Soybean Protein Fibers: Properties, Manufacturing and Uses

What are Soybean Protein Fibers (SPF)?

Soybean protein fiber (SPF), sometimes called “soy silk”. It is a regenerated protein fiber with good physical properties that are good for human health. Soybean fiber derived partially from the soybean residue during the production of soybean oil and combined with a polyvinyl alcohol substance, the predominant component. While soybean‐regenerated fibers have high protein content, 40%, compared with other protein regenerated fibers, it is, nevertheless, predominantly a fiber manufactured by extrusion through the spinneret method. Soybean fibers were given a trademark name Soy Silk® (by the Southwest Trading Company, Phoenix, Arizona) because of the silky texture of the fibers. Under the microscope, the cross‐section of soybean protein fibers is bean‐shaped.

Soybean protein fibers are blended with other fibers, such as with wool, cashmere, cotton, polyester and viscose, which extends their range of properties for other applications in apparel. Soybean fiber is relatively modern fiber offers a compelling blend of eco-friendliness, luxurious feel, and functional properties, positioning it as an exciting and sustainable option in the textile industry.

Overall, the fibers are smooth, resulting in the silky surface of fibers. However, the fibers have irregular grooves and wrinkles. These grooves will enable moisture movement along fibers. Fibers appear to have a ribbon‐like characteristic, usually seen in cotton fibers, and appear to be flattened, as is consistent with the fiber’s bean‐like cross‐sectional shape. They also have pronounced and elongated air‐bubble inclusions. It is interesting to note that corn fibers’ shape under a microscope is somewhat similar to Soy Silk fibers’, especially in cross‐section. Soybean fibers have a soft hand and are comfortable to wear. The soybean substance gives the fibers a natural antibacterial property, similar to that of regenerated cellulosic bamboo fibers. Because soybean protein fibers have a lower moisture absorption compared with regenerated cellulosic fibers, they may not be as comfortable as cellulosic regenerated fibers.

Soy isolates obtained from processing soybeans have also been used to produce fibers. The Ford motor company was probably the first to develop protein fibers from soy isolates as early as 1935. More recently, researchers at the Center for Crops Utilization Research at the Iowa State University have reported the properties of 100% SPF produced by extrusion and also by wet spinning. However, the process developed at the Iowa State University uses sodium hydroxide for dissolving the protein. Using an alkali such as sodium hydroxide hydrolyzes the proteins and reduces the degree of polymerization (DP) of the proteins.

Soybean fibers have been used for medical purposes and in baby clothing such as diapers. Multiaxial warp knitting fabrics using soybean fibers have been reported as an alternative to classic medical bandages.

Properties of Soybean Protein Fibers:

Soybean protein fibers possess remarkable properties that make them suitable for a wide variety of textile applications. The properties of SoysilkR (from soybean protein) are given in below Table.

Table: Properties of (Soy Silk®) soybean protein fibers

Interest in the fiber centres round the fact that they are produced from a renewable resource, by an eco-friendly process and are biodegradable. The fibers have a light yellow color but can be bleached to give a better quality of white. They are stable to exposure to UV light and have a good light fastness generally, but are not particularly stable to dry heat, turning a yellow color at over 120 °C.

The fibers are claimed to have a cashmere-like handle, indeed some marketing refers to them as ‘artificial cashmere’. They also have the lustrous appearance of silk. They are claimed to have anti-bacterial properties making them suitable for underwear and summer wear, as well as sportswear and sweaters. They are used in the manufacture of home textiles, such as towels, bed linen, duvets and pillows. The fibers are also used for the manufacture of soft toys and for hand-knitting yarns.

Manufacturing Process of Soybean Protein Fibers

Soybean protein fibers (SPF) are manufactured fibers, produced from regenerated soya Glycine max soybean proteins in combination with synthetic polymer (polyvinyl alcohol) as a predominant component. Unlike natural fibers like cotton or wool, or synthetic fibers like polyester or nylon, SPF is manufactured from globular proteins extracted from soybean cake, a byproduct of soybean oil production. The main component of soybean fiber is it possesses the superiorities of many natural fibers and synthesized ones and it is quite similar to those of cashmere and silk, featuring fine denier, low density, and good

tenacity and elongation. Soybean protein fiber is rarely used alone. It’s often blended with other fibers—such as cotton, wool, silk, or cashmere—to combine its softness and luster with the strength, elasticity, or cost-effectiveness of the other components. The manufacturing process of soybean fiber is presented in below Figure.

Five main production stages can be identified:

1. Separation: “Clarifying” the soya bean meal and precipitating out the protein.
2. Solubilization: Dissolving the resulting washed and dried curd to form the “spinning” solution.
3. Hardening: Forcing this solution, when sufficiently ripened, through spinnerets into a coagulating bath resulting in the formation of fibers.
4. Insolubilizing: Stretching and hardening this fibers, often using formaldehyde.
5. Controlled washing and drying followed by cutting into staple lengths.

Pure (100%) soy protein fibers were developed and used for tissue engineering and controlled drug release applications. Soy proteins (26%) were dissolved in 8M urea and 1% sodium sulfite, and the solution was aged up to 96 h. After aging, the solution was extruded into a coagulation bath consisting of 10% acid and 10% sodium sulfate using a syringe and needle. Fibers obtained were drawn and annealed to improve tensile properties. Recently, protein fibers produced from soy isolates generally called SPF are reportedly available on the market. However, the SPFs currently available on the market are not 100% SPF but are a blend of about 45% soy proteins and another synthetic polymer.

Uses of Soybean Protein Fibers

Soybean protein fiber is gaining popularity in eco-textiles due to its sustainability and comfort.

1. Apparel: Used for making children’s wear, underwear, T-shirts, sportswear, and high-end fashion garments because of its softness and moisture management.
2. Home Textiles: The cashmere-like feel of the fiber lends itself well to luxurious bed sheets, pillow covers, towels, and curtains to enhance comfort and antibacterial performance.
3. Nonwoven and Medical Textiles: Beyond fashion, soybean fiber is used in filtration textiles. Used in biodegradable sanitary products, bandages, and eco-friendly wipes.

Conclusion

Soybean protein fiber is a promising, sustainable innovation in the textile industry. Their softness, comfort, luster, and health benefits make them highly desirable for apparel and home textiles. As demand grows for sustainable, biodegradable and skin-friendly textiles, soybean fiber is set to play an increasingly important role in the global fiber market.

References

[1] Karthik, T., Rathinamoorthy, R. (2019). Sustainable Biopolymers in Textiles: An Overview. In: Martínez, L., Kharissova, O., Kharisov, B. (eds) Handbook of Ecomaterials. Springer, Cham. https://doi.org/10.1007/978-3-319-68255-6_53

[2] Veit, D. (2023). Fibers: History, Production, Properties, Market. Springer Nature.

[3] Maher, R. R., & Wardman, R. H. (2015). The Chemistry of Textile fibers, 2nd Edition. Royal Society of Chemistry.

[4] Ahmad, S., Rasheed, A., & Nawab, Y. (2020). Fibers for technical textiles. In Topics in mining, metallurgy and materials engineering. https://doi.org/10.1007/978-3-030-49224-3

Mazharul Islam Kiron

Founder & Editor of Textile Learner. He is a Textile Consultant, Blogger & Entrepreneur. Mr. Kiron is working as a textile consultant in several local and international companies. He is also a contributor of Wikipedia.

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