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News in medical-grade plastics.

News in Medical-Grade Plastics

Although it requires a considerable amount of extra service in the realm of quality certifications, resin suppliers and compounders are devoting considerable attention to this higher-margin specialty market, which is estimated to be growing at 6-8%/yr. The result was evident in the number of new medical-grade materials highlighted at the recent Medical Design & Manufacturing show in N.Y.C.


A key criterion in development of plastics for disposable medical devices has been the ability to withstand sterilization by ethylene oxide (EtO) gas, gamma radiation, or steam autoclaving. Resistance to steam sterilization is one factor that's said to give new Radel R Polyphenylsulfone a niche in medical equipment such as surgical trays. Radel R, introduced in February, is a new high-temperature thermoplastic from Amoco Perfomance Products, Inc., which moved this month from Ridgefield, Conn., to Atlanta. It has an HDT of 374 F @ 264 psi and reportedly retains impact strength and other mechanical properties at temperatures of 150-400 F, even after long-term exposure to 400 F steam. Especially important is Radel R's resistance to amine-type boiler additives whose presence in sterilizing steam reportedly tends to attack other plastics, including polysulfone. Radel R costs $7.75/lb tl for opaque 5100 grade and $10/lb for transparent amber Radel R 5000.

Rexene Products Co., Dallas, has added several new grades to its line of gamma-resistant polypropylenes for medical products. Among these is 9234 copolymer, which the company says is a first in thermoformable, radiation-resistant in PP. This product, aimed at surgical trays and other packaging, reportedly retains clarity, strength and flexibility after up to 5 megarads' exposure.

What Rexene calls another first is a radiation-resistant random copolymer (13R25A) for large, thick-walled medical disposables such as basins, tumblers and pitchers. With this formulation, Rexene claims to have overcome the tendency for the radiation-stabilization package to reduce impact strength. Loss of toughness is also said to be no longer a problem when using color concentrates. Notched Izod impact value is 0.7 ft-lb/in.

Two new impact-modified styrene-acrylic copolymers from the Clear Plastics Group of Polysar Performance Plastics, Leominster, Mass., are recommended for medical devices, small appliances, office accessories, toys, and point-of-purchase displays. For medical uses, Zylar 93-541 (the stiffer version) and 93-546 boast very low color after gamma sterilization - less than Polysar's Zylar 90 grade. Zylar 93-546 has around 30% elongation and 0.5 ft-lb/in. notched Izod impact strength.


Meanwhile, officials of Dow Plastics Medical Group, Midland, Mich., report that changes are afoot in sterilization technology that may alter the requirements on medical plastics. For one thing, the Linde Div. of Union Carbide Chemicals & Plastics Co., Inc., Danbury, Conn., is developing new formulations of EtO gas with HCFC's, or "soft" CFC's, as a carrier in place of the ozone-damaging, fully halogenated CFC's. One question that arises is whether HCFC's differ from CFC's in compatibility with medical plastics. There have already been reports from SPI that HCFC's used as blowing agents in urethane foam appliance insulation show greater tendency to attack some plastics. That's why Dow, in conjunction with Union Carbide and others, is soon due to complete a study of the short- and long-term effects of two HCFC's on optical and mechanical properties of ABS, PS, SAN, polycarbonate, PP, PVC, acrylic, and nylon. For the results, contact David Near, Dow's Technical Service & Development Group manager.

Also in development is complete replacement of EtO with less toxic chlorine dioxide ([CIO.sub.2]) gas. Dow is due to have just now completed a study of its compatibility with ABS, PS, SAN, ABS/ PC, polycarbonate, elastomeric and rigid TPU's, and polyethylene. Early results, says Near, indicate that [CIO.sub.2] causes some discoloration of PC and TPU.

Dow has also just completed what Near says is the first comprehensive study of the effects on 13 plastics of chemical sterilants and disinfectants, which are seeing greater use to counteract hepatitis and AIDS viruses. Near says these chemical agents are suspected of contributing to a greater incidence of stress-cracking of medical plastics.

It was also evident at the show that another form of radiation sterilization - electron beam - is coming in as an alternative to gamma radiation. That was the message of exhibitors such as E-Beam Services, Plainview, N.Y.; Radiation Dynamics, Inc., Edgewood, N.Y.; and Varian Associates, Inc., Palo Alto, Calif.

According to Pauline M. Pastore, director of sales and marketing for E-Beam Services, electron-beam irradiation takes place in a few seconds, vs. 1 hr or more for gamma sterilization. Although the same total dose of radiation is delivered, doing so in a shorter time provides less opportunity for oxidative degradation, says Pastore, so that this form of radiation is often less damaging to the product. What's more, data available from Mitsui Plastics, Inc., White Plains, N.Y., shows less yellowing of both stabilized and unstabilized forms of Mitsui's TPX polymethylpentene resin from exposure to 5 megarads of electron-beam radiation than from 5 Mrads of gamma exposure.


Special additives are said to make a new, plasticizer-free polylefin alloy RF weldable while retaining clarity, thus providing an alternative to PVC in medical packaging film and sheet. According to Horizon Polymers, div. of Ferro Corp., Houston, olefinic materials are normally heat sealable but not responsive to RF, unlike PVC. With new V-3450R alloy, processors can switch materials without having to purchase new sealing equipment. It also has a specific gravity less than 1.0 and reportedly permits downgauging relative to PVC. It meets applicable USP and FDA specs, according to the company, and is sterilizable by all methods. Price range is $1.45-1.75/lb, depending on additives such as for gamma stabilization.

