Rubber Materials – Types, Applications and Production

Rubber Materials – Types, Applications and Production

Except from natural rubbers, rubber market is very important for today’s technology. Rubbers constitute a very important branch of polymer market also. Synthetic rubbers has biggest share in rubebr market also. Here we explain the top ten avaliable commercial synthetic rubber that are avaliable in polymer market today.

Rubber is used in the production of lots of products. These products are produced with a bunch of production methods that we will describe here. Rubber products that you are seeing around you are probably produced by one of these processes.

Types of Rubbers

Inner tyres.

Butadiene Rubbers

Styrene-butadiene rubbers are the most impotant elastomer material in polymer chemistry. It has specific properties and because of these properties, these materials are used in various kinds of engineering applications. In here, we will state these properties and applications of styrene-butadiene rubber.

What Are The Properties Of Styrene-Butadiene Rubbers?

Styrene-butadiene rubber flooring application.

As you understand from its name, styrene-butadiene rubber is the copolymer butadiene and styrene. It has the biggest market share around other elastomers, which is reaching up to 40% of total market share. Styrene-butadiene rubber is produced alternative to natural rubber in WW2 by Germans. The most attractive property of styrene-butadiene rubber is the low cost. It can be reinforced with vulcanization process with carbon black. With that process, styrene-butadiene rubber has similar properties with natural rubber.

Mechanical properties of styrene-butadiene rubber is lower than natural rubber. But wear resistance and resistance to heat, ozone and water is superior.

General applications that styrene-butadiene is used in are; automobile tyres, wire insulation and footwear.

  • Properties of styrene-butadiene rubber: Symbol of styrene-butadiene rubber is ‘SBR’ in market. We stated that it is a copolymer of styrene and butadiene which have chemical representations C8H8 and C4H6 respectively. Elongation of styrene-butadiene rubber at failure is around 700% according to its original shape. Tensile strength of styrene-butadiene rubber is 20 MPa. Modulus of elasticity is 17 MPa. Service temperature range of styrene-butadiene rubber is between -50C and 110C.
Chemical structure of styrene-butadiene rubber copolymer.

Buthyl Rubbers

Butyl rubber is produced as copolimers of polyisobutylene and polyisoprene. The precentages of these two compounds in butyl rubber around 98-99% and 1-2% respectively. It has very low air permeability that leads to use in such applications as inflatable tubes and tubeless tyre liners.

The compound of isobutylene has chemical representation (C4H8)n and isoprene has (C5H8)n. The ‘n’ means the number of monomers that these two compunds formed. In market, the symbol of butyl rubber is BTL and you can find out commercial butyl rubber products with this symbol. The avaliable temperature limit that butyl rubber can be used from -50C to 110C. At 300% elongation, butyl rubber has modulus of elasticity of 7 MPa. Also the tensile strength of butyl rubber is 20 MPa. The maximum elongation according to its original shape is 700%. Density of butyl rubber is around 0.92 gr/cm^3.

The Properties Of Butadiene Rubber

Tyres made with butadiene rubber.

This synthetic elastomer is combined with other rubber to produce automotive tires. It is generally mixed with natural rubbers. In some applications, butadiene rubber is mixed with styrene to obtain styrene-butadiene rubber. With the combination of other rubbers, good tensile strength, tear ersistance and ease of processing is obtained.

The most important example of butadiane rubber is polybutadiene which has chemical representation of (C4H6)n. The commercial symbol of polybutadiene rubber is BR and you can find it market with this symbol. The avaliable temperature range to use polybutadiene rubber is nearly same with butyl rubber. Tensile strength of polybutadiene is around 15 MPa. The maximum elongation that polybutadiene can reach is around 500% according to its original shape. Density is 0.92 g/cm^3.

Chloroprene Rubber

Butyl rubber is produced as copolimers of polyisobutylene and polyisoprene. The precentages of these two compounds in butyl rubber around 98-99% and 1-2% respectively. It has very low air permeability that leads to use in such applications as inflatable tubes and tubeless tyre liners.

The compound of isobutylene has chemical representation (C4H8)n and isoprene has (C5H8)n. The ‘n’ means the number of monomers that these two compunds formed. In market, the symbol of butyl rubber is BTL and you can find out commercial butyl rubber products with this symbol. The avaliable temperature limit that butyl rubber can be used from -50C to 110C. At 300% elongation, butyl rubber has modulus of elasticity of 7 MPa. Also the tensile strength of butyl rubber is 20 MPa. The maximum elongation according to its original shape is 700%. Density of butyl rubber is around 0.92 gr/cm^3.

The Properties Of Butadiene Rubber

Tyres made with butadiene rubber.

