New Medical Grades of PVC Hit the Market

Originally Published MDDI July 2004

NEWSTRENDS

Erik Swain

This has been a year for breakthroughs in vinyl compounds, with several companies introducing new types of medical-grade polyvinyl chloride (PVC) that offer better performance and environmental compatibility.

Teknor Apex (Pawtucket, RI) has introduced a family of flexible vinyl compounds that it says offers better resistance to heat-related discoloration or degeneration than current medical-grade PVCs. 

“Because they withstand the heat and shear of melt processing better than conventional medical-grade vinyl, our new compounds enable extrusion processors to run at higher rates and with fewer screen changes,” said Peter M. Galland, the firm's market manager for regulated products. “Injection molders have greater assurance that vinyl will stand up to the shear forces developed when filling molds for complex or thin-wall parts.” The process improvements should lead to a reduced risk of product defects and greater shelf life, as products made from it are better able to withstand heat from sterilization and transportation, he said.

The key, he said, is a proprietary heat stabilizer formulation. Calcium-zinc stabilizer formulations are typically used in medical-grade PVC, but they do not offer strong heat-protection properties. Barium-zinc formulations are much better at heat protection, but cannot be used in medical devices because they contain heavy metals. The Apex formulation, Galland said, has long-term heat stability similar to barium-zinc formulations, but does not contain heavy metals. He noted that the Apex compounds have passed USP Class VI and cytotoxicity tests. Performance tests showed better static and dynamic stability than the vinyls with calcium-zinc stabilizers, better dynamic stability than those with barium-zinc stabilizers, and static stability nearly as good as that for the barium-zinc products.

Applications for extruded products include tubing for blood transport and delivery, enteral feeding, oxygen delivery, dialysis, catheters, and drainage systems. Applications for injection-molded products include oxygen masks, mouthpieces, adapters, valves, connectors, drip chambers, and syringe bulbs. 

In addition, Eastman Chemical Co. (Kingsport, TN) and Solvay Draka Inc. (Commerce, CA) have developed a medical-grade PVC that contains an alternative to the plasticizer di(2-ethylhexyl)phthalate (DEHP). DEHP is not classified as an unsafe product, but some device companies have been looking to phase it out.

In July 2002, CDRH reported that animal studies had shown risks to the reproductive systems of young males exposed to high levels of DEHP. Based on those studies, the center advised using caution when procedures involving exposure to high levels of DEHP are performed on male neonates, pregnant women who are carrying male fetuses, and peripubertal males.

As an alternative to DEHP, Solvay introduced a medical-grade PVC using Eastman's dioctyl terephthalate (DOTP) as a stabilizer. DOTP “is a different chemical structure and involves a different biological activity,” said Stephen Byrd, Eastman's market development representative. “It has a long history of safe use and is an alternative for customers with a sensitivity to DEHP.” He added that DOTP stabilizers provide equivalent performance to DEHP formulations.

Significantly, using DOTP has little effect on cost, said Mark Stern, Solvay's vice president of sales. “Most DEHP alternatives require different equipment and different processes, but this one does not,” he said. “Citrates and TOTM [trioctyl trimellitate] are extremely expensive, while DOTP is cost-competitive.”

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