NREL PROJECTS: Upcycling Plastics & Carbon-Fiber Research

The federal lab is exploring ways to aid the environment with new products.

One day, a plastic Coca-Cola bottle may turn into a lightweight headlamp housing or battery casing if a research team at the National Renewable Energy Labratory (NREL) in Golden, Colo., can scale up a process it has achieved on the laboratory bench scale.

The process takes recycled polyethylene terephthalate (PET) plastic and using bio-based chemicals, creates a composite with thermal and mechanical properties “as good or better” than the composites on the market, according to Gregg Beckham, an NREL senior research fellow.

For Beckham, who leads the team, this is more than just a potentially valuable piece of applied research. A longtime scuba diver who has explored seas around the world, it is a tool to address one of the world’s biggest environmental problems—massive amounts of plastic in the oceans.

“You dive off of Thailand, and there are plastics everywhere,” Beckham said. “Even in the Caymans, which is cleanish, you see a lot of plastics. We have an addiction to plastics.”

Since the 1960s, plastic production has increased twentyfold, and an estimated 8,300 million tons of plastics has been produced with just 7 percent being recycled, 10 percent incinerated and 4,900 million tons discarded. A lot of that discarded plastic ends up in the oceans.

MORE PLASTICS THAN FISH
“It is projected by 2050, there will be more plastics in the ocean than fish, which is a daunting environmental crisis that humankind has to face and deal with,” Beckham said.

One solution is to find ways to reuse plastics, which Beckham notes that while being a problem, have added a lot to modern life. The key to plastics recycling is in part a question of technology and in part a question of economics.

About 30 million tons of PET a year are created globally, making it the largest produced polyester in the world and fourth largest polymer, but only 30 percent is recycled. One big reason is that it is hardly worth doing, Beckham said.

“Before 2018, most of the plastics that were reclaimed were sent to China, and we called that recycling. In 2018, China stopped taking plastics from the United States,” he said. “Now there are stories in many cities in America that the recycling infrastructure cannot handle the plastics coming to recycling facilities.”

The problem is that those PET bottles are chopped up and mechanically refined, a process that leads to a lowervalue polymer. “It ends up in carpeting or clothing or something that will end up in the landfill,” Beckham said. “It is down-cycling, and so there is very little economic incentive to recycle.”

UPCYCLING
What the NREL team is trying to do with PET is “upcycle it.”

“There is no incentive for anybody to gather plastics and take them to a recycling facility except social and environmental good,” he said “An economic incentive is a winning proposition for the planet.”

Recycled green Mountain Dew PET bottles fetch about 30 cents a pound. A clear water bottle reclaimed is worth about 50 cents. The composite material NREL is creating would sell for the going composite price of $2.50 to $2.60 a pound. “That is significant value added,” Beckham said.

This could have a particularly big impact in Southeast Asia, which has one of the most serious plastic-pollution problems and where people live on less than $5 a day, Beckham said. “If you can make $6 a day collecting plastics, that’s an incentive.”

It might seem that recycling plastics is off the reservation for a federal laboratory known most for its work on solar energy and wind turbines, but it is right in the wheelhouse of another big NREL effort—making biofuels.

BIOMASS INTO FUELS AND FEEDSTOCKS
NREL has been working on turning biomass—wood chips, corn stover, wheat stalks—into high-value fuels and feedstocks. “The problem is exactly the same conceptually with plastics. You’ve got a waste, low-value, diffuse, solid material that we develop technologies to break down into higher value,” Beckham said.

NREL has also worked on creating bio-based monomers that could be used as chemical building blocks. “It was two sides of our brain, and we had this ah-ha moment when we realized we could put them together,” Beckham said.

The monomer of choice—one being refined at NREL—is muconic acid, which can be derived from sugars or aromatics present in waste-plant material. It can also be made from the petroleum waste stream.

“We are always looking for a way to use these diacids,” Beckham said. “It was a hammer looking for a nail, but PET recycling is a pretty good nail because muconic acid has cross-linking capabilities in its backbone, and that’s what you need to make composites.”

That strength in cross-linking was particularly important since PET is not easy to cross-link, Beckham said.

The process the NREL team developed combines reclaimed PET with a diol, something like either ethylene glycol or butanediol, which is used in anti-freeze and can be derived from biomass.

The combination partially deconstructs the PET, enabling it to be subsequently blended with malate, fumarate or dimethyl muconate (the latter two are bio-derivable oefinic acids) to produce an unsaturated polyester.

