Fibers like cotton Linen have ruled the world since the start of civilization. As we speak about innovation and technology, China with its large-scale production has invented new fibers like Milk and Soybean.
Figure 1: Extraction and spinning of milk fiber. Source: marenscott.blogspot.com
Though in the 1940’s the fibers were quite popular in America and Europe, the market collapsed due to World War II.
Now regenerated fibers are more efficient and durable than any other fiber invented before or existing today. Milk fiber was invented in the 1930‘s in Italy by Antonio Ferratti. It was manufactured from milk casein to compete with wool. Casein fibers have since being produced under various names in a number of countries.
Lanital in Belgium and France.
Fibrolane in Britain.
Merinova in Italy.
Wipolan in Poland.
Aralac in America.
Casein is obtained by the acid treatment of skimmed milk. The casein coagulates as a curd which is washed and dried, and then ground to fine powder. 35 liters of skimmed milk produce about 1 kg of casein.
Today‘s milk fiber is environmentally friendly, superior in strength and has far better qualities than man-made fibers.
Casein (milk) protein dates back many centuries when it was used as a binder for paints – paint with casein applied to 14th and 15th-century churches still appear bright and unfaded. Proteins are obtained from skim milk, evaporated milk and condensed milk. There are about three pounds of casein in every 100 pounds of milk.
Production of milk fiber:
Casein is obtained by the acid treatment of skimmed milk. The casein coagulates as a curd which is washed and dried, and then ground to a fine powder. Casein is dissolved in caustic soda solution. The solution is allowed to ripen until it reaches a suitable viscosity, and is then filtered and deaerated.
The spinning solution is wet spun by extrusion through spinnerets into a coagulating bath containing sulphuric acid (2 parts), formaldehyde (5 parts), glucose (20 parts) and water (100 parts). The jets of solution coagulate into filaments in a manner similar to the coagulation of viscose filaments.
But the next process is very critical as the fiber has to be treated chemically to harden it. The process is commonly described as “hardening”, in that it minimized the softening effects of water. Treatment with formaldehyde forms the basis of many hardening techniques.
In the plant scale bunches of filaments are collected together into a tow as they leave the coagulating bath, and are then steeped in formaldehyde solution.
The filaments are subjected to drawing at this stage. After treatment, the tow is washed and dried, crimped mechanically, and then cut into staple fiber. Otherwise, the tow to top convertor makes tops for blending with wool.
Following are the varieties available in the market.
Milk fiber has passed oeko-tex standard 100 green certifications for the international ecological textiles.
The milk fiber contains eighteen amino-acids, which is beneficial to human’s health and has the functions of nourishing and taking care of skin. The wet spinning technology, a unique spinning solvent is used, micro-zinc ions are embedded in the fiber, after drying and after treatment, zinc oxide is produced, and therefore it is bacteriostatic and durable. Casein fiber is produced almost entirely as staple, tow or top.
Figure 2: Flowchart of milk fiber production.
Properties of Milk fiber:
Milk fiber resembles wool in having a soft warm handle. The fibers are naturally crimped, and yarns have a characteristic warmth and fullness of handle. It provides good thermal insulation. They are resilient, like wool.
Casein fibers cannot be distinguished from wool fibers by chemical or burning tests, only by microscope. because the chemical composition is so similar, casein burns like wool with the odor of burning hair, has no surface scales like wool but is smooth and round when viewed under a microscope, is damaged readily by alkalis and mildews easily.
The filaments are smooth surfaced. Cross section is bean shaped. The natural color is white. When wet, the fibers lose much of their strength; tenacity falls to 0.6 to 0.3 g/den.
Milk fiber tends to absorb moisture readily, and the fibers become swollen and soft. They may become plastic and sticky as the temperature is raised. The fibers become brittle and yellow on prolonged heating at over 100 deg c. It burns slowly in air. Flammability is similar to wool.
The fiber base body does not have regular channels, which makes the milk fiber have as fine as moisture absorption as a natural fiber and better moisture conduction than synthetic fibers.
Milk fiber is both comfortable and permeable. Fibers are white, fluffy, springy and have a pleasant odor. Even though casein fiber lacks certain desirable qualities of wool it was a way to replace wool at a lower cost. When mixed with viscose and wool, casein helped in the conservation effort during World War II as a wool substitute.
Though caseins can be laundered with care the same as wool, they lose strength when wet and must be handled gently. They cannot be kept damp for any length of time due to quick mildewing.
Today’s milk fiber is environmentally friendly, superior in strength and has a far better quality than man-made fibers.
The blending of milk fiber:
When blended with other fibers casein added a soft draping quality and resiliency to fabrics. The fiber was blended with wool for creating felt and with spun rayon, wool, mohair and cotton for attractive woven and knitted fabrics in a variety of weaves, textures, and prints.
The popular blends were wool- 94% and casein fiber -6%., viscose-50% and casein fiber- 50%. Casein/cotton blends are popular for hosiery and carpets. A small amount of fiber is used for 100% casein goods, but most casein fiber is blended with wool, cotton, rayon, nylon and other staple fibers. Blends containing casein may be spun on all the usual systems.
Cotton system – viscose/casein blends.
Woolen system – Casein/ wool or viscose blends.
Worsted system – Casein /wool or viscose blends.
Flax system – Casein/viscose blends.Chemical processing of Milk Protein Fiber (Casein):
Milk protein fiber has different physical and chemical construction from natural protein fiber, care is taken in the following steps;
Desizing- Enzyme products may be used, preferably at pH 4.0 to 6.0. If water-soluble sizes have been used, sizing is not necessary.
Scouring- Synthetic detergents should be used, preferably under acid conditions, e.g. pH 6.0.
Bleaching- Casein fiber is generally white, and bleaching is not usually necessary. If required, it should be carried out under weak conditions, e.g. pH 4.0-6.0 as Casein fibers retain maximum strength and minimum swelling under these conditions. Hypochlorite bleaches should not be used. Bleaching may be carried out with Hydrogen Peroxide – 2 GPL at a pH of 8.0 using Sodium Pyrophosphate. It must be followed by careful washing and acidification with acetic acid. Normal optical bleaching agents may be applied.
Dyeing- Casein absorbs moisture readily and does not have a highly orientated structure. Dyes can penetrate into the fiber without difficulty. Casein can be dyed with dyestuffs used for wool. Acid, Basic, Direct and Disperse dyes are used where good washing –fastness is noted as a prime essential. Metal complex dyes give high wash fastness. PH of the dye liquor should be between pH 4 & 6. Dyeing is usually carried out at 90-95 deg c.
Printing- Fabrics containing casein may be printed by block, screen, & roller. Acid, basic, direct, chrome, mordant, azoic, vat or pigment dyes may be used.
Crease –resist finishes may be applied to blends containing casein fiber, using temperatures not higher than 160 deg c. for approximately 2.5 mins.
Uses of Milk Protein fiber:
One of the earliest uses for casein fiber was in the making of feeling for hats. Casein/wool blends are used for knitted berets. Casein/cotton or nylon blended fabrics are used for interlock outerwear, T-shirts, cardigans, jumpers etc. Casein blended with wool, cotton, viscose, nylon is used in Raschel cloths, coatings, and blanket fabrics. Blends of casein and wool are made into pressed felts for use as floor coverings and used in conventional and tufted carpets. Pile carpets are made using casein -50% and wool or viscose -50%.