In recent years, LCA methods for evaluating the reduction effects of environmental burdens by resource circulation of plastics are revisited, for which there seem the following reasons: （1） the simultaneous achievement of the decarbonization and the circular economy is required as the social background; （2） there remain undecided factors in the evaluation methods; and （3） the “production” perspective has recently been emphasized in addition to the “waste management” perspective in the assessment of resource circulation. As a consequence, we cannot avoid from discussion about the way how the reduction effect of burdens in the whole society should be attributed to the supply and demand sides of recycled materials. Even though a variety of approaches have been proposed for this purpose, it remains uncertain which approach should be applied to what kind of resource circulation. In this article, with the resource circulation of plastics in mind, LCA methods for evaluating and comparing cyclical use options including recycling are discussed. First, the cut-off and avoided burden approaches and approaches for attributing burdens and their reduction effects are graphically explained. Then, as remaining issues in the assessment of plastic resource circulation, those related to the choice of the evaluation approaches, selection of processes of which burdens are to be subtracted, and presentation of the effect of resource circulation are investigated.

Toward transition to the decarbonized society and the circular economy, quantitative evaluation of the reduction effect of environmental burdens by recycling of plastics has been regarded as important. In this article, recent domestic and overseas reports of LCA studies on recycling （material and chemical recycling） and energy recovery are reviewed, with the focus on the reduction effect of climate change impact including CO₂ emissions. Those studies are discussed from the viewpoints of specification of system boundaries and substituted products, the evaluation methods of reduction effects, and comparison of a variety of recycling methods and energy recovery.

The cement industry utilizes many wastes and by-products. In particular, the utilization of waste plastics in cement manufacturing processes is a method that can properly treat them while making effective use of their thermal energy. The use of waste plastics, which are conventionally incinerated due to the mixing of inorganic components or multiple resins, as a substitute for coal for high-temperature firing cement clinker is considered to have a decarbonizing effect. This paper introduces a case study where CO₂ emission reductions by energy recovery from waste plastics in the cement manufacturing process were calculated based on LCA methods. The results of the calculations using an actual plant as a model showed that replacing 32% of the required thermal energy with waste plastics could reduce CO₂ emissions by 75 kg per ton of cement, equivalent to about 10% of the emissions intensity of the entire cement manufacturing process. It is expected that a technology will be developed to allow more waste plastics to be used in the cement manufacturing process, and that this will be utilized as one of the treatment methods of waste plastics which have become an international issue.

Circular use of plastics is expected to have effects on decarbonization and resource saving as well as to solve the plastic waste management issues. However, it does not actually proceed as expected due to some barriers such as （1） a technological challenge to overcome a trade-off between the scale and economic efficiency of sorting facilities of post-consumer plastics and （2） an institutional challenge to impartially evaluate and report the effects of a variety of recycling processes. In this article, a gasification process of post-consumer plastics that has been operated by Resonac Corporation over twenty years is introduced. Moreover, not limited to the gasification process, proposals are made against challenges to widely promote the circular use of plastics.

As one of the milestones in the Resource Circulation Strategy for Plastics of Japan, a target was set for the reduction rate of single-use plastics. To achieve this target, various actions are being taken such as charging plastic shopping bags and reducing thickness of plastic packaging materials. However, there is a lack of discussion regarding the impact of individual actions on the whole single-use plastics and the feasibility of the goal achievement with the current actions. In this study, we surveyed the types of single-use plastics for which reduction actions are being taken, estimated the potential amount of reduction in each plastic type, and projected the feasible reduction rate of single-use plastics by accumulating the results of bottom-up estimations. As a result, it was found that there was a large gap between the top-down target and the feasible reduction rate. Moreover, the results suggested that current actions mainly contributed to the reduction in waste generation from the household sector, while leaving room for reduction in single-use plastics that would be generated from the industry sectors.

The novel polyvinyl chloride （PVC） dechlorination technology addresses two challenges in the industrial metabolism of PVC: the loss of chlorine （Cl） into the environment as calcium chloride （CaCl₂） or as a component of landfilled fly ash, and the loss of carbon （C）. The technology recovers Cl as sodium chloride （NaCl）, a conventional source of Cl, and also enables the recovery of carbon-containing chemicals that could potentially serve as a new source of C. The reductions in environmental impacts associated with the Cl supply chain will depend on the deployment of the process and the handling of PVC-containing products at the end of their life as a new form of composite resource. Using a multi-objective and multi-regional technology choice model developed in this study applied to 8 regions including Japan, Korea, Taiwan, India, Australia, Mexico, China, and Thailand, we found that the implementation of the dechlorination process could potentially reduce GHG emissions by up to 3.73% and reduce the area of salt farming by 44.9%, compared to a scenario with no Cl recovery process. The priority locations for the dechlorination process are regions with low GHG emission intensity in power generation and proximity to major PVC waste-generating regions.

Since Chinaʼs ban on waste plastic imports in 2017 and stricter plastic import restrictions in Japanʼs major exporting regions, there has been a growing need for promotion of domestic treatment and recycling. In this study, we apply input‒output analysis for integrated assessment of Japanese waste plastic recycling scenarios, wherein 1.61 million tonnes of waste plastic, which Japan exported in 2015, is not exported but treated or recycled in Japan. A base-case scenario of incineration and landfill and six recycling scenarios were designed depending on the recycling method and the sector in which the method is implemented. For each scenario, we quantified the environmental, economic, and social indicators （carbon dioxide emissions, income, employment, and total import） for integrated assessments. The assessment results show that neither the ‘Petroleum products’ nor ‘Chemical fiber’ sectors can accept all the waste plastic due to capacity limitation. The ‘Pig iron’ sector achieves the least carbon dioxide emissions among the recycling sectors fulfilling certain economic and social conditions. The results of this study exemplify the usefulness of input–output analysis for integrated assessment of recycling scenarios without calculating single aggregated indicators.