Sterilization methodsSterilization can take the form of a physical (thermal, radiation) or chemical process. The following processes have proven to be the most popular: Superheated steam, Radiation sterilization, Ethylene oxide.
SteamSterilization with superheated steam is the standard method in most laboratories and hospitals and occurs at 121 °C or 134 °C and an overpressure of up to three bar in the autoclave. When the steam condenses on the sterilization material, energy is released which is harmful to the microorganisms. This method is only suitable for materials which are stable in terms of temperature and hydrolysis.
ACTEGA offers a TPE formulation in the form of PROVAMED® 6145 TL, for example, which has been optimized with regard to its temperature resistance. Following autoclaving at 121 °C (15 min.), no mechanical changes could be detected. A comparison of the mechanical values of an unsterilized specimen with those of a sterilized specimen (at 121 °C and for 15 min.) shows that there are only minimal changes which do not have any impact on the final application.
RadiationIn the case of ionizing radiation, a distinction must be made between natural forms of radiation (alpha, beta, and gamma rays) and those which are generated artificially (electron beams, e-beam). The electrons are generated in an accelerator. Using a so-called scanhorn, the electron beam is then fanned out as a type of “electron shower” under which the products pass through on a transport system. The actual sterilization process only takes a few seconds and is less energy-intensive than gamma radiation.
High-energy, ionizing gamma radiation deactivates microorganisms. When this low-temperature method is applied, the minimum radiation dose must not be exceeded. The materials are sterilized with 25 kGy and 50 kGy doses and must not display any essential mechanical changes afterwards. Not all plastics are suitable for multiple sterilization using gamma rays. This method is only applied industrially and almost exclusively for single-use items.
In the form of PROVAMED® 4085 TP, which is particularly suitable for the extrusion of medical tubes required to display transparency and buckling stability, a TPE material is available which has proven in comparative tests that neither yellowing nor any impairment of the mechanical properties occur, not even after high irradiation with 50 kGy.
Ethylene oxide sterilization is a low-temperature method which kills microorganisms even at 10 °C by forming a bond with the protein molecules and destroying them. As the sterilization time is dependent on the temperature – the higher the temperature, the shorter the sterilization time – a temperature range of 37 °C to 60 °C is usually applied. Many plastics display good chemical resistance to ethylene oxide. In combination with the low process temperature, this method is suitable for a wide variety of thermoplastic materials.
ACTEGA’s PROVAMED® D1341 TP TPE formulation has proven to be particularly suitable in this regard: ultra-transparent, solvent-bondable, and without any impairment of the mechanical properties during the comparative test.
Each of these methods can prevent biological contamination. But they also display both advantages and disadvantages as well as considerable impacts on the material used. In order to avoid negative impacts, the material formulae need to be compiled very carefully with stabilizers and other supporting ingredients – as is the case with the PROVAMED® portfolio. Comprehensive tests on the various variants during which gamma irradiation, autoclaving, and gassing with ethylene oxide are compared, show that these materials are resistant to signs of wear such as swift ageing, brittleness, discoloration, or changes in mechanical properties.
If you have plans for a medical application, please feel free to contact us. Our experts will find the right material solution for you and your project.CONTACT