Under-exploiting environmental friendliness of rubber plantations

N. Yogaratnam ( PhD, London)

Chairman/ Tree crops Agro Consultants

Rubber (Hevea brasiliensis) has retained many features from it's Amazonion origins as an environmentally friendly forest tree, although it has been cultivated as a plantation crop for latex with wood as a side-product and now for carbon credits.

One key factor in the relationship between any activity and the environment is that it is impossible to consider any individual activity without reference to the overall impact. In the case of the rubber industry, it is helpful to break down the activities which impinge upon the environment ( Table 1) into those associated with (1) the production of the raw material, (2) the transformation of the raw material into finished products (3) the use of such products in service and (4) the final recycling or disposal of the products.

Many studies relating to the last-named, such as investigations of the scrap tyre problem, fail to recognise the importance of the other elements which may either amplify or mitigate the problem.

It is unavoidable that many authors tend to base their analysis upon natural rubber, frequently in comparison with synthetic rubber, but many of the factors (such as factory emissions, product service and ultimate disposal) apply to all elastomers.

In most discussions on the environment resources are divided into renewable and nonrenewable categories. The former includes most natural products. The latter includes most mineral resources, although many of these are recyclable, and fossil fuels.

The Scandinavians tend to consider their large hydroelectric capacity as a green resource. Fossil fuels are not only non-renewable, but their combustion contributes to increases in global carbondioxide levels and a possible green house effect which may even lead to higher ocean levels and the loss of global land mass.

Industrial material

Natural rubber is an unusual industrial material as it is renewable resource. As such natural rubber enjoys very considerable environmental benefits, and these have tended to be understated in most discussions. In broad energy input terms, natural rubber enjoys a very considerable advantage over synthetic elastomers, whose energy inputs is in the region of 210 - 275 GJ / tonne, as against 30 - 35 GJ / tonne in NR production.

It is probable that the synthetic rubber industry has now reduced its energy inputs for processing and that the use of yield stimulation etc may marginally increase the energy consumed in natural rubber production besides increased fuel costs.

Nevertheless, the natural rubber production data assumes long-distance transportation for the raw rubber from the producing countries to the major consumers.

Rubber wood

Since there has been a significant shift in rubber product manufacturing to the natural rubber producing countries and this will have marginally reduced energy inputs, although these will have been balanced (except in the case of latex goods) by increased energy costs for the transport of manufactured goods.

In the case of latex goods, the non-transport of water around the world must represent a very considerable environmental gain.

The use of rubber wood is growing rapidly and Hevea is even being grown primarily as a source of timber, with rubber being produced as a by-product. Rubber wood is used in furniture, flooring , building components, chipboard, etc and enjoys a growing market. Obviously, the timber so-produced is an eco-friendly material and it is highly pertinent to note that some of the companies involved are subjecting rubber wood production to environmental audits.

It has been estimated that the energy input for wood as a raw material is about 6 GJ / tonne as compared with 38 GJ / tonne for steel and around 100 GJ / tonne for most thermoplastics.

CO2 sequestration

The most understated aspect of rubber cultivation is that of a sink for the carbondioxide which is produced by animals (including man), the natural combustion of plant tissue, and especially through the burning of fossil fuels. Photosynthesis enables the carbondioxide to be converted into life-sustaining oxygen whilst fixing the carbon as biomass.

Hevea's effectiveness in this respect is probably at least equal to that of virgin forest and may even exceed it.

Tropical forests, which cover 20 percent of the earth's surface, account for at least 25 percent of global terrestrial carbon fixation, and it is becoming increasingly recognised that the forest makes a major contribution to global ecology. Hevea rubber compares well with virgin jungle in terms of biomass, especially once the trees reach maturity. Physiological studies have shown that Hevea is more effective than teak grown in plantation conditions in taking up carbondioxide.

This is probably due to the extra energy required to produce the latex inside the tree: thus, in contrast to a synthetic rubber plant, which consumes energy and produces carbondioxide to convert pure energy ( crude oil) into elastomers, the natural rubber plant converts carbon dioxide into an elastomer.

The biomass production potential of a plant species is related to its photosynthetic capacity per unit leaf area and the total leaf area produce per plant. In full sunlight the photosynthetic rate of a mature rubber leaf is around 11 æmol/m2/s1 as compared with 5 - 13 æmol/m2/s1 in other tree species. The leaf area produced by a mature rubber tree is quite substantial : the leaf area index of a mature rubber plantation can be as high as 6 or 7. Because of the high photosynthetic rate and leaf area index, the biomass production per unit land area within a given time is very high in Hevea. With a planting density of 500 trees per hectare the canopy closes in less than five years.

Agronomic efficiency

Natural rubber does not impoverish the land upon which it is grown. Fertiliser inputs are very low and the surrounding soil appears to be enriched by the abundant leaf fall.

Furthermore, biodiversity remains remarkably high in rubber plantations in marked contrast to most forms of monoculture. Excellent agronomic techniques assist in the conservation of the environment within rubber plantations.

Measures include terracing, slit pitting, bunding and mulching and the growth of leguminous cover plants between the rows to assist with nitrogen fixation. Biomass burning is now discouraged during replanting. Moreover, it is possible to grow a wide variety of crops during the tree's immature period, further enhancing its environmental credentials.

Energy inputs

It is possible to produce dry rubber with remarkably low energy inputs especially if maximum use is made of human and solar energy. It is possible to produce air-dried sheet solely by the exploitation of these two forms of energy. Most dry rubber and latex concentrate production does exploit modest inputs of electricity ( which in many producing countries is green power from hydro generators) and other forms for drying. Obviously energy is also required to convert dry rubber into a form where it can be shaped and vulcanised.

