Bamboo is a material that is often referred to when it comes to the issue of sustainability within the textile industry. In this article, we will explore this versatile, natural material within the context of sustainability, taking a look at the material itself, and analysing its application and characteristics, as well as its history as a material in the textile industry, before turning our attention to how and where it is cultivated and turned into fabrics. We will examine the use of bamboo in weighted blankets, and consider its place within a green and sustainable future.
Before we look at bamboo fibre in more depth, it is important to note that there is a range of different bamboo fibres and fabrics, which differ very broadly in terms of their properties and sustainability credentials. It should be noted that while the raw material, bamboo, is a natural material, the fabrics derived from bamboo fibre are what is usually classed as semi-synthetic. Rayon and viscose are the names given to materials that are both sometimes derived from bamboo. It is important to note that these (which are the purview of this article) also differ considerably from mechanically-derived bamboo fabrics (which are in much less common use).
It is important to distinguish traditional semi-synthetic fabrics made from bamboo cellulose (rayon/ viscose) from next-generation bamboo fabrics, such as Lyocell. The differences between the different textiles that can be created from bamboo fibre determine how they perform, and also the sustainability of each option.
How and Why Bamboo Fabric is Used in Weighted Blankets
Lyocell, or other bamboo-derived fabric, is often used in weighted blankets for its soft and silky feel. It is often used for applications where a soft skin-feel is required – on the outside layer of a weighted blanket, where it will feel good against the skin. It is often sought out by those who want a cruelty-free, vegan alternative to natural silk, offering a very similar texture and feel.
Bamboo fabrics also offer other benefits in weighted blanket applications. Studies have been carried out on jersey materials containing cotton and a proportion of bamboo fibres. One study showed that the thermal conductivity of the fabrics generally decreased with an increase in the proportion of bamboo fibre (1). This could mean that weighted blankets containing bamboo fibres as well as, or instead of, cotton could be better for warmth retention. It is notable that the same study showed that fabrics containing bamboo fibres also performed better with regard to water vapour permeability and air permeability.
All of the properties of advanced bamboo fabric mean that it can be utilised to aid in a good night’s sleep, in addition to being useful in a wide range of other applications.
However, it is important to look to the research to verify claims made regarding bamboo fibres. UV absorption and anti-bacterial properties are often claimed by fabric manufacturers, but their characteristics were rarely detected in commercial bamboo fibres(2).
Another reason why bamboo-derived fabrics are used in weighted blankets is for their sustainability credentials. As we will discover below, the ways in which bamboo is grown, harvested, and turned into fabric throughout the manufacturing stages has a major bearing on how sustainable such a finished textile can be.
The History of Bamboo Textiles
The first commercial production of synthetic fabric (rayon) was achieved in France in 1891, and English Chemist Charles Frederick Cross and his colleagues, Edward John Bevan, and Clayton Beadle, patented their ‘artificial silk’ in 1894. They named their material ‘viscose’ since its production involved the intermediacy of a highly viscous solution.
But it was not until the 1900s that commercially viable ‘artificial silk’ companies were formed in the UK, the US and around the world. Production of rayon grew over the first decades of the 20th Century to meet demand. By the mid-1920s rayon could be purchased by textile manufacturers for half the price of raw silk. This was one of the more successful early synthetic fabrics. The name ‘rayon’ was adopted in 1924, though in Europe, the fabric itself was and is known as ‘viscose’. While the terms are often used interchangeably for the finished fabric, the viscose method differs from other routes to create rayon.
High tenacity rayon was developed in the 1940s and further developments led to the creation of a high-wet-modulus (HWM) rayon in the 1950s.
In the 1970s, a new form of rayon, known as Lyocell, was developed by a team at the former American Enka fibers facility at Enka, North Carolina. The fibre, which used a different method to create the fabric, was further developed by Tencel in the 1980s at Courtaulds Fibres in Coventry and Grimsby in the UK. The new process was first commercialised in the 1990s, in Courtauld’s factories in Mobile, Alabama in 1990 and in Grimsby, UK, in 1998. The company was acquired by CVC private equity in 1998, and in 2000, the Tencel division was sold to Lenzing AG. Lenzings Tencel brand is currently the best-known lyocell producer in the world.
Bamboo is used as a source of cellulose for older viscose rayon fabrics and to produce more modern and more sustainable textiles. There is a growing interest in sustainable bamboo-derived fabrics, and a growing understanding of the environmental hazards and dangers posed by rayon/ viscose production, which has led to the recent proliferation of more eco-friendly lyocell fabrics and products.
