Leverkusen - The fascinating history of synthetic rubber started with an idea patented 100 years ago – and is far from over yet. In 1909, the chemist Fritz Hofmann succeeded in producing the elastic substance methyl-isoprene, and thus paved the way for the development of synthetic rubber. Hofmann conducted his research at the laboratories of “Elberfelder Farbenfabriken vorm. Friedr. Bayer & Co.” – a company whose tradition is continued today by the specialty chemicals group LANXESS. 

Rubber has become an indispensable part of the modern world. Wherever machines or engines have to be provided with bearings, forces transferred, liquids transported, rotating shafts or containers sealed, there’s no getting around this material. However, today’s high-performance elastomers have little in common with the materials obtained from natural rubber. Today, LANXESS is not just one of the world’s biggest producers of synthetic rubber – with 100 years of experience in synthetic elastomers the company is also a technology leader and a driving force in the industry. 

We wouldn’t get very far today with products based on natural rubber. The technology and the requirements that rubber has to satisfy have been revolutionized since the early days when the first coats, boots, inkpots and even combs were made of (hard) vulcanized natural rubber. Higher application temperatures, faster machines and ever more stringent demands on energy efficiency and cost-effectiveness are compelling engineers to opt increasingly for special grades. Even low-cost, unremarkable rubber parts play a key role in the cost-effectiveness of expensive capital goods today. For example, longer-lasting products, such as extremely robust seals and bearings, help cut maintenance costs and thus secure profitability.

An incentive and a commitment

State-of-the-art rubber goods are made of numerous synthetic rubbers by mixing them with a number of other components, such as fillers, plasticizers and antioxidants. And this can only be done once the rubber’s chain molecules have been widely crosslinked under pressure and at high temperatures in a process known as vulcanization.

For a long time, before Hofmann invented synthetic rubber, industry was dependent on natural rubber, a material obtained from plants that was subject to fluctuations in quality and price. What’s more, it was practically impossible to modify its chemical structure, which meant it could not be adapted to meet the increasing demands of technology. As a result, Elberfelder Farbenfabriken offered a prize of 20,000 German marks for the person who could find “a process for producing rubber or a suitable alternative” by November 1, 1909. 

Even the Kaiser was pleased with the results

Not a lot was known about rubber back then. For example, it was not until 1905 that it was discovered that the chain molecules of this elastic material comprised countless strings of isoprene molecules, but no one knew how to crosslink them. Nevertheless, Hofmann decided to give it a try.

As it was difficult to produce the “natural rubber module” isoprene, Hofmann quickly decided to use methyl-isoprene, which had a very similar chemical structure and was easier to manufacture. He placed the material in tins, heated them, and waited – sometimes even for months. Depending on the temperature, the substance that formed in the tins was sometimes softer, sometimes harder, but it was always elastic. As it turned out, Hofmann had invented methyl rubber. The patent for the world’s first synthetic rubber was awarded a hundred years ago on September 12, 1909.

Continental – a leading rubber company even then – started to produce the first car tires from this new material as early as 1910. Hofmann’s boss Carl Duisberg traveled 4,000 km on the tires “without a puncture”. Even the German Kaiser had his car fitted with the tires and was “extremely pleased” with the results.

Driving force in the rubber industry

Synthetic rubber became even more important as it was discovered how to form chain molecules from rubber modules, such as Hofmann’s methyl-isoprene, more quickly and successfully than before. It was the addition of sodium that made this possible. In the 1920s, Hofmann’s successors succeeded in using this metal and many process tricks to create another synthetic rubber from butadiene, a “simpler” chemical relation of the natural rubber module isoprene. This product went down in history as “Buna” – a term coined from its constituents butadiene and sodium (Na).

The rubbers that chemists produced in the first third of the last century from the new starting material butadiene got better and better. The next step was taken a short time later by the chemists Walter Bock and Eduard Tschunkur. Bock in particular was responsible for combining butadiene with another highly promising module – styrene. This gave rise to the “styrene rubber” Buna S, which – in a much evolved form – remains a key component in car tires today. The first tires with a Buna S tread were launched on the market in 1936, and attracted considerable interest because they lasted much longer than traditional tires. The patent for the copolymerization of butadiene and styrene was awarded on June 21, 1929.

