The bioeconomy at work: protein fibers from wheat gluten, similar to wool

Researchers from the University of Nebraska-Lincoln's Department of Textiles, Clothing & Design and from its Department of Biological Systems Engineering, have for the first time successfully produced protein fibers from 100% wheat gluten, with mechanical properties similar to those of wool and better than those of soyprotein and zein fibers. Wheat gluten is a low cost, abundantly available, and renewable resource suitable for bio-based fiber production. The green fibers may find applications in the textiles, biomedical and bioplastics industries and replace several categories of petroleum-based synthetic fibers.

Describing their simple production method in Biomacromolecules (open access article), Narendra Reddy and Yiqi Yang write that there is a long history of attempts to make natural cellulose fibers from lignocellulosic agricultural byproducts in an effort to add value to agricultural crops and to make the fiber industry more sustainable in the long run. Already during the 1930s and 1940s, efforts were made to use plant proteins such as soybeans, corn, and peanut and also milk proteins (casein) for fiber production. The higher cost, use of relatively environmentally unfriendly production processes, and inferior properties of the regenerated protein fibers as compared to those of the regenerated cellulose and synthetic fibers led to the abandoning of artificial protein fiber production.

Abundant feedstock, large market
However, the increasing use of cereal grains for biofuels and other industrial applications has led to the abundant availability of zein, soyprotein, and also wheat gluten as byproducts at low prices. Therefore, researchers have more recently attempted to produce fibers from zein, casein, and soyprotein and in addition from the blends of these proteins. Unfortunately, none of these attempts have been commercially successful to produce 100% protein fibers mainly due to the high cost and poor quality of the fibers. Reddy and Yang's wheat gluten fibers have now changed this situation.

Wheat gluten fibers would have a major cost advantage over both wool and silk, the two existing commercial natural protein fibers, according to the researchers. While wool sells for about US$5-8 per pound, and silk for US$10-$14 per pound, wheat gluten fetches less than 50 cents per pound and some 500,000 tons are available worldwide each year. This makes wheat gluten a cheap, abundant, and renewable source for producing protein fibers. In addition, wheat gluten has good stability to water and heat, excellent elasticity, and easy degradability, properties that are desirable for fibers. The annual world fiber market is about 67 million tons including about 2.3 million tons of the two natural protein fibers, wool and silk. Therefore, fibrous applications of the plant based material provide an opportunity for high value addition and offer a new, large market for consumption of wheat gluten:
biomass :: bioenergy :: biofuels :: energy :: sustainability :: wheat gluten :: fibers :: biomaterials :: bioeconomy ::

Although wheat gluten has previously not been used for fiber production, it has been used to produce bioplastics especially as films for food packing, as a binder for textile printing pastes, and as nanofibers via the electro-spinning process. The major limitations of the wheat gluten films are their relatively poor mechanical properties and higher cost as compared to those of the synthetic polymer-based films. Using wheat gluten as a binder is relatively expensive and also has limited market potential. This leaves the use of wheat gluten as a feedstock for biofibers.

The researchers developed a simple production method to obtain high-quality wheat gluten fibers, and the structure and properties of the fibers are promising. Wheat gluten fibers have breaking tenacity of about 115 MPa, breaking elongation of 23%, and a Young's modulus of 5 GPa, similar to those of wool. Wheat gluten fibers have better tensile properties than soyprotein- and casein-based biomaterials. In addition, the wheat gluten fibers have resistance similar to that of PLA (polylactic acid) fibers to water in weak alkaline and slightly lower resistance in weak acidic conditions at high temperatures.

In their paper, the authors discuss the method of producing 100% wheat gluten fibers, the effect of various production variables on the properties of the fibers, and the structure and properties of the fibers developed. The structure and properties of the fibers have been compared to the most common natural protein fiber, wool, and also to protein fibers produced from 100% zein and soyproteins.

They conclude that the protein fibers have mechanical properties similar to those of wool and better than those of 100% soyprotein and zein fibers have been produced successfully. They found that only a narrow range of concentration of wheat gluten, time, and temperature of aging is required to produce good quality fibers, and the properties of the fibers are improved by drawing and annealing. Although the fibers have low % crystallinity and poor orientation as compared to wool, they have good stability to weak acidic and weak alkaline conditions at high temperatures. The increasing availability of wheat gluten at low prices will provide an opportunity to develop cheap and environmentally friendly protein-based bioproducts. Wheat gluten fibers are suitable for biomedical applications because they have better properties than those of soyprotein-, zein-, and casein-based materials.


Image: Dyed Wheat Gluten Fibers, Courtesy of Yiqi Yang, Usage Restrictions: None.

More information:
Narendra Reddy and Yiqi Yang, "Novel Protein Fibers from Wheat Gluten", Biomacromolecules, Web Release Date: January 10, 2007; print release: February, 2007.