The Bamboo Plant
In order to better understand both the sustainability credentials and the physical characteristics of bamboo textiles, it is necessary to go right back to the beginning, to look at where the fibre comes from in the first place.
Bamboo is a plant – the largest member of the grass (Poaceae) family. There are over 1,600 different species of bamboo that can grow in a huge range of different climatic conditions. Certain types of bamboo are amongst the fastest growing woody plants in the world. Approximately 40 million hectares of the earth’s surface is covered with bamboo, predominantly in Asia.
In the context of textiles, Moso bamboo (Phyllostachys edulis) is the most important variety. This is the variety most commonly used in textile production. It is the most important bamboo in China, where it accounts for around 2% of the total forest cover – an area of around 3 million hectares. Aside from its commercial importance, it also performs an important ecological role (3).
The Structure of Bamboo Fibres
It is very important to note that the structure and therefore the physical properties of semi-synthetic bamboo fibres vary considerably depending on what type of bamboo is used, how the cellulose is obtained from the raw material, and other details of the finished fabrics.
When examined under a scanning electron microscope, it is also interesting to note that mechanically-produced bamboo fibres differ from bamboo rayons in that the mechanically produced fibre has nodes.
Also notable is the fact that different varieties of raw bamboo will produce fabrics that differ in their structure, and therefore their durability, tensile strength, and other characteristics (4).
The Physical Properties of Bamboo Fibres
The structure of bamboo at the raw bamboo stage, and at finished fabric level have a bearing on the sustainability of a product as well as its physical properties. Bamboo fabrics that have better tensile strength, and are better able to withstand forces applied upon them, for example, will be more long-lasting – thereby helping to reduce waste and preventing over-consumption that contributes to global warming and other forms of pollution. Therefore, in order to determine the role that bamboo fabrics can play in sustainable textiles, it is important to understand the physical properties of Bamboo fibres.
The Thermal Properties of Bamboo Fibres
The specific heat of dry rayon fibres is 1.35-1.59 J/(g K). This can be compared to the figure for this thermal property for other types of dry fibres. For example, cotton has a lower specific heat, or 1.22-1.35 J/(gK), while nylon, for example, has a higher specific heat (5).
Water Absorption and Retention in Bamboo Fibres
Chemical bamboo fibres suggest good water retention power due to the many voids in their cross-section. However, both chemical bamboo fibres and conventional viscose fibres possess a better ability for absorbing and releasing water than second-generation bamboo fibres like Tencel/ Lyocell (6). Fiber absorption and water releasing rates are only part of the equation for sweat vapor transmission, as we have learned prior. That is, when raw fibers are spun into yarns and the yarns are woven into a fabric, Lyocell fabrics are reported to have higher breathability and sweat vapor absorption than fabrics constructed from viscose at the similar yarn constructions and weaves.
How much water a fabric absorbs and retains plays a role in its performance, and can have a large bearing on the suitability of such a fabric for weighted blankets and for other applications.
Mechanical Properties of Bamboo Fibres
Studies have been undertaken into the tensile strength and specific strength of different plant fibres. Bamboo was shown to have a tensile strength of 500-900 Mpa and specific strength of 383 Mpa (7). The same study cited above also noted the diameter, length and bulk density of bamboo fibre. It is important to note, however, that, as mentioned above, the properties of the finished bamboo fabric will depend on the type of bamboo used as well as on the methods used to turn that raw material into a finished fabric. For example, comparison of the fibre breaking force (CN), and average breaking tenacity (CN/dtex) of Bambusa emeiensis and Phyllostachys edulis manufactured using both chemical and mechanical means, can show how much these characteristics can differ (8).
Lyocell fabrics are fibrillar in texture. The bonding between fibrils is weak so fibrillation occurs easily. This can be a defect, but can also be exploited to make an extremely soft fabric. Lyocell fabrics are similar to modal rayons in their tensile properties but generally are somewhat stronger and stiffer (9).
Since Lyocell and other rayon and viscose fabrics made from bamboo are cellulosic, they are made up of cellulose – the same basic component that makes up cotton and other natural fabrics. This means that they are technically compostable, and will biodegrade in the same way. This means that, like cotton, they can be a more sustainable choice than petrochemical-based fabrics like nylon and polyester. Cellulose is a material that is omnipresent in the natural world, and it can be found in most organisms. Nature, therefore, is able to break down this material, whether it is washed into water treatment plants or natural bodies of water (as materials are washed and fibres shed), or end up in landfill, in compost heaps, or in the soil. When bamboo textile reaches the end of its useful life, it can be composted and disposed of without creating a burden of waste for our planet (10).
