According to a report by Tech-On!, Mitsubishi Motors Corp has developed composite materials with plant-based resins that are reinforced by bamboo fibers and can be used in automotive interiors.
Mitsubishi Motors aims to reduce CO2 emissions by using the plant-based materials. It has been considering mass-producing the materials and “intends to reduce the cost to a level 1.5 times higher than existing materials,” according to the company.
In order to process bamboos into fibers, they are longitudinally split into four strips, their joints are removed, and then they are crushed and fibrillated using a special (undisclosed) machine. According to the copany, the new technology avoids the problems with existing methods.
Mitsubishi Motors produced composite compounds using the bamboo fiber and two kinds of resins, PBS (polybutylene succinate) resin and polyurethane resin. Both of the resins contain a substantial amount of plant-based materials.
The PBS resin was produced by direct dehydration polycondensation of succinic acid generated by fermenting sugar or starch, and petroleum-based 1,4-butanediol. The bamboo fibers and the PBS fibers were entwined to create a mat, which was then hot-pressed. The weight ratio of plant-based materials is about 83%, according to the company. The properties of PBS satisfy the requirements for automotive materials. However, there are some problems with the material . First, hydrolysis inhibitors, which are necessary in PBS, are expensive. Second, it has a low heat resistance (deflection temperature under load: 109°C).
As for polyurethane, Mitsubishi Motors replaced the majority of the polyol component with castor oil polyol and coconut oil glycerin to produce the polyurethane. Binder resin was added to the bamboo fibers to form a mat, which was then placed in a metallic mold and hardened by injecting the polyol and isocyanate components using a reaction injection molder (RIM). The ratio of plant-based materials is about 60%, according to the company. This composite material’s deflection temperature under load is as high as 193°C. However, due to the slow production speed, the production cost is higher than that of PP (polypropylene), which is commonly used in vehicles. The material is intended for use as door trim base material, seatback board and ceiling board.
In respect to the reduction of CO2 emissions, the composite material made from the bamboo fibers and the PBS resin has achieved a reduction of 51% in lifecycle CO2 emissions compared with existing petroleum-based PP resins. The material made from bamboo fibers and the plant-based urethane resin achieved a reduction of about 28%, according to Mitsubishi Motors.
Further information and pictures
Tech-On!: Bamboo Fibers Fortify Plant-based Auto Materials
Source: Tech-On!, 2008-12-01.