A brief history of plastics, natural and synthetic
When
you think of plastic, what springs to mind? Cheap toys from China?
Packaging? Or maybe a plastic bag? That would be natural, 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 plastic.
Plastics are, chemically speaking, made of long carbon-based molecules of a kind known as polymers."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.
Continue reading the main story
Dr Susan Mossman The Science Museum"By the 1930s you've got get Ginger Rogers dancing in a beautiful white laminate interior”
As well as plastics, they also
include the silicones - based on silicon rather than carbon - used in
everything from breast implants to fire retardants.
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.
Continue reading the main story
In Elementary Business, BBC World Service's Business Daily goes back to basics and examines key chemical elements - and asks what they mean for businesses and the global economy.
Find out more
In Elementary Business, BBC World Service's Business Daily goes back to basics and examines key chemical elements - and asks what they mean for businesses and the global economy.
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.
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.
Collection of objects made from Parkesine, held by the 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.
A section of the second transatlantic telegraph cable, laid in 1865, embedded in 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.
Continue reading the main story
More on Bakelite
- Developed in 1907-1909 by Belgian chemist Dr Leo Baekeland
- One of the first plastics made from synthetic components
- Used for its electrically non-conductive and heat-resistant properties in radio and telephone casings and electrical insulators
- Also used in products from kitchenware and jewellery, to pipe stems and children's toys
- Designated an ACS National Historical Chemical Landmark in 1993 recognition of its significance as the world's first synthetic plastic
It was the first synthetic plastic - the first to be derived not from plants or animals, but from fossil fuels.
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.
Cup made from bioplastic
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."
Continue reading the main story
A beautiful but poisonous metal
Why do we value gold?
A metal so light it floats on oil
Green, and deadly in the trenches
What we owe to a dull grey metal
The world's building block
Getting rid of dirt - and murder victims
Elementary Business
Why do we value gold?
A metal so light it floats on oil
Green, and deadly in the trenches
What we owe to a dull grey metal
The world's building block
Getting rid of dirt - and murder victims
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).
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.
No comments:
Post a Comment
Please leave a comment-- or suggestions, particularly of topics and places you'd like to see covered