How does bamboo get turned into fabric?
Transforming bamboo into yarn can be done mechanically or chemically. Both processes are common to the processing of any viscose/cellulose based fabric, for example from wood pulp. The mechanical process has very little environmental impact and involves crushing the bamboo and then using natural enzymes to create the cellulose which can then be combed out and spun. The chemical process is more complicated with significant environmental issues based around the use of toxic chemicals.
The majority of bamboo fabric is processed chemically, to create what is known as a ‘reconstructed’ or ‘semi synthetic’ fabric. The bamboo is reduced down at a molecular level and then reformed in the following steps:
1) Bamboo leaves and the pith inside the ‘stalk’ are extracted using a steaming process and mechanically crushed.
2) The crushed bamboo is soaked in a sodium hydroxide solution at a 20-25ºC.
3) The resulting bamboo cellulose is forced through spinneret nozzles (like a sieve) into a diluted sulphuric acid bath that hardens the solution into viscose fibre threads that can then be spun into yarn and rolled onto spools.
What are the Pro’s and Con’s of bamboo fabric?
Even after dipping briefly into the subject, it is clear that many of the claims made about bamboo being a super-sustainable fabric are controversial to say the least. There are a lot of assumptions and ‘buts’ and ‘ifs’… However, here is a summary of bamboo’s best and worst from a sustainability perspective:
Bamboo is an extremely fast-growing, renewable material.
Yields per hectare are 10 times greater than cotton.
Bamboo thrives without needing pesticides or fertilisers.
Bamboo grows well with just rainwater and no additional irrigation is required, unlike cotton which requires 20,000 litres of water per kilogram.
As a grass Bamboo is self-propogating, so does not need replanting which helps save topsoil and energy.
Bamboo fabric requires less dye than conventional cotton.
Bamboo and fabrics derived from bamboo are biodegradable.
Bamboo is anti-microbial thanks to its magically named 'bamboo kun' (a naturally occurring bio-agent), although there are conflicting stances as to whether 'bamboo kun' is still present after chemical processing. It has also been said that the anti-bacterial property of chemically processed bamboo yarn is not unique but common to all viscose/cellulose based yarns. That said, it has better anti-bacterial performance than cotton.
Bamboo is fast becoming a cash crop with vast areas of land being given over to bamboo production, and where it is grown as a mono-crop biodiversity can be reduced. This in turn can lead to an increase in pests and the need for pesticides.
The vast majority of bamboo for fabric is grown in China, on privately owned and therefore unregulated land. This makes tracing and ensuring that bamboo is grown organically more difficult.
Chemical processing of Bamboo uses caustic soda (sodium hydroxide) and toxic bleaching agents such as chlorine, carbon disulfide, and sulfuric acid. If these chemicals are not handled responsibly they can be damaging to both the environment and to the factory workers.
So, is bamboo a sustainable fabric?
In short, yes. Bamboo is one of the most sustainable, fast-growing, organic crops on the planet. It wins hands down against cotton and polyester on that front. Unfortunately, its eco-credentials take a hit when it comes to the chemical processing. Yes, chemicals that can be harmful to humans and the environment are used BUT if the processing operates a closed loop system, whereby the chemicals are reused and/or made safe before being released into the environment, then the impact can be greatly reduced. Better still would be chemical free processing, an area in which developments are already being made. It is also important to note that many of these same chemicals are also used in the processing of cotton.
The current lack of regulations governing both growth and processing of bamboo has resulted in a lack of clarity and mis-reporting of facts about bamboo, which has helped to both elevate and undermine Bamboo as a sustainable fabric. It is possible to buy bamboo socks, underwear, t-shirts that have been made from organic bamboo manufactured using a closed loop or even chemical free process. Unfortunately, until regulations catch up, it is extremely difficult to trace the whole process. As consumers we can help too, by asking or checking for organic certification, closed loop or even chemical free processing. The goes for any textile we buy… not just bamboo. If you don’t ask (enough)… you don’t get!
The need for internationally recognised standards is paramount, long overdue and seems to be a wider issue within the textile industry as a whole. It is hindering efforts already being made to improve bamboo fabric production. For example, a Chinese factory has developed a water-based process. No chemicals. However, their process is more intensive and therefore more expensive than the chemical process. Certain international authorities do not recognise the difference between chemical and water based processing and will therefore not approve the fabric as ‘natural’. Without such a classification the fabric simply cannot compete in the market.
THE VISCOSE PROCESS
There is more than one way to make rayon. The most common way—and the one widely used for bamboo—is called the viscose process. In this process, cellulose material (such as bamboo) is dissolved in a strong solvent to make a thick, viscous solution that is forced through a spinneret into a quenching solution where strands solidify into fiber.
The dissolved bamboo material is forced through a spinneret where strands solidify into fiber.
This is sometimes called hydrolysis alkalization or solution spinning because the fiber is “spun” in a chemical solution. The solvent used for this process is carbon disulfide, a toxic chemical that is a known human reproductive hazard. It can endanger factory workers and pollute the environment via air emissions and wastewater.
The recovery of this solvent in most viscose factories is around 50 percent, which means that the other half goes into the environment. Other potentially hazardous chemicals are also used in the viscose process, including sodium hydroxide and sulfuric acid. Because of these environmental issues, Patagonia does not use rayon fabric or bamboo fabric made by the viscose process.