General Introduction to EPDM

EPM and EPDM, generally referred to as EPDM are classically produced via Ziegler-Natta catalysis in solution or slurry processes. Over the last decade metallocene catalysis [4, 5] and gas phase technology [6] have been developed. EPDM is produced on a commercial scale in a variety of chemical compositions. Typically, the ethylene content 

As a result of its saturated polymer backbone, EPDM is more resistant to oxygen, ozone, UV and heat than the low-cost commodity polydiene rubbers, such as natural rubber (NR), polybutadiene rubber (BR) and styrene-butadiene rubber (SBR). Therefore, the main use of EPD(M) is in outdoor applications, such as automotive sealing systems, window seals and roof sheeting, and in under-the-hood applications, such as coolant hoses. The main drawback of EPDM is its poor resistance to swelling in apolar fluids such as oil, making it inferior to high-performance elastomers, such as fluoro, acrylate and silicone elastomers in that respect. Over the last decade thermoplastic vulcanisates, produced via dynamic vulcanisation of blends of polypropylene (PP) and EPDM, have been commercialised, combining thermoplastic processability with rubber elasticity [8, 9]. 

EPDM was developed and commercialised in the late 1950s. With an annual production capacity of more than 1,000 kt in 1998 [10]. EPDM is currently the fourth elastomer by volume and has become more or less a commodity rubber. Actually, EPDM is the largest non-tyre rubber. The annual growth rate is about 4%. DSM and Exxon are market leaders with a combined market share of approximately 40%. PP/EPDM-based thermoplastic vulcanisates which have currently the fastest growing rubber market (8% per year). 

Most EPDM applications require crosslinking except when used as an impact modifier for PP, polystyrene (PS) and polyamides or as an oil additive, e.g., as viscosity index improver or dispersant. Most commonly, accelerated sulfur vulcanisation is used for the crosslinking of EPDM. As a result of the low amount of unsaturation in EPDM ( 1 mole/ kg versus NR -15 mole/kg), sulfur vulcanisation of EPDM is rather slow and a relatively large amount of accelerators is needed. Because of the low polarity of EPDM the solubility of polar accelerators is limited, often resulting in low effectivity and/or blooming. Typically, up to 5 different accelerators are used in EPDM formulations. As for other rubbers environmental issues, such as nitrosamine formation and may be in the future the presence of zinc, are prompting the development of new accelerator systems. 

Resols (phenol-formaldehyde resins) are commercially used for effective crosslinking of EPDM in the production of thermoplastic vulcanisates [8]. General studies on rubber crosslinking for different diene rubbers are presented here. 

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