Polymers
Special Assets: Materials may be formulated to impart outstanding tensile strength, abrasion resistance, resilience, and resistance to flex fatigue and compression set. Good general-purpose rubber. Generally resistant to moderate chemicals, organic acids, alco¬hols, ketones, and aldehydes. Natural rubber compounds exhibit excellent low-temperature properties without the use of plasticizers. Uncured materials have good building tack.
Restrictions: Generally not suitable for uses requiring resistance to petroleum derivatives, non-polar solvents, fats, or corrosive chemicals. Not the polymer of choice for resistance to sunlight, ozone, oxygen, heat, or outdoor exposure.
Special Assets: General-purpose, low-cost elastomer with prop¬erties resembling those of polyisoprene. Has slightly better resist¬ance to heat aging and flex fatigue than natural rubber.
Restrictions: Similar to those of polyisoprene. Uncured SBR compounds are not generally known for their building tack.
Special Assets: EPDM materials can be compounded to be very economical, and they generally provide exceptional resistance to oxygen, ozone, and heat degradation. They are often recom¬mended for outside use. Products are suitable for use in animal and vegetable oils. Vulcanizates can also be compounded for out¬standing color retention and resistance to hot water and steam. Flexible at extremely low temperatures.
Restrictions: Not generally suitable for uses requiring resistance to petroleum derivatives, non-polar solvents, or mineral oils. EPDM materials usually do not possess outstanding compression set resistance and may be difficult to bond to certain substrates.
Special Assets: Properly formulated butyl compounds show out¬standing resistance to permeation by gasses. They are useful for air-holding materials and in applications where resistance to diffusion by gasses or moisture is important. Butyl products can be formulated for good resistance to ozone, weather, and chemical attack, and can provide excellent vibration dampening properties.
Restrictions: Not generally suitable for uses requiring resistance to petroleum derivatives, non-polar solvents, or coal tar solvents. Products may be difficult to process. Tensile strengths of butyl compounds are generally lower than those of natural rubber.
Special Assets: Nitrile elastomers are outstanding for applications requiring a high degree of resistance to oils, fuels, and solvents at a reasonable cost. Nitrile is the polymer of choice for general¬purpose oil resistant materials. Compounds possess moderately good stress/strain properties. Special compounds can be formu¬lated for use up to 265ûF. Compression set properties are com¬parable to those of natural rubber.
Restrictions: Not usually suitable for use in polar solvents such as ketones, esters, chlorinated solvents, or nitro carbons. Many Nitrile compounds are attacked by ozone, heat, and weather. Extreme low-temperature flexibility can only be achieved by sac¬rificing some oil resistance.
Special Assets: Neoprene is a versatile general-purpose elastomer. Compounds can be formulated for good resistance to ozone, oxygen, heat weathering, and many chemicals. They can provide good resilience, tensile strength, and compression set resistance. Materials have moderate resistance to many solvents and petrole¬um-based products. Properly formulated neoprene compounds can provide a high degree of flame resistance.
Restrictions: Neoprene products possess moderate oil resistance, but are not recommended for demanding uses such as contact with fuels or hot oils. Strong oxidizing agents, esters, ketones, and chlorinated solvents generally attack them. Polychloroprene is priced higher than general-purpose elastomers such as SBR, EPDM, and natural rubber. White or very light-colored products tend to discolor slightly during aging or exposure to sunlight.
Special Assets: Hypalon material is noted for outstanding resistance to abrasion. Vulcanizates also withstand deterioration by weather, ozone, sunlight, heat, and moderately corrosive chemicals. Compounds exhibit excellent color retention and can be formulated for flame resistance. Hypalon is similar to neoprene in oil resistance.
Restrictions: Restrictions are similar to those of neoprene. Hypalon is more costly than general-purpose polymers. Compounds generally do not have outstanding resilience or compression set resistance. Hypalon products are not generally recommended for use in contact with fuels, aromatic solvents, hot oils, or other areas requiring exceptional oil resistance.
