Fiber Focus: Bamboo Yarn

Fiber Focus: The Good, The Bad, & The Eco… Bamboo
With the shine and shimmer of silk, but with a different touch, Bamboo is the new kid in fiber. First developed as a yarn (mixed with wool) patented in 1881 (1), bamboo stayed quiet in the fiber industry until it was “rediscovered” at Beijing University in the early 2000s (2). Since then, bamboo yarns began to pop up in indie dyers and commercial ventures alike. A recent trend towards the name Bamboo Viscose (or Viscose from Bamboo) reveals much about this fiber. Let’s dig deeper into bamboo to discover the good, the bad, and the eco!

The Good
Sourced from readily renewable bamboo plants, the question “is bamboo yarn eco” gets a hearty “yes” answer. This grass can grow “up to a yard a day” and is ready to harvest “in about four years.”(3) A forest of bamboo grass serves as a great carbon sink as this grass doesn’t require human intervention to regrow after harvest. Its anti-microbial properties serve as natural bug deterrents, so pesticides and herbicides are not required. (Sadly, that doesn’t stop all farmers from using them). When processed into yarn in the method of linen or hemp, the fiber retains the eco-value. “The mechanical way is by crushing the woody parts of the bamboo plant and then use natural enzymes to break the bamboo walls into a mushy mass so that the natural fibers can be mechanically combed out and spun into yarn… sometimes called bamboo linen.”(4) “Natural bamboo fiber would be recognizable as bamboo under microscope. Bamboo fiber produced by this process though considered eco-friendly is less used because it is time consuming, labor intensive, costly and serves a very specific niche of the textile market.”(5)

The Bad
Like all cellulose fibers, bamboo goes through a break down before it’s converted from pulp to fiber. It is this step where the “is bamboo yarn eco?” gets it’s biggest “no” response. These are called by several names – bamboo, bamboo viscose, bamboo rayon, rayon from bamboo, and viscose from bamboo yarns. Producing the fiber through viscose methodology is the most common way of converting bamboo to fiber. Two methods are the most popular; one is chemical intense and the other water intense. Thus both get a “bad” rating for different eco reasons.

The (chemical process/ rayon process) method essentially follows the same process as used to manufacture regenerated viscose rayon using hydrolysis alkalization with the multi-phase bleaching principle (Erdumlu and Ozipek 2008; Waite 2009; Ogunwusi 2013) and the process is as follows.
1. The bamboo culm is crushed into smaller fractions and soaked in a solution of 18 % NaOH at 20–25 °C for 1–3 h to form alkali cellulose.
2. The bamboo alkali cellulose is pressed to remove excess NaOH solution, crushed by a grinder and left to dry for 24 h.
3. In this stage, CS2 is added to the bamboo alkali cellulose to sulfurise the compound, causing it to jell.
4. The remaining CS2 is removed by evaporation due to decompression, resulting in sodium xanthogenate.
5. A diluted solution of NaOH is added to the cellulose sodium xanthogenate, which dissolve it into a viscose solution consisting of about 5 % NaOH and 7–15 % bamboo fiber cellulose.
6. The viscose solution is forced through spinneret nozzles into a larger container of diluted sulfuric acid (H2SO4) solution which, hardens the viscose and reconverts it to cellulose bamboo fiber which are spun into yarns (to be woven or knitted).
This process… produce regenerated bamboo fiber which is essentially a rayon fiber which is silky, strong and elegant but just like any other rayon, involves toxic chemicals and harmful byproducts. Unless methods are used to capture and recycle the caustic chemicals, harmful byproducts can be released into air and water.”(6)

