EPDM Chinese name: EPDM rubber
EPDM EPDM foam
EPDM EPDM foam
English full name: Ethylene-Propylene-Diene Monomer (abbreviation: EPDM)
EPDM rubber is a terpolymer of ethylene, propylene and non-conjugated diene, which was commercialized in 1963. The annual consumption worldwide is 800,000 tons. The most important feature of EPDM is its superior resistance to oxidation, ozone and erosion. Since EPDM is a polyolefin family, it has excellent vulcanization characteristics. Among all rubbers, EPDM has the lowest specific gravity. It absorbs a large amount of fillers and oils and has little effect on properties. Therefore, it is possible to produce a rubber compound which is inexpensive.
EPDM is a terpolymer of ethylene, propylene and a non-conjugated diene. Diolefins have a special structure, only one of the two bonds can be copolymerized, and the unsaturated double bonds are mainly used as a crosslink. Another unsaturation will not become the polymer backbone, it will only become a side chain. The main polymer chain of EPDM is fully saturated. This property makes EPDM resistant to heat, light, oxygen, and especially ozone. EPDM is essentially non-polar, resistant to polar solutions and chemicals, low in water absorption, and has good insulating properties.
In the production process of EPDM, the characteristics can be adjusted by changing the amount of the three monomers, the ethylene-propylene ratio, the molecular weight and its distribution, and the method of vulcanization.
The third diene type monomer is produced by copolymerization of ethylene and propylene to produce an unsaturation in the polymer to effect vulcanization. The choice of the third monomer must meet the following requirements:
Up to two keys: one polymerizable and one vulcanizable
The reaction is similar to two basic monomers
Primary key random aggregation produces uniform distribution
Sufficient volatility for easy removal from the polymer
The final polymer vulcanization speed is suitable
Methylidene norbornene (ENB) molecular structure
Methylidene norbornene (ENB) molecular structure
At present, the third monomer for industrial production of EPDM rubber has only the following three types:
Ethylidene norbornene (ENB)
(This monomer is currently only used by a company in the US Du Pont)
Effect of Diene Type and Content on Polymer Properties
The production of EPDM is mainly based on ENB and DCPD.
The most widely used of EPDM is ENB, which is much faster than DCPD products. Under the same polymerization conditions, the nature of the third monomer affects long-chain branching, increasing in the following order: EPM < EPDM (ENB) < EPDM (DCPD)
Other EPDMs affected by the third monomer of diene are:
ENB-fast vulcanization, high tensile strength, low permanent deformation
DCPD-focal resistance, low permanent strain, low cost
As the third monomer of diene increases, the following effects will occur: faster vulcanization rate, lower compression set, higher definition, diversity of accelerator selection, reduced anti-focus and elongation, and higher The cost of the polymer.
Ethylene to propylene ratio
The ethylene to propylene ratio can be varied during the vulcanization stage, and the commercial ethylene propylene polymer ethylene propylene ratio is from 80/20 to 50/50. When the ethylene to propylene ratio is changed from 50/50 to 80/20, the positive effects are: higher green strength, higher tensile strength, higher crystallization, lower glass transition temperature, and raw materials. The polymer is converted into pellets, as well as better extrusion properties. Bad effects are poor calendering mixing, poor low temperature properties, and poor compression set.
When the proportion of propylene is higher, the benefits are better processing properties, better low temperature properties and better compression set.
The molecular weight of the elastomer is usually expressed in terms of Mooney viscosity. In the Mooney viscosity of EPDM, these values are obtained at high temperatures, usually 125 ° C. The main reason for this is to eliminate any effects (crystallization) caused by high ethylene content. Mask the true molecular weight of the polymer. The Mooney viscosity of EPDM ranges from 20 to 100. There are also higher molecular weight commercial EPDMs that are also produced, but are generally oil-filled for mixing.
The molecular weight and distribution in EPDM can be polymerized during the polymerization by:
Type and concentration of catalyst and cocatalyst
The molecular weight distribution of EPDM can be measured by gel permeation chromatography using dichlorobenzene as a solvent at a 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. This value varies between 2 and 5 depending on the normal and highly branched structure. Due to the split bond, the ethylene-propylene-containing EPDM rubber has a broader molecular weight distribution.
By increasing the molecular weight of EPDM, the positive effects are: higher tensile and tear strength, higher green strength at elevated temperatures, and the ability to absorb more oil and filler (low cost). As the molecular weight distribution increases, the positive effects are: increased mixing and milling processability. However, a narrower molecular weight distribution can improve the vulcanization rate, vulcanization state, and injection molding behavior.
Type of vulcanization
EPDM can be vulcanized using organic peroxides or sulfur. However, compared to sulfur vulcanization, peroxide crosslinked EPDM has higher temperature resistance, lower compression set and improved vulcanization characteristics for the wire and cable industry. The bad thing about peroxide vulcanization is the higher cost.
As mentioned earlier, the crosslink speed and cure time of EPDM vary with the type and amount of vulcanization. When EPDM is mixed with butyl, natural rubber, styrene-butadiene rubber, the following factors must be considered when selecting the appropriate EPDM product:
When mixed with butyl, since the butyl has a lower degree of unsaturation, it is preferred to select a relatively low level of DCPD and ENB content of ethylene propylene to accommodate the butyl vulcanization rate.
When blended with natural rubber and styrene-butadiene rubber, it is best to choose 8% to 10% ENB content of EPDM to meet its vulcanization rate.
EPDM rubber is a rubber obtained by copolymerization of ethylene and propylene, and a third monomer (ENB) is introduced. EPDM rubber is basically a saturated high polymer with excellent aging resistance, good weather resistance, excellent electrical insulation performance, good chemical corrosion resistance and good impact elasticity. The main disadvantage of ethylene-propylene rubber is that the vulcanization rate is slow; it is difficult to use with other unsaturated rubbers, and the self-adhesiveness and mutual viscosity are very poor, so the processing performance is not good.
According to the performance characteristics of ethylene-propylene rubber, it is mainly used in several fields requiring anti-aging, water resistance, corrosion resistance and electrical insulation, such as light-colored sidewalls for tires, heat-resistant conveyor belts, cables, wires, anti-corrosion linings, and gaskets. , building waterproof sheet, door and window seals, household appliances accessories, plastic modification, etc. The nature and use of ethylene propylene rubber.
Ethylene-propylene rubber is synthesized from ethylene and propylene as main raw materials, and its aging resistance, electrical insulation properties and ozone resistance are outstanding. Ethylene-propylene rubber can be filled with oil and filled with carbon black. The price of the product is low. The chemical stability of ethylene-propylene rubber is good, and the wear resistance, elasticity, oil resistance and styrene-butadiene rubber are close. Ethylene-propylene rubber is widely used as a tire side, rubber strip and inner tube, as well as automotive parts. It can also be used as wire and cable sheathing and high-voltage, ultra-high-voltage insulation materials. It can also manufacture light-colored products such as shoes and hygiene products.