 TIMPRENE |
| Timprene is an elastomeric compound that is highly resistant to acidic environments |
| and ozone at elevated temperatures. Timprene is highly flame resistant. Timprene was |
formulated specifically to function in the harsh environment of high efficiency (90+), |
condensing gas furnaces. |
|
| EPDM---Ozone Resistance |
| Ethylene-Propylene-Diene Modified (EPDM) is a copolymer of ethylene and propylene |
| which has outstanding resistance to aging, weathering, ozone, oxygen and many |
| chemicals. High and low temperature stability as well as steam and water resistance |
| are excellent. Dynamic and mechanical properties are, in general, between natural |
| rubber and SBR. |
| EPDM finds uses in many static and dynamic applications where the above properties |
| are important. It can be extruded or molded. It should not be used where continual |
| contact with petroleum based products is required. |
|
| NEOPRENE---Better Sunlight/Ozone Resistance |
| Neoprene is a polymer of chloroprene and has several properties superior to natural |
| rubber, such as better resistance to gasoline, sunlight, ozone and oxidation. It is not |
| only flame resistant, but will not support combustion. It has good resistance to the |
| corrosive action of chemicals, and its water resistance to heat, and does not soften as |
| does natural rubber under severe exposure. Resilience is almost equal to natural |
| rubber, being surpassed today only by the butadienes. Compression set and creep |
| characteristics vary in different forms, from types that are inferior to natural rubber to |
| other types which are better-particularly under high-temperature long-time service. The |
| tear resistance is equal to natural rubber at room temperature; at elevated |
| temperatures tear resistance is poor but can be improved to some extent by |
| compounding with reinforcing materials. |
| Neoprene is commonly blended with other polymers for various applications. The term |
| "commercial" neoprene will vary widely. |
|
| SILICONE RUBBER--- Extreme Temperatures |
Silicone rubber is one of the versatile family of semi-organic synthetics known as silicones |
| that look and feel like organic rubber, yet have a completely different type of structure |
| than other elastomers. The backbone of the elastomer is not a chain of carbon atoms but |
| an arrangement of silicone and oxygen atoms. This structure gives a very flexible chain |
| with weak interchain forces. This accounts for the remarkable small change in dynamic |
| characteristics over a wide range of temperature. Silicone elastomers show no molecular |
| orientation or crystallization on stretching and must be strengthened by reinforcing |
| materials. |
| Silica-reinforced elastomers available today have tensile strengths approaching 2000 |
| PSI compared with peak values of only 600 psi for earlier grades. In addition, |
| elongations of more than 600% have been achieved as compared to a maximum of |
| 300% for the earlier materials. |
| Silicone elastomers can be made that will withstand temperatures as high as 600 F |
| without serious deterioration, and at the other end of the temperature scale will remain |
| flexible at 150 F. The elastomers remain flexible and are serviceable over this entire |
| temperature range. No plasticizers are needed that might cause some sacrifice in |
| properties in some temperature range. |
| While silicone elastomers have lower strength than other elastomers, they are They do |
| amazingly fatigue and flex resistant, probably as a result of their chemical inertness. |
| not require high tensile and tear strength to make suitable for dynamic applications. |
| Fall off in tensile properties at higher temperatures is less than for other elastomers and |
| these values are retained on extended exposure. Resistance to chemical deterioration, |
| oils, oxygen and ozone is also retained under these conditions. Chemical inertness |
| makes these materials of special interest for surgical equipment and food processing. |
| By changing molecular arrangement, silicone elastomers can be produced with special |
| characteristics such as: low compression set, low temperature resistance,high-temperature |
| resistance, or high dielectric strength. These types provide a tremendous range of property |
| balance, and still others are under development or in final stages of field testing. |
|
| NITRILE |
NBR or nitrile elastomers are copolymers of butadiene and acrylonitrile, used primarily |
| for application requiring excellent resistance to petroleum oils and gasoline. Resistance |
| to aromatic hyrocarbons is better than Neoprene but not as good as polysulfide. NBR has |
| excellent resistance to mineral and vegetable oils, but relatively poor resistance to the |
| swelling action of oxygenated solvents such as acetone, methylethyl ketone and other |
| ketones. It has good resistance to acids and bases with the exception of those having |
| strong oxidizing effects. Resistance to heat aging is good, often a key advantage over |
| natural rubber. |
With higher acrylonitrile contents, the solvent resistance is increased but low
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| temperature flexibility is decreased. Low-temperature resistance is inferior to natural |
