Rayon, Modal, and Tencel - Environmental Friends or Foes

Most everyone is familiar with rayon (also called viscose). Fewer people are familiar with modal and lyocell. Most people, even those familiar with rayon, don’t realize that all three of these fibers are called “cellulosic fibers” since the natural material that makes up the fiber is cellulose, a component of all plants. The cellulose is often derived from wood which has an average cellulose content of 40%.

Before answering the question in the title of this article, I’ll provide an understanding of these fibers and their properties. I don’t want to play favorites, however one company stands out above all the rest in regard to these three fibers. Since it’s not possible to discuss all companies, and due to the prominence of this company in particular as an innovative leader in fiber development and environmental protection, I will refer to them while also discussing the generic factors of these fibers.

This company is Lenzing AG of Austria. They manufacture more cellulosic fiber from trees than any other company in the world. Lenzing has been producing viscose, the first generation cellulose fiber, since 1938. Throughout this article I’ve interspersed dates of development and manufacturing capabilities by Lenzing as representative of the historical development and growth of these fibers.

Three Generations of Technology

Rayon was the first generation of these cellulosic fibers. Rayon is known by the names viscose rayon and art silk (abbreviated from “artificial silk”) in the textile industry. It usually has a high luster quality giving it a bright shine. Modal is the second generation and is known for its softness. Lyocell is third generation technology. Tencel® is Lenzing’s brand name for lyocell. Lyocell’s advantages include its environmental friendliness of the chemical processing combined with its softness, drape, resistance to growth of bacteria which create odors, and other properties.

Unlike most man-made fibers, rayon, modal, and lyocell are not synthetic. They are made from cellulose, commonly derived from wood pulp, and more recently from bamboo. They are neither a truly synthetic fiber, in the sense of synthetics coming from petroleum, nor are they natural fibers, in the sense of processing fibers that are produced directly from plants or animals (such as wool). However, their properties and characteristics are more similar to those of natural cellulosic fibers, such as cotton, flax (linen), hemp and jute, than those of thermoplastic, petroleum-based synthetic fibers such as nylon or polyester.

All three fibers are referred to generically as “regenerated cellulosic fibers” due to the combination of the natural raw cellulosic material and the chemical manufacturing process that breaks down the cellulose so it can be “regenerated” into a fiber from the original pulp.

Let’s Take Them In Sequence Starting With Rayon

Rayon is the first generation of these fibers and the one that further enhancements were built upon. Rayon was the first manufactured (regenerated) fiber. Although the first process for its manufacturing occurred about 1855 and was called “artificial silk”, it wasn’t until the 1890s that a commercially viable process was created for its manufacture. The first patent for “artificial silk” occurred in 1894. It took until 1910 for the first U.S. commercial rayon fiber production to begin. The term rayon was officially adopted by the textile industry in 1924.

Although the first staple fiber useable for clothing was produced in 1916, rayon was only produced as a filament fiber until the 1930s. High performance rayons, such as tire cord, did not appear until the late 1930s. Invention of modifiers in 1947 brought on super tire cords and marked the beginning of the high-performance rayon fibers.

Basic Principles of Rayon Fiber Production

There are many different processes for manufacturing rayon that vary between the chemicals used and their subsequent impact on the environment. As a very shortened summary of the manufacturing process, the production of rayon, which also applies to modal and lyocell, chemically converts purified cellulose (often from trees) into a soluble compound. A solution of this compound is passed through a spinneret (similar to the holes in a showerhead) to form soft filaments that are then converted or “regenerated” into almost pure cellulose in the final product.

Much of the commercial rayon manufacturing utilizes the “viscose” process dating to the early 1900s. In this process the purified cellulose is converted to xanthate, dissolving the xanthate in dilute caustic soda, and then regenerating the cellulose from the product as it emerges from the spinneret. 

Rayon fabrics have different strength and stretch characteristics created by adjusting the drawing process applied in spinning. “Regular rayon” has the largest market share. Typically found in apparel and home furnishings, it is identified on labels as “rayon” or "viscose.” The distinguishing property of regular rayon is its low wet strength. As a result, it becomes unstable and may stretch or shrink when wet. Dry cleaning is usually recommended to preserve the appearance of regular rayon fabrics. If machine washed, untreated regular rayons can shrink as much as 10 percent.

The desire for creating a higher wet strength of rayon led to the development of modal as the second generation of this cellulosic fiber. Modal is a High Wet Modulus (HWM) rayon which has virtually the same properties as regular rayon plus high wet strength. HWM rayons can be machine washed and tumble dried and perform much like cotton in similar end uses. HWM rayons can also be mercerized, like cotton, for increased strength and luster.

Other types of rayon have been developed for specialized end uses. These include disposable, non-woven markets, and high-absorption rayon fibers with moisture-holding properties for disposable diapers, hygiene and incontinence pads, as well as medical supplies.

