Lyocell is a partly man-made fiber used to create fabrics for clothing and other uses. It is made by dissolving wood pulp and using a special spinning method called dry jet-wet spinning. Unlike rayon, which uses a different method called viscose, Lyocell does not use carbon disulfide, a harmful chemical for workers and the environment. Lyocell was first trademarked as Tencel in 1992.

The word "Lyocell" is now a common name used to describe the process of making cellulose fibers. The United States Federal Trade Commission defines Lyocell as "a fiber made from cellulose that forms when it is removed from an organic solution. The cellulose structure remains unchanged, and no other chemicals are created during the process." It is classified as a type of rayon.

Names

Other brand names for Lyocell fibers include Tencel, made by Lenzing AG, Newcell from Akzo Nobel, and Seacell from Zimmer AG. The Aditya Birla Group sells Lyocell under the brand name Excel. Other companies, such as Sateri, sell their product using the common name Lyocell.

History

The development of Tencel was driven by environmental concerns. Researchers aimed to make rayon using methods less harmful than the viscose process.

The Lyocell process was created in 1972 by a team at the now defunct American Enka fibres facility in Enka, North Carolina. In 2003, the American Association of Textile Chemists and Colorists (AATCC) honored Neal E. Franks with their Henry E. Millson Award for Invention for Lyocell. Between 1966 and 1968, D. L. Johnson of Eastman Kodak Inc. studied NMMO solutions. From 1969 to 1979, American Enka attempted but failed to commercialize the process. The fibre was called "Newcell" within Enka, and development reached the pilot plant stage before the project was halted.

The process of dissolving cellulose in NMMO was first described in a 1981 patent by McCorsley for Akzona Incorporated (the parent company of Akzo). In the 1980s, Akzo licensed the patent to Courtaulds and Lenzing.

The fibre was developed by Courtaulds Fibres under the brand name "Tencel" in the 1980s. In 1982, a pilot plant producing 100 kilograms of fibre per week was built in Coventry, England. Production increased to 1 ton per week by 1984. In 1988, a semi-commercial production line producing 25 tons of fibre per week opened at the Grimsby, UK, pilot plant.

The process was first used commercially at Courtaulds' rayon factories in Mobile, Alabama (1990) and at the Grimsby plant (1998). In January 1993, the Mobile Tencel plant reached full production of 20,000 tons per year. By this time, Courtaulds had spent £100 million and 10 years on Tencel development. Tencel revenues in 1993 were expected to reach £50 million. A second plant in Mobile was planned. By 2004, production had increased to 80,000 tons per year.

Lenzing started a pilot plant in 1990 and began commercial production in 1997. A plant in Heiligenkreuz im Lafnitztal, Austria, produced 12 metric tonnes of fibre per year. In 2003, an explosion occurred at the plant, which was producing 20,000 tonnes per year and planning to double production by year's end. In 2004, Lenzing produced 40,000 tons [sic, probably metric tonnes]. In 1998, Lenzing and Courtaulds resolved a patent dispute.

In 1998, Courtaulds was bought by Akzo Nobel, a competitor. Akzo Nobel combined the Tencel division with other fibre divisions under the Accordis brand, then sold them to CVC Partners, a private equity firm. In 2000, CVC sold the Tencel division to Lenzing AG, which merged it with their "Lenzing Lyocell" business but kept the Tencel brand. Lenzing took over the plants in Mobile and Grimsby. By 2015, Lenzing became the largest Lyocell producer, making 130,000 tonnes per year.

Uses

Staple fibers are used in many everyday fabrics, such as denim, chino, underwear, casual wear, and towels. Filament fibers, which are usually longer and smoother than staple fibers, are used in items that have a silkier look, like women's clothing and men's dress shirts. Lyocell can be blended with other fibers, including silk, cotton, rayon, polyester, linen, nylon, and wool. When mixed with other fibers, the resulting fabric becomes stronger and more resistant to wear, tear, and pilling. Lyocell is also used in conveyor belts, specialty papers, and medical dressings.

Properties

Lyocell has many similarities to other fibers like cotton, linen, silk, ramie, hemp, and viscose rayon (which it is closely related to chemically). Lyocell can absorb 50% more water than cotton and moves moisture away from the skin farther than modal fabrics of the same type.

Compared to cotton, people often describe Lyocell as feeling softer and more breathable because it moves moisture away more effectively. Claims that Lyocell resists wrinkles better than other fabrics have not been proven. Lyocell fabric can be washed in a machine or dry cleaned. It hangs smoothly and can be dyed in many colors, requiring slightly less dye than cotton to reach the same level of color depth.

Manufacturing process

The Lyocell process uses a direct solvent instead of an indirect method, like the xanthation-regeneration method used in the viscose process. Lyocell fiber is made from dissolving pulp, which has a high amount of cellulose and very little hemicellulose or lignin. Hardwood logs, such as oak and birch, are cut into small squares about the size of a postage stamp. These squares are treated with chemicals using either the prehydrolysis-kraft process or the sulfite process to remove lignin and hemicellulose. The pulp is then bleached to remove any remaining lignin, dried into a sheet, and rolled onto spools. The pulp is thick, like posterboard, and each roll weighs about 500 pounds (230 kilograms).

At the Lyocell mill, the pulp is cut into one-inch squares and dissolved in a chemical called N-methylmorpholine N-oxide (NMMO), creating a solution called "dope." This solution is filtered and pumped through spinnerets, which are devices with tiny holes, similar to a showerhead. When the solution passes through the spinnerets, long strands of filament form. These strands are stretched in the air to align the cellulose molecules, giving the fiber its strength. The strands are then placed in a water bath, where the cellulose solidifies. The bath contains a small amount of amine oxide. The fibers are washed with demineralized water and then dried.

Next, the fibers are treated with a lubricant, such as soap or silicone, depending on how the fiber will be used. This step helps prevent the fibers from tangling before they are processed further. The fibers are then formed into a bundle called "tow," which is a large, untwisted group of long filaments. The tow is compressed by a machine called a crimper to add texture and bulk. The fibers are then combed by mechanical carders to separate and arrange them. Afterward, the fibers are cut and baled for shipment to a fabric mill. The entire process, from raw material to finished fiber, takes about two hours. Once made, Lyocell can be combined with other fibers, like cotton or wool, and woven or knitted into fabric. It can also be treated to have different textures, such as soft or silky.

The NMMO used in the process is recycled, with about 99% of it recovered. NMMO breaks down naturally without creating harmful substances. This makes the process environmentally friendly, although it requires a lot of energy.

Lyocell does not have antibacterial properties, which limits its use in medical settings. However, because it is biodegradable, safe, and comfortable, it could be useful for antibacterial clothing. Scientists have tested three methods to add antibacterial properties: blending antibacterial agents into the spinning solution, chemically bonding them to the fibers, or applying them to the fiber surface after production. Blending and post-treatment methods are the most promising for large-scale use. Choosing the best method requires careful consideration of cost, time, and effectiveness. Improving Lyocell’s antibacterial properties could help create products like lab coats, scrubs, sanitary items, and clothing such as socks and underwear.