| rubber, and although NBR can be compounded to give improved performance in this |
| area,the gain is normally at the expense of oil and solvent resistance. As with SBR, this |
| material does not crystalize on stretching and reinforcing materials are required to |
| obtain high strength. With compounding it is possible to get a fairly good balance |
| between low creep, good resilience, low permanent set and good abrasion resistance. |
| Tear resistance is inferior to that of natural rubber and electrical insulation is lower. NBR |
| is used instead of natural rubber where added resistance to petroleum oils, gasoline or |
| aromatic hydrocarbons is required. The properties of this elastomer make it useful for |
| carburetor and fuel pump diaphragms, aircraft hoses and gaskets, where it competes with |
| polysulfide and the neoprene elastomers. |
|
| NATURAL RUBBER--- Extremely Resilient |
This is nature's main "ready-made" contribution to the elastomer field. Its chief source is |
| the Hevea Brasiliensis, a commercially grown tree found principally in the Far East. The |
| bulk of natural rubber used for today's engineering applications is plantation rubber, |
| smoked sheet and pale crepe being the best and most important. Natural rubber, |
| polyisoprene, still offers the optimum balance of properties necessary for high |
| performance in many demanding mechanical applications. Quality compounds can be made |
| for a wide range of stiffness requirements. |
| It has high resilience, outperformed only by some of the more recent man-made a wide |
| polyisoprenes and polybutadienes. It exhibits very good tensile and tear properties over |
| stiffness range and has excellent resistance to cold flow. It is possible to make |
| compounds that exhibit low permanent set at temperatures up to 200 F. Abrasion |
| resistance is good, though inferior to BR (polybutadiene) and SBR (styrene-butadiene). |
| Natural rubber has better low-temperature flexibility than most synthetics, but is not as |
| good as silicone rubber or some of the special butadiene and SBR compounds. Natural |
| rubber compounds can be made with a wide range of electrical properties. |
| Natural rubber does not age as well as many of the synthetics nor is it as chemically |
| inert as some. It is inferior to many of the synthetics for heat aging, resistance to |
| sunlight, oxygen, ozone, solvents or oils. |
| It can be bonded satisfactorily to a wide range of materials and is used in a variety of |
| application, including tires, gaskets, seals, rolls, hose, tubing, vibration isolators, shock |
| mounts, electrical components, bumpers, drive wheels, etc. It is the material used for |
| most high performance applications unless some specific environmental condition is met. |
|
| SBR---Superior Water Resistance |
SBR is a synthetic copolymer of styrene and butadiene. Although it is one of the earlier a |
| synthetics, it still represents the largest variety being made today. The copolymer includes |
| number of types, each developed for specific applications. It can be obtained in the form of |
| latex or as a dry product, similar to natural rubber. |
| The general balance of properties that can be obtained is a little below that obtainable |
| with natural rubber, but the cost of the base material is lower and fluctuates less. |
| Certain types give slightly better wear resistance in tire treads; others provide better |
| low-temperature flexibility. It has about the same resistance to solvents and chemicals |
| as natural rubber but has superior water resistance. |
| On heat aging, it hardens and becomes brittle instead of softening as does natural to a |
| rubber. Pure gum (unreinforced) high-strength compounds cannot be made since |
| molecular alignment to oppose stress is difficult; crystallization does not occur. |
| Resistance to sunlight and ozone is about the same as natural rubber. It can be bonded |
| wide variety of materials and used in many products interchangeably with natural |
| rubber. |
| Broadly then, SBR allows controlled cost preparation of materials providing good wear |
| resistance, low-temperature flexibility and good resistance to sunlight and ozone, with wide |
| bonding latitude. |
|
| BUTYL---Low Resilience |
| Butyl was originally known as "the inner tube rubber." Butyl is resistant to ozone, |
| weathering, and many chemicals. Butyl is abrasion resistant and exhibits low |
| resilience. Butyl has excellent damping properties. |
|
| FLUOROCARBON POLYMER(VITON)-Resistant to Ozone,Sunlight,and Oxygen |
Fluorocarbons are the end product of the co polymerization of highly fluorinated olefins. |
| Fluorocarbons find unique usage in hot oil environments where outstanding compression |
| set is also required. Typical properties at 400 F for a 70 Shore A hardness compound would |
| be 15% to 30% compression set and less than 5% volume swell in ASTM #3 oil or |
| automatic transmission fluid. |
| Fluorocarbons are resistant to the effects of ozone, oxygen and sunlight. Practical |
| compounds are available in 60-90 Shore A durometer hardness. Typical examples of trade |
| names are "Viton" and "Flourel". |
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