Rayon’s Characteristics

Rayon's cellulosic base contributes many properties similar to those of cotton or other natural cellulosic fibers. Rayon is more moisture absorbent than cotton, soft, comfortable to wear, drapes well, and is easily dyed in a wide range of colors. It does not build up static electricity, nor will it pill unless the fabric is made from short, low-twist yarns. Rayon does not insulate body heat making it ideal for use in hot and humid climates.

Rayon has moderate dry strength and abrasion resistance. Like other cellulosic fibers, it is not resilient, which means that it will wrinkle. Rayon withstands ironing temperatures slightly less than those of cotton. It may be attacked by silverfish and termites, but generally resists insect damage. It will mildew, but that generally is not a problem.

Modal

Modal is a second generation regenerated cellulosic fiber and a variation of rayon. Lenzing Modal® is made from sustainably harvested beech trees in PEFC (Programme for the Endorsement of Forest Certification schemes) certified European forests. PEFC is the world's largest forest certification organization. Modal fibers with a high wet modulus were originally developed in Japan in 1951. Lenzing started selling modal fibers in 1964. In 1977, Lenzing started using an environmentally friendly bleaching method for pulp for their cellulosic fibers.

Modal’s distinguishing characteristics are its high wet strength and its extra softness. It is sometimes referred to as “soft as a feather” and the “softest fiber in the world.” In addition to its use in general apparel, its softness makes it especially ideal for body contact clothing such as lingerie and under garments.

Due to its high wet strength, modal can be machine washed and tumble dried. Modal fibers are dimensionally stable and do not shrink or get pulled out of shape when wet like many rayons. They are also wear resistant and strong while maintaining a soft, silky feel. Modal fibers have found a wide variety of uses in clothing, outerwear and household furnishings. They are often blended with cotton, wool or synthetic fibers and allow easy tone-in-tone dyeing (may be done with environmentally friendly dyes depending on the manufacturer).

Modal is about 50% more hygroscopic, or water-absorbent, per unit volume than cotton. It’s designed to dye just like cotton and is color-fast when washed in warm water. Even after repeated washing, modal remains absorbent, soft and supple.

The colors in modal typically remain brilliant and strong. Graying, as with 100 % cotton textiles, does not occur. Bleaches or whiteners may not be necessary at all. However, if you do use these in any of your laundering, be sure you use environmentally friendly ones.

The smooth surface characteristics of the modal fiber make it impossible for mineral deposits from water, such as lime scum, to be deposited on the textiles thus preventing fabric hardening after repeated washings. This “dry rigidity” in some fabrics is caused by the mineral incrustation on the fiber after repeated washing.

Lyocell

Lyocell has numerous advantages over rayon and modal in its properties as well as its manufacturing process. One of the major “claims to fame” of lyocell is its ability to absorb excess liquid (perspiration) and quickly release it into the atmosphere. It does this while being resistant to developing odors.

In 1990, Lenzing’s lyocell pilot plant started production. “Lyocell” is the generic name of the manufacturing process and fiber. Tencel® is Lenzing’s brand name. A full-scale lyocell plant went into operation in 1997.

The skin is the largest human respiratory organ. Lyocell supports the natural ability of the skin to act as a protective shell to regulate body temperature and maintain water balance. A subjective feeling of well-being depends considerably on moisture absorption and on surface structure of the fibers.

Nanofibrils are the key to the performance of lyocell. This is the first cellulose fiber to use this nano technology. The nanofibrils are hydrophilic (a strong attraction to absorb water) and optimize absorption of moisture with excellent cooling properties by releasing moisture to the air. Lyocell controls and regularly absorbs moisture, 50% more than cotton and even more than wool. By contrast synthetics do not absorb moisture.

Rougher fibers can lead to skin irritation. The microscopic surfaces of lyocell fibers, due to the nanofibrils, are smoother than the surfaces of modal, cotton and wool. It is the combination of this extremely smooth surface of lyocell and excellent moisture absorption that makes lyocell textiles feel so soft and pleasant to the skin, making lyocell ideal for active wear, clothing for sensitive skin and home textiles such as bedding.

Lyocell prevents the growth of bacteria, which cause odors, naturally without the addition of chemical treatment which may cause allergic reaction and are environmentally unfriendly. Bacterial growth is prevented through the moisture management of the fiber. When moisture is produced it is directly absorbed from the skin and transported to the inside of the fiber. Thus no water film is produced on the skin where bacteria could grow.

Clothes remain odor free for multiple wearings much longer than cotton. This also means fewer washings and saving on water and energy as well as on the wear and tear that occurs on any fabric from the washing and drying processes. The wear and tear is revealed from all the lint coming off your clothing that you see in your dryer. It is machine washable in cool water. Fabric softeners are not needed or recommended.

