. It may also be attacked by insects, especially if left dirty.

8. It is a poor conductor of electricity and thus susceptible to static cling.

9. It has a high emissivity for infrared light, making it feel cool to the touch.

10. Unwashed silk chiffon may shrink up to 8% due to a relaxation of the fiber macrostructure, Dry cleaning may still shrink the chiffon up to 4%.

11. It has a linear density of approximately 1 den or 1.1 dtex.

Chemical Properties of Silk

1. Silk is a natural protein fiber that consists of two main proteins, sericin, and fibroin.

2.  The high proportion (50%) of glycine allows tight packing.

3.  It is resistant to most mineral acids, except for sulfuric acid, which dissolves it.

4.  It is yellowed by perspiration.

5.  Chlorine bleach will also destroy silk fabrics.

6.  Silk is readily decomposed by hot concentrated acids.

7.  Caustic soda, when it is hot and strong dissolves the silk fiber.

8.  Silk fibroin is not severely affected by the H2O2 solution.

Chemical composition of Silk

Fibroin:                      75%

Sericin:                      22.5%

Fat and Wax:             1.5%

Ash of Silk Fibroin:    0.5%

Mineral Salt:              0.5%

Type of Silk

There are many types of silk commercially known and produced around the world. Some of the common types of silks include;

A. Tussar silk

Tussar silk is alternatively spelled as tussah and it also is known as Kosa silk. It is produced from larvae of several species of silkworms belonging to the moth genus Antheraea, including A. These silkworms live in the wild forests of Terminalia species and Shorea Robusta as well as Jamun and Oak food plants found in South Asia, eating the leaves of the trees they live on. Tussar silk is valued for its rich texture and natural deep gold color and varieties are produced in many countries including China, India, Japan, and Sri Lanka. The saree is the most important Tussar silk product although it is also used as the base material for handicrafts, furnishing fabrics, and stitched apparel. Tussar silk is a popular additive to soap. Short silk fibers are usually dissolved in lye water, which is added to oils to make soap. Soap made with Tassar silk has slippery qualities and is considered more luxurious-feeling than soap making. Tussar silk roving can be bought at soap-making supply stores.

B. Mulberry Silk

It is the most common and widely used silk in the world. The most well-known silk captive mulberry silkworm Bombyx is found in Mori's larvae cocoon. It accounts for about 90% of the world’s supply. Much of the silk produced around the world comes from mulberry varieties. Thus, the word silk usually refers to silk obtained from a mulberry. This type of silk is produced by the Bombyx mori silkworm who feeds on mulberry bushes. The silkworms are entirely domesticated and reared indoors. Mulberry silk is popular in the world, especially in China, Japan, and Korea. The production of silk involves the killing of worms in their cocoons to extract the silk fiber. The disadvantage of using mulberry silk is that it needs extra care to maintain its smooth texture.

C. Eri Silk

It is also known as Endy or Errandi Silk. It is creamy white silk. Eri silk is derived from two native species of silkworms known as Samia ricini and Philosamia ricin. It is cool silk as it is cut from silk cocoon without destroying worms, unlike shell and Taser silk. The castor silkworm, which produces Eri silk, is reared in the castor oil plant. Silk, wool, and cotton have a matte look. Castor silkworms and mulberry silkworms are the only domesticated silkworms that both rely on human intervention for development. It is durable and makes great material for clothing and soft furniture such as curtains. However, silk is heavy to wash and can damage microorganisms as it is easy for them to stick to the fabric. Eri silk is a major fiber, which is an integral filament compared to other silks. The texture of the fabric is thick, delicate, and dense. It is very strong, durable, and resilient. Eri silk is darker and heavier than other silks and blends well with wool and cotton. Due to its thermal properties, it is hot in winter and cool in summer. Eri silk products are promoted as environmentally friendly and natural and provide jobs and money for tribes practicing Eri culture.

D. Muga Silk

It looks like golden yellow silk. Muga silkworms also belong to the same family as Taser silkworms. Silkworms feed on semi-domesticated animals, especially in Assam, and the fragrant leaves of Somali trees. Muga silk is known for its glossy texture and golden-brown color. The supply of silk is limited and it is used only in the state of Assam to make traditional garments, especially for the royal family. Its high quality makes it popular for making saris and sheets. Extensive production of Muga silk is possible, as its production is environmentally friendly and silkworms do not require delicate care. The thrill of Muga silk can sometimes be a problem as bleaching is limited.

