TECH TIPS | 4 April 2025
Engineering Tech Tips: Plastic Part Sterilization
Sterilization Methods, Explained
Sterilizing plastic parts targets dangerous bioburden, killing microorganisms and eliminating pyrogenic toxins from the surfaces of polymer products.
Common sterilization methods include steam or heat-based processes, chemical treatments like ethylene oxide, and radiation.
Autoclave (Steam)
Plastic parts are placed in the pressurized chamber of an autoclave, where they're subjected to saturated steam.
This approach actually requires a lower temperature and shorter exposure time than dry heat methods. It's only suitable for plastics with high heat-resistance, however, and it runs the risk of compromising a part's integrity by releasing previously undetectable molded-in stresses.
Dry Heat
This method might be the least common choice among the sterilization options listed in this guide.
It exposes plastic parts to high heat for an extended period of time — which eliminates bioburden but comes with a high risk of degradation.
Ethylene Oxide
A precise, low-heat method that needs an airtight containment vessel. Suitable for plastics with good chemical resistance, the ethylene oxide sterilization process calls for careful handling, since the gas used is flammable when exposed to air, and the EPA lists it as toxic.
Plasma
A method that uses low-temperature, low-pressure plasma to sterilize microbial pathogens like bacteria, fungi, and viruses.
A gas, typically hydrogen peroxide, is ionized using an electrical field to create the plasma. The process' byproducts are non-toxic, eliminating any need for aeration afterwards.
Irradiation, Gamma, and Electron Beam
Each of these three methods uses radiation to sterilize plastic parts.
On the lower end of the energy spectrum, irradiation can use non-ionizing radiation with long wavelengths that isn't strong enough to change physical properties.
Gamma sterilization uses much higher-energy electromagnetism and is the method of choice for single-use medical devices. Irradiation also sometimes uses gamma rays, but not all materials are compatible with them. Cobalt 60 is the go-to isotope used for gamma sterilization.
Electron beam sterilization is the highest-energy method of all, though its radiation doesn't have as much penetrating power as gamma rays. It's very safe and effective, but not suitable for the densest plastics.
