The knowlage of Nitrile Elastomers

The ratio of key monomers (butadiene, acrylonitrile and styrene) influences how these properties are expressed. For example, a higher amount of acrylonitrile provides better oil and solvent resistance but reduces softness and flexibility. In fact, the amount of acrylonitrile used to make nitrile elastomers is so important that the whole family of elastomers is organized into a series of grades based on how much acrylonitrile is present. High acrylonitrile grades contain more than 45 percent acrylonitrile, which produces elastomers with excellent oil/gas/grease resistance but with reduced flexibility and elongation. Medium acrylonitrile grades contain between 30 and 45 percent acrylonitrile, which still have good oil/gas/grease resistance but with added flexibility and softness. And, finally, low acrylonitrile grades contain less than 30 percent acrylonitrile, which have superior flexibility and softness but are far less resistant to hydrocarbons.

Beyond the ratio of acrylonitrile to other monomers, the performance of nitrile elastomers can also be manipulated through other chemical processes and reactions. For example, crosslinking through heat-reactive or carboxylated monomers can enhance toughness, abrasion and chemical resistance. In the former case, crosslinking can be achieved by heating the polymer film to approximately 150°C to 175°C. In the latter case, cross-linking agents, such as melamine formaldehyde, urea formaldehyde, phenolic and epoxy resins, can be introduced. Or, for chemical cross-linking, the process uses zinc oxide or zirconium ammonium carbonate. 

Nitrile elastomers can also be vulcanized. Charles Goodyear invented the process of vulcanization in 1839 when he added sulfur and additional ingredients, known as accelerators, to natural rubber at high heat. The result was a rubber with improved durability over a broad temperature range. This same process can be achieved with nitrile elastomers — when they are treated with sulfur, accelerators and heat, they become much more durable.

Chemists can also control nitrile emulsions by manipulating the surfactant system used in their formulation. Latexes made using natural emulsifiers, such as fatty acid and rosin acid-based surfactants, will exhibit superior water resistance and are easily precipitated by cationic salts. This makes these products well suited for gasket manufacturing and specialty papermaking processes. Products made from synthetic surfactants — sulfate and sulfonate — will often exhibit superior mechanical stability, which makes them well-suited for certain paper coatings and other high-shear applications, including asphalt emulsion modification, adhesives, metal coating and textiles.

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