RECENT ADVANCES IN EPDM and DYNAMICALLY VULCANIZED THERMOPLASTIC ELASTOMERS

Ethylene Propylene Diene Rubber (EPDM) is widely used in a variety of applications.  Majority of these applications demand high elasticity.  In addition, use of EPDM in applications such as engine mounts has been limited due to its deficiency in resiliency relative to natural rubber.  Resiliency can be improved through the use of ultra-high molecular weight (MW) EPDM.  However, such polymers are typically oil extended at high levels (40-50%) and not suitable in some compound formulations.  Recent advances in the control of polymer architecture has led to the development of EPDM that demonstrates in thermoset applications, improved elasticity, improved resiliency and allows production at low oil extension level.

Dynamically vulcanized thermoplastic elastomers also known as dynamically vulcanized alloys (DVA) or thermoplastic vulcanizates (TPVs) are typically made up of a uniform dispersion of cross-linked rubber phase in a plastic matrix that serves as the continuous phase.  Such an alloy enables the production of elastomers that can be processed and recycled like plastics while retaining the elastomeric properties of thermoset rubber.  One such alloy that is most widely used consists of cross-linked EPDM as the rubber phase and isotactic polypropylene (iPP) as the plastic phase.  High MW oil extended EPDM is typically used as the rubber phase.  Lowering the polymer MW and the concomitant level of oil often leads to inferior DVA properties.  The polymer design that resulted in above mentioned improvements in thermoset applications provided an alternate EPDM lower in MW with lower levels of oil extension and improved properties when converted to a DVA.  The polymer structure and the properties of the DVA produced are presented.  Potential reasons for the improved elastic and mechanical properties observed relative to other low MW EPDM are discussed.