However, it is important to note that finished bamboo-derived fabrics are not only composed of cellulose. Depending on the methods that have been used to create the fabrics, they may also contain substances that can be harmful when released into the environment. This is why, when determining the sustainability and environmental credentials of a certain textile, it is important to examine not only the end product but the process that has led to that point.
How Bamboo is Grown Today
We can begin our analysis of the sustainability of bamboo-derived textiles by looking at the raw material – the bamboo itself – and how it is grown.
Low Use of Pesticides and Herbicides
One of the biggest benefits of bamboo as a component of sustainable textiles is that there is no need for pesticides, herbicides and other harmful chemicals for its growth. Bamboo contains a substance called bamboo-kun, an anti-microbial agent that provides a natural source of pest and fungi resistance. While some pathogen problems can still develop in bamboo plantations, these are far less problematic than those experienced by, for example, the cotton industry. Choosing bamboo as opposed to cotton can lessen the problem of pesticide and herbicide pollution. While cotton covers just 2.4% of the world’s arable land, it accounts for 24% of the world’s insecticide use (11). Bamboo-derived textiles help to reduce pollution of this kind.
Low Water Use
What is more, bamboo growth is also more sustainable than most cotton growth in a number of ways. For example, while cotton often uses vast quantities of water to grow, bamboo plantations are rarely irrigated. There is evidence to suggest that the water-use efficiency of bamboo is twice that of trees (12). This means that bamboo can be a more water-wise solution than tree-derived cellulose for textile manufacture. It also means that bamboo is a more resilient crop, better able to survive the extreme droughts, floods and high temperatures that are becoming increasingly prevalent due to global warming.
Less Soil Erosion
Bamboo is also less damaging to the world’s soil than cotton production. Bamboo has an extensive root system which can help to stabilise and preserve the soil. The world’s top soils are in threat, and monocrop cotton plantations worsen such problems. They can worsen the problem of soil erosion through the processes of yearly planting and mass-agricultural mismanagement.
Bamboo plantations, on the other hand, can create an effective watershed, ensuring that the natural water cycle is allowed to function as it should. The roots help to stick together fragile soils on slopes and along watercourses, reducing the incidence of mudslides and greatly reducing rainwater run-off (13). Since they do not need to be replanted each year, but simply continually send up new shoots, they also significantly reduce soil disruption and so growing bamboo as opposed to other crops can be beneficial as it can help to preserve and protect the fragile and essential soil ecosystem.
Increased Yield and Reduced Land Use
Land use is an increasingly pressing concern in today’s world. As the world’s population continues to grow, competition increases for the fertile growing areas on our planet. We need land to grow food – and this is, of course, paramount to our continued survival on this planet as a species. The textiles industry also requires a vast amount of land – especially as we experience energy descent and pass peak oil into a future in which fossil fuels can no longer be used to meet our many needs. Choosing natural textiles or textiles derived from natural materials like bamboo can, of course, help us to move away from petrochemical-derived synthetic fabrics. But natural materials need land to grow.
Bamboo grows at a very high density and can grow incredibly quickly. Since more bamboo can be grown on a given area than cotton, wood, or other crops, this can ease pressure on land use and increase the yield of fibre per given area. The average yields of around 60 tonnes of bamboo per hectare, compare extremely favourably with the yields for most trees (20 tonnes) and cotton (2 tonnes) and so bamboo can be viewed as far more sustainable from a land-use perspective.
Another thing to consider is that bamboo is such a resilient crop that it can often be grown on marginal land or land that is unsuitable for other agricultural production, and so it can be grown in such a way that it makes use of the land area that may not otherwise be productively used.
Sequestration of Carbon
Another benefit of growing bamboo for textiles, as opposed to trees or cotton, is that bamboo cultivation not only reduces the emission of carbon (by reducing the need for farming machinery, etc.) but also sequesters more carbon while in growth than an equivalent stand of trees. Planted in large groves, bamboo can store four times the about of CO2 as a stand of trees of similar size and will release approximately 35% more oxygen. One hectare of bamboo will sequester 62 tonnes of CO2 per year, while in comparison a young forest covering the same land area will sequester only 15 tonnes (14).
Slowing of Deforestation
What is more, bamboo planting can also help to reduce CO2, and prevent other forms of environmental and social damage by slowing the rate of deforestation. By providing an alternative source for the textile industry, bamboo plantations can help local communities turn away from the destruction of their native forests and create sustainable bamboo plantations that can be harvested each year without the destruction of the groves. While trees need to be chopped down to yield cellulose for fabrics and then replanted, bamboo will keep on growing and can be harvested year after year.
In the past, there were concerns over the fact that old growth forests were being destroyed in order to create space for bamboo plantations. However, this has become a lot less of a concern since China overhauled its forestry policies in the 1990s.
