New Way to Chemically Recycles Bioplastics into Nitrogen-rich Fertilizers
Scientists from Tokyo Institute of Technology (Tokyo Tech) have demonstrated an environmentally friendly and facile way to into nitrogen-rich fertilizers. Their findings pave the way towards sustainable circular systems that simultaneously address issues such as plastic pollution, petrochemical resource depletion, and world hunger.
Poly (Isosorbide Carbonate) and Its Ammonolysis
The team focused on poly (isosorbide carbonate), or "PIC," a type of polycarbonate that has garnered much attention as an alternative to . PIC is produced using a non-toxic material derived from glucose called isosorbide (ISB) as a monomer. The interesting part is that the carbonate links that join the ISB units can be severed using ammonia (NH3) in a process known as ‘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 on polymer degradation have focused on the potential uses of all the degradation products instead of only the monomers.
First, the scientists investigated how well the complete ammonolysis of PIC could be conducted in water at mild conditions (30°C and atmospheric pressure). The rationale behind this decision was to avoid the use of organic solvents and excessive amounts of energy. The team carefully analyzed all the reaction products through various means, including nuclear magnetic resonance spectroscopy, the Fourier transform infrared spectroscopy, and gel permeation chromatography.
Although they managed to produce urea in this way, the degradation of PIC was not complete even after 24 hours, with many ISB derivatives still present. Therefore, the researchers tried increasing the temperature and found that complete degradation could be achieved in about six hours at 90°C! Assistant Professor Daisuke Aoki, Tokyo Tech, highlights the benefits of this approach, "The reaction occurs without any catalyst, demonstrating that the ammonolysis of PIC can be easily performed using aqueous ammonia and heating. Thus, this procedure is operationally simple and environmentally friendly from the viewpoint of chemical recycling."
Finally, as a proof-of-concept that all PIC degradation products can be directly used as a fertilizer, the team conducted plant growth experiments with Arabidopsis thaliana, a model organism. They found that plants treated with all PIC degradation products grew better than plants treated with just urea.
The overall results of this study showcase the feasibility of developing fertilizer-from-plastics systems. The systems can not only help fight off pollution and resource depletion but also contribute to meeting the world’s increasing food demands. Dr. Aoki concludes on a high note, "We are convinced that our work represents a milestone toward developing sustainable and recyclable polymer materials in the near future. The era of ‘bread from plastics’ is just around the corner!"
Source: Tokyo Institute of Technology
» Publication Date: 01/11/2021