
The Ultimate Guide to Identifying Modal and Lyocell
Modal fiber is a regenerated cellulose fiber with high breaking strength and wet modulus. The raw material of the fiber is wood pulp, which is processed into fiber through a special spinning process. This product’s raw materials are all-natural, harmless to the human body, and can be naturally decomposed and harmless to the environment. Its dry strength is close to that of polyester, and its wet strength is much higher than that of ordinary viscose. Its luster, softness, hygroscopicity, dyeability, and color fastness are all better than pure cotton products; the fabric shows a silky luster, with a pleasant soft touch and drape and excellent wear resistance.
The modal currently sold on the market mainly includes LENZING MODAL produced by Austrian LENZING Company and FORMOTEX Modal produced by Taiwan Chemical Fiber Corporation (FCFC). Others include BILRA MADAL and BILRA MADAL MICRO produced by Thailand THAI RAYON and BILRA MADAL MICRO produced by India GRASIM. Modal fibers produced by different companies have different surface characteristics due to different production processes.

Lyocell fiber is the trade name of regenerated cellulose fiber produced by COUR TAULDS in the UK, commonly known as “Tencel” fiber. Lyocell fiber is known as the environmentally friendly fiber of the 21st century. It is made of wood pulp mainly from coniferous trees, water and solvent amine oxide, which are mixed and heated until completely dissolved. No derivatives or chemical reactions are produced during the dissolution process. After impurities are removed, it is directly spun. Its molecular structure is a simple carbohydrate. Its production process does not pollute the environment or damage the ecology.

The following briefly introduces the characteristics and identification methods of Lenzing Modal, Formotex Modal and Lyocell fibers commonly found on the market.
1. Microscopy
Lenzing Modal occupies most of the Chinese market. It is made of European beech wood pulp by the Austrian company LENZING, and then processed into fiber through a special spinning process. Under a microscope, the cross section of Lenzing Modal is dumbbell-shaped, without a central cavity, and the longitudinal section surface is smooth with 1 to 2 grooves.

Formotex Modal is a kind of wood pulp fiber produced by Taiwan Chemical Fiber Co., Ltd. Its cross section is close to circular and has no central cavity. The surface of the longitudinal section is smooth, and some have intermittent and inconspicuous vertical lines.

When observed under a microscope, the cross-section of Lyocell fiber is an irregular circle with no central cavity, and the longitudinal section surface is smooth, with some having intermittent, inconspicuous vertical lines.

In summary, Lenzing Modal can be distinguished by microscopy. The cross-sections of Formotex Modal and Lyocell are the closest in both longitudinal and cross-sectional views. From the longitudinal cross-sectional view, it can be seen that when water is used as the medium, Formotex Modal is also a smooth cylinder like Lyocell, but its diameter is relatively large and it is not as shiny as Lyocell; and sometimes you can see intermittent, inconspicuous stripes as shown in the above picture. When nitric acid is used as the medium, both Formotex Modal and Lyocell swell, and the longitudinal cross-section of Formotex Modal becomes close to a flat ribbon shape, and the luster is weakened. Lyocell only has a larger diameter, and it is still very shiny. Another point is that Lyocell is not a completely smooth cylinder, there will be bumps and bumps as shown in the above picture, and sometimes you can observe points like small bubbles.
2.Combustion method
Modal and Lyocell fibers burn immediately when they come into contact with flames, with a burning smell of paper and soft, flocculent ash as the residue; it is generally impossible to tell the difference by smelling the burning smell.
Cellulose fibers that are not fully burned will have ash. According to data and experience, ash appears slightly white when it contains light metal salts, and black when it contains heavy metal oxides. The raw materials of Formotex Modal come from a wide range of sources and are very diverse, so its ash will appear black and gray. Lenzing Modal’s pulp comes from Austrian beech trees that are about 10 years old, while Lyocell is mainly made of coniferous wood pulp, which contains more minerals. Its ash will be slightly black, but the difference is very subtle, and the ash will be affected by the residue of the finishing reagent, so it is difficult to accurately judge it with the naked eye alone.
Lyocell fiber uses wood pulp as raw material and organic solvents of organic amine oxides are used to dissolve lignin during manufacturing. Therefore, it has a lower impurity rate than Modal fiber and burns more fully. Sparks will fly out continuously during combustion, and only a small amount of ash will remain after burning. This dust-flying phenomenon is unique to Lyocell fiber.
3. Dissolution method
Take a small amount of Lenzing Modal, Formotex Modal, and Lyocell fibers respectively, and compare their dissolution conditions, as shown in the figure below.

According to the table above, the longer the dissolution time between Modal and Lyocell, the more obvious the difference is – Lyocell is more difficult to dissolve. At room temperature, Modal is dissolved after 5 minutes of treatment with 59.5% sulfuric acid and 37% hydrochloric acid reagents. The same is true for the treatment with 70℃ formic acid/zinc chloride reagents. However, Lyocell is still jelly-like and more difficult to dissolve. Therefore, when doing quantitative analysis, Lyocell blended fabrics should decide whether to extend the dissolution time or increase the temperature based on the actual situation.
Microscopic observation, Formotex, and Lyocell can distinguish Lenzing Modal can be preliminarily identified by observing whether there is ash flying during combustion, and then observing the diameter and gloss of the fiber through a microscope; then the dissolution method is used to observe the difficulty of dissolution for final judgment to qualitatively analyze these three fibers. However, since they are all regenerated cellulose fibers with similar chemical compositions, quantitative analysis cannot be performed using chemical methods at present.
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