Material series part III: the facts about bamboo
Updated: Jan 29, 2020
Let’s talk bamboo! There are a lot of beautiful products that can be made of bamboo; think floors, kitchen utensils, toothbrushes, tables, watches, glasses, chairs, toys, paper and also textiles, clothing, towels... And it is exactly the textile part I would like to explore more in this article.
Bamboo fabric has some beautiful qualities: soft, smooth, it flows, natural material, natural sheen, hypoallergenic, anti-bacterial, highly absorbent, breathable and generally less expensive than materials such as silk or cashmere. It has gained popularity over the last years and generally has a good reputation when it comes to sustainability. But is it?
Bamboo is botanically categorised as a grass. It is the fastest growing plant on earth with 1 species known to grow as fast as 1 meter a day and they can get as high as 35 meters! There are over 1600 species found in diverse climates from cold mountains to hot tropical regions. About 40 million hectares of the earth is covered with bamboo, mostly in Asia. Pretty impressive statistics if you ask me.
The bamboo species used for clothing is called Moso bamboo. Moso bamboo is the most important bamboo in China, where it covers about 3 million hectares (about 2% of the total Chinese forest area). It is the main species for bamboo timber and plays an important role in the ecological environment.
Very little bamboo is irrigated and there is sound evidence that the water-use efficiency of bamboo is twice that of trees. This makes bamboo more able to handle harsh weather conditions such as drought, flood and high temperatures. Compare bamboo to cotton which is a thirsty crop – it can take up to 20,000 litres of water to produce 1kg of cotton and 73% of the global cotton harvest comes from irrigated land.
A huge benefit of using bamboo as the organic base for textile fibres is that there is no need for pesticides or fertilizers when growing bamboo. However, herbicide and fertilizer applications are common in some places to encourage edible shoot growth. Bamboo also contains a substance called bamboo-kun – an antimicrobial agent that gives the plant a natural resistance to pest and fungi infestation, though some pathogen problems do still exist in some bamboo plantations. By contrast, only 2.4% of the world’s arable land is planted with cotton, yet cotton accounts for 24% of the world’s insecticide market and 11% of the sale of global pesticides. Many of these pesticides are hazardous and toxic.
So, we can conclude that as a “crop” bamboo can definitely be categorized as sustainable provided that existing plantations are used.
There are 2 techniques to turn the plant into fibre: mechanically or chemically.
The mechanical way is as follows: the woody parts of the bamboo plant are crushed and then natural enzymes are used to break the bamboo walls into a paste-like substance so that the natural fibres can be mechanically combed out and spun into yarn. This is essentially the same eco-friendly manufacturing process used to produce linen fabric from flax or hemp. Bamboo fabric made from this process is sometimes called bamboo linen. Very little bamboo linen is manufactured for clothing because it is more labour intensive and costly.
The second method is chemical and it quite similar to extracting rayon from other cellulose fibres such as wood. While specifics can vary, the general process for chemically manufacturing bamboo fibre using hydrolysis alkalisation with multi-phase bleaching technology – which is the most common technology for producing regenerated bamboo fibre – goes like this:
Bamboo leaves and the soft, inner pith from the hard bamboo trunk are extracted and crushed. The crushed bamboo cellulose is soaked in a solution of 15% to 20% sodium hydroxide at a temperature between 20°C to 25°C for 1-3 hours to form alkali cellulose. It is then pressed to remove any excess sodium hydroxide solution and is crashed by a grinder and left to dry for 24 hours. Roughly a third as much carbon disulphide is added to the bamboo alkali cellulose causing it to solidify. The result is a viscose solution consisting of about 5% sodium hydroxide and 7% to 15% bamboo fibre cellulose. The viscose bamboo cellulose is forced through spinneret nozzles into a large container of a diluted sulphuric acid solution which hardens the viscose bamboo cellulose and reconverts it to cellulose bamboo fibre threads which are spun into bamboo fibre yarns to be woven into reconstructed and regenerated bamboo fabric.
This gives some feel for how chemically intensive the hydrolysis-alkalization and multiphase bleaching manufacturing processes are for most bamboo fabrics that are promoted as being sustainable and eco-friendly.
Newer manufacturing facilities have begun using other technologies to chemically manufacture bamboo fibre that are more benign and eco-friendly.
The chemicals used should be contained within the factory, however, depending on where it is produced, regulations and controls might not be as strict as here in the West with the risk of heavy environmental pollution.
Another issue with this process is that both sodium hydroxide and carbon disulphide have been linked to serious health problems. Breathing in low levels of carbon disulphide can cause tiredness, headaches, nerve damage, psychosis, heart attacks, liver damage, blindness and can even cause neural disorders in workers at rayon manufacturers. Low levels of exposure to sodium hydroxide can cause irritation of the skin and eyes.
Be mindful of false advertising: textiles labelled as being made from bamboo are usually not made by mechanical crushing. They are generally synthetic rayon made from cellulose extracted from bamboo.
In the US, the Federal Trade Commission (FTC) has ruled that unless a yarn is made directly with bamboo fibre — often called “mechanically processed bamboo” — it must be called "rayon" or "rayon made from bamboo". The EPA (Environmental Protection Agency) noted that the manufacturing process further purifies the cellulose, alters the physical form of the fibre, and modifies the molecular orientation within the fibre and its degree of polymerization. The end product is still cellulose and is very similar to rayon made from cellulose from other sources, such as wood pulp.
Even though bamboo fabrics are often advertised as antibacterial, finished bamboo fabric only retains some of bamboo's original antibacterial property. Some studies have shown rayon-bamboo to possess a certain degree of anti-bacterial properties. Studies in China (2010) and India (2012) have investigated the antibacterial nature of bamboo-rayon fabric against even harsh levels of bacteria such as Staphylococcus aureus and Escherichia coli. While the Indian study found that “bamboo rayon showed excellent and durable antibacterial activities against both gram-positive and gram-negative bacteria”, the Chinese study concluded "the bamboo pulp fabric just like cotton fabric has not possessed antimicrobial property".
The FTC charges companies with fake antimicrobial claims when the fibre has been made with rayon. Critics cite the cotton industry's powerful lobbyist groups in influencing the FTC decision and dismissal of the international studies proving otherwise.
I realise all of this might be a bit overwhelming and maybe also disappointing. However, please don’t dismiss bamboo altogether. Just be aware and inform yourself accordingly on how your bamboo products or garments were made.
Bamboo is not perfect but it is still better than conventional cotton or polyester!
Bottom line is that growing bamboo is very environmentally friendly and sustainable however the manufacturing and processing of bamboo into fabric raises both health and environmental concerns related to the strong and toxic chemicals used during the process.
Sources: Wikipedia and Organic Clothing Blog