Plastic packaging is designed around appearance, convenience, and function, but what happens after disposal is often considered separately—yet managing this waste is key to building a circular economy, since good recycling requires sorting plastics correctly by type. Transparent polyethylene terephthalate and polystyrene, for example, can be difficult to distinguish visually, making accurate separation challenging.
Addressing this challenge, a research team led by Mr. Juniya Yoshihara, a master’s graduate student, together with Professor Tadao Tanabe and Professor Mitsuhiro Shigeri from the Department of Engineering and Design, Shibaura Institute of Technology (SIT), Japan, developed a design framework incorporating terahertz (THz) sensing into plastic packaging design. The researchers focused on transparent soba noodle containers and considered material identification alongside geometry, consumer needs, and transport efficiency. “ We wanted to rethink packaging design so that recyclability becomes part of the design process while everyday usability and practical requirements are retained,” says Mr. Yoshihara. The study was made available online on July 16, 2026, and will be published in Volume 32 of the journal Results in Engineering on December 01, 2026.
The research began with a community-based collection experiment in Isesaki City, Gunma Prefecture, Japan. Residents brought washed transparent food containers to a collection site equipped with an automated identification system. Among 383 collected samples, most were correctly identified, but some were misclassified. Analysis suggested that container shape and surface structure contributed to THz signal variations. The fixed model was not retrained during collection, providing an independent field-test evaluation under real-world conditions.
The researchers then explored how geometry could support stable identification. They created different bottom surface shapes and evaluated their THz transmission alongside image-based measures of complexity. The results showed that ribs, slopes, grooves, and other uneven features could affect measurements. A stable, flat region at the center helped provide a more consistent area for THz sensing, particularly when measurements were sensitive to shape.
Using these findings, the team developed four prototype soba containers. One prototype offered a strong balance between identification performance and practical use. It combined a regular triangular bottom pattern with a central flat area while retaining an uneven surface that could help prevent noodles from becoming soggy. The design also incorporated spaces for condiments and dipping sauce and considered how the container could be held during recycling.
A small survey indicated favorable impressions of the selected design, including durability, handling, and innovative appearance. The final container was designed for easy handling and placement that directs the central sensing area toward the identification system. Its stacking arrangement also allowed more containers to be transported together than the general container used for comparison.
Importantly, the final design maintained stable THz transmission while preserving the practical functions expected from a food container. The findings demonstrate that recycling considerations need not come at the expense of usability, appearance, or transport efficiency. Instead, sensing requirements can become part of product development itself.
“ By integrating sensing considerations into product geometry, we can explore packaging that is easier to identify after disposal without giving up its familiar functions,” says Mr. Yoshihara. The study points toward a broader shift in sustainable product development in which recyclability is considered alongside everyday performance from the beginning.
Overall, the study presents a case-based framework combining THz sensing, machine learning, image analysis, and product design to improve material identifiability after disposal. While further validation is needed across different packaging types, materials, and real-world conditions, the approach could support everyday products designed for more efficient resource recycling and reduced environmental impact.
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Reference
Title of original paper: Designing a Sustainable Plastic Container Based on Terahertz Spectroscopy
Journal: Results in Engineering
DOI: https://doi.org/10.1016/j.rineng.2026.112028
About Shibaura Institute of Technology (SIT), Japan
Shibaura Institute of Technology (SIT) is a private university with campuses in Tokyo and Saitama. Since the establishment of its predecessor, Tokyo Higher School of Industry and Commerce, in 1927, it has maintained “learning through practice” as its philosophy in the education of engineers. SIT was the only private science and engineering university selected for the Top Global University Project sponsored by the Ministry of Education, Culture, Sports, Science and Technology and had received support from the ministry for 10 years starting from the 2014 academic year. Its motto, “Nurturing engineers who learn from society and contribute to society,” reflects its mission of fostering scientists and engineers who can contribute to the sustainable growth of the world by exposing their over 9,500 students to culturally diverse environments, where they learn to cope, collaborate, and relate with fellow students from around the world.
Website: https://www.shibaura-it.ac.jp/en/
About Mr. Juniya Yoshihara from SIT, Japan
Mr. Juniya Yoshihara is a master’s graduate student and researcher in the Department of Engineering and Design at SIT, Japan. He is a member of the Design Process Laboratory (Shigeri Lab), where he focuses on design projects for everyday products. For this research, he studied and applied terahertz technology developed in the Recycle Design Laboratory (Tanabe Lab) within the same department. His work explores how advanced technologies can be incorporated into product design to support recycling and sustainability. He aims to develop practical design approaches that address environmental challenges while maintaining everyday product functionality and usability.
https://banbutsusekkeikatei.studio.site/
https://recycledesignsit.com/
Funding Information
This research was partly supported by a grant from the Fuji Seal Packaging Foundation.
Results in Engineering
Case study
Not applicable
Designing a sustainable plastic container based on terahertz spectroscopy
1-Dec-2026
The authors declare the following financial interests/ personal relationships which may be considered as potential competing interests. Kazuaki Okubo reports financial support was provided by Fuji Seal Packaging Foundation. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.