This synthetic elastomer is combined with other rubber to produce automotive tires. It is generally mixed with natural rubbers. In some applications, butadiene rubber is mixed with styrene to obtain styrene-butadiene rubber. With the combination of other rubbers, good tensile strength, tear ersistance and ease of processing is obtained.

The most important example of butadiane rubber is polybutadiene which has chemical representation of (C4H6)n. The commercial symbol of polybutadiene rubber is BR and you can find it market with this symbol. The avaliable temperature range to use polybutadiene rubber is nearly same with butyl rubber. Tensile strength of polybutadiene is around 15 MPa. The maximum elongation that polybutadiene can reach is around 500% according to its original shape. Density is 0.92 g/cm^3.

Ethylene-Propylene Rubber

What Are The Properties Of Ethylene-Propylene Rubber?

Ethylene-propylene rubber is an actually terpolymer. The third constituent monomer in this terpolymer is diene, which has a very small propotion compared with ethylene and propylene. This terpolymer rubber called as EPDM also in rubber market. General applications of ethylene-propylene rubbers are; cable insulation and automative parts.

Constituents ethylene, propylene has chemical representations of C2H4, C3H6 respectively. Diene monomer is generally added to obtain cross-linked structure in this rubber. The service temperature limits of ethylene-propylene is from -50C to 150C. Ethylene-propylene rubber has density of 0.86 g/cm^3. And tensile strength of ethylene-propylene rubber is 15MPa. The maximum elongation of ethylene-propylene rubber according to its original shape is around 300%.

Properties And Applications Of Isoprene Rubber

Chemical representation of isoprene rubber.

This synthetic rubber is synthesized as the equivalent of natural rubber. It has same characteristics with natural rubber. Synthetic polyisoprene is also softer that natural rubber and much more easlity molded. Some of applications that isoprene rubber is used in; caulking, footwears, conveyors etc.

The rubber that obtained from isoprene is polyisoprene. Polyisoprene has chemical representation of (C5H8)n. ‘n’ means the number of copolymers in the polymer. The symbol of isoprene rubber is ‘IR’ in market that ou can find it with this symbol. The temperature avaliability of isoprene rubber is from -50C to 80C. Modulus of elasticity of polyisoprene is around 17 MPa at elongation of 300% of its original shape. Tensile strength is around 25 MPa. Failure elongation of polyisoprene is 500%.

Styrene-butadiene rubber.

Nitrile Rubber

What Are The Properties Of Ethylene-Propylene Rubber?

Ethylene-propylene rubber is an actually terpolymer. The third constituent monomer in this terpolymer is diene, which has a very small propotion compared with ethylene and propylene. This terpolymer rubber called as EPDM also in rubber market. General applications of ethylene-propylene rubbers are; cable insulation and automative parts.

Constituents ethylene, propylene has chemical representations of C2H4, C3H6 respectively. Diene monomer is generally added to obtain cross-linked structure in this rubber. The service temperature limits of ethylene-propylene is from -50C to 150C. Ethylene-propylene rubber has density of 0.86 g/cm^3. And tensile strength of ethylene-propylene rubber is 15MPa. The maximum elongation of ethylene-propylene rubber according to its original shape is around 300%.

Properties And Applications Of Isoprene Rubber

Chemical representation of isoprene rubber.

This synthetic rubber is synthesized as the equivalent of natural rubber. It has same characteristics with natural rubber. Synthetic polyisoprene is also softer that natural rubber and much more easlity molded. Some of applications that isoprene rubber is used in; caulking, footwears, conveyors etc.

The rubber that obtained from isoprene is polyisoprene. Polyisoprene has chemical representation of (C5H8)n. ‘n’ means the number of copolymers in the polymer. The symbol of isoprene rubber is ‘IR’ in market that ou can find it with this symbol. The temperature avaliability of isoprene rubber is from -50C to 80C. Modulus of elasticity of polyisoprene is around 17 MPa at elongation of 300% of its original shape. Tensile strength is around 25 MPa. Failure elongation of polyisoprene is 500%.

Polychloroprene sheet.

Styrene-Butadiene Rubber

Styrene-butadiene rubber flooring application.

As you understand from its name, styrene-butadiene rubber is the copolymer butadiene and styrene. It has the biggest market share around other elastomers, which is reaching up to 40% of total market share. Styrene-butadiene rubber is produced alternative to natural rubber in WW2 by Germans. The most attractive property of styrene-butadiene rubber is the low cost. It can be reinforced with vulcanization process with carbon black. With that process, styrene-butadiene rubber has similar properties with natural rubber.

