Synthetic rubber developments

By David Shaw

There has been a marked contrast in the rate of development of synthetic rubber compared to that of natural rubber. In the most recent decade, that contrast has accelerated rapidly.David-Shaw310

We should not forget that much progress has been made in the natural rubber sector. There have been improvements in quality, in yield and in disease resistance. Different international rubber research institutes have made significant progress in these areas.

With the introduction of technically specified rubber, the amount of ash and other contaminants has fallen considerably. Some countries, notably Malaysia, have further tightened the specifications to improve quality and purity for the customers.

We have seen average yields increase toward 2000 kg/ha/year. Malasian statistics show that yield in 2010 was fractionally under 1500 kg/ha/year, up by more than 50 per cent from the figure of 960 in 1999. When we consider that a Tree takes seven years or more to reach maturity and has a further life of 15 or so years; that is a considerable achievement.

Furthermore, we have seen new diseases become more prevalent, such as Corynespora Leaf Blight and White root disease. Our researchers have made great efforts to combat these ills. Despite these efforts, however, these diseases are still a challenge both for farmers and for the researchers.

Despite the real progress in these areas, much less has been achieved in terms of technical specifications such as molecular weight distribution; average molecular weight ans suchlike.

When we compare the progress in synthetic rubber, the contrast is even more marked.

Beginning around 1980, suppliers of synthetic rubber developed new materials for the tyre industry, and the progress continues today, at ever faster rates.

Modern materials are almost unrecognisable from previous generations. When I started in this industry, suppliers offered a series of grades which might have included a distinct ratio of cis– to trans– isomers. We had high-cis butadiene rubber and so on.

Over the last 25 years the processes for making synthetic rubber have changed beyond all recognition. So have the catalysts and the process control.

These developments have combined to produce tailor-made elastomers which meet the very specific requirements of different types of tyre application. This is not just tread rubber as opposed to carcass rubber – as you might find in carbon black, Instead there are different materials which are appropriate to high performance tyres, winter tyres, tyres which require high grip or improved rolling resistance or better wear.

Each of these performance parameters requires a different type of elastomer.

For example, one source of energy loss in a rubber compound is the chain-ends. As the bulk rubber distorts, the molecular chain ends can move around. This chain-end movement is a significant source of energy loss in the compound. Rubber makers have two or broad families of solution to this issue.

These involve either anchoring the chain end to another molecule in the mixture, or reducing the total number of chain-ends for a given mass of rubber.

(Full Text in PTA, April-May issue)

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