I've been mentally debating about doing this post for a long time... last time I did an honest environmental post about ten percent of my readers left. But, darn it, I'm a treehugger and I can't shut up about it. (FYI, much of this is cribbed from "The Intentional Spinner" by Judith MacKenzie McCuin. Only honest discussion of synthetics I've ever seen in a fiberhead book. I hit Wikipedia for chemical info; *quotes are from there.)
Below, find discussion on how a lot of synthetic fibers are made. Decide for yourself if you consider them eco-friendly 'green' knitting, or not.
TRUE SYNTHETICS (nylon, acrylic, polyester):
All made from petrochemicals. If not oil, than coal, tar, or natural gas. To my knowledge, it does not rot under normal conditions. Researchers appear to have found a way to make it break down, using a fungus. Polyester appears to be made out of the same plastic (PET, polyethylene terephthalate) that uses antimony (a heavy metal, similar to arsenic) in its processing; the web sites are rather vague.
REGENERATED CELLULOSE (rayon, viscose, bamboo, Lyocell, Tencel, SeaCell):
These are produced two ways: The Viscose Process (nearly everything), and the Lyocell Process (Lyocell, Tencel, and SeaCell).
VISCOSE PROCESS: this accounts for all the bamboo, rayon, modal, 'art silk', and viscose used in knitting yarns, that I know of.
This one's kind of interesting. You get some cellulose fiber (trees, bamboo, leaves, anything plant-like, really), and you 'digest' it. That means dissolving it in lye. (No one talks too much about what they do with the lye, later.) Then it's dried, re-crumbled, 'aged' by exposing it to oxygen, re-dissolved in carbon disulphide (a chemical that's an emission of volcanic eruption, and may be "...life-threatening because it affects the nervous system. Significant safety data come from the viscose rayon industry..."*) left to 'ripen', filtered and degassed, then extruded through something that looks like a fancy shower head, to form the fibers. The newly extruded fibers go into a bath of sulfuric acid to harden (no one talks too much about what they do with the acid, later), then further processed by stretching and washing and sometimes cutting.
There may be some more chemicals in there, but after the lye and carbon disulphide it gets kind of blurry.
LYOCELL PROCESS: this produces Lyocell (duh), Tencel, SeaCell, and probably some other fibers I don't know about.
Supposedly, this process is just like the Viscose Process, but they substitute another chemical for the lye (N-methylmorpholine-N-oxide, if you MUST know), and the hardening bath is water and alcohol rather than sulfuric acid. They claim to use low-emission mills that recycle chemicals and even water, and won an award for environmental consciousness in the EU. They try to use farmed trees for the process. Apparently, due to the different manufacturing process, the fiber is harder to dye and needs more chemical additives to avoid pilling. No word on what those chemical additives are.
REGENERATED PROTEIN (corn/Inego, milk/Casein, soy, and even peanut/Ardil) dunno if this is the proper term for them - probably not - but that's how I think of them:
SOY: It was developed in 1937, so anybody thinking it's a new idea can scuttle that notion. It has been redeveloped in China, since, using more chemicals (dunno what, but I'm suspicious) to make the soy more workable. Sulfuric and hydrochloric acids are used.
CASEIN: It takes a hundred pounds of milk to produce three pounds of casein fiber. This strikes me as wasteful but that's another issue for another day. Otherwise, the process is a mystery. Having read the soy process, I'm suspicious.
CORN: Also probably wasteful (grinding up unused wood scrap to make fiber makes more sense than grinding up perfectly good food/ethanol/animal fodder). "For Super-Hero Zein, see AK Comics."* Teeheehee.
CHITIN: This is the cool stuff made out of shrimp and lobster shells and like that. It's put in sock yarn for anti-fungal and anti-stink properties, and used to be used to make bandages (and may be used again).
It was developed in the 1800s, can you believe it? Sounds so clever and space-aged when really it was cooked up at the beginning of industrial chemistry. Chitin isn't protein OR cellulose so it really does get its own category. How it's made is something of a mystery (no one will tell), but it's a polymer that's somehow close to cellulose - they say - so I'm betting the process is pretty cool (and maybe polluting; don't know).
There you go. Make up your own minds.