Soy plastics targeted for electronic circuit boards.

Zhan, M and RP Wool. 2010. Biobased composite resins design for electronic materials. Journal of Applied Polymer Chemistry 118:3274-3283.

Synopsis by Evan Beach
New materials made from soybean oil have excellent electronic properties and offer a low-carbon-footprint alternative to conventional plastics that are used in printed circuit boards.

Soybean oil can be mixed with conventional chemicals and converted into a strong, rigid plastic that could be used for high-speed, energy-efficient, electrical components, report researchers at the University of Delaware.

The greasy liquid could provide a cheap, abundant and renewable alternative to some of the plastics, resins and other petroleum-based materials now used to make the parts. The use of renewable ingredients in the new plastics may reduce greenhouse gas emissions and slow depletion of petroleum resources. In principle, other plant oils besides soy would work in the same way.

One target area for the new plastic is circuit boards – the internal units that relay signals in computers, radios and other electronics. They are often made from materials called epoxy resins, a family of plastics that frequently rely on bisphenol A (BPA) for stiffness. BPA is known to interact with the hormone system, most famously as an estrogen. The use of BPA has raised health concerns over harmful effects seen in animals at low doses. Human exposure is widespread and studies suggest the chemical may contribute to obesity, behavior problems and altered fertility and reproduction in people.

The researchers wanted to modify soybean oil so the individual oil molecules would create a chain and the other added ingredients would lend rigidity. They mathematically predicted that structures similar to benzene – six carbon atoms linked together in a planar ring – would give the desired properties. Bisphenol A, for example, contains two benzene rings in its structure.

The researchers manufactured the soybean-based material to validate the theory. A key ingredient needed was phthalic anhydride, which is best known as a raw material for phthalate plasticizers that are used in a variety of products and have been linked to health effects in animal studies. At levels of 10 – 20 percent, it improved both the mechanical and electrical properties of the soy-based plastics.

All of the soy-based materials had lower dielectric constants than epoxy resins – about 3.6 to 3.8 compared to 4.2 to 4.7. A low dielectric constant is important for high signal speed and low “crosstalk” of signals between lines in a circuit. The materials also have very low dissipation factors – a measure indicating that circuits could operate using less power.

Further research is needed to improve the environmental impacts of the soy plastics. It would be ideal to progress away from adding chemicals such as phthalic anhydride that have known health effects and moving toward a 100 percent biobased material. More benign sources of benzene ring structures also should be considered.