“Only we humans make waste that nature cannot digest.” These are the words of oceanographer Captain Charles Moore, who discovered the Great Pacific Garbage Patch in 1997. Of-course, he’s talking about plastic.
Most people reading this probably have something that made from plastic within their line of sight. This material is ubiquitous: we are now producing more than 300 million tons (272 metric tons) of plastic a year and roughly half that’s intended for single use, meaning that it’s discarded immediately after it’s served its purpose. This has led to a mounting problem of plastic-waste going to landfills and a few of this waste gets blown & makes its way into rivers & ultimately the sea. In fact, about 8 million tons (7.2 million metric tons) of plastic pollution enters the ocean per annum, where it entangles marine life, pollutes coral reefs & ultimately subjected to degradation by water, wind & sun, breaks apart into trillions of tiny microplastic pieces.
These particles of plastic look tons like food to several marine species, who then gorge on the pollution and end-up starving from lack of real nutrition. The surface of microplastics also attract pollutants within the ocean, and find yourself transporting these into the bodies of animals, with effects we’re still trying to understand. There is a possibility that microplastics might be harming humans, because we consume them via seafood & even in drinking water. In 2019, the World Health Organization (WHO) called more research into the potential impacts of microplastic pollution on our health.
Underpinning all this is often the very fact that, depending on the ingredients used to make it, plastic is incredibly resilient & might never truly biodegrade. Pair that with the volume of plastic pollution in our environment & that we have a clear problem. Most single-use plastics entering the ocean, as an example, will stay there for hundreds of years.
How did we create this crisis of persistent plastic? The solution lies in the process we use to form plastic itself. But first, it is vital to know that “plastic” is not just the shopping bags we picture floating in the ocean.
What is plastic?
“The term plastic often covers a much range of heterogeneous materials, each with differing applications that need very different physical properties,” said Carl Redshaw, a chemist at University of Hull in the United Kingdom & a participant in the university Plastics Collaboratory project, which conducts research to enhance the sustainability of the plastics industry. “In fact, more than 300 sorts of plastics are known,” said Redshaw.
So, if plastics are so different, what do they need in common? They’re made from polymers, which are molecules comprising many of repeating units, in formations that give plastics many of the desired qualities like flexibility, malleability & strength that they often share. Beyond that, plastics generally fall under one among two broad categories: bio-based plastics, in which polymers are derived from sources like cornstarch, vegetable fats & bacteria and so-called synthetic plastics, in which polymers are synthesized from crude oil & gas.
Despite the Earth friendly name, bio-based polymers don’t automatically have a good environmental track record, because they’ll also persist in the environment & not biodegrade. “Not all bio-based plastics are biodegradable polymers and not all biodegradable plastics are bio-based,” Redshaw explained. Nevertheless, oil & natural gas-derived materials comparably cause the starkest environmental harm, because plastics in this category tend to persist in the environment for longer, while causing other environmental impacts, too.
To understand why, we’re getting to look at an example of oil-derived plastic: take the milk bottle chilling in your fridge. This carton begins its life somewhere much more dramatic, deep in the bowels of the earth, as crude oil. This substance, pooling in high-pressure chambers within the earth’s crust, is drilled & pumped to the surface and carried through pipelines to grease refineries. Its dense sludge is formed from hydrocarbons, compounds made up of combinations of carbon & hydrogen atoms that form chains of varying lengths, giving them different properties. These hydrocarbons are the earliest raw materials of plastic, ready-made by the earth.
At the refinery, plastic production is actually-set in motion. Here, molasses-like crude oil is heated over a furnace that separates the hydrocarbons into different groups, based on the amounts of atoms they contain & their resulting relative molecular mass and then feeds them into a close-by distillation tube. Inside this tube, the longer, typically heavier hydrocarbons sink to the bottom, while the shorter, lighter ones rise to the top. The result’s that crude oil gets separated into several distinct groups of chemicals to be used like petroleum, gasoline & paraffin, each of which contains hydrocarbons of an identical weight & length. One among these groups is naphtha, a chemical which will become the primary feedstock for creating plastic.
Naphtha is like gold dust for plastic production, because 2 of the various hydrocarbons it contains are ethane & propene. These 2 compounds are crucial to the formation of the most commonly produced and ubiquitous plastic products on Earth, including the sort used for that milk carton. But to be made into something which will actually be used to build plastic, ethane & propene have to be broken down from their raw hydrocarbon state into smaller units.
There are various ways to do this. One method is to use high-heat & high-pressure in a zero-oxygen environment. This process, called “steam cracking“, breaks-down the hydrocarbons into shorter molecules called monomers.
