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BY 2000, half the recoverable material in Britain’s dustbins will be
recycled – that, at least, was the target set last November by Chris Patten,
Secretary of State for the Environment. But he gave no clues as to how we
should go about achieving it. While recycling enthusiasts debate the relative
merits of different collection systems, it will largely be new technology,
and the opening up of new markets, that makes Patten’s target attainable:
a recycling scheme is successful only if manufacturers use the recovered
materials in new products that people want to buy.

About half, by weight, of the contents of the typical British dustbin
is made up of combustible materials. These materials comprise 33 per cent
paper, 7 per cent plastics (a growing proportion), 4 per cent textiles and
8 per cent miscellaneous combustibles.

Of the rest, hard non-combustibles (metals and glass) each make up another
10 per cent, and ‘putrescibles’, such as potato peelings and cabbage stalks,
account for 20 per cent, although this proportion is decreasing as people
eat more pre-prepared foods. The final fraction is ‘fines’ – nameless dust.
This mixture is useless to industry, and in Britain most of it is disposed
of in landfill sites – suitable holes, such as worked-out quarries, in which
the waste is buried under layers of soil and clay. That still leaves about
40 per cent of the mixture – glass containers, plastics, and some paper
and metal containers – as relatively clean when discarded. This clean element
is the main target for Britain’s recyclers.

The first question, then, is how best to separate the clean element
from the rest. The method of collection is important because manufacturers
will not reuse collected material unless it is clean and available in sufficient
quantities. A bewildering assortment of different collection schemes operates
in the rest of Europe, and pilot schemes are now under way in many British
cities including Leeds, Milton Keynes, Sheffield and Cardiff. Sheffield,
Cardiff and Dundee are testing out alternatives as part of a government-monitored
recycling project initiated last year by Friends of the Earth.

A realistic target for recycling mixed refuse is somewhere between 15
and 25 per cent by weight, according to researchers at the Department of
Trade and Industry’s Warren Spring Laboratory. This proportion would include
metals and perhaps some glass. Statistics compiled by researchers at the
University of East Anglia show that we could almost halve the total weight
of domestic waste going to landfill by a combination of ‘collect’ schemes
(such as doorstep collections for newspapers), ‘bring’ schemes (such as
bottle banks) and plants for extracting metals.

This estimate makes two important assumptions. One is that the government
will bring in legislation to encourage the creation of markets for products
made from recycled materials, especially glass, paper and plastics. The
other is that industry will continue to introduce new technology that will
improve both the products and the techniques used to separate recoverable
materials from mixed refuse.

One of the most difficult wastes to recycle is mixed plastic, often
used in wrappers and containers. Plastics manufacturers turn their own offcuts
into granules that are melted down for reuse. They can also reuse any single,
pure thermo plastic material – plastics such as polythene that are not chemically
cross-linked. The British firm Meyer-Newman of Gwent recycles complete telephones
into new ones. But mixed plastics have unpredictable properties and low
structural strengths because the different plastics in the mixture are not
bonded at a molecular level. So, it is difficult to make a material with
good and predictable properties from mixed plastics waste.

In the grip of the octopus

One answer is the compatibiliser. This is an octopus-like molecule in
which each ‘arm’ represents a section of a different polymer, that in turn
is characteristic of a different plastic. Stirred into a mixture of molten
plastics, each arm of the octopus grabs and reacts chemically with a molecule
of one polymer in the mixture. The result is an alloy rather than a mixture.
It is strong because of intra-molecular bonding and has highly predictable
properties, so it is potentially reusable.

During the past two or three years many plastics manufacturers have
developed their own compatibilisers. But perhaps the most advanced, ‘Bennet’,
was produced independently two years ago, after 15 years of research, by
the Dutch engineer Ben Van der Groep. His invention is already being used
widely, largely in secret as manufacturers do not want to be seen to be
using recycled plastics in their quality products.

Bennet is made up of short sections of several polymers representing
the arms of the octopus, each able to link the molecules of a different
polymer in the mixture. The reliable strength of the plastic ‘alloys’ made
with Bennet suggests that they could be used in high-grade, high-cost applications,
such as car bumpers.

