Rubber! It starts out as a goopy material harvested from special trees, and is then processed into a resilient, flexible material used for innumerable important purposes. In the vast majority of applications, rubber is prized for its elasticity, which eventually goes away with repeated stress cycles, exposure to heat, and time. When a rubber part starts to show cracks, it’s generally time to replace it.
Researchers at Harvard have now found a way to potentially increase rubber’s ability to withstand cracking. The paper, published in Nature Sustainability, outlines how the material can be treated to provide far greater durability and toughness.
Big Flex
The traditional method of producing rubber products starts with harvesting the natural rubber latex from various types of rubber tree. The trees are tapped to release their milky sap, which is then dried, processed with additives, and shaped into the desired form before heating with sulfur compounds to vulcanize the material. It’s this last step that is key to producing the finished product we know as rubber, as used in products like tires, erasers, and o-rings. The vulcanization process causes the creation of short crosslinked polymer chains in the rubber, which determine the final properties and behavior of the material.
Harvard researchers modified the traditional rubber production process to be gentler. Typical rubber production includes heavy-handed mixing and extruding steps which tend to “masticate” the polymers in the material, turning them into shorter chains. The new, gentler process better preserves the long polymer chains initially present in the raw rubber. When put through the final stages of processing, these longer chains form into a structure referred to as a “tanglemer”, where the tangles of long polymer chains actually outnumber the sparse number of crosslinks between the chains in the structure.
This tanglemer structure is much better at resisting crack formation. “At a crack tip in the tanglemer, stress deconcentrates over a long polymer strand between neighbouring crosslinks,” notes the research paper. “The entanglements function as slip links and do not impede stress deconcentration, thus decoupling modulus and fatigue threshold.” Plus, these long, tangled polymer chains are just generally better at spreading out stress in the material than the shorter crosslinked chains found in traditional vulcanized rubber. With the stress more evenly distributed, the rubber is less likely to crack or fail in any given location. The material is thus far tougher, more durable, and more flexible. These properties hold up even over repeated loading cycles.
Overall, the researchers found the material to be four times better at resisting crack growth during repeated stretch cycles. It also proved to be ten times tougher than traditional rubber. However, the new gentler processing method is fussy, and cannot outperform traditional rubber processing in all regards. After all, there’s a reason things are done the way they are in industry. Most notably, it relies on a lot of water evaporation, and it’s not currently viable for thick-wall parts like tires, for example. For thinner rubber parts, though, the mechanical advantages are all there—and this method could prove useful.
Ultimately, don’t expect to see new this ultra-rubber revolutionizing the tire market or glove manufacturing overnight. However, the research highlights an important fact—rubber can be made with significantly improved properties if the longer polymer chains can be preserved during processing, and tangled instead of excessively cross-linked. There may be more fruitful ground to explore to find other ways in which we can improve rubber by giving it a better, more resilient structure.
I heard of a method to chemically revitalize old dried and hardened rubber by boiling it in wintergreen oil. So that does not work, in case anybody else is tempted to try it. Definitely stinks up your shop, though.
Thanks for testing that theory for the rest of us.
Interesting, this actually worked for me. Definitely stinks, but the party became fully pliable and no noticeable degradation after an hour in very warm oil. Didn’t boil though.
I’ve used that method successfully many times. You do have to be very careful not to overdo it, as it will still swell the rubber.
Not sure about long term, but a bit of silicone based lubricant left to soak has worked well for me! (… Personal lubricant,I didn’t try specialist WD-40 yet lol)
Purely short term though, I don’t know about long term degregation so keep that in mind.
How do inner tube punctures happen (mechanistic view)?
Natural rubber inner tubes seem to be fussy already, but I now wonder whether / how the tear resistance translates into resistance to puncture, or tear propagation around something stabbing into an inflated tube.
Context: I recently came across a materials comparison for inner tubes ([GCN Tech : “What Are The Best Inner Tubes For Cycling? | Butyl Vs Latex Vs TPU” https://www.youtube.com/watch?v=ukwHARK7Pgc).
Better rubber would hurt their ability to sell more rubber products so dont hold your breath.
No problem–just market to consumers that are willing to pay a premium for more resilient rubber, such as the military.
‘The Elastic Perfolactic’
Hand it down from father to son!
‘Duraphram Diaphragm’
Hand it down from mother to daughter!
Was a classic SNL fake commercial.
Particular fun was the diaphragm trampolines.
Then a competitor would use the process and take business from them.
Never mind tires, I wonder if this could be used in the automotive industry to make more durable belts? If a timing belt or fan belt snaps on an interference ICE engine it can cause ruinously expensive damage.
See above comment about selling more rubber for likely applicable context. I could see better belts as a premium price aftermarket part though, at least until all the counterfeits showed up a few weeks later. Aerospace might be a better market if they can make stuff thicker.
Is it the rubber or the embedded fiber that most determines durability?
I’ve always thought that a timing belt was a really bone-headed idea. I like chains and gears better. I’m not a mechanical or automotive engineer, so that’s not an educated opinion.
I thought that synthetic rubber had replaced natural rubber in most applications.
Natural rubber isn’t used for timing belts. It’s all artificial rubber.
make non-interference engines and stop worrying about it altogether. Problem solved.
We used to be able to make rubber that lasted. I have a gasoline hose from the 70’s that are still in use. Soft, and no cracks or leaks. It has seen all sorts of gas, leaded, lead free, ethanol spiked, etc. Parts of it has also been exposed to sunlight. I’ve had new hoses turn into gasoline sprinklers in a year. Same cracking issues in just months on rubber mounts, grommets, and covers. I have always assumed they removed some highly cancerougenous additives that became illegal to use, or something. But it may also be something in the manufacturing process that changed.
I’ve long ago stopped trying to hold bundles of cables and wires together with rubber bands. While it’s fine for temporary use, long term the rubber bands always disintegrate and sometimes make a mess.
This reminds me of when 19th c. scientists were first trying to determine the evolutionary tree of spiders and came to the conclusion that the orb-weavers that make beautiful and perfectly regular webs were the pinnacle of evolution and surely were much later developments than the messy tangle-web spiders. Phylogenetics showed that assumption was wrong. Sometimes, being messy is useful.
In reality, they’re both wrong. God made all spiders on the same day.