Properties and advantages of EPDM rubber

The main chain of EPDM is composed of chemically stable saturated hydrocarbons, and the side chains contain only unsaturated double bonds, so it is basically a saturated rubber. Because there is no non-polar substituent group in the molecular structure, the intermolecular cohesion energy is low, and the molecular chain can maintain flexibility in a wide temperature range. The chemical structure of ethylene propylene rubber gives the vulcanised product unique properties.

Low density and high filler:

EPDM rubber is a low density rubber, its density is 0.87. Coupled with the fact that a large number of oil-filled, filler, can reduce the cost of rubber products, to make up for the shortcomings of the high price of raw rubber EPDM, and high Mooney value of EPDM

Ageing resistance:

EPDM rubber has excellent weather resistance, ozone resistance, heat resistance, acid and alkali resistance, water vapour resistance, colour stability, electrical properties, oil filling and ambient fluidity.

Corrosion resistance:

EPDM has good resistance to various polar chemicals such as alcohols, acids, alkalis, oxidants, refrigerants, detergents, animal and vegetable oils, ketones, lipids, etc. due to its lack of polarity and low degree of unsaturation; however, petrol, benzene, and other aliphatic and aromatic solvents, and mineral oils are very unstable. Performance must decline even with the long-term action of concentrated acids.

Water vapour:

Ethylene propylene rubber has excellent resistance to water vapour and better heat resistance. There is no change in appearance after nearly 100 hours in superheated steam at 230. On the other hand, fluoroelastomers, silicone rubbers, fluorosilicone rubbers, butyl rubbers, nitrile rubbers, and natural rubbers experience a significant deterioration in appearance in a shorter period of time under the same conditions.

Superheated water resistance:

EPDM rubber has good thermal resistance, but it is closely related to the vulcanisation system used. EPDM rubber vulcanised with disulfide bis and TMTD as the vulcanisation system shows very little change in mechanical properties after 15 months of immersion in superheated water at 125, with a volume expansion of only 0.3%.

Electrical properties:
EPDM rubber has excellent electrical insulation properties and resistance to coronavirus, electrical properties better than or close to styrene butadiene rubber, chlorosulphonated polyethylene, polyethylene, cross-linked polyethylene.

Elasticity:

The molecular structure of EPDM rubber has non-polar substituents, low molecular cohesion energy, the molecular chain can be maintained in a wide range of flexibility, second only to natural rubber and butadiene rubber, can be maintained at low temperatures.

Adhesion: EPDM rubber due to the lack of active groups in the molecular structure, low cohesion energy, add the mixing rubber is easy to scrape the cream, self-adhesive and poor mutual adhesion.

Molecular structure and properties

Ethylene-propylene, ethylene-propylene and non-conjugated diene terpolymer. Diene has a special structure, only one of the two bonds can be copolymerised, unsaturated double bond is mainly cross-chain part. The other unsaturated one will not become the main polymer chain, only the side chain. The main polymer chain of ethylene-propylene is completely saturated. Based on this property, tripropylene is resistant to heat, light, oxygen, and especially ozone. Tripropylene is inherently non-polar, resistant to polar solutions and chemicals, has low water absorption and good insulating properties.

In the manufacturing process of ethylene-propylene, the properties can be adjusted by changing the ethylene-propylene ratio, molecular weight and its distribution and vulcanisation methods.

Selection of EPDM third monomer

Triolefin-type monomers are vulcanised by copolymerisation of ethylene and propylene to produce unsaturation in the polymer. The selection of the third monomer must fulfil the following requirements:

Up to 2 bonds can be polymerised: one, 1 can be vulcanised

Reaction similar to two basic monomers

Random polymerisation of the primary bonds produces a homogeneous distribution

sufficient volatility to be easily removed from the polymer

The rate of vulcanisation of the polymer is suitable

Molecular Weight and Molecular Weight Distribution

The molecular weight of ethylene propylene rubber is usually expressed in terms of the Mooney viscosity. In the case of the Menni viscosity of tripropylene, these values are obtained at elevated temperatures, usually 125, the main reason for which is the elimination of the effect of the high ethylene content (crystallisation) which masks the true molecular weight of the polymer. The Menni viscosity of tripropionic acid ranges from 20 to 100. Although higher molecular weight commercial ethylene-propylene is also produced, it is generally filled with oil for blending purposes.

The molecular weight and distribution in tripropylene can be polymerised in a polymerisation by the following methods:

In addition, the molecular weight distribution of modifiers such as catalyst type and concentration, temperature, and hydrogen concentration can be measured at elevated temperatures (150) using gel permeation chromatography as a solvent. The molecular weight distribution is often referred to as the ratio of the weight average molecular weight to the number average molecular weight.

By increasing the molecular weight of the tripropylene, the positive impact ratio: has higher tensile and tear strength, can absorb more oil and filler (at low cost) at higher temperatures with higher green strength. As the molecular weight distribution increases, the positive effects are: increased mixing and milling processability. However, a narrow molecular weight distribution improves the speed of vulcanisation, the state of vulcanisation and the injection behaviour.

Vulcanised

Ethylene-propylene can be vulcanised with organic peroxides or vulcanised. However, EPDM with peroxide chains offers higher temperature resistance, lower compression set and improved vulcanisation characteristics in the wire and cable industry compared to vulcanisation with peroxides. The bad thing about peroxide vulcanisation is that it is more costly. As noted above, the rate of crosslinking and vulcanisation time between ethylene-propylene-propylene varies with the type and content of vulcanisation. When blending ethylene-propylene with butyl, natural rubber, and styrene butadiene rubber, the following elements need to be considered when selecting the appropriate ethylene-propylene product:

When blending with butyl, butyl has a low degree of unsaturation, so to cope with the vulcanisation rate of butyl, a tripropylene with a relatively low content of DCPD and ENB is preferred.

When mixing natural rubber and styrene butadiene rubber, in order to cope with the vulcanisation speed, it is preferred to choose EPDM with enb content of 8 %~10 %.

The above is the performance and advantages of EPDM rubber how much you know, for more information, feel free to contact us!