Fiber can be broadly classified as chemical fiber and natural fiber, and chemical fiber can be further broken down into the categories of regenerated fiber, semi-synthetic fiber, synthetic fiber, and inorganic fiber.
The total volume of fiber production in the world is 73,576,000 tons. As shown in the following graph, polyester, nylon, and acrylic are known as the three major synthetic fibers. The production volume of acetate is extremely small, at approximately 1%.
Acetate fiber is the man-made fiber that is made of cellulose acetate, which is the acetic acid ester of cellulose. It has a very long history, and was first produced in 1923 by an English company, Celanese, in the form of diacetate silk. At the beginning of 1930, companies such as Celanese (U.S.), American Viscose, E.I. DuPont, and Eastman Kodak began to produce diacetate fiber. The United States became the top producing country for acetate fiber.
Ryokou Acetate Co., Ltd. commenced production of diacetate in 1958. For triacetate, Celanese (U.S.) and Courtaulds (U.K.) first started production in 1954, while Mitsubishi Acetate Co., Ltd. began to produce triacetate in Japan in 1967.
Acetate fiber is produced by reacting high purity wood pulp with acetic anhydride. The acetate flakes that are produced through this chemical reaction are dissolved in a solvent, filtered, and adjusted to obtain spinning stock solution. The spinning stock solution is extruded through controlled nozzles with extremely small pore diameters ranging from 30 to 50μm. The solvent is then evaporated, and the yarns are formed. This process for producing acetate fiber is known as the dry spinning method. The cross-section of acetate fiber is called a “chrysanthemum,” and is shaped uniquely with many lobes. After the spinning stock has been extruded through the pores, it takes on a round-shaped cross-section. However, rapid evaporation of the solvent from the surface results in the formation of a skin layer on the surface of the fiber. After that, evaporation of the solvent from the inside of the fiber causes the skin layer to cave in toward the fiber cross-section, giving rise to the final multi-lobal cross-section.
Acetate fiber can be classified as diacetate fiber and triacetate fiber. Diacetate (generally known as acetate) is defined as cellulose acetate fiber for which more than 74% and less than 92% hydroxyl has been acetylated (degree of esterification above 2.22 and below 2.76). Triacetate is defined as cellulose acetate fiber for which more than 92% hydroxyl has been acetylated (degree of esterification above 2.76 and below 3.00).
These characteristics arise from the properties of acetate fiber. The properties of acetate fiber, compared with the properties of other major fibers, are summarized below (Table 1). We can see that acetate fiber feels natural and gentle on the skin because it is made from high purity pulp. The fiber cross-section for each yarn is random and multi-lobal, and has a low refractive index. These properties give it the elegant gloss and clear coloring that are similar to silk. Acetate fiber also has a lower Young’s modulus than polyester or cotton, thereby allowing it to drape flexibly. In addition, the moderate level of official moisture regain (3% to 7%) and multi-lobal cross-section create a diffusion effect through capillary action. This in turn gives the fiber an ideal degree of water absorbency and quick-drying performance. Compared to rayon and other fibers, acetate fiber also has greater stability for dimensions and measurements, as well as strong pleating durability, because it does not swell much in water.
One of the drawbacks that acetate has is its poor fiber strength. However, by combining it with other fibers that have sufficient strength, such as polyester, it has become possible to use acetate fibers for practical applications. Polyester fiber has a mottled appearance and elasticity, so it can add to the texture of acetate fiber. The combination of the two fibers can produce knitted and woven fabric that feels wonderful on the skin.
Acetate fibers are characterized by their silk-like gloss and texture. Typically, they are combined with other fibers such as rayon and polyester to produce ladies’ apparel. In particular, triacetate fiber has a soft texture and drapes well. It is therefore ideal for use in luxury couture for women. Diacetate fiber is also used for sleepwear, lining for clothes, gift box lining, labels and tags attached to clothes, ribbons, packing tape, and other sundry goods.