Rubber

Rubber is used for hundreds of years and is known for its high elasticity and abrasion resistance.

Rubber is a very elastic polymer i.e. an elastomer and this elasticity is created in the vulcanisation of the rubber where the individual polymers are cross-linked to create a three dimensional network.

Although the high elasticity and a number of other excellent properties, rubber is not famous for its strength and therefore has to be reinforced, normally using different type of textiles.

Natural rubber

Natural rubber is the sap of the rubber tree - Hevea Brasiliensis - which today mainly grows in Indonesia, Thailand and Malaysia. Originally, however, the rubber trees grew in South America and in the 1770's they were first brought to Europe where the rubber technology was then developed mainly in England and Germany. Today approximately 40% of all rubber produced per year is Natural rubber.

The sap, called rubber latex, is collected from the trees by hand and then coagulated/dried to form rubber sheets. Depending on how the rubber sheets are treated, there are different qualities of natural rubber but they all have in common the high elasticity , outstanding abrasion resistance and watertightness.

Being a natural product Natural rubber mainly consist of polyisoprene molecules but also about 5 % other materials such as proteins, fatty acids and resins. It is typically the proteins that causes Latex Allergy with some people.

Synthetic rubber

Synthetic rubber was invented already in the end of the 19th century, but the industrial production was initiated after WW1, as a result of lack of natural rubber, and continued developing a lot the coming 30 -40 years. Today approximately 60% of all rubber produced per year is synthetic rubber.

Synthetic rubber is manufactured in large chemical factories all over the world and the base components (monomers) comes from oil, for example methane, ethane and propane. Other components are added to modify the properties of the rubber, for example chlorine and fluorine, and a catalyst is needed to start the chemical reaction. The advatage with synthetic rubber is the possiblity to design the rubber to have, more or less, the exact properties you want!

 

Rubber / Trade name Typical properties Example of products
Butyl rubber Very gastight, high chemical resistance Hoses, chemical protective suits
Chloroprene rubber / Neoprene Good resistance against oil and weather.  
EPDM Excellent resistance to weather and high tempereatures Sealings for windows
Fluro rubber / Viton Excellent resistance against chemicals, weather, ozon and high temperatures Gaskets & sealings in demaning environments, chemical protective suits
Nitrile rubber Very good oil resistance Gaskets & hoses in aoutomotive applications
SBR High abrasion resistance Tyres, conveyor belts

 

Rubber COMPOUNDING

The base rubber, wether natural or synthetic, needs to be mixed with a number of different chemicals/ingredients to actually give a rubber compound that can be processed and made into a finished product.

A recipe for making a rubber compound includes, except for the rubber, approximately 10 -15 different chemicals. The different chemicals are divided into groups, depending on their function, and one of the most important chemicals is the vulcanization agents which crosslinks the rubber molecules into a three dimensional network, giving the rubber its unique properties.

 

Group Chemical Function in the rubber compound
Filler Carbon black Stronger, harder
Filler Titanium oxide Stronger, harder
Filler Clay Harder, cheaper
Softener Oil, parrafin Softer
Pigments Iron oxide, Colour
Antioxidants Amines Ageing resistance
Antiozonants Phenols Ozon and ageing resistance
Flame retardants Aluminium hydroxide, Burning resistance
Vulcanizing agent Sulphur, peroxides Crosslinks the rubber molecules
Vulcanizing activator   Starts vulcanizing
Vulcanizing accelerator   Speeds vulcanizing
Vulcanizing retarder   Slows vulcanizing
  • Last updated 3/8/2012
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