What happened to cheap inner tubes?
11-19-20, 11:41 PM
#51
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And not to beat this to death but here is a post on R****T that echoes what Cyccomute says...
Chemist here - natural rubber is a polymer (long chain-like molecules). Vulcanizing adds cross-links (through disulfide bonds) to the rubber, basically turning the strands of rubber molecules into a net, greatly increasing strength. Bike tubes are vulcanized rubber, but the outer surfaces are treated such that all those cross-linking sulfur groups aren't reaching out and trying to grab anything. You put on some vulcanizing fluid (henceforth "glue") and a few disulfide bonds in the tube get broken and re-formed with bonds to the polymers in the glue. Once the glue dries (there's a bit of solvent that has to evaporate) the inner side of the glue spot is chemically bound to the tire. The outer side is left with a bunch of free sulfur groups waiting to grab onto some other sulfur groups. Then you peel that piece of foil off the orange side of the tire patch (which exposes the free sulfur groups left on the patch) and press it to the glue spot - you've now made millions of chemical bonds between the patch and the glue spot. It's not really glued, though - the patch-"glue"-tire system is now one single molecule all chemically bound together.
The chemical bond holding things together is why:
Chemist here - natural rubber is a polymer (long chain-like molecules). Vulcanizing adds cross-links (through disulfide bonds) to the rubber, basically turning the strands of rubber molecules into a net, greatly increasing strength. Bike tubes are vulcanized rubber, but the outer surfaces are treated such that all those cross-linking sulfur groups aren't reaching out and trying to grab anything. You put on some vulcanizing fluid (henceforth "glue") and a few disulfide bonds in the tube get broken and re-formed with bonds to the polymers in the glue. Once the glue dries (there's a bit of solvent that has to evaporate) the inner side of the glue spot is chemically bound to the tire. The outer side is left with a bunch of free sulfur groups waiting to grab onto some other sulfur groups. Then you peel that piece of foil off the orange side of the tire patch (which exposes the free sulfur groups left on the patch) and press it to the glue spot - you've now made millions of chemical bonds between the patch and the glue spot. It's not really glued, though - the patch-"glue"-tire system is now one single molecule all chemically bound together.
The chemical bond holding things together is why:
- The tube has to be clean and dry - the sulfur groups reaching out for something to grab onto will grab dirt, water, and other gunk instead of the patch.
- You can't use duct tape or regular glue - these are sticky substances that don't vulcanize the rubber together. Rubber cement may hold a patch in place but it is NOT the same stuff.
- Glueless patches kinda suck - the vulcanizing fluid in the little tubes works better at making bonds with the punctured bike tube.
- You can make patches out of old tubes - at its most basic you're vulcanizing two pieces of rubber together, so two pieces of bike tube will stick to each other.
The problem with just trying to “vulcanize” bits of rubber with rubber cement is that there is neither the activator nor the zinc diethyldithiocarbamate. Rubber cement has neither. It forms no new rubber bonds. If you had a two part system like Rema uses, you could paint it on bits of old tube and it would do the job but I don’t know of any system that odes that. It’s just not worth it. I suppose you could develop something but why re-invent the wheel.
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Stuart Black
Plan Epsilon Around Lake Michigan in the era of Covid
Old School…When It Wasn’t Ancient bikepacking
Gold Fever Three days of dirt in Colorado
Pokin' around the Poconos A cold ride around Lake Erie
Dinosaurs in Colorado A mountain bike guide to the Purgatory Canyon dinosaur trackway
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Stuart Black
Plan Epsilon Around Lake Michigan in the era of Covid
Old School…When It Wasn’t Ancient bikepacking
Gold Fever Three days of dirt in Colorado
Pokin' around the Poconos A cold ride around Lake Erie
Dinosaurs in Colorado A mountain bike guide to the Purgatory Canyon dinosaur trackway
Solo Without Pie. The search for pie in the Midwest.
Picking the Scablands. Washington and Oregon, 2005. Pie and spiders on the Columbia River!
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11-22-20, 03:45 PM
#53
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