Dow Plastics will soon complete a study of the long-term effects of EtO and gamma sterilization on ultrasonic weld integrity in medical plastics. Dow is also developing an ultrasonic weldability chart for 24 plastics used in medical products, from polyethylene to polycarbonate.


Dow also announced commercial availability of a sulfonation surface post-treatment for plastics parts that boasts a wide range of benefits for blood-handling devices used in surgical procedures. First, it makes the surface hydrophilic and wettable, so that air bubbles do not adhere - a major problem until now. Second, Dow claims this is most practical and effective method yet developed for making a plastic surface thromboresistant - i.e., so it won't promote clothing. Normal, hydrophobic plastic surfaces cause the clotting process to start in a matter of seconds. Beyond making the plastic hydrophilic, sulfonation provides a polar surface to which the anticoagulant heparin or other biological agents may be easily grafted. Unlike current methods of washing or grafting the plastic surface with heparin, which Dow says are short-lived, complex (16-18 steps), and toxic to some degree, the sulfonation process permits heparin grafting in an economical, simple (two-to four-step) process whose results are nontoxic and longer lasting. Dow has applied for patents on this heparinizing technology, which is now about 70% developed, according to Dow's Dave Near.

Other merits of sulfonation include its ability to withstand EtO and gamma sterilization, and to promote adhesion of silver metallization, which has antimicrobial properties. Sulfonation also adds vapor-barrier, lubricity, and antistatic properties.

Sulfonation is a virtually instantaneous and permanent treatment, which uses either a gaseous or liquid fluorocarbon medium. It works on most plastics, including cellulosics and silicones, but not on fluoropolymers. In a three-way joint venture with Michigan State University and Detroit-based International Marketing Coalition, Dow has formed Coalition Technology Ltd., based in Midland, to license sulfonation technology for medical applications, and to provide design, start-up and ongoing technical support.


What's said to be the first dip molding process for liquid thermoplastic urethane solutions that's capable of producing a seamless product has been developed by Aukland Medical, Inc., Cary, N.C., a producer of medical and dental devices. The process itself is said to be basically similar to latex rubber dip molding, although fume handling to deal with evaporated solvents becomes an added consideration. The real key to the process is Aukland's proprietary TPU material, called Aukuflex. Aukland is using the process to make specialty medical gloves, and is seeking a patent on an Aukuflex condom. Also being investigated are application in diaphragms, heart valves, tissue expanders (used in healing burns), and other specialty membranes. Aukland is considering licensing the process for making condoms and possibly other products. It would supply Aukuflex raw material to any licensees.

This Spring, Aukland also became a supplier of custom compounded medical-grade thermoplastics, specializing in TPU's and other TP elastomers. It acquired custom compounder Pacrim International, Inc., formerly of Branford, Conn. (now in Cary, N.C.), and also acquired the assets of another TPE compounder, Perfomance Polymers, Inc., formerly of Nashville, Tenn. These have been merged into Aukland Polymers, Inc., a subsidiary of Aukland (USA), Inc., the parent company of Aukland Medical. Total compounding capacity is 1 million lb/yr.

Proprietary pelletized compounds include Aukuthane, an MDI-based TPU. This month, Aukland is introducing Aukuthane 2363 for extruded medical tubing, designed to compete with Pellethane 2363 from Dow Plastics.


Among a handful of other new medical plastics unveiled at the show, Dow introduced two families: the Magnum 2600 series of five high- and low-gloss ABS resins, and medical versions of four Attane ultra-low-density PE (ULDPE) film resins. According to market manager Ellen C. Brindley, both new lines are distinguished from similar existing products by extra attention to documenting purity and lot traceability. There is no price premium over comparable non-medical grades, said Brindley.

Monsanto Chemical Co., St. Louis, just recently attained USP Class VI certification of its new Lustran Sparkle SAN, and is now testing its sterilization performance.

Monsanto also has a couple of new plastics in development that could have medical applications. One is a clear alloy that's tougher and more chemical-resistant than SAN, according to Jeff D. Lenger, medical market manager. He expects it to be released in early 1991.

The second material, which might not appear before 1992, is clear and moderately tough, with barrier to oxygen and moisture, which could be used in containers for diagnostic fluids.

New from Colorite Plastics Co., Ridgefield, N.J., are nontoxic PVC foam molding and extrusion compounds containing a chemical blowing agent, designed for hardnesses from 40 Shore A to rigid and densities below 1.0. These compounds are suggested for uses where amine compounds in rubbers cause skin irritation.

Also new from Colorite are Elastochem PVC extrusion and injection molding compounds from 40A to 90A hardness, which are said to be resilient and elastic and to have low coefficient of friction. They're also said to be self-frosting, low in gels, and processable at unusually high extrusion rates for low-durometer compounds. Tensile strengths range from 1300 to 4480 psi, elongation from 215 to 500%, and 100% modulus from 266 to 3625 psi.

PHOTO : Sterilizability is a major consideration in development of new medical plastics. Brand-new sterilizing and disinfecting approaches may make new demands on polymers.
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Author:Naitove, Matthew H.
Publication:Plastics Technology
Date:Sep 1, 1990
Previous Article:Downstream equipment for precision extrusion.
Next Article:Melt thermal conductivity data become more readily available.

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