Breathing new life into old materials – using waste plastic to create high-value products
The problem of plastic in our environment is one that has gained national attention. It's hard to ignore it with provocative images of our discarded plastic affecting marine life, and the widely used statistic that at current rates of pollution, there will be more plastic in the ocean than fish by 2050. The solution to this problem, however, is multifaceted.
It is overly simple to seek to eradicate plastics from our society – they help us to lead happy and healthy lives and have many advantages over competitor materials that include lightweighting, low-cost and low-energy usage to create and recycle them. Try to imagine a world without plastics: there would be no mobile phones, many medical treatments would be drastically different and our overall energy consumption would go up as a result of them being replaced by heavier materials such as metals or glass. Instead, we must be more responsible with our use, collection and post-life treatment of this resource.
Incredibly, more than 40 years after the launch of the recycling symbol, only five per cent of the estimated 8,300 million metric tonnes of synthetic and semi-synthetic organic polymers (plastics) that have been produced to date, are recycled. Typically, this results in secondary products due to contamination in the plastic from previous contents and additives. This leads to a lower-value product that is at best discoloured, and at worst does not perform as well as the virgin plastic. The rest are either poured into landfill, burned to produce CO2 and other harmful greenhouse gasses or worse, released into the environment. While most plastics are for single-use application and their intended useful life is typically less than one year, we require them to be hardy in order to provide shelf life and perform their role. Imagine a bottle of shampoo that would degrade in the shower! As such, without an external stimulus with which to depolymerise them, plastics persist for decades – or even centuries – in the environment. This presents the central paradox of the plastic problem: our desire to have plastic perform a specific role that cannot be reconciled with our desire for disposability.
While a government can legislate within its own borders and lobby others to encourage and reward more responsible use and put processes in place to more adequately collect plastic, global change can only be brought about by advancements in technology to provide solutions of how to deal with waste plastic at the end of its useful lifetime.
An ideal solution would economically incentivise plastic collection to produce chemicals and materials that have a higher intrinsic value than the polymer itself. One area of interest is the so-called circular economy (see chart) in which plastics are depolymerised to the building blocks from which they were initially made. While this recycles old plastic to new virgin material and has significant promise, current chemical recycling processes are highly costly, largely unselective and often provide an energetically unfavourable method to produce low-value monomers at high cost.
While further development will lead to improvements in this area to make it economically viable, instead, we could consider discarded plastic (both in bulk as in the form of microplastics) as a raw material to produce high-value molecules and materials. In this ‘added value plastic economy’ (see figure) chemical upcycling of this waste will create high-value materials. Such a solution could incentivise recycling and even provide an economic justification for the recovery of the plastic from our environment. Innovations in this area will in turn deliver new solutions to high-value problems in energy (ie, plastic electronics), pharmaceuticals (ie, synthons for drugs), composites (ie, lightweighting) and health care (ie, biomaterials) that could further transform and revolutionise our society.
School of Chemistry, University of Birmingham