Through copolymerization of acrylic esters with monomers, which allow subsequent crosslinking reactions to take place, one obtains saturated and amorphous polymers which are very polar. The acrylic esters are primarily ethyl acrylate and/or butyl or acrylate, as well as ethylmethoxy or –ethyloxy. As expected, these copolymers have excellent oil, heat, aging, and ozone resistance.
As with other special rubbers, the tensile properties of ACM vulcanizates do not reach the level of those from NR or NBR. ACM grades, and particularly the new generation ones, can be used under certain conditions for 1000 hours at 160 to 170ºC. However, one has to remember that ACM vulcanizates soften at high temperatures.
ACM vulcanizates are much more resistant to swelling in animal, vegetable, and mineral oils than all the rubbers discussed so far, and this applies also to swelling at high temperatures, where ACM is surpassed only by FKM.
Over 90% of ACM is used in automative. The main application is in shaft seals of all constructions, namely seals for crankshafts, automatic and differential transmissions, valves, o-rings and oil hose. The relatively high price of ACM restricts its applications. ACM is threatened by FKM in some applications.
The typical property spectrum of CRs can be modified through blends with other elastomers. At the blends with NR, elasticity and flexibility at low temperatures improve; with NBR swelling resistance to industrial oils improves.
Like the other rubber materials, mechanical properties are due to filler grades at chloroprene rubber. With its excellent oxygen endurance, CR has much more resistance to air and ozone. For the material that mixed with, process temperature can be between -45ºC to 100ºC. This grade can be 130ºC at short periods.
Because of chlorine content, CRs have a favourable flame resistance, and in this respect they are superior to other rubbers. With using some plasticizers like phosphoric acid this resistance can be increased.
The oil resistance depends, significantly on the type of oil. CR vulcanizates have a good resistance to paraffinic and naphtenic oils of high molecular weight, but swell extensively in aromatic oils of low molecular weight.
In general, CR vulcanizates are fairly resistant to chemicals. Contrary to aliphatic compounds, esters, ketones, aldehydes and chlorinated or aromatic hydrocarbons swell and soften CR vulcanizates considerably.
Due to its polarity, CR is a better conductor of electricity than the non-polar NR and SBR, but a poorer conductor than NBR.
Due to these properties chloroprene rubber is used in; gaskets, profiles, belts, couplings, V-belts, shoe solings and many applications in the construction industry, such as window and construction profiles, roofing membranes, and also cable jackets.
EPDM is a kind of material which is used in the media where phosphate-ester based non-flammable hydraulic fluids, hot water and steam need to be sealed.
Fillers need to be used definitely; not suitable for compounding with other elastomers, aromatics, mineral and petroleum products.
Chemical and structural factors are need to be paid attention on the choice of EPDM, that will be used. Molecular weight, Mooney viscosity, ethylene-propylene ratio, type and amount of terpolymer are the other important points that determines the choice.
The factors that make this rubber more important and functional are like;
- Excellent resistance to light, heat and ozone;
- Resistance to chemicals;
- Keeping the elasticity at low temperatures;
- Good dielectricity;
- High capability of absorbing fillers and oil.
High resistance to ozone of EPDM rubbers, provides to compound with unsaturated NR, SBR, BR blends. The ratio can be 30 phr EPDM – 70 phr NR/SBR. Also the compounds with NBR provide products that have resistance to ozone and oil.
Most important reason to use fillers on EPDM’s is to improve the physical properties. Carbon black is the most common filler. Intensification degree and processability mostly depend on type, properties and the amount in the mixture of carbon black. On the other hand using of fillers aids to reduce the cost. Because fillers can be used on EPDM on high ratios. Mineral fillers can be used to reduce the cost as well as they are used in the production of white coloured materials.
For EPDM’s properties of high absorbing of fillers and oil; amount and kind of the process oil have an importance. As the most common ones, paraffinic oils have high heat resistance. Better physical properties are provided by naftenic oils and they are preferred at coloured products. For weakening the physical properties, aromatic oils sholud not be used. For the resistance of EPDM rubbers to heat, light and ozone there is no need for additional oxidant and anti-ozonate.
Besides electrical properties are excellent. EPDM is mostly used in production of cable coatings, tyres, hoses, windows, doors and architectural profiles.
