Peroxide or Sulphur Cured EPDM

23 Jul 2015 | Posted by Andrew Onions

Peroxide or Sulphur Cured EPDM

Learning what's new in the Rubber Sheeting industry is challenging - I read plenty of technical articles that make me wish I had listened more during my chemistry and physics lessons at school - #manwithnosociallife - and yet the questions that are frequently asked of our Technical Team are not about what's new but about clearing some of the fog that surrounds the mysticism that sometimes surrounds the industry.
So here is the Idiots Guide to why we have both Peroxide and Sulphur cured EPDM with a little wander into explaining what EP or EPR or EPDM's are as these are the Polymer grades that the question is most often linked to - there is a small pun in there but don't worry it will make sense later - everyone still with me - good.
So what's the Process called?
Vulcanization or Curing - this is the creation of long polymer chains linked to each other to create a homogenous material - or more simply than that - its like taking long pieces of spaghetti and gluing them all together end to end and then laying them out in an orderly way to produce a finished shape, be that a flat sheet or a moulded part.
Why do we use Sulphur or Peroxide?
The reaction of either of these two compounds within the vulcanization process are used to link the Polymer Chains together creating Carbon-Carbon bonds (C-C) or Carbon-Sulphur bonds (C-S). Sulphur was originally used to generate the chemical reaction for vulcanizing rubber as it worked across most of the polymer types available at the time, but polymers have evolved other means of achieving the same reaction have led to Peroxide being used. Other chemical agents and processes or modifications to the above have been developed to best suit the polymer type and or outcome required.
In the range of ethylene-propylene (EP) rubber we have two types of product #EPR = EP copolymer and #EPDM (EthylenePropyleneDieneMonomer) = EP terpolymer- what I hear you cry does that mean - warning we are about to go Greek.
The polymer chains are made up of one or more 'monomers' (Greek for single unit) which link together (refer back to spaghetti analogy earlier). A copolymer is made up of two monomers (two units) and terpolymer is made up from three monomers (three units). On this basis EP is a copolymer produced from two monomers, Ethylene and Propylene; EPDM is a terpolymer with Ethylene, Propylene and the additional third monomer being Diene.
What are the Benefits of using either?
There are few benefits you can derive from using one or the other, particularly as there are other additives that can be used to compensate or improve the finished materials performance, it will often simply come down to cost and processing capability.
It is true to say that Peroxide curing does produce very stable Caron to Carbon bonds and the resulting material generally performs better at high temperatures and have good resistance to heat ageing and compression set, where Sulphur cured material will often demonstrate better tensile and tear strength. A graphic representation of recognized benefits:
Peroxide Cured EPR, EPDM
Higher Temperature Resistance
Good Heat Ageing Resistance
Lower Compression Set
Improved Resistance to Chemicals & Oils
No Staining or Discoloration of Metals and PVC's
Unlikely to Bloom or Discolor
Sulphur Cured EPR, EPDM
Higher Tensile Strength
Higher Tear Strength
Less restrictive on choice of fillers
Low odour during curing process
From a manufacturing perspective Peroxide curing is more difficult as the selection of fillers that won't react negatively during the curing process is likely to be more restrictive and post curing can sometimes be necessary. Consequently the use of Sulphur curing agents of EPDM's is more common and generally more commercially attractive.
There is a lot more knowledge that we can add to this article but I did say it was an idiots guide and we have covered a lot of the basics.
If you want to learn more about the range of Rubber Sheet materials that we offer and the Technical Solutions that can be achieved through our extensive production facilities please contact your Account Manager or contact our Sales Office on 01902 307711