This article on chemical recycling process is the 4th article on the series of textile recycling. You are already aware that there are two types of textile recycling, mechanical and chemical recycling and these are based on the use of mechanics and chemicals in recovering the fibre from the fabric. To know about the mechanical textile recycling read the previous article. This article will discuss the chemical textile recycling highlighting on the types, process, advantages and disadvantages.
Industry giants such as Birla Cellulose and Lenzing have both come up with such technologies. With similar technology, the process starts with depolymerizing the 100% cotton fabric mostly from pre-consumer waste or post-consumer waste. The depolymerized pulp is then converted to cellulosic fibre in a process similar to that of recovering viscose from wood pulp. But in the conversion process, the polymer chains formed are not as strong as that from the wood pulp resulting in a decrease in physical properties such as strength. Due to this, the regenerated fibres have to be mixed with virgin viscose fibres to improve on the physical properties. Currently for an optimal recycled viscose yarn around 20-30% of regenerated viscose can be used but with technological improvements, this percentage is in the rise and Birla Cellulose is already making a drive towards developing solutions for 50%+ recycled content by 2020.
This recycling process is very much promising but is also having a lot of conditions which if not set right there can be loss in quality of the final product, uneven reaction and lower process efficiency. These are:
This leaves us with knit and woven 100% cotton fabric of lighter and medium shade in both post-industry as well as post-consumer waste. Post-industry waste can be in the form of cutting waste from different factory and these waste yield the maximum recycling efficiency.
Similar to this there are several other companies who in the process of developing chemical textile recycling technologies but only a handful of them at present are looking to be promising when it comes to commercializing the technology. This is mainly because of the very little control over the raw material if post-consumer waste is considered else post-industry waste is the best choice to recycle. Also, there are various pre-processing that have to be done to remove chemicals and contaminants from the fabric waste which results in increased cost. With the present scenario in mind, the demand for sustainability surely has suffered but rest assured in coming times these technologies will light the world towards a more sustainable future and contribute to the circular economy in textiles.
References and further reading on textile recycling
https://hmfoundation.com/recycling-the-green-machine/
https://www.chemistryworld.com/features/recycling-clothing-the-chemical-way/4010988.article?adredir=1
https://greenblueorg.s3.amazonaws.com/smm/wp-content/uploads/2018/05/Chemical-Recycling-Making-Fiber-to-Fiber-Recycling-a-Reality-for-Polyester-Textiles-1.pdf
What is chemical recycling of textiles?
Chemical textile recycling adopts a series of chemical processes to depolymerize/dissolve the fibre from of the fabric into monomer/solvent form either to make newer fibre compound of it or extract one compound from a mix. The output products are most often the same in quality as their virgin counterparts, with no loss in physical properties through the recycling process. This is much superior to mechanical recycling when it comes to technology with the use of chemicals, enzymes, controlled environment etc. for its process thus having added benefit of lesser limitation in the form of fabric such as woven, knits catering to a wide range of products like jackets, auto-parts, home decors etc.Recycling cotton to viscose
One of the most commercialized examples of chemical textile recycling is the conversion of cotton to viscose. This recycling works by depolymerizing the pure cotton fabric into a pulp which is then converted to viscose in a process similar to that made from wood pulp.Industry giants such as Birla Cellulose and Lenzing have both come up with such technologies. With similar technology, the process starts with depolymerizing the 100% cotton fabric mostly from pre-consumer waste or post-consumer waste. The depolymerized pulp is then converted to cellulosic fibre in a process similar to that of recovering viscose from wood pulp. But in the conversion process, the polymer chains formed are not as strong as that from the wood pulp resulting in a decrease in physical properties such as strength. Due to this, the regenerated fibres have to be mixed with virgin viscose fibres to improve on the physical properties. Currently for an optimal recycled viscose yarn around 20-30% of regenerated viscose can be used but with technological improvements, this percentage is in the rise and Birla Cellulose is already making a drive towards developing solutions for 50%+ recycled content by 2020.
This recycling process is very much promising but is also having a lot of conditions which if not set right there can be loss in quality of the final product, uneven reaction and lower process efficiency. These are:
- Only recycling of 100% cotton is possible and no other fibres.
- There should be no contamination in the waste. Contaminations can be in the form of foreign fibres like viscose, polyester, spandex, etc. or any other material like paper, dirt, tape, etc. This makes the use of blended fabric void as the other fibres affect the chemical reaction which is very sensitive.