PTFE is a polymer of tetrafluoroethylene. For PTFE’s smooth surface, it is being used in applications which dust and dirt undesired. Products have high chemical resistance and widest working temperature range. The working temperature can change from -250 to +250°C and none of mechanical properties considerably change until minimum temperature.
Mechanical properties like elasticity modulus and tensile strength depend on temperature with inverse ratio. Among all polymers, PTFE has the smallest coefficient of friction. This causes of FEP products are being used in most of the applications with high slippery and low friction force.
Additional to these properties adhesiveness and moisture absorption is low. Mechanical properties can be improved with some additives.
FEP is mostly used in production of sealing elements like gaskets, piston rings, u-cups and o-rings.
FKM is used for oil gaskets in automotive industry. For a long term exposure to 205ºC and short term to 315ºC vulcanizates are endurable. FKM’s high temperature and chemical resistances are good as low swelling and gas permeability.
The tensile strength depends greatly on the temperature, and it drops considerably at higher temperatures. The same applies to the hardness, which can be compounded for a range of Shore A 50 to 95, preferably 70. FKM vulcanizates are not very elastic.
FKM has the best resistance of all rubbers, and continous service for 1000 hour will be 220ºC and even a service life at 250ºC is possible. FKM vulcanizates also resist degradation from weathering and ozone.
FKM is a relatively expensive material and its low temperature properties are poor.
Can be used widely in o-rings, hydraulic seals and pneumatic seals.
The introduction of the fluoronated hydrocarbon moiety increases the polarity of FVMQ considerably over that of VMQ, with the result that FVMQ vulcanizates have a considerably better resistance to oils, motor fuels, and chemicals. Even after exposure for 1.000 hours to high-test motor fuels or methanol-containing fuels, the tensile strength of the vulcanizates has retained about 80 to 90% of its original valuei which is suprisingly high. FVMQ vulcanizates also swell very little in alcohols, but somewhat more in esters and chlorinated hydrocarbons.
The brittleness temperature is, at -65 to -70ºC. Thus, FVMQ combines the good swelling resistance of fluoro elastomers with the good low temperature flexibility of silicone rubbers. The long-term heat resistance is somewhat poorer than that of VMQ elastomers. Nevertheless the maximum service temperature is still above 200ºC. Hardness value is flexible from 30 to 80 Sh.A.
FVMQ vulcanizates are mostly used in static applications which need high level technology like space and automotive industries, with outdoor applications which requires low temperature and various products which contacts directly to human skin
HNBR is prepared from normal NBR polymers by complete or partial hydrogenation of the double bond in the component butadiene. Obtained by hydrogenating the nitrile copolymer, HNBR fills the gap left between NBR, EPDM and FKM elastomers where high temperature conditions require high tensile strength while maintaining excellent resistance to motor oils, sour gas, amine/oil mixtures, oxidized fuels, and lubricating oils.
Completely saturated NBR grades can be crosslinked with peroxides. Peroxide cross-linking through this double bond raises the heat stability and the oxidation stability.
The vulcanizates gives the highest resistance to hot air and hot oils that can be achieved with NBRs, a high resistance to oxidative and ozone degradation, high resistance to sulphur-containing oils, even hydrogene sulfide, sulfur and nitrogen-containing oil additives and a high resistance to industrial chemicals.
The material so prepared are characterised by high mechanical strength and by improved abrasion resistance. HNBR is suitable for temperatures from -30 °C to +150 °C
In non-aueous solutions, and by using suitable catalysts, such as pyridine-cobalt complexes, or complexes from rhodium, ruthenium, iridium, and palladium, it is possible to hydrogenate NBR partially or even completely.
Completely hydrogenated NBRs have a fully saturated polymer chain, which, conceptually, could have been derived from ethylene and acyrlonitrile. Therefore, the code ENM has been proposed for this copolymer.
Completely saturated NBR grades can be crosslinked with peroxides. The vulcanizates gives the highest resistance to hot air and hot oils that can be achieved with NBRs, a high resistanceto oxidative and ozone degradation, high resistance to sulphur-containing oils, even hydrogene sulfide, sulfur and nitrogen-containing oil additives and a high resistance to industrial chemicals. In addition, the fully saturated HNBRs have an excellent tensile strength, good low temperature flexibility and very good abrasion resistance. After exposure to high temperatures, these HNBRs retain their mechanical properties much better than, for instance, FKM vulcanizates, so that, inspite of their lesser heat and sweling resistance, fully saturated HNBRs can compete with FKM. Because of the excellent mechanical properties also at high temperatures, the good low temperature flexibility and the good chemical resistance, fully saturated HNBR is able to replace even FKM in various applications.
