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Soyabean fiber- properties, processes and uses

After nearly a hundred years of development, chemical synthetic fibers gradually matured in the 20th century. Despite the fact that  chemical  synthetic fibers (polyester, acrylic, nylon) of various  features have  become  one of the major  raw  materials  of  the  global textile  industry, they have  certain serious  weaknesses which are as follows;

a. Synthetic fibers rely on gradually depleted oil resources
b. Some products produce pollution during production
c. The comfort of chemical fiber products is less than that of natural fibers.

In order to overcome the fatal weaknesses of chemical fibres, efforts will mainly be made in three aspects:

a. Adopting natural resources from agriculture, animal husbandry and forestry, which are abundant and cheap.
b. Using production processes which must be clean and friendly to the environment.
c. Being more comfortable  to  the  skin  of  the  human  body .

One of the fibers, which pass all above mention characteristics, is Soyabean fiber. It is the healthy and comfortable fiber of the 21st century. At present , only industrialized countries  have  invested  heavily  in  developing  new  fibres for  the new century .

Figure1: Soyabean meal used in making automobile parts in Ford Rouge Plant in 1935.
Figure1: Soyabean meal used in making automobile parts in Ford Rouge Plant in 1935.

Soyabean is mainly cultivated for its seeds. It is widely believed that the Soyabean originated in China, 4000-5000 years ago. Soyabeans have been one of the staple foods of oriental countries for thousands of years. They are rich in a protein which resembles casein. In America, Soyabeans are now cultivated in great quantity as a source of edible oils and protein. Many attempts have been made to spin this protein into useful fibers. The Ford Motor Company has pioneered in this field; production by company began in 1939 and reached more than  three  tons  a week  by 1942 . The fibre was used for making car upholstery. Production was taken over in 1943 by the Drackett Products Co. of Cincinatti, but stopped after a few years .

At the  moment , the United  States  of  America  has  become  the world  leader  in  Soyabean production with  46 %of the world market. Other  countries  with  high Soyabean production are  Brazil ( 20 % ), Argentina ( 14 % ), and China ( 9 % ). Soyabean  Protein Fiber ( SPF ) is a kind of regenerative  plant  fibre .  It is made directly from vegetable sources rather than animal sources. It is the only renewable botanic protein fibre we can touch today.  SPF is a unique Active Fiber. Its 16 amino acids are healthy and nutritional to people skin.

Production of Soyabean fibre:

Soyabeans have a  high protein content ( about 35 % ) and they are grown in abundance in  U S A  and eastern countries. China has taken the world lead in the industrialized  production of soyabean  protein fibre . They provide a cheap and readily available source of protein for  fibre  production. Soyabean fibre can be obtained from soyabean. 100 kg of soyabean residue can be extracted  from 40 kg of protein .  There are five main steps to produce soyabean fiber.

  1. Extraction of oil to obtain oil-free meal:

First the beans are cleaned, cracked, decorticated and dehulled. After a conditioning step at about 70 deg c, the beans are steeped in hexane to remove the oil.  The oil can be extracted by pressing and extraction. The hexane solution is drawn off and the oil is extracted from this solution. The oil free bean is known as meal. The oil is a valuable by-product and so it is separated out. The resulting oil-free soybean meal is passed through a steam –jacketed pipe for removal of the solvent.

  1. Extraction of protein:

The separation of protein from the oil-free meal is accomplished by steeping the meal in dilute alkalis like 1% Sodium Sulphite for one hour to one half hour. The protein is dissolved by this treatment and can be filtered out to separate the protein. The protein is precipitated by means of acid. Sulphuric acid is added and the pH of the solution is made to 4.5. This is near the iso-electric point of Soyabean protein, i.e . At its minimum solubility and therefore will be precipitated. This Soyabean protein thus separated out is a creamy –white powder.

  1. Preparation of spinning solution:

The spinning solution is prepared by dissolving the extracted protein in an alkaline solution.  Caustic soda is used for dissolution. The solution is filtered and deaerated by means of vaccum to remove all undissolved particles and air bubbles. After filtration , the solution  is allowed to age at the requisite temperature .During the ageing period , the solution becomes more viscose and develops the proper consistency for spinning .

  1. Fiber formation:

Soyabean fiber is formed by wet spinning method. The spinning operation consists of forcing the spinning solution through spinneret. The spinneret consists of several holes and it is emerged in the coagulation bath.  The solution emerging from the spinneret holes is referred as liquid jet. The liquid jet precipitated as fine filaments in the coagulating bath containing 2% sulphuric acid and 15% sodium sulphate or sodium chloride for dehydration.

  1. After –treatments:

Further treatments are required for the development of properties of the fibres like stretching and hardening. Stretching can be done in a separate bath, while the filament is soft and it induces orientation by rearrangement of the molecules and it enhances strength and durability of the filaments. Hardening can be done with formaldehyde to enhance the filaments with more strength and elasticity. The fibre performance can also be stabilized through hydroformylation.  It is dried under controlled humidity and temperature, after which it is cut into desired lengths. It is then ready for shipment.


 Properties of Soyabean fiber:

The Soyabean fibers are of low strength, and are sensitive to moisture to the extent of losing 69 percent of their tenacity when wet. It has better fineness, low specific gravity, high tensile elongation, and good acidic and alkali resistance. It is similar to natural fibres such as wool, silk. This new fibre is considerably cheaper than real silk (around one third of the cost of silk) and can partially replace silk. Its moisture absorption performance is equivalent to cotton, and its permeability is greatly better than cotton, ensuring better comfort.

