By Eman Abdallah Kamel
Contact the author: emanabdallahkamel@gmail.com
Eman is a writer and textile engineer. She received a bachelor’s degree in textile sciences from the Faculty of Applied Arts, Egypt.
Synthetic fibers are manufactured using many harmful chemicals. In this article, you will learn about the history of synthetic fibers, manufacturing processes, and their uses. Risks to humans and the environment.
Synthetic Fibers
Synthetic fibers are man-made fibers. Most synthetic fibers are made from polymers resulting from polymerization. Synthetic fibers are usually manufactured from oil, coal, or natural gas.
Sometimes cellulose (the main component of cotton fiber) and the pulp of wood are used to make materials such as acetate and rayon (artificial silk).
A polymer is a chemical substance consisting of large molecules made from many smaller molecules: some polymers, such as nylon, are artificial. Proteins and DNA are natural polymers.
Synthetic fabrics are the most prevalent in the world. China is the largest producer, accounting for 70% of total global production. India is the second-largest producer of synthetic fiber, but only 7.64% of global production comes from India, while the European Union is the largest importer of synthetic filament fibers. Turkey and the United States come after the EU. Within the European Union, Germany and Italy are among the largest importers. There are many other importing countries, such as the Middle East and African countries.
Although synthetic fibers are the most common and attractive, they are the most common fiber that causes diseases.
The American Chemical Society has warned that synthetic fibers are ‘the biggest plastic pollution issue you haven’t heard of yet.
Also, the Swedish Chemicals Agency (Kemikalieinspektionen) has shown the risks of chemicals used in synthetic fabrics, especially in the finishing process and dyeing, to humans and the environment.
History of Synthetic Fibers
In 1865, French chemist Paul Schützenberger discovered cellulose acetate (acetate rayon) through the reaction of cellulose with acetic anhydride.
Around 1870, a French engineer named Hilaire de Chardonnet invented an artificial silk called Chardonnet silk.
In the early 1880s, the English inventor Joseph Swan invented synthetic fibers formed by chemically modifying cellulose liquid. These fibers are now known as semi-synthetic fibers.
The synthetic fibers produced by this process were chemically identical in their potential applications to Swan’s carbon filament, developed for his incandescent light bulb. Then Swan realized the fiber’s ability to revolutionize the textile industry.
By 1894, English chemists Charles Cross and his collaborators Edward Bevan and Clayton Biddle had invented the viscose fiber, so named because of the highly viscous solution of xanthate produced by the reaction of carbon disulfide and cellulose in basic conditions.
In 1965, Kevlar was developed by Stephanie Kwolek at DuPont. Kevlar is heat-resistant and used in bulletproof vests.
In 1905, the UK company Courtaulds Fibers produced the first commercial viscose silk. In 1924, the name “rayon” was adopted because of the use of viscose in the viscous organic liquid used in the manufacture of rayon.
In the 1930s, Wallace Carothers, an American researcher at the chemical firm DuPont, developed nylon, the first fully synthetic fiber.
In 1941, the first polyester fibers were introduced by John Rex Winfield and James Tenant Dixon, British chemists who worked at the Calico Printers’ Association. They produced the first polyester fiber, known as Dacron.
Around 1950, DuPont added acrylic (plastic fiber) fibers that looked like wool.
Joseph Shavers invented Spandex or Lycra at the DuPont Binger Laboratory in Waynesboro, Virginia, in 1958. Lycra is stronger than natural rubber and is used in the medical industry.
In 1965, Kevlar was developed by Stephanie Kwolek at DuPont. Kevlar is heat-resistant and used in bulletproof vests.
Classification of Synthetic Fibers
Stages of Manufacturing Synthetic Fibers
Synthetic fibers can be manufactured into continuous filaments that are infinite in length. During thread production, filaments can be continuously assembled to form yarn.
