Ever since Dustin Hoffman heard the word “Plastics” in 1967, these materials have blossomed into every aspect of modern life. I cannot find an area of life where plastics are not ubiquitous. According to the EPA, each year America generates over 35 million tons of plastics. Over 70 billion tons worldwide.
But we just aren’t recycling enough of it to address the resulting pollution or climate change or just our need to stop the astronomical piles of garbage that are growing worldwide.
Microplastic particles are more and more common as a pollutant in the world today. In 2014, NOAA estimated that there were up to 51 trillion individual pieces of microplastic in the world’s oceans.
China will no longer take our recycling junk. A few years ago, Beijing banned imports of twenty-four varieties of solid waste, including types of plastic commonly sent from the United States. The reason given was for environmental protection, since large amounts of dirty and hazardous constituents are often mixed in with these materials.
Contrary to what many of us think, most plastics are just landfilled. But it makes us feel quite good to put these into those recycle bins. Plastic Starbuck’s cups, ketchup squeeze bottles and plastic spoons, we assume anything with a number inside a rounded triangle of arrows will end up being recycled.
But that is not the case. As Maria Temming’s recent in-depth coverage in Science News shows, almost all of it goes into landfills or gets dumped in the ocean. Some of it gets burned (see figure above). Even though the absolute amount of plastic that is being recycled is going up slightly, the amount being landfilled is still going up much much more.
According to the EPA, America landfilled 27 million tons of plastic in 2018 but only recycled 3 million tons. It’s even worse worldwide, where only 0.5 out of 6.3 billion tons of plastics have been recycled. Just 0.8 billion tons was burned.
Only plastics with the numbers 1 and 2 in the triangle ever get recycled, even a little, and these only make up about a quarter of the total. These include those in plastic soda bottles, polyethylene terephthalate or PET, and the plastic found in milk jugs and detergent containers, high-density polyethylene or HDPE (see figure below).
And even these plastics aren’t good for much when recycled. You have to melt PET down which changes its state, requiring it to be mixed with brand-new plastic to make a final product. Recycling HDPE makes a dark plastic only good for making things like park benches and waste bins.
There are many hurdles to fixing this issue. First, every material has to be separated and separately processed, they don’t mix. It’s easy to separate metal from plastic using magnetic or density separators, but separating different plastics from each other takes people and machines. This is followed by washing, shredding, melting and remolding.
But that works only for materials with the same composition. Some articles, like spray bottles, can have different plastics for the bottle, the cap and the sprayer. Or packaging plastics for food that can have several layers of different incompatible plastics.
Another issue is that recycled plastics inherit all the other contaminants in the original plastic like dyes, flame retardants and other additives. Few manufacturers can use plastic with a random mishmash of properties and chemicals to make something new.
In addition, recycling breaks some of the chemical bonds in the plastic molecules, which affects the strength and consistency of the material. As Maria Temming puts it, “Melting down and remolding plastic is sort of like reheating pizza in the microwave — you get out basically what you put in, just not as good. That limits the number of times plastic can be recycled before it has to be landfilled.”
So what can we do?
Some propose replacing plastics with biodegradable materials, but those replacements fail in the strength and cost departments.
Plastics have become such a part of modern society that we probably will not get rid of them…ever. So chemists are trying to figure out how to make it easier to recycle existing plastics and make the result more useful, as well as making completely new plastics that are easy to recycle.
For multiple-layers of incompatible plastics, chemical engineers like George Huber of the University of Wisconsin at Madison have devised processes that use a series of liquid solvents to dissolve each individual plastic component, choosing the right solvents to dissolve each individual kind of plastic in sequence.
These engineers are also looking at additives called compatibilizers that can link otherwise incompatible plastic molecules, making newly strong plastics.
Another solution could lie in a new kind of recycling process, called chemical recycling, which involves taking plastics apart on the molecular level, separating these plastic molecules from dyes and other contaminants, and piecing the molecules back together into new plastic.
This would allow the materials to be recycled an infinite number of times.
There are other research directions that look promising as well. Temming discusses a French company called Carbios which is testing and redesigning enzymes produced by microorganisms to break down various plastics, especially PET.
“The enzyme is like a molecular scissor,” says Alain Marty, chief scientific officer at Carbios. To make the enzyme better at snipping apart PET as opposed to its natural organic matter, “we redesigned what we call the active site of the enzyme,” Marty says.
Enzymes are actually biologically-produced catalysts, so other researchers are looking at using traditional chemical catalysts, like platinum, under various conditions, to chop the tougher plastic polymers into useful bits.
But the long-term solution is to make plastics that last, ones that never need to go into a landfill, plastics so tough they will last a lifetime. Or plastics that fall apart on command to be reformed into the next product.
Of course, it will take lots of time and lots of money to get to the point where we’ve mostly solved this issue.
So we better get going.