A new technique creates high-quality fibers from gelatin—which can then be spun into yarn and turned into textiles, such as mittens.
Gelatin consists chiefly of collagen, a main component of skin, bone, and tendons. Large quantities of collagen are found in slaughterhouse waste and can be easily made into gelatin.
That’s why Professor Wendelin Stark and PhD student Philipp Stössel of ETH Zurich’s Functional Materials Laboratory (FML) decided to use the biomaterial for their work.
In his experiments, Stössel noticed that when he added an organic solvent (isopropyl) to a heated, aqueous gelatin solution, the protein precipitated at the bottom of the vessel. He removed the formless mass using a pipette and was able to effortlessly press an elastic, endless thread from it. This was the starting point for his unusual research work.
As part of his dissertation, Stössel developed and refined the method, which he has just recently presented in the journal Biomacromolecules.
656 feet a minute
The refined method replaces the pipette with several syringe drivers in a parallel arrangement. Using an even application of pressure, the syringes push out fine endless filaments, which are guided over two Teflon-coated rolls. The rolls are kept constantly moist in an ethanol bath; this prevents the filaments from sticking together and allows them to harden quickly before they are rolled onto a conveyor belt.
Using the spinning machine he developed, Stössel was able to produce 200 meters (656 feet) of filaments a minute. He then twisted around 1,000 individual filaments into a yarn with a hand spindle and had a glove knitted from the yarn as a showpiece.
Extremely fine, the individual fibers have a diameter of only 25 micrometers, roughly half the thickness of a human hair. With his first laboratory spinning machines, the fiber thickness was 100 micrometers, Stössel recalls. That was too thick for yarn production.
Whereas natural wool fibers have tiny scales, the surface of the gelatin fibers is smooth. “As a result, they have an attractive luster,” Stössel says. Moreover, the interior of the fibers is filled with cavities, as shown by the researchers’ electron microscope images. This might also be the reason for the gelatin yarn’s good insulation, which Stössel was able to measure in comparison with a glove made of merino wool.
Gelatin yarn with wool grease
Gelatin’s major drawback is that it its water-solubility. Stössel had to greatly improve the water resistance of the gelatin yarn through various chemical processing stages.
First he treated the glove with an epoxy in order to bond the gelatin components more firmly together. Next, he treated the material with formaldehyde so that it would harden better. Finally, he impregnated the yarn with lanolin, a natural wool grease, to make it supple.
As he completes his dissertation over the coming months, Stössel will research how to make the gelatin fibers even more water-resistant. Sheep’s wool is still superior to the gelatin yarn in this respect. However, Stössel is convinced that he is very close to his ultimate goal: making a biopolymer fiber from a waste product.
Growing demand for natural fibers
Roughly 77 million tons of fibers are worldwide every year. Synthetic fibers manufactured from products of petroleum or natural gas account for almost two-thirds of this total. The most commonly used natural fibers are wool and cotton, but they have lost ground against synthetic fibers.
Despite their environmental friendliness, fibers made of biopolymers from plant or animal origin remain very much a niche product. At the end of the 19th century, there were already attempts to refine proteins into textiles. For example, a patent for textiles made of gelatin was filed in 1894. After the World War II, however, the emerging synthetic fibers drove biological protein fibers swiftly and thoroughly from the market.
Over the past few years, there has been increased demand for natural fibers produced from renewable resources using environmentally friendly methods. Wool fiber in particular has experienced a renaissance in performance sportswear made of merino wool. And a few years ago, a young entrepreneur in Germany started making high-quality textiles from the milk protein casein.
Three years ago, the researchers applied for a patent on their invention. Stössel explains that they have reached the point where their capacity in the laboratory is at its limit, but commercial production will only be possible if they can find partners and funding.
The method was developed in cooperation with the Advanced Fibers Laboratory at Empa St. Gallen. Earlier research from the project appears in Macromolecular Materials and Engineering.
Source: ETH Zurich