The stages of manufacturing synthetic fibers are:
- Polymerization,
- Pumping,
- Filtration,
- Spinning,
- Drawing,
- Texturing,
- Finishing and dyeing.
1. Polymerization
In polymerization, small molecules are reacted together to produce polymer chains.
There are two types of polymerization:
- Condensation polymers are formed by the gradual reaction of functional groups of monomers, usually containing heterogeneous substances such as oxygen or nitrogen.
- An addition polymer is a mechanism in which monomers react to form a polymer without forming by-products. In addition, polymerization processes are performed in the presence of catalysts.
2. Pumping
The molten polymer is pumped through a filter bed and then through small, deep holes. Both units will lead to high-pressure drops along the flow direction of viscous liquids.
There are two main types of devices used for pumping liquids: centrifugal pumps and gear pumps. Centrifugal pumps are used to move low-viscosity liquids around in a process, while gear pumps are used to pump high-viscosity liquids at a controlled flow rate.
3. Filtration
It is cleaning the spinneret plate. Filtration must adhere to very strict standards.
4. Spinning
The fibers are formed by extruding molten polymer through small holes in the spinneret plate. A plate may contain 1,000 or more holes. The filament thickness is not determined in linear dimensions but in terms of mass per length. There are three methods of spinning:
- Melt spinning: spinning of molten polymers, such as polyester, nylon, and polypropylene. As soon as the molten polymer leaves the spinneret hole, it begins to cool and expand. After the finish is applied, the fibers are gathered at high speed in a process known as spin drawing.
- Dry spinning: In the process of dry spinning, solvents are used in which the polymer dissolves, and the solvent evaporates after the solution (spin dope) leaves the spinneret. This process is followed by stretching, applying the finish, and taking follow-up on the spindle or cutting into the staple. This process is more expensive than conventional melt-spinning processes.
- Wet spinning: This method is used for polymers that do not dissolve easily. The polymer is dissolved in a solvent, which is extracted into a liquid (water) after the solution (the spin dope) leaves the spindle. The fibers are dried on large, heated cylinders. Then the fibers are sent to a cutting machine to be cut into lengths of 2.5–15 cm. The fibers produced by wet yarns include rayon, Kevlar, and acrylic fibers.
5. Drawing
Stretching or drawing the filament is the process of pulling long polymer chains to align along the longitudinal axis of the fibers, bringing them together, and developing cohesion. During the drawing process, the polymer chains slide over each other as they are pulled to align along the longitudinal axis of the fibers.
6. Texturing
It is the process of the formation of curls, coils, and loops along the length of filaments to increase porosity, smoothness, and flexibility. From the methods of textured yarns:
- Gear crimping: Similar to wool, staple fibers need a crimp to be spun into yarns. This wrinkle may be mechanically inserted by bypassing the filament between gears or chemically by controlling the coagulation to create fibers with an asymmetrical cross-section, with one side thick-skinned, almost soft, and the other thin-skinned and serrated. When wet, the fibers swell to a large extent on the skin-thin side rather than the thick-skinned side, causing wrinkles.
- Stuffing: Fiber yarns are woven from very large bundles of fibers called tows, which are typically zigzagged by feeding two of the tows into a stuffer box, where the tows are folded and pressed against each other to form a plug of the yarn. The plug can be heated by steam, and when cooling, the filaments are curled.
- Air-Jet: This method is performed by feeding the threads over a high-velocity jet of air that forces the filament into loops. The textured yarns in this process contain a large number of very fine filaments, which increases the possibility of tangles.
- Knit-de-knit: This texture produces a wavy look like a knitted loop. In this process, the threads are woven into a tubular weave. The fabric is then heated and unwrapped to produce textured yarn.
- False Twist: During this method, the filaments are twisted and heated, and then untwisted when cold, thus preserving the heat-set spiral shape of the twist.
7. Finishing and Dyeing
During the final process, the synthetic fibers are treated with several chemicals to develop and improve their appearance. Dyes may be added to the molten solution before the fibers are spun.
