John B. wrote:
:On Tue, 03 Jan 2017 17:04:40 -0800, Joerg
:wrote:

:Gentlemen,
:
:Is there something stronger than the usual rubber cement in the patch
:kits? Ideally something that won't dry out so fast or where multiple
:cheap small tubes are available.
:
:The reason is that I sometimes have larger holes from side wall
:blow-outs. Not inch-long gashes but one or two tenths of an inch long.
:The tubes I use are super thick and, therefore, expensive. $15-20 each
:and that's not something to be thrown out lightly. Instead of the li'l
:REMA patches I need to use thicker rubber from an older sacrified tube
:but this has to be vulcanized/cemented really well.

:My LBS usually has small sealed tubes of glue. When I see them I buy
:four or five and when I open a sealed tube, in the kit on the bike, I
:replace it with another sealed one as find the glue has dried up is
:not quite so much of a catastrophe at home :-)

:Or you might try contact cement what I suspect is what is in the usual
:tire patching kit.

:By the way, "vulcanizing" implies the use of heat, and sulphur, and I

Vulcanizing may have the connotation of involving heat, but it's a chemical
reaction, which results in the sulphur in the rubber becoming
crosslinked. Patches, at least the good ones such as Rema and park,
are a multi-layered assembly. The top layers are for strength, the
bottom (closest to the tube) consists of unvulcanized rubber, mixed
with a vulcanizing ultra-accelerator (there are a number of zinc
thiols that are suitable, which ones are used are trade secrets. ZDDP
is typical, though). vulcanizing cement consists of a unvulcanized
rubber particles, a solvent to carry them, and a vulcanizing
activator. Cyclohexylamine is common, but there are others that will
work, and are less toxic. The activator reacts with the zinc thiol,
and causes the patch, the rubber in the cement, and the surface of
tube to become vulcanized. There's not much free sulphur in the tube,
because it's vulcanized, which is one of the reasons that it's
important to properly scarify the tube surface before patching; it
greatly increases the surface area of the patch. The reaction is not
instant, but it happens pretty fast at room temperature, and
continues for some time, until all the sulphur available has linke.d

The accelerator in the cement is one reason that tubes of glue
sometimes are just rubber, and not cement.



--
sig 56