Teknor Apex Co. and Eastman have teamed up to test the bond between Medalist thermoplastic elastomers (TPEs) and Eastman Tritan copolyester. The Medalist compounds are specifically formulated to adhere to copolyester and other engineering thermoplastics, and overmolding TPEs onto copolyester offers medical device designers a combination of hard and soft materials that are advantageous in medical components, the companies reported in a news release.
“By combining Medalist TPEs and Tritan copolyesters, manufacturers can improve the ergonomics, aesthetics, or functionality of medical devices,” said Dr. Yubiao Liu, global medical technical platform lead, Eastman, in the release. “The combination of soft TPEs with rigid copolyester substrates can enhance grip, add texture or comfort, yield a tight seal, or provide damping characteristics.”
In 90-degree peel tests of test specimens produced in a two-shot molding process, three Medalist medical-grade TPEs from Teknor Apex provided durable bonds to four of Eastman’s Tritan copolyesters. The tests that showed high peel strengths with adhesive failures demonstrate excellent Tritan TPE over-molding performance. The combination of high peel strength and adhesive failure is considered desirable for over-molded applications, it was explained in the release.
As depicted In the above image, peel strength was measured in the 90-degree pull test on a Zwick tensionometer with 100 mm/min. pulling rate in accordance with DIN EN 1464.
Further, the bond strength between Medalist TPEs and Tritan exhibited very little loss even after soaking test samples for 48 hours in disinfecting chemicals, including a 70% isopropyl alcohol, Clorox bleach, and a 20% intralipids solution, which is a fat emulsion used as an intravenously administered nutrient, the firms reported.
Medalist compounds tested included three grades: MD-34940, MD-34950, and MD-34959, with Shore A durometers of 42, 50, and 59, respectively. Tritan grades MX711, MX811, MXF321, and MXF421 provided a good range of physical properties. All three Medalist compounds in combination with all four Tritan resins showed very little loss of bond strength after chemical exposure, it was reported.
Ross van Royen, senior market manager for Teknor Apex, reported that the company “developed Medalist TPEs to meet the most stringent requirements of the health care industry and produce them in multiple ISO-13485-certified facilities with only FDA-listed food-grade ingredients. All grades are biocompatible in accordance with ISO-10993-5, are RoHS and REACH SVHC compliant, and contain no phthalates, latex proteins, or BPA.”
In the graph below, peel strength test results are shown for one Medalist TPE over-molded onto four Tritan substrates. Blue shows average peel strength, while peak peel strength is indicated by gray in background.