Synthetic rubber: types, properties and use in technical elastomer molded parts
| Characteristic | Synthetic rubber |
| Definition | Synthetic rubber is an industrial-produced polymer that is predominantly made from petrochemical monomers such as butadiene, styrene, acrylonitrile, ethylene, propylene, or chloroprene. |
| Main types | NBR, HNBR, EPDM, FKM, silicone rubber (VMQ), CR and SBR are the most commonly used for industrial rubber parts. The abbreviations are standardized in DIN ISO 1629 and ASTM D1418. |
| Advantage over natural rubber | Synthetic rubber grades can be individually specified for oil, ozone, chemical, or temperature resistance and can be used over a wide temperature range from −65 °C to +320 °C. |
| Market share | Synthetic rubber covers 60–70% % of the total demand for rubber in each region. |
| Definition | Thermoplastic elastomers (TPE) do not count as synthetic rubbers in the strictest sense, because TPE is not vulcanized but melted and shaped like a thermoplastic. |
Table 1: Brief overview of synthetic rubber
1. What is synthetic rubber?
Synthetic rubber is an uncrosslinked, plastically deformable polymer that is produced in chemical plants through the polymerization of monomers. Natural rubber, on the other hand, is obtained as latex from the rubber tree. Hevea brasiliensis won.
Most synthetic rubbers are based on petroleum and natural gas fractions. Typical monomers are 1,3-butadiene, styrene, acrylonitrile, chloroprene, isobutylene, ethylene and propylene. Silicone rubber has a main chain that is not composed of carbon, but of silicon-oxygen chains (polysiloxanes).
In technical language, three terms are distinguished:
- Rubber is the un-crosslinked raw material. It is plastic-formable, but not permanently elastic.
- Elastomer is the highly interconnected material that forms after vulcanization. An elastomer deforms strongly under load and then largely returns to its original shape.
- Rubber is the colloquial term for vulcanized rubber, that is, an elastomer.
How elastomers differ from thermoplastics and duroplasts is explained in our article „Thermoplastics, Duroplastics and Elastomers“.
2. Synthetic rubber compared to natural rubber
Natural rubber (NR) It is considered the most mechanically stable elastomer. Synthetic rubbers, on the other hand, are particularly resistant to oil, ozone, chemicals, and temperature. Therefore, seals and molded parts for medical technology, aviation, and hydraulics almost always consist of synthetic rubber.
| Criterion | Natural rubber (NR) | Synthetic rubber (e.g. NBR, EPDM, FKM, VMQ) |
| Origin | Latex from the rubber tree Hevea brasiliensis | Chemical synthesis from petroleum derivatives |
| Breaking and tearing strength | Very high, due to strain-induced crystallization | Dependent on type, mostly influenced by fillers |
| Oil resistance | Low | High in NBR, HNBR, FKM and ACM |
| Ozone and weather resistance | Poor without protective equipment | High in EPDM, VMQ, FKM and CR |
| Temperature range (recommended value) | approx. −55 °C to +70 °C | Depending on the type, from approximately −65 °C (FVMQ) to +320 °C (FFKM) |
| Batch consistency | Natural fluctuations possible | Even and reproducible |
| Typical applications | Truck tires, shock absorbers, bearings | Seals, O-rings, membranes, bellows, hoses |
Table 2: Comparison of synthetic rubber and natural rubber
3. How is synthetic rubber produced?
On the way from the raw material to the finished component, synthetic rubber undergoes three stages, which are usually carried out by different companies. One chemical company produces the raw rubber, while a compounding plant processes it with additives to create a ready-to-process rubber mixture (Compound) and a mold manufacturer produces elastomer components from it. In detail, the process involves the following steps:
- Extraction of raw materials: Crude oil or natural gas is converted into small molecules (monomers) such as butadiene, ethylene or styrene through steam cracking. Silicon rubber is based on silica from quartz.
- Polymerization: In a reactor, monomers are linked into long molecular chains that form the basis of the raw rubber. The combination of the monomers determines the type, for example. NBR or EPDM.
- Mixing: Fillers, The plasticizer, aging protection and crosslinking agents are added to the raw rubber and kneaded in the mixer. The individual formulation of the rubber compound determines the hardness, strength and resistance to various media.
4. The most important groups of synthetic rubber
According to DIN ISO 1629, rubbers are divided into seven groups based on the chemical composition of their main chain: M, O, Q, R, T, U, and Z. The last letter of the abbreviation indicates the group.
Classification according to DIN ISO 1629
| Group | Construction of the main chain | Examples (abbreviations) |
| M | Saturated polymethylene main chain | EPDM, EPM, FKM, FFKM, FEPM, ACM, AEM, CSM |
| O | Carbon and Oxygen | ECO, CO, GECO |
| Q | Silicon and oxygen | MQ, VMQ, PVMQ, FVMQ |
| R | Unsaturated double bonds in the carbon chain | NR, IR, BR, SBR, NBR, HNBR, XNBR, CR, IIR |
| T | Carbon, oxygen and sulfur | OT, EOT (polysulfide rubber) |
| U | Carbon, oxygen and nitrogen | AU, EU (polyurethane rubber) |
| Z | Phosphorus and nitrogen | FZ, PZ (polyphosphazenes) |
Table 3: Groups of synthetic rubbers
This classification applies to both natural and synthetic rubber. Thus, NBR, as well as natural rubber (NR), belongs to the R group, EPDM to the M group, and VMQ to the Q group. Membership in a group allows initial conclusions about the properties. Polymers of the M and Q groups do not contain double bonds in the main chain and are therefore ozone and weather resistant, whereas polymers of the R group are usually ozone-sensitive without protective agents.
