Effect of ethylene and propylene content on EPDM properties

Effect of ethylene and propylene content on EPDM properties

Text/Meteor Polymer NOVA

EPDM is an elastomer with a wide range of applications. E is ethylene, P is propylene and D is a diene (that is, third unsaturated monomer. There are mainly three types, namely linear alkanes 1,4-hexadiene, dicyclopentadiene DCPD, ethylidene norbornene ENB). EPDM has a rich polymethylene backbone, which has excellent weather resistance and heat resistance. Due to its high molecular weight, it can be filled with cheap filler oils and fillers in large quantities, so rubber compound cost is low and has a market competitiveness.

The performance of EPDM varies greatly depending on ratio of ethylene to propylene in polymer. An ideal interleaved ethylene-propylene copolymer should contain 40% (50% by moles) ethylene and 60% by weight (50% mole fraction) propylene. , polymers with this composition are amorphous, however, commercial polymers usually contain 50-80% ethylene, and choice of ethylene limit must be based on reality. EPDM above 75% ethylene can be very hard and difficult to blend in an internal mixer. When content of ethylene is less than 50%, it is difficult for traditional vanadium-based Ziegler-Natta catalyst to achieve commercially acceptable performance. This type of catalyst is much more reactive with ethylene than with propylene, so production of high propylene grades of EPDM is slower and cost will be higher because more carbon atoms are attached to α-olefin chains. on other hand, reactivity of Ziegler-Natta catalyst will decrease, which will affect polymerization rate.

1. Low Ethylene

Low ethylene polymers, polymer products containing 50%-55% ethylene, are amorphous, have a low glass transition temperature, and do not exhibit ethylene crystallinity above glass transition temperature. This polymer is relatively soft and has excellent flexibility at low temperatures. and low temperature permanent deformation, but can not add many fillers.

For EPDM with ethylene content of 56%-62%, ethylene chain region is longer or ethylene chain region appears more frequently and melting point is lower than room temperature.

The glass transition temperature of low ethylene EPDM is low, even below room temperature, so its product form is usually block rubber, which cannot be made into granular products.

Effect of ethylene and propylene content on EPDM properties

2. Average ethylene content

Polymers with an average content of ethylene, that is, polymers containing 63%-67% ethylene, its products have both crystallinity below room temperature and a small degree of crystallinity at higher temperatures of 40-60°C.

3. High ethylene content

Ethylene-rich polymers, i.e. polymers containing 68%-80% ethylene, have higher green rubber strength at room temperature, higher tensile strength and toughness of vulcanized rubber, and can also add a large amount of fillers. product does not contain lamellar crystals, which may indicate true crystallinity of polyethylene due to obvious transition of crystalline melting below room temperature and at 40-60°C. Polymers prepared with titanium-based catalysts at 60° C. may experience higher melt transitions.