The next stage of the process to consider from an environmental and sustainability standpoint is the harvest of the raw material. New bamboo shoots will generally reach their full height in just eight to ten weeks and will reach maturity in three to five years. As a grass, bamboo will regenerate upon being cut just like a domestic lawn. Felling of bamboo canes has been shown to lead to vigorous re-growth, and an increase in the biomass yield the following year (15).
The bamboo harvest can be favourably compared to the harvest of other materials for the textiles industry. As mentioned above, bamboo is a renewable resource, which will naturally regenerate year after year. Clear felling is not required, as it often is for most large-scale timber harvesting. Bamboo stands will send up new shoots and bamboo has even been shown to regenerate more quickly after a harvest has been taken. This stands in stark contrast to other forms of agriculture employed to feed the ever-growing textile industry.
Unlike cotton, which (even in organic production) generally requires the destruction of the entire crop, bamboo harvesting does not mean leaving bare areas post-harvest, which bake in the sun and release carbon dioxide into the atmosphere. It does not mean leaving bare soil vulnerable to erosion, run-off or nutrient leaching. Bamboo harvesting does not involve a tilling and replanting process, and so can significantly reduce the carbon footprint of the finished product, since not as much machinery will have been involved in the much less disruptive and intense harvesting process.
Bamboo Textiles Manufacture
In order to make rayon (or viscose), bamboo leaves and the soft, inner pitch layer from bamboo trunks are extracted using a steaming process. They are then usually mechanically crushed in order to extract the cellulose. The cellulose that is derived from the raw material is then purified, treated with lye, and dissolved (often in carbon disulfide) and reformed to make the finished yarn, which then will be made into fabrics.
It is at this stage of the process that environmental and sustainability concerns regarding certain bamboo fabrics can creep in. As mentioned earlier in this article, the sustainability of a bamboo-derived textile will depend, to a large extent, on how the raw bamboo material is turned into a fabric.
Regular Rayon or Viscose Manufacture
Regular rayon, or viscose, is the most widely produced form of rayon. It is manufactured using methods that have been around since the early 1900s and can produce either filament or staple fibres. The process begins with the processed cellulose, in the case of bamboo-derived rayon or viscose, that from the bamboo plant. The pulp must have a cellulose content of around 87 to 95%.
This cellulose pulp is then dissolved in caustic soda. This process is a chemical reaction which converts cellulose to alkali cellulose and removes impurities. This is often referred to as the ‘immersion’ stage of the process.
Next, the solution is pressed between rollers to remove excess liquid. A press weight ratio is used to calculate the relation between the pressed alkali cellulose sheet weight and the weight of the air-dried pulp. It is adjusted to 2.7 -3 (16).
The pressed pulp is then crumbled and shredded to create a substance that is known as ‘white crumb’. The white crumb is aged through exposure to oxygen and then mixed with carbon disulfide in a process known as ‘Xanthation’. In a controlled process, cellulose crumbs are heated to 20-30 degrees and react with the carbon disulfide to form cellulose xanthate. This process changes the product into ‘yellow crumb’.
The yellow crumb is then dissolved in a caustic solution and becomes viscose. The viscose is set aside for a period of time to ‘ripen’ and then filtered to remove any undissolved particles. It is pressed to remove any air bubbles and extruded through a spinneret, a structure that resembles a shower head with a number of tiny holes.
After being extruded from the spinneret, the viscose lands in a bath of sulfuric acid, which regenerates the substance, converting cellulose xanthate back into cellulose. The regeneration step is rapid and does not allow for proper orientation of the cellulose molecules and so in order to delay the process, zinc sulfate is used in the bath. The zinc sulfate allows time for the proper orientation of cellulose molecules to occur.
Finally, the rayon fibre is spun in a wet spinning process, drawn, to straighten out the fibres, washed, to remove residual chemicals, then cut into the desired lengths.
Lyocell is a next-generation cellulosic textile. It uses a somewhat different manufacturing process. Rather than using an indirect xanthation/regeneration process as described above, lyocell fibre is produced by dissolving pulp in a direct solvent. The pulp is dissolved in N-methyl morpholine N-oxide, giving a solution called ‘dope’. The dope is then passed through spinnerets.
Unlike in the process described above, lyocell filaments, once extruded through the spinneret, are drawn in air to align the molecules. This gives lyocell fibres their characteristic high tensile strength.
The fibres are then immersed in a water bath, where desolvation of the cellulose sets the fibre strands. The baths contain some dilute amine oxide in a steady state concentration.