(The Litrax/ Water method) It is made from bamboo using a high-tech process that includes opening up and refining the culm fiber cells through an enzyme process that separates longitudinal bamboo cells into textile fiber strands ready for further processing through carding and combing.
In order to turn bamboo into a fiber, the culm must first be crushed mechanically. The crushed bamboo strands are then treated with designed enzymes to separate the fibrous material from the glue-like lignin within the plant. This includes a series of precisely timed alternate steam-washing and enzyme treatment cycles, which also act on the vertical and horizontally aligned lignin of the resulting fiber bundles. The final step is to bleach the fibers with hydrogen peroxide. The resulting natural staple length varies between 70 and 150 mm, but can be cut to shorter lengths for processing, i.e. 50 or 38 mm staple. Litrax provides the LITRAX-1 (L1) natural bamboo fibers with a special DNA coding to protect its vertical supply chain and customers. The DNA coding will guarantee that customers are buying the original, authentic bamboo fiber from Litrax. The fiber is strong and durable.(7)

The Eco
For me, I’d love to see regulated labels to identify bamboo linen versus bamboo rayon versus bamboo LITRAX. It would solve a lot of the misinformation issues as well as enable consumers to accurately judge the eco value of the bamboo yarn they select. If bamboo rayon is the method used to create knitting yarn, again my preference for keeping it as eco as possible, is to use the water method, especially when responsible water recycling is implemented in the process! I’d definitely pop a water processed bamboo where the water is recycled sustainably back into “the Good”. However, since the supply chain between knitter and manufacturing is so distant, terminological regulation (by the US Federal Trade Commission) versus marketing pitches are in constant conflict, and the fact that manufacturing method is not readily available, it’s hard to ignore the probability that it was processed chemically rather than with water and enzymes.

A bit out of the scope of this article, but truly interesting subtopic, is the “anti-microbial” claim of bamboo fiber. To clear up the massive misinformation around the claims of bamboo being “anti-microbial,” I suggest reading the “Facts regarding the antimicrobial performance of bamboo fiber” section from “Prospect of bamboo as a renewable textile fiber, historical overview, labeling, controversies and regulation” paper by Lopamudra Nayak and Siba Prasad Mishra https://fashionandtextiles.springeropen.com/articles/10.1186/s40691-015-0054-5. To summarize, bamboo linen is anti-microbial. Yarns produced using the other methods vary in anti-microbial efficacy due to the chemicals used to process the raw material. While breaking the bamboo down, the chemicals also eat away at the naturally occurring anti-microbial attributes in the bamboo. And once gone, they don’t regenerate during the yarn creation process.

Working with Bamboo

Unfortunately, my experience with 100% bamboo is very limited. Early in my knitting years I found a 100% bamboo source, but it was milled in Italy and whatever they use there, regardless of the fiber, the migraine I got when I touched it seemed to be a constant (and that’s with any fiber milled in Italy… thus far). After 40 washes I finally was able to touch it without a resulting migraine. Yes, 40! I knit it up double stranded to mock a worsted weight. It is by far my favorite house sweater (pre-snuggly Puddly cuddly Great Dane, that is). It grows enormous when I wear it from the sheer weight of the garment. I wash and pop it in the dryer and it looks like it could fit a kid. Put it back on again and within hours it looks like a perfectly fitting sweater. A few days of wear later, and the growth is apparent as I swim through the sleeves to my knitting. That’s the useful take-away I have – bamboo GROWS with weight!!

The other brand of 100% bamboo served as a sample for Savvy hat. This particular fiber weave didn’t grow to the same degree, but then again it was a hat size item, not a double stranded full sweater. Also, the way the fiber was spun, in a chain like structure, helped to keep each fiber a bit short and in line. But, before I got to publication and the needed second skein to make a sample that fit, the company resourced to Turkey and added in so many scented products that after months of attempting to descent and not even making it to the washer stage, we ended up giving the yarn away. Sad, but true, my allergies do come first.

Most of my experience comes from organic cotton and bamboo blends. These bring together the best of both worlds and the positive characteristics of each fiber helps keep the negative characteristics in check. For instance, since organic cotton tends to grow wide and bamboo tends to grow long, they work with each other to help hold overall shape well. This full-size sweater, though it lacks cables, is wearing beautifully through the years without the need of washing to purposefully shrink back to size.

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Sources
1, 2, 5, 6, 7 https://fashionandtextiles.springeropen.com/articles/10.1186/s40691-015-0054-5
3, 4 https://organicclothing.blogs.com/my_weblog/2007/09/bamboo-facts-be.html