What’s the composition of the (slighlty sticky) substance we find on foam earplugs that allow them to be easily moldable?
This substance slows down the expansion of the foam, so it makes the foam a little bit more rigid and help the foam to stick into the ear canal. (It might also have some insulation property in combination with the foam.) This substance get out when you wash the earplugs with soap, it's probably sprayed on the foam, or impregnated on the foam.
Any idea ?
That sticky oily substance found in the ear plug foam is the plasticizer leaching out. The plasticizer is unlikely to be added on after the foam is made, I think it would be mixed in with the source polymer before it gets foamed.
Usually the more plasticizer there is, the softer the foam gets, and the slower the foam recovers from being compressed.
What is likely happening when you wash them, is that the soap is removing the oil based plasticizer from the foam. A short wash should only remove plasticizer from the surface of the material, but since it is a foam, internally it has a high surface area, making more plasticizer available to be washed away.
Mouldable earplugs are often made from PU foam which can be self skinning ie the foam structure is created in a mould (as opposed to being cut from bulk material). I n this case the smooth skin is just a change in the density of the material, created as it is forced against the surface of the mould rather than a separate coating. again in this case the 'slow recovery' is a material property of the foam rather than any additional coating.
It might not be an answer, but it's an interesting explanation
Washing of foam earplugs does not have a major effect on strength or attenuation, but... foam earplugs do retain moisture. You can never "squeeze" it all out. And that has two negative after-effects:
First, the moisture causes the foam to swell in size a bit (affecting fit and expansion time).
A way to test that hypothesis would be to wash a new earplug in water, without soap to see if it affects its structure. If it does that would confirm the moisture hypothesis which could increase the size of bubbles inside which could affects its compression and soundproofing properties.
So the following question would be: how can we efficiently dry the foam?
Any idea?
source: http://www.hearforever.org/blogs/01/24/2011/qa-washing-foam-earplugs-good-or-bad-idea
I have had to reuse washed ear plugs in a pinch. If they have lost the elastic effect I use my wife's hair molding or sculpting cream (Bed Head). I believe the ingredient used to give the consistency needed is PVP (poly N-vinyl-2-pyrrolidone).
Interesting thread. I believe the ear plugs loose the ability to compress properly due to the oils from the ear and fingers. I originally thought washing would solve that. As the poster said, it didn’t. I did manage to dry them properly over time on a radiator and they did shrink to original size. But still expanded very quickly resulting in a poor seal when used so not as effective as when new. I definitely think another something is added to create the tacky effect. And look forward to trying the final commentators beheld PVP idea. It would be nice not to have to be so wasteful!
