From Science & Research
From Science & Research By: Takumi Abe, Rikito Takashima, Hideyuki Otsuka, Daisuke Aoki Department of Chemical Science and Engineering, Tokyo Institute of Technology Takehiro Kamiya The Laboratory of Plant Nutrition and Fertilizers, Graduate School of Agricultural and Life Sciences, The University of Tokyo Choon Pin Foong, Keiji Numata Department of Material Chemistry, Graduate School of Engineering, Kyoto University B ioplastics can be chemically recycled into nitrogenrich fertilizers in a facile and environmentally friendly way, as recently demonstrated by scientists from the Tokyo Institute of Technology (Tokyo Tech). Their findings pave the way towards sustainable circular systems that simultaneously address issues such as plastic pollution, petrochemical resource depletion, and world hunger. To solve the plastic conundrum, circular systems need to be developed, in which the source 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 Daisuke Aoki and Hideyuki Otsuka is pioneering a novel concept. In their new environmentally friendly process, plastics produced using biomass are chemically recycled back into fertilizers. This study was published in Green Chemistry [1], a journal of the Royal Society of Chemistry focusing on innovative research on sustainable and ecofriendly technologies. The team focused on poly (isosorbide carbonate), or PIC, a type of biobased polycarbonate that has garnered much 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 links that join the ISB units can be severed using ammonia (NH 3 ) 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 Biobased polymers to fertilizers present. Therefore, the researchers tried increasing the temperature and found that complete degradation could be achieved in about six hours at 90 °C. Daisuke Aoki 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 (see picture). The systems can not only help fight off pollution and resource depletion but also contribute to meeting the world’s increasing food demands. Daisuke 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!” Reference [1] Plastics to Fertilizers: Chemical Recycling of a Biobased Polycarbonate as a Fertilizer Source; Green Chemistry; Oct. 2021; DOI: https://doi. org/10.1039/d1gc02327f www.titech.ac.jp/english | www.jst.go.jp/EN 28 bioplastics MAGAZINE [06/21] Vol. 16
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