Name: kathryn

Message: Hello,
I am presently interested in understanding how the acetylating process makes bamboo into a yarn-worthy fiber and also how soy protein is altered to make into yarn. Jan thinks you can help me in this area. I'd appreciate any input you'd like to share.

I had not heard of the acetylating of bamboo fiber until now. Most bamboo fiber is a form of rayon, as far as I have been able to find out. Rayon is a regenerated cellulose fiber which can be dyed like any other cellulose fiber, such as cotton. When rayon is acetylated, it turns into rayon acetate, also known as acetate, a fiber which no longer has the comfortable natural characteristics and easy dyeability of rayon. 

Apparently a small fraction of the available bamboo fiber on the market is prepared using enzymes to digest the plant and separate the fibers, in a way that retains the original cellulose fibers of the bamboo plants, much as cotton retains the original fiber length and other characteristics produced by the cotton plant. However, most commercially available bamboo fiber is a chemically regenerated cellulose and thus similar to any other rayon. The chemical processing requires sodium hydroxide and carbon disulfide. 

It is clear that regenerated cellulose from bamboo can be subjected to the same acetylation processes used to produce rayon acetate from other sources of cellulose. I do not know how large the amounts of bamboo acetate actually being produced might be. The chemicals used in this process are acetic anhydride, acetic acid, and sulfuric acid. An excellent article on the bamboo fiber industry is available at the the Organic_Clothing blog, dated September 27, 2007.

I would not want to buy bamboo acetate yarn, myself, because I don't like rayon acetate in general. It can't be dyed except with the same special dyes that are required for polyester, and it does not absorb moisture for comfort in the way that rayon does. That said, as a predyed synthetic yarn, bamboo acetate may be desirable in other ways. The texture is likely to be quite different, smoother and silkier, I would guess.

The bamboo top fiber that I purchased from Mielke's Fiber Arts dyes marvelously, like other (nonacetylated) rayons, and has very long fibers. It seems strong. It can be dyed with any dye that works on cotton, and takes cool water fiber reactive dye very well. I don't know whether it is the regenerated cellulose or the rarer natural bamboo fiber that is not regenerated chemically. What I have heard about purchased garments made with bamboo is that they do not wear well at all; this is typical of rayon fabrics. Rayons in general are very weak when wet and are therefore subject to wear during laundering. (Tencel, a trade name for lyocell, which is another cellulose fiber regenerated by a different chemical process, is supposed to wear better due to greater wet strength, but my experience with readymade Tencel clothing was that it showed wear long before cotton garments of the same age, in spite of the care I took in laundering.)

I have an excellent 1995 book called "Cellulosics Dyeing", edited by John Shore, which I mail-ordered from the Society of Dyers and Colourists in the UK for £9 (used copies of this book sold in the US tend to be hugely overpriced). It gives a brief (two-page) description of the aceylation of regenerated cellulose to make acetate. Here is an excerpt:

The chapter goes on to explain that the technology of viscose production is too complicated to be discussed in that book.

As far as soy protein fiber is concerned, I found it to be a little more difficult to dye than other protein fibers, that is, the same concentration of the same acid dye produced a much lighter color on the Soy Silk® unspun fiber that I purchased than it did on some real silk top that I dyed for comparison. The Silk Latte® azlon fiber made from milk was similar ("azlon" is the generic term for any regenerated protein textile fiber). They both felt lovely, but were inferior for dyeing purposes. I don't know whether this is because of the different amino acid profile of the proteins used to make the fibers, or whether it has to do with the texture or any chemical or physical treatments that may have been applied in processing.

I have seen many claims about how environmentally friendly the soy silk manufacturing process is. Unfortunately, I have seen plenty of similar claims made for regenerated cellulose bamboo (for example) which are clearly not at all true, so it is difficult to know what to believe. One site after another blithely claims that "the soy protein is liquefied then extruded into fiber in a chemical free process." In fact, it appears that acetylizing may be an important part of this process, and that the fiber may be a byproduct of the soybean oil industry, rather than the tofu industry as is so ubiquitously claimed; this is logical given that the soy oil industry in the US is vastly larger than the tofu industry here. The best source of information I've been able to find on soy protein textile fibers is at the website of a Swiss company, Swicofil AG Textile Services.
It says, 

However, I cannot tell how closely this description may apply to the fiber sold under the brand name Soy Silk®. I cannot even determine which country the Soy Silk® fiber is manufactured in. Can you? That might be a very useful clue. China seems likely, since so much textile material is coming from China these days.


The owner of the soysilk website, SWTC, Southwest Trading Company, claims that Ingeo® corn fiber can be dyed successfully with Rit® All Purpose Dye. This further casts their credibility into doubt.  Ingeo®, a brand name for polylactic acid, is said by industry sources to be dyeable only with disperse dyes, the special kind of dyes manufactured for use on polyester, acetate, and other synthetic fibers. Rit® is an all-purpose dye, which means that it is a blend of direct dye for cellulose fibers and acid dye for protein fibers. I myself did not test Rit dye on Ingeo, but I did try one acid dye and one fiber reactive dye. Both left the fiber completely white after rinsing. I suspect that the particular Rit dye color that Southwest Trading Company used may have temporarily stained the Ingeo fiber, but I very much doubt that it would stand up to laundering.


(Please help support this web site. Thank you.)