HNBR can satisfy the reqiurments of the oil and automotive industry for rubber components with a good oil, gasoline and ozone resistance, and with a high level of property retention after exposure to high temperatures of about 150ºC.
HNBR is prepared from normal NBr polymers by complete or partial hydrogenation of the double bond in the component butadiene. Peroxide cross-linking through this double bond raises the heat stability and the oxidation stability. The material so prepared are characterised by high mechanical strength and by improved abrasion resistance. Temperature range of use is -30ºC to +150ºC.
HNBR has recently been developed to meet higher temperatures than standard NBR while retaining resistance to petroleum based oils. Obtained by hydrogenating the nitrile copolymer, HNBR fills the gap left between NBR, EPDM and FKM elastomers where high temperature conditions require high tensile strength while maintaining excellent resistance to motor oils, sour gas, amine/oil mixtures, oxidized fuels, and lubricating oils.
HNBR is resistant to mineral oil-based hydraulic fluids, animal and vegetable fats, diesel fuel, ozone, sour gas, dilute acids and bases. HNBR also resists new bio-oils (biological oils). HNBR is suitable for high dynamic loads and has a good abrasion resistance. HNBR is suitable for temperatures from -30°C to +150°C
NBR is a material which oil resistance is high and most common used in sealing elements. The ratios of acyrlonitrile and viscosity have mainly effects on NBR’s properties. Suitable for medias like mineral oil, water and water-oil emulsions. Working temperature is between -30ºC to 100ºC.
Mooney viscosity of rubber is related directly to its molecular weight.. However branching and structural properties may change the relationship too. With the increase of Mooney viscosity; absorbability of filler and oil, breaking strength rise, surface view improves and pores reduce.
With NBR, its possible to mould various products which hardness can be 20 Shore A to ebonite hardness. The breaking strength of a product from raw rubber, without additional fillers, is 3 MPa. With using the right and suitable fillers, this value can be increased to 35 MPa. High strength is provided mostly at 70-80 Shore A hardness.
NBR rubber wears relatively high if supplier fillers are not used. Furthermore high wear and tear resistance can be provided with minor carbon blacks and collapsed silicas.
Generally elasticity of NBR vulcanizates is lower than natural rubber, SBR and CBR. To strengthen the elasticity values; NBR polymers with low ACN, carbon blacks (SRF) and vulcanization systems, which secure crosslinking at high temperatures, have to be used in the mixture.
NBR’s cost is lower when it is compared with other synthetic rubbers. NBR is used at medias like fuel oil and oil that high mechanical properties, heat resistance and abrasion resistance is desired. NBR is typically used in; statical gaskets, o-rings, crank shafts and valves as a sealing element, membranes, couplings and pneumatic hoses, conveyor belts, friction coverings, work boots and shoe soling.
Natural rubber is a high molecular isoprene. It is characterised by high mechanical strength and elasticity as well as by good low temperature. The most important specification of NR is its high processability.
Being non-polar, NR can be readily blended with a great number of other non-polar rubbers. Blends with SBR and BR are technically exploited. In these instances, some of the properties of the SR (synthetic rubber) are transferred to NR (regarding abrasion resistance, heat resistance), or from NR to the SR (regarding processibility, dynamic properties, price etc.)
NR vulcanizates can be produced in a wide range of hardness, from very soft (Shore A 30 to 50) up to ebonite hardness. This can be done by changing the amount of fillers and softeners in the compound on the one hand, or through the sulphur concentration on the other.
NR has, contrary to most types of SR, a high tensile strength of 20 Mpa and more. By adding reinforcing fillers to compounds, the tensile strength can rise up to 30 Mpa. Even at high temperatures, NR vulcanizates have a good tensile strength. The tear resistance is also influenced by the strain cyrstallization, and it is therefore very good.
Elastic, abrasion and isolation properties are good. Resistance at castor based oils is high, but weak to oil and ozone.