PET-FRPs SYNTHESIZATION
A series of PET-FRPs (fiberglass reinforced plastics) were synthesized by dissolving the unsaturated polyester in a reactive diluent, such as styrene methacrylic or acrylic acid, along with a free radical indicator (azobisisobutyronitrile, AIBN) to form a resin, which is then applied to a fiberglass mat and reacted.

The process is described in the paper, “Combining Reclaimed PET with Bio-based Monomers Enables Plastics Upcycling,” published in the February 2019 edition of Joule.

The auto industry has been interested in FRPs because of their low weight coupled with incredible strength, along with good fatigue, impact and compression properties. Plastics accounted for around 440 pounds of a vehicle’s weight in 2014, and industry analyst IHS Chemical of Englewood, Colo., expects that figure to rise to nearly 770 pounds by the year 2020, an increase of 75 percent. IHS analysts see the use of carbon fiber in automotive manufacturing to jump to 9,800 tons by the year 2030, up from 3,400 tons in 2013.

The first question the NREL researchers asked once they found they could create a reclaimed PET composite was whether it was worth creating the material.

“We wanted to know was it worth it from the standpoint of economics, energy and greenhouse gas emissions,” Beckham said. “Is this better than the way composites are made today, and is this better than chemical recycling PET back to bottles?”

The process was analyzed using NREL’s Materials Flows through Industry (MFI) supply chain breakdown tool, a cradle-to-grave or in this case, cradle-to-cradle evaluation.

RECYCLING PET SAVES ENERGY
In terms of energy, the analysis calculated that the process of recycling PET to composites saves about 90 percent of the embedded energy.

“The manufacture of virgin polymers from petroleum feedstocks is an energy-intensive process, with most polymers requiring 90–200 MJ/kg” [megajoules per kilogram],” the research paper said. “The MFI tool estimates that the virgin PET production supply chain requires 124 MJ/kg. Meanwhile, the MFI tool predicts that the current fossilbased FRP supply chain requires 89 MJ/kg.”

On average, the researchers estimate that the recycling process used 57 percent less energy than making petrobased composites. The energy savings also translate into a 40-percent reduction in greenhouse gas emissions—an analysis that included emissions for all combustion processes in the supply chain, such as process heat heating, electricity generation and transportation.

As for the economics compared to chemical recycling, which returns PET to its original state so that it could be used again as a beverage bottle, the NREL process also fared well.

Among the problems with chemical recycling is that it may require costly and energy-intensive separation to remove any contaminates from the PET. It also requires expensive catalysts or extensive reactor times to deconstruct the polymer. It remains relatively inexpensive to just make new bottles.

ECONOMIC ANALYSIS OF PRODUCTS
In the economic analysis for the current method of recycling PET, the NREL process produces a product potentially much more valuable.

“Not only are the resulting composites worth more than double the original PET, the FRPs exhibit twice the strength and improved adhesion to fiberglass when compared to the standard petroleum-derived FRP,” according to NREL. Potentially good news for the automotive industry since fiber-reinforced plastic composites are lighter in weight and similar in strength to aluminum and steel.

Despite the success at the bench scale, there are considerable hurdles in moving to a pilot and commercial scale.

“One of the biggest challenges is commercial access to bio-based monomers we used,” Beckham said, “You can’t buy six tons of muconate from BASF or BP. No company is making it. So that’s one challenge. It is a huge hurdle to economic viability and scalability.”

The NREL team, including Nic Rorrer, who previously worked with bio-based muconic acid and PET, makes the acid themselves in small batches.

The production of the composite itself so far has been limited to pieces the size of “small dog bones,” Beckham said.

LOOKING FOR LARGER YIELDS
The next goal is to produce something as big as a conference table. “That’s what a Ford, General Motors or a Vestas or Burton want to see,” he said, referring to the Danish wind turbine maker and snowboard manufacturer—which both use composites.

That is what is needed is to accelerate aging tests and to test the material relative to standard composite on the market today. “They want to know that is as good or better,” Beckham said.

The aim is to work with the Composites Manufacturing Education and Technology (CoMET) facility at the lab’s National Wind Technology Center to develop larger quantities of the PET composite.

What will really determine the future of the project, however, are industry partnerships. “That is what we are on the hunt for,” Beckham said. “If industry is interested, we are interested in working with them.”

The PET composites have been tested for thermal and mechanical properties. “Those tell you a lot,” Beckham said. “But every company that sells a widget for a car has a long list of specifications. We have to know what properties they need.”

“Getting connected to end users is really the key because they are going to be the ones who tell what kinds of applications they could potentially use these things for and the parameters we are not considering now,” he said.

“If we can onboard industrial partners, we could do this in the time scale of several years” to make it commercial, he said.

The NREL team is working on one more element to their research with the goal of recycling the recycled PET composite. “Can you add one more functionality?” Beckman said. “These composite materials go into products that last for 10 years or decades … Can you make a wind turbine blade out of a wind turbine blade?”

The work reported in Joule was enabled by funding from NREL’s Laboratory Directed Research and Development program, with additional funding from the U.S. Department of Energy’s Bioenergy Technologies Office.

ACN RESEARCH
The NREL upcycling project is not the only one of interest to automakers. In this second one, researchers had to go to the past to find the future.

NREL scientists traveled back in time to find a new way to produce acrylonitrile (ACN) from renewable sources. Acrylonitrile is used to make acrylic fiber, which produces rugged plastics for automotive components. Acrylic fiber is also used in the manufacture of polyacrylonitrile (PAN)- base carbon fibers, increasingly important materials for lightweight, high-strength automotive applications.

If the research pans out, biomass could be used instead of petrochemicals to turn ACN into carbon fiber—as was done at the turn of the 20th century.

NEW IS OLD
The NREL team came across this “new” method in a 1916 journal article written by two Johns Hopkins chemistry professors. NREL’s chemical engineer Eric Karp and others realized it could lead to a cleaner way to change ACN into carbon fiber, replacing petrochemicals with biomass as the starting point.

“In the early 1900s, researchers—and people in general— didn’t have access yet to the vast petrochemicals that are available today,” Karp said. “That’s because the petrochemical industry really wasn’t developed yet. Researchers were forced to use what was easily available to them, and that mostly included natural products.”

When the petrochemical industry pushed to the forefront in the 1940s and ’50s, making chemicals from natural products was “mostly forgotten,” according to Karp. Today, renewable feedstocks have renewed interest. The methods of 100 years ago are guiding modern research.

LIGHTWEIGHT CARBON FIBER
This is of great interest to the lightweighting world because “Carbon fiber is this amazing lightweight material,” Karp explained. “Imagine replacing all the steel and aluminum in a car with carbon fiber. Think of how far a car would go with the gas mileage you could get. You’re looking at 60 miles per gallon for the average car on the road with existing engine technology.”

Karp, chemical engineer Violeta Sànchez i Nogué, Todd Eaton (then an NREL postdoctoral researcher) and their colleagues produced 50 grams of bio-derived ACN. That came in the first phase of a DOE-funded program. The second phase is aiming for 50 kilograms of ACN converted into carbon fiber.

More than 7 billion kilograms of ACN are produced globally each year. It derives from an energy-intensive, petroleum-based process that produces hydrogen cyanide as a toxic byproduct. The DOE was looking for a cleaner way to make carbon fiber—one not subject to the swings of oil-market prices. Among the questions DOE asked were: Is there a green way to get to ACN? Can it be done at less than $1 a pound?

“We came up with six different ways to make bio-based acrylonitrile,” said Beckham. He, Karp, senior research engineer Derek Vardon, principal scientist Bob Baldwin and associate laboratory director for bioenergy science and technology Adam Bratis, wrote the proposal that secured the DOE funding. As a side benefit, the NREL-led Renewable Carbon Fiber Consortium was created. Three of six methods were tested, including a new catalytic process the team developed called nitrilation.

This process, described in the journal “Science” in 2018, produced a 98-percent yield of ACN. The yield from the petroleum-based method ranges from 80 to 83 percent.

CORN STOVER
Different feedstocks are used in nitrilation. During the first phase, it was corn stover, which is the stalks and leaves left after harvest. The sugars in this biomass are converted by a microorganism into 3-hydroxypropionic acid (3-HP), which in subsequent steps is transformed into acrylonitrile.

“This is a genetically modified strain because the microorganisms that we were using for the 3-HP production, they don’t naturally produce it,” said Sànchez i Nogué, who oversaw the biological component of the research.

For the second phase, the global company Cargill Incorporated will produce larger volumes. “They have an industrial strain that can produce 3-HP with much higher efficiency than we have in-house,” she said.

As members of the Renewable Carbon Fiber Consortium, Cargill and other companies will play vital roles in furthering the research. A West Virginia nonprofit research institute, MATRIC, will convert Cargill’s 3-HP into ACN. Then a Portuguese company will produce the carbon fiber and hand it off to the Ford Motor Company. Ford will fashion the carbon fiber into parts and compare the biomass-derived versions against those made through the traditional process.

“I’m just so excited to see this start being applied out in the real world, beyond here, just to see it go somewhere beyond a paper,” Karp said.

 

Authored by Mark Jaffe

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