I know glass and aluminum can be recycled pretty efficiently, but if plastics have lower melting temperatures I would assume they’d denature less therefore offering better methods of recycling.
In: Chemistry
You can bake a cake, but you can’t rebake a cake in to a different cake.
A lot of plastics have their properties changed by being melted and won’t cool to have the same properties the had before.
Glass and Aluminum are quite different from plastic.
Aluminum is made of matching atoms, its pretty much pure. Melt it down, cook off any impurities and you’ve got yourself fresh aluminum which is indistinguishable from the original. Making fresh aluminum is also ludicrously energy intensive so there’s a lot of incentive to collect and recycle previously used aluminum
Plastic is tricky because not all plastics are created equal. In general, plastics are long spaghetti strands that all stick together to give you the nice plastic you want, they’re polymers which means they’re made from long strings of monomers that are connected together. When you recycle your plastics you break your spaghetti strands, after a couple rounds of recycling you have couscous instead of spaghetti which doesn’t work at all.
Making it even harder, “plastic” encompasses a broad variety of materials and if you don’t separate your #1 plastic from your #2 or #6 you don’t get plastic you can reuse at the end, you just get mush with uncertain properties, and since there isn’t a great way to separate plastics by material quickly it greatly adds to the cost of plastic recycling because you need a manual sorting stage early on.
Where I live (Alberta, Canada) we have a blue bin that we put all our recyclables in. Cardboard, glass, tin cans, paper, plastics etc. We have a chart indicating which ones are accepted. For plastic, they take everything (#1 thru #7) but not expanded polystyrene (stryofoam).
Ours it taken to a facility and hand sorted.
*Very* simply, when glass and metal are recycled they can be melted at a temperature that burns off the various contaminants still attached (no cleaning process is perfect) and then the burnt stuff can be removed.
When plastic melts it doesn’t get that hot, so the contaminants are mixed in with the plastic, resulting in a lower quality material. If you heated the plastic enough to burn the contaminants, you would burn the plastic too.
The need to clean the plastic better, and also sort it into various types of plastic, increases the cost of recycling significantly.
why? well because unlike aluminum it’s cheaper to make new plastic than to recycle it.
Unlike glass old plastic isn’t needed to make new plastic. Modern float glass requies ground old glass in its manufacture and aside from that ground glass in itself is a useful commodety.
There’s economic utility in recycling glass and aluminum none in plastic.
As an aside, surgical masks are made of a cloth-like polypropylene. That’s just plastic that’s been extruded into very thin light fibers. The best way to get rid of this from the environment is to incinerate them. While combusting plastics seem like a toxic emanation of chemicals, it’s actually cleaner than burying them into the ground. They basically burn to nothing and won’t leave anything behind.
What makes it hard to recycle efficiently is what makes plastics very useful in the first place. It is cheap to produce, inert, strong (easy to make containers), durable.
To recycle plastics, economically, it has to be done at a low cost, degrade something inert (heat, chemicals, mechanical processing) and containers are volumetrically inefficient for transportation (end up delivering mostly air, unless they are pre-crushed properly).
Basically you’re going against the very reasons they were useful in the first place.
Plastics are produced using plastic resin which are tiny pellets of plastic. Resins vary drastically by industry and brand based on the type of plastics being used and colorant that is being added.
This makes recycling extremely complex and expensive. Plastic must be sorted by type HDPE, PPE, etc. and by color. The plastic is then reduced back into pellets based on type and then reproduced.
When recycled, plastic will have impurities and depending on the type and number of times the plastic has been recycled it will also be weaker (more brittle). Eventually plastic can no longer be recycled because it has become too weak from the process and will crack.
Ultimately, it is much cheaper for companies to not use recycled plastic and their packaging looks cleaner. There are biodegradable resins in the works but none that I’m aware of are completely biodegradable and as you’d expect they cost more.
Source: 6 years in product development for a hair care brand.
Because plastic is cheap enough to buy new, so there is not a big demand for efficient plastic recycling methods and processes.
Why can’t we throw our garbage into an active volcano?
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