Toyota Boshoku Corp and Toyota Central R&D Labs Inc co-developed a bioplastic whose impact resistance is about 10 times higher than that of polypropylene (PP) used for auto interiors and announced it at JSAE Annual Congress (Spring).
The bioplastic is an alloy of polyamide (PA) 11 and PP. It is a bioplastic using 100% plant-derived PA 11 made from castor oil extracted from castor beans.
The Charpy impact strength of the bioplastic is about 90kJ/m2 at normal temperature. It is about 13 times that of an alloy of PP/polylactic acid, which is a bioplastic used for auto interiors, and about 80% higher than that of an alloy of polycarbonate (PC) and acrylonitrile butadiene styrene (ABS), which is a highly impact-resistant polymer alloy, Toyota Boshoku and Toyota Central R&D Labs said.
According to the two companies, the improvement in impact resistance might drastically expand the use of bioplastic. In regard to auto interior parts, it is possible to use the new bioplastic not only for door trims and other parts for which currently PP is used but also for the base materials of instrument panels, impact energy absorbers and other parts that need high impact resistance and rigidity to protect passengers at the time of impact.
Furthermore, the new bioplastic is expected to be employed for auto exterior parts such as bumper modules and resin fenders.
Of course, it can also be used for non-automotive applications including traveling cases, helmets, casings of mobile devices and general home appliances and other parts that currently use highly impact-resistant polymer alloys.
According to Toyota Boshoku, the high impact resistance of the bioplastic was realized partly because of the employment of a compatibilizing agent (reactive rubber) that improves the affinity between PP and PA 11 and mixes them. Also, Toyota Boshoku and Toyota Central R&D Labs found appropriate process conditions for the (reaction, melting and kneading) process of making the materials react with each other and mixing them.
As a result, PA 11 spreads in the "sea" of PP while three-dimensionally diverging. And the reactant of the reactive rubber and PA 11 spreads at the interface between PP and PA 11 and in PA 11. This structure, which they call "co-continuous phase salami structure," contributed to the drastic increase in impact resistance, they said.