Fiber is usually dyed after spinning with pigments dissolved in boiling water baths.
Synthetic fibers have a very coherent and intertwined structure because the molecular chains are regular and have a high degree of crystallization. The dye molecules settle in the spaces between the molecular chains. Depending on the nature of the synthetic fiber material, space varies in size from one type to another, and it is noted that all synthetic fibers consist of materials that are not water-loving. Therefore, the dyeing rate depends on the internal structure of the fibers.
The dyeing rate is low in the case of synthetic fibers compared to other natural fibers, so the dyeing time is longer. To overcome this, catalysts are added to the dye bath to help penetrate the fibers. Also, increasing the temperature and pressure of some dyes increases the dyeing rate. As an example, when dyeing polyester, a benzophenone (organic compound) is used to transfer or carry dyes into fibers under pressure. The carrier is used in a quantity of 0.05 to 1.2% by weight based on the dyeing solution. The popular dyes of synthetic fibers are the following:
- Disperse dyes are the only non-soluble dyes in water that dye polyester fibers and acetate. The dispersed dye molecule is based on the azobenzene molecule or anthraquinone with amine, nitro, or hydroxyl groups.
- The reactive dye can react with fiber directly. The chemical reaction takes place between the dye and the molecules of the fiber, making the dye part of the fiber. These dyes are also used for dyeing natural fibers such as cotton and silk.
- Basic dyes are also cationic dyes that act as bases when they dissolve in water. They form a colored cationic salt, which can interact with anionic sites on the fibers.
- Acid dye is a dye that is usually applied to the fabric at a low pH. Mainly used for dyeing woolen fabrics. It is effective in dyeing synthetic nylon fibers.
- Azo dyes are organic compounds carrying the functional group R−N=N−R′, where R and R’ are usually aryls. Azo dyes are widely used for textile treatment.
Uses of Synthetic Fiber
Polyester is used in coats, jackets, and ropes.
Rayon is used for bedsheets and carpets. Ropes, fishing nets, and seatbelts are made from nylon.
There are many uses for spandex, including sportswear, belts, bra straps, swimwear, shorts, and gloves. Additionally, it is used to make skinny jeans, socks, underwear, and home furnishings.
Risks of Synthetic Fibers to Human
Textile dermatitis is a skin reaction caused by direct contact with synthetic fibers that causes inflammation, redness, and itching. There are two types of textile dermatitis: allergic and irritant.
The allergenic textile stimulates the immune system to a strange substance that penetrates the skin. The development of the allergic reaction occurs in two stages: the sensitization stage, when the immune system recognizes the substance and mobilizes the response, and the induction stage, when the immune system causes an allergic reaction, which means the symptoms of allergic fiber dermatitis develop over time and not upon first contact with allergens.
Irritant textile dermatitis occurs due to a substance that causes direct skin irritation and can occur after the first exposure to the material.
Epidemiological studies of textile dermatitis have indicated a significant number of patients with textile allergies. Most textile dermatitis occurs on the upper body and is caused by wearing tight clothing made of synthetic fibers. However, occupational exposure may also be a problem, especially hand lesions from wearing work gloves.
1. Hazardous chemicals used in the manufacture of synthetic fibers:
Polyester fibers are manufactured from both dihydric alcohol and terephthalic acid. Both are highly toxic and are not completely removed after manufacturing, leading to easy access to the body through the wet skin, causing dermatitis and respiratory infections.
Rayon is made of recycled wood pulp processed with carbon dioxide, sulfuric acid, ammonia, acetone, and caustic soda. Carbon dioxide emitted from Rayon’s filaments can cause headaches, nausea, muscle pain, and insomnia.
Nylon relies on petroleum and undergoes many chemical treatments using caustic soda, sulfuric acid, and formaldehyde during manufacturing. In addition, bleaching and softening factors like chloroform, pentane, limonene, and terpineol are present. Even after the manufacturing process, the fiber still retains toxins that can be harmful. Diseases associated with repeated wear of nylon clothes include allergic skin, dizziness, headaches, and spinal pain.
