Cotton recycling is the process of converting cotton fabric into fibers that can be reused into other textile products.
Recycled cotton is primarily made from pre-consumer cotton which is excess textile waste from clothing production. It is less commonly made from post-consumer cotton which is discarded textile waste from consumers such as second hand clothing. The recycling process includes assessing the quality of cotton fibers through systematics collection, manually sorting the materials, and undergoing a mechanical or chemical process to break down the textile fabric into reusable fibers. In the mechanical process, fabrics are torn into individual fibers through a machine, and in the chemical process, the fabrics’s chemical properties are broken down through chemical reaction processes such as Lyocell process and dissolution in ionic liquids. The mechanical process is the primary way to recycle textiles because the chemical process is not commercially used.
A barrier to recycling cotton is the mix of materials in fabrics which makes separating cotton difficult. Recycled cotton is less durable than virgin cotton because of the shorter length of recycled cotton fibers from mechanical recycling; as a result, recycled cotton requires the addition of polyester for added durability. Therefore, recycled cotton is often used in products that do not require high-quality cotton fibers such as casual clothing and home building materials.
The environmental impact of cotton recycling can be assessed using the Life Cycle Impact Assessment (LCIA) which uses a variety of impact categories to quantitatively measure cotton recycling’s potential effects on the environment. Harvesting raw cotton is a resource intensive process that uses a lot of water, energy, and chemicals. Cotton recycling mitigates wastage and can be a more sustainable alternative to disposal because products can be made out of existing textiles instead of raw materials, therefore, reducing the resources required to harvest raw cotton. However, there are costs associated with cotton recycling, such as the risk of problem shifting and the impact of transporting collected materials which could exceed its intended benefits. 
There are online platforms, brand-led promotions, and government policies as initiatives to increase cotton recycling rates. Researchers and governments are looking for new technologies and industrial management solutions to improve the social impact of the collection processes for recycled cotton.
Pre-consumer cotton is excess textile waste that is collected during the production of yarn, fabrics, and textile products such as selvage from weaving and fabric remnants from factory cutting rooms. The majority of recycled cotton is made from pre-consumer cotton, such as fabric scraps, because it is more likely that the scraps have not undergone the mixing of materials and color dyes and do not have to be heavily sorted before recycling.
Post-consumer cotton is textile waste that is collected after consumers have discarded the finished products, such as used apparel and household items. Post-consumer cotton which is made with many color shades and fabric blends is labor intensive to recycle because the different materials have to be separated before recycling. Post-consumer cotton can be recycled, but the recycled cotton made from post-consumer cotton is likely of much lower quality than virgin cotton.
Methods for collecting recycled materials can be categorized into the following initiatives: internet-based recycling, brand-led recycling, and government-led recycling. Internet-based recycling relies on the internet to create a channel of communication between people who would like to recycle clothing waste and groups who are collecting clothing waste. Brand-led recycling occurs when fashion brands create self-led programs to support recycling or oversee clothing recycling. Government-led recycling refers to policies, laws, and regulations implemented by governments that promote the recycling of waste-clothes. 
After pre-consumer and post-consumer textile products are collected, the textile products are manually sorted into reusable and disposal groups. The sorting process is labor intensive because there can be up to 350 subcategories that reusable textiles can be manually sorted into.
One approach to combat the low efficiency of manual sorting is Near Infrared Spectroscopy (NIRS) which automates the recognition and sorting process of textiles. NIRS analyzer identifies the corresponding group for textile by sensing the coating and finishing of the textile. There are also limitations to using NIRS, where if the textile is very thin or experiences chemical changes through aging, NIRS could misclassify the textile.
In order for cotton waste to be recycled into high-quality products, the quality of the cotton waste should not jeopardize the quality of the resulting product. While there is no specific index for the quality assessment of recycled cotton, a variety of quality indexes have been applied to determine how suitable cotton waste fibers are for recycling.
Common indexes to measure the quality of cotton fiber are Fiber Quality Index (FQI) and Spinning Consistency Index (SCI). Each index uses a mathematical model to yield a quantitative value. A value with a higher quality indicates that the cotton waste has higher quality. FQI relates the tenacity, mean length, and fineness of cotton fibers. SCI considers properties such as the upper half mean length, uniformity, and fiber color to determine the spinnability of cotton. Properties of these quality indices are often modified and merged to create one overall quality index that can be used to calculate whether cotton waste is suited to be recycled for a particular product. A standardized instrument to obtain data regarding the various properties of cotton waste is the Uster HVI machine.
Mechanical recycling is the process of shredding textile fabric into fibers to be spun back into yarn without the use of chemicals. A Garnett machine is used for this process, which is a machine equipped with rollers and cylinders covered with metal pins that rotate to break down the textile into individual fibers. The textile fabric must be sorted before putting it through the machine because an unsorted mixture of different materials and colors in fabrics results in low-quality yarn after the fiber is spun back into yarn. The fibers shorten in length with each time of processing because of the mechanical strain from the machine. Using short fibers results in a lower quality of yarn, so polyester is commonly added to the recycled cotton to increase the strength and quality of the fiber.
Chemical recycling is the process of solubilizing textile wastes in chemicals to cause chemical reactions that produce recycled fibers. Chemical reactions dissolve the polymers that make up fibers, thus do not reduce fiber length but instead fully regenerate the fiber. This process overcomes the issue of fibers being shortened by mechanical recycling, but its scale of use is limited to research experiments and studies such as Eco Circle (Teijin), Worn Again, Evrnu, Re:newcell, and Ioncell.
