材料を評価対象とするLCA

抄録

Life cycle assessment (LCA) has been developed for evaluating the environmental impacts associated with a product through its life cycle. LCA is used in product environmental footprint programs. In carbon neutrality, greenhouse gas emissions associated with a product and an organization are of great interest, where methodologies and databases developed for LCA are used. Thus, LCA has become an essential tool for the zero-emission society and circular economy. However, when LCA is applied to materials, a material life cycle may contain several product life cycles due to its recycling. Therefore, evaluation methodologies for consuming secondary raw materials and for recovering them should be seriously considered. This article provides basic knowledge of LCA and advanced knowledge for recycling effects. As basic knowledge, the difference between attributional LCA and consequential LCA and their selection depending on the purpose of assessment are described. As for the recycling effects, characteristics of three possible modeling approaches, cut-off, portioning, and avoided burden approaches, are introduced. In the avoided burden approach, the allocation factor between two product life cycles that secondary raw materials are supplied from and demanded by should be determined. Although the fundamental concept for defining the allocation factor is widely accepted, the methodology for that is still under discussion. Based on the state-of-the-art methodologies, two major applications of LCA in material industries are described, such as evaluating the environmental impacts avoided by new materials or technologies and comparing different materials in terms of environmental impacts through a product life cycle.