Silk Dyeing - properties of silk fiber

 

What is silk?
Silk is natural protein filament produced by a caterpillar of butterfly - silkworm. It is a strong, soft thread neither phytogenous nor animal which is produced by a caterpillar before turning into a pupa (chrysalis).
Silkworm is the most widespread insect-manufacturer on the Earth. It produces filament for taffeta, atlas, sateen, organza, and chiffon.

The noblest (and most expensive) silk is reeled off not boiled; its thread is pulled out from inside the cocoon.

To receive 3 kg of silk thread it is necessary to provide caterpillars with leaves of approximately 30 mulberry trees.

Artificial silk was invented only in the 19th century; before that only natural silk was used for fabrics manufacturing.

What is a cacoon?
While a lot of people have probably heard about caterpillar Cocoons, they may not know for sure just what these are. Basically, they are nothing more than a protective casing that is around an insect. This is made of either silk or some other similar fibrous material that is then spun around the the insect during their pupal stage, which is the life stage of an insect that is undergoing transformation. While the most common type of Cocoon are those that are found around butterflies or moths, the egg case of a spider is also a type of Cocoon.

Usually an insect will enter into a Cocoon so that they will be protected from a harsh or unfriendly environment. This is why, most of the time insects will spend the wintertime in their Cocoons. So, as the days get shorter and cooler in the fall, these insects will start to spin a silky envelope around themselves. They will then retreat into this Cocoon and spend the winter without the need for food or water. 

You may be wondering just how these Cocoons are made. Well, they are actually made of silk. This silk is spun from 2 glands that are located inside of an insect. These glands are filled with a material that is thick and glue-like. An insect will then work in a figure 8 in order to wrap themselves up inside of this silk. This material is pressed out of the insect's 2 slender threads. These threads will then stick together as they emerge and then grow hard when fresh air touches them. 

This is a very interesting process because it has oftentimes been said that the most beautiful butterflies have actually emerged from the ugliest Cocoons. For this reason, many people consider the process of the Cocoon to be a miracle of nature itself.
What is spider silk? Details of spider silk.
Spider's silk is made up of chains of amino acids. In other words, it is simply a protein. The two primary amino acids are glycine and alanine.
Spider silk is extremely strong -- it is about five times stronger than steel and twice as strong as Kevlar of the same weight. Spider silk also has the ability to stretch about 30-percent longer than its original length without breaking, which makes it very resilient.

How silk is produced?
Silk - the most beautiful of all textile fibers is acclaimed as the queen of textiles. It comes from the cocoon of the silk worm and requires a great deal of handling and processing, which makes it one of the most expensive fibers also. Today China is the leading silk producer of the world. Other major silk producing countries include Japan, India and Italy.
Production of Silk
Characteristics of Silk
Identifying of Silk
Four Varieties of Natural Silk

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The Silk Worm

 Production of Silk from Cocoon to Factory
Sericulture: The production of cocoon for their filament is called sericulture. The species Bombyx mori is usually cultivated and is raised under controlled condition of environment and nutrition. The life cycle of silk worm encircle in the four stages. The egg, the silk worm, the pupa and the moth. The silk worm which feeds on mulberry leaves forms a covering around it by secreting a protein like substance through its head.

 

This stage is called cocoon, the desirable stage for the silk producers.
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Filature operations: The cocoons raised by the farmer are delivered to the factory, called a filature, where the silk is unwound from the cocoons and the strands are collected into skeins. Some cocoons are scientifically bred in such factories. The filature operations consist of the following stages.



a) Sorting cocoons : 
The cocoons are sorted according to the color, size, shape and texture as these affect the final quality of the silk. Cocoons may range from white and yellow to grayish.

b) Softening the Sericin : Silk filament is a double strand of fibroin, which is held together by a gummy substance called sericin or silk gum. After the cocoon has been sorted, they are put through a series of hot and cold immersions, as the sericin must be softened to permit the unwinding of the filament as one continuous thread.

c) Reeling the filament : Reeling is the process of unwinding the silk filaments from the cocoon and combining them together to make a thread of raw silk. As the filament of the cocoon is too fine for commercial use, three to ten strands are usually reeled at a time to produce the desired diameter of raw silk which is known as "reeled silk". The useable length of reeled filament is 300 to 600 m.

d) Bailing : The silk filament is reeled into skeins, which are packed in a small bundles called books, weighting 2 to 4.5 kg. These books are put into bales weighing about 60 kg. In this form raw silk is shipped to silk mills all over the world.


