EPDM is a copolymer of ethylene, propylene and a small amount of non-conjugated diene. It is a kind of ethylene propylene rubber. It is represented by EPDM (Ethylene Propylene Diene Monomer) because its main chain is made of chemically stable saturated hydrocarbons. It contains only unsaturated double bonds in the side chain, so it has excellent aging resistance such as ozone resistance, heat resistance, weather resistance, etc., and can be widely used in automobile parts, construction waterproof materials, wire and cable sheaths, heat-resistant hoses, tapes , Automotive seals and other fields.

Structural characteristics

EPDM rubber is a terpolymer of ethylene, propylene and non-conjugated diene. Diene has a special structure. When the copolymer is reacted, only one double bond with large activity participates in the reaction, and the remaining double bond with less activity remains on the molecular chain of the copolymer to become an unsaturation point. The main chain of sulfur vulcanization using EPDM is saturated. This feature makes it resistant to heat, sunlight, and ozone. EPDM rubber is essentially non-polar, resistant to polar solutions and chemicals, has low water absorption, and has good insulating properties.

The third monomer

The non-conjugated diene monomer in the synthesis of EPDM rubber is copolymerized with ethylene and propylene to generate unsaturated bonds in the polymer to achieve vulcanization. Ethylene norbornene (ENB) and dicyclopentadiene (DCPD) are mainly used in the production of EPDM. One of the most widely used is ENB, which cures much faster than DCPD products. With the increase of the third monomer of diene, the following effects will occur: faster curing rate, lower compression set, high fixed elongation, variety of accelerator choices, reduced scorch resistance and ductility, and higher The cost of the polymer.

Molecular weight

The molecular weight and distribution of EPDM rubber can be measured by gel permeation chromatography using dichlorobenzene as a solvent at high temperature (150°C). The molecular weight distribution is often referred to as the ratio of weight average molecular weight to number average molecular weight. Depending on the normal and highly branched structure, this value usually varies between 2 and 5. The Mooney viscosity of EPDM rubber can reflect the size of its molecular weight. The Mooney viscosity of EPDM rubber usually ranges from 20 to 100.

Increasing the molecular weight of EPDM rubber has positive effects: higher tensile and tear strength, higher green strength at high temperatures, and ability to absorb more oil and fillers (low cost). As the molecular weight distribution increases, the positive effects are: increased mixing and milling processability. However, the narrower molecular weight distribution can improve the vulcanization speed, vulcanization state, and injection behavior.

performance

Compared with other commonly used general rubbers or special rubbers, the main performance advantages of EPDM are as follows:

(1) High cost performance. The density of raw rubber is only 0.86～0.90kg/m3, which is the lightest common rubber with raw rubber density; and it can be filled in large quantities to reduce the cost of rubber.

(2) Excellent aging resistance, weather resistance, ozone resistance, sunlight resistance, heat resistance, water resistance, water vapor resistance, ultraviolet resistance, radiation resistance and other aging properties. It is compatible with other unsaturated diene rubbers such as NR, SBR, When BR, NBR, and CR are used together, EPDM can act as a polymer antioxidant or antioxidant.

(3) Excellent chemical resistance, acid, alkali, detergent, animal and vegetable oil, alcohol, ketone, etc.; outstanding water resistance, superheated water resistance, water vapor resistance; polar oil resistance.

(4) Excellent insulation performance, volume resistivity 1016Q·cm, breakdown voltage 30-40MV/m, dielectric constant (1kHz, 20℃) 2.27.

(5) The applicable temperature range is wide, the minimum operating temperature is -40～-60℃, and it can be used at 130℃ for a long time.