Klarinet Archive - Posting 000189.txt from 2001/11

From: "Keith" <100012.1302@-----.com>
Subj: [kl] RE: klarinet Digest 5 Nov 2001 09:15:01 -0000 Issue 3435
Date: Mon, 5 Nov 2001 10:12:20 -0500

Clark, and anyone interested:

Rubber is hardened by a process called "vulcanisation", which involves
heating natural rubber (a very soft material, like an elastic band) with
sulphur compounds. Rubber is a polymer with many double bonds in its long
molecular chains; these take up fixed angles with adjacent bonds, and it is
the stretching and straightening of these that cause its elasticity. The
sulphur breaks these bonds and attaches to them across the molecules,
pinning adjacent chains together - cross-linking. This cause the hardness.
After a long time, and aided by e.g. ultraviolet light, these links break
down, causing the change in properties. I couldn't say how long this would
take - would depend on the detailed chemcial process of manufacture, and on
the conditions under which it was kept.

Keith Bowen (yes, former teacher of Materials 101 ...)

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in reply to
Date: Sun, 4 Nov 2001 16:03:20 -0800
From: "CLARK FOBES " <reedman@-----.com>
Subject: Sulphur in mouthpieces
Message-ID: <000d01c1658d$490764e0$831efea9=computer>

My understanding (and I make no claims to being a chemist!) is that Sulphur
is used as a hardening agent and a "binder". I am not certain what causes
the sulphur to migrate out, but it clearly does - probably superficially
only. I notice the differences in aged rubber when I reface mouthpieces over
about 5 years old. How the transformed rubber works must have something to
do with the original rubber content, the mix of other fillers and how the
mouthpiece was molded. A lot of variables!

Aged rubber works differently than new rubber. Sometimes it comes off on the
paper very evenly and presents almost a "creamy" feel as you work it. These
mouthpieces tend to sound very good when refaced properly. The Zinner rubber
has this feel initially, but it feels even more agreeable under the hand
after a few years.

I have worked on some older mouthpieces that had become so soft that the
material seemed to "crumble" as I worked on the mouthpiece. One mouthpiece
in particular would change in a period of about 6 months. I refaced that
mouthpiece for a customer about 5 times and we finally had to give up on it.

There are fellows out there that do much more refacing than I do and may
have had similar experiences.

Hope that helps a little,

Clark

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