On Wed, 17 Mar 2021 11:28:24 -0500, Leon lcb11211@swbelldotnet
wrote:

On 3/16/2021 1:57 PM, wrote:
On Tue, 16 Mar 2021 13:10:24 -0500, Leon lcb11211@swbelldotnet
wrote:


[snip]

But, but, but, I have had silicone stuff break down into a gooey mess
when they haven't been exposed to high heat or oil. It may take years
but it's happened, and far more than once.

I was told, by a chemical engineer some time back, that what's
happening is that plastics have what is called a "plasticizer" (what
else?) that's used to make plastics softer (or harder). These
plasticizers are somewhat volatile and when they leave, what's left
breaks down into goo.

Yes! I have a small space heater in my garage. It's knobs are coated
with a silicone type material that has gone to goo in less than 5 years.

I don't think that silicone rubber needs or has plasticisers.

The knobs may not be silicone rubber. It may be depolymerizing. With
urethane rubbers, this is called "reversion".

One can tell by burning a sliver of the rubber. If silicone, the char
will be sand, not carbon.

Joe Gwinn