Unfortunately, primary processing of natural rubber can lead to significant environmental pollution, especially of water courses and through localized unpleasant odours. Considerable progress has been made in reducing water-borne pollution. especially in India, Malaysia and Sri Lanka. But, in most countries, a considerable problem still remains. This endangers many other activities such as the use of water for agriculture for industrial use and for fish cultivation.

In-service segment

There are both positive and negative environmental factors in the in-service segment of an elastometric product life cycle. The positive factors include a reduction in environmental noise., although tyre noise is a major contributor to environmental disturbance from roads, especially where vehicles travel at high speed. A clear positive contribution to noise and vibration control is to be found in the application of elastometric mountings and bearings.

The negative factor, for it is essentially one, is that the main outlet of rubber is in association with the automotive industry. The road transport industry accounts for disproportionate uptake of the world's natural resources. In the USA, it has been reported that approximately 25 per cent of crude oil is consumed in personal transportation.

This industry is a major contributor to global increases in carbondioxide emissions and endangers health, especially that of children, through asthma and other dangers. It must be stressed that these effects are not directly associated with the use of rubber, but that the system which induces them is inherently dependent upon rubber for its tyres, its engine mounts, its weatherstrip and so on.

In the product lifecycle, it is seen that the energy required to manufacture or dispose of a passenger car tyre is trivial in proportion to that associated with its use in service.

The need for physical travel will be reduced by the general availability of modern methods of telecommunication and increases in computing power. As is so often the case with global problems, solutions are found just when the problem appears to be becoming insurmountable.

Working at home is increasing and this will go some way towards resolving the problem for some people of commuting by road. People may learn to make less use of their personal vehicles and make greater use of public transport.

The United Kingdom's Royal Commission towards public transport considered the human attitudes will have to be changed towards public transport.

Obviously, if this happens there will be a decrease in the demand for elastomers especially in the traditional western markets, but this will be offset by uptake in the developing nations which really need road vehicles to survive - to avoid localised famine and disease and to provide relief from natural disasters.

Product life extension

Product life extension is an important contributor to lessening the environmental impact of any activity. This can either be achieved by extending the life of individual components, or through prolonging the life of the system in which they are situated, or both. In some cases it may be possible to prolong product life through reconstruction once or more during the lifecycle.

An excellent example of this was the multiple retreading of aircraft tyres. The automotive industry demands that products should , as far as possible, last for the entire life of the vehicle and this has greatly affected the character of many elastrometric components.

At one time, cautious motorists used to carry spare fan belts and even radiator hose as it was anticipated that there was a reasonable probability of failure. Such caution is no longer required. Hose and belts last the life of a vehicle unless some catastrophe occurs. Wiper blades and tyres are still changed, but at decreasing intervals.

It has been predicted some time ago that car tyres will last for the life of the vehicle within the period 2010 - 2020 and that truck tyres will have 2,400,000 km casings. These forecasts are probably to be no more than wishful thinking. Nevertheless, some progress is being made towards increasing tyre life.

Careful design of tyres can save weight and reduce fuel consumption and thus produce marginal improvements in what is an extremely wasteful system. Similar enhancements could be achieved by reduced speed limits. Such measures would also reduce pollution and would marginally increase road capacity. Reduced speed limits would also encourage the use of other less wasteful transport modes such as train services.

Retreding

An increase in retreading activity is probably the greatest contribution made by the tyre industry. There had been far greater retreading activity in truck tyres, than in passenger tyres, and as noted aircraft tyres were routinely retreaded many times. The lack of a vigorous retreading industry for passenger tyres stems from (1) the great variety of sized and styles of original equipment, (2) the relatively low carcass strength ( which partially reflects the quest for lower weight to reduce fuel consumption), and (3) the dangerous tendency for car drivers to use tyres to beyond the point at which they are retread able - and safe. There is also a lack of the strong infrastructure which enables companies to have their tyres serviced on a routine basis : this infrastructure enables retreading to be performed as part of a tyre supply operation. Clearly, it is impossible to envisage such an operation for private cars, unless Government regulation and standardization are imposed. Such an imposition would have the benefit of discouraging motorists to drive with tyres which are no longer fit for service.

Recycling

A few elastomeric products are disposable, especially those manufactured from latex ( gloves and balloons, for instance). In the case of balloons these will naturally degrade within about a month if left upon the ground. Unfortunately, medical gloves have to be burned alongside other disposable medical items to eliminate the pathogens which may be present.

Elastomers are difficult to recycle. The problem can be eased through the use of thermoplastic elastomers, although damage in service ( especially through exposure to fuels and the combustion products from fuels) may lessen the value of such materials to a point below which it is valid to expend the effort required for recycling. It is possible to reclaim rubber but this industry is only exploited on a large scale in India where there is a plentiful supply of labour and the demand for elastomeric raw materials greatly exceeds the supply.

It must be remembered that the carbondioxide produced is not a problem for the natural rubber element of the tyres as this will be recycled by the rubber trees that produced it in the same way that it is possible to grow biomass as source of fuel Pyrolysis is interesting as there is no air pollution problem and the products other than heat, are in the form of gases ( which can be burned), solids include a form of carbon black, which if the input consists predominantly of natural rubber, can be clamed to be 'green".

There is a growing recognition that the global ecosystem cannot continue to tolerate the present wasteful use of materials. The rubber industry is fortunate in that over one third of its key raw material is based upon a self-sustaining resource which is not only capable of reabsorbing the carbon dioxide generated from its disposal and through it use, but also provides timber as valuable, environmentally-friendly by-product. The natural rubber industry is based upon minimal environmental disturbance, and is far less than that required to produce typical food crops. Nevertheless, it cannot be forgotten that the primary end use is in personal transportation, much of which is extremely wasteful in terms of resources.

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