Abstract
Naturally derived carbon neutral bio-plastics are being developed as a step
toward creating a recycling-oriented society. Toyota has already developed environmentally
friendly plastics based on polylactic acid (PLA), which have been commercialized as a spare
tire cover (PLA + kenaf) and a floor mat (PLA fiber). However, PLA has yet to be adapted
for use as injection molding parts, which make up the largest proportion of the plastic used in
automobiles. This is because PLA requires long molding cycle times, has low heat resistance,
and is brittle (poor impact resistance). The molding cycle time and heat resistance of PLA
depends on its degree of crystallization and crystallization kinetic, and impact resistance
depends on the compatibility of the soft component with PLA.
The aim of the research described in this article was to develop a bio-plastic for injection
molding capable of being used for automotive parts. High-order structure control of PLA was
performed to secure and find a balance between molding cycle time, heat resistance and
impact resistance to enable the application of PLA as an automotive injection molding
material. As a result, PLA components with the ability to improve formability and heat
resistance were discovered, along with a soft component capable of balancing PLA
crystallinity and compatibility. These results indicate the potential of PLA as an automotive
injection molding material.
Keywords - polylactic acid, crystallinity, heat resistance, impact resistance, high-order structure