Lyocell

Production Process

The production process for lyocell begins by treating wood chips approximately the size of a coin until they form a substance similar to a thick paper, which is then sent to a fabric production factory. Once there, it is broken down into about 1 inch (2.5 cm) squares and chemically dissolved. The resulting slurry is then forced through a device called a spinneret, which has many small holes in it, somewhat like a strainer. This causes the mixture to form long fibers, which are chemically treated again, rinsed and dried, and lubricated before being compressed, combed, and cut. After this, they can be spun into yarn for use, either alone or in combination with other materials.

Characteristics and Uses

In its pure form, this material is very strong both when wet and dry, and lasts a long time. It can be mixed with many other types of fibers, including cotton, wool, linen, silk, and Lycra®; and can also be treated to have a variety of textures, from silky to denim-feel. It drapes well and resists wrinkles, which makes it popular for dress clothing. Additionally, it's very absorbent and wicks moisture well, and so is often used to make athletic clothing and summer garments. Depending on how it's treated, lyocell can be either machine washed, hand washed, or dry clean only.

Besides clothing, lyocell is used in making linens, some cigarette filters, vehicle carpeting, baby wipes, and bandages. Its durability makes it well-suited for industrial uses too: it's commonly found in conveyor belts, oil filters, and capacitor separators. It is also used to reinforce some plastics and in making some types of paper.


The manufacturing process

Hardwood logs are chipped into squares about the size of postage stamps. The chips are digested chemically, to remove the lignin and to soften them enough to be mechanically milled to a wet pulp. This pulp may be bleached. Then it is dried into a continuous sheet and rolled onto spools. At this stage, it has the consistency of thick posterboard paper. The roll of cellulose weighs some 500 lb (227 kg). The waste liquor may be reworked to produce tall oil, used to make alkyd resins.

At the Lyocell mill, rolls of pulp are broken into one-inch squares and dissolved in N-methylmorpholine N-oxide, giving a solution called "dope." The filtered cellulose solution is then pumped through spinnerets, devices used with a variety of manmade fibers. The spinneret is pierced with small holes rather like a showerhead; when the solution is forced through it, long strands of fiber come out. The fibers are then immersed in another solution of amine oxide, diluted this time, which sets the fiber strands. Then they are washed with de-mineralized water. The Lyocell fiber next passes to a drying area, where the water is evaporated from it. The strands then pass to a finishing area, where a lubricant, which may be a soap or silicone or other agent depending on the future use of the fiber, is applied. This step is basically a detangler, prior to carding and spinning into yarn.

The dried, finished fibers are at this stage in a form called tow, a large untwisted bundle of continuous lengths of filament. The bundles of tow are taken to a crimper, a machine that compresses the fiber, giving it texture and bulk. The crimped fiber is carded by mechanical carders, which perform an action like combing, to separate and order the strands. The carded strands are cut and baled for shipment to a fabric mill. The entire manufacturing process, from unrolling the raw cellulose to baling the fiber, takes about two hours. After this, the Lyocell may be processed in many ways. It may be spun with another fiber, such as cotton or wool. The resulting yarn can be woven or knitted like any other fabric, and may be given a variety of finishes, from soft and suede-like to silky.[6]

The amine oxide used to dissolve the cellulose and set the fiber after spinning is recycled. 98% of the amine oxide is typically recovered. Since there is little waste product, this process is relatively eco-friendly. However, it uses a substantial amount of energy, and uses an organic solvent of petrochemical origin.


Fabric and garments from Lyocell fiber

After the fiber is created it is provided to manufacturers for weaving into fabric, then the fabric is used to create garments. Manufacturers may use environmentally unfriendly or chemical treatments to overcome the natural reluctance of the fiber to take dye and to overcome its natural pilling tendency. Although the closed-loop manufacturing process makes Lyocell inherently the most eco-friendly of the naturally regenerating fibers, different fabric and garment manufacturers vary in this respect.

Uses

 It is used in many everyday fabrics. Staple fibres are used in clothes such as denim, chino, underwear, casual wear, and towels. Filament fibers are used in items that have a silkier appearance such as women’s clothing and men’s dress shirts. Lyocell can be blended with a variety of other fibers such as silk, cotton, rayon, polyester, linen, nylon, and wool. Lyocell is also used in conveyor belts, specialty papers and medical dressings. (Textiles, Kadolph & Langford). Tencel is also used for making some brands of baby diaper wipes.

Producers


Lyocell is manufactured under the brand Tencel by Lenzing AG in Mobile, Alabama, at the Grimsby plant, England, and in Heiligenkreuz, Burgenland, Austria and in Lenzing Austria. Also under the brand Excel from Grasim (Birla group) in Nagda. Also under the brand Lyocell from Baoding Swan in Baoding.