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For at least a decade, Bill Rearick, Director of Textile Chemistry Research at Cotton Incorporated, has been facing a trend he finds vexing in its seeming contradiction: the growing popularity of synthetic fibers in recreational performance apparel (RPA), often referred to as
activewear.
For the serious athlete, certainly performance is an issue. But for the majority of consumers – from weekend warriors to hip-hoppers to couch potatoes – RPA is mostly about comfort. “We own comfort,” states Rearick in the plainspoken manner born of his Queens, NY, upbringing and tempered by an adult life spent mostly in North and South Carolina. The “we,” of course, are the employees of Cotton Incorporated, whose mission is to increase the demand for and profitability of cotton, often through promoting and enhancing the fiber's many virtues; among them, a soft, appealing hand and its ability to breathe.
However, as the market for RPA grew, so did the use of a new buzz phrase, moisture management. “Hang tags on these garments, usually made from synthetic fibers, carry all kinds of miraculous claims,” Rearick notes. “These include moisture management properties superior to cotton, and in some cases, assertions that defy the laws of physics and thermodynamics. There seemed to be a growing belief that this 'new' synthetic fiber technology out there makes water evaporate faster.” As a chemical engineer who spent many years developing processes for dyeing and finishing cotton, Rearick, a 25-year veteran of Cotton Incorporated, can smell half-baked science from a mile away. “Basically, cotton is not perceived as 'high-tech', even though it is one of the most chemically reactive and versatile fibers. I know that for everyday use, cotton has excellent moisture management properties. It's one of the reasons it's so comfortable. But through all the hype, there was no clear definition of exactly what moisture management means.”
Rearick saw an opportunity to increase the use of cotton in the important RPA market by developing new finishes and/or processes that would improve the moisture management properties of 100% cotton fabrics. “RPA is important not only due to its market potential in sports and exercise wear, but we see more and more cross over,” Rearick observes. “RPA is growing for use as everyday street wear. In some cases, it’s cool to look like a jock or maybe just have a sports related logo on your shirt.”
His initial realization was that he had to look beyond chemistry, and put his engineering instincts to work. “We saw a likely need to focus on construction, as well as finish, to get improved moisture management properties,” Rearick recalls. This meant he would not only be working with his colleagues in Textile Chemistry, but also with the Cotton Incorporated Fabric Development team.
“It first became clear that the thickness of the fabric is a key and controlling variable when it comes to moisture management – the thicker the fabric, the more moisture it holds,” Rearick says. “Most of the synthetic RPA fabric, like those made from micro fiber polyester, were considerably thinner than cotton fabrics.”
Another big difference between cotton and polyester is that cotton fibers are more absorbent, or hydrophilic, while polyester and other petroleum-based synthetics are not as absorbent, or hydrophobic. “Synthetic fabric that wicks absorbs less water, due to the thin construction and not as much due to their underlying hydrophobic nature. The drying time was much less for synthetics because they were thinner. However, the drying rate was essentially the same for all fabrics that wick,” Rearick reported after running trials using the Gravimetric Absorbency Test System. When Fabric Development created a thinner cotton fabric, a single jersey knit from 30/1s yarn, “the absorbent capacity was similar to 100% polyester of similar thickness. And,” Rearick adds, “drying time was similar, and in some cases, slightly less for cotton.”
Other important performance differences were also found. “While the last 5 or 10% of moisture in cotton fabric dries slower because of its hydrophilic nature, it feels dry at a standard moisture regain of about 7.5%,” Rearick explains. “But if polyester fabric contains more 2 or 3% moisture, it still feels clammy.”
In addition to fabric thickness and construction, Rearick and his team have been experimenting with a variety of finishes and other mechanical and wet processes that might impact moisture management properties. This includes work with North Carolina State funded by the Importer Support Program. “The focus has been on how to reduce absorbent capacity while maintaining wicking, which is the capillary movement of liquid moisture within a fabric structure.” “
In some cases,” he continues, “we are looking at the impact of fiber and yarn properties, which has led to some very complex research. We are testing a number of techniques, including treating some cotton yarn with flourochemicals to make it hydrophobic, and blending it with regular cotton yarn in plaited constructions. This,” he emphasizes, “could allow a manufacturer to create a whole line of clothing with different levels of performance characteristics depending on the use it's being designed for. Different results can be obtained depending on the yarn, the chemistry used on the yarn, as well as different construction. The variables can allow for a great deal of flexibility.”
Trials are also being done on a variety of standard cotton fabrics, including both knits and wovens, and how proper scouring and bleaching during finishing can enhance wicking. “One challenge has been that there is no standardized test accepted by the industry that is useful for cotton to show that is has moisture management properties,” Rearick says. ”Almost any properly scoured cotton fabric that we’ve tested passes the wicking and drop absorbency tests that are used to show that a synthetic garment has good moisture management properties.“
Surface treatments are another area of moisture management study. “For example, if you coat the inside or outside surface of a cotton garment with a flourochemical, it will certainly reduce absorbency.” An avid racquetball player, Rearick did his own anecdotal test. “With the inside of the tee-shirt totally covered with the flourochemical, it repels the moisture, but there's no way for it to evaporate out of the fabric. Eventually, the sweat just ran down to my shorts. From this, we decided to try printing a fine pattern of a particular flourochemical on the inside surface of the garment,” Rearick explains. “This reduced absorbency and created small 'wicking windows,' which allowed the moisture to be transported to the outside surface of the fabric.” In this way, breathability is not effected in any way,“ he reports.
With moisture management research continuing at Cotton Incorporated, Rearick sees infinite possibilities for cotton activewear in the future. “We have been getting out to the mills and actually applying some of this technology,” he relates. “Once the industry sees the practicality of this, and the fact that the consumer prefers the comfort of cotton, performance improvements will not be far behind.”
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