“Monomers like ethylene from ethane, or propylene from propene, are often derived straight from naphtha after thermal cracking,” said Payal Baheti, a postdoctoral researcher at Aston University focusing on sustainable polymer materials. The simplified ethylene & propylene, finally, are the valuable ingredients needed to form plastic’s backbone.
This next-step unfolds through a process called polymerization, wherein those individual monomer ingredients are combined chemically in new arrangements to produce the long-repeating chains referred to as polymers. In this case, ethylene & propylene form polyethylene & polypropylene, the 2 commonest & widely produced polymers on Earth.
So, why are these 2 polymers so popular? Polyethylene’s makeup allows it to be used to make plastics of various densities, meaning it can flimsy & pliable or sturdy & tough, thus making its applications extremely diverse. Meanwhile, polypropylene’s configuration makes it particularly flexible & resilient. Consequently, we see these sorts of plastic every-day, predominantly in single-use items like the milk carton, not to mention plastic wrappers, straws, water bottles, shopping bags, shampoo containers, bottle caps, the list goes on.
Yet, these are just 2 sorts of synthetic plastics out of the many dozens more. Other sorts of hydrocarbons are isolated & broken down from different sources, not only from crude oil but also from natural gas and are used to make plastic, too. In some cases, polymers could be made from one monomer, repeated, as we see in polyethylene & polypropylene, or they could involve combinations of a couple of sorts of monomers.
What’s more, each of these polymer chains will then be processed a sort of ways & mixed with various additives, antioxidants, foaming agents, plasticizers, flame retardants, that equip them to fulfil the variety of niche functions that make plastics so versatile.
“Different plastics got to have different properties,” said Baheti. “Take the instance of food packaging, which should deter the passage of excess oxygen or sunlight, to avoid degradation, so it contains additives to form it so. “One could say it is the additives that provides a polymer its properties & results in the formation of a plastic.”
Now, let’s fast-forward through that production process once more. Plastic that’s synthesized from oil & natural gas is formed by isolating hydrocarbons, breaking them down into their component parts then reconstituting these parts into entirely new formations never before-seen in nature. Simply speaking, this creates an “alien“ material unfamiliar to microbes in Earth’s water & soil, Baheti explained. “The carbon backbone found in synthesized plastic isn’t recognized by soil’s bacteria, meaning they can’t digest and convert it into water & carbon dioxide.”
“The likes of polyethylene can-take centuries to decompose in landfill sites,” Redshaw said. “This means much of what has-been produced during our lifetime still remains in its near original form. And persistence is not the only issue: because it gradually breaks apart under the influence of sunshine, water & wind, oil & natural gas-derived plastic releases greenhouse emissions contained within, also as leaching the chemicals added during production back into the environment. The sheer volume of single-use plastic pollution, especially, combined with its persistence and an ongoing environmental impact which will last for hundreds of years, has created the environmental catastrophe we see today.
But there could a way-out of this mounting pile of trash. Redshaw believes biodegradable plastics, which are focus of research, might be one potential solution. To rehash, making biodegradable plastic doesn’t necessarily mean producing it from bio-based sources such as corn starch. More specifically, it entails making plastic from polymers which can be broken down reasonably efficiently by microbes in water & soil.
For this to have real planetary impact, biodegradable polymers would require to exchange the likes of oil-based polyethylene & polypropylene, but while also maintaining properties like strength & adaptability that make these conventional polymers, so desirable. That’s a tall order, made trickier by the very fact that conventional polymers remain competitively cheaper to create.
But a couple of biodegradable options are beginning to make headway. First type called polylactides, which are getting used to form single-use items like cups, cutlery & straws, that would biodegrade more effectively when they’re in the environment. These sorts of inventions are likely to increase as global pressure grows to form plastic more sustainable, Redshaw reckoned.
There are hints of optimism elsewhere. In 2016, researchers discovered plastic-eating bacteria and others have since identified polyethylene-munching worms. They’ve also found enzymes which will be engineered to interrupt-down plastic waste.
“Maybe, in the years ahead, we’ll learn from the bacteria & worms that possess the ability to broken-down & digest plastics, even stuff like polyethylene carrier bags and style large, artificial worms which will eat their way through our plastic waste, just like the giant maggots that featured in ‘Doctor Who‘ back in the ‘70s!” Redshaw said.
In any case, within the process of making plastic, humans have managed to require raw materials from nature & transform-them so thoroughly that nature not recognizes them. Our ingenuity is what got us in this mess, now, hopefully, it can get-us out.