Special Assets: Polyurethane technology is progressing quickly, and many polymers can be custom-tailored for specific end uses. In general, urethanes are resistant to ozone, hydrocarbons, mod¬erate chemicals, fats, oils, and greases. They usually possess excel¬lent low-temperature crack resistance, outstanding tensile strength, abrasion resistance, tear strength, and elongation. Urethane materials can be formulated for a number of special properties including dielectric seal ability, high or low coefficients of friction, and vibration dampening.
Restrictions: Polyurethanes are generally attacked by strong acids, ketones, esters, chlorinated solvents, and nitro carbons. They usually exhibit poor compression set resistance and are sometimes susceptible to degradation by weather, sunlight, or hydrolysis. Polyurethane polymers, as a rule, are more costly than Nitrile.
Special Assets: Polyacrylics are high-heat- and oil-resistant special¬ty elastomers. In many circumstances, properly compounded vul¬canizates are serviceable for use up to 350ûF. An outstanding feature is the ability to resist the deteriorative effects of hot oils, including those containing sulfur. Polyacrylic materials are inher¬ently ozone- and weather-resistant, and they exhibit good color retention.
Restrictions: Acrylics are generally attacked by alcohols, glycols, alkalis, esters, aromatic hydrocarbons, chlorinated solvents, and phenol. They are not recommended for continuous contact with water. Polyacrylic materials tend to be more flammable than standard polymers. They are moderately high in cost. Vulcanizates compounded for low-temperature flexibility will not provide optimum high-temperature service.
Special Assets: Polysulfide elastomers display excellent resistance to oils, solvents, thinners, ketones, esters, aromatic hydrocar¬bons, and dilute acids. Products have good ozone resistance, extremely low permeability to gasses, and excellent low-tempera¬ture properties without the use of plasticizers.
Restrictions: Polysulfide vulcanizates do not possess exceptional tensile strength. Products are attacked by strong oxidizing acids, many chlorinated solvents, nitro carbons, ethers, amines, hetero¬cyclics, and mercaptans.
Special Assets: Silicone rubber is a specialty elastomer designed to remain serviceable over an extremely wide range of tempera¬tures. Special compounding can lead to materials that are suitable for continuous service at temperatures up to 400ûF. Some mate¬rials can withstand a temperature of 9000ûF for a few minutes. Silicone formulations are generally more flame-resistant than gen¬eral-purpose elastomers. They are often used in medical applica¬tions because of their high degree of biocompatibility. Compounds show excellent resistance to weathering, oxygen, ozone, compression set, and moderate chemicals. Vibration dampening properties are quite good.
Restrictions: Silicone elastomers are more expensive than most specialty rubbers.
Special Assets: Hydrin is a specialty elastomer with solvent resist¬ance similar to that of Nitrile. Additional benefits are good heat resistance, excellent low-temperature properties, ozone resistance, and very low gas permeability. Dynamic properties are similar to those of natural rubber.
Restrictions: Hydrin compounds are likely to be more costly than Nitrile compounds. Products are not generally suitable for use in polar solvents such as ketones, esters, chlorinated solvents, or nitro carbons. Contact with peroxide forming materials (i.e., sour gasoline) will interfere with performance.
Special Assets: Fluoroelastomers are high-technology elastomers designed for extreme heat, and oil and chemical resistance. Products are nearly equal to silicone materials in heat resistance, while resisting aliphatic aromatic and halogenated hydrocarbons, concentrated acids and alkalis, and animal and vegetable oils. Vulcanizates have higher tensile strength than silicones.
Restrictions: Fluoroelastomers are not generally resistant to ketones, low molecular weight esters (such as ethyl acetate), or nitro containing compounds. Products are not usually serviceable below 15ûF. Fluoroelastomers are premium priced materials.
Special Assets: Fluorosilicone polymers are the only elastomers available that offer outstanding resistance to fuels, oils, solvents, and chemicals and also match the unsurpassed environmental stabili¬ty and resistance to the temperature extremes of silicone rubber.
Restrictions: Fluorosilicone elastomers are the most expensive commercially available polymers. They are not suitable for use in some brake fluids, hydrazine, and ketones.