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Second Life

Researchers develop a simple way to turn plastic food packaging into valuable specialty chemicals worth more after recycling

By Melissa Van De Werfhorst
Convergence Podcast

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Researcher Frank Leibfarth explains how he turned bioplastics into value-added materials. + Listen on iTunes
Tomatoes in plastic box

Americans go through 14 million tons
of plastic food packaging on a yearly basis, more than any other country in the world. Factors such as food safety, food preservation, and consumer appeal drive the packaging market, a multi-billion dollar global industry. With more than 90 percent of these millions of tons of plastic ending up as landfill or litter, researchers at UC Santa Barbara are asking if there’s a more practical approach to harnessing the lifecycle of valuable polymers that can benefit industry, the consumer, and nature.

Traditional recycling is a process that turns used plastics into a raw but impure form of the original material. Polyethylene terephthalate (PET), the most commonly used plastic in packaging materials, can be recycled into a lower grade material to make bottles, carpet fibers, or a canvas bag, as examples. Recycling-savvy consumers know to look for the number on the bottom of a soda bottle or container of tomatoes. Of these resin identification codes, numbers 1, 2, and 3 are the most commonly accepted plastics by curbside recycling services — largely thanks to the recycling industry infrastructure in place in the U.S.

But the mysterious code number 7 is considered “other” materials that are typically non-recyclable. Code 7 includes bioplastics, or polymers made from biomass — such as the oils, fibers, and starches from corn, sugarcane, and other plants. Biomass used by commercial producers of bioplastics is typically made from throw-away scraps: unused crops, post-harvest chaff, or waste brush.

It’s this increasingly popular bioplastic packaging that chemistry PhD student Frank Leibfarth and his colleagues have been deconstructing in the Materials Research Laboratory at UCSB. They are transforming the bioplastic material polylactide into value-added materials, or specialty chemicals that are already used in large quantities by industrial and food manufacturers. It was easy to find: Leibfarth and his research team purchased 4-packs of fruit at the local Trader Joe’s store and cut up the packaging for their experiments.

“For the same reason you can compost it, polylactide plastic is much easier to work with,” said Leibfarth. “If you look at its chemical bond structure, it’s easier to manipulate than petroleum based plastics.”

Leibfarth Group in lab
From left: Frank Leibfarth and researchers Alex Hakwer, Justin Shand, and Nicolas Moreno

Packaging based on Polymerized Lactic Acid, or PLA, is becoming more attractive to distributors and stores that want to see more sustainably sourced materials on the shelves. The PLA packaging market annual growth is close to 19% with a projected market value of around $3.8 billion by 2016. It’s the fastest growing market segment of bioplastics, making it cost competitive with petroleum-based plastics.

“There’s a major bioplastic resin plant in Blair, Nebraska, that produces about 150,000 tons of PLA per year, but before that it was a very niche product.” This Nebraska plant is the world’s largest lactic acid manufacturing facility. It’s run by NatureWorks, LLC, an independent company with a list of clients that have a strong interest in bioplastic for products ranging from cell phones to copy machines. Their manufacturing process uses half the energy as traditional polymers like PET, and produces about 60 percent less greenhouse gases.

The problem is the current lack of infrastructure to divert PLA and other bioplastics from the landfill. Even though polylactide is capable of biodegrading into soil-enriching compounds, it takes exposure to oxygen over several years. It will biodegrade in an aerobic compost heap, but not necessarily in a covered and compacted landfill that tends toward anaerobic conditions. The modern way to recycle PLA into new PLA relies on harshly acidic (low pH) or basic (high pH) conditions and high temperatures in an energy intensive process.

“Industry is not that good at recycling this kind of plastic,” said Leibfarth. “PLA is so new to the market that the recycling infrastructure isn’t in place. It makes more sense to turn polylactide into value-added materials than to use tons of energy to recycle it.”

“People think of recycling as producing an imperfect or less valuable product from used plastics. But we can take plastic and turn it into new materials that are equally useful and valuable.”

Leibfarth’s research team engineered a catalysis process to break down polylactide into useful component chemicals. Their novel process is surprisingly fast and energy efficient. It uses an organocatalyst molecule and ethanol to depolymerize the PLA, breaking down the long chains of lactide into individual molecules. The resulting soup of molecules is distilled to isolate component products.

“The entire process takes about 10 minutes at room temperature,” explained Leibfarth. “We cut up plastic packaging, add a little ethanol and 1 percent of a very active organic catalyst. The catalyst does all the work.”

“This is very translatable for industry,” he added.

One of the resulting components is ethyl lactate, a sweet-smelling, clear liquid commonly used by the cosmetics and food industries. Because it’s soft, creamy, and smells slightly of coconut, it’s often used as a fragrance in hair and skin products. It is a non-toxic food preservative and found naturally in wine and fruits. Perhaps the largest demand for ethyl lactate is as a degreaser and industrial solvent that is far less toxic than chlorinated or halogenated solvents.

Ethyl lactate has historically been produced from petroleum sources. Producing it directly from biomass is a relatively simple process of adding yeast or bacteria to ferment the biomass. The end result is a chemical compound identical to that made by processing petroleum.

Turning millions of tons of postconsumer PLA into ethyl lactate makes even more sense, according to Leibfarth. Recycling PLA into ethyl lactate actually adds economic value to the supply chain. The current market price of commodity PLA is around $1.00 per pound. Ethyl lactate is twice as valuable.

“If we can take people’s garbage and make ethyl lactate, we’re extending the lifecycle of this non-petroleum based material,” added Leibfarth.

Another product of depolymerizing PLA in this way is methyl lactate, a lactate ester very similar to ethyl lactate. Methyl lactate as an industrial commodity is used to make flavors, fragrances, and dyes, but is also a common chemical base for producing many pharmaceuticals. For example, Leibfarth added, “Pfizer starts with methyl lactate to eventually produce an antiretroviral drug to treat HIV that is currently in clinical trials.”

Leibfarth and other polymer scientists see prospects in the chemical afterlife beyond single-use plastics. Lactate esters are just the beginning, and polylactide just one of many biomass-based materials.

“Having such a synthetically versatile material in the waste stream is an opportunity that is ripe for exploiting and makes sense from both energy and environmental viewpoints,” said Craig Hawker, Director of the Materials Research Laboratory at UCSB and advisor for Leibfarth’s study. Details of their study will be published online in the Journal of Polymer Science this September.

“The entire lifecycle of biomass to plastic to value-added materials could be extended,” added Leibfarth. “People think of recycling as producing an imperfect or less valuable product from used plastics. But we can take many kinds of plastic and turn them into new materials that are equally useful and valuable.”