Title of Research:
19_D08-01

Elucidation of the formation mechanism of microplastics
Principal Investigator:
Kuroda Shinichi (Graduate School of Science and Engineering, Gunma University)
29-1 Honmachi, Ota City, Gunma Prefecture 373-0057(tel) 0276-50-2434 (e-mail) skuroda@gunma-u.ac .jp
Collaborators:
Kouzai Hiroaki (Department of Science and Engineering, Kanto Gakuin University), Kuriyama
Takashi (Graduate School of Organic Materials and Systems Science, Yamagata University)
Ohtani Hajime (Graduate School of Engineering, Nagoya Institute of Technology), Igarashi Toshio(Research Division for Science and Technology, Kanazawa University), Hiejima Yusuke (ResearchDivision for Science and Technology, Kanazawa University), Tokumitsu Katsuhisa (Materials
Science Division, Faculty of Engineering, University of Shiga Prefecture)
Summary of Research:
The following conclusions were obtained with using various methods to clarify the mechanisms
by which secondary microplastics are formed from the viewpoint of polymer science and polymer
engineering.
In the Py-APGC-MS measurement of plastics, by focusing on fragment ions characteristic ofplastics and recording extracted ion chromatograms, we succeeded in extracting individualcomponent information from plastic mixture samples of PP, PE, PVC, PS, and PET. We also
succeeded in detecting PS taken up by Daphnia magna (adult).
As a result of comparative study of seawater degradation and photo-degradation of various
plastics, it was found that the presence of seawater suppressed the progression of degradation ofHDPE, PP, and PET by inhibiting the increase in sample temperature and oxygen diffusion, while
the elongation at break of PA66 decreased significantly with irradiation time in seawater
degradation. However, PA66 showed a significant decrease in elongation at break with irradiationtime, suggesting that seawater was the main factor in the degradation.
In the case of PP, the surface of the micro-cut powder showed a brittle fracture surface and the"crack pattern" grew inside, suggesting that MP was generated from the consolidated growth ofcracks, similar to the outdoor exposure. Crack patterns were also observed in the river MPs afterpulverization by glass beads, but no brittle fracture surfaces were observed in most of the leaking
marine MPs, suggesting that the MPs have smooth surfaces and are less prone to collapse-typeweathering mechanisms.
On the other hand, the PET bottles recovered from the river retained their shape despite being
left in the environment for nearly 20 years. The outer surface of the PET bottles showed no signsof becoming microplastics, although some degradation such as a decrease in molecular weight
was observed.
Finally, it was confirmed that all types of plastics, including elastomers, could be miniaturized toa spherical shape of less than 1 mm in a short time by treatment with a new type of jet mill device
with multiple blades arranged in an air flow channel and additional treatment with a regular jet mill.
In addition, it was confirmed that the bead-mill treatment efficiently progressed the plastic
refinement in a water atmosphere.
Timeline:
March 1, 2020 - February 28, 2021.
Topics:Oral presentation at JCIA LRI Annual Workshop 2020 “Elucidation of the formation mechanism ofmicroplastics” (On-line, August 21st, 2020)
Publications: Presentations: (Only the PI's presentation)
1. Shinichi Kuroda, "Elucidation of the formation mechanism of microplastics," 69th Symposiumon Macromolecules, September 16, 2020 (online)

2.

Shinichi Kuroda, "Elucidation of the formation mechanism of microplastics," MICRO 2020,
November 25, 2020 (online)