The vehicles recycling industry is keen to recycle more plastics. Despite
the environmental benefits, they fear that the steady increase in the use
of unreclaimable plastics will soon make it uneconomic to recover vehicles
for the metals they contain. Some car manufacturers, such as BMW and Mercedes,
are now designing products and requesting components that are easier to
recycle; for example, car bumpers made from one material instead of up to
seven.

Ferrous metal is both valuable – it is worth between Pounds sterling
20 and Pounds sterling 60 per tonne – and relatively easy to pick out of
domestic waste with magnets, so much of it is already reclaimed. Until recently
the only remaining large-scale source of iron in domestic refuse was the
‘tin can’. In fact, tin cans are made of steel (an iron-based alloy) covered
with a thin layer of expensive tin. One problem has been how to clean the
cans before detinning. Now AMG Resources at Hartlepool is able to shred
cans to make this possible. Its ‘Cutler Shredder’ has a steel cage rotating
in one direction containing rollers rotating in the opposite direction.
The rollers feed cans into the cage, and the cans smash into each other,
scratching and stripping paint and leaving small metal shreds. Air blasts
and washing remove dirt easily and magnets then pick out the steel, leaving
behind aluminium ring-pulls.

AMG has also improved detinning procedures based on electrolysis (in
which dissolved tin accumulates on electrodes) rather than chemical leaching,
to remove tin more effectively from the small dense pellets that the shredder
creates.

Collection centres for domestic refuse in Newcastle, Merseyside, Manchester
and the West Midlands now extract steel cans from refuse by magnets to feed
the Hartlepool plant, but for the plant to work at full capacity more magnetic
separators are needed. Similar shredders are operating, or being built,
at three cities in the US – Baltimore, Gary and Pittsburgh – with another
three in continental Europe, in Greece and Czechoslovakia.

Such machinery would be profitable to build and operate near any medium-sized
city, and would reduce the volume of refuse going to landfill by 15 per
cent, according to studies carried out by Warren Spring Laboratory and the
University of East Anglia. Techniques for extracting other nonferrous metals
from mixed waste have also improved. Gold and platinum are already routinely
extracted from electronic equipment by melting it in furnaces at selected
temperatures. Now, some companies, including the Bird Group at Stratford
on Avon and Meyer-Newman at Newmarket are working with researchers at Warren
Spring Laboratory to develop technology for extracting copper, brass and
aluminium, not only from shredded cars, cookers, refrigerators, washing
machines and computers, but also from ‘fines’. The metals are separated
by melting them in furnaces – each metal has a different melting point –
or by flotation in tanks of magnetite (an iron oxide) and ferro-silicon
liquids. The densities of the liquids are carefully adjusted so that one
metal floats and others sink.

Nonferrous metals in scrap vehicles comprise about 10 per cent stainless
steel, 15 per cent brass and copper, 25 per cent zinc – and 50 per cent
aluminium. Aluminium is worth recycling since it costs 20 times as much
to smelt the metal from its ore, bauxite, as to remelt scrap aluminium.
K K Aluminium is separated easily from other metals – by flotation, for
example – because it is so much lighter. But it is often contaminated with
other light materials, such as plastic and fabrics. In 1985, Tony Bird of
the Bird Group was inspired while reading an article about Professor Eric
Laithwaite’s linear motor. Laithwaite’s motor is effectively an ordinary
electric motor turned inside out and unrolled to form a long strip. Bird’s
invention, the Cotswold separator, uses the same principle to throw aluminium
scrap off a conveyor belt, leaving the other materials behind. It could
also be used to separate aluminium cans from domestic refuse.

Perhaps the most pernicious ‘domestic’ waste is car tyres. Like mixed
plastics, these are extremely difficult to reuse. The only big market for
recycled rubber, carpet underlay, collapsed in the 1960s and early 1970s
with the advent of plastic foam-backed carpets. The tyres are neither biodegradable
nor suitable for landfill, where they rise to the top and prevent air and
water from circulating properly. If stored above ground, they harbour vermin
and mosquitoes and are a serious fire risk, as a 17-day fire at Hagersville
near Toronto, Canada, showed earlier this year.

