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Even better than the first time?

2 March 2023

How recycling can make PVC-U frames even stronger.

Recycled products, it seems, have an image problem.

Even though more and more of us understand the importance of recycling for the environment, there’s still a feeling among the general public that anything made from recycled material is somehow ‘second best’. Fine for utility items like toilet paper or bin liners. Less so for expensive purchases we expect to last for years, like replacement doors and windows.

But is that strictly true? Scientific studies have shown recycling PVC-U can actually make it stronger, so we put the question to Dr. Michele Edge, a leading figure in polymer science research at Manchester Metropolitan University, to see if things really can be better the second time around.

Dr Edge, is it true that recycled PVC-U can be harder wearing than the virgin plastic?

Absolutely. It sounds odd because we’re used to thinking of materials like wood or paper losing quality when they’re recycled.

But PVC-U that’s been recycled from old windows and doors and made into new ones can be even tougher than it was before. That’s not the case with all plastics – in fact, we’ve only found it to be true of PVC-U.

So what’s different about PVC-U that makes it behave this way?

It’s all to do with the molecular structure of the plastic itself, and how it mixes with other ingredients that make up the finished product. If you look at a piece of PVC-U under a powerful microscope, you’ll see its made of long spaghetti-like strands called polymers. These strands twist around each other during manufacture, and that’s what gives PVC-U its strength.

But we also add other ingredients called impact modifiers that bind the strands together even more tightly so your window frames have extra resistance to bumps and knocks.

We already know the long polymer strands don’t break down when the plastic is melted and reformed. That’s why recycled frames are just as strong as the originals. What we hadn’t realised was that some kinds of impact modifier change their structure and link the strands together in more places than they did before, making a sort of latticework that adds even more strength to the recycled product.

When did you make this discovery?

It was about eight years ago, during a research project into recycled plastic. After the first few experiments, the research team began to notice the recycled plastic was consistently stronger than the original sample.

When something seems too good to be true, your first response as a scientist is to ask ‘why?’. Sure enough, when we conducted more detailed tests, we discovered this tendency for impact modifiers to bond more readily to the polymer strands and strengthen the plastic itself.

How much stronger are the recycled frames? Can you put a number on it?

We can safely say PVC-U is up to 6% stronger when it’s recycled the first time. The next four of five times its recycled after that, it will still get stronger but by a smaller amount each time. When you think windows and doors can last up to 35 years before they’re replaced, that means they could potentially be getting stronger and stronger for over 200 years!

What does it mean for the PVC-U window and door industry?

It opens up all sorts of possibilities. There’s already a fair number of products out there with some recycled PVC-U content, but once people realise ‘recycled’ doesn’t mean inferior – it actually means even better – then that reluctance to specify or buy windows and doors made from recycled PVC-U should start to disappear.

And of course, the more recycled PVC-U there is in circulation, the less we need to rely on oil as a raw material and the less plastic there is going to landfill or incineration.

Ultimately, it’s as much about changing attitudes as it is about the science of recycling. Forward-looking companies know that if they control the quality of the recycling waste stream, they control the quality, performance and value of their recycled products.

And consumers who are becoming more aware of the world’s environmental problems, especially plastic waste, will start to see recycled PVC-U as a better choice not just on ethical level, but because it gives them stronger, longer lasting window and door frames too.

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