Curious Kids: why can some plastics be recycled but not others?

Why can some plastics be recycled but others not?

Jessica, ten years old, Sydney

Great question Jessica! We use a lot of plastic in Australia and it’s disappointing to discover how little is recycled.

I work at a university with a team trying to find new ways for people to use less plastic, recycle more and not waste anything. So this is a question I think about a lot.

Basically, some plastics can be recycled because they are easily melted down and turned into other products. Others cannot be, or contain additional ingredients that make them difficult to recycle, such as dyes or chemicals that stop them from catching fire.

But even if you can recycle the plastic, then you have a whole new problem: you have to find someone to 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 soda bottles looks and feels so different from the plastic used for other types of containers like yogurt tubs, lunch boxes or even plastic bags?

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

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

However, plastic is synthetic, which means it is not natural. Long chains of molecules are stitched together to make polymers (from the Greek poly, meaning many, and mer, meaning part). Different polymers produce 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 the top seven types: polyethylene terephthalate, found in soft drink bottles.

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

Other plastics such as type number three, polyvinyl chloride, found in plumbing pipes, and number six, polystyrene like Styrofoam, are much more difficult to recycle. This is mainly because they tend to contain a lot of additional ingredients, which makes it difficult to melt and recycle.

These additional ingredients may include dyes to make the plastic bright, or chemicals to stop the plastic from burning. But these extra ingredients can make the plastic more difficult to recycle.

Did you know that almost 300 billion plastic coffee cups have found their way into landfills around the world? These cups were not recycled because they were made from a plastic-coated paper blend.

It is difficult to separate plastic from other materials. This makes it difficult to recycle them. But we can choose to use reusable or compostable coffee cups instead.

Plastic can also be too dirty to recycle. This is why you should always rinse plastics before putting them in the recycling bin.

Here’s a little tip. Check the label on plastic bottles, containers and packaging for the symbol that looks like a triangle made of arrows, with a number in the middle. Read the table below to see what the numbers mean and whether or not it’s worth putting that plastic in your recycling bin.

Just because it has a logo on it doesn’t mean it can be recycled. This depends on the recycling services available near where you live.

Search your local council’s website to see what facilities they have for recycling plastics. If it’s not clear, you can ask your council to explain what they can and can’t recycle.

Will anyone use recycled plastic and pay for it?

But if no one wants to use recycled plastic, then it’s hard to find anyone willing to recycle it in the first place.

We need to make it easier for people to sell the plastic they’ve collected to someone who wants to buy it and turn it into something else.

To do this work, we need:

• people to properly put used plastic in the recycling bin

• someone who wants to collect it

• a business that can recycle that type of plastic, and

• other businesses that will buy the recycled material.

In Australia, many people are willing to recycle their plastic and we have good recycling facilities, but not enough people are willing to buy items made from all recycled plastic.

One idea is for governments to get local businesses and councils to buy products made from recycled plastic. Then people who make products from recycled plastic will be able to sell them.

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Hello curious children! Have a question you’d like an expert to answer? Ask an adult to send your question to curiouskids@theconversation.edu.au