(3) Polylactic Acid as Sustainable Developmental Goals（SDGs）－From a View Point of Biodegradable towards Smart Plastic－

Synthetic polymer products made from oil as their feedstock source of the 20 century has led to three big problems, exhaustion of oil reserves, increases in greenhouse gas emission, and solid waste management like ocean contamination by plastics. In the coming 21st century, a sustainable social system from the view point of feedstock resource reservation, reduction of greenhouse gas emission and solid wastes management is expected to emerge. The current crisis in solid waste management, in particular, has led to focused attention on the development of bio-based polymers such as polylactic acid（PLA）that can biodegrade in the natural environment in soil, in sea water, or in the course of bio-recycling like composting. PLA is not only a biodegradable plastic but also smart plastic that can cover from single use to durable product applications required high performance, owing to the advanced technologies in addition to its inherent biodegradation mechanism. Also PLA has excellent antibacterial/antifungal property, regardless of its biodegradability. In this article, biodegradation mechanism, the key performance features and potential applications of PLA are discussed.