2. The risk of textile dyes:
A large European multi-center study found that 3.6% of the patients tested had a contact allergy to disperse dyes, assessed as clinically relevant in one-third of cases, and among these, Disperse Blue 124, Disperse Blue 106, and Disperse Yellow 3.
Disperse dyes easily rub off from the fabric and migrate to the skin.
Another study found that about 25% of patients diagnosed with an allergy to dispersed dyes reacted not to the dye molecule but to other substances in the dye. This indicates that commercial textile dyes may contain unidentified allergens. There are reports of epidemiological studies that also reported patients with textile dermatitis due to some reactive dyes, basic dyes, and acidic dyes.
Cancer has been mainly linked to exposure to carcinogenic aryl amines, which can be formed as a product of the division of azo dyes.
3. Hazardous chemicals used in the finishing process:
Many finishing resins release formaldehyde, which can be released from the fabric and cause dermatitis.
Many EU countries have national regulations on formaldehyde in textiles to reduce risks to human health. However, some reports suggest that the release of formaldehyde from resins used in textile finishing remains a concern.
Epidemiological studies show that 2.3–8.2% of all patients with textile dermatitis are sensitive to formaldehyde, and one study shows that formaldehyde sensitivity is more common among people who have been exposed at work.
Statistics from the European Union’s Rapid Alert system for the exchange of information on products posing a serious health risk to consumers show that formaldehyde accounts for about 3% of all notifications of hazardous substances in textiles.
Risks of Synthetic Fibers to the Environment
Synthetic fibers made from petroleum, such as polyester and nylon, pose a significant risk to the environment because they are not biodegradable.
The synthetic fiber industry is responsible for more than 20% of industrial water pollution in the world, as the production of these fibers requires a lot of water, and the polluted water is pumped back into the oceans, seas, and rivers after use, posing a serious threat to aquatic organisms.
The production of nylon releases nitrous oxide, which is very dangerous for the ozone layer, 300 times more than carbon dioxide.
A study at Plymouth University in the UK analyzed what happened when a range of synthetic fabrics were washed at different temperatures in domestic washing machines with different combinations of detergents to determine the number of microfibers that shed. The researchers found that an average 6 kg wash load could release an estimated 137,951 microfibers of polyester mixed with cotton, 496,030 fibers of polyester, and 728,789 acrylic fibers.
In this case, one of the considerations that led policymakers to intervene was the lack of clear societal benefit from the inclusion of microplastic particles in cosmetics, coupled with concerns about the impact on the environment. The societal benefits of textiles are beyond question. Therefore, any voluntary or policy intervention should aim to reduce emissions, either through changes in textile design, filtration of effluent, or both.
Professor Thompson, who heads the International Marine Litter Research Unit at Plymouth University.
In this video, Bryan Clement, director of the Hippocrates Institute in West Palm Beach, Florida, discusses the dangers of chemicals in synthetic fabrics.
The Solution to Reduce the Risk of Synthetic Fiber
After knowing the chemicals used in synthetic fibers from the beginning of manufacturing until the final processes and their great danger to humans and the environment, we must avoid these fibers as much as possible.
I think the solution to reducing the production of chemical fibers is to return to nature and revive the production of natural fibers. On the other hand, consumers should try as much as possible to buy natural fibers such as cotton, linen, natural wool, and other natural fabrics instead of synthetic fabrics.
Sources
- Industry Structure and the Marketing of Synthetic Fibers.
- Washing clothes releases thousands of microplastic particles into the environment, study shows – University of Plymouth. Plymouth University news: More than 700,000 microscopic fibers could be released into wastewater during an average washing machine cycle, according to new research from Plymouth University.
©Eman Abdallah Kamel, 2023
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