Because plastics contribute to healthy and sound everyday life, global usage volume of plastic is expected to increase. However, the chemical industry is facing challenges in plastics from the viewpoints of resource depletion and environmental burden. These trends have led to discussions on how plastics should move forward in a sustainable society and a circular economy considering resource conversion, efficient after‐use utilization, and environmental protection. Bioplastics, both bio‐based and biodegradable, have reemerged as potential solutions. To clarify the role of bio‐based, biodegradable, and fossil‐based plastics, it is meaningful to assess lessons learned from experiences in the 1990s and 2000s. Although industries have been delivering solutions through the provision of materials, a coordinated and innovative approach throughout the value chain is necessary to achieve an integrated business model that incorporates efficient resource utilization, applications, and after‐use utilization, including chemical recycling, mechanical recycling, and energy/thermal recovery.

The chemical industry and subsequent value chain of plastics are facing significant challenges from the viewpoints of resource conversion and environmental burden. Now is the time to explore the future direction of plastics, which will require an integrated scheme using resource circulation, carbon neutrality, and a social system to promote after-use treatment under the concept of a circular economy. Polylactic acid (PLA) should help reduce greenhouse gas (GHG) emissions as a biobased material and contribute to waste management after use due to its biodegradability if managed properly. That is, it will be necessary to treat biodegradable products appropriately in closed systems such as composting facilities after use and recovery. To realize the implementation of fully approved composting facilities in society, simply evaluating biodegradability in the laboratory is insufficient. In this study, a pilot-scale test using PLA under actual composting conditions was conducted in accordance with both international standards and domestic evaluation methods. The results not only confirm its biodegradability and disintegration, but also demonstrate that the presence of a biodegradable plastic product has a negligible impact on the composting process. The obtained compost did not adversely affect plant germination or growth, demonstrating its safety and high quality. Such a multifaceted perspective makes this study unique and useful for creating a social framework.

A simple chain‐extension reaction using diisocyanate as a chain extender was adopted to increase the molecular weight of low‐molecular‐weight (LMW) poly(lactic acid) (PLA) synthesized via direct polycondensation and to recover the molecular weight of commercial PLA after service life. The slow reaction between diisocyanate and the carboxylic acid terminus of PLA was successfully accelerated using a Mg(II) catalyst, affording a linear chain‐extended PLA (cePLA) connected through amide bonds. To increase the number of amide bonds, which exhibit higher thermal stability than the urethane bonds that are formed in the more common chain‐extension reactions between isocyanates and the hydroxy terminus of PLA, a telechelic LMW‐PLA having carboxylic acid groups at both termini was prepared. Subsequent reaction of this LMW‐PLA with diisocyanate in the presence of a Mg(II) catalyst afforded a cePLA with high molecular weight (Mw > 180 × 103 g/mol) and enhanced stability against thermal degradation, while showing identical mechanical properties and biodegradability as commercial PLA.

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A new Nocardiopsis species that degrades polylactic acid (PLA) was isolated from pig dung-based compost from a municipal composting facility in Japan. To obtain strains capable of e cient PLA degradation, we minimized the effect of non-enzymatic degradation of PLA by maintaining the temperature at 37°C or below. After screening a total of 15 animal waste-based compost samples, consisting of pig dung, cow dung, horse dung, or chicken droppings, we found that compost derived from pig dung was most e cient for degradation of PLA lm, and used it for isolation of PLA-degrading microorganisms. Screening for PLA-degrading microorganisms in compost was performed using an agar plate-based method; an emulsi er was omitted to avoid selection of strains that assimilated the emulsi er instead of PLA in the medium. After repeated enrichment, six strains were obtained. One strain that exhibited stable PLA degradation on agar plates was subjected to genomic analysis and identi ed as Nocardiopsis chromatogenes, an actinomycete.