CycleBanter.com - View Single Post - Elmer's Rubber Cement is not the vulcanizing kind!

**[email protected]** · April 25th 09, 06:50 AM posted to rec.bicycles.misc,rec.bicycles.tech

On Fri, 24 Apr 2009 20:58:24 -0700, l (Tom
Keats) wrote:

In article ,
Tom Sherman writes:
Ablang ? wrote:
I bought a 4oz jar (UPC 0 269050 8) of this stuff from Home Depot last
year for about $2.50. Pretty cheap stuff.

I finally got a chance to use these on my inner tubes for my 27" x
1-1/4" tires (100 psi) and found out that they don't really stick
permanently. The next day I discover that some part of the patch has
breached.

In trying to figure out what I did wrong (I have successfully patched
other tires before using the glue from patch kits), I figure it's that
I'm either using too thick of a layer of Elmer's or that this rubber
cement really isn't the vulcanizing kind.

What do you guys think?

Where can I buy (in bulk) a large amount of the vulcanizing cement
from at the best price?

I was under the impression that vulcanizing requires heat and a curative
to produce cross-linking of the polymers, and "vulcanizing fluid" is a
marketing term.

As I understand it, so-called "vulcanizing" rubber cement
chemically integrates with the existing rubber to which
it is applied. This effect should be desirable with
regard to tire repairs, since holes in tires are external
and thereby exposed to all kinds of stresses and tensions.

I've long been under the impression that patch kit cement
is of the vulcanizing kind, but upon further research I'm
prepared to admit to error on my part.

If patch kit rubber cement truly is non-vulcanizing, it
nevertheless works for inner tube patches when it's properly
applied, the layers of cement are allowed to set ("cure")
for a few minutes before applying patch to hole, and the
patched tube is rested overnight before inflating.

I suspect the reason for letting the cement dry for a
few minutes before sticking the patch on, is to let it
become more viscous so that Surface Tension pulls (pushes?)
the patch more firmly into place against the tube. I think
the "good" rubber cement for tube patching has a solvent
in it, like acetone or some kind of pentane or other volatile
solvent who's job is to keep it storable & fluid enough
to spread it, and that's the solvent's only purpose. Once
the cement is applied, the next step is to let that solvent
evaporate so the remaining cement can do it's job.

I might be wrong about that, too -- I'm just guessing.
Maybe Jobst will set us all straight.

Maybe it's better to patch inner tubes during a rainy day,
when the air pressure is higher? Surface tension, 'n
all that.

cheers,
Tom

Dear Tom,

"Rubber cement works by a mechanism of cohesion [also called
autohesion, or 'self-sticking-to-self] but this is true both for the
paper gluing example and the rubber gluing example, provided there is
cement on both pieces of paper."

"Cohesion occurs when the long polymer chains of the adhesive material
are able to penetrate and mix with the polymer chains of the adherend
[the substrate]. This process is also called 'interdigitation' in
reference to the simile of fingers of opposite hands interlaced, as if
in prayer. It is much harder to separate hands with interlaced fingers
than when the hands simply lay one on the other."

"When rubber cement is used to bond rubber to itself, the solvent in
the cement swells the substrates somewhat and facilitates the
interdigitation process. After the solvent evaporates, it is hard to
distinguish just where the joint lies. The bonding force is not a
chemical bond -- no bonds are made or broken; the strength of the bond
is purely a physical phenomenon involving van der Walls and London
forces between two intimately mixed and chemically similar non-polar
hydrocarbon rubber molecules."
http://www.madsci.org/posts/archives...3004.Ch.r.html

Cheers,

Carl Fogel