A lot of plastic is impossible to recycle. Chemists are trying to change that

It feels good to recycle. When you sort soda bottles and plastic bags from the rest of your garbage, it seems like you’re helping the planet. The more plastic you put in the blue bin, the more you’re keeping out of landfills, right?

Wrong. No matter how much plastic you try to recycle, most ends up in the trash heap.

Take flexible food packages. Those films contain several layers, each made of a different type of plastic. Because each type must be recycled separately, those films are not recyclable. Even some items made from only one kind of plastic are not recyclable. Yogurt cups, for instance, contain a plastic called polypropylene (Pah-lee-PROH-puh-leen). When this gets recycled, it turns into a gross, dark, smelly material. So most recycling plants don’t bother with it.

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Only two kinds of plastic are commonly recycled in the United States. One is the type used in soda bottles. That’s called PET, short for polyethylene terephthalate (Pah-lee-ETH-uh-leen TAIR-eh-THAAL-ayt). The other is the plastic in milk jugs and detergent containers. That’s high-density polyethylene, or HDPE. Together, those plastics make up only a small fraction of plastic trash. In 2018 alone, the United States landfilled 27 million tons of plastic, according to the U.S. Environmental Protection Agency. A mere 3 million tons was recycled.

Low recycling rates aren’t just a problem in the United States. Only 9 percent of all the world’s plastic trash has ever been recycled. Twelve percent was burned. Seventy-nine percent has piled up on land or in waterways.

Even when plastic does get recycled, it isn’t good for much. Recycling changes the consistency of a plastic. So recycled plastics have to be mixed with brand-new material to make sturdy products. What’s more, recycling a bunch of different colored plastic together creates a dark mixture. That means a lot of recycled plastic can only be used to make items whose color doesn’t matter, such as benches and dumpsters.

Plastic recycling clearly has a lot of room for improvement. And with plastic piling up everywhere from mountaintops to the seafloor, there is an urgent need for better recycling. Luckily, chemists around the world are on the case. Some are trying to make it easier to recycle more types of plastic. Others are trying to turn recycled plastic into more useful products. Both strategies could cut how much plastic winds up in landfills or oceans.

False advertising
Many plastic products are labeled with a number inside a triangle that symbolizes recycling. Yet, only plastics with 1 (polyethylene terephthalate) or 2 (high-density polyethylene) are widely recycled in the United States. The rest typically get buried in landfills.

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Making plastics mix
There may be shortcuts to recycling unsorted mixes of plastics. Chemicals called “compatibilizers” help different plastics blend. There is no chemical that allows every type of plastic to mix. But Coates’ team has made one to combine polyethylene and polypropylene. That could make recycling much easier. Those two plastics make up the bulk of the world’s plastic trash.

The new compatibilizer contains specially designed molecules. Each molecule has four pieces. Two pieces of polyethylene alternate with two pieces of polypropylene. Those segments latch on to plastic molecules of the same kind in a mixture. It’s as if polyethylene were made of Legos, and polypropylene were made of Duplos. The compatibilizer molecule is like a connector that fits both types of blocks. That helps polyethylene and polypropylene molecules link up. The researchers reported this work in 2017 in Science.

The first test of this compatibilizer involved using it as a glue. Coates’ team spread a layer of the chemical between a strip of polyethylene and a strip of polypropylene. Then, the researchers tried to peel the plastics apart. The two plastics would normally separate easily. But with the glue between them, the plastic strips broke before the seal.

The researchers also mixed their compatibilizer into a melted blend of the two plastics. Adding just 1 percent of the new chemical created a tough plastic product.

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Good as new
Making it easier to recycle plastic isn’t enough. To reuse the same material over and over, recycled plastic needs to be as good as new. Right now, it’s second-rate.

One problem is all the extra chemicals in plastic trash. Plastic items often contain dyes, flame retardants and other additives. Current recycling cannot get rid of those contaminants. As a result, recycled plastic comes with lots of impurities. Few manufacturers can use plastic with a random mishmash of properties to make something new.

Read the full original article here: https://www.sciencenewsforstudents.org/article/new-recycling-technologies-could-keep-more-plastic-out-of-landfills

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