‘Next-best’ plastic alternatives have higher emissions – but what about bioplastics?

Substituting plastics with conventional alternatives is likely to cause increased greenhouse gas emissions, according to new research from the University of Sheffield.

The study, published earlier this week (8 April) in collaboration with the University of Cambridge and the KTH Royal Institute of Technology in Sweden, compared plastic products against alternatives in 16 applications. In 15, plastics resulted in lower emissions.

In each of the applications, from packaging and furniture to construction, automotive and textiles, the ‘next-best’ alternatives were considered – paper, aluminium, steel, glass, concrete, ductile iron, copper, fibreglass, wood, wool and cotton.

The life cycle assessments did not include compostable, biodegradable and reusable bioplastic alternatives however, which many hope could offer more sustainable ways of manufacturing packaging and other products. Excluded due to “small market values and a lack of reliable data about reuse”, the research team said that the newer alternatives could be included in future modelling.

The overall picture could change as more bioplastics mature, said Mark Dorris from Edinburgh seaweed cellulose firm Mercel, who was not involved in the new research. Emissions are a significant focus for teams working on new bioplastics, said Dorris, previously a senior research fellow and lecturer in materials science at Edinburgh Napier University.

“It has to be the most sustainable process possible, the lowest energy, zero waste,” he said to Professional Engineering. “Certainly bioplastics are in a position where we can challenge a lot of these different plastic areas, and it’ll tell a different story.”

His company’s seaweed cellulose product has a 98% reduction in carbon dioxide (CO₂) emissions during processing when compared to wood pulp cellulose, he said, because of how easy it is to extract it. The extracted cellulose is purer and easier to break down, he said, which massively reduces energy costs.

The sheer size and scale of the plastic industry plays a major part in making the materials more efficient, Dorris said, thanks to the vast amounts of money available in the petrochemical industry.

“If you had investments in any other industry, you could optimise these processes to reduce carbon emissions during the processing stages. Obviously carbon emissions are wholly dependent on scale,” he said.

Dorris questioned whether emissions are the main issue that people have with plastics. “I’m not sure it is,” he said. “People think about plastic in the oceans, the Blue Planet episode. What people think about is the persistent effect of plastics on the environment.”

The Sheffield researchers, led by Dr Fanran Meng, acknowledged the same issue. “Our research highlights the importance of using the life cycle assessment tool to better understand how plastics and their alternatives can affect the environment, but I would also like to stress the importance of not overlooking the impact of plastics on marine ecosystems and potential impacts on human and ecological health,” Dr Meng said.

“We need to consider all of these impacts when choosing which materials to use in products, to ensure we are using the right materials for the right purpose and to help us develop a sustainable plastics sector.”

Bioplastics and biodegradable plastics might not produce more CO₂ in general, said Dr Ulugbek Azimov, associate professor of mechanical engineering at Northumbria University, who was not involved in the research – although they might in some situations such as composting.

“During the decomposition process, bioplastic or biodegradable plastic will release CO₂, but that CO₂ will come out of the balance from when bioplastics are produced from plants, which take CO₂, and that CO₂ is again released to the atmosphere,” he said to Professional Engineering.  

Dr Azimov’s own team has developed a biopolymer material that can be used as a plastic alternative, but in that case the material can be turned directly into fertiliser, avoiding the composting process and CO₂ release. “During the conversion of material into fertiliser, we use hot water that can be produced using solar thermal, avoiding burning fuel to heat up the water.”

Optimising plastic use, extending product lifetimes, boosting recycling rates, and enhancing waste collection systems could offer ways of improving the sustainability of plastic products, the Sheffield researchers said.

They also highlighted the “crucial role” plastic packaging plays in preserving the quality of food across a wide range of categories, helping to prevent spoilage and the emissions it causes. “This essential function highlights the unmeasured environmental benefits of plastic packaging when compared to alternative materials,” they said.

The work was published in Environmental Science & Technology.

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