Characteristics by type of elastomer

NR – Natural Rubber

This elastomer, the basis of all rubbers, is used in a large proportion in the tire industry, leaving the rest of the consumption distributed in mechanical articles, latex articles, footwear, adhesives and other uses.

There is a synthetic version, the synthetic polyisoprene (IR), which has not been able to replace it because molecules of such high molecular weight as those of the natural polymer can not be obtained and because their cost is high compared to the latter.

  • Strengths
  • • Excellent mechanical properties, breaking load, elongation, abrasion and tear.
    • Low compression set and high resilience
    • Excellent dynamic and rebound properties.
    • Temperature range is -50º C to + 90º C.
    • Good resistance to acids, bases and salts.
    • Excellent electrical properties.
  • Weaknesses
  • • Poor resistance to aging.
    • Poor ozone resistance
    • Poor resistance to temperature
    • Poor resistance to oils, fats or hydrocarbons.

SBR – Styrene Butadiene Rubber

Butadiene-styrene rubbers are probably the most widely used synthetic rubbers in the world. Its use covers the tire, footwear, technical articles and adhesives industries.

  • Strengths
  • • Excellent mechanical properties, moderate to tear.
    • Lower resilience compared to natural rubber.
    • Good resistance to aging and temperature.
    • Temperature range: between -50ºC and 110ºC.
    • Good chemical resistance to many inorganic chemicals.
  • Weaknesses
  • • Poor resistance to oxidizing acids.
    • Resistance limited to mineral acids, not being suitable for organic liquids in general.

IIR – Isobutylene Isoprene Rubber

That is a copolymer of isobutylene with a small amount of isoprene. The main characteristic of Butyl is its excellent impermeability against gases.

Its incompatibility with other elastomers led to the development of compatible versions: halobutyl chlorobutyl (CIIR) and bromobutyl (BIIR).

  • Strengths
  • • Excellent resistance to weathering, oxidation, ozone and heat.
    • Very low resilience, which provides a high capacity for shock absorption or non-sustained vibrations.
    • Excellent impermeability to air and gases in general.
    • Excellent in contact with vegetable and animal fats and oils.
    • Temperature range: between -45 ° C and 130 ° C, and even higher, with suitable formulations.
    • Moderate resistance to abrasion and compression set.
    • Resistant to most inorganic chemicals, mineral acids and alkalis.
    • With reinforcing loads a high breaking load can be achieved.
    • Good electrical properties
  • Weaknesses
  • • Limited resistance to oxidizing chemicals.
    • Poor mechanical properties

NBR – Nitrile Butadiene Rubber

These are copolymers of butadiene and acrylic nitrile or acrylonitrile, and are often referred to simply as nitrile rubbers. Along with the fluorinated, the nitriles are synthetic rubbers with better resistance to oils and aliphatic hydrocarbons.

Its resistance to oils and hydrocarbons is higher the higher the content of acrylonitrile. According to their content in ACN they can be classified as Low content (<25% ACN), Medium content (25-35% ACN) and High content (> 35% ACN).

The fraction of polybutadiene is what gives it its elastic characteristics, while the polyacrylonitrile fraction, strongly polar, is what gives it its resistance to non-polar compounds, such as gasolines, oils and hydrocarbon solvents.

To improve its properties, two versions have been developed: the carboxylated nitrile (XNBR) for high temperatures and the hydrogenated nitrile (HNBR) to resist oxidation.

  • Strengths
  • • Very satisfactory resistance to aliphatic oils and hydrocarbons (hexane, heptane, methane, ethane, octane, butane, pentane).
    • Good adhesion to steel.
    • Resists acids (except oxidants), fatty acids, vegetable or animal fats.
    • They resist alkalis and salts.
    • High impermeability to air and other hydrocarbon gases such as natural gas, propane and butane.
    • Moderate resistance to low temperatures and to the elements.
  • Weaknesses
  • • Limited resistance against aromatic hydrocarbons (benzene, toluene, xylene) and even more against chlorinated ones (chloroform, trichlorethylene, perchlorethylene).
    • Limited temperature resistance
    • Poor ozone resistance

It is considered that the nitrile products can be used permanently at a temperature not higher than 120 ° C. Under immersion in oil they can retain their initial flexibility until after 70h at 150ºC. The compounds of this rubber are very useful for resisting high temperatures in short periods, retaining the flexibility after 1 h at 204 ° C and half an hour at 230 ° C.

EPDM – Ethylene Propyelene Diene Methylene

These are synthetic low density polymers, formed by a saturated polymer chain (without double bonds) of the polymethylene type, which is precisely what contributes to its excellent resistance to degradation.

  • Strengths
  • • Excellent resistance to aging, even in the open or at high temperature, to ozone and oxidation.
    • Very good resistance to hot water and water vapor.
    • Very good resistance to alkalis and even oxidizing acids and in general to all non-hydrocarbon chemical compounds.
    • They are not suitable in contact with gasolines, fats, oils and hydrocarbon solvents.
    • They are good electrical insulators
  • Weaknesses
  • • They are not suitable in contact with gasolines, fats, oils and hydrocarbon solvents.