An outdated method mixes cellulose fiber (cotton) with carbon disulfide, dissolves the product in caustic soda, and spins it with sulfuric acid and mineral salt to produce a fiber different from cotton called viscose rayon. This method is proven to be environmentally hazardous and is prohibited.
The lyocell process is the method of dissolving cellulose (cotton) in N-methylmorpholine N-oxide (NMMO) to form a solution that has hydrogen bonds (NMMO•H2O). The solution is then spun in a water bath, resulting in pure, reusable cellulosic fibers. The lyocell process could recover 99% of its solvent and produces minimal and non-toxic waste, therefore it is recognized by the United Nations and the industry as environmentally improved textile products (EITP).
Another method dissolves cellulose in ionic liquids such as 1,3,-dibutylimidazolium chloride ([C4mim]Cl) to produce regenerated fibers. While this method, like the lyocell process, could recover almost all of its solvent, its hazardous impacts to the aqueous ecology is still being researched.
Since mechanical recycling, the primary process used commercially, recovers cottons of less durability and length, recycled cottons are used in products that require lower-quality cotton fiber including casual clothing, filters, agricultural storage bins, flooring materials, home insulation materials, home furnishing materials, and building materials such as concrete.
The environmental impact of cotton recycling can be examined using the Life Cycle Impact Assessment (LCIA). The LCIA is a method that evaluates the potential environmental impacts of cotton recycling. It has three mandatory steps: selection, classification, and characterization. The LCIA can use a variety of impact categories, such as climate change potential, terrestrial acidification potential, freshwater eutrophication, ozone depletion, water depletion, human toxicity, and land occupation.
The production of organic cotton can have detrimental environmental impacts due to its usage of water, land, chemicals, and emissions. Approximately 2.6% of global water use can be attributed to the production of cotton. Cotton cultivation is also responsible for about 11% of global pesticide consumption. During the spinning phase of virgin cotton production, large amounts of electricity are consumed which can lead to increased CO2 emissions and acidification potential. In order to give organic cotton an artificial color, the dyeing phase of cotton production consumes a vast amount of water, energy, and chemicals. The plants required to dye cotton can potentially lead to the contamination of oceans.
Since cotton recycling avoids cotton cultivation, spinning, and dyeing, it reduces the negative environmental impacts of producing organic cotton by minimizing of the use of water, fertilizers, and pesticides.  For example, using 1000 kg of recycled cotton instead of organic cotton can save 0.5 ha of agricultural land, prevent 6600 kg CO2 eq of emissions from entering the atmosphere, and conserve 2783 m^3 of irrigation water.
The benefits of cotton recycling can be undermined due to the risk of problem shifting which occurs when one benefit is achieved in a particular region, but that benefit creates a detriment to another region. For instance, an increase in cotton recycling in the UK minimized the environmental impacts of virgin cotton production in the USA, but also increased the use of energy in the UK. Cotton recycling also requires transportation to move waste fibers between consumers, brands, collection facilities, and sorting facilities. If the products developed from cotton waste require replacement after an insufficient period of time due to poor quality or lack of consumer contentment, then the environmental impact of transportation may surpass the benefits of avoiding cotton cultivation.
Cotton textiles are made of materials other than cotton such as plastic, dye, and other fabrics. The current sorting, mechanical, and chemical processes are not capable of splitting dye from the raw cotton which highly limits the color and appearance of a new product made with recycled cotton.
Currently, the most common collection methods are organized based on online platforms, brands, and government. Though these methods are available, many consumers still choose to throw away their clothes.
Online platforms are a way for consumers to make recycling requests through websites and those in charge of collection will reach out to the consumers to retrieve those items. A study on Consumers’ clothing disposal behaviors in Nanjing, China in 2020 showed that fewer than 10% of the population consider online clothing recycling platforms as their first choice.
Some researchers have worked to increase the popularity of online platforms by integrating artificial intelligence into the site to spread information about cotton recycling. The Technology Acceptance Model and the Theory of Planned Behavior which are used to predict consumer’s acceptance and use of new technologies like online platforms for cotton recycling expect users are increasingly likely to use these platforms in the future.
Fashion brands offer programs to recycle clothes after consumption or oversee the recycling process. Consumers can drop off their old clothing at the store and the store will send these clothes to be recycled. The company offers incentives through promotions or discounts to persuade consumers to recycle through the firm’s website, social media, and in-store advertising. A US clothing brand called American Eagle promoted their recycling program on their blog on April 1st, 2019, by stating “Bring in your old pair of jeans to recycle and get $10 off, a new pair”.
Based on the case studies of clothing brands, the recycling advertisement could be paradoxical since promoting customers to recycle actually encourages them to consume more, thus not helping to reduce pollution. Research on the clothing product and global warming relationship shows that adopting sustainable recycle habits does not make the production of new cloth to be eco-friendly because producing new fabric generates more than half of the total carbon dioxide emission related to garments.To resolve the dilemma, brand-led recycling is trying to find a balance between consumer incentives and educational purposes of sustainability.
The cotton recycling chain involves the group collecting, modifying, and reproducing the material. Because the industry lacks a commonly shared standard in material collections and classification, the collaboration between each party has experienced difficulties and deficient the industry’s development.
Government-led recycling programs mostly involve policymaking. Multiple countries have set up policies to promote cotton recycling. In 2023, the European Union plans to publish a revision of the Waste Framework Directive. The commission will provide clear guidance to improve the current fabric recycling system. Also, non-EU countries including Britain, Japan, the United States, China, and Korea have also released laws and policies about wasted cotton material and the corresponding recycling guidance.
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