Ambitious roadmap for circular carbon plastics economy

Researchers from the Oxford Martin Programme on the Future of Plastics, University of Oxford, have outlined ambitious targets to help deliver a sustainable and net zero plastic economy. In a paper published in Nature, the authors argue for a rethinking of the technical, economic, and policy paradigms that have entrenched the status-quo, one of rising carbon emissions and uncontrolled pollution.

Currently the global plastics system results in over 1 gigatonnes per annum (Gt/annum) of carbon dioxide equivalent emissions which is the same as the total combined emissions of Europe's three largest economies (UK, Germany and France). If left unchecked, these emissions could rise to 4-5 Gt/annum with other sources of pollution also causing concern.

Another problem is the lack of effective recycling -- in 2019, only 9% of the world's plastic waste was turned into new products through mechanical recycling.

The majority ended up in landfills or was incinerated, and a significant proportion was mismanaged, ending up polluting terrestrial and marine ecosystems.

The authors analyse the current and future global plastics system, proposing technical, legal, and economic interventions from now until 2050 to allow it to transition to net zero emissions and to reduce other negative environmental impacts.

The study includes a future scenario centred on four targets:

• Reducing future plastics demand by one half, substituting and eliminating over-use of plastic materials and products.
• Changing the way plastics are manufactured to replace fossil fuels as the hydrocarbon source to use only renewably raw materials, including waste biomass and carbon dioxide.
• For plastics which are recoverable, maximising recycling very significantly, targeting 95% recycling of those materials which are retrievable from wastes.
• Integrating plastic manufacturing and recycling with renewable power and minimising all other negative environmental impacts, including of additives.

The authors emphasise the need for concerted action across all four target areas to ensure the global plastics systems curbs its climate impacts and meets UN Sustainable Development Goals.

Charlotte Williams, Professor of Chemistry at the University of Oxford's Department of Chemistry and lead author said:

'We need plastics and polymers, including for future low emission technologies like electric vehicles, wind turbines, and for many essential everyday materials.

Our current global plastics system is completely unsustainable, and we need to be implementing these series of very bold measures at scale, and fast.

This is a solvable problem but it needs coherent and combined action, particularly from chemical manufacturers.'

To successfully transition the plastics system, the authors set out principles to ensure 'smart materials design' and differentiate between plastics which are recoverable and irretrievable after use, noting that there is not a one size fits all solution.

Rather, the authors propose careful use of the design principles to help select the optimum production methods and appropriate use of resources, deliver the required performances, ensure waste management, and minimise broader environmental impacts.

A timeline of technical-economic-policy and legal interventions helps readers focus on the actions needed to reach net zero emissions by 2050.

'The time for action has arrived, we cannot afford to wait any longer,' study co-author Fernando Vidal, Postdoctoral Researcher in Chemistry at POLYMAT in Spain and former Oxford Martin School Fellow on the Future of Plastics concluded.

'We must change our concepts around the way we make, use, and dispose of plastics, otherwise we risk perpetuating this problem.

The upcoming UN Global Plastic Treaty is the opportunity to make a lasting change in the right direction.'

Study co-author Cameron Hepburn, Battcock Professor of Environmental Economics at the Oxford's Smith School of Enterprise and the Environment, said: 'The problem is that plastics, while contributing hugely to global pollution and greenhouse gas emissions, are extraordinarily useful.

Our research finds that creating a circular economy for plastics in order to reduce their negative impacts is possible, but only if we can reduce future demand by half, switch to renewable plastics that aren't made from fossil fuels, recycle 95% of what's left, and minimise environmental impacts at every step of the process.

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Building on CO2

The construction industry as a CO2 sink? Researchers at Empa's Concrete & Asphalt lab are working on this. By incorporating biochar into concrete, they are exploring the potential of CO2-neutral or even CO2-negative concrete. For optimal applicability, they process the biochar into pellets and use them to replace conventional aggregates.

To achieve the goal of a climate-neutral Switzerland by 2050, strategies and processes with a negative CO2 balance are necessary.

These so-called negative emission technologies (NET) are intended to counterbalane the remaining "hard-to-avoid" emissions in 2050 and should help ensure that we eventually achieve net zero.

As one of the main emitters, the construction sector has a particular obligation.

Around eight percent of global greenhouse gas emissions are caused by cement production.

At the same time, initial efforts are emerging to use the construction sector, with its massive consumption of resources, as a possible carbon sink.

What sounds paradoxical will succeed if we start "building with CO2" -- or rather, using carbon to produce building materials and thus removing it from the atmosphere in the long term.

For such visions to become reality, a great deal of research is needed -- such as is currently being done at Empa's Concrete & Asphalt lab.

A team led by Pietro Lura is developing a process for integrating biochar into concrete.

Difficulties due to porosity

Biochar is produced by a pyrolytic carbonization process of biomass in the absence of oxygen and consists to a high extent of pure carbon -- the carbon that the plants have extracted from the atmosphere in the form of CO2 as they grow.

While CO2 is emitted when plants are burned, it remains bound in the biochar over the long term.

The first concrete products with integrated biochar are already on the market.

However, biochar is often introduced into the concrete untreated, which can lead to difficulties.

"Biochar is very porous and therefore not only absorbs a lot of water, but also expensive admixtures used in concrete production," explains Empa researcher Mateusz Wyrzykowski.

"Moreover, it is difficult to handle and not completely harmless either." The fine coal dust is problematic for the respiratory tract and carries a certain risk of explosion.

For these reasons, the researchers propose in a paper that has just published in the Journal of Cleaner Production processing the biochar into pellets.

"Such lightweight aggregates already exist from other materials such as expanded clay or fly ash. The knowhow in handling these materials is available in industry, and this increases the chances that the concept will be put into practice," says Wyrzykowski.

Net zero at 20 percent share

To produce the pellets, the team used a concrete mixer with a rotating pan in which they mixed the biochar with water and cement and, as a result of the rotation, obtained small pellets with a diameter of between 4 and 32 millimeters.

In turn, they used these pellets to produce normal concrete of strength classes C20/25 to C30/37 -- the classes that are most widely used in civil engineering today.

"With a proportion of 20 percent by volume of carbon pellets in the concrete, we achieve net zero emissions," says Mateusz Wyrzykowski.

That is, the amount of carbon stored offsets all the emissions produced in the production of both the pellets and the concrete.

While the limit has probably not yet been reached for normal concrete (density between 2,000 and 2,600 kg/m3) with 20 percent by volume, the negative emission potential is particularly striking for lightweight concrete (density approx.

1,800 kg/m3): An admixture of 45 percent by volume of carbon pellets in the concrete leads to total negative emissions of minus 290 kg CO2/m3. By comparison, conventional concrete emits around 200 kg CO2/m3.

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