In search of further alternatives

This period also saw the invention of a further rubber from Leverkusen that became popular first and foremost because of its oil resistance – the nitrile rubber Buna N invented by the chemists Eduard Tschunkur, Helmut Kleiner, and Erich Konrad. The team continued in search of further interesting alternatives, and struck gold when they invented “acrylonitrile”. Once again, varying the chemical modules in a targeted manner resulted in a new rubber with completely different characteristics. Acrylonitrile is polar and, therefore, oil-repellent. A patent for the new oil-repellent rubber was awarded on April 26, 1930. From 1938 – three years after the start of large-scale production – this remarkable elastomer was marketed under the name Perbunan to distinguish it more clearly from Buna S.

Gradually, the chemical industry launched more and more rubbers onto the market that all exhibited new technical properties, for example, Baypren, Levapren and Buna EP, which are used in adhesives, hoses, fire-safe cable sheathing, weather-proof and UV-resistant seals, and translucent rubber articles. Customized special-purpose rubbers from LANXESS endure high temperatures and aggressive liquids, e.g. in hydraulic cables. They can also withstand millions of load changes without showing any signs of fatigue and are resistant to oxygen and ozone, which can cause decay of vulcanized products made of natural rubber.

Along with these came countless innovations in the field of rubber chemicals that are essential for manufacturing rubber, for example, antioxidants (antidegradants) and vulcanization accelerators such as Vulkanox and Vulkacit. Chemists and technicians from LANXESS have played a key role in many of these developments.

Synthetic rubber overtook its natural ancestors long ago

In 2007, some 13.6 million metric tons of synthetic rubber were used worldwide, compared to around “only” 9.7 million metric tons of natural rubber. Experts expect that the share of synthetic rubbers will continue to grow faster than natural rubber as a result of its properties. Today, LANXESS produces hundreds of different grades of synthetic rubber designed for a diverse range of applications, making it the manufacturer with the broadest product range.

Innovations for the tire sector

Based on the know-how of Fritz Hofmann, the rubber experts at LANXESS have made a major contribution to the almost revolutionary improvements in vehicle tires in terms of performance, safety, and energy efficiency. SSBR rubbers have enabled the tire sector to boost the wet grip of its products, for example. Wear and rolling resistance have also been improved by replacing the carbon black filler used in the past with silica. Neodymium rubbers such as Buna CB and Taktene from LANXESS – in practice the modern successors of the first Buna rubbers – help cut rolling resistance and thus save fuel. The chain molecules of these elastomers exhibit a very linear structure, which means that they are much more elastic than many other tire rubbers.

High-tech innovations for the rubbers of the future

LANXESS has recently also started manufacturing ESBR rubbers with particle sizes down to the nano range. Tires with Nanopren nanoparticles added to their tread mix have much better dry road grip and demonstrate improved wear resistance with no detrimental effect on rolling resistance or wet grip.

Application examples

In high-speed letter sorting machines, conveyor belts made of carboxylated nitrile rubber ensure an uninterrupted flow of materials. This product is ideal for special-purpose applications with excellent resistance to abrasion and dynamic loading, and a hydrophilic surface that grips paper extremely well.

Ethylene vinylacetate copolymers (EVM) from the Levapren rubber series from LANXESS are ideal for the production of solar modules. During assembly, silicon wafers are embedded into films made of the transparent rubber Levamelt and secured to the substrate. This simplifies a number of complex processes involved in aligning and securing cells.

Only two manufacturers worldwide have the technological know-how to produce hydrogenated nitrile rubber. LANXESS markets more than 50 different grades of this elastomer under the brand name Therban. Therban is oil-resistant like nitrile rubber but, thanks to a complex chemical modification, is much more resistant to aging. This makes it ideal for rubber products that are subject to particularly high mechanical loads. It also has a higher service life and helps cut machine downtimes. This makes it possible, for example, to extend maintenance intervals, thus cutting operating costs. Therban is used, for instance, in drill heads for oil exploration and in components subject to high dynamic stresses, such as toothed belts in car engines. The latest Therban grades with increased acrylonitrile content offer improved resistance to aggressive media, making it the material of choice for hoses and seals used in biofuel applications.

Synthetic rubber is used today as the basis for a wide range of high-performance rubber products and it will continue to be used to unlock the potential of new opportunities and applications in the future.

Detailed information can be found at:
http://techcenter.lanxess.com/bur/
http://techcenter.lanxess.com/pbr
www.therban.de, www.levapren.de, www.levamelt.de,
www.buna-ep.de, www.baypren.com, http://techcenter.lanxess.com/trp