Mechanical properties of styrene-butadiene rubber is lower than natural rubber. But wear resistance and resistance to heat, ozone and water is superior.

General applications that styrene-butadiene is used in are; automobile tyres, wire insulation and footwear.

  • Properties of styrene-butadiene rubber: Symbol of styrene-butadiene rubber is ‘SBR’ in market. We stated that it is a copolymer of styrene and butadiene which have chemical representations C8H8 and C4H6 respectively. Elongation of styrene-butadiene rubber at failure is around 700% according to its original shape. Tensile strength of styrene-butadiene rubber is 20 MPa. Modulus of elasticity is 17 MPa. Service temperature range of styrene-butadiene rubber is between -50C and 110C.
Chemical structure of styrene-butadiene rubber copolymer.

Thermoplastic Elastomers

Actually, they are thermoplastic materials but have elastomeric behaviors. In elastomer market, they have very important place. Thermoplastic elastomers does not take their elastomeric behavior from their cross-linked molecular structure, they take their elastomer characteristics from their chemical connections between different phases in that are exist. These phases are soft and hard phases that they constitutes the thermoplastic elastomer.

They have block copolymer of styrene-butadiene-styrene block copolymer which is a very characteristic for this group. Thermoplastic elastomers includes different two materials that are not chemically incompatible to each other. So they for different phases. So chemical bondings between these phases constitutes the thermoplastic elastomer materials.

General applications of thermoplastic elastomers are; automotive molded parts, extruded tubes, wire coating and footwear.

  • Properties Of Styrene-Butadiene-Styrene: The symbol of this polymer in market is ‘SBS’. It hase very important place in elastomer market which has market share of 12%. Service temperature limit is between -50C and 60C. At higher temperatures, it shows thermoplastic properties. Elongation at failure of SBS is around 400% according to its original shape. Tensile strength is 14 MPa.

Vulcanization of Rubbers

The vulcanization process is a special application for rubbers to obtain more cross-linking structures between mers/molecules. These cross-linkings provide a much more stiff structure than thermoset plastics. As you know that also, elastomers are very flexible compared with other polymers. With the vulcanization method, elastomers lose nothing from their flexibility but gain stiffer structure. 

How The Vulcanization Is Applied? 

Explanation of the effect of vulcanization process chemically(Source Of Image:https://www.sciencedirect.com/topics/chemistry/vulcanization)

In the most basic aspect, vulcanization is the application of sulfur to elastomers. This method is first founded by Goodyear, in which nearly 8% of sulfur is added inside the elastomer constitution. 

But in today’s technology, that type of vulcanization process is evolved. Because this old type of process takes very long hours. With the addition of very small amounts of zinc oxide(ZnO) and stearic acid(C18H36O2), the total vulcanization process reduces to minutes. 

Vulcanization Applications In Different Rubber Shaping Processes

Vulcanization tank(Image Source: moontanks.com)

You know that there are various kinds of rubber shaping processes available in the manufacturing world to shape different kinds of rubber parts. According to this fact, various kinds of application styles available in rubber shaping. But in general, vulcanization is applied in two different principles; 

  • Application of vulcanization to batch production processes of rubber parts, 
  • Application of vulcanization to continuous production processes of rubber parts. 

Batch Production Vulcanization

In this kind of rubber shaping processes, discrete rubber parts are obtained from discrete molds or production machinery. So, vulcanization is applied to these discrete parts. 

Generally, autoclaves or gas curing methods are applied to vulcanize the rubber parts. Autoclaves are the heated and pressurized vessel in which vulcanization of rubber parts takes place. In the gas curing method, inert and heated gas is directed on rubber parts to make vulcanization. 

Continuous Application Of Vulcanization

There are lots of continuous production of rubber parts are available in manufacturing. In these methods, produced rubber parts or shapes are not discrete parts. They are in continuous shape such as wire coatings, extrudates, etc. 

For these kinds of rubber production processes, continuous drums or hot-air tunnel types of vulcanization methods are applied. 

Additives and Compounding of Rubbers

In most rubber applications, both natural and synthetic rubbers are not used single-handedly. Because there can be other mechanical and physical feature requirements changes from application to another application that rubber materials are used.

To obtain these additional features from rubbers, some additives or reinforcements are used. Here, you will find a brief information on some additives and compounds are used in rubber part production.

Additives Used In Rubber Compounding

There are several additives are used in rubber compounding applications. The most important compounding operation of rubbers is vulcanization. Vulcanization is the chemical process that is applied to increase the density of cross-linking between rubber molecules. So rigidity and other mechanical properties can be achieved with vulcanization. Vulcanization is generally made with sulfur addition.

Carbon black is obtained from soot.

