Fibers are divided into three main categories:
- Natural – like flax, wool, silk and cotton
- Manufactured – made from cellulose or protein
- Synthetic – made from synthetic chemicals
The difference between “manufactured” and “synthetic” fibers is that the manufactured fibers are derived from naturally-occurring cellulose or protein, while synthetic fibers are not. And manufactured fibers are unlike natural fibers because they require extensive processing (or at least more than is required by natural fibers) to become the finished product. The category of “manufactured” fibers is often called “regenerated cellulose” fibers. Cellulose is a carbohydrate and the chief component in the walls of plants.
Rayon is the oldest manufactured fiber, having been in production since the 1880s in France, where it was originally developed as a cheap alternative to silk. Most rayon production begins with wood pulp, though any plant material with long molecular chains is suitable.
There are several chemical and manufacturing techniques to make rayon, but the most common method is known as the viscose process. In the viscose process, cellulose is treated with caustic soda (aka: sodium hydroxide) and carbon disulfide, converting it into a gold, highly viscous liquid about the color and consistency of honey. This substance gives its name to the manufacturing process, called the viscose process.
The viscous fluid is allowed to age, breaking down the cellulose structures further to produce an even slurry, and is then filtered to remove impurities. Then the mixture is forced through fine holes, called a spinerette, directly into a chemical bath where it hardens into fine strands. When washed and bleached these strands become rayon yarn.
Although the viscose process of making rayon from wood or cotton has been around for a long time, it wasn’t until 2003 that a method was devised for using bamboo for this process.(3) Suddenly, bamboo was the darling of marketers, and the FTC had to step in to remind manufacturers to label their products as “bamboo viscose” rather than simply bamboo.
Now we hear about fabrics made from eucalyptus, or soy. But it’s the same story – the fibers are created using the viscose process. Because the FTC did not specifically name these two substances in their proclamation regarding bamboo, marketers can claim fabrics are “made from eucalyptus”. The reality is that the viscose process can produce fibers from any cellulose or protein source – chicken feathers, milk and even bacteria have been used (rayon comes specifically from wood or cotton). But those inputs are not nearly as exciting to the marketers as eucalyptus or soy, so nobody has been advertising fibers made from bacteria.
After the brouhaha about bamboo viscose hit the press, many people did a quick scan of viscose and declared it “unsafe” for the environment. The reason the viscose process is thought to be detrimental to the environment is based on the process chemicals used. Though sodium hydroxide is routinely used in the processing of organic cotton, and is approved by the Global Organic Textile Standard (GOTS), carbon disulfide can cause nervous system damage with chronic exposure. And that “chemical bath” to harden the threads? Sulfuric acid. But these chemicals do not remain as a residue on the fibers – the proof of this is that almost all of the viscose produced can be (and often is) Oeko Tex certified (which certifies that the finished fiber has been tested for any chemicals which may be harmful to a person’s health and contains no trace of these chemicals.)
The environmental burden comes in disposing of these process chemicals: the sodium hydroxide (though not harmful to humans) is nevertheless harmful to the environment if dumped into our rivers as untreated effluent. Same with carbon disulfide and, certainly, sulfuric acid. And there are emissions of these chemicals as well, which contribute to greenhouse gasses. And the reason that these fibers can be Oeko Tex certified: Oeko Tex certifies only the final product, i.e.,the fibers or the fabric. They do not look at the production process, which is where the majority of the environmental burden is found. And then of course there is the weaving of these viscose fibers into fabric – if done conventionally, the environmental burden is devastating (in terms of chemical and water use) and the fabric itself probably contains many chemicals known to be harmful to our health.
Certainly the standard viscose production process is definitely NOT environmentally friendly, but then there is Tencel ® and Modal ®. These fibers are manufactured by the Austrian company Lenzing, which advertises its environmentally friendly production processes, based on closed loop systems. Lyocell is the generic name for the fibers produced by Lenzing, which are not produced by the traditional viscose process but rather by solvent spinning.
According to Lenzing:
- There is an almost complete recovery of the solvent, which both minimizes emissions and conserves resources. Lenzing uses a new non-toxic solvent (amine oxide) and the cellulose is dissolved in N-Methylmorpholine N-oxide rather than sulfuric acid. Water is also evaporated, and the resulting solution filtered and extruded as filaments through spinnerets into an aqueous bath. Over 99% of the solvent can washed from the fiber and purified for re-use. The water is also recycled.
- The by products of production, such as acetic acid, xylose and sodium sulphate are key ingredients in the food and glass industry. Remaining materials are used as energy for the Lenzing process.
- Tencel ® is made from eucalyptus, which is grown on marginal land unsuitable for food crops; these trees are grown with a minimum of water and are grown using sustainable forestry initiatives.
- The final fibers are biodegradable and can decompose in soil burial or in waste water treatment plants.
So Lenzing fibers can be considered a good choice if you’re looking for a sustainable fiber – in fact there is a movement to have Lenzing Tencel® eligible for GOTS certification, which we support, because the production of these fibers conforms with the spirit of GOTS. They already have the EU Flower certification.
But Lenzing does not make fabrics – it sells yarns to mills and others which use the yarns to make fabric and other goods.
So we’re back to the beginning again, because people totally forget about the environmental impact in the weaving of fibers into fabric, where the water and chemical use is very high – if done conventionally, the environmental burden is devastating and the finished fabric itself probably contains many chemicals which are outlawed in other products.
It’s critically important to look at both the fiber as well as the weaving in order to make a good choice.