- The fabric selected cannot be white no as they contain optical brightener that disrupts the chemistry of the depolymerization.
- No yarn-dyed and printed fabric can be recycled as they have multiple chemical components that do not react well with the chemical process.
- Only solid dyed fabric will be accepted for recycling. Limitations can be further narrowed down to only light and medium shade fabric. This is due to the presence of higher dye particles in dark shade fabric than that of light or medium shade.
- There are extra costs included in pre-processing which comprises of washing, opening, separation process, removal of contaminations, decolour, etc.
Related post: Companies Pioneering in Textile Recycling Process
HKRITA (Hong Kong Research Institute of Textiles and Apparel) has been in the forefront of this recycling technology came up with a solution to separate polyester fibre from polycotton blend with a solvent-based technology named The Green Machine. This process used only heat and water with less than 5% biodegradable green chemical to convert the cotton in the blend into liquid cellulose. After drying the cellulose, the outputs are polyester fibre with no quality loss and cellulose powder. There is also a development of a second polycotton recycling process by enzyme hydrolysis of the cotton component in a bioreactor dissolving the cotton leaving behind the polyester fibres.
Worn Again Technologies is also trying to commercialize chemical textile recycling with a different approach than from the above. Their process depends on the melting of polyester from the blend at high temperature leaving behind the polyester solution and cotton in solid form. The polyester is then recovered from the solvent, brought to correct molecular weight and send-off to be spun back into polyester yarn. The remaining cotton is then dissolved using a novel ionic liquid to make a pulp similar to that of wood pulp to be used for making cellulosic fibres such as viscose and lyocell.
Recycling of poly-cotton blends
Along with this, another type of chemical recycling where a chemical reaction is used to separate the fibre constituents from the mix of different fibres of both natural and man-made origin. This can be considered the most useful form of recycling as most of the fabric present are there in some percentage of blends and the first step of recycling them is to separate its constituent fibres. With a homogeneous mix of fibres in the fabric, mechanical separation is very difficult but this can be achieved chemically by working with different physical properties of the fibres.HKRITA (Hong Kong Research Institute of Textiles and Apparel) has been in the forefront of this recycling technology came up with a solution to separate polyester fibre from polycotton blend with a solvent-based technology named The Green Machine. This process used only heat and water with less than 5% biodegradable green chemical to convert the cotton in the blend into liquid cellulose. After drying the cellulose, the outputs are polyester fibre with no quality loss and cellulose powder. There is also a development of a second polycotton recycling process by enzyme hydrolysis of the cotton component in a bioreactor dissolving the cotton leaving behind the polyester fibres.
Worn Again Technologies is also trying to commercialize chemical textile recycling with a different approach than from the above. Their process depends on the melting of polyester from the blend at high temperature leaving behind the polyester solution and cotton in solid form. The polyester is then recovered from the solvent, brought to correct molecular weight and send-off to be spun back into polyester yarn. The remaining cotton is then dissolved using a novel ionic liquid to make a pulp similar to that of wood pulp to be used for making cellulosic fibres such as viscose and lyocell.
Image courtesy: Worn Again | Source: GREENBLUE
Similar to this there are several other companies who in the process of developing chemical textile recycling technologies but only a handful of them at present are looking to be promising when it comes to commercializing the technology. This is mainly because of the very little control over the raw material if post-consumer waste is considered else post-industry waste is the best choice to recycle. Also, there are various pre-processing that have to be done to remove chemicals and contaminants from the fabric waste which results in increased cost. With the present scenario in mind, the demand for sustainability surely has suffered but rest assured in coming times these technologies will light the world towards a more sustainable future and contribute to the circular economy in textiles.
References and further reading on textile recycling
https://hmfoundation.com/recycling-the-green-machine/
https://www.chemistryworld.com/features/recycling-clothing-the-chemical-way/4010988.article?adredir=1
https://greenblueorg.s3.amazonaws.com/smm/wp-content/uploads/2018/05/Chemical-Recycling-Making-Fiber-to-Fiber-Recycling-a-Reality-for-Polyester-Textiles-1.pdf
https://www.birlacellulose.com/download_files/brochure_10.pdf
https://www.birlacellulose.com/press-release/birla-cellulose-visco-fibre.pdf
https://www.birlacellulose.com/press-release/birla-cellulose-visco-fibre.pdf