Rethinking cotton in nonwovens

May 1st, 2015 / By: / Advanced Textiles, Markets

Sustainability concerns and better processes are making the use of cotton in nonwovens more attractive.

By Paul Sawhney, D.Sc.

The words “cotton” and “advanced textiles” have not, typically, been used in the same breath. There are some good reasons for that, including the price tag. But new processes for integrating small amounts of cotton into engineered nonwoven fabrics are bringing it back into the fold and offering fabric manufacturers—including the makers of advanced textiles and its applications—choices worth considering.

A long history
Today, cotton’s global market share of textile fibers is about 30 weight percent, although cotton still retains about 65 percent market share for apparel and common household products, globally. The main reason for such popularity among consumers is cotton’s excellent moisture absorption, moisture transportation within the fiber’s lumen and rapid dissipation of the moisture, which provides comfort.
However, with the advent of some regenerated fibers, such as rayon(s) from natural cellulose pulp, and some synthetic fibers—such as nylon, polyester and polypropylene from fossil byproducts—in the first half of the 20th century, the use of cotton, even in its traditional apparel and other end uses, began to shrink.

There may be quite a few legitimate reasons for the gradual decline of cotton’s global market share. The so-far subdued use of cotton in modern nonwovens can be attributed to cost competitiveness, in part, but there are additional factors.

As these concerns are overcome, cotton and/ or cotton blends may have a larger role to play in the development of value-added, disposable, semi-durable and even durable nonwovens for certain commodity and specialty markets. These could include applications as varied as function-specific wipes, personal hygiene products, bed sheets that can prevent patients from getting sores, fire-retardant and/or antimicrobial uniforms, undergarments, household furnishings and geotextiles. Institutional and industrial products and applications could include drapes, air filters and automotive components.

But even beyond these more familiar uses, novel composites could be developed, such as a revolutionary fire-proof and anti-termite “manufactured wood.” This could conceivably save property and even lives—and do so in an environmentally friendly way by offering safe alternatives to using our planet’s depleting forests.

Cotton’s place
In the second half of the 20th century, a major new field of technologically advanced nonwoven fabrics was developed. Initially, they were made primarily with newly discovered manmade or manufactured fibers, although some cotton felts and woolen blazers, which essentially are also nonwoven fabrics, and which have been produced and used by mankind for centuries, were still made with natural fibers. In fact, straw mats and fibrous felts that are very like nonwovens were produced for shelter among ancient civilizations, so materials like today’s nonwovens have been used for centuries.

Cotton, especially in its lint form, is rarely used in any significant quantity in modern nonwoven textiles. Today, the manufactured textile fibers, such as polypropylene, polyester and rayon(s), make about 96 percent (by weight) of all worldwide nonwovens markets. The market share (by weight) of cotton lint in modern nonwovens is estimated to be only about 2 to 3 percent and of other natural fibers is about 1 percent.

“Trash” and cotton
Classical greige (ginned/raw/unbleached) cotton lint, as it is generally supplied in 480-pound bales to user mills, inevitably contains varying amounts of foreign (non-lint) matter known as “trash” that must be removed at the first opportunity at any cotton user mill or facility. Since the nonwovens roll-goods manufacturing industry today mostly uses the manufactured fibers, which, as supplied, are mostly clean, white in color, uniform, consistent in quality and therefore ready to be processed without any fiber cleaning, the industry obviously does not feel the need to install any special equipment for cleaning greige/raw cotton in its own roll-goods manufacturing plants and facilities.

Contamination of the nonwovens industry’s existing non-cotton processes and products by cotton fiber, cotton trash and any other cotton-borne contaminants has also been a significant concern and a major deterrent to the use of cotton in modern nonwovens. Furthermore, the most efficient—also rapidly growing—hydro-entanglement system of commercially producing nonwoven fabrics from staple fibers requires efficient filtration of the system’s effluents for recycling, and thus conserving the system’s water usage.

Although several water filtration systems are now commercially available, it is difficult to predict whether these systems would perform as well as claimed and as expected in a real world scenario where the greige cotton is processed.

The classical greige cotton lint as supplied in bales has two types of impurities:

1. Physical impurities, mostly consisting of plant debris (leaves, stem, bark,), dirt, seed-coat fragments (SCF), neps (entangled fiber masses) and extremely short fibers. These impurities are mostly generated by the cotton’s “production and ginning environment” and must be removed in a user facility.

2. Cotton fiber’s native and natural impurities, such as waxes, sugars, pectin, peptides and coloring matter. However, depending on the ultimate cotton conversion route, there may be some flexibility of options as to when and how to remove these impurities.

Use of cotton in nonwovens
In view of the above scenarios, nonwovens manufacturers, if they must use cotton in some of their products, would prefer commercially available bleached cotton fiber, or, preferably, bleached cotton motes, wastes and/or cotton byproduct called comber noils, which generally are more cost competitive than bleached cotton lint fibers.

This strategic industrial approach of using commercially bleached cotton fibers instead of the greige cotton obviously eliminates the need for a subsequent wet processing of cotton or a cotton-blend fabric, especially when the latter contains only a small amount of cotton fiber, anyway.

However, cotton’s scope and especially that of greige cotton in nonwovens is now expected to grow rapidly for three main reasons:

1. Commercial availability of post-gin, pre-cleaned greige cotton that does not require traditional cotton cleaning. At least four U.S. and foreign companies are now known to produce post-gin, pre-cleaned cotton lint that is much better cleaned than traditional mill/user cleaned greige cotton. This pre-cleaned cotton can be successfully used as such without any further cleaning by a modern nonwovens roll goods manufacturer.

2. Current interest in natural fibers and eco-friendly materials are significant drivers in encouraging nonwovens goods manufacturers to incorporate at least 15 percent cotton in their products.

3. The advent of the rapidly growing, highly efficient and versatile nonwovens production technology of hydroentanglement—commonly (however, incorrectly) known as ‘spunlacing,’ especially for staple fibers such as cotton. Based on the ARS-USDA research on this system, the system indeed is ideal for processing pre-cleaned greige cotton that potentially could reduce or even eliminate the traditional wet chemical processes of scouring and bleaching that almost all greige cotton products need to undergo, but that carry potential cost and environmental concerns.

Although the whiteness index of a hydroentangled, greige cotton, nonwoven fabric may only be about one-third of a comparable fabric made with commercially bleached cotton, the whiteness can be considerably improved by incorporating up to 60 percent of a suitable manufactured fiber, such as rayon or polyester, that typically is very white and thus brings the overall whiteness of the fabric blend to almost that of a bleached cotton fabric.

This fiber blend feature alone could be an incentive for the nonwoven manufacturers to consider blending cotton lint and/or its co-products or derivatives with certain manufactured fibers to produce products that may not require costly and environment-sensitive chemical processes.

Paul Sawhney, D. Sc. (ap.singh@ars.usda.gov) is a senior research cotton technologist and a former lead scientist at the Southern Regional Research Center, Agricultural Research Service, USDA, in New Orleans, La. The SRRC is a federal research facility of the U.S. Department of Agriculture. The names of the companies and/or their products, if mentioned, are solely for the purpose of identifications and do not imply their endorsement over others by the USDA.

The author acknowledges the National Program staff of the Agricultural Research Service of the U.S. Department of Agriculture and his co-workers, especially Michael Reynolds, for providing support to conduct and report the work presented in this article.

Leave a Reply