E. Pat Silk

Pat silk is a variety of domestic silk in Assam, India. It is usually bright white or off-white. Its fabric can be dried in the shade. Noni leaves are the larvae of Pat Silkworm's favorite food. Silk has a natural white color and is known for its durability and glossy texture. Other Assamese silks like pat silk are used in products like mekhelas, sheets, and other textiles. Indigenous silkworms are heavily dependent on humans for reproduction as a result of millennia of selective breeding. Wild silk moths differ from their domestic cousins; these are not commercially effective in silk production. Sericulture in Assam is an ancient art brought by the Tibetan-Burman Kachari tribes.

Type of Silk based on Origin

There are many countries that produce silk, such as below-

1. China Silk

The silk used in the fabric was first developed in ancient China. The earliest evidence of silk is the presence of silk protein fibroin in soil samples from two tombs at the Neolithic site Jiahu in Henan, dating to about 8,500 years ago. Legend has it that a Chinese empress, Leizu, was credited with developing silk. Silks were originally reserved for the Chinese emperor for their own use and gifts to others but were increasingly traded in Chinese culture both geographically and socially and later in many parts of Asia. Due to its texture and luster, silk quickly became a popular luxury fabric in various areas accessible to Chinese merchants. Silk was in great demand and pre-industry became the mainstay of international trade. Although historians are skeptical of the long history of the structural textile industry in ancient China, this discovery of silk textiles using complicated techniques of weaving and dyeing provides evidence of the date of silk before Mawangdui-discovery and other silks related to the Han Dynasty. In order to maintain the monopoly of China, the emperors of China tried to keep the knowledge of silk cultivation secret. Nevertheless, sericulture reached Korea with technical assistance from China in the early 200 BC, the ancient kingdom of Khotan in 50 AD, and India in 140 AD. Many civilizations, such as the Eurasian continent and the ancient Persians, benefited economically from trade.

2. Indian silk

Silk is known as Resham in eastern and northern India and pattu in southern India. India has a long history. Recent archaeological discoveries at Harappa and Chanhu-daro indicate that the sericulture of wild silkworms, a species of natural silkworms, occurred in South Asia during the Indus Valley Civilization between 2450 BC and 2000 AD. Although there is hard and fast evidence for silk production in China until 2570 BC. Shelagh Vainker, a silk expert at the Ashmolean Museum in Oxford saw evidence of silk production in China significantly before 2500-2000 BC. He suggested the people of the Indus Valley Civilization either harvested silkworm cocoons or traded with people who knew enough about silk. After China, India is the second-largest producer of silk in the world. About 97% of raw mulberry silk comes from six states of India, Andhra Pradesh, Karnataka, Jammu and Kashmir, Tamil Nadu, Bihar, and West Bengal. The 20 million Silk City of North Bangalore, Ramanagara, and Mysore, the incoming site contributes to most of the silk production in Karnataka. In Tamil Nadu, shell farming is concentrated in Coimbatore, Erode, Bhagalpuri, Tirupur, Salem, and Dharmapuri districts. Hyderabad, Andhra Pradesh, and Gobichattipalayam in Tamil Nadu was the first automated silk railing unit in India. In silk consumption, India is also the largest consumer of silk in the world. The tradition of wearing a silk sari for weddings and other auspicious occasions is a tradition in Assam and southern India. Silk is considered a symbol of royalty, and historically, silk was primarily used by the aristocracy. The silk garments and saris produced in Kanchipuram, Pochampally, Dharmaram, Mysore, and Arani in the south, Banaras, Bhagalpur in the north, and Murshidabad in the east are quite recognized.

3. Thai silk

It is produced from the Thai silkworm cocoon. Thai silkworm farmers cultivate both types of domestic silkworms that produce silk commercially: Samia ricini, commonly known as Eri Silkworm, which produces matte Eri silk, and Bombyx Mori, the producer of the more well-known, glossy mulberry silk. The second is the largest silk producer of the two so far. In Thailand, the Silk in Excellence in Center Sericulture research at Kasetsart University's Kamphaeng Saen Campus plays a leading role in research on silkworm egg supply and how Thai farmers can learn. It was not very interesting in Thai silk and was only considered suitable for fancy clothing, to be able to easily identify authentic Thai mulberry silk, the Thai Ministry of Agriculture used the peacock symbol to authenticate Thai silk and protect it from counterfeiting. These are the golden peacock, the silver peacock, the blue peacock, and the green peacock. Thai silk has a unique luster, a sheet with two unique blends: one for color straps and the other for weaving. Its color will change when viewed from different angles of light. When Thai silk burns, it smells like hair. Silk is similar to the combination of human hair and nails. When the flame is removed, the Thai silk stops burning immediately. Thai silk is usually 10 times more expensive than synthetic silk. An easy way to identify authentic silk is to test the wedding ring. It will pass easily when pulling the silk fabric through a ring. Imitation fabrics will become bunches and it will be difficult or impossible to pull with the ring.