In the case of Q-group silanes, the initial letters indicate the side groups in the siloxane chain: M for methyl, V for vinyl, P for phenyl and F for fluorine. FVMQ is therefore a fluorine-vinyl-methyl silicone rubber.
5. The most important types at a glance
The following overview shows the synthetic rubbers that are most commonly used in technical molded parts. The values mentioned are guidelines and depend on the individual composition of the mixtures.
| Abbreviation | Name | Trade names | Group | Temperature range (recommended value) | Strengths | Borders |
| NBR | Acrylonitrile-butadiene rubber | Perbunan, Krynac, Europrene N | R | −30 °C to +110 °C | Mineral oils, fuels, hydraulic oils | Ozone, weather, polar solvents |
| HNBR | Hydrated NBR | Therban, Zetpol | R | −30 °C to +150 °C | Oils at high temperatures, abrasion, strength | Higher price than NBR |
| EPDM | Ethylene-propylene-diene rubber | Keltan, Nordel, Vistalon, Dutral | M | −50 °C to +130 °C | Ozone, weather, hot water, steam, glycols | Mineral oils and fuels |
| FKM | Fluoroplastic | Viton, Tecnoflon, Dai-El | M | −30 °C to +220 °C | High temperatures, fuels, oils, many chemicals | Cold flexibility, ketones, amines, hot steam |
| VMQ | Silicone rubber | Elastosil, Silastic, Silopren | Q | −50 °C to +220 °C | Wide temperature range, physiologically safe and adjustable | Further tear strength, abrasion resistance, fuels |
| FVMQ | Fluorosilicone rubber | Silastic LS, Elastosil FLR, FSE | Q | −65 °C to +200 °C | Fuels and oils at lower temperatures | Mechanical strength, price |
| CR | Chloroprene rubber | Neoprene, Bayprene, Skyprene | R | −40 °C to +100 °C | Weather, moderate oil resistance, non-flammable | High-quality mineral oils, high temperature |
| SBR | Styrene-butadiene rubber | Europrene, Intol, historical Buna S | R | −45 °C to +90 °C | Abrasion, lower price | Oils, Ozone |
6. Frequently Asked Questions about synthetic rubber
What are the disadvantages of synthetic rubber?
Synthetic rubber is based on fossil raw materials and is less tear-resistant than natural rubber and is difficult to recycle after vulcanization. Furthermore, each synthetic rubber type has resistance gaps, for example NBR against ozone or EPDM against mineral oil. Fluorine rubber (FKM) is very resistant to a wide variety of media, but costs many times as much as NBR, for example, and is also subject to the ongoing EU restriction procedure for PFAS.
What is synthetic rubber made from?
Most synthetic rubbers are made from monomers derived from petroleum and natural gas fractions, such as butadiene, styrene, ethylene, and propylene. Silicon rubber, on the other hand, is based on siloxanes, whose silicon is extracted from quartz.
Is synthetic rubber better than natural rubber?
Synthetic rubber is not generally better, but can be individually adapted to suit a wide range of applications. Natural rubber has higher tensile and durability properties, while synthetic rubber offers better resistance to oils, ozone, chemicals and high temperatures.
Which synthetic rubber is most heat-resistant?
Perfluorocarbon rubber (FFKM) is the most heat-resistant synthetic rubber with long-term temperatures of up to about +320 °C. Fluocarbon rubber (FKM) and silicone rubber (VMQ) follow with long-term temperatures of up to +220 °C.
Which synthetic rubber is oil-resistant?
NBR, HNBR, FKM and fluorosilicone (FVMQ) are particularly resistant to mineral oils and fuels. EPDM, SBR and butyl rubber are not suitable for use in mineral oils and therefore do not have the same properties as mineral oils.
What is the name of a synthetic rubber with 4 letters in a crossword puzzle?
The common crossword solution for „synthetic rubber“ with 4 letters is Buna. This was the trade name of IG Farben for synthetic rubber based on butadiene. The name is composed of Butadien and WellTrium together, which served as a catalyst in early processes.
Is synthetic rubber toxic?
Vulcanized synthetic rubber is generally harmless when used as intended, as the polymer chains are firmly bonded and not water-soluble. Individual starting and auxiliary substances, such as 1,3-butadiene or chloroprene monomers, are classified as carcinogenic; however, in the finished component they are only present in trace amounts. Certain vulcanization accelerators can form nitrosamines, and soot or plasticizers can contain polycyclic aromatic hydrocarbons (PAHs). For rubber parts with skin contact, REACH limits the content of individual PAHs to 1 mg/kg, for toys to 0.5 mg/kg. When burning, halogen-containing types such as CR and FKM also release chlorine or fluorine hydrogen.