NR, which physical properties are stabilized well, is used on; mostly vibration dampers, engine equipments, rubber-metal suspension parts and diaphragms. Additionally it is used only in castor based hydraulic fluids (automotive hydraulic brake systems and some plane hydraulic systems) and applications that need low heat resistance as a sealing element’s material.
Styrene-butadiene rubber is a polymer of styrene and butadiene. SBR can be considered a general purpose rubber, same as NR or IR, since it can be used in many applications and especially in tire compounds. The styrene content in SBRs ranges usually from about 23 to 40%.
For the production of SBRs, the following parameters are important:
- Monomer ratio (mostly 23.5% styren, and in some instances, also 40%);
- Polymerization temperature;
- Chain modifiers (differences in Mooney viscosity, processibility);
- Stabilizers;
- Oil, type and amount;
- Carbon black, type and amount.
Being of low polarity, SBR can practically be blended with all non-polar rubbers over the whole range of blend concentrations. Blends with BR or NR are of great importance in tire applications.
The tensile properties of SBR vulcanizates depend in great measure on the type and amount of filler in the compound. Particularly advantages are the dynamic fatigue resistance, the aging resistance, and the heat resistance of SBR vulcanizates. Without antiozonants, the SBR vulcanizates are, however, not resistant to weathering and ozone degradation. SBR’s resistance to abrasion and elasticity is relatively high. SBR grades, being non-polar, and their vulcanizates, are poor conductors of electricity. Yet, the electrical properties of SBR depend to a great extent on the production process, namely residual emulsifier and electrolyte content.
For a sealing elements material SBRs are used in castor based hydraulic fluids.
Polyurethane elastomers have become an important class off organic materials for many technological applications. By reacting a great variety of low and higher molecular wight compounds with diisocyanates, it is possible to obtain polymers with a corresponding variety of chemical structures and physical properties. Another attractive feature of polyurethane chemistry is the opportunity to tailor-make materials to specific property requirements, simply by changing the chemical components.
It is possible to produce PU polymers, which can be prosessed adn subsequently cured using conventional mixing and processing methods of the rubber industry.
The polyurethane elastomers have the characteristics of elastomers – high tensile properties at high ultimate elongations, high hardness, and usually a high heat-resistance. Hardness of compounds have the variety between Sh.A 60 – 90. At working temperatures which reaches to -60 / -80ºC, products can be used securely. Also all mechanical properties effect directly from working temperature.
Vulcanizates are mostly used in automotive industry like seats, indicators, wheels and internal equipments; refrigerators and some applications on medicine with the help of their great compatibility with human skin.
Silicone rubber has a wide range of working area in sealing elements for its excellent heat resistance and isolation specifications. It is used in sealing of crank shafts, stove and oven gaskets, freezer and refrigerator and ozone units.
VMQ vulcanizates are not resistant to aliphatic, aromatic and chlorinated hydrocarbons. They are to a certain extent swell resistant in paraffinic oils. Because of their polarity, the vulcanizates are also attacked by acids and bases.
The tensile properties, and particularly the impact resistance and the abrasion resistance, are considerably poorer than those of other elastomers. The relatively vulnerability, particularly due to mechanical impact, is a real weakness of silicone vulcanizates. However, that unlike other elastomers the vulcanizate properties of Q change very little with increasing temperatures. Above approximately 150ºC silicone elastomers show the best mechanical properties of all. Q vulcanizates can be obtained in hardnesses of Shore A 30 to 80, but those in the hardness range of 50 to 60 generally have the best mechanical properties. Silicone vulcanizates a long-term exposure to hot air at 180ºC, and even at 250ºC, their elasticity remains infact after 1000 hours’ exposure. The vulcanizates even endure a short exposure to temperatures of 300 to 400ºC (heat shocks). However, steam of 120 to 140ºC attacks and corrodes silicone vulcanizates after a certain time, therefore the vulcanizates should not be exposed to steam.
Working temperature is between -80 to 300ºC. The resistance of ozone, weather and moisture is excellent. Silicone rubber is a very good dielectric and can be transparent. And it’s resistance to aging is well.
Mechanical properties and abrasion resistance are poor as VMQ vulcanizates are tore easily. Resistance to EP additives and oils is poor. Furthermore of these specifications, with being an expensive material, silicone is used in electrical, electronical, space, automotive, food and textile industries as well as lighting and cables.