SOYA PROTIEN FIBRES

BY NCFA TEAM

Fig.1: Soya Bean Seeds, products and Soya Fibre manufacturing Cycle

• Introduction

• Soya bean fibre (SPF) is a natural regenerated protein fibre that is obtained from soya bean waste or residue.
• The fibres utilise the waste produced by the agro-industry and are by-products produced during soy oil extraction and soy food products like tofu.
• China is the largest producer of soy fibres. Soybean is believed to have first originated around 4000-5000 years ago in China.
• Soybean is mainly cultivated for the food industry as a source of edible oil and protein.
• Soya fibre has an incredibly soft texture and is often compared to silk – some might even know it under the name of “soy silk”. 
• The Initial attempts to manufacture textile fibres from soybean protein were carried out in Japan and U.S.A.
•  Soy fabric’s cost is generally comparable to low-priced synthetic and natural textiles such as cotton and polyester. The novelty of the bean structure may drive the price of this textile material to the higher side. Additionally, the cost of producing the bean structure is much higher than manufacturing similar natural and artificial fibres. However, with technological advancements in the field of textile manufacturing, the prices are expected to come down.
• Different Types of Soya Fibres- Fabrics: Broadly three types of fibres are available in the market.
• Pure Soya Fibre- Fabric: Soy fabric created from processed soy protein is shiny, breathable, and stretchy. However, it is not suitable for the dyeing process, and it is not durable.
• Soy-Cotton Fibre-Fabric: Various manufacturers blend soy fibre with cotton to enhance its durability. Blended soy cotton retains a silk-like shine along with cotton-like strength. 
• Soy-Wool Fibre Fabric: Soy wool fabric is a less popular textile though it was a popular combination during the mid-twentieth century. It retains the smoothness and elasticity of soy fabrics. 

• Morphology 

• Soybean fibre is a man-made regenerated protein fibre from soybean protein blended with PVA (Polyvinyl alcohol).
• Polyvinyl alcohol is used to improve the strength of soy fibre.
• Soy fabric is the most eco-friendly fabric, with the quality being soft.
•  It is also known as “vegetable cashmere”. 
• Outfits made from soy fabrics give excellent drapes and are highly elastic. 
• Soybean fibres have a cream colour, and their diameter is around 20 μm. 
• Scanning Electron Microscopic (SEM) view of soybean fibre indicates longitudinal striations on the surface parallel to the axis, varying in length and depth.
• SEM micrographs of the cross-section of soybean fibre showed a kidney bean-like cross-sectional shape. However, the transverse cross-section depends on the shape of the spinneret
• The most important proteins in soybeans are globulins.

3. Manufacturing Process of Soybean Fibre 

• Pretreatment and Preparation of the Soy material/bean for fibre manufacture

Soybean is the raw material used for oil and soy meal manufacture. Therefore, the process of getting the waste/by-product involves the extraction of oil and extraction of protein. Extraction of oil involves cleaning of beans followed by decortication and dehulling which removes the outer cover of the beans. Extraction of protein involves treatment of the solid extract with dilute alkali (1% sodium sulphate and ammonium sulphate) in water for 1 hour thereby facilitating the base material preparation for spinning of the fibres by wet spinning process. Recent research on the cross-section of soybeans correlates well with the previous finding indicating kidney form shape. Studies on cross-sectional shapes of wet-spun fibres have been associated with the coagulation rate with the cross-section. It is suggested that non-circular cross-sections occur due to high coagulation rate in wet spinning

• Soya fibre is a reproducible plant protein fibre. To begin with, the oil is extracted from soybean, and then a high polymer residual cake is found. Using the residual cake, a spinning solution of a certain concentration is prepared, and a filament bundle of a single fibre is spun from the solution by the wet spinning method. The fibre performance is stabilised through hydroformylation during coagulation and then it undergoes winding, heat setting and cutting. In this way, soybean fibres of various lengths and specifications for spinning can be produced. Soybean protein is a globular protein in its native stage and is not suitable for spinning. Therefore, it must undergo denaturation and degradation to convert the protein solution into a spinnable dope (Fig. 2).

