Eli5 why are so few plastics recyclable? Why cant you just melt it down and reuse it like glass?
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Non thermoset plastics are recyclable like that if, and only if they’re pure, not contaminated (such as food oils soaked into surface) or chemically damaged (like sun damage). Technology can handle some of this, but too much of any of these problems can mean that the final product of this kind recycling isn’t useful or is at best not as good. Notice that recycled plastic products can feel flimsier for example.
If plastics are highly mixed with other plastics they simply can’t be recycled as a mixture. If this is tried one plastic might get damaged at the others melting temperature, or one might melt while the other stays solid.
Problem is, waste is, by its very nature, mixed. So unless plastic is sorted into pure(ish) states this isn’t possible. It’s hard to tell the difference between some plastics (e.g. PVC and PE films) so sorting cant fix it all. Automatic sorting technology for plastics isn’t that great and there comes a point where the cost of the energy to sort is high enough to prevent profit making or environmental harm of recycling is higher than landfilling it. At that point it’s unrecyclable.
Glass doesn’t suffer from these issues because it is more chemically stable, doesn’t absorb things, and sorting is simply by colour. The only issue is that that making colourless glass is hard due to contamination with green/brown glass.
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