Butyl rubber (IIR)

AL-Gummi Butyl-Kautschuk (IIR) (auch Isobuten-Isopren-Kautschuk)

Registered trade name: Polysar

Butyl rubber is a copolymer of isobutylene and isoprene. The characteristic property of butyl is its low gas permeability, which is why one of its main applications is air hoses for tyres. Compared to NR and other synthetic rubbers, IIR has a very low permeability to air, water vapour and gases. Other advantages include good resistance to heat, oxygen, ozone and chemicals.

IIR cannot be blended with other elastomers due to its chemical structure and behaviour during the vulcanisation process.

Property spectrum of IIR

Hardness 40 to 85 Shore A
Elongation at break normally between 400 to 800%, also above 1000
Maximum temperature +90° C
Minimum temperature -30°C
Electrical properties very good insulating properties
Gas permeability very low, about 10 times lower than NR
Ageing and ozone resistance good to very good
Chemical resistance good chemical resistance with the exception of mineral oil and grease

Areas of application for IIR

Butyl rubber is used wherever low gas permeability and good heat and ageing resistance are required. The main areas of application are tyre tubes and the air-tight inner liners of tubeless tyres. The low gas permeability is also used for special protective clothing (e.g. gloves).
Due to its good chemical resistance, butyl is used for chemical hoses, seals and tank liners.

Other areas of application: Bicycle hoses, inner layers of tubeless tyres, acid protection linings, boiler seals and membranes.


Chewing gum

AL-Gummi Kaugummi

Chewing gum: Gum from petroleum

Modern chewing gums consist almost exclusively of synthetic raw materials. The “gum” part is usually made up of petroleum-based polymers. In plain language: we chew plastics. And they are not only questionable in terms of taste – they are above all ecologically and healthwise questionable.

Sugar is an essential component of chewing gum, accounting for 50 to 70 per cent. For the production of sugar-free chewing gum, the natural sweetener xylitol is used instead of sugar. Softeners, humectants, emulsifiers, colourants and fillers are also added to the gum mass.

Additives ensure that the mass remains elastic and supple when chewed. Tree resins such as rubber or other natural substances cannot meet the demand of the world market. Chewing gum is not biodegradable due to its plastic content.

Chloroprene rubber (CR)

AL-Gummi Chloropren-Kautschuk (CR)

Registered trade name: Neopren® (DU Pont)

CR is known in practice under the trade name Neoprene. CR has many good properties among the other elastomers, without achieving corresponding peak values. With appropriate protective agents, quite good ozone and ageing resistance as well as satisfactory oil resistance can be achieved.

CR has good flame retardancy due to its high chlorine content. However, flame retardancy is strongly dependent on the type of plasticiser used. In the course of the development of synthetic rubbers, it was possible to produce an all-purpose rubber in the form of chloroprene rubber (CR), which is similar to SBR and BR, but with significantly improved ageing properties.

This special property, coupled with good mechanical behaviour, but also significantly better resistance to acids, alkalis and polar chemicals, made chloroprene rubber the most important speciality rubber for many years.

CR is also resistant to oils and greases, and to a certain extent also to fuels.

Property spectrum of CR

Hardness 30 to 90 Shore A
Elongation at break 100 to 800
Maximum temperature +90° C
Minimum temperature -30°C
Electrical properties
Gas permeability slightly worse than NBR
Resistance to ageing and ozone very good with appropriate additives
Chemical resistance good

Areas of application for CR

Wherever high flame retardancy, stable ageing properties and chemical resistance are required. CR is used in technical rubber goods, thanks to its favourable combination of properties for moulded parts, conveyor belts, seals, hoses, roller coverings, linings, belts or cable sheaths. CR is also used in the manufacture of sports articles and clothing (surf and diving clothing) in contact with seawater. Here it is often used as a foamed variant. In dissolved form, CR is a main component of many adhesives.


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Ethylene propylene diene rubber (EPDM)

AL-Gummi Ethylen-Propylen-Dien-Kautschuk (EPDM)AL-Gummi Ethylen-Propylen-Dien-Kautschuk (EPDM)

EPDM rubber is produced by the copolymerisation of ethylene, propylene and a diene. The absence of double bonds in the main chain results in good oxygen, ozone and temperature resistance.
EPDM has very good ozone resistance, very good weathering resistance and low heat ageing. It is also resistant to temperatures of up to 150 °C and resistant to polar substances and steam. However, these compounds have little resistance to petrol, fuels and mineral oils. However, EPDM is used in particular for seals and hoses in washing machines because of its resistance to alkalis.

