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The Rupp Report

The Rupp Report: Physiological Apparel Part III: The Right Yarn For A Functional Product

Jürg Rupp, Executive Editor

The fundamental cornerstone of every functional fabric is the yarn. The property of the yarn defines predominantly the final product, its functions and uniqueness. In the third round of its Physiological Apparel series, the Rupp Report highlights some fundamental characteristics of the applied yarns.
A look back in history shows that between 1878 and 1884 Count Hilaire de Chardonnet achieved a breakthrough in the manufacture of the first natural man-made fiber — artificial silk, or rayon — from dissolved dinitrocellulose. Rayon was produced industrially from 1890 on, followed by the manufacture of cuprammonium, or “copper rayon” — later called Bemberg silk — from a solution of cellulose in copper oxide ammonia.
The Beginning
Ever since then, functional fabrics and sports apparel have been produced mainly using man-made fibers. In this context, two names must be mentioned: first, U.S. scientist and inventor Wallace Hume Carothers. In 1928, DuPont opened a research laboratory to develop artificial and synthetic material, and Carothers became the director of this lab. In 1930, he discovered neoprene, a synthetic rubber, and synthesized the first polyester. In 1934, his trials ended up with the discovery of polyamide 6,6 (PA 6,6), also known as nylon. When Carothers discovered the excellent properties of PA, he was convinced that this new fiber material could challenge silk.
Another name to be mentioned is the German scientist Paul Schlack. He discovered in 1938 the ability to polymerize caprolactam to produce polyamide 6 (PA 6), also called perlon, the big competitor of DuPont’s nylon. From the 1960s on, it was possible to develop and produce tailor-made yarns. So it is no coincidence that the man-made fiber industry started early to deal with the drafting and elaboration of guidelines for proper functional sportswear. In addition to using these yarns for fashionable outerwear, other new areas opened up with success. However, the development of man-made fibers didn’t stop there.
No Comparison Possible
This report is not a crusade against natural fibers; yet, natural fibers tend to soak up moisture, up to 50 percent of their own weight. This property is undesirable in a garment worn while engaged in physical effort. The material soaks up moisture, sticks to the body and sags — and creates unwanted chills, even in extreme heat. That’s why man-made fibers are most used in apparel for active sports, mainly for ski trousers and jackets, anoraks and overalls, swimwear, track suits, and gym and other activewear.
Considering the requirements for modern functional fabrics and sports apparel, this report is mainly about man-made fibers. In this context, natural fibers are used to act like a wick and transfer the body moisture from the inside to the outside, and — according to the so-called “onion skin principle” — they are used as the second layer on top of the man-made-fiber layer. But more of that later. The most important yarns in functional fabrics and sports apparel are made with PA 6,6, polyester (PET) and partly polyurethane elastomer (PUE), or spandex.
Polyamide 6,6
The most important properties of PA fibers are their high strength, high elongation capacity, excellent abrasion and crease resistance, as well as dimensional stability. PA 6,6 fabrics are mainly used for particularly durable and hard-wearing products.
Sometimes, the acronym for polyester is PES; however, the polymer for polyester is polyethylene terephthalate (PET). Over the years, PET has became the top runner of all man-made fibers. Blends of PET and natural fibers such as wool or cotton are standard products for outerwear. In the sports sector, PET is characterized by an excellent performance. It can be particularly finely spun, and it has good tensile strength and elongation. PET fabrics have a further, particularly fashionable advantage: PET was the first man-made fiber that could be printed using the transfer process.
Polyurethane Elastomer
PUE yarns are particularly elastic, and are called elastanes or spandex in the United States. PUE can be described as a synthetic rubber. Elastanes are used when the fabric — mainly warp knitted —must be especially resilient and fit the body without wrinkling. The tight fit of the jerseys worn by the players during the recent soccer World Cup games offers an illustration of the properties of elastic yarns. DuPont™ LYCRA® is the most famous elastic brand. PUE is also used in many other sports goods, such as shells for ski boots.
Customer Prejudices
Man-made fibers are particularly suitable for appropriate functional sportswear. They take up virtually no moisture; and are easy to clean, durable and dimensionally stable. In spite of all testing to show the contrary, there are still rumors that man-made fibers cause allergies, are not skin-friendly and make you feel like you are sitting in a sauna. And, above all: that man-made fibers are not hygienic. These notions are far wrong: Virtually every surgeon uses man-made fibers to close wounds after an operation. And the hot sauna effect is caused by an inappropriate fabric construction and the making-up of the apparel.
For decades, the consumption ratio between man-made and natural fibers was 50:50. Because of further improvements in man-made fibers, this ratio has drastically changed to some 75:25 percent in favor of man-made fibers. “In 2012 global fiber demand reached another record of 85.8 million metric tons, an improvement by 4.5 percent over 2011,” reported “The Fiber Year 2013: World Survey on Textiles & Nonwovens,” published by IVC, the Association of Man-Made Fibers Producers in Germany, Austria and Switzerland. “This was mainly attributable to historic highs in man-made fiber production: For the first time, the output of synthetic man-made fibers exceeded the mark of 50 million tons. The output of cellulosic man-made fibers was more than 5 million tons, the first time in their 100-year history.
“The segment of man-made fibers saw an encouraging increase in global demand by 6.0 percent to 56.0 million tons, with the demand for synthetic man-made fibers alone climbing by 5.6 percent to 50.8 million tons,” the report continues. In comparison, cotton consumption rose by 2.2 percent 23.3 million tons.
In terms of size, continuous man-made fibers are categorized as coarse, medium, fine filaments and microfibers. Some 25 years ago, microfibers started their conquest throughout the entire textile world, and everybody is talking about them. But who knows exactly what microfibers are? For this a little bit of terminology again: The yarn count of endless filament yarns is described today using the metric system, decitex (dtex), and is composed of the weight in grams and the number of filaments in the diameter: for example, 167 f 48. In this example, 10,000 meters of the filament yarn weigh 167 grams. The letter "f" indicates the number of fibrils, or filaments; in this case, 48. If one divides 167 by 48, the result is 3.4. This is particularly important when it comes to microfibers. The smaller the result, the finer the individual filament. Now, if the yarn count is 156 f 248, the result is 0.62. Every result below 1 indicates a microfiber. This calculation will be of an outstanding importance when it comes to woven fabrics for functional textiles and sports apparel.
There will be more about fabric forming for functional fabrics and sports apparel in an upcoming edition of the Rupp Report.
August 5, 2014