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Re: EVOH oxygen barrier

Hi, Dave, As I understand it, the packing of the polymer chains in EVOH is such that there are no spaces through which the oxygen molecules can pass. It is a physical barrier rather than a chemical one. PVdC, which was used as a barrier on PET bottles, worked in the same way. I'm not sure if any patents exist, but there have been some attempts to add an oxygen scavenger to PET, which would mop up any oxygen in the material. I believe one of these was a nylon, originally added to the PET by mistake.

Regards, Bill

You wrote:

After reading up on oxygen barriers in PET/PEN beer bottles and in > cross linked PE heating pipes, I couldn't find the answer to my > central question: > How do ethylene-vinylalcohol copolymers prevent the O2 migration? > What's the mechanism?
Reply to
Bill
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I spent some time on food packaging and would like the answer myself but your's appears fuzzy. Don't think antioxidants would work to improve PET barrier and nylon if added by mistake would have been blend. Blends have been studied but usually food barriers are set up as layers or laminates. EVOH works well as the internal resin in these laminates since, I don't think, it makes a physical contribution to the food package itself. The order of oxygen permeability ( and usually CO2) is something like: aluminum and/or glass > PVDCl > EVOH > PEN > PET >PE Frank

Reply to
Frank Logullo

Hi, Frank and Dave, Sorry, didn't mean my reply to be fuzzy! Agreed antioxidants wouldn't work to improve oxygen barrier. I worked in a food packaging co. too

- Europe's biggest at the time - and I did quite a bit of work on PET bottles, mostly with PVdC barrier added as an aqueous coating and then cured, especially for beer. However, I believe that during the materials work which was done at this co. a blend of PET and a nylon was produced, by mistake, and this material was found to have a very high oxygen barrier. I was not close to the material development, but I believe that it was found to work with some grades of PET, and not with others, and that this was put down to the catalyst residue in the PET. Some catalysts enabled the oxygen scavenging of the nylon, but not others. I'm not sure if this material is used in production, nor if the technique was patented. I did wonder whether there was found to be a toxicity problem with one of the materials, alternatively further investigation may have proved the results erroneous.

regards, Bill

You wrote: I spent some time on food packaging and would like the answer myself but

Reply to
Bill

Thanks both of you!

Slowly but surely i am convinced that the EVOH oxygen barrier works indeed like the polyamide and the nanocomposite barriers: pure Physics! All the cristalline areas are impenetrable for oxygen so it has to "diffuse around these areas" and therefor has a very long way to go, thus slowing down O2 transfer to about 0. The thinner the crystallin domains and the more lying next to each other, the longer the diffusion path, the more effective the barrier is. How does that sound?

cheers

Reply to
dave.lister

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