The fibres are next washed with de-mineralised water and passed to a drying area, where water is evaporated from them. From this point on, the fibres undergo the same processes as other forms of rayon or viscose.
The Sustainability of Bamboo Textile Manufacture
All bamboo-derived semi-synthetic textiles share the ecologically beneficial characteristics with regard to the raw material used. As described above, bamboo can be an extremely eco-friendly and sustainable material, with plenty of promise when it comes to sustainability in the textiles industry. Unfortunately, however, there are a number of problems that become apparent when we look at the manufacture of the textiles from the raw material.
Problems in Regular Rayon Manufacture
The carbon disulfide used in the manufacture of regular rayon or viscose is an environmental cause for concern. Whether wood-pulp or bamboo is used as the raw cellulosic material, the carbon disulfide can be a serious environmental pollutant. Around 75% of the pollution from the bamboo viscose process takes the form of air pollution, largely from this highly volatile substance (17).
Unfortunately, the process also exposes workers in the textile industry to this air-borne substance, which can cause significant and serious health problems. While the carbon disulfide is lost before the rayon or viscose gets to the consumer, the damage to rayon workers should be a consideration for consumers who wish to make ethical and sustainable purchasing decisions. Historically, there have been a number of poisoning incidents, and while some production facilities have taken measures to improve worker safety, worker safety continues to be a major concern (18).
Lyocell & Sustainability
By avoiding the use of carbon disulfide, lyocell fibre manufacture does not share the environmental and worker safety concerns mentioned above. Lyocell textiles are processed using a closed loop process. 98% of the amine oxide used in the manufacture is typically recovered and so there are fewer concerns relating to environmental pollution. The amine oxide is classed as non-toxic on the MSDS (Material Safety Data Sheet) for lyocell. What is more, production plant air emissions from smokestacks and wastewater generation are far lower for lyocell production than they are for many other man-made fibre operations. All of this means that bamboo lyocell is a far more eco-friendly and sustainable product than other forms of bamboo-derived rayon or viscose.
It is notable that the European Union awarded the Lyocell process the Environmental Award 2000 in the category of ‘technology for sustainable developments.
It is important to note, however, that though the manufacture of lyocell bamboo fabrics is broadly eco-friendly and sustainable, post-processing can still be damaging both to the environment and human health. It is important to look at the processes involved in turning the finished fibre into a dyed and treated fabric for use in a given application.
Sustainability in the Dyeing Process
If you wish to determine whether or not a product you are considering is sustainable and eco-friendly, it is important to look not only at how it has been manufactured but also how it has been dyed and treated post-manufacture. Lyocell’s tendency to fibrillate, or pill, and its relatively low surface energy mean that it does not always accept dyes well. Manufacturers use a variety of chemical processes, enzyme baths and dye treatments which may or may not be eco-friendly (19).
The best way for consumers to determine whether or not harmful or polluting dyes or other chemicals have been used in the production of textile is to look for sustainability certifications. The Oeko-Tex standards, for example, can give consumers the reassurance that the entire process has been sustainable, and that a range of harmful substances has not been used.
In conclusion then, bamboo is an extremely useful and versatile material, with great potential for use within the sustainable textiles industry. It can be used to create second-generation sustainable fabrics such as lyocell, which lessen the environmental cost when compared to traditional, regular rayon or viscose fibre textiles. Such textiles are ideal for use in weighted blankets and for a wide range of other applications. They are soft, silky and strong. They also have excellent characteristics when it comes to thermal performance, water retention and water, and air permeability. However, care must be taken when choosing ‘bamboo fabrics’ as not all are quite as eco-friendly as they may seem, utilising polluting substances and posing a risk to human health, while others may be treated with harmful dyes or other post-processing substances. Environmental certifications and standards can guide consumers to choose the right bamboo fabric products.
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(3)Jinhe Fu ‘Chinese Moso Bamboo: Its Importance’, The Magazine of The American Bamboo Society, October 2001
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(12)‘Can Bamboo Replace Thirsty Trees?’ http://www.worldagroforestry.org May 2009
(13)Nathan Singleton, ‘ Bamboo About’ , https://web.archive.org/web/20130302045445/http://www.bs-bamboo.co.uk/bamboo_about.html
(14)Janssen, Jules A., Technical University Eindhoven, 2000
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(17)Ray A. Smith, ‘Shades of Green: Decoding Eco Fashion’s Claims’, The Wall Street Journal, 2008
(18)Paul David Blanc (2016). Fake Silk The Lethal History of Viscose Rayon. Yale University Press. p. 325
(19)Tencel: Sustainable but not necessarily healthy https://organicclothing.blogs.com/my_weblog/2005/11/tencel_sustaina.html