Most creep resistant rubber?

[geneiusxie]

I need something stretchy like a rubber band for holding things together, but it has to be very creep resistant because it needs to withstand a constant ~50% elongation for at least 3-5 years without significantly changing length/tension. I tried it with natural latex rubber but after only a few months it lost its shape and thus, its tension. Note that I did not protect the rubber latex from oxygen, although it was not exposed to UV and was kept indoors mostly so I'm not sure if that's what caused it.

I'm thinking spandex might be suitable but I'm not sure if its creep resistance is superior to natural rubber. Btw, cost is not a problem.

 

[MintJulep]

All elastomers will experience creep. You'll need to quantify the amount of tension loss that is allowable, then maybe you will be able to find something allowable.

Would something like this

http://www.clampco.com/products/t-bolt-spring.asp

work for your application?

 

[geneiusxie]

Not exactly because I need something that is stretchy. I think I'll try a coil spring or something of that sort.

 

[tom1953]

You probably would have gotten better creep results if you did have antioxidant AND antiozonant in the rubber. Have you considered contacting a rubber band manufacturer (e.g., Alliance Rubber

http://www.rubberband.com/)

to see if they have a product that'd work for you?

 

[geneiusxie]

What kind of chemicals and at what concentrations would protect natural rubber from oxygen and ozone like you suggested?

 

[tom1953]

I don't work with NR latex, and haven't really worked with solid NR in a while, but there's a fair amount of info available from rubber chemical suppliers like Lanxess, RT Vanderbilt, Akrochem. The antiozonant 77PD (sold by several companies with different tradenames; Flexzone 7 and Vulkanox 4030 are two that I recall) seems to be a good antiozonant as well as providing antioxidant properties, although it's a staining material. I'd suggest you contact one of the rubber chemcial suppliers for their recommendations.
Good Luck!

 

[Compositepro]

You will not find a rubber that meets your stated requirements. Only a metal or composite spring will work.

 

[GrahamBennett]

For low levels of creep in an NR compound you need a fairly high filler level (e.g. 70-ish phr N772), a really tight cure system (probably an EV one based on sulfur-donors such as TMTD or a urethane-type system based on TARRC's Novor 924), 2 or 3 phr 6PPD and 1.5phr TMQ.

 

[stancom]

In the absence of any ageing, a well cured gum or lightly filled natural rubber formulation should provide the best resistance to creep/stress relaxation among different elastomers. But ageing will occur in practice to the detriment of resistance. Even diffuse light can lead to photo-oxidation and that is a major reason why a traditional rubber band perishes. It is not designed to last long. Ozone attack is another threat for a stretched product. As others have said, resistance can be raised by adding antidegradants, and light ageing can be reduced quite effectively by a light loading of a reinforcing black which performs as a UV absorber. The antiozonant needs to be of the dialkyl p-phenylenediamine type in order to raise threshold strain. 6PPD, an alkyl, aryl type, can be used but needs the assistance of wax. However, natural rubber may not be the best choice overall and polychloroprene (neoprene) may be a better starting point. I would not have thought spandex was an option for creep resistance.

In many ways I share Compositepro's view that a metal spring might be a better solution.

I not sure I agree with GrahamBennett that a high level of black will help, because fillers usually increase creep/stress relaxation, not withstanding the change in stiffness.