Plastic, once a nuisance, can now be used as fertilizer! What is the earth-friendly plastic developed by a research team of Chiba University and others? | FRIDAY DIGITAL

Plastic, once a nuisance, can now be used as fertilizer! What is the earth-friendly plastic developed by a research team of Chiba University and others?

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Will a new plastic material from Japan change the world?

Plastic waste is thrown away in large quantities every day. Although there are calls for recycling, many plastics cannot be broken down, and progress is slow. The recycling rate is said to be less than 10%.

The team of Dr. Daisuke Aoki, Associate Professor of the Graduate School of Engineering, Chiba University, has created a plastic that breaks through this status quo.

On May 29, a meeting was held at UNESCO’s Paris headquarters to discuss an international convention to combat plastic pollution. In this photo, a child sits in a canoe loaded with empty plastic bottles collected for recycling in Nigeria (PHOTO: AFRO).

Dr. Aoki and his colleagues have created a plant-derived plastic that, when decomposed in ammonia water, produces urea, a fertilizer that promotes plant growth.

When the plant-derived polycarbonate developed this time is decomposed in ammonia water, the molecules that make up the plastic break apart and are separated into urea and other molecules (monomers). If the monomers are decomposed by microorganisms, they are not harmful even if they are spread on fields, so they can be spread on fields as is.

Recently, plastic bags and other plastic products are made from biomass plastic, which is a plastic made from plant-derived materials. Can this also be used as fertilizer?

Dr. Aoki replied, “Just because something is derived from plants does not mean that it can be used as a fertilizer. We have found that isosorbide, a compound derived from glucose, the most abundant monosaccharide found in nature and abundant in fruits and grains, can be used as a fertilizer when combined with urea.

Plants grown with fertilizer (urea) extracted from degraded plastic. Urea has long been used in agriculture as a chemical fertilizer.

Polycarbonate, which is “derived from petroleum,” can also be used as fertilizer, and plastic can be made again.

Plastic can be used as fertilizer! It would be wonderful if it were possible, but it would take a lot of time and money to make new plastic. However, the company’s president, Mr. Kato, is not so optimistic,

However, there are plastics that can be used as fertilizer.

That is polycarbonate, which is derived from petroleum.

There are various types of plastics, and polyethylene is the most commonly used. In 2008, a whopping 2.9 million tons of polyethylene was produced per year, accounting for 35.3% of all plastics. Polypropylene was next, at 1.9 million tons, accounting for 23.1% of the total. Polystyrenes and vinyl chlorides were next, followed by PET bottles and polycarbonates. Unfortunately, polycarbonate accounts for only 2 to 3% of the total.

Most of the polycarbonate used today is made from petroleum,

Even petroleum-derived polycarbonate can be broken down into urea and monomers when decomposed in ammonia water.

In fact, Dr. Aoki’s research team is already conducting research on growing edible vegetables using urea extracted from broken down polycarbonate as fertilizer.

However, since polycarbonate is made from petroleum, the monomer is petroleum. The monomer that breaks down the polycarbonate cannot be spread directly on the fields.

Instead, the monomer can be used again as material for plastic.”

Currently, plastic waste is used as recycled plastic in some cases, but the quality of the plastic deteriorates when it is recycled. However, if they can be broken down to the molecular level and made again, they can provide a completely new product with guaranteed quality.

When plant-derived plastics are decomposed in ammonia water, they are converted into urea and monomers. Since the monomer is also plant-based, it is not harmful even if it is spread on fields. The monomer can also be reused to make plastic (Source: Japan Science and Technology Agency).

Research is underway to convert all plastics to polycarbonate.

Polyethylene and polypropylene, which together account for more than 50% of all plastics, are cheap to make and strong, but they cannot be broken down. If that is the case, why don’t we just use polycarbonate for all plastics?

Polycarbonate is an engineering plastic used mainly in industrial applications, such as the plastic parts of water servers and copiers, helmets, and bullet train windows. Polycarbonate is an engineering plastic used mainly in industrial applications, such as water servers, plastic parts of copiers, helmets, and bullet train windows. It is also susceptible to surface scratching and cracking when made thin, making it difficult to replace all plastics with polycarbonate at this stage.

Even if it is not possible to replace all plastics with polycarbonate right now, the gradual replacement of acrylic panels, air conditioners, washing machines, and other plastic parts with polycarbonate, and the increase in production volume, may accelerate polycarbonate recycling.

We are now trying to make petroleum-derived polycarbonate, which can be used in a variety of applications, from soft to hard, in parallel with our research on plant-derived polycarbonate,” said Dr. Kohara. Our goal is to make all plastics into polycarbonate that can be degraded into fertilizer in the near future.”

With the enactment of the Plastic Resources Recycling Law in 2010, there are calls for the recycling of plastic resources. Plastics that return to the soil or decompose in seawater have already been developed, but it takes time for them to return to nature and they cannot be reused.

On the other hand, the plant-derived polycarbonate and petroleum-derived polycarbonate developed by Dr. Aoki and his colleagues can be quickly decomposed in ammonia water, and the monomer can be used to make plastic again.

If we are talking about resource recycling, why don’t we start by using polycarbonate for all the plastic parts used in home appliances?

Dr. Aoki during an experiment. He says it is not a “dream” but a “goal” to develop various types of polycarbonate and to make all plastics from polycarbonate.

Daisuke A oki Associate Professor, Graduate School of Engineering, Chiba University. Formerly at the Graduate School of Science and Engineering, Tokyo Institute of Technology, and the School of Physical Engineering, Tokyo Institute of Technology, before assuming his current position. Specializes in plastics (polymers). He has teamed up with Tohoku University, Yamagata University, University of Tokyo, Osaka Public University, Kobe University, and others to conduct research on the “synthesis,” “functionalization,” “evaluation of physical properties,” and “degradation” of polycarbonate, as well as the “separation” of degradation products and their use as fertilizer.

  • Interview and text by Izumi Nakagawa

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