Peas to Plastic

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Far from being just a summer treat however, the nutritious pea has long been a staple food of many cultures; from European peasants in the Middle ages far back into prehistory, where once in the ‘Spirit Cave’ on the border between Burma and Thailand, an ancient group of humans dropped a few peas on the ground in 9750 BC.

Archaeological evidence traces the spread of peas across the world, following human cultures through Turkey and Jordan to Afghanistan, India, Egypt, China and Switzerland. Peas have played witness to our burgeoning civilizations over millennia and yet the world in which they grow now is very different to the world of those wild peas scattered at the feet of ancient Burmese hunter-gatherers.

Through our civilization we have altered our world with chemicals and pollutants galore, taking our natural resources and changing our soils, seas and atmosphere and struggling to cope with our own increasing waste. Yet glimmers of hope are often found in the least likely places and with the advent of more environmentally minded technologies, peas are now providing a very different service to humanity in the form of the raw ingredient of biodegradable plastics!

Biodegradable plastics on the increase

Plastic pollution is a huge problem, from overflowing landfills and the greenhouse gases of the petrochemical industry to ‘mermaid’s tears’, tiny particles of broken-down plastic waste that are filling our seas and poisoning marine food chains. Biodegradable plastics provide a possible solution to this, derived from renewable sources such as vegetable oils and starches rather than petroleum. Bioplastics are not a new idea and the industrious Henry Ford developed a new method for manufacturing plastic car parts from soya beans, exhibiting a prototype in 1941 before WWII overshadowed this endeavor and the idea was shelved. Today, however, bioplastics popularity is on the up again, as scientists and engineers seek suitable alternatives to eco-unfriendly petroleum plastics. Packaging is popping up all over the place made of “compostable’ plastic and bioplastics are now used for everything from plastic cutlery and straws to carrier bags, carpet fibers and even mobile phone casings. Not all bioplastics are biodegradable but at least 50 per cent of the bioplastics market is dominated by biodegradable thermoplastic starch, derived from vegetables such as peas and corn.

How peas are turned into plastic

You might wonder how you turn a pea into a plastic bag but the process is actually so simple that it is possible to experiment with it at home.

Plastics are carbon-based polymers, made from long-chain molecules that repeat their structures over and over. We currently make them mostly from petroleum as this conveniently contains many of these long flexible molecules.

Peas come into the equation because starch is biopolymer created by the plants for storing their carbohydrates. This means along with other plants, they are a natural source of just the right kind of molecules. Pure starch possesses the characteristic of being able to absorb humidity from the atmosphere, a property utilized in creating plastics which will break down in weeks to months under the right conditions, rather than hundreds to thousands of years.

To extracted pea starch is added a flexibiliser such as sorbitol (found in fruit and seaweed) and a plasticizer such as glycerin (usually from animal fat) so the starch can be processed thermo-plastically. By varying the amounts of these additives, the characteristic of the material can be tailored to specific needs such as a flexible plastic wrapping or a stiff plastic cup.

Recent developments have shown pea starch being made into antimicrobial food wrappings and plastic film for bailing hay and silage on farms. This second product could revolutionize farms, reducing the build-up of plastic waste in the soil and the amount being sent to landfill; as although waterproof while intact, after use it can be ploughed into the soil. When cut up, it absorbs water and bacterial action degrades it into harmless humus-like mineral compounds. All this sounds wonderful, but there have been many concerns raised about whether all bioplastics are really less polluting than standard ones.

In producing plastic from peas, energy is still used in manufacture that currently largely comes from non-renewable fossil fuel sources and there are worries that the increased need for crops for plastic will increase deforestation. These are valid concerns unless sustainable farming practices and renewable energy sources are used.

However, biodegradable plastics like pea starch are plant-based so they sequester as much carbon during growth as they release when they break down, unlike petroleum plastics, closing the embodied CO2 loop neatly. They are also made from renewable sources of biomass, can be designed to break down in as little as a few weeks; and studies show that bioplastic production can represent an up to 42 per cent reduction in overall carbon footprint compared to standard plastic production.

It’s an imperfect new technology but on balance I say ‘give peas a chance’ and choose compostable packaging where you can. 

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