Cotton fiber undergoes several process to reach the stage of final cloth. The processes are as mentioned below:
Ginning
Ginning is the method of separating the cotton fibers from the seedpods, and sometimes with the sticky seeds. This is done in the cotton field with the help of machines.
Spinning
Spinning is the succeeding step to ginning. This process involves the making of yarn from the cotton fiber. The cotton yarns are made of different thickness in this stage.
Weaving
Weaving is the most important process in the making of cotton cloth. In this process, two yarn is placed to make warp and weft of a loom which successively turn them into a cloth.
Fabric finishes and treatments
After weaving the cotton fabric passes through different processing stages till it reaches to the state of final product. The stages are mentioned below, but it is not necessary for the fabric to undergo all the process for e.g. grain bags cloth are used unbleached.
- Singeing - This process burns off the fibers sticking in the goods.
- Desizing - This process involves removing the size material from warp yarns in woven fabrics.
- Scouring - The cleaning part of the fabrics are involved in this process.
- Bleaching - The fabrics are bleached here to make it more whiter and lighter.
- Mercerizing - In this process, the fabric is immersed in alkali to make it more strong, shining, durable, shrink free and stretch free.
- Dyeing - This process involves the changing of the fabric color by the treatment with a dye.
Leather Fabric
Pre-tanning
- Animal skin is cleaned and salted to prevent decay.
- The hide or pelt then is sent to tannery for trimming and sorting.
- Next, it is soaked in water to restore moisture content, which is lost during salting process.
- It is treated mechanically with rollers and blades to remove fat/muscle and flesh (Fleshing).
- During liming the skin is soaked in lime solution to remove the hair, inter-fibrillary protein and epidermis.
- In De-liming the hide or pelt is washed in water containing ammonium chloride or ammonium sulphate to neutralise it.
- Bating involves treating the leather with digestive enzymes to remove non-fibrous protein.
- Scudding is done with a blunt knife to remove remaining hair roots, skin pigmentation, and surface fats.
- Lastly, it is put in sulphuric acid to lower the pH.
Tanning is the process where the leather gets the necessary feel and physical characteristics. In this process, the collagen, an insoluble fibrous protein, which carries the major property of the hide or pelt gets less susceptible to decay and are kept flexible. This is done by removing the water molecules from the gap of protein molecules and replacing it with chemicals that retain flexibility.
The main tanning processes are mineral/chrome tanning, vegetable tanning and oil tanning.
- Mineral/chrome tanning is the most common and modern method, which uses chromium salts. This makes leather water proof and stretchable.
- Vegetable tanning, or bark tanning is the process where the hide is soaked in a solution of bark of oak/chestnut which is chopped or boiled. The leather becomes moldable and can be tooled. Moreover when dry, the leather will not stretch.
- Oil tanning is a process where fish and animal oil is used. The leather becomes very soft and flexible. It cope up with wetted condition without causing damage to the leather. Chamois leather is best example of oil tanning.
After tanning, the leather undergoes different processes according to the use of the final product.
- Vegetable-tanned leather which are used for shoe soles is bleached, lubricated and then run through rolling machines to make it firm and glossy.
- Chrome-tanned leather, for shoe uppers, is split and shaved and then placed in a rotating drum for the dyeing process using several types of coloring materials to give color fastness and durability.
- Before or after dyeing, it is rolled in a fat liquor containing emulsified oils and greases. Next, the leather is pasted on glass or ceramic frames and then passed through drying tunnels with controlled heat and humidity.
Silk Fabric
From Cocoon to Yarn
Silk from cultivated silkworms is more used though silk of wild worms is also valuable. The worms feed on mulberry leaves and increases their body size by nearly 10,000 times in a short span of time. The worm ceases to eat by the end of thirty days and attach itself to a piece of straw and begins to spin its cocoon. After the spinning of cocoon and before the hatching of the worm into a moth, the cocoon is soaked in hot water unraveling and producing long size thread. This fine thread is the basic component of silk yarn and fabric.
Washing and bleaching of the silk threads
The natural fiber extracted from the silkworm holds some glutinous substance (gummy substance or glue) which is removed by washing and bleaching.
Weaving
Weaving is a process where the fabric is created by interlacing the warp yarns and the weft yarns. It is either done by machines or hand. Hand woven fabric is better than the machine woven. It can make delicate designs with different colored thread. Modern machines use lances, projectiles, a jet of compressed air to shoot the weft-yarn between the warp-yarns. It leads to greater yield and productivity.
A good quality of silk begins with a warp of approximately 2,000 threads for one meter width. 1,600 threads or 1,800 threads are considered to be poor quality fabric. Loosely woven fabrics are difficult to sew.
Dyeing, Printing and Finishing
There are two main types of silk fabrics. One which is yarn-dyed or dyed-woven, like taffeta, duchess satin and many pattern-woven fabrics. The other type is piece-dyed fabrics, which is carried out after weaving, like crepes, twills, etc. The dyeing process gives the silk different shades.
Printing is giving pattern to the fabric. It is either done by block-printing method, roller-printing method or screen printing. Screen printing is widely used in silk fabrics.
Embroidery process gives embellishment and the perfect finish to the fabric to make it look more beautiful.
All fabrics has to be finished. It is here the fabric gets the desired appearance and feel. Finishing process is either physical or chemical. It give treatments like crease-proofing, water-proofing, fire-proofing, etc.
Final soaking in a chemical solution
This process helps to preserve the sheen and luster of the silk fabric. It adds weight and makes the fabric soft, smooth, easy to iron and wrinkle resistant.