Thanks to its outstanding properties, EPDM has replaced the originally used natural rubber in many areas. In the automotive sector as well as in the construction industry, this type of rubber is the most frequently used material for seals.
EPDM vulcanisates are characterised by excellent chemical resistance to dilute acids, alcohol and hydraulic fluids such as brake fluid.

Property spectrum of EPDM

25 to 90 Shore A

Elongation at break:
150 to 800%

Maximum temperature:
+150° C

Minimum temperature:

Electrical properties:
very good insulating properties with appropriate design of the mixture

Gas permeability:
high, similar to NR

Ageing and ozone resistance:
very good, even better than IIR

Chemical resistance:
above-average chemical resistance, but rather poor against mineral oil and grease resistance

Fields of application of EPDM

In terms of quantity, EPDM is most widely used in the automotive industry, e.g. for sealing profiles for doors, windows and headlights, brake and coolant hoses.
EPDM is also used for seals and hoses in washing machines and dishwashers because of its good hot water resistance. In addition, EPDM has gained a high market share for building profiles and roofing membranes due to its good weather resistance.


Fluorine rubber (FKM/ FPM)

AL-Gummi Fluor-Kautschuk (FKM/ FPM)

Registered trade name: VITON® (DuPont)

FKM is known in practice under the trade name Viton. The DuPont company brought this onto the market in 1958.

Fluororubber is often not filled with carbon black, this is visible externally through coloured settings. FKM is flame retardant and has a resistance to high temperatures, ozone, oxygen and chemicals that surpasses all elastomers. Fluororubber is a class of rubber that is characterised by its excellent resistance to most chemicals, oils, greases and fuels, but also by its very good resistance to high temperatures up to above 200 °C. At the same time, fluororubbers have an outstanding resistance to high temperatures. At the same time, fluororubbers have good resistance to ageing and weathering.
The main areas of application are seals for the automotive and aerospace industries.

Property spectrum of FKM

Hardness 50 to 95 Shore A
Elongation at break 100 to 300
Maximum temperature +200° C
Minimum temperature 0 to -20°C
Electrical properties
Gas permeability slightly lower than IIR
Resistance to ageing and ozone excellent
Chemical resistance excellent

Applications of FKM

Wherever high temperatures prevail and excellent chemical resistance is required. Examples are O-ring seals and fuel hoses for motor vehicles, moulded parts, seals for oil production as well as for hydraulic systems, hoses, cable insulation.


Gummy bears

AL-Gummi Gummibärchen

Gummy bears are fruit gums in the shape of stylised bears about 1.5 centimetres tall. They are produced in different colours and essentially consist of sugar, glucose syrup, water and gelatine, which gives them their gummy consistency.

The gummy bear was invented in 1922 by the Bonn entrepreneur Hans Riegel. His company Haribo brought them to market for the first time and is still the market leader today.
The original gummy bears were made of gum arabic, which gave them a gummy consistency. Today, gelatine is used instead of gum arabic to make them.


Hydrogenated nitrile rubber (HNBR)

AL-Gummi Hydrierter Nitrilkautschuk (HNBR)

Registered trade name: Therban

HNBR (Hydrogenated Nitrile Butadiene Rubber) is produced from NBR by catalytic hydrogenation and peroxide cross-linked. Complete hydrogenation of NBR produces a saturated rubber with characteristic properties such as resistance to heat, oil and ozone, combined with good mechanical properties.
As a result, the material gains temperature resistance. This elastomer is often used where NBR would be optimal, but temperatures are too high.
The main areas of application are heat-resistant seals and hoses, as well as toothed and V-belts. The catalytic hydrogenation of NBR is a very complicated process, so HNBR costs many times more than NBR.

Property spectrum of HNBR

Hardness 50 to 90 Shore A
Elongation at break 100 to 600
Maximum temperature +155° C (+175° C)
Minimum temperature -35°C
Electrical properties
Gas permeability very low, but lower than IIR
Resistance to ageing and ozone very good
Chemical resistance good against mineral oils, hydraulic fluids of low flammability, hot water, steam, aqueous acids and alkalis

Applications of HNBR

HNBR is used in many areas where good heat and oil resistance as well as good wear resistance are required. For example, in seals and hoses in the automotive sector and in mechanical engineering and for special seals in oil production.
In sealing technology, HNBR, which is significantly more expensive than NBR and is also a proven standard material for timing belts in car engines, is used primarily where higher temperatures and/or mechanical strength are required. Its strength is particularly in demand for applications such as O-rings, radial shaft seals, bellows and diaphragms. Particularly in the process industry, HNBR offers wide-ranging application possibilities. For example, HNBR is excellently suited as a flap seal material in the process industry. In dairies, the beverage industry and applications in contact with very greasy media, HNBR is the best solution.