                 

                        Fig 2: Typical Flow Chart of the Manufacture of Soybean fibre

• Coagulation Bath (Fig.2)

The solution consisting of soybean and PVA is filtered and forced through the spinneret where orientation of the molecular chains occurs. The chain of molecules- polymer chains are then arranged into a structure consisting of crystalline regions and amorphous regions. The orientation of molecules is highly maintained in the two consecutive coagulation baths of sodium sulphate and ammonium sulphate in water with 1M. sulphuric acid. The temperature of the initial and last coagulation baths is maintained at 50 to 700 C, respectively, based on the spinning condition of PVA. The cross-section of fibre produced is dependent on the coagulation rate and the blend of soybean /PVA used apart from the dimensions of the spinneret.                                                           

• Cross Linking (Fig.3)

This is the next processing step followed to enhance the mechanical properties. After winding fibres from the coagulation bath, the fibre is passed into a crosslinking bath that contains formaldehyde. Formaldehyde was one of the first crosslinking agents used with protein. It is known that formaldehyde can react with amine, amino, guanidyl, hydroxyl, phenolic and indole groups and reduce disulphide

• Washing, Drying, Drawing (Fig.2)

In the final stages of production, the fibres are washed, dried and subsequently drawn to enhance their tensile properties.

Fig.3: Types of structures and bonds in the manufacture of Soybean Protein Fibre

• Chemical Properties of Soy Fibres

The amino acid composition of the soy protein fibres is given in Table 1.

Table 1: Amino Acid Composition of Soya Fibres

Amino Acid	Soybean Fibres	Nature of the side chain
Glycine	8.8	Hydrocarbon
Alanine	7.5
Phenylalanine	4.4
Valine	6.3
Leucine	9.8
Isoleucine	4.8
Serine	6.4	Polar
Threonine	4.3
Tyrosine	—
Aspartic acid	12.8	Acidic
Glutamic acid	18.2
Histidine	5.5	Basic
Arginine	0.8
Lysine	3.9
Methionine	0.8	Sulphur-Containing
Cystine	0.1
Tryptophan	—	Heterocyclic
Proline	5.6

• Physical Properties of Soy Bean Fibres

Typical physical properties of the soybean fibres are given in Table 2.

Table 2: Typical Physical Properties of Soya Bean Fibres

Sl. No	Properties	Unit	Values
1	Tenacity	cN/tex	7.0
2	Elongation(dry)	%	50.0
3	Specific gravity	g/cc	Nd
4	Moisture Regain	%	11
5	Effect of temperature	o C	Nd
6	U.V Resistances	_	Good
7	Resistances to Moth /Fungus	–	Good
8	Dry Breaking Extension	%	18-21
9	Loop Strength	%	75 – 85
10	Knot strength	%	85

• Features of Soy Bean Protein Fibres

• Lustre: The soya bean protein fibre is lustrous like silk.
• Drapeability -This fibre also has an excellent drape ability.
• Comfort -This fibre has a soft, smooth, and light handle, which is the same as the fabric made of silk blended with cashmere. Soya fibre has the same absorption as that of cotton and better moisture transmission that of cotton. 
• Absorbency – soy fabrics have a better moisture transmission in comparison to cotton.         
• Strength – It has a great breaking strength in comparison to wool, silk, and cotton.
• Shrinkage – Under the effect of hot water, soy fabric does not shrink.
• Easy-Care -Soy fabric is crease-resistant and easy to wash.
• The fibre is known for its soft feel, breathability and comfort but has quite low strength as a result they are not commercially popular. The soy fibres are often blended with silk, cotton, cashmere, Lycra, and other synthetic fibres to enhance their properties.

• Uses and Application of Soy fibre-based Fabric  

            Clothing: dresses, tank-top, skirts, underwear, sleepwear, sportswear, children’s          

            & infants’ clothes, etc.          

          Home – furnishing -Upholstery, towels, Bedding, etc

Bibliography

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