Comparison of processability of medical resins reveals effect of physical properties on moldability

Both physical properties and processability play key roles when injection-molded parts are mass produced. When producing medical parts, a consistent, high degree of accuracy is also vital. It is relatively simple to adjust a process to account for differences in molecular weight once that process is optimized for a specific polymer. It is much more complex to adjust the process for changes in polymers.

Bayer MaterialScience LLC engineers Ian Menego and Mark Yeager along with Bayer scientist Dr. Pierre Moulinie performed a study to determine the processability of three resins and the effect their physical properties have on their moldability.

Menego examined how these differences affect productivity when he recently presented the “Material Properties and Their Influence on Molding Productivity and Efficiency of Medical Resins,” at ANTEC® 2013 technical conference. His presentation was part of the Injection Molding session.

ANTEC, produced by The Society of Plastics Engineers (SPE), is the largest technical conference dedicated to the plastics industry in the United States. It’s taking place April 21-25, at the Duke Energy Convention Center in Cincinnati.

The study looks at three transparent resins – a standard medical grade polycarbonate, a high heat polycarbonate and a medical copolyester resin – molded into a part with precise features typical in medical part designs. Through this process, the authors considered the physical properties of the materials and how they influenced their cycle times. They also compared the variability of molded parts and the energy consumed during production. These factors serve as bases for insights into the relative total costs to manufacture medical devices using each of the three resins.

Menego explained that in their efforts to determine the optimal cycle time for each resin, they discovered that the cycle time depends more on the modulus of a material – particularly at the cooling temperature – than on the material’s heat resistance or viscosity. Due to their high stiffness properties, both the polycarbonate and high-heat polycarbonate resins achieved very rapid cycle times. On the other hand, a copolyester with a lower modulus required a much longer cycle time.

“We observed greater weight variability in the medical copolyester that we tested,” said Menego. “We feel that it’s at least partially because of the greater viscosity fluctuations that copolymers undergo as well as the greater viscosity fluctuations with temperature change.”

The study’s final experiment investigated the energy consumption of each of the three resins as they were processed for use in a medical device. Energy consumption for the copolyester resin was found to be greater than the two polycarbonate resins, potentially due to the copolyester’s relatively longer cycle time. Going against conventional wisdom, explained Menego, increasing the polycarbonate resins’ melt temperatures actually reduces the energy consumed per part.

About Bayer MaterialScience LLC

Bayer MaterialScience LLC is one of the leading producers of high-performance plastics in North America and is part of the global Bayer MaterialScience business with approximately 14,500 employees at 30 production sites around the world and 2012 sales of 11.5 billion euros. The company manufactures high-tech polymer materials and develops innovative solutions for products used in many areas of daily life. The main segments served are the automotive, electrical and electronics, construction, medical, and sports and leisure industries. Sustainability is central to Bayer MaterialScience LLC’s business and is based around the key areas of innovation, product stewardship, social responsibility and respect for the environment.