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Engineers and materials scientists are struggling to establish the three
conditions necessary to make money from recycling waste plastics: large-scale
reclamation, the development of new products and mass markets for them.
Although we produce around 100 million tonnes of plastics a year worldwide,
not enough is reclaimed to enable the manufacturing industry to develop
and market products made of recycled material. Plastics consumption in the
EC amounts to about 10 per cent of the world’s total and yet, at the end
of last year, Germany gave up the idea of trying to run a recycling plant
at Coburg economically because it could not find 5 tonnes of waste plastics
a day within 100 kilometres.

According to the industry, the best end for used plastics in incineration
with municipal waste. If plastics are removed from waste along with other
flammable solids such as paper, what is left is organic waste that is too
wet to burn. But if the waste is burned with plastics still there, potentially
useful energy is generated. ‘But the public has a mental block about recovering
energy incineration,’ says Bill Moffitt, the British Plastics Federation’s
recycling consultant. ‘Why is it that 93 per cent of oil can get burnt straight
away yet the 4 per cent used for plastics production cannot have a second
life as energy?’

However, environmental pressure and the prospect of much tougher legislation
to encourage reclamation have forced the industry to continue its development
of recycling processes. In Britain a year ago, for example, there was no
large scale retrieval of plastics packaging. Packaging represents about
a third of all plastics produced and public reclamation schemes depend on
it. Although Britain still salvages only a few hundred of the 1-3 million
tonnes of packaging consumed each year, there are now at least 130 ‘bottle
banks’ for plastics and this figure will treble or quadruple by the end
of 1991.

Support for more reclamation schemes in Europe comes from Adamanti Schaefer-Sotiropoulou,
an official of the EC’s directorate on the environment. She proposes a lower
rate of value added tax on recycled products and recommends spending on
research into collection and automatic sorting, which remain the most uneconomic
operations in the reclamation process. She also wants the plastics industry
to divide itself into seven product sectors, each responsible for reclaiming
and recycling its own waste. Before too long, Moffitt expects to see a levy
on industry or sponsored collection schemes or deposits on bottles and containers,
in line with some states in America, the Netherlands and Germany.

Besides packaging, of which the three most common forms are polyethylene
terephthalate (PET), polyvinyl chloride (PVC) and the polyolefins, such
as polyethylene film, there are also the more robust engineering polymers
to deal with . The average car contains around 140 kilograms of plastics,
which save weight and cut fuel consumption but end up as an anonymous ‘fluff’
when a vehicle passes through the shredder at the end of its useful life.
Consumer goods, such as refrigerators and washing machines, pose a similar
problem. Both vehicle and electrical goods manufacturers are concerned that
environmental pressure will inhibt them from using plastics altogether if
they do not do something to help the reclamation industry to sort and separate
the different types of plastics in waste. As a result, they are considering
printing bar codes on plastics components or moulding identification marks
onto them.

At least 60 companies in Britain, another 300 across Western Europe
and 600 in Japan specialise in recycling plastics. Most of these companies
make granules out of clean, single polymers. These polymers may be in the
form of offcuts or sub-standard products form processes such as the manufacture
of PVC pipes and window frames. They may also be polypropylene casings that
are retrieved from vehicle batteries sent to have their lead content salvaged.

These clean polymers represent a tiny fraction of Britain’s total production
of plastics products. The 60 British firms salvage only 50,000 tonnes (10
per cent) of polyethylene film production for recycling into black refuse
bags or builders’ sheeting. At least 25,000 tonnes (around 7 per cent) of
annual polypropylene production is recycled each year. More than 70 per
cent of this salvage comes from bottle crates or car batteries and returns
to life in a similar product.

Better design will reduce material consumption and help the collection
and sorting of plastics. Already reverse vending machines, which give small
sums of money in return for a used bottle or two, identify containers in
particular materials by the specific neck shape. Water-soluble adhesive
for labels, or even labels of the same polymer, should speed up the recycling
of packaging films.

In the late 1970s, Eduard Klobbie, a Dutch engineer, decided to sidestep
the problem of sorting and cleaning waste plastics. He developed a process
that melts dirty mixtures of plastics and injects them into moulds to form
simple, sturdy shapes suitable as posts or planking. The Klobbie process
uses waste plastics that contain at least 65 per cent polyolefins to act
as a kind of adhesive. The rest of the feedstock consists of polymers such
as polycarbonate, compacted granules of PET fibres and no more than a small
proportion of PVC. Up to 5 per cent of the feedstock can be impurities such
as metal, wood or paper.

