Textile Recycling: The Mechanical Recycling of Textiles Wastes

In two earlier posted articles, we have described what textile recycling is along with the various companies who are trying to bring forward a change to the current system. But it is a must to know about the technologies so that industry bodies are aware of the requirements of textile recycling to design their system and products which favour textile recycling.

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. This article will discuss the mechanical textile recycling highlighting on the requirements, process, advantages and disadvantages.

What is Mechanical Recycling of textiles?

Mechanical recycling of textiles is the process of recycling the textile fabric back into fibres without the use of any chemicals. This process includes shredding and carding process to extract the fibres from the fabric. This fibre can then be spun to make yarn for either woven or knitted fabric. Mechanical recycling is used best for the mono-fibre fabric of cotton and rarely viscose due to the fibre structure and higher fibre yield.

It starts with the shredding of the waste fabric into smaller pieces which are then send to garnett machine for fibre extraction. These machines perform heavy and rough carding actions by tearing the fabrics with opposite sets of strong sharp teeth transforming it to its component fibres. Since the teeth are mounted on the surface of cylinders rotating on a parallel axis, the teeth of several opposing cylinders travel all in parallel planes and the yarns which happen to extend in the direction of the travel of the teeth in radial planes can and do pass through the machine in end-on relation and thus escape being opened into individual fibres.

The fibres collected are then mixed with virgin fibres with higher fibre length in different blend percentages. The more the virgin fibres used, the finer the yarn will be. These fibres can be polyester both in recycled polyester or usual and cotton both in organic cotton or usual. After that, the blend can be spun to yarns for woven or knitted fabric. As mentioned earlier textile recycling is nothing new as garnett machines have been around for a few decades but due to machine limitations the final product has always been shoddy yarns used for making rags, carpets, fillings for insulation, car sits etc. But development in machinery has allowed for recovering quality fibres enough to spun yarns for wearable grade fabric.

Fibre length is the sole most important factor for the fineness of yarn, and modern machines can recover fibres of the length of above 2cm making it possible to spun through open-end spinning. Also, recycling of knitted fabric gave much higher efficiency with about 75% as the fibres in the yarn are loosely spun. For a woven fabric recycling gets complicated as compact fabric and warp yarns are densely woven and spun resulting in tearing of the fibres during the shredding process resulting in shoddy yarns and poor recycling efficiency. Here recycling efficiency denotes the amount of usable fibred recovered from the garnett machine. 


Figure 1. Previous generation garnett machines used to downgrade textile waste to fibres used in rags, insulation etc. Image courtesy: Rathi Textile engineering works.


Figure 2. Newer garnett machines capable to shred fabrics to apparel grade fibres (Shangdong new Haina machineries co.ltd, n.d.)

For a 28s recycled poly-cotton yarn (cotton being recycled) with blend ration of 45-55, the CV% of the yarn was about 1.87 which is a bit high with a normal value of about 1.4. This means that the yarn will suffer breakage during warping but can be used as weft yarn. The woven fabric made can thus be used for suiting with little possibility for shirting. But it is recommended for knitted fabric as a fabric of 140-145 gsm can be made with this recycled yarn. Also, the cost of the yarn is 15-18% lower than a yarn made of virgin fibres of similar composition and thus can have a huge impact on the cost of the fabric.


Figure 3. Fabric to Fibre stage (Ref: https://www.youtube.com/watch?v=9j_lP7lJ_DY)

Advantages of mechanical recycling 

The advantages for using these yarns are that there is minimum need for chemical processing in the form of dyeing as the fibres have colour from the previous dyeing thus making the entire process waterless. For newer colours, the white fabric waste can be shredded and the fibres recovered can be dyed in the required colour. Also with variation in blend percentage and fibre choices numerous fabric variations can be made for different types of products. Most of the prominent recyclers in India can make recycled yarns of count range 24s-28s but higher count can be achieved by altering the mix of the recycled and virgin fibre in the yarn.

Disadvantages of mechanical recycling 

The only disadvantage of mechanical textile recycling is that the fibre quality is not as much as of virgin fibres. The yarns are slightly coarse, like that from yarns made from virgin raw material but this can be solved by the use of chemical finishing which is an opportunity yet to be explored.

With the advantages overshadowing the disadvantages, this recycling process surely has the potential to be used in mainstream apparel. The only thing that this need is a steady rise in demand for recycled apparel products which will boost both its development and accessibility.

Reference: 
http://rathitex.com/product_info.php?products_id=213


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