Degradation of natural rubber vs. epdm due to sunlight and ozone 1

[durablack2]

We are currently selecting material for a rubber bumper that will be used in loading docks. I am looking to find sources that show degradation of natural rubber (or SBR) vs EPDM due to sunlight, weather, ozone, etc. I know natural rubber is rated as 'poor' in these categories whereas epdm is the ideal material, but if our part can last at least 5 years or so before loosing its damping ability we could get away with using natural rubber which costs significantly less.

Does anyone know of any good studies on degradation of natural rubber vs epdm due to factors mentioned above?

 

[btrueblood]

Why not cover the natural rubber blocks with epdm roofing membrane or liquid coating?

 

[durablack2]

We could do that but the cost will still be higher than just natural rubber (but probably not as high as epdm). These are molded rubber bumpers so companies buy them because they look more professional compared to using d-profile extruded rubber. So I'm wondering how the surface finish will compare if they were dipped in liquid coating - will it be noticeably more uneven in some areas, inconsistent, etc? I guess the only way to tell is to test this out. Definitely sounds like a possible alternative to epdm though.

 

[TugboatEng]

The failure of opaque rubbers by UV is from the outside in so it could possibly last quite a long time before the core is affected and the mechanical properties change. You seem concerned about appearance and I would expect cracking on the surface. FYI, I believe car tires are some form of SBR and they have an expected life of around 10 years.

How much of a price difference are you talking? These guys say 1:1 cost ratio between EPDM and SBR.

https://moldeddimensions.com/cost-comparison.php

If people are going to be coming into contact with it, EPDM forms a black ash on its surface that rubs off on clothing and such. That may not be desirable.

 

[GrahamBennett]

Most loading dock bumpers are made from natural rubber based compounds. As long as the compound is formulated with carbon black as one of the fillers, you will have no problems with UV degradation over at least the 5yr life span you are looking for.

http://www.over50sforum.com

 

[durablack2]

Thanks TugBoatEng for the insight. It is probably most important that the core maintains mechanical properties after several years. It would be nice for the outside to maintain it's appearance but i don't think anyone will complain about surface cracking after it is installed in a loading dock as long as it does it's job in terms of damping. We are seeing a 50% cost increase w/ EPDM overseas..

 

[durablack2]

Thanks to you GrahamBennet as well. Adding carbon black seems to be a good solution to our problem. Hopefully it will not drive up cost very much (doesn't seem like it would).

 

[Luis.Tormento]

because you do not use a blend of NR and EPDM? Its difficult but possible, and you achieve the benefits of each rubber in your compound

 

[Luis.Tormento]

USE a blend of ENR nad EPDM and you will shr the benefits of both rubbers. IS a difficult composition to achieve those properties but is a good solution - No more than 30 phr of EPDM can be used

 

[GrahamBennett]

In my opinion there is no need to use a speciality grade of NR, nor is there any need to use EPDM, in this application. If formulated properly, a compound containing just natural rubber (e.g. TSR20) plus carbon black, oil, antioxidant, etc will more than suffice.

http://www.over50sforum.com

 

[Deep Rai]

Grahambennett you are right NR based formulation with containing carbon black and, wax as antioxidant is enough for protect from sunlight crack as our tyre formulated there is no need to any special rubber.

 

[tom1953]

I agree with Graham that properly formulated NR should be acceptable for 5 yr (+) service, although if longer lifetime is needed (10-20 yrs), EPDM would be desirable. There are published studies of EPDM aging, especially for the roof sheeting application, but I don't know of any that evaluated NR.
For the NR compound, I'd think an antiozonant would be a desirable addition, along with the antioxidant and wax.