CR – Chloroprene Rubber

Invented by Dupont for its industrialization through the Neoprene brand. They are polymers of 2-chlorobutadiene or chloroprene. It is used for the production of seals, hoses, profiles, transmission belts, rubberized fabrics and roofing. It also has an important application in the field of contact adhesives.

It has special properties that combine excellent resistance to multiple aging agents with very good mechanical properties.

  • Strengths
  • • They have excellent mechanical and abrasion properties.
    • Good gas impermeability
    • They have good resistance to heat and ozone.
    • Its resilience is somewhat lower than that of natural rubber in low hardness but higher than 60ºShore A.
    • They have good adhesion to metal.
    • Its resistance to oils, greases and hydrocarbon solvents is comparable to that of a low-medium content nitrile rubber.
    • In terms of chemical resistance, it is resistant to inorganic chemicals (except oxidizing and halogen acids).
    • They are self-extinguishing, that is, although they burn under the action of the flame, they do not spread the combustion and go out as soon as the flame is removed
  • Weaknesses
  • • Does not resist most organic compounds, except alcohols.
    • Does not resist oxidant and halogen acids

ACM – Acrylic Rubber (Alkyl acrylate copolymer)

They are special elastomers with high resistance to oils and heat.

They are usually ethyl acrylate copolymers and a minor proportion of a second chlorine-containing monomer. Its continuous working temperature can reach 150ºC, and intermittent peaks of 180ºC.

It is commonly used in transmissions in the automotive and hoses sector. It is also used in shaft sealing, adhesives, belts, gaskets and O-rings. It is used in vibration dampening assemblies due to the damping properties.

  • Strengths
  • • Superior to nitrile rubber in resistance to aging by hot oils, especially those containing sulfur and other additives.
    • Excellent temperature resistance
    • Good resistance to ozone and low gas permeability.
  • Weaknesses
  • • Little flexibility at low temperature
    • Poor resistance to flame
    • Low resistance to water, moisture, acids and bases

ECO – Ethylene Chlorhydrin

In addition to fluorinated, offer the best resistance to swelling in oils and solvents, at high temperatures. They also add resistance to ozone, good dynamic properties and good flame resistance.

The presence of chlorine in the side groups and the ether bonds give the rubbers of Epichlorohydrin a marked polar character and with it a good resistance to hydrocarbon compounds.

  • Strengths
  • • Excellent resistance to oils and fats, intermediate between medium and high NBR and comparable to polyacrylic.
    • Excellent resistance to ozone and weather
    • Good resistance to heat and fire
    • Excellent dynamic properties
  • Weaknesses
  • • Low resistance low temperatures
    • They are not good water vapor raincoats
    • Are attacked by oxidizing agents and chlorine
    • Limited resistance to most organic chemicals.

FPM o FKM – Fluorocarbon monomer / Viton ®

The most remarkable property of the fluor elastomers is its resistance to the heat that, perhaps, is the biggest of all the well-known rubbers: It is possible to obtain a continuous service, 1000h to 220ºC. If flexibility at low temperatures is not as good, even so, in some grades the rubbers retain their properties up to 40ºC below zero.

  • Strengths
  • • Excellent resistance to oils and chemicals at elevated temperatures
    • Excellent resistance to ozone and weather, UV rays, …
    • Excellent compression deformation at high temperatures.
    • Non-flammable, self-extinguishing
    • They do not use plasticizers
  • Weaknesses
  • • Weak resistance to esters and ketones
    • High price
    • Require post-curing

VMQ – VinylMethylsilses Quioxane

Compact Silicone rubbers do not contain any carbon atoms in their main chain, but consist of silicon and oxygen atoms, which is chemically designated as a polysiloxane chain. The molecular chains then have a nature both organic and inorganic.

Silicone rubbers are odorless, tasteless and non-toxic. When formulated and manufactured correctly, it is not staining or corrosive or deteriorating of any material with which it is contacted. They are physiologically inert and this has led to a wide variety of applications in the field of medicine. They are absolutely unalterable by ozone, weathering and ultraviolet radiation.

They have comparatively low mechanical properties with other rubbers (breaking load, elongation and tear) although it keeps them constant even at high temperatures. However, it is not advisable to subject them to steam under pressure. They are considered among the elastomers as the best electrical insulators.

The most outstanding quality of this rubber is its resistance to temperature: its compounds can work for extended periods of time in temperatures of up to 350ºC. On the other hand, in extreme cold conditions, this material will retain its original elasticity and flexibility. Up to -100ºC.

  • Strengths
  • • High resistance to high and low temperature
    • Excellent electrical insulation
    • Good values of permanent deformation by compression
    • Tolerance with the human body
    • Excellent resistance to extreme aging
  • Weaknesses
  • • Require post-curing (some types are non-post cure)