Recent Advances in EPDM and Dynamically Vulcanized Thermoplastic Elastomers

摘要

Ethylene Propylene Diene Rubber (EPDM) is widely used in a variety of applications (1). However, high chain flexibility of EPDM results in poor dynamic properties. The long lifetime of EPDM rubber parts derived from its outstanding ozone resistance has led to a desire to design an EPDM molecule with improved dynamic properties and yet is not so high in molecular weight that it demands a high level of extension oil for its production. An alternate approach for EPDM polymer design that could lead to improved dynamic properties is described. 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. The EPDM that is typically employed is a very high molecular weight (MW) polymer extended with high levels (40-50 weight%) of oil. Lowering the polymer MW and the concomitant level of oil often leads to inferior DVA properties. Thus, the need to develop an alternate EPDM lower in MW with lower levels of oil extension and improved properties is driven by both thermoset and DVA application. The polymer structure and the properties of the thermoset compound as well as the DVA produced are presented. Potential reasons for the improved properties observed are discussed.