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 expressed by EPDM(Ethylene Propylene Diene Monomer). Because its main chain is composed of chemically stable saturated hydrocarbons, it only contains unsaturated double bonds in the side chain, so it has excellent aging resistance such as ozone resistance, heat resistance and weather resistance, it can be widely used in automobile parts, waterproof materials for construction, wire and cable sheaths, heat-resistant rubber hoses, adhesive tapes, automobile seals and other fields.

Structural characteristics

EPDM is a terpolymer of ethylene, propylene and non-conjugated diene. Diolefin has a special structure. During the copolymer reaction, only one double bond with large activity participates in the reaction, while the remaining double bond with small activity remains on the copolymer molecular chain as an unsaturated point. The main chain of EPDM rubber used for sulfur vulcanization is saturated. This characteristic makes it heat-resistant, sunlight-resistant and ozone-resistant. EPDM is essentially non-polar, resistant to polar solutions and chemicals, low water absorption, and good insulation properties.

Third monomer

The non-conjugated diene type monomer in the synthesis of ethylene-propylene-diene monomer is to produce unsaturated bonds in the polymer by copolymerization with ethylene and propylene in order to achieve vulcanization. EPDM is mainly used in the production of ethylidene norbornene (ENB) and dicyclopentadiene (DCPD). The most widely used of these is ENB, which vulcanizes much faster than DCPD products. With the increase of the diene third monomer, the following effects will occur: faster cure rate, lower compression set, high set elongation, diversity of accelerator selection, reduced scorch resistance and elongation, higher polymer cost.

molecular weight

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

The positive effects of increasing the molecular weight of EPDM are: higher tensile and tear strength, higher green strength at high temperatures, and the ability to absorb more oil and fillers (low cost). The positive effect with increasing molecular weight distribution is: increased mixing and milling processability. However, a narrower molecular weight distribution can improve vulcanization speed, vulcanization state, and injection molding behavior.

Performance

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

(1) cost-effective, raw rubber density is only 0.86~0.90kg/m3, is the lightest density of raw rubber commonly used rubber; and 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. When combined with other unsaturated diene rubbers such as NR, SBR, BR, NBR, and CR, EPDM can act as a polymer antioxidant or antioxidant.

(3) excellent chemical resistance characteristics, acid, alkali, detergent, animal and vegetable oil, alcohol, ketone, etc.; excellent water resistance, resistance to superheated water, water vapor resistance; resistance to polar oil performance.

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

(5) a wide range of applicable temperature, the lowest temperature -40 ~-60 ℃, can be used for a long time at 130 ℃.