Plastic is all around us. Over the course of the 20th century it has become one of the most commonly used materials for all manner of goods and appliances. It is estimated that 288 million tons of plastic were produced in 2012 [1]. But plastic is made from oil, the same non-renewable crude oil resource that we burn to fuel cars and generators.

The world uses around 80 million barrels of crude oil a day [2]. It is only a matter of time before we exhaust the world’s supply of readily accessible oil, and with demand increasing all the time this may not be far away. This raises the alarming question of what happens when we do run out of oil. There are sustainable alternatives to oil when it comes to generating electricity and fuelling our cars, but is there a sustainable way to make plastic?

Fortunately the answer is yes.



Plasticity

Plastic isn’t just one material but a whole family of materials, all of which have different properties and are used for different purpose. Plasticity is actually the property of being easily shaped and moulded, which plastics share with a number of other materials. What we think of as “Plastics” are actually defined as “synthetic organic polymers”, so what does that mean, and what are the implications for sustainably sourcing this material?

Being synthetic means that plastics do not generally occur in nature. Plastics have to be manufactured using energy intensive processes. This means that plastic will never be a massively environmentally friendly material, even if we can replace crude oil with another source material.



Polymers

A polymer is a large molecule composed of very long chains of repeating subunits. Most of these units have a backbone of carbon atoms, with groups of other atoms hanging from it. The fact that these polymers are primarily composed of carbon is what makes them “organic”. This means that plastics will always be organic molecules, regardless of whether they are derived from fossil oil, or other sources. This is good, because carbon is a resource which we have in abundance.



Carbon as a feedstock

It is thus possible to substitute renewable feedstocks for the fossil oil usually used to make plastics. This works in much the same way that biofuels are derived from recently grown biomass, rather than fossil fuels. These feedstocks don’t have to be purpose grown. Waste from agriculture and wood preparation can be recycled as a feedstock for plastic manufacture. This has major advantages over setting aside arable land which could otherwise be used for food [3].



Methane to plastic

There are also processes which can extract carbon from the atmosphere to produce the polymers which form the building blocks of plastic material. “AirCarbon” is a material manufactured by Newlight Technologies [2]. They capture methane (CH4) from the atmosphere and use a catalyst to extract the carbon atoms, which can then be assembled into polymers for use in the manufacture of plastic. Newlight point out that this technology is effectively carbon negative, as they are trapping a dangerous greenhouse gas in order to manufacture their product. Methane results in a 21 times stronger greenhouse effect than carbon dioxide (CO 2 ).



Carbon dioxide to plastic

Other groups are working on methods to trap CO 2 as a source material for plastic. It can be reacted with compounds derived from agricultural waste, and heated to very high temperatures in order to create organic polymers. The result is polyethylene furandicarboxylate (PEF), an alternative to the polyethylene terephthalate (PET) which is used to manufacture bottles and synthetic fibres [4].

Even substituting a small fraction of alternate feedstocks into our plastic manufacturing process has the potential to massively reduce annual oil usage, so sustainable plastic is a field which will hopefully continue to grow.

References

Image Credit: Tony Alter via Flickr

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