As far as possible, the operator sorts the incoming waste by colour
and polymer before granulating it. The aim is to build up stocks or known
material, such as broken beer crates, substandard goods or contaminated
compounds, to mix with household waste and additives. Although the Klobbie
process tolerates impurities, finished products that contain a high proportion
of low density polyethylene, for example, tend to be elastic. Similarly,
high proportions of polypropylene in the melt lead to brittle articles.

Horizontal mixers blend the different polymers to produce a reasonably
homogeneous mix of granules. The mix then passes to an extruder, a rotating
steel screw inside a steel barrel. Friction melts the mix inside the barrel
as the screw extrudes the melt into a horizontal mould. The mould is one
of 10 on a carousel that turns in a bath of water. As the top mould fills,
others cool in the water, shrinking the mouldings inside before ejection.

Mouldings from the Klobbie process can be up to 4 metres long, 12 to
50 millimetres in diameter and up to 125 by 125 millimetres in cross section.
They resist rot and can be sawn, planed, nailed or painted just like wood.
These properties make the moulding suitable for road signs, fencing, pallets
or slatted floors for animal pens.

No one has yet explained how to recycle these mouldings and there is
a limit to the world’s need for pigsties made of mixed plastics. However,
there are other ways to make dissimilar polymers work together in a blend.

Generally, virgin polymers have different chemical and molecular properties
that make it difficult for an extruder to mix them into a homogeneous compound.
The chemicals industry has overcome this problem with additives called compatibilsers.
Now the recycling industry wants to do the same with waste materials (‘Recycling
Britain’, New ÐÓ°ÉÔ­´´, 8 September).

Compatibilisers work in one of two ways. Either the additive can make
one polymer disperse physically inside a matrix of another or it creates
chemical links between the materials. The recycling industry has several
hopes of these additives. All polymers oxidise during their life: clear
materials lose translucency and those good at resisting bangs and bashes
become brittle, for example. Compatibilisers should help to improve the
properties of waste plastics by compounding them with virgin material.

High Tech Plastics, a Dutch manufacturer, claims to have developed a
compatibiliser that can turn mixed waste into useful products. The company
mixes polycarbonate, a brittle polymer found in crates with 10 per cent
polyethylene and 5 per cent of its compatibiliser to produce a robust material.
Mixing the compatibiliser with polyvinyl chloride and polypropylene can
yield plstics that slow down the spread of fire, says the company.

Even if exotic additives prove to be viable, most waste plastics will
still have to be sorted, washed, chopped, dried and granulated. The process
varies slightly according to the type of polymer and its source. For example,
most polyethylene film scrap needs little more than cleaning and shredding
before reprocessing into simple objects such as plant pots and garden containers.
PVC must be ground to particles 500 micrometres or less in diameter for
reprocessing.

Manufacturing technologies can now attach up to nine layers of polymers
and adhesives into a film, half a millimetre thick, for laminated packaging,
in which every layer offers a particular property. One layer may be a good
gas barrier; another may help the packaging keep its shape; others, of recycled
PET for example, will provide strength. One device, in which concentric
nozzles feed a mould, makes bottles that consist of a layer of recycled
PET sandwiched between layers of virgin material. When the bottle is full,
the virgin polymer seals the contens from the recycled material. These laminated
bottles cost 20 per cent less than those containing no recycled material,
estimates the industry.

The industry has also begun to investigate ways of ‘cracking’, or breaking
down, polymers that cannot be recycled or that have lost their visual or
mechanical qualities. One way to crack just about any type of polymer is
to heat it in a vacuum for 30 minutes at 800 °C. The solids break down
into gases, such as hydrogen, methane and ethane, and an oily tar that sticks
to the walls of the reactor. This process, which is known as dry distillation,
is a lengthy one because polymers are poor conductors of heat.

A quicker means of depolymerisation, called destructive distillation
or pyrolysis, uses the heat generated by burning a small proportion of a
load of waste in a fluidised bed of sand to crack the rest of the load in
the furnace. The process is expensive however; it costs 70 Pounds to destroy
a tonne of waste plastics even after the useful products have been sold.
Dumping the waste at a landfill site would cost 80 per cent less.

Adding a reagent, such as alcohol, acids or amines, to a distiller is
an even more efficient way to break down particular materials, ICI, for
example, recycles scrap PET to breaking it down with alcohol. Pyrolysis
and alcoholysis are both at the laboratory stage, or, at best, running on
a small scale.

The University of Stuttgart has built a pilot plant to use alcoholysis
to crack a mixture of polyurethanes with polyamide and polyester fabrics.
The materials come from the Ford car factory in Cologne, where they are
used to make vehicle seats. In one experiment the plant cracked the waste
into 100 kilograms an hour of simple hydrocarbons, which could be converted
into rigid polyurethane foam.

