A brief history of plastics, natural and synthetic
- 17 May 2014
- From the section Magazine
When you think of plastic, what springs to mind? Cheap toys from China? Packaging? Or maybe a plastic bag? Of course you would. But how about a woolly jumper? Or cornflakes? Or an antique oak wardrobe?
Believe it or not, from a chemist's perspective all these things are made of the same class of materials: Polymers. And the distinction between which ones we happen to call "plastics" and which ones we don't is fairly arbitrary.
Polymers are extremely long repetitive molecules which, in the case of plastics, are primarily made of carbon.
"You take a simple organic molecule and you react it with itself again and again and again," explains chemistry professor Andrea Sella of University College London.
"A little bit like a bicycle chain, you attach one link, and you click on the next one and the next one and the next one, almost ad infinitum."
Polymers are a very broad category.
As well as plastics, they also include the silicones - based on silicon rather than carbon - used in everything from breast implants to fire retardants.
They even include DNA.
The polymers' shape is what gives plastics their plasticity, allowing them to be moulded into any shape. The individual strands "can simply slide past each other" says Sella. "Think of cold spaghetti."
Humans have been using naturally derived plastics for far longer than you may imagine.
For example, medieval craftsmen made lantern windows out of translucent slices of animal horn. Horn is made of keratin - a mixed carbon-nitrogen polymer - the same stuff that skin and hair, including wool, is made of.
But the history goes back further.
A millennium and a half before Christ, the Olmecs in Mexico played with balls made of another natural polymer - rubber.
It was not until the 18th Century that the first European, French explorer Charles-Marie de La Condamine, stumbled upon the rubber tree in the Amazon basin.
And it was only in the 1840s that the American Charles Goodyear and the British Thomas Hancock took out patents on either side of the Atlantic for "vulcanised" rubber - treated with sulphur to make it more durable.
Vulcanisation made possible the rubber tyre for the bicycle, and later the motor car (hence the Goodyear tyre company). Thomas Hancock, meanwhile, collaborated with Charles Mackintosh to make water-resistant clothing.
But the story of plastics goes back earlier even than the Olmecs, in fact as long as man has been using wood. That's because about half of your average piece of wood is cellulose - a polymer that provides the tough walls of plant cells, and wood its stiffness and durability. It is the long strands of cellulose that are separated by the pulping industry, and that give paper its strength.
It was also cellulose that provided the raw material for the next great breakthrough in modern plastics - the material "Parkesine", modestly named by the British inventor Alexander Parkes, who put it on display at the 1862 international exhibition in London.
Many early examples of Parkesine products - printers' moulds, cutlery handles, buttons, combs - can be found on display today at London's Science Museum.
"Although he's a fantastic inventor, he's not a brilliant businessman," explains curator Dr Susan Mossman. "So he goes bankrupt."
It was left to two Americans, the Hyatt brothers, to make a mint from the material - much to Parkes' chagrin. They added camphor, improving the plastic's malleability, and renamed it celluloid in 1870, thus providing what would become the raw material for the film industry.
Cars and films are not the only technologies whose birth was facilitated by these early plastics.
Electrification was first made possible by rubber, which could be used to insulate electrical switches, while the first submarine cables for telecommunications from 1851 were coated in a protective layer of a cousin of rubber called gutta percha.
But the big breakthrough - arguably the birth of the modern plastics era - came in 1907, with the invention of Bakelite by the Belgian-born American Leo Baekeland.
It was the first synthetic plastic - the first to be derived not from plants or animals, but from fossil fuels.
Baekeland used phenol, an acid derived from coal tar. His work opened the floodgates to a torrent of now-familiar synthetic plastics - polystyrene in 1929, polyester in 1930, polyvinylchloride (PVC) and polythene in 1933, nylon in 1935.
These brand new materials were considered the very height of glamour.
"By the 1930s you've got synthetic plastics that can be produced in whites and pale luminescent colours," says Mossman.
"You get Ginger Rogers dancing in a beautiful white laminate interior."
But what really drove the industry's growth was the war effort, as plastics were used in everything from military vehicles to radar insulation.
