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‹ The Weekly Green

Plastic Matters

December 8, 2015

The woplasticrd ‘plastic’ comes from a Greek word meaning ‘malleable’. In that sense, the use of natural plastics goes back more than 3500 years, when the Meso-Americans shaped rubber into game balls and other objects.

The first man-made plastic was invented in 1856 by the Englishman Alexander Parks. It was chiefly used to make artificial ivory.

The first truly synthetic plastic was invented by Leo Baekeland in 1907 and named after him as ‘bakelite’. It was Leo who introduced the term ‘plastic’ for such materials.

There are two basic kinds of plastic, thermoplastics and thermosetting plastics. Thermoplastics can be remelted and reshaped but thermosetting plastics cannot, because the temperature at which they crack up is lower than their melting point. Most of the plastic in your recycling bin are thermoplastics, but the vulcanized rubber of your car tires is not.

Plastics are polymers, meaning that their molecules are made up of long chains of repeating subunits. Wool and cotton are polymers too, as is cellulose, and so is DNA. Like DNA, plastics are built around a backbone consisting of carbon rings.

Polymer molecules are gigantic, which is one reason why they are indigestible to most creatures, the other being that they are not water-soluble.

The carbon rings of the backbone can bind readily to other elements. It is these added ingredients which give particular types of plastic their unique properties. These ingredients may over time leach out of the chemical structure. That produces the peculiar smell of a new car, for instance. Unleashed from their carbon collar, some of these substances are quite toxic.

It would seem that recycling thermoplastics should be easy – just melt them, recast them in whatever shape and presto. But of course, it is not that easy, because not all thermoplastics get along well when melted together. So they have to be separated by chemical affinity, which is why there is the Plastic Identification Code, those numbers on the bottom of the package with the chasing arrows around it.

A higher PIC number does not mean that the plastic is harder to recycle, only that it requires a different process from the others and that is were the bottle neck is, because recycling companies are disinclined to invest in all the different types of equipment needed for each of them.

Thermosetting plastics can only be recycled by crumbling them up and using them as a filler material, which can be used in, for instance, black top. Roads coated with such materials promise to be less prone to weathering, which is to say: potholes. So that is a good thing.

There are certain fungi and microbes whose digestive system can deal with plastic. There is a fungus in Ecuador which can reduce the mass of a plastic bag by 40% in just three months. The majority of these critters originate from rain forests, by the way, which is just another good reason to do all we can to preserve those.

Although plastics are a serious pollutant, they also work in favor of the environment because of their relative lightness. When they replaced metal in the bodies of automobiles, fuel-efficiency was increased significantly. Replacing glass with plastic for packaging, in particular for liquids, made for less energy consumption in transportation.

So it is not entirely fair to cast plastic as an environmental villain. Quite the contrary, it can be a great asset in attaining sustainability.


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