It seemed particularly apt at IRC ‘96 to present the life history of natural rubber on what was almost exactly 500 years to the day (11 June 1496) that Christopher Columbus returned from his second voyage, bringing back the first rubber balls from the West Indies. There was, Spanish observers said, ‘nothing comparable in the world to the way that the balls bounced’. Previously only packed leather balls had been known in Europe, and this new rubber was a total novelty. The next landmark in the history of natural rubber was the Spanish discovery of the use of latex for the water proofing of leather and fabrics in 1615. Because no method of preserving latex was known at that time, a thriving fabric proofing industry grew up in Mexico and the finished product exported.
The Beginnings of the Rubber industry ion Europe
The rubber industry in Europe really started with Charles Macintosh in 1818. Many had sought suitable solvents for rubber since its arrival in Europe as a raw material in the late 1700s, but none had been successful. Charles Macintosh was an industrial chemist in Glasgow, then a major centre of the chemical industry, and was eager to exploit the waste products of the new coal gasification process. James Syme, a medical student, found that coal tar naphtha was a good solvent for rubber and so Macintosh’s specific skill came in exploiting the naphtha-based rubber solution as a waterproofing layer between 2 fabrics. Hence the ‘macintosh’ was born. Only 2 years later, in 1820, Thomas Hancock discovered mastication. Hancock was using rubber in elastic fastenings for gloves, shoes and stockings. These ‘garters’ were made by cutting strips from ‘bottles’ of pure rubber, and led to much waste. Hancock noticed that fresh cut edges of rubber would unite perfectly and it occurred to him that if such pieces were minced up very small, the amount of fresh cut edges would be greatly increased and with heat and pressure might unite sufficiently for some purposes. So was developed Hancock’s famous ‘Pickle’ or wooden masticator. He found that the effort to shred the rubber did not decrease with time, but increased, and when opened a homogeneous roll of rubber was found. He used his ‘pickle’ to supply the Macintosh factory, and kept his mastication process secret until he was forced to patent in 1837.
The Discovery of Vulcanization
The final landmark in the early history of rubber was the discovery of vulcanization by Charles Goodyear. Whilst the rubber industry was developing rapidly in the temperate climate of Britain, with Macintosh and others producing a whole range of products from rubber fishing dinghies to beer hoses, the US industry was losing confidence with factories closing down due to the extremes of climate. Excessive high temperature made products sticky, whilst at very low temperatures they became rigid. Thus Charles Goodyear in the US was seeking modifications to rubber to avoid these temperature defects. He tried magnesia, boiling in lime, bronze powder, and nitric acid, but all were of no avail. In September 1858, however, a Nathaniel Hayward introduced Goodyear to the idea of sulphur on, rather than in, the rubber. Unfortunately at that time Goodyear suffered both financial and personal difficulties so it was not until 1841 that he actually accidentally over-heated a mixture of rubber, sulphur and white lead, which resulted in the discovery of vulcanization, and a rubber which did not harden in winter and soften in summer. This was patented on 6 December 1842. Public opinion in the US was still hostile to rubber, however, and Goodyear entrusted his idea to a Stephen Moulton, who was about to return to England, to take his improved rubber to the Macintosh Company. Samples reached Thomas Hancock via a certain William Brockendon (who is reputed to have coined the name ‘vulcanization’) and Hancock deduced from the bloom that sulphur had been used. He subsequently discovered that strips of rubber immersed in molten sulphur changed its character and patented the process in November 1843 - only a few weeks before Goodyear’s belated English patent. Hence both names being ascribed to the discovery.
