Even today, the flexibility of thermoplastic polyurethanes is testing manufacturers’ ability to find new applications and processing methods.
TPUs are used in all kinds of wiring and cable. (Image: Lubrizol Advanced Materials)
The plastics industry has experienced many firsts. In the past 50 years, the industry has changed a great deal as a direct result of the introduction of new technologies and innovative processing methods. January 27, 1959, marks one important first for the industry; it was the date that a patent was filed for a new elastomer. This highly versatile and flexible plastic became known as thermoplastic polyurethane, more commonly known as TPU. It was patented under the Estane trade name as part of what is today the product portfolio of The Lubrizol Corp., Wickliff, Ohio.
The innovation was the result of an effort by the R&D department of what was then part of BFGoodrich to reduce manufacturing costs associated with tire production. The goal was to create an injection moldable tire. Polyurethane was investigated but quickly dismissed for this application. Seeing that there were no patents for thermoplastics at that time, Goodrich seized the opportunity and created a specialty product: a synthetic polymer that could be fabricated from small, clear plastic beads into molded parts, thin coatings, and films.
“The company immediately understood that the innovation offered an opportunity to expand into a variety of markets due to its unique combination of performance characteristics,” explains Larry Hewitt, R&D manager for Lubrizol. “It was like nothing else on the market and completely changed what we knew about plastics. It was highly elastic and afforded manufacturers the opportunity to modify it or melt it and still manipulate it. With most other polymers, once they are shaped, they can’t be re-modified or reshaped. But TPUs proved to be highly versatile in that they could be processed through a variety of methods.”
Estane TPUs were flexible, but they also offered outstanding abrasion and wear resistance, tremendous temperature flexibility down to -10ºC, and superior toughness and durability. Chemically stable, they are resistant to water and oils that cause other materials to deteriorate after prolonged exposure.
TPUs wear many hats
The material’s great wear characteristics led to one of the first major applications for the Estane TPUs: fabric coatings. TPUs were actually credited with helping to create one of the big fashion fads of the 1960s and early 1970s. Known as “the wet look,” the new, shiny, breathable material found its way into boots and mini skirts. Millions of pounds of Estane TPU were sold just to keep up with demand for the hot, shinier-than-leather look.
Around the time that the wet look died, the government was pushing for anti-damage products on the exteriors of automobiles to help protect against the effects of impact at high speeds. Estane TPUs again found a niche in their ability to be molded into a variety of automobile parts, especially bumpers, to help manufacturers meet the increased regulations. Shortly after, Kimberly-Clark, Dallas, Texas, discovered that a thin layer of TPU inside an elastic band provided the perfect water barrier for its new disposable diapers.
“During these early years, we pursued whatever application seemed to be a fit for TPU,” says Hewitt. “Our primary focus at the time was injection molding, and we worked very hard just to identify enough applications to keep the division profitable.”
TPUs were extremely successful in the automative industry, almost to a fault. Now, however, the applications list is far more diversified.
“Our customers continue to find new processing methods that open the doors for an array of end-use applications,” says Mike Vaughn, VP at Estane Engineered Polymers.
Versatility leads to a wealth of uses
Estane TPUs are now processed through film, sheet and fabric coating, extrusion molding, injection molding, calendaring, overmolding, and blowmolding for markets like wire and cable, hose and tube, optical, industrial, agriculture and many more. They are found in applications including:
• After-market automobile paint finishes to guard against chipping
• Water resistant and breathable hunting apparel
• Bullet-proof glass and Kevlar adhesive to protect Humvees used in Iraq
• Helmets for athletes and soldiers
• Wiring and cable that utilizes flame-retardant TPUs
• Soft-touch hand tools
• Athletic shoes
• Sewer liners to help renovate deteriorating municipal storm lines and eliminate the need to tear up the street
• Alternative pressure system mattress pads that help prevent bed sores from forming in long-term care patients
• Medical gowns and accessories
“We see our future growth in our customers’ abilities to convert TPU into fibers through such state-of-the-art processes as melt-blown technology and electro spinning,” says Vaughn. “As these methods become perfected, more and more manufacturers will learn to weave different structures to replace more traditional materials. We see TPU being able to displace metals in certain applications where weight reduction is critical. It is also seen as a more environmentally friendly alternative to rubber in various applications.”
Highly versatile TPUs can be processed through a variety of methods, unlike most other polymers, which cannot be re-modified or reshaped once processed. (Image: Lubrizol Advanced Materials)
New chemistries broaden TPU market
According to Vaughn, it is these new processing technologies that are allowing Estane TPUs to become harder or softer, more flame resistant, highly breathable, and bio-compatible. Partially as a result of its bio-compatible attributes, Estane TPU has also made major inroads into the medical field. Newer TPU processing methods are making possible a number of life-saving devices as a result of the product’s breathability combined with its function to create a barrier layer. In 2003, Lubrizol incorporated Thermedics Polymer Products into its Estane Engineered Polymers division which will help to propel Lubrizol’s TPUs deeper into the medical field.
Demand for innovations in the medical field and other life-saving devices has created more options for TPUs:
• High-tech care for wounds that allows for an aqueous drug to be put into a patch and administered at the site of the wound over several days.
• High-precision catheters used in conjunction with ports or heart surgery.
• HeartString II Proximal Seal System, a new procedure for bypass surgery that eliminates the need for a heart-lung machine.
Other applications that are in the works include:
• A new medical device that seals off parts of the lung affected by emphysema.
• Specially woven socks for soldiers with diabetes to help heal sores.
• A new Roto Rooter-like medical device that removes artery scale; not only does the device break up the plaque, but it also captures it, so it doesn’t move to other parts of the body and create life-threatening blockages.
According to Lubrizol, the technology for processing TPUs is still largely unexplored.
“For a product that originally started with few applications, we see a tremendously bright future,” says Vaughn.
Published in R & D magazine: Vol. 51, No. 1, February, 2009, p.27