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PLA Eto and Sterrad sterilization

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Posted · PLA Eto and Sterrad sterilization

I recently tried sterilizing a hollow PLA part under Eto (ethylene oxide) and the part warped. It was sterilized for 3.5 hours between 45 - 60°C and then left some hours resting.

 

Has anyone succeded sterilizing PLA prints under Eto or Sterrad (hydrogen peroxide gas plasma) methods? Is it possible to sterilize using different temperatures or times?

 

I will try again with a 100% dense part and check if the outcome is different.

 

Any help would be appreciated.

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Posted (edited) · PLA Eto and Sterrad sterilization

More than 50°C is too much for PLA, it will warp. It is best to stay below 45°C.

 

While ethylene oxide may sterilise well, I am not sure if it is a good idea to use it. It is extremely explosive and requires very little ignition energy. It can explode in concentrations between 3% and 100%, contrary to most other gasses which only explode between 5% and 15% or so. The smallest spark is enough, e.g. from dropping a steel screwdriver. Almost all production plants in the world have suffered severe explosions. The plant I have worked in, also exploded a year after I left in 1986, and that shock was felt like an earthquake over 30km away, even though it was only one destillation column that had exploded. And even though the column was designed to "take off like a rocket", instead of exploding. According to witnesses it did take off indeed, but then still exploded at 500m high in the air...

 

When in storage, ethylene oxide may spontanously decompose, or polymerise, both of which are very exothermic and often lead to explosion. Thermal runaway can occur from a bit above 50°C, if I remember well. Shaking it (e.g. during transport), or any contact with almost any other material may also lead to exothermic reactions and explosion, if in sufficient quantities. Usually, contact with other materials lowers the thresholds, making it more dangerous.

 

Further it is chemically very agressive towards human tissue: it penetrates the skin deeply, without you noticing it. And then it starts burning and eating away the flesh, without any way to stop the reaction. Probably that is why they use it to sterilise? Spilling is not a problem if you spill a drop on your bare hand: it feels ice-cold and evaporates immediately, before it has time to penetrate. But if you wear gloves or clothes, it can not evaporate, and then it penetrates the skin. It goes through chemically resistant safety shoes, if you step in a puddle. We had several people severely wounded by these chemical burns.

 

Know the risks before you start playing with this. If using ethylene oxide, all equipment should be equipped with good flame arresters, and be explosion-safe. And all bottles should have good safety valves, even small glass bottles.

 

Maybe you could look into things like "isopropylalcohol + water" instead? They are less dangerous. I don't know anything about sterrad.

 

Edited by geert_2

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Posted · PLA Eto and Sterrad sterilization

Hello geert_2, thank you for answering! Thanks for your security concerns, the sterilizing is not done by me but by a hopital supplier, they have all the safety measures and have both sterilizing methods.

 

I will try talking to them and see if they can sterilize at 45°C and maybe for longer periods of time.

 

Thanks

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