AL-Gummi Latex

Natural rubber is mainly obtained from the sap of the Hevea Brasiliensis (rubber tree), a tropical tree species. This tree grows exclusively in a zone 15° north and south of the equator (rubber belt). Originally native to Brazil, the most important plantations are now located in Southeast Asia.
The liquid, also known as latex or milky sap, is usually released by scratching the bark of the tree.
Latex is an aqueous dispersion of rubber polymer particles that also contains resins, proteins and minerals.
The coagulated latex itself is used to make so-called diving articles such as gloves, balloons or condoms.


Natural rubber (NR)

Natural rubber, a material produced by nature, has very high tensile strength, elasticity, low-temperature flexibility and excellent dynamic properties. Synthetic elastomers do not achieve this combination of outstanding functions. This is why NR is still indispensable for some applications today.
The main areas of application are tyres and engine mounts.

Property spectrum of NR

Hardness 20 to 90 Shore A and harder (hard rubber)
Elongation at break 100 to 800%, also over 1000
Maximum temperature +70° C
Minimum temperature -40°C
Electrical properties good insulating properties to electrically conductive (depending on formulation)
Gas permeability high (approx. 10 times higher than IIR)
Resistance to ageing and ozone only low without appropriate finishing with protective agents
Chemical resistance good to moderate, but not resistant to greases and mineral oils

Application areas of NR

Vehicle tyres, conveyor belts and belts,
Technical articles of all kinds, such as seals, membranes, hoses, etc.
Due to its high tear resistance, natural rubber is used in the agricultural sector, especially for belts and straps, but also in a wide variety of moulded parts and roller coatings. Furthermore, natural rubber is used in the field of rubber-metal spring elements or buffers. Other areas of application are consumer goods such as shoe soles, rubber boots, gloves, sponges, adhesives and elastic threads.

Nitrilkautschuk (NBR)

AL-Gummi Nitrilkautschuk (NBR)

Acrylonitrile butadiene rubber (NBR), also called nitrile rubber
Registered trade name: Perbunan (formerly Buna N)

The copolymerisation of acrylonitrile and butadiene gives NBR exceptionally good resistance to mineral oil and fuel, as well as a low compression set. It is therefore the ideal sealing material for the media mentioned. NBR has its main areas of application where, in addition to good properties, high swelling resistance to mineral oils and fuels as well as resistance to ageing, heat and abrasion are required. The main applications are seals, hoses and diaphragms.

Property spectrum of NBR

Hardness 40 to 90 Shore A
Elongation at break 100 to 700% and higher
Maximum temperature +100° C
Minimum temperature -20°C
Electrical properties not suitable for electrical insulation, as NBR is to be regarded as a semiconductor
Gas permeability lower than NR, SBR, EPDM but higher than IIR
Ageing and ozone resistance Ageing better than NR and SBR, ozone resistance lower than NR
Chemical resistance Very good against grease and mineral oil

Applications of NBR

Nitrile rubber is used for oil and fuel-resistant seals, moulded parts, diaphragms and hoses in motor vehicles and mechanical engineering. Further applications are roller covers, gas and air conditioning hoses, according to its good oil and grease resistance. Pneumatic and hydraulic seals can be made from this rubber as well as O-rings and radial shaft seals.



AL-Gummi Kautschuk

Originally, there was only natural rubber – until the large-scale technical production of synthetic rubber succeeded at the beginning of the twentieth century. However, natural rubber still has unrivalled mechanical and dynamic properties, which is why most natural rubber is still used in the tyre industry today.

Natural rubber, formerly simply called caoutchouc, also known as gum elasticum or resina elastica, is a rubbery substance found in the latex of many different rubber plants. The rubber-bearing latex is usually present as a milky liquid, but it can also be present in semi-solid form in the plants.

Washing and coagulation with acetic or formic acid yields the solid rubber, which is pressed into skins or dried. For preservation, the rubber is either smoked (smoked sheets) or chemically treated, resulting in pale-coloured skins (pale crepes).
Due to increased quality requirements, technically specified natural rubber grades (TSR) are used, which must meet certain purity requirements, e.g. SMR Standard Malaysian Rubber.

To produce TSR, the coagulated and washed latex is processed into crumbs (granules?), dried and compressed into bales. The rubber obtained in this way is therefore still plastic, because it is uncrosslinked and also contains no crosslinking chemicals.


Shore hardness

AL-Gummi Shore-Härte

The most common hardness test for elastomers is the Shore hardness test according to DIN ISO 7619-1.
Shore hardness is the resistance of a rubber sample to the penetration of a cone-shaped body of specific dimensions under a defined compressive force. To test the Shore hardness, the penetration depth of a needle with a standardised tip is measured.
Common elastomer compounds for technical moulded parts lie in a hardness range of 20-90 Shore A. The tolerance is +/- 5 Shore A. The usual tolerance is +/- 5 Shore A.
The low values characterise “soft” objects, very hard objects have 80 to 90 Shore A.