Table 1: Properties of Soyabean fiber and comparison with other major natural fibers.

Properties Soyabean Silk Wool Cotton
Tenacity g/den 0.25-0.8 1-1.5 1.5-2.0 2-5.5
Elongation ,% 50 25-45 25-40 6-10
Density gm/cm3 1.29 1.34-1.38 1.33 1.50-1.54
Moisture regain , % 8.6 11.0 14-16 9
Acid resistance excellent excellent excellent Bad
Alkali resistance good good bad Excellent
Resistance to moth/fungus good Resistance to fungus but not to moth Resistance to fungus but not to moth Resistance to moth but not to fungus
U.V resistance good bad bad good
Dry breaking extension % 18-21 14-25 25-35 7-10

The breaking strength of single filament of this fibre is over 3.0 cN/dtex, higher than the strength of wool, cotton and silk , and equivalent to chemical fibres like polyester. The fineness can reach even 0.9 dtex. The initial modulus of Soyabean protein fiber (SPF) is quite high, the boiling water shrinkage is low, and so the size stability of fabric is good. The anti-crease performance is also outstanding, and it is easily and quickly cleaned and dried. The Soyabean protein fiber (SPF) has good affinity to human skin. The natural colour of Soyabean fibre is light yellow, very like the colour of silk.  With good fastness to light and perspiration, it also has good dyeing brilliance and dyeing fastness in comparison with real silk products. Fabric from pure soyabean protein fibre (SPF) has got natural colour and pure with abundant fluff on the surface without pilling, excellent hand and drape and softness.

Blending of Soyabean fiber:

The development of textile process makes the Soyabean fiber able to be blended with any other fibers at any proportion, without problems in production. It can be easily blended as below

  1. Soyabean/ Cashmere blended fabric has natural softness and puff feeling like cashmere. It is suitable for cashmere sweater, shawl and coat.
  2.  Soyabean/Silk blended fabric has good luster, draping, sweat transfer properties. It is suitable for printing silk, knitting underwear, sleepwear, shirts and evening dress.
  3. Soyabean/ Wool blended fabric reduce the shrinkage of wool which is important for manufacturing & processing of sweater. It is suitable for wool sweater, interlock underwear and blanket.
  4. Soyabean/Cotton blended fabric has soft handle, good moisture absorption and better resistance to bacteria. It is suitable for men and women underwear, t-shirt, infant wear, towel and beddings.
  5. Soyabean/ Synthetic blended fabric has good wrinkle resistance .It is suitable for spring and summer fashion apparel, underwear, shirt and sportswear.
  6. Soyabean /lycra blended fabric- by adding a small portion of lycra the fabric becomes more elastic and easier for washing and caring. It is quite active and charming.

Chemical processing  of Soyabean  protein fiber:

Soyabean protein fiber (SPF) has different physical and chemical construction from natural protein fiber, care is taken in the following steps;

  1. Desizing:

In pretreatment of Soyabean fiber oil, lubricants and pigments and other additives, which are added in the production process, are removed. Desizing is  done by using   enzyme, alkali or oxidant desizing. Mercerization is avoided because Soyabean is unable to bear the strong caustic soda. The enzyme desizing  is done typically by using the following recipe:

Amylase enzyme 2-6 gpl.
Glauber Salt 2-3 gpl.
Wetting Agent 1 gpl .
Temperature 55 60 deg c.
Time 60 mins.

  1. Scouring & Bleaching :

The natural color of Soyabean is curcuma – it is difficult to remove Soyabean’s pigment therefore bleaching of Soyabean is done by any of the following three ways

a. Hydrogen peroxide bleaching.
b. Reduction bleaching.
c.  By using both .

Typical recipe for Hydrogen peroxide bleaching is as below:

Hydrogen Peroxide 20-40 gpl.
Soda Ash 3-5 gpl.
Wetting Agent 2-3 gpl.
Stabilizer 3-8 gpl.
pH 11
Temperature 92-95 deg c.
Time 60-80 mins.

Similarly  typical recipe for reduction bleaching is as below:

Rongolite 3-8 gpl.
Soda Ash 2-4 gpl.
Scouring Agent 1-2 gpl.
pH 11
Temperature 92-95 deg c .
Time 60-80 mins.

If required suitable optical brightener is also used.

  1. Dyeing:

Soyabean can be dyed using reactive, acid, basic and 1: 2 metal complex dyes.  Dyes are selected according to end uses of fibres and required fastness. In industry Soyabean fiber is dyed using vinyl sulphone and bifunctional type of reactive dyes . The dyeing method is just like dyeing of cotton and viscose with reactives.  It can be dyed in form of loose fiber, tops, yarn, hank and fabric. (both knitted and woven).

Uses of Soyabean   Protein Fiber (SPF):

The  fabric  made of  Soyabean  protein  fibre  shows the luster of real silk; its drapability  is also very  good, giving  people the  sense of elegance; the textile woven with  high count  yarn  has  fine  and clear grain, suitable  for high grade shell fabric for shirts . The knitting fabric which uses Soyabean protein fiber has a soft and smooth handle, and the texture is light and thin, with the sense of blending real silk and cashmere. With regard  to its  moisture absorption  and  discharge  performance, permeability performance, heat-retaining  performance  and spinning performance, this fibre is referred now as ‘a healthy and comfortable fiber in the 21st century.”

If anyone has any feedback or input regarding the published news, please contact: info@textiletoday.com.bd

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