4. Bangladeshi Rajshahi Silk

The silk which is produced in Rajshahi is called Bangladeshi Rajshahi silk. It is like other types of silkworms. Very thin fibers obtained from this process are covered with sericin, a special protein. It is popular because its quality is high, for this reason, it is used for making high-quality clothing, especially for saris. Records date the beginning of silk production in this region in the 13th century. It was called Bengal Silk or Ganges Silk. In 1952, the government of Pakistan started silk production in Rajshahi. Rajshahi Silk Factory is a state-owned factory established in 1961. In 1976, it was handed over to the Bangladesh Silk Cultivation Development Board. It has been doing damage ever since. There are three main types of silk: Mulberry Silk, Eri Silk, and Tassar Silk.

Cultivation of Silk

Silk moths lay their eggs mainly on prepared paper. The eggs hatch and the caterpillars are fed high-quality mulberry leaves. After about 35 days and 4 hatchings, the caterpillars become 10,000 times heavier than the cubs and are ready to start cutting a cocoon. A straw frame is placed on top of the caterpillar tray and each caterpillar moves its head in a pattern and begins to spin a cocoon. The two glands produce liquid silk and force it through the opening of the head called spinnerets. Liquid silk is coated with sericin, a water-soluble protective gum, and is strong in contact with air. Within 2-3 days, the caterpillar spins about a 1-mile filament and is completely enclosed in a cocoon. Silk farmers heat the cocoons to kill them and turn some into insects to breed the next generation of dry ones. The cut cocoons are boiled and the silk fibers soaked in water hold the silk fibers together to form a cocoon. The fibers are then unwrapped to form unbroken threads. Since the single thread is very delicate and fragile for commercial use, a single thread of silk is made anywhere from three to ten strands.

Which Insects produce Silk?

A. Silkworms produce silk when undergoing larval to adult metamorphosis. These include not only the pet bombyx mori but also a wide variety of insect species, most of which are used commercially for silk.

B. Raspy cricket produces silk to make nests.

C. Honeybee and bumblebee larvae produce silk to strengthen the wax cells in which they pupate.

D. Bulldog ants spin cocoons to protect themselves during pupation.

E. Weaver ants use silk to connect leaves together to make communal nests.

F. Webspinners have silk glands on their front legs.

G. Hornets

H. Silverfish

I. Mayflies

J. Thrips

K. Leafhoppers produce silk nests under the leaves of the trees where they live to protect them against predators.

L. Beetles

M. Lacewings

N. Fleas

O. Flies

P. Midges

Q. Caterpillars of many butterfly species use silk to create shelters or attach to substrates for pupation.

R. Parasitic wasps such as braconids use silk cocoons for pupation.

Diseases of Silkworm

There are different kinds of diseases that are found in silkworms. Such as below-

A. Beauveria bassiana

It is the name of a fungus that destroys the entire silkworm body? This fungus generally appears when silkworms are held in cool conditions with high humidity. The disease is not passed from insects to eggs because infected silkworms cannot survive in the insect stage. It can spread to other insects.

B. Grasserie

It also is known as nuclear poly-hydrolysis, milky disease, or hanging disease is caused by infection with the Bombyx mori Nucleo poly-hydro virus. If it is observed in the chawkie stage, then the chawkie larvae must have been infected while hatching or during chawkie rearing. Infected eggs can be disinfected by cleaning their surfaces before hatching. Infections may occur as a result of improper hygiene in the chawkie rearing house. This disease develops faster in early instar rearing.

C. Pebrine

It is a disease caused by a parasitic microsporidian, Nosema bombycis. Diseased larvae show slow growth, undersized, pale, and flaccid bodies, and poor appetite. Tiny black spots appear on the larval integument. Additionally, dead larvae remain rubbery and do not undergo putrefaction after death.

D. Flacherie

Its infected silkworms look weak and are colored dark brown before they die. The disease destroys the larva's gut and is caused by viruses or poisonous food.

Various diseases caused by a variety of funguses are collectively named Muscardine.

Remedies

To prevent this disease, it is important to deactivate all eggs from infected moths by examining the moth's body fluids under a microscope.

