By Steve Crandall, Vice President, Sales & Marketing Ashaway Racket Strings
One of my pet peeves are those TV ads that tell you a product is wonderful because it “contains Hydromethoxoflam,” or some such miracle ingredient, but then never tell you what “Hydromethoxoflam” is, or why it makes the product so good. Well, it should be no secret by now—at least, I certainly hope it’s not a secret—that Ashaway is introducing a new line of Zyex® strings. And we’re making claims about how wonderful they are (which in our case are all true, of course). So, I think it’s a reasonable question to ask, just what is Zyex, and why does it make such wonderful string?
Actually, Zyex is rather neat stuff, and I’ll try to describe it with as little technical jargon as possible. Zyex is the trade name for a high temperature, engineering grade polymer known as polyetheretherketone, or PEEK. According to the online encyclopedia, Wikipedia, “Polyketones are a family of high-performance thermoplastic polymers. The highly polar ketone groups in the polymer backbone of these materials gives rise to a strong attraction between polymer chains, which increases the material’s melting point. Such materials also tend to resist solvents and have good mechanical properties.”
In layman’s terms, this means that PEEK materials like Zyex have several physical properties of interest to manufacturers. Specifically, PEEK monofilaments and fibers are very tough and durable, and have excellent abrasion resistance, particularly at higher temperatures. The material’s melting point is 633ºF (334ºC), very high for plastic, and it has a maximum continuous service temperature of 500ºF (260ºC). Short-term service can be up to 570ºF (300ºC). This means that when exposed to hot air, PEEK retains approximately 90% of its strength up to 570°F. PET, the material typically used for soda bottles, loses strength rapidly as temperatures reach 200°F. Even vaunted aramid fibers begin to lose it around 450°F. So PEEK is hot stuff!
In terms of abrasion resistance, PEEK also offers good performance. In tests measuring “thread on thread” abrasion conducted at room temperature, PEEK multifilaments outlasted aramid fibers by a factor of approximately 5.5. PEEK also has very low moisture uptake at 0.1%, which means you don’t need to worry about carrying your racquets around in thunderstorms. And if perchance you want to play outside in thunder and lightning, PEEK is a very good insulator.
In fact, one of the original applications for PEEK was as aerospace insulation designed to protect electrical wiring from abrasive damage especially at extremes of temperature. PEEK monofil braids have also been successfully used in automotive and nuclear installation wiring. According to the Zyex website, the material can be ideal in “any enclosed situation when toxic fumes from burning wiring could pose a threat to life.” I don’t know if this will help with those old socks in the bottom of your gym bag, but you can’t be too careful.
Other interesting applications include very fine filaments tightly woven into precision filters for fuel or clean air systems. Tougher versions of PEEK yarns are woven in multi-layers to withstand the pressure dewatering of chemical slurries or the heat compaction of fibrous board.
In composite structures, PEEK fibers are mixed with carbon fibers at between 40% and 60% by weight. The PEEK fibers melt and coat the carbon fibers, encasing and protecting them. These are used to make advanced aerospace components, lightweight surgical tools and other medical devices, taking advantage of PEEK’s inherent cleanliness and biocompatibility.
But perhaps the most interesting application for Zyex—other than racquet strings, of course—is in music instrument strings. A number of manufacturers now offer Zyex violin, guitar and other musical strings. Zyex provides a subtle but appreciably fuller tone than other synthetic string materials such as nylon. It also stays in tune much longer on a guitar or violin than is possible with other conventional music strings. So when squash players say they love the sound their Zyex strings make, they have good reason.
In racquet strings, Zyex offers low dynamic stiffness which allows it to deform and recover more completely than other synthetic materials. It can also be made to have exceptionally low creep under continuous tension, allowing racquet strings to maintain tension and playability longer. And as noted previously, the manufacturer of Zyex continues to improve and “tweak” the material, making it even better for string applications. Recent advances have produced Zyex filaments that are even finer and stronger than before.
However, it takes more than Zyex to make a string. We’ve been working with these new filaments in our R&D lab to develop even thinner multifilament core packages with increased linear density and more cross-sectional strength. The result, we feel, is a significant advance in string technology: thinner, softer, lighter-weight strings that provide superior feel, more power, and improved ball control, while still offering the well-known Zyex playing characteristics and tension holding properties. Any questions?