The “On habitats” series is designed to help me (us) take a moment and reflect on where the fiber in our yarn comes from. Part One of this series looked at Natural Plant Fibers, Part two: Synthetic Plant Fibers took a look at tencel, bamboo and corn. We’ll finish off synthetic plant fibers this week with soy, rayon, and modal.
Soy: According to Interweave, the first time soy was used as a textile was in the 1930s, when Henry Ford produced car-seat upholstery by blending soybean and sheep’s wool. Soybeans have a high protein content and are currently being produced in large quantities by the United States and China.
There are five main steps to creating soybean fiber, the first being the extraction of oil. Soybeans are cleaned, cracked, decorticated and dehulled before being conditioned and steeped in hexane. The hexane solution collects the oil, which can be extracted and reused. The soybean is then passed through a steam pipe to be rinsed of the solvent.
Next, the soybean is soaked in a 1% sodium sulfite solution for around an hour then filtered. This results in a creamy-white powder that is then dissolved into an alkaline solution. This solution is then allowed to age until it develops the proper consistency for spinning. The fiber is then formed by wet spinning or forcing the spinning solution through a spinneret.
Finally, the fibers are treated to baths that help it develop stretching and hardening properties. From here, the fiber can be blended and dyed.
This process doesn’t appear too bad, until you begin to look into the beans themselves. According to the World Wildlife Foundation, the soybean industry is causing widespread deforestation and displacement. Many are calling for transparent land use and an increase in proper safeguards, but until those come to pass this may not be the best yarn for an environmentally focused individual.
Rayon: Rayon has an interesting history as an alternative to silk starting in the 1860s when the French silk industry was threatened by a disease affecting the silkworm. In 1885, Count Hilaire de Chardonnet patented the first successful process of creating a silk-like fiber from cellulose and is considered the father of rayon (despite more cost-effective ways of being created nowadays).
The major sources of the cellulose used for creating rayon include pine, spruce, hemlock, and cotton linters (residue fibers which clung to cotton seeds after the ginning process). Regardless of whether wood pulp or cotton linters are used, the materials must be processed to extract/purify the cellulose. This results in sheets that are steeped in sodium hydroxide, dried, shredded into crumbs and aged in metal containers for 2-3 days.
Next, the crumbs are combined and churned with liquid carbon disulfide and then bathed in sodium hydroxide again. The honey-like solution (look and feel) then has any dyes or delusterants added before being filtered and stored to age (4-5 days).
After aging, the solution is forced through a spinneret and into an acid bath. Once bathed in acid, the fiber can be spun into yarn.
Unfortunately, the chemical by-products of rayon have received a lot of attention as they generate a lot of water and air emissions (the worst being zinc and hydrogen sulfide). Producers are currently trying different techniques to reduce pollution, and as the demand for rayon grows so does the demand for new technologies that make rayon better and cheaper.
Modal: Modal comes from pure beech tree chips and is more or less a variety of rayon. The main difference between modal and rayon is that rayon can be made of variety or materials, while modal is only made from beech trees.
In other words, modal is made using the same process as rayon and has the same concerns. That being said, like rayon steps are being taken to make the process better and cleaner.
Main Takeaways: I think the main thing I’ve taken away from my readings on synthetic fibers is that there is no way to make them perfect. Even if the process to make the fiber is sustainable, the farming technique often isn’t (although the same can be said about cotton, which is not synthetic). All in all, I’m not sure there are many changes that I will make to my knitting — as I work mostly with animal fibers — but the curiosity around using bamboo yarn is no longer there. As this project continues, it will be interesting to learn about how chemicals are sneaking their way into my knitting. I may end up breaking my spinning wheel back out and going straight to the sheep! Or at least upping my yarn snobbery to organic yarns, depending on what I learn about man-made synthetics and animal fibers.