Plastics have taken the world by storm over the past century, finding applications in virtually every aspect of our lives. However, the rise of these synthetic polymers, which form the basis of plastics, has contributed to many serious environmental problems. The worst of them is the excessive use of petrochemicals and the disposal of non-biodegradable materials without recycling; only 14% of all plastic waste is recycled, which hardly solves the problem.

To solve the plastic conundrum, we need to develop “circular” systems, in which the raw materials used to produce the plastics come full circle after disposal and recycling. At the Tokyo Institute of Technology, a team of scientists led by Assistant Professor Daisuke Aoki and Professor Hideyuki Otsuka is pioneer of a new concept. In their new environmentally friendly process, plastics produced from biomass (bioplastics) are chemically recycled into fertilizers. This study is published in Green chemistry, a journal of the Royal Society of Chemistry focused on innovative research into sustainable and environmentally friendly technologies.

The team focused on poly (isosorbide carbonate), or “PIC,” a type of bio-based polycarbonate that has received a lot of attention as an alternative to petroleum-based polycarbonates. PIC is produced using a non-toxic material derived from glucose called isosorbide (ISB) as a monomer. The interesting part is that the carbonate bonds that join the ISB units can be cut using ammonia (NH₃) in a process called “ammonolysis”. The process produces urea, a nitrogen-rich molecule that is widely used as a fertilizer. While this chemical reaction was no secret to science, few studies of polymer degradation have focused on the potential uses of all degradation products instead of just monomers.

First of all, the scientists investigated to what extent the complete ammonolysis of PIC could be carried out in water under mild conditions (30 ° C and atmospheric pressure). The rationale for this decision was to avoid the use of organic solvents and excessive amounts of energy. The team carefully analyzed all reaction products by various means, including nuclear magnetic resonance spectroscopy, Fourier transform infrared spectroscopy, and gel permeation chromatography.

Although they were successful in producing urea in this way, the degradation of PIC was not complete even after 24 hours, with many derivatives of ISB still present. Therefore, the researchers tried to increase the temperature and found that complete degradation could be achieved in about six hours at 90 ° C. Aoki highlights the advantages of this approach: “The reaction proceeds without any catalyst, demonstrating that ammonolysis of PIC can be easily carried out using ammonia and heating. Thus, this procedure is operationally simple and environmentally friendly from the point of view of chemical recycling.

Finally, as a proof of concept that all degradation products of PIC can be directly used as fertilizer, the team conducted plant growth experiments with Arabidopsis thaliana, a model organization. They found that plants treated with all of the degradation products of PIC grew better than plants treated with urea alone.

The overall results of this study show the feasibility of developing plastic-based fertilizer systems. Systems can not only help tackle pollution and resource depletion, but also help meet the world’s growing demand for food. Aoki concludes on a positive note: “We are convinced that our work represents an important step towards the development of sustainable and recyclable polymer materials in the near future. The era of “plastic bread” is fast approaching!

– This press release was originally posted on the Tokyo Institute of Technology website