Abrasion is the removal of material by wearing, grinding, or rubbing the surface of a substrate with hard particles or hard protuberances. In general, vulcanized rubbers such as NBR that are blended with reinforcement fillers have higher abrasion resistance than unfilled rubbers. In many cases, the abrasion resistance can be enhanced by compounding with internal lubricants such as Teflon, molybdenum disulfide or naphthenic plasticizers. The abrasion resistance can be also improved by copolymerization with high Tg monomers. For example, the abrasion resistance of NBR generally improves with a higher acrylonitrile content.
Activators (Vulcanization) are important rubber processing additives that activate sulfur cure and improve the efficiency of sulfur-based cure systems. The most common activators are zinc fatty acid esters which are often formed in-situ by reaction of fatty acid with zinc oxide. The catalyst is zinc whereas the fatty acid functions as a solubilizing agent for the zinc which forms a complex with the accelerator or is covalently bonded to sulfur atoms in the accelerator molecule.
Acrylic Rubber, also called ACM rubber, is an synthetic elastomer composed of acrylic monomers. The most common repeat units are ethyl acrylate and butyl acrylate or a blend of both. Many other vinyl monomers can be included which allows for a wide variation of the thermophysical and mechanical properties. The combination of a saturated backbone with polar side groups results in a class of elastomers with excellent resistance to heat, oxidation and hydraulic oils. This type of rubber is sometimes an economical alternative to more expensive high-performance elastomers such as fluorocarbon polymers (FKM), silicones (VMQ) and fluorosilicones (FVMQ).
AEM Elastomers are synthetic elastomers composed of ethylene and acrylic monomers. The ethylene repeat units impart good low temperature properties, while the acrylic portion improves the swelling resistance in non-polar oils. The combination of a saturated backbone with polar side groups also provides improved resistance to heat, ozone (weathering), and many chemicals. These elastomers are primarily used where combined resistance to ozone, heat and oils is required. Typical applications include automotive transmission and power steering seals and O-rings that have to be resistant to transmission fluids and common automotive lubricants and hydraulic fluids.
Acrylonitrile butadiene rubber, also called nitrile rubber and usually shortened to nitrile or NBR, are important high-volume elastomers. They are statistical copolymers of acrylonitrile and butadiene produced by free-radical emulsion polymerization of butadiene with 15 to 45 percent acrylonitrile. NBR rubbers have good abrasion and chemical resistance but are not resistant to ozone and polar solvents and have only moderate mechanical properties. Because of their excellent oil resistance and low cost, NBRs are often used for hoses, O-rings, gaskets, V-belts and many other (automotive) rubber parts that have to withstand oil and gasoline. They are also used for disposable laboratory gloves, foot wear, synthetic leather, printer rollers, and cable jacketing.
Antioxidants or antiaging additives are added to plastics and elastomers to suppress free radical reactions that occur during oxidation. They are free-radical scavengers that react with chain-propagating radicals such as peroxy, alkoxy, and hydroxy radicals in a chain terminating reaction. Common antioxidants include hindered phenols and secondary aromatic amines. The former are often preferred because they have a lesser tendency to stain plastics and rubbers.