Why can some plastics be recycled but others can’t?

Why can some plastics be recycled but others can’t?

From The Conversation (27/5/24)…

(If you’re like me and can’t remember which plastic can be recycled, this might help.)

Why can some plastics be recycled but others can’t?

Basically, some plastics can be recycled because they are easy to melt down and make into other products. Others can’t be, or they contain extra ingredients that make them hard to recycle, such as dyes or chemicals that stop them catching fire.

But even if you could recycle the plastic, then you have a whole new problem: you have to find someone who will buy the recycled material to make new products.

There are many different types of plastic

Have you ever wondered why the plastic used to make soft drink bottles looks and feels so different to the plastic used for other types of containers – such as yoghurt tubs, lunch boxes or even plastic bags?

It turns out there’s more than one type of plastic. We classify plastic into seven main types. But there are many more when you consider all the mixtures and new or unusual varieties.

The raw material is almost always fossil fuels (oil or gas). Although these days, people can also make plastic from plants such as corn.

Either way, plastic is “synthetic”, which means it’s not natural. Long chains of molecules are stitched together to make “polymers” (from the Greek “poly”, meaning many, and “mer”, meaning parts). Different polymers make different types of plastic.

Some polymers are easier to recycle because they can be melted down and reshaped into new products. This includes number one on our list of seven main types: “polyethylene terephthalate”, found in soft drink bottles.

It also includes type number two, the “high-density polyethylene” in some milk bottles, and number five, “polypropylene”, which makes things like yoghurt containers.

Other plastics such as type number three, “polyvinyl chloride”, found in plumbing pipes, and number six, “polystyrene” such as Styrofoam, are much harder to recycle. That’s mainly because they tend to contain lots of extra ingredients, which makes melting and recycling difficult.

These extra ingredients can include dyes to make the plastic brightly coloured, or chemicals to stop the plastic catching fire. But these extra ingredients can make it harder for the plastic to be recycled.

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