Polymer chemistry and the problem with plastics
by Professor Anthony J Ryan OBE, Director, Grantham Centre for Sustainable Futures
As Director of the Grantham Centre for Sustainable Futures, I hear a great deal about how bad plastics are for the environment. But I’m also coming at the challenges of a sustainable food-water-energy nexus from my perspective as a University of Sheffield Professor of Polymer Chemistry – that is, a researcher in plastics!
Polymer production accounts for less than three per cent of crude-oil consumption and less than one per cent of the global energy budget. Overall, there is a beneficial (ie, net negative) effect on global emissions due to polymers’ use in lightweight vehicles that have improved fuel consumption, thermal insulation that recues the need for heating and air conditioning, and sensible food packaging that cuts down on waste, to give but three examples.
Polymers have an important role to play in energy capture (photo-voltaics and wind turbines) and storage (batteries and water splitting) too. We're even using polyurethane foam as a synthetic soil in precision horticulture. So what we need to do is stop burning the fossil resource and maximise its beneficial use – in making plastics and other petrochemicals, and get our business leaders, policy makers and politicians to understand this.
The UN defines sustainability as “meeting the needs of the present without compromising the ability of future generations to meet their needs”. It’s a definition that has stood the test of time and comes from the 1987 Brundtland Report, Our Common Future, from the United Nations World Commission on Environment and Development. The United Nations Sustainable Development Goals provides another guide – in particular goal nine, “Build resilient infrastructure, promote inclusive and sustainable industrialization, and foster innovation”, and goal 12, “Ensure sustainable consumption and production patterns”. My discipline offers it’s own definition: according to the International Union of Pure and Applied Chemistry, green chemistry is “the invention, design and application of chemical products and processes to reduce or eliminate the use and the production of harmful substances”. With words such as these, we can start to see through the greenwash.
These definitions can also help us perceive environmental impacts differently. The waste charity WRAP did a life cycle analysis to show that an ‘bag for life’ made from hessian has to be used 140 times to be less energy intensive per use than taking a new polythene carrier bag each time. And, if you reuse the polythene bag then the effect is compounded. Yet green consumers prefer hessian and paper to ‘nasty’ plastics, even when the evidence tells them otherwise.
Are there similar attitudes behind the current emphasis on ‘sustainable’ (that is, renewable) polymers? The feedstocks for sustainable polymers could come from renewable resources, but the production of those resources should use less water and energy than the petrochemicals they replace. Current commercial ‘sustainable polymers’ may be made from plant starch or oils, or from agricultural waste streams that do not compete with food production. But we don’t know whether using a renewable feedstock to make a plastic might, in fact, result in much greater greenhouse gas emissions because of all of the processes involved.
A full life cycle analysis is needed to make the decisions about whether polymers are sustainable or not. Focusing on whether the feedstock is renewable isn’t enough. But who knows? Making polymers from CO2 and disposing of them into landfill, might turn out to be a great way to sequester carbon!