Discolourization of PVC tubes

PVC, and all flexible plastics absorb solvents. Rigid plastics do, too, but not as much. Try for your self. Place a single drop of IPA on the outer surface of the tube. Wait a few minutes, then wipe it off. You should see a swolen area where the drop of slovent was.

As the plastic gives up the solvent, the swelling will disappear, mostly.

Don't know what the use is, so I have no opinion about it's usability.

OK, I do have an opinion. Don't use it without testing for your application.

_{(Don't use it)}

I don't know if thats solvents that are doing it, but if its sanitary food grade, it probally came from the chemicals from the wash cycle.

Just going by what the OP said, "I recently used isopropyl alcohol (99% USP) to clean out some transparent food grade PVC tubing".

Whenever a tube etc is in question in which chemicals were used and a noticable change happened as a result of the introduction of any chemicals. If any edible in injested substance was to pass through the tube, I'd replace it to be safe than sorry. PVC tubes are usually very inexpensive to replace. I'd just replace them if you can vs taking any chances.

We agree. See the last _small sentence of my first response.

Don't use. Read the "Health and Safety" section of the wiki, talking right away about PVC leaching phthalates. Discard any product intended for human consumption that went through the damaged tubes.

99% IPA is extremely aggressive on many types of plastics. 70% IPA is much less aggressive. The alcohol may have leached the plasticizers out of the PVC, making it more rigid. It may have also started numerous microcracks in the material. I would not use the PVC for food grade applications, or anything requiring pressure. Actually, I would hesitate to use it at all, since just flexing it may cause it to crack. The surface is most likely not as smooth as new tubing and may allow bacteria to grow in the microcracks.

My suggestion: replace the tubing!

Just an aside, I wouldn't use isopropyl alcohol in any concentration as a sterilant for surfaces that contact a food or other consumption product.

In general, alcohols on plastic are a bad idea. Ethanol is a dandy sterilant for surfaces other than plastic. If the tube has to be plastic, I would use hot water and detergent to clean it, and rinse thoroughly with cold water as the final rinse to minimize any leachate in its next use.

If a sterilant is absolutely necessary... I remember in home brewing we used cold water/sulphite solution as sterilant for our gear (including plastic tubing), followed by a cold water rinse to get rid of the residue. It certainly did not affect the flexibility of the tubing, so it didn't seem to leach the plasticizer compounds (though always rinsed immediately afterwards).

Plastics of course also take up stuff as well as releasing it. Even at 10-15% ethanol, plastic vessels and tubing used for wine would end up colored and 'flavored' by the contents if used extensively or for a long time. I have seen plastics 'flavored' by a hot liquid alone (no etOh). The flavors can then be released into the next batch, and there's nothing that I know of that will clean a plastic or prevent this from happening, once it has been affected by its contents. More economical, in the long run, to invest in glass.