Alcohol may cure the automotive industry’s problem of waste plastics.
Relieving the headache of the plastics recycling industry will take stronger
political medicine.

John Bell, former technology editor of New ÐÓ°ÉÔ­´´, is now a freelance
journalist.

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Plastic varieties that hamper effective recycling

Designers classify the hundreds of different types and blends of polymers
by their properties. Chemists split them into two main families, thermosets
and thermoplastics, each of which has its own problems for the recycling
industry.

Molecules in thermosets form cross-links, analogous to the knots in
a fishing net, that prevent the material from softening when it is heated.
Thermosets are robust and durable and they tend to be used in engineering
components. They are easy to reclaim but difficult to recycle.

Heat softens thermoplastics, making the molten molecules behave like
strands of cooked spaghetti that can be reformed for another life. Thermoplastics
make up 85 per cent of plastics consumed in the European Community.

One of the biggest groups of thermoplastics are the olefins, best known
as polyethlene (PE) or as polypropylene (PP). Polyethylene is made by exposing
ehthylene to high pressures in tubes up to 30 metres long and less than
25 millimetres in diameter. As polyethylene’s density increases, it becomes
more crystalline, stiffer and its resistance to bursting forces improves.
High density polyethylenes are found in bottles, tanks, barrels and heavy
duty wrapping film. Low density materials find uses in small bags, mulching
film, all kinds of packaging and electrical insulators.

Polypropylene, or polymerised propylene, is harder and stiffer than
polyethylene. Its resistance to fracture through repeated bending, which
is known as ‘fatigue’, makes it a useful hinge in luggage. Vehicle manufacturers
also use the polypropylene to produce automotive trims and panels.

Polyvinyl chloride (PVC), another common thermoplastic, is a polymer
of vinyl chloride and vinyl acetase. The basic polymer is rigid. Compounders
add plasticisers to PVC to increase its flexibility. Plasticised PVC appears
in clothing, flooring, wallpapers, toys and steel coating. Unplasticised
PVC, or uPVC, is a commom material in window frames, ducting for chemical
plants, drainpipes and guttering as well as underground pipes. Rigid PVC
is one of the stiffest and most impact-resistant polymers in everyday life.

Polyethylene terephthalate (PET) is a common packaging material. Stretch
a sheet of PET in two directions at right angles above 80 °C, and it
works as a shrink wrapping film. One moulded form of the polymer is the
hardest plastic known. PET is also a good electrical insulator.

* * *

Finding ways to collect and sort dumped plastics

There are more good economic and technical reasons against recycling
plastics than there are for it, says a spokesman for EVC, one of Europe’s
biggest producers of PVC. Nevertheless, the company, a subsidiary of ICI,
has set up Reprise, a joint venture with two recycling firms to research
the best way to sort plastics automatically. EVC will supply scientific
expertise while its partners add their practical experience of handling
waste.

Plastics waste is hand sorted because prototype machines are slower
and less accurate than people at separating old bottles and containers into
streams of PET, PVC or polyolefins.

One Italian machine, which detects chlorine in PVC with an X-ray source,
processes three bottles a minute. Reprise has just started tests with an
American prototype sorter that creates a static charge on PVC bottles in
plastics waste as it falls down a chute. The sorter detects the charged
bottles with about 95 per cent accuracy and blows them out of the waste.
The rest of the reclaimed polymers pass to a water bath where the polyolefins
float and the PETs sink.

Workers in Sheffield, where the British Plastics Federation and the
local council are running one of the country’s biggest demonstration projects
to reclaim domestic waste, have developed another method. The sorters have
learnt to recognise the three main commodity plastics by sight from the
tonnes of material that arrives each week from bottle banks and kerbside
collections all over the city.

As much as half of the material arriving at the sorting depot is thrown
away; some is contaminated, some is plastics that no-one yet knows how to
recycle and the rest is not plastics.

Containers made of the three main commodity plastics each have their
own name in Sheffield. ‘Milks’ are large milm containers and semi-translucent
bottles made of high density polyethylene. ‘Washing-ups’ is a reference
to opaque white or coloured bottles and containers, often for domestic cleaning
liquids, in the same material. ‘Dilutes’ and (PET) and ‘pops’ (PVC) refer
to bottles for mineral waters and carbonated drinks respectively. Then there
are ‘Yellows’, ‘Greens’ and ‘Browns’, which are references to bottles made
of PET with coloured coatings.