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 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 water-tightness.
Being a natural product, Natural rubber mainly consists of polyisoprene molecules but also about 5% other materials such as proteins, fatty acids and resins. It is typically the proteins that cause Latex Allergy with some people.
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) come 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 advantage with synthetic rubber is the possiblity to design the rubber to have, more or less, the exact properties you want!
|Rubber / Trade name
||Example of products
||Very gas-tight, high chemical resistance
||Hoses, chemical protective suits
|Chloroprene rubber / Neoprene
||Good resistance against oil and weather.
||Excellent resistance to weather and high temperatures
||Sealings for windows
|Fluro rubber / Viton
||Excellent resistance against chemicals, weather, ozone and high temperatures
||Gaskets & sealings in demanding environments, chemical protective suits
||Very good oil resistance
||Gaskets & hoses in automotive applications
||High abrasion resistance
||Tyres, conveyor belts
The base rubber, whether 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 are the vulcanisation agents which crosslink the rubber molecules into a three-dimensional network, giving the rubber its unique properties.
||Function in the rubber compound
||Ozone and ageing resistance
||Crosslinks the rubber molecules