Expansion of the Natural Rubber Industry
From that time on, the natural rubber industry really began to expand and was fuelled by the additional supplies of rubber that became available from the Far East. This was due to Sir Henry Wickham who transported 70,000 seeds from Brazil to Kew Gardens in 1876. Some 1900 of these germinated and the resulting seedlings were shipped onto Ceylon and Singapore, from which virtually all the rubber trees in the Far East are descended. Also at about that time Henry Ridley (Director of the Singapore Botanic Gardens from 1888 to 1911) developed tapping techniques and instigated many of the methods used to this day. The discovery of the pneumatic tyre, or really its re-nvention, by John Boyd Dunlop in 1888 set the scene for increased consumption as early vehicles moved away from solid tyres and became more sophisticated. Aircraft tyres were first marketed in 1910 and the earliest pneumatic truck tyre emerged in the USA circa 1917.
Natural Rubber Developments in the 1940s, 1950s and 1960s
There were then a whole series of developments in natural rubber science and technology in the 40s, 50s and 60s, which led to a range of new materials derived from it and new uses. For example ‘rubber in roads’ is not new. The first rubberised bitumen was laid in the Rue Ferrier, Geneva in 1947 by Ashaltiques Geneva, and subsequently in Acre Lane in London in 1950. By 1955, 70 miles had been laid in UK. It was reported to give non-slip properties, one-third improvement in life and was much more resistant to low temperatures. In 1952, the first liquid rubber Rubbone was produced by the mechanical working of softened rubber with chemical plasticisers (6-8 hours in a 2-blade mixer at 120-140°C. This was used for textile machinery components, printers’ rollers and for prototype manufacturing. Then there was Positex in 1952, a latex which was processed to give the rubber particles a positive charge for the wool industry, and methyl methacrylate grafted (MG) rubber in 1954 for making very hard rubber (96 IRHD), or adhesives if only 30% is grafted. New uses saw the first rubber-metal laminated bridge bearings in 1957 on the Pelham Bridge in Lincoln, and oil-extended natural rubber to improve the grip of unstudded winter tyres in 1967.
Natural Rubber Developments in the 1970s and 1980s
In the 1970s and 1980s the natural rubber industry still forged ahead. Further new materials and new uses have appeared. We have seen the advent of epoxidised natural rubber, a rubber derived from natural rubber but with high damping characteristics, oil resistance and gas permeability equal to halobutyl rubbers. Thermoplastic natural rubber is a blend of natural rubber with polypropylene to give a recyclable rubber, and new liquid natural rubbers have been developed for a variety of uses.
Laminated Rubber Bearings for Buildings and Bridges
The early work in the 50s on laminated rubber bearings for bridges, now used universally to accommodate bridge deck movements, spawned bearings for the base isolation of whole buildings against ground-born vibrations (e.g. underground railway systems). These in turn were further developed in the mid 1980s and 1990s for bearings to protect buildings against earthquakes.
Natural Rubber in Tyres
Seventy percent or more of all natural rubber goes into tyres mostly into large truck tyres, off-the-road giant tyres and aircraft tyres. Here, low heat generation properties in service are of paramount importance, along with low rolling resistance. Recent work in the 80s has seen the development of natural rubber-based compounds for truck tyre retreading to match the wear of all synthetic compounds, and these, because of their lower rolling resistance, give the added benefit of better fuel economy. More recently, the advent of all-season passenger car tyres has called for improvement in grip on ice and snow. Here, the earlier oil-extended natural rubber technology used for winter tyres can provide better grip on ice and snow combined with lower rolling resistance.
The Future for Natural Rubber
The future for natural rubber looks bright. Ever increasing volumes are being produced. At 5.92million tonnes per annum, natural rubber has 39% of the world rubber consumption of 15.14 million tonnes per annum. The earthquake-bearing market will take off when people realise that such systems not only save lives, but also the contents of the buildings. Powder-free surgical gloves are on the way and this, achieved by polymer coatings both on the inside and out, will eliminate the protein allergy problem. All predictions of future cars see them continuing to use rubber tyres. The space shuttle lands on all natural rubber tyres because of the superb performance of this 500 year old polymer. With space travel around the corner, surely natural rubber has a guaranteed future!