Characteristics of Silk

Silk 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.
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 a protein fiber like wool. This gives it many of its characteristics. It is sensitive to a range of chemical situations and cannot withstand prolonged exposure to either high alkalinity or to acid or oily soils. It will become brittle with age and exposure to sunlight.  


Identifying Silk

The burn test is the best way to be sure. Burning silk will leave a powdery ash and will extinguish itself when the flame is removed, just like wool. The easy way to tell silk and wool apart in the burn test is the smell. Where wool will have the smell of burning hair, the silk will have a much more disagreeable smell.


Four Varieties of Natural Silk

Out of the numerous species of silk moths, scientists have enumerated about 70 silk moths which are of some economic value. But of these only a very few have commercial value. The four commercially known varieties of natural silk are (1) Mulberry silk (2) Tasar silk (3) Muga silk and (4) Eri silk. Although the bulk of world silk supply comes from the silk moth Bombyx Mori which is domesticated, the other varieties of silk are known as wild silk, as they are grown in remote forest trees in natural conditions.




A wide range of silk fabrics are produced at different production centers   both Handloom and Powerlooms. A brief account of the range of fabrics is furnished below, as is known by its popular names.

Mulberry Varieties
Some important mulberry varieties are discussed below:
(a) Plain Silk Fabrics

A range of thin silk to deluxe qualities are produced in this category using filature. Fabrics ranging from 20 gm to 70 gm are produced in this category using both handloom as well as powerloom. The fabrics is available as per the requirements in different shades as well as in checks and stripes. Beautiful pin stripes are a specialty for shirting. Plain silk is mostly used by exporters for making ladies blouses, fashion garments, made-ups and scarves. Deluxe and super deluxe qualities are also produced as per specific orders.

(b) Dupion Fabrics

A specialty of Bangalore Handlooms, Dupion is the craze of the west. Produced out of twisted filature warp and dupion weft is available in different quality ranges and shades. Dupion checks and stripes are elegant in look. Mainly used for dress material and cushion covers and furnishings, dupion is a popular name among the overseas silk importers.

(c) Charka Silk 

Using filature in warp and Charka in weft a thicker fabric is made on handlooms. For most of the zari decorative sarees charka yarn is popularly used by the sari manufactures.

(d) Chiffon

Using highly twisted yarn, a thin but strong fabric is produced on power looms, which after processing and finishing attains a soft and smooth texture. Chiffons are used for varied end-uses for ladies garments and scarves/stoles.

(e) Chinnon

This is also produced from highly twisted yarn of filature in power loom. After the final processing and finishing the fabric gets a soft but crimp effect. Chinnon is ideal for ladies dresses and scarves/stoles.

(f) Crepe

Produced from 2-ply twisted yarn of 's' and 'z' twist and woven on power loom, crepe is used for varied uses. Mysore crepe saris are very popular in domestic and export front.

(g) Organza

A very thin fabric produced from highly twisted yarn. After a starchy finish the fabric gets a rough texture. Organza is used as sari material as well as for embroidered garments.

(h) Satin

Silk satins are a popular variety of fabric used for a varied end use. When made into dresses satin gives an elegant Look. Banarasi Satin Saris are popular for export and domestic markets.

(i) Tabby Silk

A type of plain silk fabric produced in Kashmir. Tabby silk is mostly used for printed saris and scarves.

(j) Murshidabad Silk 

A popular silk fabric produced in the Murshidabad district of West Bengal. Used mainly for saris and scarves, the fabric is available in different qualities known as 16s, 18s, 20s, and so on .

(k) Matka Fabric

Using Matka yarn for both warp and weft, a thicker fabric is produced mostly for furnishing. The fabric mostly produced in Bhagalpur is a very popular export item at present. By using multiple yarns the texture and thickness of the fabrics can be modified according to the end use.