Apec® 1745 high-heat polycarbonate from Covestro is a transparent engineering thermoplastic with heat-resistance beyond that of Makrolon® polycarbonate, yet is also tough and rigid. A comparison of some of the properties of Makrolon® and Apec® is given in the Table below:
|Resin||Vicat Softening Temperature (°C)||Heat Distortion Temperature (°C)||Charpy Impact (kJ/m2)||Tensile Modulus (MPa)|
|ISO 306||ISO 75-1, -2||ISO179-1 eU||ISO 527-1, -2|
|50N ; 120° C/h||1.80 MPa||0.45 MPa||25° C||25° C|
Like medical-grade Makrolon® resins, Apec® 1745 is a medical-grade copolycarbonate that meets certain biocompatibility test requirements of USP Class VI and ISO 10993-1 requirements for up to 30-day patient contact. Its combination of properties make Apec® 1745 a clear choice for medical devices intended for sterilization by steam, especially where some autoclaves can reach temperatures as high as 135° C.
In this article, property retention of Apec® 1745 after multiple high-pressure steam sterilization cycles is shown by measuring physical properties after up to 100 cycles.
Test specimens that were injection molded from Apec® 1745 551022 were used for this study. Recommended drying and processing parameters were followed. Covestro’s autoclave used deionized water and was set to maintain a pressure of +3 Bar (i.e. absolute) which, according to widely available “Steam Tables” corresponds to a temperature of approximately 136° C. Test specimens molded to either ISO or DIN standards were taken out of the autoclave for testing at intervals of 25 cycles, up to 100 cycles. Each sterilization cycle lasted at least 15 minutes, and the total duration of heating, sterilization and cooling totaled ca. 45 minutes.
The following tests were performed on the sterilized test specimens:
- Charpy Impact Strength (ISO 179-1 eU) at room temperature
- Multi-axial Impact (ISO 6603-2) at room temperature on 60x60x2mm plaques
- Yellowness Index (DIN 5036-1) measured in transmission mode on 4mm-thick color chips
The impact-strength properties measured at 25 sterilization cycle intervals are compared in the Figures below. The values shown reflect the average from all test values recorded, which were sometimes mixtures of broken and unbroken samples. For samples which yielded “No Break” after Charpy Impact strength testing, a value of 250 kJ/m2 was used for calculation purposes (i.e. the maximum value the instrument could record).