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The limitless application of rubber

Posted on 08/11/2016

Of all the materials we use in manufacture, plastics and rubbers are most like organic life.

From an ancient Mayan ball game to rocket fuel rubber is infinitely useful and adaptable.

You probably take everyday objects made of plastic for granted, and rubber as its pungent cousin; but then you would be missing the point that both these materials (polymers) are pretty ubiquitous for good reason.

On the molecular level polymers are like a very long chain of very small beads where the beads can be of varying types and sequences of such. One can shape and mould this mass of ‘beads’ into a multitude of objects both intricate and crude, nano-scale and massive, and with a huge range of properties. In the case of rubbers you can also bend and flex them before they return to their original state (envisage stretching an elastic band then releasing it). Rubbers are smart and responsive materials.

Of all the materials we use in manufacture, plastics and rubbers are most like organic life. In fact life itself abounds with polymers; DNA, proteins and starches are all polymeric molecules.

Negative press associated with plastic in our oceans, and rubber tyre mountain waste, has tainted many individuals and groups against polymer materials. However it’s not polymers that are ‘bad’, but the humans who discard them thoughtlessly. Polymers are enablers of modern life and should be valued as such.

There’s polymer in your credit card, computer, kitchen appliances, cycle helmet, clothes, furniture, tyres, asthma inhalers, and may even be giving you the ability to read this (if you wear contact lenses). Imagine all those, and thousands more, useful products around you disappearing!

Rubber is a special case of polymer. It possesses the longest chain lengths of all polymers and it also has a glass transition temperature of -70C, much lower than that of most plastics. This means that the small movement of millions of the ‘strings of beads’ at ambient temperatures translates into macroscopic deflections that can be ten times greater than of any other material. Rubber also possesses the ability to be cross-linked in order to give it great strength and longevity under dynamic conditions.

 

Historically man came to use rubber before plastics (which are almost exclusively manmade). Natural rubber is a sustainable bio-based material, which is collected from the sap of trees, and was used by the ancient Mayans in 1,400 B.C. to play a ball game using the feet and hips.

It wasn’t until the 19th century that rubber was collected en masse and in 1847 the cross-linking of rubber lead to the development of the pneumatic tyre. Without tyres it’s unlikely that either manmade flight or the automobile industry would exist today. In the applications in which it is used there are no practical alternatives, it cannot be replaced; it is a material that is critical to modern industrial civilisation.

World War II fuelled extensive research into synthetic alternatives to natural rubber as supply was halted when the Japanese occupied plantations in Southeast Asia in 1942. Whilst there are now numerous synthetic polymers, used in many applications, natural rubber remains the dominant rubber worldwide by volume and is the only material with the strength and resilience to land a jet engine plane upon. Imagine all air travel ceasing!

In practice rubber formulations are complex mixtures, a typical compound is usually composed of between 8 to 15 ingredients, all of which are selected to modify the final properties. Whilst this is complex it also allows for great flexibility and widens the diversity of final applications.

Elastomeric seals found in down-hole drilling applications, for example, can withstand 15,000psi and temperature ranges of -65C to 320C; elastomers used in medical applications need to be inert and resist antimicrobial growth; modified synthetic rubbers can be used as rocket fuels, burning hotter and more uniformly than other alternatives and are used for launching spacecraft. There are thousands more of other elastomeric applications.

The KTN is working closely with those in the rubber community in the UK to bring together knowledge and expertise across the diverse range of elastomer types, sectors and applications. To this end it has recently published a UK Elastomer and Rubbers Roadmap for 2015-2020. One of the major outcomes of the report indicated a need for knowledge transfer and accessible centres of excellence, to assist with understanding of the complexity of rubber materials.

Dr Sally Beken – Knowledge Transfer Manager, Polymers