The yarn manufacturing process of Silk

The silk yarn manufacturing process manual is as follows-

1. Sericulture

The cultivation of silkworms to produce silk is called sericulture. The best raw silk is obtained from insects of the species Bombyx mori. Silkworms breed once a year but can be kept up to three times a year under scientific conditions. About 3 mm larvae emerge from the eggs. Female silkworms lay 300 to 500 eggs. Silkmoth eggs form larvae or caterpillars known as silkworms. The larvae feed on the leaves of the larvae. After growing several times, the silkworm pulls out a silk fiber and forms a net to hold itself. It rotates to one side by itself in the ‘8’ figure, distributing the saliva that will make the silk. Silk solidifies when it comes in contact with air. The silkworm spins about a mile of filament and in about two or three days completely enclose itself in a cocoon. As a result, about 2,500 silkworms are needed to produce about one thousand pounds of raw silk. Silk is obtained by brushing the useless cocoon to find the outer edge of the filament. The filaments of silk are then wound into a relay. A cocoon contains about 1000 yards of silk filament. At this stage, this silk is called raw silk. A thread has 48 separate silk filaments.

2. Cocoon picking

The cocoons are selected according to color, size, and texture, as they all affect the final quality of the silk. Cuckoos can range from white or yellow to gray, depending on the source and type of food when eating at the insect stage. Cocoons from China are white, Japanese cocoons are creamy-white and yellow, and Italian cocoons are yellow.

3. Soften the sericin

After the cocoons are picked and the silk gum is called sericin, which cements the filaments. The sericin is removed by placing the cocoon in hot water, which frees the silk fibers and prepares them for reeling. This is known as the degumming process. Immersion in hot water also kills silkmoth pupa.

4. Reeling

Reelings can be achieved manually or automatically. The end of the cocoon fiber is brushed to identify. The process is as simple as it is laborious. It is threaded through a porcelain eyelet, and the fiber is reeled on a wheel. Meanwhile, diligent operators check for filament errors as they are being rebuilt. As soon as each filament is almost finished reeling, a new fiber is twisted into it, creating a long, unbroken thread. Ceresin contributes to the attachment of fibers to each other. The average cocoon reels about three hundred yards away in a single thread.

5. Throwing

The production of yarn from silk, known as throwing, involves adding a twist and twisting these strands to the desired shape. The single filaments are joined together to form a thread, which is drawn by pulling through several guides and hitting the reels. Threads can be driven to make yarn. After drying, the raw silk is packed according to the quality.

The weaving process of Silk

The production process of silk begins with the Bombyx mori a small silkworm that comes from the eggs of a silk moth. For their first year, these insects feed on the leaves of the mulberry tree before making a cocoon with their spit. In its original cocoon form, the raw silks are heavy and irregular. Silk weavers separate the completed cocoons from the mulberry bush and soak them in a vat of boiling water to separate the silk thread from the caterpillar inside the cocoon. The Bombyx mori generally produces silk threads of varying colors, ranging from light gold to very light green, with lengths varying from 500 to 1,500 yards per cocoon. A single-thread filament is too thin to use on its own, so weaver women combine many threads to produce a thicker and more usable fiber. They do this by spreading the threads by hand over a wooden spindle to produce a uniform strand of raw silk. The process is a tedious one as it takes nearly 40 hours to produce a half kilogram of silk. Many local operations use a reeling machine for this task, but the majority of silk thread is still hand-reeled. The difference is that hand-rolled threads produce three grades of silk: two fine grades which are ideal for lightweight fabrics and one dense grade for heavy material.

The silk fabric is then soaked in hot water and bleached before dyeing to remove the natural yellow coloring of Thai silk yarn. To do this, silk thread skins are immersed in large tubs of hydrogen peroxide. Once washed and dried, the silk is then woven using traditional hand-woven looms.

End-Use of Silk

i. The absorption of silk makes it comfortable to wear in warm weather and inactive condition. Its low conductivity keeps warm air close to the skin during cold weather. It is often used for clothing such as shirts, ties, blouses, formal dresses, high fashion clothes, lining, lingerie, pajamas, robes, dress suits, sundresses, and Eastern folk costumes.

ii. Fabrics that are often made from silk include charmeuse, habotai, chiffon, taffeta, crepe de chine, dupioni, noil, tussah, and shantung, among others.

iii. Silk's attractive luster and drape make it suitable for many furnishing applications. Silk is used for upholstery, wall coverings, window treatments, rugs, bedding, and wall hangings.

iv. Silk had many industrial and commercial uses, such as parachutes, bicycle tires, comforter filling, and artillery gunpowder bags.

v. A special manufacturing process removes the outer sericin coating of the silk, which makes it suitable for non-absorbable surgical sutures.

vi. New uses and manufacturing techniques have been found for silk for making everything from disposable cups to drug delivery systems and holograms.