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Polyketone / Zyex Information Center

A Quick Look at the History of Zyex® with Inventor, Bruce McIntosh

By Steve Crandall
Vice President, Sales & Marketing
Ashaway Racket Strings

Bruce McIntoshCredited as the inventor of ZYEX®, Bruce McIntosh is a polymer scientist and textile technologist who originally took his degree in Physics from Edinburgh University.
If you look around the room you're in right now, chances are at least half a dozen different kinds of plastic are within easy reach. The fact is, we live our lives surrounded by plastics; polymers to be precise. Yet few of us really know anything about them. Of course, most of our eyes would quickly glaze over if someone really tried to describe the technology, but with ZYEX-based racquet strings showing such great potential, we thought it might be interesting to take a closer look at how this material was developed and who thought to make it into a tennis string in the first place.

There's no one better able to provide information on this history of ZYEX® than its inventor, Bruce McIntosh. Currently a New Developments Consultant to ZYEX Ltd., Bruce is a polymer scientist and textile technologist who originally took his degree in Physics from Edinburgh University. In the 1980s it was Bruce who initiated the ideas that led to the first fiber products being made from a newly invented class of polymers, polyketones (better known as PEEK polymers). He served for many years as Project Leader for ZYEX fibers, and authored patents for industrial, music string and sports string products, which have been produced from special ZYEX fibers. He is also credited with the invention of Tactel® from Invista, a breathable synthetic fiber much used as a tracksuit material and in other sports garments. He and his wife Sheila have three sons, and currently six great little grandchildren.

Here's the gist of our conversation:

SC: Most people harbor a rather cartoonish image of scientists in their labs, madly mixing chemicals until they explode, then emerging from the smoke all blackened and disheveled. But how does one really go about developing a new polymer material like ZYEX? Can you explain the process in layman's terms?

Bruce: Well, there were test tubes involved, but fortunately in this case, no explosions. ZYEX grew directly out of an understanding in the early 1980s that a new category of polymers - polyketones - was becoming available.

That it should be possible to make synthetic fibers from these new polymers seemed likely from basic chemical stability and melt flow data. That the fiber properties achievable would be unique, was also proved to be true. By 1985 enough potential from samples made on a small lab scale extrusion rig had been seen to justify the launching of a trademark, ZYEX. As just about the last word in any directory of trademarks, it also might also be 'the last word' in fibers too!

SC: Once a new material exists, how are its properties determined? And how are applications developed?

Bruce: ZYEX was at first only able to be extruded as fairly coarse diameter, tough monofilaments, clearly a good possible replacement for polyester monofilaments in woven fabric for industrial uses, especially in those applications where tension, heat, and abrasive forces were all present. Conveyor belt fabrics used during the manufacture of paper and for drying pasta were some of the first successful uses.

SC: ZYEX is said to be a Polyketone. Are there other, perhaps more commonly known materials, in this category?

Bruce: Polyketones are a family of polymers able to be manufactured in small quantities. However once PEEK (polyetheretherketone) stood out as being more readily purified and scaled up for manufacture, it has dominated the market. To date, well over 90% of all polyketones sold have been from PEEK, and in fiber form this is predominately our ZYEX. About 50% is currently available as injection moldings; with powder impregnation of carbon fiber composites, film and fiber manufacture making up most of the remainder.

SC: In the case of ZYEX, what types of applications did you initially pursue?

Bruce: The main markets are in the aerospace, automotive, medical device and specialized industrials areas - very little that the average consumer would be aware of, with the possible exception of guitar and violin strings.(which are ZYEX patented products.)

SC: Would you say the material has gained wide acceptance in the marketplace, or are there still many application areas to be developed?

Bruce: Polyketones are still basically very young materials, and many other application areas are likely to be opened up, especially if a way can be found to reduce fundamental polymer cost. In many applications PEEK may already be technically the 'best solution,' but its high price will often hold back its implementation.

SC: What led you to think of racquet string (and particularly tennis) as a possible application for ZYEX, and what specific properties led you to think so?

Bruce: The background to the involvement of ZYEX in the tennis string business is somewhat surprising. A comment was made to the I.C.I. Chairman (The ZYEX Group was then part of I.C.I. Fibres) following Wimbledon one year that, "surely, somewhere in his vast materials based organization there must be a good synthetic substitute for natural gut?" This casual comment passed down the organizational chain to me as a firm instruction: "Evaluate a tennis string made with ZYEX." It had always been on the list of potential developments to follow, but now it was promoted at a stroke from about 20th to 1st priority!

Being a keen racquet sports player and having already had some local contact with the technical team at Dunlop Sports, I was more than interested to take up the challenge.

The key identifying property was quickly discovered to be low dynamic stiffness, which is the ability of a material to resist stiffening up as it is rapidly stretched and released - become "boardy," as it were. This property was low for natural gut and stayed low at a wide range of operating tensions. All other synthetic fibers used in the construction of sports strings at that time - especially nylons and polyesters - might or might not start low, but all registered a rapid increase in stiffness as the string tension was increased.

The very first testing of a rudimentary ZYEX string showed very little increase in stiffness, so it clearly had real potential to emulate the response of natural gut.

SC: In terms of physical properties, how are ZYEX filaments comparable to ribbons of beef serosa used in natural gut strings?

Bruce: Not only does ZYEX have by far the most similar playing characteristic to natural gut of any synthetic, it also has the great advantage of being highly stable to environmental factors - moisture, heat, abrasion, etc. - so it plays the same for much longer. In this respect it is vastly superior to the natural product.

SC: ZYEX has been used in string applications for a number of years now, and seems to keep getting better. Do you see the possibility of further improvements down the road, and if so, what can we expect?

Bruce: ZYEX is still a relatively young product (who is seriously old at 27 anyway!) We have seen improvements in polymer quality, and processing technique over the years, and expect more. These improvements will normally convert to more consistent and higher physical properties in the final products, allowing wider ranges to be developed. Ultimately the ZYEX product range may routinely encompass other polyketones, which will certainly lead to potentially more stable products for many applications.

SC: Translation, 'better and better racquet strings?'

Bruce: Most assuredly.

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