Plastics

14/07/2017

We produce and consume them by the millions of tons, our societies depend on them, they are found everywhere and they will last for thousands of year.

I What are plastics?

To speak about plastics, we first need to introduce the concept of polymers. A polymer is a group of units called monomers, linked together by chemical bonds. Those monomers are small molecules (formed by atoms). A good example of a natural polymer is rubber: the sap from the hevea tree forms a polymer when exposed to oxygen from ambient air.

A plastic is a synthetic polymer mixture, molded, usually upon heat and pressure, in order to form an object. There are different types of plastics:

  • Thermoplastics, which melt when hot and solidify when cold in a reversible manner. They are mainly used for packaging (see detail of their uses by the Ellen MacArthur foundation below);
  • Thermosetting polymers, where this transformation is irreversible. Textures and uses vary, from foams used in mattresses to thermal insulating materials used in kitchenware (pan handle, etc.);
  • Elastomers, that can deform under physical constraints and go back to their initial shape: typically latex (disposable gloves) and rubber (tires, etc.).

Plastics are part of our daily life: they are everywhere, in our houses, furnitures, electronics, sport gear… In particular, thermoplastics account for about 85% of today’s total plastic production.

Most of the plastics is used from packaging, which represent about 40% of all plastic production.

Source: Plastics Europe

II The plastic problem

Why and how did plastic become a problem?

Synthetic polymers were developed from the middle 19th century, initially to replace natural rubber used to make tyres. Since then, the industrialisation of plastic production has deeply transformed the global economy and people’s lifestyle all around the world.
Plastics are cheap and light: on average, they weigh about a quarter of the weight of any other material used for manufacture, such as wood, glass, paper, and most metals. Therefore, using plastics enables to manufacture cheap, light and easy to transport consumables. Paradoxically, their use reduce the environmental impact of goods transportation. Lastly, plastics are durable, as they are neither biodegradable nor corrodible.
Plastics quickly grew to become essential to the day-to-day functioning of our modern societies, finding their way into packaging and daily items of all size and type. Nevertheless, their low cost is a double edged sword, as it enabled the generalisation of disposable products and the emergence of the “throw-away” society, where convenience replace durability – especially in people’s mind. As a consequence, the amount of generated plastic waste reaches the hundreds of millions of tons annually.

Manufacturing: polluting and energy consuming

Considering the amounts produced, plastics start to be problematic from manufacturing. The main raw materials for making plastics is naphtha, obtained from refining raw petrol, a non-renewable fossil resource. Raw petrol is a mixture of liquid hydrocarbons, which are separated by distillation. To do so, the mixture is heated to 400°C in a column where it boils, each component evaporating and the vapour reaching a height depending on its composition – the lighter the component, the higher it goes – and where it is then collected.

Naphthas obtained from this process are a mixture themselves. They are then cracked (heated at 800°C and abruptly cooled down, which “breaks” their compounds in smaller molecules), polymerised and shaped. All those steps are significantly energy-consuming.

Stunning, ever-increasing quantities

To meet our needs, the global production in plastics is constantly increasing : from 250 million tons (MT) in 2009 to 322 MT in 2015; we thus produce about 55 times the mass of the Great Pyramid of Giza in plastics each year. Europe accounts for about 20% of the total.

Source : Plastics Europe

Ocean pollution: 15% of plastic waste end up contaminating natural sites

In 2010, it was estimated that 32 MT of plastic were badly managed globally, which means this fraction is neither buried, nor incinerated, nor recycled. 20% of these misplaced wastes end up in the ocean – that is 8 MT. Ocean pollution keeps increasing every year, impacting marine life, tourism and fishing. According to the United Nations (UN), this pollutions costs 13 billion dollars every year.
Plastic is durable. Its degradation is slow and the average lifespan of a single water bottle in the ocean is about 400 years. Furthermore, it is light and can easily travel for miles on end, lead by wind and marine current. Plastic debris that were brought to sea during the march 2011 Japanese tsunami have reached the north-american west coast less than a year later.
However only 1% of ocean plastic waste is visible. As it breaks down, it makes “micro-plastics”, a fraction that is too small to be seen, actually composes most of the marine pollution. These micrometric particles were first observed along the British coasts in 2004, as reported in Science. Since then, they were found everywhere: a recent study published in Nature indicated their presence in most commercial table salts. They are found up to the Antarctic ice and are ingested by plankton, thus reaching the food chain.
Algaes and bacterial colonies have been observed growing on those surfaces, which are just recently introduced in the marine world. These observations lead the scientific community to start wondering about the following points:
  • Further to visible damages (hurt or dead animals), what is the impact of ingesting micro-plastic on marine animals and their ecosystems?
  • Is ingesting those plastics — through consuming fish and seafood — toxic for humans?
  • Considering their durability and ease to travel, can these particles be a new vector for pathogen propagation between continents?

What are the solutions to limit pollution?

There are currently three principal types of initiatives aiming at reducing plastic pollution:

– Government initiatives regulating packaging plastic usage, for example:

– Recovery can be either material (recycling), energetic (incineration) or chemical (depolymerisation).

– Producing biodegradable alternatives to usual plastics or environmental friendly packaging.

Read the next article: plastic waste recovery.

This work is under CC-BY SA licence: