DuPont’s Approach to Bio-based Plastics
Addressing the demands of OEMs for more sustainable materials and recognizing the changes in the cost and availability of petroleum, DuPont is working to develop bio-based plastics that are, in some cases, even better than their traditional alternatives.
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Alternative materials. Alternative bio-based materials. Hear either one of those, and the thought that immediately comes to mind is something along the lines of: “Chances are these materials are, in some way, going to be less than what has ordinarily been used. Sure, they may be better from some environmental standpoint—assuming, of course, that they truly are seriously bio-based and not just something that a little ‘green’ has been sprinkled in so as to provide a marketing platform—but presumably they’re going to require substantial changes in the process and the resulting parts are going to be sort of grainy and crunchy and not exactly what we’re looking for in terms of finish and performance.”
So you might think.
Richard L. Bell, development manager, DuPont Company Performance Polymers (dupont.com), describes the development of the vanes, or louvers, for the HVAC outlet in the instrument panel of a car. The car, admittedly, is a Toyota Prius. Which might bring to mind the aforementioned “it’s green so it is going to be not as good as it otherwise might be.”
So you might think.
The vanes for the HVAC outlet had been made with a glass-reinforced PBT (polybutylene terephthalate). A whole gang of participants went to work on the project of making the change to the use of a PTT polyester-based material, Sorona EP thermoplastic. In addition to Toyota, there were DuPont Kabushiki Kaisha, Kojima Press Industry Co., and Howa Plastics. The material in question, explains Bell, has industrial corn as its feedstock.
[Quick explanation of how it goes from corn to an engineering plastic: the corn is harvested, then brought to a mill, where the kernels are cooked for 24 hours. The goal is to extract the starch from the corn. The kernels are milled twice, which has the effect of separating out the gluten, which is used for animal feed, and the starch, which is fed to enzymes that transform it into glucose. The glucose goes into a vat, where it is fermented by a mixture of a genetically modified organism, vitamins, and minerals. The result of this is PDO, a three-carbon molecule. That is, in plastics terminology, a “monomer.” So in order to get to a polymer, the PDO is sent to a plant where it is mixed with another monomer, terephthalic acid (TPA). This mixing means that the materials have been polymerized. The TPA is petroleum-based. The result of this polymerization is strands of material, which are chopped up into pellets. And the end result is the Sorona polymer.]
“So Sorona is bio-based,” Bell says. “It’s not 100%. But 37% comes from bio-material.” He adds that DuPont scientists and engineers are working on a second-generation process to attain the feedstock that will use the corn stalks and husks. “Instead of having to import oil, you can grow the feedstocks,” Bell says.
Back to the HVAC vanes.
When they were being produced with PBT, the glass was visible on the surface of the molded parts. So they needed to be painted. But with the PTT (polytrimethylene terephthalate) polyester, the painting isn’t necessary. The parts are used as-molded. No painting. Which means not only are they using a bio-based material to mold the components, but there are none of the VOCs associated with painting.
Bell admits that on a pound-for-pound basis, the PTT is more expensive than a PBT. But in this case, there is both a cost savings (no secondary painting operation) and an environmental advantage.
So the bio-material has an obvious functional advantage in this application. Bell says that in addition to the surface finish benefit of the PTT, there is also low warpage, which makes it suitable for use in large, flat trim pieces in vehicle interiors, where polycarbonate ABS blends might be used.
Sorona is not necessarily a drop-in replacement,” Bell says. “But there are certain applications where the properties of the material are better.” Like if the application in question otherwise requires painting, or if warpage is a problem.
There is another form of Sorona that has automotive application: fibers. According to Bell, five different car lines (yes, the Prius and Nissan LEAF are included) are using it for carpet in place of nylon 6. The environmental benefit of this is that it takes 30% less energy to produce and reduces greenhouse gas emissions by 63%.
“DuPont’s overall approach is to improve sustainability not only within DuPont—reducing the materials going to landfills and what comes out of our smokestacks; decreasing our dependence on petroleum—but we also make products that help our customers improve their sustainability,” Bell says. Which sounds very organic apple pie. But there’s more: “DuPont invented a lot of plastics, going way back to nylon. We view this as the new era in plastics, switching from petroleum-based to renewably based feedstocks.”
In other words, this is a strategic decision being made by a company that recognizes that in order to continue to be competitive, it is going to have to do things differently.
“DuPont’s goal,” he says, “is to make products that are cost-competitive and functionally competitive because we know the customer is not going to pay a premium price for these products.”
At this point, he says, the price of oil is such that there is improved parity between the bio-based materials and the oil-based polymers.
“DuPont’s long-term goal is to switch the majority of our polymers to bio-based.”
But if we go back to that initial thought about whether there is “a little ‘green’ sprinkled in,” the question comes up: Just what does Bell mean by “bio-based”?
Turns out they are quite serious about this. They do life-cycle analyses of the materials, looking at the entire manufacturing process. “If it involves corn, they we look at the planting of the seeds, the water usage, the gas required for transport . . . all aspects of the process.”
And they use the terms “bio-based” and “renewably sourced” interchangeably. They don’t describe materials that have less than 20% of their content from renewable sources with either of those terms.
There is an automotive plastic that they have that is 100% bio-based, polyamide (PA) 1010. This material (the DuPont trade name is Zytel RS), a nylon, uses castor beans as its feedstock. Bell says that castor plants grow wild on mountain sides in places like India and Asia. They require no irrigation. No fertilizer. They don’t compete with food sources.
Oil (yes, the stuff that you may have had to swallow as a child) is converted into sebacic acid, which is used to make the PA10 monomer. (There is a PA610 Zytel RS material, which is approximately 60% bio-based, as it uses a PA6 monomer that is derived from a petroleum source.)
While Sorona can be used to make end customer-facing products like the HVAC vents and carpet, the Zytel RS is typically used to produce things that are found under the hood, like fuel lines.
One interesting bio-intensive application is a fuel line produced for several Fiat diesel products including the 500 and Panda, Lancia Delta, and Alfa Romeo Giulietta. The fuel line had to be suitable for use with biodiesel.
Bell says that ordinarily, a PA12 is used to produce diesel fuel lines, but a monolayer construction isn’t idea for biodiesel exposure. So what some companies do is to co-extrude a thin layer of fluoropolymer on the inside of the PA12 tube. Again, an additional operation.
The supplier to Fiat, Hutchinson SRL (hutchinsonworldwide.com) opted to use a Zytel RS grade based on PA1010, which is more than 60% bio-based by weight, as it can be used to produce a monotube with the high temperature resistance needed for the biodiesel application.
“Car companies, given a choice, will use a bio-based material,” Bell says. But the choice is predicated not wholly on “greenness,” but on competitiveness: cost competitive, functionally competitive.
Which brings us back to the start: The materials are equal to or better than what have been ordinarily used. They are not only better from the environmental standpoint—and with a minimum of a 20% sustainably sourced content, there is more than a “sprinkle of green”—but they can produce parts that can have superior finish and performance compared with their petroleum-based competitors.
So you might think differently.
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