Another compounding process of rubbers is the addition of carbon black which is a colloidal carbon mixed with water. Carbon black is obtained by the thermal decomposition of soot which is a basic hydrocarbon. If the rubber is compounded with carbon black, tensile strength and abrasion, and tearing resistance of produced product will be increased.

You know that most of the automobile tires are black in color. This is because of the addition of carbon black into the rubber which is a compounding material of tires.

Calcium carbonate can be also used as a nonreinforcing filler to obtain much more volume of material. Another nonreinforcing filler is silica. But depending on the particle size, silica can act as reinforcing filler inside the rubber.

Hydrous aluminum silicates are also used as a reinforcing agent in rubber. When compounded with rubber, it gives tensile strength and abrasion resistance. If we compare with carbon black, carbon black is superior in terms of the addition of these features to rubber. But, hydrous aluminum silicates can be preferred if the black color is not desired in the application.

Rubber is also compounded with other additives to prevent aging which are also called aging retarders. Ozone-protective additives are also very important compound elements of rubbers.

When a rubber part is produced by using molds, mold release compounds are also added to rubber. Plasticizers are also important compounds of rubbers.

Reinforcements In Rubber Products

Steel-belted radial tire overview(Image Source: razitire.com).

Fiber reinforcement is one of the most important applications of rubber products. Glass fibers can be used to obtain much better mechanical properties from rubber products.

Also, steel fibers are used in tire production. Steel fibers give lower extensibility to tires but better mechanical properties to resist conditions that dynamically use by automobiles.

Rubber Compound Mixing Operations

Rubber mixing machine(Image Source: internalmixers.com).

Cross-linking formation is a very important phenomenon for rubbers. The degree of cross-linking must be controlled specifically to obtain the required properties. So, monitoring of cross-linking formation is very important in the mixing operations of rubber compounds.

The vulcanization process is the formation of cross-linking between rubber molecules. Viscosity decreases immensely with cross-linking formation. So, mixing with vulcanization agents must be done after the mixing with other agents.

The first mixing process is called masterbatch mixing which includes carbon black, colorants, and other agents. Very homogeneous mixing is accomplished in this stage.

After the masterbatch mixing, rubber that mixed with other agents is mixed with sulfur to obtain cross-linking formation.

Two-roll mils or internal mixer systems are used to mix the rubber with other components.

Natural Rubber

What Is Natural Rubber?

Natural rubber is the long chained elastomer that is constituted with isoprene(C5H8). High molecular weight is most important characteristic of isoprene. Latex is the source of isoprene that is obtained from rubber tress which are grown in tropical regions. Latex is not the pure polyisoprene. It includes high amount of water and other ingridients. Some processes are applied to latex to extract the polyisoprene from it. These processes are generally are coagulation, dying and spraying.

Vulcanization process must be applied to this natural rubber to obtain a useful material. Because natural rubber is very elastic in hot weather and very stiff in cold weather.

Latex extraction from latex tree.

In vulcanization process, cross-linkings are enhanced in natural rubber. With this application, elastomer that has very good resilience property is obtained.

In vulcanization process, sulfur and other chemicals are mixed with natural rubber. Sulfur addition with heat application, cross-linkings are obtained in natural rubber. After the process, vulcanized rubber is obtained. Suldur itself also vulcanize the natural rubber, but it will take hours to obtain desired cross-linked structure. Addtivives are used to accelerate the cross-linking formations in natural rubber.

Vulcanized rubber that is produced from natural rubber has very good tensile strength and resiliance characteristics. But with the heat, oil and sunlight applications, vulcanized rubber can degrade. With the use of some additives, there drawbacks for vulcanized rubber are prevented.

Applications of natural ruıbbers are; show soles, seals, bushings and shock absorbtion.

The most important application of vulcanized rubber is automobile tyres. They have additive called as carbon-black to obtain wear and environmental resistant material.

What Are The Properties Of Polyisoprene Vulcanized Rubber?

Modulus of elasticity of polyisoprene is around 18 MPa in %300 elongation. Also tensile strength of it around 25 MPa. The elongation that is needed to tear apart vulcanized polyisoprene is 700% according to its original shape. It can be used between temperatures of -50C to 80C. It has very big market share in elastomer materials which is around 22% of total elastomer market.

Natural Rubbers vs. Synthetic Rubbers

Rubber is obtained from both natural and synthetic sources. The main natural source is the ‘latex’ that is proced from special plants that are grown in tropical regions of World.

The synthetic source of rubber is the petroleum. There are some kinds of processes applied to petroleum to obtain synthetic rubber.

How The Natural Rubber Is Produced?

Natural latex rubber drying process.

