NEW YORK - Exxon Chemical Co. claims it has achieved the three most-requested characteristics in medical-grade polypropylene through the use of its much-heralded metallocene technology - clarity, radiation tolerance and autoclavability. Though closely guarding the names of companies applying the resin to new medical uses, R.C. Portnoy, Exxon senior applications scientist based in Baytown, Texas, said uses include syringes and luer locks in fluid-delivery systems. The company, Portnoy said, is targeting the injection molding market for its product.
Portnoy discussed the metallocene catalyst technology's advantages in a June 4 news conference at the Medical Design & Manufacturing East Show in New York.
W.R. Schmidt, Exxon Chemical sales manager for polymers applications business, said the company does not permit the use of its proprietary technology in medical devices permanently implanted in the body - largely because of legal liability questions. Several other large chemical producers also have taken similar resins off the market for implant applications.
``Until recently,'' Portnoy said, ``it was thought that the three attributes desired in premium polypropylene were incompatible.''
Reducing the brittleness and cloudy appearance that comes from radiation sterilization can be managed by just about any stabilized, nucleated random copolymer, he said. And the attributes of radiation tolerance and resistance to softening in an autoclave can be had in a properly stabilized homopolymer.
He said the use of metallocene technology in PP can replace several resins in medical applications, including PVC.
The most significant advantage is the relative clarity of the finished product, Portnoy said, noting that the addition of the elastomer to PP adds negligible clouding.
But to have all three, Exxon claims, requires addition of plastomeric ethylene polymers produced from metallocene catalysts. It markets these plastomers under the Exact trade name.
Portnoy said no special mixing technology or equipment is required to use the plastomer with clarified, isotactic polypro-pylene, but that additional mixing with polyolefins is better and compounding capability is helpful.
Portnoy said the usual blending uses 10 percent elastomer. Addition of 30 percent elastomer and higher in the polymer mix is possible, he noted.
Dow Chemical Co. of Midland, Mich., also has demonstrated the technology in its polyolefin plastomer resins.
Dow has accented the downgauging capabilities of its products by as much as 30 percent compared with similar nonmetallocene-catalyst resins.