Petrochemicals companies built plants to turn crude oil into plastic by the lorryload, with the predictable result that, come the end of the War in 1945, the industry faced a horrendous glut.
To keep production running, they were forced to think outside the box - or should that be inside the box? - as they turned their attention to the mass consumer goods market, with new products such as Tupperware, launched in 1948.
Andrea Sella offers the example of polyethylene terephthalate (PET) invented in 1941, to show how versatile these cheap new materials could be.
Today it is used to make fizzy drinks bottles, because it is strong enough to hold two atmospheres of pressure.
He then flourishes a soft winter glove, as well as a sheet of plastic for wrapping flowers. "It's the same material," he says. The only difference is the way in which it has been cast.
And that is just one plastic.
"There are literally now hundreds of thousands of different kinds of polymers," says Sella.
And their properties can be changed just by tweaking their structure.
"A standard British milk bottle is made of polyethylene, made from a building block C2H4.
"If you add just one carbon, and go to polypropylene, what you have is a much more robust material."
He takes out a baby's drinking cup and lets it drop to the concrete floor. It bounces cheerfully back.
"This was completely transformative. When they came in, they were replacing things like pewter, which gets dented, and glass and ceramics, which have the terrible problem that they smash."
Synthetic plastics had the added advantage that they seemingly lasted forever. No organisms had evolved that were capable of digesting these complicated and alien materials.
But that advantage is, of course, also a great disadvantage.
Plastic might sit in a landfill, or litter a street, for thousands of years without decomposing.
More worrying are reports that much of our plastic junk - including gazillions of tiny plastic micro-particles that might have broken off from plastic-based clothes in washing machines - have found their way into our oceans, where they collect in giant floating junkyards that go round and round in natural gyres in the ocean currents.
There is some evidence that bacteria may be evolving to feed on this junk, exploiting the energy embodied in the polymers' hydrocarbon bonds. But there are surely better solutions - such as plastics designed to decompose.
Polylactic acid (PLA) for example, is derived from corn starch, the same stuff that corn flakes are largely composed of. Starch, like cellulose, is a polysaccharide - a long chain of sugar molecules fused together.
PLA can be used to make plastic bags, and fibres for clothing.
Meanwhile, cellulose can be turned not only into celluloid, but also the food wrapper cellophane, or the fibre rayon.
All of these polymers are compostable. Over months or years, they will be gradually broken down by microbes.
Apart from the steady accumulation of plastic junk, there is another looming problem - where we get our plastics from in the first place.
Currently, most of them come from oil and gas. But when these finite sources eventually run out, the obvious solution will be to go back to the days of Parkes and Goodyear, and look to biology.
"The market is looking for more bio-derived plastics that are chemically identical to the plastics we use now," says Dr Jeremy Tomkinson, a York-based consultant who advises the UK government on bio-fuels and bio-materials.
"The main thrust at the moment is polyethylene."
Partly this has been driven by brand considerations - Pepsi and Coca Cola competed in recent years to boast the first 100% bioplastic PET bottle (Pepsi won).
Normally derived from crude oil, the stuff is now being produced from sugar cane by the Brazilian petrochemicals firm Braskem. It uses vats of yeast that have been genetically modified to turn the sugar into ethanol, which can then be converted by stages into ethylene, polythene and PET.
Such bioplastics also help battle climate change, Tomkinson argues, as the sugar cane draws carbon dioxide out of the atmosphere, sequestering it into a product that can be recycled like any other - even if it is ultimately burned to generate energy, and the carbon dioxide released back into the atmosphere.
But Tomkinson says that in the longer term, the main driver for the bioplastics renaissance will not be eco-friendly altruism, but the profit motive.
The big chemicals companies realise that they need to find alternative feedstocks to replace crude oil, and this is already reflected in their research and development spending.
For now, the oil price remains steady. And, thanks to the shale revolution, American gas prices are exceptionally low, turning the US into a major producer of PVC.
"But when oil hits a certain dollar price per barrel, it will become too expensive to use," he says.
"That's where industrial bio-technology could really begin to take effect."
And that's where mankind's brief love affair with synthetic plastics will come to an end.