Tikalon Blog by Dev Gualtieri

Soybean Graphene

March 23, 2017

One memorable scene from the 1967 film, "The Graduate" (Mike Nichols, Director),[1] has a neighbor mentoring the recent college graduate on a career choice.[2]

Mr. McGuire: I just want to say one word to you. Just one word.
Benjamin: Yes, sir.
Mr. McGuire: Are you listening?
Benjamin: Yes, I am.
Mr. McGuire: Plastics.

As I survey my home, I see that this was good advice. The wooden toys of my youth were replaced by plastic versions for my children and grandchildren, and most of the high-tech items such as computer monitors, televisions, and cellphones are encased in plastic. The automotive industry has always been a materials innovator; and, as the chart shows, the plastic content of light vehicles has increased while the weight of cast iron pieces has declined, principally as a fuel economy strategy.

Light vehicle material weights, 1995 and 2008.

Not shown are other materials, such as copper, brass, glass, textiles, fluids, etc., 2,382/2,513 pounds in 1995/2008.

(Graphed using Gnumeric from data in ref. 3.[3])

Two factors presently affect the viability of plastic materials in many applications. One is sustainability, since most plastics are derived from petroleum, about 4% of petroleum is used as plastic feedstock, with an additional 4% used as energy for plastic manufacture.[4] The other is plastic pollution. Although Tikalon's Northern New Jersey township has a very active recycling program, less than half of plastic is recycled worldwide.[4] The United States is a most egregious polluter, since only 9% of its post-consumer plastic was recycled in 2012, with 32 million tons being discarded.[4]

Plastic degrades very slowly in the environment, and this poses many problems for humans and other organisms. More than 250,000 tons of plastic particles are estimated to be floating in the oceans.[4] One way to handle this problem is to make plastic biodegradable, often through combination with starch. Protein derived from the soybean (Glycine max) can be used to make protein polymers that are not only biodegradable, but also biorenewable.

The history of using soy as a material goes back quite a few years. A "Soybean Car" was built by Ford and exhibited in 1941. They say that "necessity is the mother of invention," and the soybean car was developed in anticipation of the rationing of steel during World War II. Only the body contained soy, along with other agricultural materials, and it was about a quarter of an inch thick. There was no further development of this automobile concept after that, but it's interesting to speculate how the history of the automobile, and agriculture, would have progressed if Ford had continued development.

Ford's 1941 "Soybean Car."

(Still image from a YouTube video by Aleksei Germanovich.)

Soy is a species of legume that's native to East Asia, but the United States is a major soybean producer (see chart). Soybeans are an oilseed, rather than a pulse. Soy, which is 38-45% protein and nearly 20% oil, yields a high quantity of protein per acre. Soy is used as a protein source in animal feeds and the tofu that I enjoy in several recipes. Soy is used as a milk substitute (I prefer almond milk), as a vegetable oil, and is fermented to produce soy sauce.

Soybean plant and estimated 2016 production.

Left, a soy field; right, estimated 2016 soy production. Soy is third only to wheat and corn as a US agricultural export. (Left, a Wikimedia commons image by Harry and Carol Rose; right, a pie chart of U.S. Department of Agriculture data using Gnumeric.[5])

Since soy is a renewable resource that's successfully used as a structural material, it would be worthwhile investigating whether it might be used as a starting material for other purposes. That's the idea pursued by Australian scientists from CSIRO Manufacturing (Lindfield, New South Wales, Australia), the University of Sydney (Sydney, Australia), the University of Technology (Sydney, Australia), and Queensland University of Technology (Brisbane, Australia).[6-8] This research team has developed a single-step process that they call GraphAir for making uniform and continuous graphene films in ambient-air using soybean oil as the precursor.[6,8] As they write in their paper describing this process, this is the first time that graphene synthesis has been accomplished in an ambient-air environment without any compressed gases.[6]

Graphene is typically grown using chemical vapor deposition techniques that require a 1,000 °C temperature, purified gases, such as methane, hydrogen, and argon, and a vacuum chamber.[6] The novel process uses an ambient-air environment and soybean oil to produce graphene films with properties comparable to graphene synthesized using other methods.[6]

As shown in the figure, a polycrystalline nickel foil of 25 micrometers thickness and 99.5 % purity, used as the growth substrate, is contained in a sealed quartz glass tube, 100 cm in length and 5 cm in diameter. An alumina plate coated with 0.14 ml of soybean oil is also contained in the quartz glass tube, and the tube is thermally cycled as shown by increasing the furnace temperature to 800 °C at a rate of 30 °C/min, holding at 800 °C for three minutes, then sliding the foil section out of the furnace for quenching at a rapid rate.[6]

Soybean graphene process. Graphene films are grown on polycrystalline nickel foils that are thermally annealed together with a soybean oil precursor. These graphene films are then transferred onto glass substrates. (Portion of fig.1 of ref. 6, licensed under the Creative Commons Attribution 4.0 International License.)

Transfer of the graphene was accomplished by spin coating the layer with poly(methyl methacrylate), PMMA, drying in air for twelve hours, and etching away the nickel foil in a ferric chloride solution. The PMMA with attached graphene, which was floating atop the ferric chloride etchant, was rinsed with deionized water and transferred to a glass slide where the PMMA was removed with acetone.[6] The properties of such graphene layers are shown below.[6]

Properties of soybean graphene, as grown on polycrystalline nickel foil and transferred onto glass. Shown are four-point resistance and optical transmittance. (Portion of fig.3 of ref. 6, licensed under the Creative Commons Attribution 4.0 International License.)

Says CSIRO scientist and co-author of the paper describing this research, Zhaojun Han, "This ambient-air process for graphene fabrication is fast, simple, safe, potentially scalable, and integration-friendly."[8] The team has even made graphene from waste oils.[8]

Soybean Graphene

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