Medical Device Link.

Originally Published EMDM August 2002

SPECIAL REPORT

An extensively tested new PVC plasticizer gets a clean bill of health. Also, a look at electrically conductive polymers that are helping design engineers build smaller, lighter devices, and a sulphone polymer that reduces scaling during processing and improves productivity.

Norbert Sparrow

Electrically conductive polymers are available from PolyOne Corp in formulations derived from more than 20 rigid and elastomeric thermoplastic base resins.

Despite concerns that have been raised about the potential harmful effects of the plasticizers commonly used in PVC, the medical device industry has been reluctant to abandon the material. PVC has a 40-year history of use in the device industry and is present in approximately one-third of all medical disposables. Its cost advantage over alternative materials and the wealth of clinical and real-life data make a compelling case for its continued use in medical product applications.

Nevertheless, public perceptions of the material's hazards, buttressed by scientific studies, have led some manufacturers to seek alternatives. They may want to reconsider, based on news from chemicals giant BASF (Ludwigshafen, Germany). The company has announced the development of a plasticizer for soft PVC compounds for sensitive applications such as medical devices that has tested safe with no side effects or characteristics that could be deemed dangerous to humans.

Hexamoll Dinch is a di-ester-based cyclohexanedicarboxylic acid that was discovered in an internal BASF programme, Sustainable Plasticizers, that was initiated in 1997. Since then, the company has spent < 1 million on tests; by the time the testing has been completed, the company will have spent more than double that amount. This will make the material the most extensively tested plasticizer on the market.

"We didn't want to fuel false expectations based on hasty conclusions," says BASF product safety expert Rainer Otter. "We began thoroughly examining Hexamoll Dinch much earlier than required by the German Chemicals Act, and it has paid off. The data show that [the resulting PVC material] is ideally suited for use in food packaging and medical equipment such as intravenous tubes," says Otter.

Manufacturers will be pleased to note that the plasticizer does not alter the properties of PVC nor change its final characteristics, so that it can be processed on existing processing equipment. Many PVC alternative materials require new production lines or extensive retrofitting, thus increasing overall costs beyond what the marketplace will bear. Processing the new BASF PVC material, however, only requires fine-tuning the formulation and the processing temperature to achieve the same results as PVCs with conventional plasticizers. BASF reports that it has sent out more than 100 product samples to potential customers, with excellent results. One of the first companies to switch to the product is Rottolin, a manufacturer of medical products using soft PVC as well as a range of consumer items, based in Bayreuth, Germany. Managing director Jürgen Rotter believes that the material has a bright future. "If you consider the current status of the toxicological tests, then the market will likely be prepared to accept the slightly higher price. Hexamoll Dinch offers good value for money overall."

Some observers question whether Dinch can save PVC, whose market share in medical disposables is in decline. According to a report published by Frost & Sullivan (London), PVC will account for 47.7% of total unit shipments of plastic for medical disposables by 2005, down from 58.1% in 1995. BASF, however, is undeterred. A production facility with an annual capacity of 25,000 t is currently being brought on-stream, and the company is investing approximately < 10 million to ramp up production at its Ludwigshafen site. BASF has applied for worldwide patent protection for the product and the manufacturing process.

Electrically Conductive Polymers Aid in Product Design

Electrically conductive engineered materials protect medical equipment from static buildup, electrostatic discharge (ESD), and radio-frequency or electromagnetic interference (RFI/EMI). With formulations derived from more than 20 rigid and elastomeric thermoplastic base resins, the Stat-Tech product line from PolyOne (Avon Lake, OH, USA) is formulated to provide these capabilities while helping design engineers to enhance performance and safety in ever-smaller packages.

According to the firm, Stat-Tech materials are specified where key performance issues such as surface resistivity, processability, use environment, shrinkage, colourability, chemical resistance, and dimensional stability are critical to the safe and effective operation of a device. The company's use of antistatic additives as well as fillers and reinforcements such as carbon black, carbon fibre, and metallized fibre offers benefits not found in antistatic coatings, according to the firm.

BASF's Ludwigshafen plant for the production of its new PVC plasticizer Hexamoll Dinch went on-stream in July.

The use of additives ensures that conductive properties are present throughout the entire part and do not wear off with use. Surface resistivity of the Stat-Tech compounds ranges from 100 to 1012 (omega)/cm². RFI and EMI shielding applications typically are at the low end of the spectrum, while antistatic and ESD applications are at the high end. Conductive property ranges can be custom formulated for specific OEM needs. Fine-tuning formulations to suit processes and equipment is one of the company's strengths, notes director of global market development Jeff Frankish.

"We understand how differences in process equipment and tooling can affect the electrical properties of a given component," says Frankish. "This is particularly important as products and applications are translated globally to new processors," he adds. PolyOne prides itself on working closely with OEMs and moulders to develop compounds that will produce predictable, consistent results. For example, "other suppliers will often offer compounds with higher loadings of carbon fibre than is needed, simply because it's easier not to have to fine-tune the loading level to fit a customer's particular process and equipment," says Frankish. By tailoring the load level to customer requirements without overengineering, the company is able to lower overall costs, he adds. The company also offers a number of support services, such as in-house computer-aided engineering, analysis, and testing, to OEMs and moulders.

Applications for the Stat-Tech compounds include oscilloscopes and monitors, laser collimation and calibration equipment, conductive pipettes, and a variety of medical devices. Rigid resin families available in Stat-Tech grades include ABS, acetals, LCPs, polycarbonates, melt-processable fluoropolymers, PEEK, polyethersulphones, polyethylenes, and polypropylenes. Elastomeric compounds range from copolyesters and copolyamides to PVC and nitrile blends.

New Polysulphone Grade Reduces Scaling

A sulphone polymer with reduced levels of cyclic dimer is said to reduce scaling and improve productivity compared with traditional grades. Cyclic dimer, which is normally produced during the manufacture of polysulphone, leaves a deposit on pipes and other conduits during the manufacturing process. When this occurs, production equipment may need to be shut down and cleaned. Solvay Advanced Polymers LLC (Alpharetta, GA, USA), part of Brussels-based Solvay S.A., introduced low-cyclic-dimer (LCD) UDEL P-3500 in July at the International Conference on Membranes in Toulouse, France.

According to Judy Melville, global industry manager for membranes, the material represents a number of economic advantages for membrane manufacturers over UDEL P-3500, which has been in use for more than 20 years. In addition to a reduction in cyclic dimers, the material offers higher fibre strength and fewer surface defects. According to the firm, the LCD polysulphone also improves the stability and shelf life of the doping solution that is used during solution processing, thus increasing production efficiencies. "This is the first in a series of resins that we plan to introduce over the next several years that have been developed specifically with the needs of membrane manufacturers and their end-users in mind," says Melville.

The material is suited for the fabrication of semipermeable barriers used in medical filtration, gas separation, and a range of industrial filtration applications.

Now available in commercial quantities, the material is manufactured at the company's plant in Marietta, OH, USA.

Copyright ©2002 European Medical Device Manufacturer