Eli5 why are so few plastics recyclable? Why cant you just melt it down and reuse it like glass?

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Eli5 why are so few plastics recyclable? Why cant you just melt it down and reuse it like glass?

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Anonymous 0 Comments

Many materials can’t just be melted down the way glass and metals can. Take wood for example, or cotton. However, this is not what is responsible for so mnay plastics not getting recycled. It’s not that plastics CAN’T be recycled, it’s that it’s too expensive to do so. Sadly it’s purely a matter of matter of cost, and that virgin (new) plastic is so cheap it’s not worth recycling.

Anonymous 0 Comments

The plastics that *are* recyclable can be melted down because when they are made, they don’t undergo a chemical change. They simply get melted, formed into a shape, and then cool/harden. (thermoplastic polymer)

The plastics that *are not* recyclable *cannot* be melted down because when they are made they undergo a chemical reaction that causes them to hold their shape and harden. Once that chemical reaction has occurred, it can’t easily be reversed by simple reheating. (thermosetting polymer)

Anonymous 0 Comments

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Anonymous 0 Comments

There are 2 broad categories of plastics. Thermoset plastics and thermoplastics. Thermoset plastics don’t melt, they burn so you can’t melt them down. When they’re made, they cure and are much stronger than thermoplastics. Thermoplastics melt but are much weaker, because they’re weaker, manufactures often put glass fiber in them to reinforce it which makes it much more difficult to recycle.

The major problem is among all the recyclable plastics is they need to be separated into their different types in order to be recycled, and the plastic degrades so virgin material needs to be added into each batch. You can mix different types, but the material you out of it is usually of lesser quality and used to make things like carpet and insulation for winter coats.

Anonymous 0 Comments

I’m not an expert so I can’t give a proper answer, but I’ll share what I know in case someone can fill in more (and teach me something):

A plastic object isn’t a uniform substance. A part made of, say, polyethylene will contain other chemicals. It might contain talc or other substances to make it stronger, or additives to absorb UV light. Each chemical added serves a purpose for that specific part. While it is easy to regrind waste from the production process back into that same part, it isn’t pure polyethylene (or whatever plastic) so it can’t be readily used in other parts if they need different properties.

If working with unknown plastics costs more than new plastic, then the manufacturer won’t buy recycled plastic.

Anonymous 0 Comments

In addition to the other comments here, certain types of recyclable plastic are extremely picky about only being with the exact same type of plastic. A single bottle of the wrong type ruins an enormous amount of plastic that was the right type …. throw the whole load into the garbage and start fresh.

Anonymous 0 Comments

Because they are really long chains of elements and when you start cutting up those chains their properties change.

The boiling point increases.

The boiling point decreases.

The chain breaks then it reforms back with another chain making a frankenplastic.

The chain breaks and reforms into rings. Or P’s, R’s, G’s. Basically, any knotty bendy twisty shape

All of these factors lead to a jumbled mess of molecules that eventually just seize up as a form of tar

Which…

Is just a really shitty thing to deal with.

Anonymous 0 Comments

Not an expert here but I remember it being explained this way: if you have a 2L bottle – the strands of plastic are as long as that bottle – say 14-inches. You can melt it down but those “strands” can’t be lengthened to make something longer / bigger than those original 14” strands. So the recycled material is only really usable as a filler etc. Though there are some companies that are burning recycled plastic to generate electricity.

Anonymous 0 Comments

Those non recyclable plastics might be turned into something else like an alternative aggregate material for concrete rather than sand. The advantages, to name two, would be disposal of something unwanted and reduced weight.

Anonymous 0 Comments

I was reading that just one wrong type mixed in with a batch can turn an entire vat into useless goo that will take hours if not days to clean out.

but there’s just no money in it. except for some minor amounts used to make fleece and some lumber decking substitutes, it costs far more to carefully separate, to truck it over, to clean it well enough…. than to get some petroleum waste product to make fresh new plastic.

Even glass isn’t profitable, our local refuse won’t take it anymore.