What is Rubber or as it is often referred to as an ''ELASTOMER''
They are very useful engineering materials employed where their properties including both physical properties such as flexiblity, elasticity, resilience, as well as their chemical properties such as oil and chemical resistance are required.
Rubbers are made from basic monomers (small molecules) that are joined together to form long chain molecules called polymers. The process for doing this is called polymerisation and involves a lot of chemistry and physics so we will not go into this (mainly because it is far too complicated) but suffice it say you end up with very long chain molecules. Usually arranged in a random matrix
The polymer chain or backbone can be made of various materials but most often carbon or silicone. The raw materials or feed stock for these polymers come from a variety of sources including the fractional distillation of oil. Not all polymers are made from these sources and it is worth mentioning Natural Rubber- the orignal rubber. This is derived from Latex- the milky sap from a tree. The Polymer chains (in this case Polyisoprene) are held in a supension in water and it is when the water is removed the rubber is formed. The water can be removed by air drying or by coagulation using an acid such as formic acid. The addition of acid de- stabilses the suspension causing the particles of rubber to coagulate together, As a natural product there are many different grades and these are classisfied by criteria such as colour dirt content and viscosity.
The properties of these polymers can be changed by introducing other chemcials into the polymer chain or adding them as a side chain. These additions can improve such properties as oil resistance heat resistance chemical resisitance. The range of raw polymer available to us now is extensive and there are lots of trade names that are commonly used instead of the generic name for example Neoprene is the DuPont trade mark for Polychloroprene. Viton is another DuPont trade mark for FKM or Fluoronated polymers.
For these rubbers to be useful elastic, resilient materials there needs to be links or bonds formed between the polymer chains. These links create a three dimensional maxtrix setting the rubber in shape. The process of creating the links between the polymer chains enables the rubber to become the useful elastic, resilient material we recognise as rubber and is part of the manufacturing processes used to make finished rubber articles.
There are two basic types of rubber that are defined by the way they are processed into finished articles.
TPR/TPE and Thermoset Rubbers
TPE or TPR- These are Thermoplastic Elastomers or Thermoplastic Rubbers. As the name suggests they process like plastics but often feel very rubber like. This means we can process them by heating them in the barrel of an injection moulding machine or an extruder until they melt and then injecting them into a cold mould or extruding them into a cold bath to set them into shape. Cooling them down creates the physical bonds between the polymer chains that change plastic material into a useful elastic material at room temperature. This process is reversible so heating them will destroy the bonds and the material will melt. The cycle times for moulding these types of material are generally much faster than the thermoset rubbers as all that is required is to cool them down.
Thermoset Rubbers- As this name suggests we change these materials into useful elastic ''rubbery'' materials by heating them with materials like sulphur or peroxides. This process is called '' Vulcanisation'' These materials form chemical cross links or bonds between the polymer chains. This sets the matrix in position making the elastic ''rubbery'' material. Generally these crosslinks are very stable at normal temperatures and depending upon the polymer type and the cross linking agent used they can be made very stable at high temperatures thus making the finished rubber thermally stable.
Industrial Rubber is always pleased to help with the selection of material that will best suit your application. We do have some information on the properties of different materials on our website but our Material Technologist is always please to discuss your specific application.
Would you like any further information on a particular rubber or would you like a free swatch to illustrate the various hardness of rubber including sponge?
