Special use synthetic rubbers

The fundamental difference between both types is that EPM is an ethylene-propylene copolymer, that’s why its bond is saturated, and it can only be vulcanised with peroxides. The EPDM contain a diene in its structure which allows it to be vulcanised by sulphur. The great advantages of these rubbers are:

• Excellent ageing resistance, both room temperature and high temperature
• Excellent ozone and rust resistance, it does not need the use of anti-rust nor antiozonant products
• Excellent resistance to water-steam, alkalis, acids, and normally all non hydrocarbon chemical compounds
• Extremely low density

These rubbers can also show some disadvantages, for example:

• Low oil resistance
• They have medium mechanical characteristics.

Chloroprene rubber is the most balanced in terms of properties:

• Good mechanical characteristics even with low load level, as it happens with natural rubber
• Good resilience from 60º Shore A on
• Medium hydrocarbons resistance
• Good oxygen and ozone resistance
• It is self-extinguishing / fire resistant; it burns if we apply a flame on it, but it goes out when the flame is moved away

Concerning the factors against it, we must point out its great power “it can be used for everything, but there is a better rubber for everything”

Normally we have to say that Nitrile Rubbers stand out because they show:

• Exceptionally good resistance to aliphatic hydrocarbons
• Exceptionally good resistance to fatty acids and animal and vegetable fats
• Good resistance to solutions diluted in salts, acids and non-oxidant alkalis
• Low permeability to gases / fumes
• Good tensile, tear and abrasion strength
• Good heat resistance

Among the cons, we can point out:

• Low resistance to aromatic hydrocarbons (toluene, xilene, etc.)
• Low resistance to chlorinated hydrocarbons (trichloroethylene)
• Low resilience
• Poor resistance to low temperature

Hydrogenated Nitrile rubber is, as its name suggests, a nitrile rubber whose main double-link bonds have been catalytically hydrogenated, making it completely saturated. Therefore, the only way this rubber can be vulcanised is by means of peroxides.

With these modifications to nitrile rubber, the original rubber properties do not become modified, as the branches of the main bond do not become affected, but some of the properties which limited its use are improved, such as:

• Excellent oxygen and ozone resistance
• Better low temperature resistance

The most outstanding property of this rubber is the wide spectrum of temperatures where it keeps its elastic properties, only exceeded by the Silicone Rubber ones. The performance temperature range of this rubber can go from -60ºC to 150º C in continuous.

Further to the above mentioned, this rubber shows the following properties:

• Excellent resistance to elements and ozone
• Good high temperatures compression set
• Mechanical properties medium values

Their main property is that the main bond does not contents any carbon atom as all the rest of the rubbers do, but it is made up of alternating silicon and oxygen atoms. This property makes the thermal stability much higher than that of its competitors.

Among the advantages of the Silicone Rubbers use, we could point out:

• A very wide temperatures range, from -100ºC to 200ºC, being able to reach up to 250ºC
• Although the mechanical characteristics are low at room-temperature, they can keep them at high temperature as per their thermal stability, beating those rubbers which show better properties at room-temperature
• They are resistant to elements and ozone
• They are perfect thermal insulation materials
• They do not burn easily and they are auto extinguishable
• They have a remarkably low gases/fumes permeability

As per their physiological safety and their tolerance to alive organisms, they are ideal to manufacture products which will be in direct contact with food of medical-pharmaceutical items, etc.

Among the cons, we could mention:

• Their low resistance to alkalis and acids, as well as to chlorinated hydrocarbons, esters, ketones and ethers

The great heat and chemical agents’ resistance are the main property of this rubber. Besides, fluorocarbon rubbers show:

• Great aliphatic, aromatic and chlorinated hydrocarbons resistance
• Great resistance to water and water-steam and to acids and alkalis
• Great resistance to elements and ozone
• As per its halogen contents it is auto-extinguishable

It does not show many disadvantages, but some of them which point out read as follows:

• They have the highest density of the whole of the studied rubbers.
• Low esters and ketones resistance

The range of synthetic rubbers existing in the market is diverse. These are some of the synthetic rubbers of special use:

• Poly-Isobutylene Isoprene (butyl) (IIR)
• Butyl Halogenated Rubbers (Chlorobutyl CIIR, Bromobutyl BIIR)
• Polynorbornene (PNR)
• Polyurethane (AU) (EU)
• Polysulphide (TR)
• Chlorosulphonated Polyethylene (CSM)
• Chlorinated Polyethylene (CM)
• Epichlorohydrin Rubbers (CO, ECO)
• Acrylic Rubbers (ACM)
• Ethylene, Vinyl Acetate Rubber (EVA)