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Special use synthetic rubbers

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Synthetic rubbers are artificial elastomers (not natural) that are used in applications that require special characteristics.

The main existing difference between both types is because EPM is an ethylene-propylene copolymer, that’s why its bond is saturated and it can only vulcanize with peroxides. The EPDM contain a diene into their structure which let them vulcanize by means of 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 antiozone products
  • Excellent resistance to water-steam, alkalis, acids, and normally all non hydrocarbon chemical compounds
  • Very low density

These rubbers can also show some disadvantages, for example:

  • Low oil resistance
  • They count with medium mechanical characteristics.

The choloroprene rubber group of properties make of it the most balanced one:

  • Good mechanical characteristics even with low loads level, as it happens with natural rubber
  • Good resilience from 60º Shore A on
  • Medium hidrocarbons 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 point out because they show:

  • Very good resistance to aliphatic hydrocarbons
  • Very 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

Against it 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 per its own name, a nitrile rubber whose main double-link bonds have been catalytically hydrogenated, turning the bond completely saturated. Therefore, the only way this rubber can be vulcanized is by means of peroxides.

With this modifications of the nitrile rubber, the original rubber properties do not become modified, as the branches of the main bond do not turn affected, but some of the properties which limited the use of this rubber get improved, and they read as follows:

  • 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 ones do, on the other hand it is made by alternating silicon and oxygen atoms. This property makes the thermal stability be much higher than their competitors one.

Among the advantages of the Silicone Rubbers use, we must 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 absolutely resistant to elements and ozone
  • They are perfect thermal insulation materials
  • They do not burn easily and they are auto-extinguishable
  • They count with a very high gases/fumes impermeability

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.

On the negative side we must 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 is 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 really wide. These are some of the synthetic rubbers of special use:

  • Poli Isobutileno Isopreno (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)