Scientists turn bioplastic into fertilizer

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Single-use plastics are a major environmental problem, polluting everything from the Mariana Trench to Mount Everest.


Because only 14% of plastics are actually recycled, many experts and advocates argue that the solution to the problem is to create a circular system in which plastics are reused instead of being thrown away. To this end, a Tokyo-based research team has developed a way to convert bio-based plastics into fertilizer. But they say their findings have even wider implications for plastic reuse.

“We are convinced that our work represents an important step towards the development of sustainable and recyclable polymeric materials in the near future,” said study co-author and assistant professor at Tokyo Institute of Technology Daisuke Aoki. , in a press release. “The era of ‘plastic bread’ is fast approaching.”

The research, published Thursday in Green Chemistry, focused on bio-based poly (isosorbide carbonate) plastic (PIC).

Bio-based plastics are plastics made from biomass that have been proposed as a more sustainable alternative to petroleum-based plastics. PIC in particular is made from a monomer called isosorbide (ISB), a non-toxic byproduct of glucose. ISB can be made into fertilizer through a process called ammonolysis: Ammonia is used to separate the carbon connecting ISB monomers. This creates urea, which is a substance rich in nitrogen that makes a popular fertilizer.

While scientists have long known about ammonolysis, researchers sought to complete the reaction using as little energy and as few organic solvents as possible. First, they tried the reaction in water at 30 degrees Celsius at atmospheric pressure. They were able to create urea, but the reaction was not complete within 24 hours and the ICP did not completely degrade. However, they found that increasing the temperature of the water to 90 degrees Celsius resulted in a complete reaction within six hours.

“The reaction proceeds without any catalyst, demonstrating that ammonolysis of PIC can be easily accomplished using ammonia and heating,” Aoki said in the press release. “Thus, this procedure is operationally simple and environmentally friendly from a chemical recycling point of view.”

Tokyo Institute of Technology

The Tokyo-based team is not the first to turn plastics into fertilizer. Startup Neptune Plastic developed a plastic from food grade material that could be composted in a vegetable garden, as Forbes reported at the time.

However, there is debate as to whether bio-based plastics are truly an environmentally friendly solution to the plastic pollution crisis. On the one hand, they do not always biodegrade as quickly as advertised. A UN report concluded that they decomposed too slowly in the ocean to be a meaningful alternative.

Circular solutions like the one proposed by the Aoki team would of course solve this problem. However, there are still concerns that the growth of biomass for biobased plastics could contribute to climate and biodiversity crises by occupying valuable land that could be used for carbon storage or habitat.

“To meet the need for land to replace plastics used for packaging around the world, 61 million ha [hectares] would be needed to plant biobased plastic raw materials, an area larger than France, ”wrote the authors of a recent study on climate change and plastic pollution.

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