Tears of the Tree: The Story of Rubber — A Modern Marvel

  • John Loadman
Oxford University Press: 2005. 336 pp. £19.99, $37.50 0198568401 | ISBN: 0-198-56840-1

In 1770, an artists' supply shop in London offered for sale half-inch cubes of a mysterious material that was called ‘rubber’ because it could be used to rub out pencil marks. The price was 3 shillings per cube, a large sum at the time — but then, nothing else was as effective in correcting artists' mistakes.

This is one of many pieces of information offered in John Loadman's miscellany of a book, Tears of the Tree. The book's purpose, he announces at the outset, is “to examine the story of natural rubber in its social context”. In fact, about half the book is devoted to the social context, and this is its main merit.

The story of rubber begins with its discovery and use by Meso-American civilizations in what are now Guatemala and Mexico. In particular, rubber balls were used for formal competitive games; the losers were usually killed, their heads cut off and coated with latex from the rubber tree to make the next (properly weighted) balls. But the most horrendous stories in the book are about the ‘rubber barons’ in the western extremes of Amazonia, and the exploitation by Belgian King Leopold II of the natives of the Congo in the late nineteenth century. The social context of primary rubber production was uniformly depressing until 1877 when, after numerous abortive attempts, seeds of the wild rubber tree were at last successfully (if unofficially) transferred from Brazil to the Royal Botanic Gardens at Kew, near London. They were then germinated and transferred to the Far East, Malaya in particular, establishing a major primary industry.

The exploitation of rubber provided extensive benefits for developing industrial societies. The story — especially the slow, faltering steps to find the best way to harden raw rubber by vulcanization — is told in interesting detail. Patents play a major role in this tale, and the biographies of the principal players are excellently presented. The cycle is completed with a critical survey of attempts to recycle waste rubber.

The book then changes gear and focuses on the production technology of vulcanized variants of rubber, both natural and synthetic. The treatment becomes extremely technical in terms of the organic chemistry of different kinds of polymeric molecules, and even more so when the minutiae of the chemical deterioration of rubber are set out. At this point, in my view, the book begins to stutter.

Tapping into nature: the production of tyres and medical gloves starts here, at the rubber tree. Credit: D. WALL/ALAMY

The science and technology of polymers in general, and of elastomers in particular, has three essential constituents: physics, chemistry and production technology. With a background in chemistry and long experience in a research institute focused on natural rubber, Loadman knows about chemistry and production technology, and his presentation of the chemical aspects is technically detailed. But explaining the chemistry is not enough.

The problem comes with the physics. Loadman claims that the physical theory of ‘rubber-like elasticity’ is too involved to present in any detail, so the source of rubber's elastic restoring force and of the very large elastic strains that can be attained is left unexplained. The elastic behaviour of rubber is fundamentally different from that of other, non-polymeric, solids: it is entropy made tangible, and no explanation is adequate unless it takes into account the probabilities of different microstructural arrangements of the polymer chains.

One difficulty in the book is the author's use of the word ‘elastic’. He uses it to denote the capacity to generate very large reversible strains — that hasn't been the sole meaning since Hooke's work on elasticity in the seventeenth century. Furthermore, rubber, especially before it has been vulcanized, is not elastic but viscoelastic: the strain generated by an applied force varies with time under stress. This characteristic governs many features of rubber, including the adhesion of a tyre to the road surface and the comfort of someone sleeping on an elastomeric mattress.

The book is full of interesting information. But it is uneven, and the gear changes are so abrupt that the narrative tyre tends to skid.