As with mixed plastics, researchers are now developing technology that
will enable manufacturers to recycle rubber into materials that are more
like alloys than mixtures. Rubber in tyres cannot be returned to its original
state, unlike thermoplastic materials such as polyethylene. In the final
stage of tyre manufacture the long-chain hydrocarbon molecules of rubber
are permanently cross-linked with sulphur atoms. Until researchers discover
links that can be ‘unzipped’ at the end of a tyre’s life, they must search
for alternatives. One such alternative is to distil gases and oils from
the rubber in the absence of oxygen, for use as fuel or raw materials. This
method – pyrolysis – is environmentally attractive but, like incineration,
it is expensive.

Now researchers with the American company Air Products and Chemicals,
of Allentown in Pennsylvania, can treat small shredded particles of recycled
rubber so that they become highly reactive both chemically and physically.
Otherwise, rubber particles will not react chemically to form strong bonds
when mixed with other materials, such as melted plastics or ‘new’ rubber.
This means that they weaken and lower the value of any materials they are
mixed with, which can then be used only as cheap fillers.

From tyres to additives

Air Products pulverises the tyres into tiny, clean rubber particles,
which are then treated with oxygen and other reactive gases such as fluorine
or chlorine, so that the inert surface becomes coated with reactive groupings
such as hydroxyl (OH) groups. By adjusting the mix of gases, these reactive
groups can be tailored to react with specific polymers.

A team led by Tom Kulikowski at Air Products tested the treated rubber
particles as additives to polyurethane (the company sells improved polyurethanes).
They found that hydroxyl groups on the surface of the particles reacted
with isocyanate (-NCO) groups on polyurethane molecules, to give them a
polyurethane with several useful properties: reduced water absorption, better
grip in wet conditions when used in conveyor belts or wheels, reduced cycle
time for moulding, greater tear resistance, and greater resistance to penetration
by oil, all at low cost.

The process has the added advantage that it saves energy. It takes about
90 000 BTUs (British Thermal Units) to produce one pound of polyurethane
resin. In comparison, the total energy used up in collecting, grinding and
modifying the surface of a pound of rubber is 9000 BTUs.

The US Department of Energy has given two grants to Air Products for
further research and the company is talking to a number of potential users.
Possible applications include shoe soles, non-pneumatic tyres, conveyor
belts, car window seals, roofing, rollers and gaskets. The main problem
to be overcome is prejudice against incorporating rubber into plastics,
despite the excellent properties of these composites.

Two other large components of domestic refuse are glass and paper. Recycling
of paper needs encouragement from governments to be a success, following
the example of West Germany and Sweden, by making government departments
use it; crediting paper recyclers with the amount they save the waste disposal
authorities; helping to set up collection stations, and by forbidding the
use of combinations that are almost impossible to recycle, such as plastic-coated
paper, latex in self-sealing products and glues that will not dissolve in
water.

Some progress has been made. Newsprint made by Cheshire Recycle of Ellesmere
Port near Liverpool routinely contains more than 60 per cent recycled fibre,
and de-inking is now extremely effective: there are new techniques for disposing
of ink by washing it out of paper and combining it with clay ‘filler’ to
produce a harmless, disposable solid.

For glass, economic considerations alone will never promote much recycling;
energy saving offers only slight advantages. The raw materials that go to
make glass – sand, limestone and salt – are virtually inexhaustible. At
present only about 20 per cent of British glass is recycled, but this must
increase: the European Community is drafting a directive demanding that
by 1997, 70 per cent of all soft drink containers, including glass ones,
must be recycled. Sweden and the Netherlands are among the countries that
already recycle more than half of their glass.

Overall, a combination of ingenious technology, shrinking resources
and vanishing landfill sites, means that the target of recycling half of
Britain’s domestic refuse by 2000 should be a realistic one.

John Newell is editor of science, industry and medicine at the BBC World
Services.