COCs challenge nylon, PVC for medical bags

The initial application for the industry's first cyclic olefin copolymer (COC) elastomer is expected to debut soon in an extruded medical application.

The newly developed material targets plastics such as nylon and polyvinyl chloride (PVC) in medical applications including tubing and bags. The benefits of the COC elastomer for film are toughness, purity and moisture barrier.

Transparent COCs are increasingly used for syringes.

"These transparent polymers are candidates for applications requiring toughness and flexibility," said Timothy Kneale, president of TOPAS Advanced Polymers, Inc. (Florence, KY) in an interview with Plastics Today. The polymer is more expensive than nylon or PVC, but it offers in-plant recyclability making the economics more competitive.

"No one can compete with PVC on price, but there are a lot of multilayer structures that contain nylon or PVC that are not recycled by processors," said Kneale. "The new elastomeric TOPAS can be combined with other polyolefins, and the whole structure can be recycled."

Scrap is an issue

Right now the gold standard for medical forming webs used in bags is laminated or coextruded nylon structures.  Nylon offers excellent toughness and barrier. The ability to reuse manufacturing scrap, however, can be an important issue because film extruders typically generate 20% to 30% scrap.

COC is normally brittle but it can be made elastomeric in the polymerization process. "We run the ethylene content high enough to get into the semi-crystalline range, and the properties change dramatically," Kneale said. "This is a developmental product where we have advanced market testing going on."

Tensile modulus for the new TOPAS formulation is reported at 6400 psi while elongation at break is greater than 450%. In addition, the material's low dielectric properties are comparable to some fluoroelastomers, providing strong electrical insulation performance. Another feature is the material's ability to maintain excellent ductility at temperatures below -80°C.

The initial grade of TOPAS elastomer has an 89 Shore A hardness. It meets USP Class VI requirements for use in medical devices.

The medical forming web application is expected to spread globally after a projected U.S. launch in the second quarter. The TOPAS material does not compete in applications where oxygen barrier is required.

Very high purity

Kneale said that a big draw for the TOPAS COC materials is their high purity, which he described as even better than glass. Extractables are a growing issue with PVC, leading one major health provider (Kaiser Permanente) to abandon its use for bags and tubing. "We operate a very high-yield polymerization process," said Kneale. "We use a very small amount of catalyst, and then we filter the catalyst out. It's as pure a polymer as you can get."

Another major developmental project in the medical field for COC is in cartridges for the next-generation insulation devices. "There has been a lot of talk about an 'artificial pancreas' and new devices are being reviewed by the Food and Drug Administration." OEMs like the purity and transparency of the material for the molded cartridges, which would carry several days' supply of insulin. Moisture barrier is also important.

Insulin pumps have been around for several years and the reliability of the glucose sensors in the human body have been improving. "All you have to do now is couple those things reliably and you have a pancreas," said Kneale. "There are some incredibly compact designs being developed."

In the medical equipment approach to the artificial pancreas, insulin levels are continually monitored in a diabetic patient, and a pump supplies insulin in a closed-loop system.

Kneale said another emerging application is for microfluidic devices that operate like a "lab-on-a-chip" for diagnostic tests. "A lot of these technologies use ultraviolet light and TOPAS is the best polymer available for UV transmission."  

In an interesting demonstration at NPE 2012, Sodick Plustech will be molding TOPAS COC to produce syringes in a mold provided by Nypro, which is a molder and a developer of proprietary medical products.

COC, first developed by Hoechst in Germany, was introduced in the United States in the late 1990s.

Applications for TOPAS COC are split between extruded and molded applications. COC is increasingly blended with lower-cost polyolefins for films to improve thermoformability, tear resistance, twist properties, shrink properties and barrier.

TOPAS is polymerized from norbornene and ethylene. All TOPAS production is in Oberhausen, Germany. In 2005, Celanese sold the TOPAS line to Daicel Corporation and Polyplastics, a joint venture between Daicel and Celanese.








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