Silicone rubber (Q/ VMQ)

AL-Gummi Silikon-Kautschuk (Q/ VMQ)

Silicone elastomers differ from other elastomers in that they are not purely organic compounds. Instead of the carbon polymer chain of normal elastomers, the silicone polymer chain consists of alternating silicone and oxygen atoms (siloxanes).
Silicone rubbers are differentiated according to their aggregate state (solid/liquid) and their vulcanisation temperature:

  • Hot vulcanising, solid (HTV – high temperature vulcanizing)
  • Hot vulcanising, liquid (LSR – liquid silicone rubber)
  • Cold vulcanizing (RTV – room -temperature vulcanizing)

Silicone elastomers are very resistant to heat, ozone, ageing and chemicals. The mechanical properties, however, are rather below those of other elastomers.
In order to achieve optimum heat resistance, post-curing is necessary in many cases.
Silicone rubber is flame retardant and physiologically inert, but has a high gas permeability. Silicone elastomers are resistant to hot water, vegetable and animal fats, paraffinic mineral oils as well as glycol and alcohols.

Property spectrum of silicone rubber (Q/ VMQ)

Hardness 20 to 80 Shore A
Elongation at break 100 to 600
Maximum temperature +180° C
Minimum temperature -70°C
Electrical properties excellent insulating properties even at higher temperatures, but can also be made extremely conductive
Gas permeability worst gas tightness of all elastomers
Resistance to ageing and ozone excellent
Chemical resistance good

Fields of application of Q

Elastomers made of hot vulcanising solid (HTV) and liquid (LSR) silicone rubber are used in pharmaceutical and medical articles as well as in many articles that come into contact with food.
Other technical applications include hoses, membranes, cables, and seals for the aerospace industry.
Seals for freezers, cookers, drying cabinets, shaft seals, O-rings, switch mats as well as electrical insulation for ships, aircraft, heating cabinets.

Styrene butadiene rubber (SBR)

AL-Gummi Styrol-Butadien-Kautschuk

Styrene-butadiene rubber is the oldest and, in terms of quantity used, the most important synthetic rubber. Styrene-butadiene rubber (SBR) was developed at the beginning of the 20th century with the aim of obtaining a cheap alternative to expensive natural rubber and reducing dependence on imports from Brazil and East Asia. At the same time, it was intended to compensate for the sometimes scarce availability of natural rubber, especially for countries like Germany.
With the development of modern synthesis processes, SBR has become the most commonly produced synthetic rubber and is indispensable for passenger car tyres, especially due to its excellent wet grip properties.

Compared to NR, SBR has better abrasion resistance, higher heat and ageing resistance, but low elasticity and less favourable cold flexibility.

To improve the mechanical properties of SBR, it is often blended with NR.

Property spectrum of SBR

Hardness 30 to 90 Shore A and harder (hard rubber)
Elongation at break normally between 100 and 800%, also up to 1000
Maximum temperature +70° C
Minimum temperature -30°C
Electrical properties good insulating properties to electrically conductive (depending on formulation)
Gas permeability
Resistance to ageing and ozone slightly better than NR, can be improved by protective agents.
Chemical resistance as NR, slightly better mineral oil resistance

Applications of SBR

SBR is a typical general purpose rubber. Two thirds of the world production is used for tyre production. SBR is a good compromise between abrasion and wet slip resistance. It is usually used in the same way as NR, but very often NR is blended with SBR, e.g. in tyre construction. SBR is also used for technical rubber goods such as conveyor belts, plates, construction profiles and floor coverings.



AL-Gummi Vulkanisation

Vulcanisation is a chemical-physical transformation in which predominantly plastic rubber changes into a rubber-elastic state. This process, which takes place by linking macromolecules at their reactive sites, is called cross-linking or vulcanisation.

In 1839, Charles Goodyear invented the process of vulcanisation, more or less by scientific accident. After adding various materials and chemicals to rubber, a sulphur-rubber mixture fell on a hot cooker top and the result was a dry and permanently elastic substance. When heated, the rubber mixed with sulphur turned into a new substance, rubber. With this, Goodyear had discovered vulcanisation.

Vulcanisation therefore requires a vulcanising agent. The oldest and most common vulcanising agent is sulphur. The classic example of vulcanisation is the sulphur vulcanisation of natural rubber.


wdk Wirtschaftsverband der deutschen Kautschukindustrie e.V.

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