Breakthrough in recycling plastics

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BERKELEY, Calif. – Earlier this month, the Lawrence Berkeley National Laboratory, or Berkeley Lab, a part of the US Department of Energy, reported a major technical advance. They have developed a new process that increases the efficiency of recycling plastics. It involves a new kind of plastic, poly(diketoenamine) or PDK. When soaked in a highly acidic solution for 12 hours, many parts of that plastic can be recovered and re-used. This advance increases the efficiency and cost-effectiveness of recycling plastic and possibly its potential negative impact on environmental systems.

Currently, recycling plastics faces technical or economic barriers. As a result of these barriers, most plastics are incinerated, put in a landfill, or discarded in a manner where it ends up in the ocean. All have dreadful ecological consequences. PDK may provide a way out of this dilemma.

Drinking straws are commonly made of plastic and are a common contaminant of ocean systems. [Source: S. Ciotti]

Plastic Use

Plastic has great flexibility. It can be molded into any shape, given any color, and any degree of firmness. Chemical additives give plastic its color and firmness.

The Wild Hunt spoke with Felicity Grove, a Witch with a DPhil from Oxford in biochemistry. She has had a career in Biochemistry research at Oxford University and the University of California, San Francisco. She discussed the technical aspects of this advance. Her comments have been lightly edited for brevity and clarity. Any errors belong to the author not Grove.

Grove said “The noun ‘plastics’ mean[s] substances made from sources like oil. Oil itself is a rich mixture of chemicals [that] we separate out in the refining process. In the process of making plastic we use some of those chemicals.” She said that some of those chemicals resembled beads or LEGO bricks. Chemists call these beads or LEGO bricks “monomers.” Chemists assemble these monomers into long chains, called “polymers.” Grove described this process as similar to “putting the beads on the string or building the LEGO structure.”

Grove explained the significance of Berkeley Lab’s advance. She said that they “used the particular type monomer called diketoenamine. And strung them together to form a polymer called poly(diketoenamine). This compound can be easily broken down from the polymer back down to the monomers.”

According to Grove, some plastics can already be broken down and are recyclable into a new plastic. The additives in these plastics, however, greatly limit the amount of recoverable monomers. This reduction in recoverable monomers limits the number of times a plastic can be recycled.

PDK differs. After the additives are removed from PDK, the number of monomers remain largely the same. PDK plastic can be recycled many more times than other plastics. The use of PDK plastic increases the efficiency of the recycling process.

Plastic waste

The enormity of plastic waste disrupts the delicate balance in nature, ideas central to many Pagan beliefs. In the Pacific, the Atlantic, and the Indian Oceans, plastic waste forms huge “garbage patches.” Bits of plastic end up in the digestive systems of air, sea, and land animals, crowding out nutrients. Plastics can also ensnare wildlife and limit their ability to feed or reproduce.

Estimating the amount and final location of plastic waste is difficult. According to an article in Science Advances, humans have produced about 6,300 metric tons of plastic waste. They have only recycled about 567 metric tons of that waste. Of the non-recycled plastic waste, humans have incinerated about 11%. The rest ended up in landfills or the environment. Plastic bags may take 20 years to decompose; plastic bottles may take up to 450 years.

Ocean currents sweep up plastic waste. These currents form the five major subtropical gyres. These gyres funnel plastic trash into mid-ocean garbage patches. Sunlight, wind, and saltwater break the plastic debris into smaller and smaller bits. Most plastic in the ocean measures less than 1 cm (0.39 inches) in diameter. Some have entered the digestive track of Marine animals. Plastic garbage patches exist in each of the five major subtropical gyres, vast circulating ocean currents depicted in the graphic below.


Diagram of the five major ocean-wide gyres with the North Pacific gyre highlighted. [Source: Wikimedia]

In 1997, Captain Charles Moore discovered the Great Pacific Garbage Patch. Some people have estimated that the Great Pacific Garbage Patch is twice as large as the continental US.

Organic material, like food, decomposes relatively quickly and moves through ecological systems. Synthetic material, such as plastic, does not move along. Plastic lasts a long time, sometimes they slowly emit dangerous chemicals, some toxic, into the environment.  Other time, plastics simply linger in their original forms. Either way, they present a danger to the balance in the ecology.

Recycling difficulties

According to Grove, “The recyclable plastics are ones where their polymers can be easily broken down back to monomers. It’s a bit like taking the beads off the string or taking apart the LEGO construction.” She said that non-plastic additives make it difficult to recycle because “the monomers cannot easily be recovered to be used to make new plastic.”

Even when people can recycle plastic, problems arise. Recycling workers have to manually examine each piece of waste to find the “resin identification code.” That code identifies how to process plastic waste. Plastic caps and lids are not always recyclable. This labor intensive process increases the cost to recycle some plastics. Generally, it is not cost-effective.

The economics of recycling

In addition to technical problems recycling plastics, a major economic problem looms. Recycling functions like other economic activities. Workers collect material for recycling. They bring it to a facility where other workers process it. The facility produces scrap and sells it to someone. That someone has been China, but not for long. In 2017, China bought over half of the global recycled material. China recently announced that, in 2020, it would stop buying recycled scrap. China has already stopped buying most paper and plastic.

According to reports, some recycling facilities have a surplus of scrap ready for sale but no buyers. Some have resorted to sending it to landfills. The loss of a major buyer threatens that product’s survival. If no replacement buyer emerges, the market for that product will collapse.

Currently, no other buyer has emerged. The market crisis has impacted the US, Canada, Australia, Great Britain and some parts of Europe. If no other buyer emerges, this could end the recycling business.

Our planet and its living systems face many challenges. The failure to plan for disposal of synthetic material after use threatens many species. PDK has technical potential for creating multi-use plastics and mitigating some of those threats.