TPEs a viable alternative to silicone in medical applications

Fairlawn, Ohio — Silicone remains one of the most sought-after materials in the medical market, and its availability is rebounding following the supply chain headaches of recent memory.

In many cases, silicone is the only elastomer that can be used for a given medical application.

But in many other cases, according to Hilarie Rubin, senior market manager for the custom compounder Teknor Apex Co., a tried-and-true silicone component can be replaced with a thermoplastic elastomer product without any drop in performance.

And it behooves those in the medical space to consider a TPE alternative, should supply chain challenges arise once again, Rubin said.

"A lot of worry was created by silicone shortages," Rubin said May 8 during a presentation at the Healthcare Elastomers Conference, organized by Rubber News, a sister paper of Plastics News.

"The Cadillac of elastomeric resins for the past 60 years was in short supply," Rubin said. "And customers were asking, 'Is there an alternative material I could use?' "

As it turns out, there is.

And TPEs are gaining in popularity with their lower cost, lower specific gravity, ease of tooling and simplicity in processing.

TPEs, a mixture of plastic and rubber with the stiffness and elongation properties of each, comprise a broad category.

They include thermoplastic vulcanizates, thermoplastic polyurethanes and thermoplastic polyolefins, among other subsets.

Rubin noted that TPEs are not thermosets like most rubbers, meaning they do not have a curing phase in production.

TPEs come in the form of pellets and typically are injection molded or extruded into "whatever widget you want to make," Rubin said.

As Teknor Apex supplies medical resins to customers, Rubin said representatives "like to sit down with customers in advance to determine the right TPE for a given application."

"We can go back to our database and see if it already exists [as a proprietary formula], and if it does, great," she said. "If not, we can incorporate a new resin for the customer.

"That is where our suppliers come into play. But application typically drives the material."

Teknor Apex, established in Pawtucket, R.I., will celebrate the century mark next year. It has about 2,000 employees worldwide, producing TPEs (specifically, its properietary Medalist TPEs) domestically in California and Tennessee.

"We shoot for right-the-first-time," Rubin said. "But there are several iterations, especially with medical devices, before you get something perfect."

Teknor Apex even assists customers in designing and building a new mold or "funky die" of some sort, Rubin said.

"We can then install it in our own equipment and run our materials through it," she said. "Essentially we give them a blueprint as to how to process it, and I think that is unique and special. This promotes continuity and eliminates risk."

Silicone, at its most basic production process, is formed by obtaining the metal silicon from silica sand, then reacting the silicon with methyl chloride over a catalyst. A reaction with water then removes the chlorine atoms.

More than 50 billion tons of sand and aggregate is used every year to make silicone materials, including silicone rubber, Rubin said.

But the medical industry represents a miniscule portion of the overall silicone market, Rubin said.

"The top uses for silica are building and construction, and transportation," Rubin said. "Urban areas have quadrupled in size since 1950.

"But we are talking about medical products. All of these other, bigger users of silica represent competition for the material. Medical is at the bottom as far as sand and silica."

As Rubin presented the argument for consideration of a TPE alternative, she noted that the specific gravity of a TPE part is lower than one made of silicone, allowing for more parts per pound in production — and lower cost, with a lower CO2 footprint, in transport.

In processing, there are several additional stages involved with silicone molding, and the molds for silicone are very specific and detailed, using molds that are mostly designed in Europe, Rubin said.

Cycle time with TPEs is drastically lower than the cycle time for silicones, since no drying is needed. Silicones require about twice the heat of a TPE mold, Rubin said.

And the economics of TPE processing are typically better than silicones, based solely on resin costs.

"With TPE it is easy to make molds and they are easy to find," Rubin said. "Most injection molders in the U.S. are familiar with molding TPEs."

TPEs cannot replace all silicone products—not even close, Rubin said.

But there are opportunities everywhere with TPEs, in medical, military and defense and many other industries.

"If a medical part does not have the most stringent requirements ... but you have used silicone for 60 years simply because it has been there, you might want to consider an alternative," Rubin said.