By contrast, synthetics have hundreds to thousands of times higher bacteria count over the same time periods as lyocell. Chemical additives are often used on synthetics and many cotton products to reduce the growth of bacteria.

Lyocell itself is hypoallergenic meaning that it is not likely to cause an allergic reaction in sensitive individuals. This is why it is used for clothing and home furnishings by individuals with Multiple Chemical Sensitivities (MCS) and those with allergy sensitivities, psoriasis, and neurodermatitis. It is also anti-static and doesn’t cling.

Lyocell Variations

Lyocell manufacturing is extremely flexible to create a diversity of fabric aesthetics. Manipulating or controlling the fibrils, the very fine hairs found on the outer fibers, produces a wide variety of fabrications, from rugged denim to suede-like or peach touch surfaces to a clean, smooth silky touch. As with silk, this fibrillation is responsible for the pleasant and soft hand of lyocell fabrics.

Lyocell can also be manipulated to create an excellent fill material. Lyocell “fill” for bedding has excellent moisture management and temperature regulation to create a pleasant and dry climate during sleeping.

Lyocell fabrics with natural elongation and recovery properties can be created without having to use elastomeric fibers such as spandex. The high tenacity of lyocell in both a wet and dry state increases the dimensional stability of the end product.

As a side note, bamboo for clothing is also a regenerated cellulose fiber. The manufacturing process is typically either the rayon process or the more environmentally friendly lyocell manufacturing process.

Environmental Friends or Foes? Can These Fabrics Be Organic or Sustainable?

Rayon, modal, and lyocell are produced from renewable cellulosic plants such as beech trees, pine trees, and bamboo. All three fibers are bio-degradable. Specifically Lenzing Viscose® and Lenzing Modal® are produced from sustainably harvested beech trees. Tencel® is produced from sustainably harvested eucalyptus trees. Eucalyptus grows very quickly and without any artificial irrigation, pesticides, fertilizers or gene manipulation that may be used in “wood farms” for industrial use. Eucalyptus can also be planted even on “marginal” lands which cannot be used for the production of food products.

Since rayon, modal, and lyocell are regenerated fibers they do not qualify for Organic certifications. Therefore, other recognized eco standards that review the entire process chain for growing and harvesting the trees through the manufacturing and treatment processes must be applied to these fibers. One such award that has been given to Lenzing for Tencel® is the European Eco-Label that addresses compliance with high environmental standards for production and products. Another is the PEFC certification, as mentioned above, that also applies to the forests from which the trees are harvested to make Tencel®.

As early as 1963, Lenzing started recycling the chemicals from pulp production after the company switched from the calcium bisulphite method to an environmentally friendly magnesium bisulphite method for Lenzing Viscose®. However, there are many manufacturers of rayon. Even with the advancements that have been made over time, most rayon manufacturing processes in use today would not be considered environmentally friendly.

Also, bamboo, if processed with the rayon process, would not be considered environmentally friendly manufacturing. This accounts for almost all bamboo processing as of 2009. However, I consider the use of bamboo to be an evolutionary process in that the farming of it is much more favorable than non-organic cotton farming and it has many advantages even over organically farmed cotton. We must push for it to use the lyocell process in the manufacturing of bamboo in order to consider bamboo textile to be a truly environmentally friendly product. (See our article: Bamboo - Luxurious and Practical for Clothes, Towels, and Sheets.)

The various chemical and waste products which result from Lenzing’s production process are recycled or sold. For example, xylose, which is the base material for xylitol, a caries-inhibiting natural sweetener is used in the food industry while sodium sulphate, a by-product of fiber production, is used in the production of glass. The remaining wood not used for pulp production is used in thermal plants to generate heat as well as energy for the Lenzing production facility.

Lyocell manufacturing, and Tencel® in particular, is an extremely environmentally friendly process and the most friendly of these three fibers. The revolutionary aspect of Tencel® manufacturing is the recovery and reuse of up to 99.8% of the solvent and the remaining emissions are broken down in biological water treatment plants. In fact, the solvent is not acidic. The harmlessness of the solvent has been proven in dermatological and toxicological tests. One can put their bare hand in the solvent without harm (although it’s probably not advisable to leave it there). Also, no toxic substances remain in the fiber.

The fiber yield per acre from the trees used in the Lenzing fibers is up to ten times higher than that of cotton. Also, cotton needs up to 10-20 times more water than required for lyocell fibers.

Of the total environmental impact of textile goods, much of it comes from the care of the textiles while in use. With lyocell fabrics, there is no need for fabric softener or whitening agents or bleach which add cost to the consumer and chemicals to our environment. Without these added agents, energy and water use can be decreased for spin and rinse cycles since shorter washing machine cycles can be used.

Lyocell is truly an environmental achievement in fiber production. It is derived from a renewable and sustainably harvested raw material, its manufacturing is sustainable, and its disposal is biodegradable to complete the full cycle.