Natural rubber is obtained from special plants grown in tropical places in ‘latex’ form. This latex includes nearly 30% of polyisoprene which is the constituent of natural rubber, colloidal mixture with water. To obtain 100% of natural rubber from latex, there must be some processes and operations applied.

To decompose the natural rubber from the colloidal mixture of latex, the coagulation technique is applied. In this process, latex is diluted with water, then acetic acid or formic acid is added. These acids lead to the formation of coagulate of natural rubber in the form of thin slabs. The coagulation process generally takes around 12 hours.

These thin slabs of natural rubbers are squeezed with rolls to decompose the remaining water. The obtained sheet must be dried in special smokehouses. In these smokehouses, natural rubber slabs are covered with wooden frames to prevent mildew.

Getting latex from its plant.

This smoke includes creosote which also prevents the natural rubber from oxidation. After several days of smoking and drying process, the produced natural rubber is sent to the manufacturer.

Better grades of natural rubbers can be produced with the application of hot air instead of smoke. And also the much better grade of natural rubbers can be produced with the application of multiple coagulation processes and other additional processes after the air drying processes.

Production Of Synthetic Rubber

Synthetic rubbers are used generally in tire production.

Synthetic rubbers have the biggest market in rubber part manufacturing because of the abundance of the source material to produce synthetic rubbers.

Production of synthetic rubbers depends on the same production characteristics asthermoplastic polymers. But the produced synthetic rubber is supplied to rubber part manufacturers as in the form is large bales.

There are several types of synthetic rubbers are produced and used by manufacturers.

Polychloroprene type of synthetic rubber is generally used in sheet production.

You can find out the mechanical and material properties of another synthetic rubber from this link; Ethylene-Propylene and Isoprene.

Butadiene and buthyl rubbers are also very important synthetic rubbers in the manufacturing market.

Rubber Shaping Processes

There are a bunch of rubber shaping processes available in the industry. Let’s explain these types of rubber shaping processes.

Rubber Calendering Method

Rubber calendering illustration(Image Source:rubbermachineryworld.com).

Calendering is a process that gives required thicknesses to rubber materials by passing them through a set of rolls. The distance between rolls defines the thickness of rubber to be calendered. This method is also applied to thermoplastics, but the application temperatures of much lower than thermoplastics, for rubbers.

Lower application temperatures are used because of the cross-linking occurrence after a specific temperature. This premature cross-linking is not desired in the shaping process.

Like thermoplastics, swelling occurs after the rolls. So, swelling effects must be considered in the calendering process design for rubbers.

Rubber Extrusion Method

Extruded rubber profiles(Image Source: therubbercompany.com).

Extruded rubber profiles(Image Source: therubbercompany.com).

The extrusion of rubbers is nearly the same as the extrusion of thermoplastics. The main difference between rubber extrusion and thermoplastic extrusion processes is the barrel length.

Barrel lengths for rubber extrusion machines are much lower than thermoplastic extrusion. This is because of preventing the premature cross-linking occurrence in rubber molecules which is not desired thing.

Swelling is also a problem after exiting from extrusion machine die. This must be considered in the design stage.

Rubber Molding

Rubber molding application is slightly the same as thermoplastic injection molding processes. There are a barrel and screw mechanism that pushes the rubber material inside molds. Like the other processes, there is a risk of premature cross-linking occurrence in molds.

There is another kind of rubber molding process which is called compression molding. The importance and difference of this process is the cross-linking formation inside the mold. Transfer molding is also used.

Mold expenses are one of the biggest downsides of rubber molding processes. But if the serial production manner of high-quality parts is adopted, it can be profitable.

Gaskets, seals, shoe insoles, bottle stops, and parts like that from rubber are produced with rubber molding processes generally.

Rubber Coating Processes

Rubber coating processes comprise several methods to impregnate or coat the other materials or parts with rubbers to produce composite parts or products.

Calendering operations are used also in rubber coating and impregnating operations.

Skimming is a type of rubber coating process that fabrics made from other materials are fed from spool to rubber solution. And this rubber and fabric coating passed through heat chambers to take the solvent from rubber, then obtain cross-linkings. The excessive rubber coating is skimmed with special doctor blades.

Spraying is another process that materials are coated with rubber spray. This is simple like that.

Dip Casting Of Rubbers

Dip coating illustration(Image Source: ossila.com).

In the dip casting or dipping method, a type of negative mold is dipped inside a rubber bath. And it’s dried with cross-linking on that mold. This sequence can be repeated to obtain the desired thickness. With this method, hand gloves can be produced.

Do not forget to leave your comments and questions about elastomers below. Your precious feedbacks are very important for us.

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