Rubber Grommets Chemical Question

[xcoyle]

Paul, I am looking to buy some rubber grommets and they come in many types of rubber like products. They are offered mainly in:

Silicone, Neoprene, SBR, BUNA-A

But also: EPMD, Viton, Nitrile, Hypalon, Fluorelastomer, Natural Rubber, Pure Gum

I figured Silicone would be bad for a guitar finish, but how about the rest. I am leaning towards Neoprene but not sure.

[jingle_jangle]

The issue here is the reaction of the plasticizer in vinyl grommets, which are often mistaken or substituted for rubber. This plasticizer (phthalate) is highly reactive with many materials (it's formulated to be sacrificial in order to maintain the flexibility of the vinyl into which it's blended). It reacts with many plastics, including styrene, ABS, acrylic, and the polyurethane that is the primary solids component in conversion varnish.

Unfortunately, neoprene also uses a phthalate ester plasticizer. I'd recommend SBR or BUNA-N. Both are available from McMaster-Carr in quantity.

[johnallg]

David, if you are looking for the ones RIC uses to mount pickups and such, they are available here:

http://www.rickenbacker.com/cart.asp?vi ... cellaneous

[xcoyle]

Thanks Paul, that's a great price for a reasonable quantity.

[doctorwho]

You knew a chemistry lesson was coming, right?

... a phthalate ester ...

By definition, a phthalate is an ester of phthalic acid, so "phthalate ester" is a redundant construction. (Well, at least to a chemist! )

Nearly all plastics contain additives of various types, and phthalates, as Paul has pointed out, are among them. Additionally, some of these additives can chemically react with the finish as well as migrate into it (and thereby soften it); the latter is what Paul is referring to to as "reacting".

[jingle_jangle]

Thanks, Gary...again!

[charlyg]

I love this repartee! Paul answers the question way better than most folks could even dream of, and then Gary comes along, and cleans up the "syntax"!

[jingle_jangle]

We're a hell of a team...Burns and Allen, Laurel and Hard(l)y, Robinson Crusoe and Friday...

[johnallg]

We're a hell of a team...Burns and Allen, Laurel and Hard(l)y, Robinson Crusoe and Friday...

Moe, Larry, Curly......

[jps]

Dr. Frankenstein and Eye-Gore!

[doctorwho]

"What hump?"

[jingle_jangle]

That's Franken-SHTEEN!!!

[jps]

What took you so long?