Eli5 why can’t tires be melted down and reused?
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The molecules in rubber are chemically cross linked together forming a network of polymer strands that cannot move, like a huge net.
In comparison a thermoplastic is made of long molecules which are tangled together, but are not chemically linked so they can still move past each other and flow.
So rubber can’t be recycled but plastics can.
There is a Canadian company that has a patented reverse polymerization process for recycling tires. Tires are reduced to reclaimed carbon black, steel,hydrocarbon oil and gasses. All of which is either sold or used to generate electricity. Capable of processing 25 tonnes of tires per day. Practically 0 emissions. Don’t mean to pump the stock because I’ve owned some for a looong time but they CAN be ‘melted down and reused’ but there’s probably no profit in it.
If world would not run on greed, we would use those tires for life and be done with it https://youtu.be/vSNtifE0Z2Q
I used to work at a plant that recycled automotive tire by melting them in a lead bath. It produced 2 gases, a lighter one that we would use to help heat the lead, one heavy gas that we would capture and and sell to oil recyclers. The solids were steel and carbon black, both would be separated out and sold in bulk.
Tires need to be solid to work properly.
You wouldn’t even be able to attach a melted tire.
While a few comments have talked about mechanical recycling to shred the tyres into crumb thay can be repurposed I haven’t seen any mentions of chemical recycling by pyrolysis yet. If you take the rubber and make it really hot in the absence of oxygen you can turn it into pyrolysis oil, gas and char. The char can be used to make new carbon black for tyre production, the oil can be blended into fuels or cracked to be a feedstock for the petrochemical industry.
It is an energy intensive process and not great for the environment but it is infinitly better than just piling them up and letting them rot or burn.
I like the recycling idea — used tires can’t be melted down and the rubber re-used, however, take the metal out and shred them and they can be re-used in many ways! From the “gravel” in playgrounds to being added to macadam to make roads more flexible, increasing elasticity and endurance of roads.
While you can’t “unscramble the egg”, there are different ways to use them!
they can’t be melted down, but they can be shredded up and used for all sorts of thing like mixing with asphalt to make roads (the rubber chunks flex more than gravel so are less prone to cracking and erosion)
I can offer an engineering ELI5 view here, I used to work in a rubber research lab as a test engineer.
When you look at new rubber (sometimes called green rubber) on a very small scale it is separate, long chains of molecules before you heat it. These chains can be thought of as cooked spaghetti. When you make rubber, it goes through a process called vulcanization. Basically you heat it up to change the structure of your spaghetti shaped molecules.
During vulcanization your floppy cooked spaghetti begin to make bonds to its neighbors. So visualize your cooked spaghetti making more connecting spaghetti strings to each other. Eventually you have a big mass of spaghetti that is all connected and you let that connected mass dry out. You’re basically left with one big ugly spaghetti noodle. That’s your finished product of rubber.
Now undoing this process is tricky, the spaghetti-like molecules don’t want to unbind and go back to being separate, the new spaghetti bonds are rather strong. If you try and heat it up again your rubber will burn before it melts. The combustion reaction destroys your big ugly spaghetti noodle and you’re left with a pile of not so useful ash/mush and nasty smoke. This is because the melting point of a rubber that goes through vulcanization is higher than its combustion point.
One of the cornerstones of recycling plastics and rubbers is trying to melt them down to reshape them. There are two big classes of polymers (rubbers, plastics, and a few other things like them) and those are thermoset or thermoplastics.
The thermosets are like our ugly spaghetti noodles, they have new spaghetti string bonds that make them nearly impossible to reshape or melt down.
The thermoplastics are kinda like the unvulcanized rubber in structure, lots of cooked noodles that DO NOT make links between the noodles when heated. They have a lower melting point than combustion point so you can melt them down and reshape them. Though sometimes those points are closer than you would like, it can be exciting when you overcook your thermoplastic spaghetti molecules.
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