Creation of Green Plastics for a Circular Society

Plastics have become indispensable to our lives due to their excellent functionality, durability, and longevity, and are used in large quantities in all fields. However, they are chemically synthesized from fossil resources such as petroleum, which has led to problems like resource depletion and the generation of carbon dioxide from incineration. Furthermore, they are not easily broken down by microorganisms (biodegradation), and when discarded into the natural environment, they accumulate as scattered litter. Against this backdrop, there is an urgent need to create green plastics that reduce the total environmental impact from raw materials to manufacturing and disposal.

Green plastics are made from renewable resources (biomass) such as plants, manufactured through low-environmental-impact processes, can be returned to their raw materials after use through a simple operation (chemical recycling), and are biodegradable when discarded into the environment (Figure 1).

To create plastics that meet these requirements, we considered the use of enzymes. Enzymes, also known as biocatalysts, exist in all living organisms and are involved in specific biological reactions. Figure 2 shows the life cycle of green plastics using enzymes. We discovered that by applying enzymes to green plastics, they can be easily returned to their raw materials, and we have developed this for chemical recycling (yellow section in Figure 2). Such plastics are decomposed and broken down into smaller molecules by microorganisms in nature, ultimately becoming carbon dioxide and water. The carbon dioxide is then regenerated as plant biomass through photosynthesis (green section in Figure 2).

We are advancing our research toward practical application in the near future. As an example, Figure 3 shows a scheme for the synthesis and recycling of PBS, a type of green plastic, using enzymes. Once this is realized, plastics made from plant biomass will become widespread. These plastics can be recycled back to their raw materials any number of times, and if they become scattered litter, they can be buried in a garden, where they will eventually disappear and be reborn as plant biomass. Through the creation of green plastics using such biomass, we aim to contribute to the building of a circular society.

Figure 1

Figure 2

Figure 3