Retaining plastic transparency

Okay, so i realized that i put this in the wrong forum section, apologies for that. I’ve moved it here instead 🙂

`Okay, so i would like to explore whether it is possible to use recycled plastics to make something that would at least resemble window panes. It’s meant to be fitted for a greenery as part of a eco friendly city. So, if i take clear plastics (from for example water bottles), and i melt it, would it stay clear, or turn opaque? I don’t expect it to stay completely see through, but that shouldn’t really be needed. So has anyone tried something like this?


Thanks for the answer, very useful. Hope i can get to experimenting soon 🙂

Not yet,
We think our pressing plate is too lose. So instead of increasing pressure in the plate, the material starts to flow out of the mold. Planning to do more research on it. Although, the air-bubbles do give a nice effect as well.
Other thing we found out: with transparent objects it is easy to see the smallest scratches, so use a clean mold and sand a lot!

This is really nice for future reference! Have you done further research in how to avoid air bubbles? Must have something to do with pressure, temperature and time in the mold.

Hi Emil,
I am testing some transparency these days. In this slide show you will find transparant objects in the end of the document. Pc (cd boxes) are getting pretty clear. Pc is only brittle and I got some air bubbles.


Compression tests

Thanks man! i might just advice the guy with the green house to stick with glass then. Will present him with the different properties of PET, PC, PP and PVC, and maybe suggest we put it up and see what happens. But all in all it seems like it will cause some headaches.
I think i’ll do some further research and see what happens. Nonetheless, i can use all the info for other stuff than windows 🙂

They will turn yellow and brittle. This can cause some issues, since it will have very low overall strength, but if it is not a part of the stable structure of the greenhouse, it should have little to no influence.

Wind is of course a factor, but here in the north, never forget snow – it is so heavy and it creeps into cracks and expands with forces strong enough to crack glass-fiber boat hulls.

PC might be an option, but as you note yourself it is not easy to source. PC is often filled with crap as well (BPA for instance) which might be a concern in a greenhouse, so it belongs in the type ‘7’ category, so you’ll never know if you’ve found PC from reading marks or labels.

I think PVC is the most resilient thermoplastic you can find, this is the drain-pipe plastic – but as you might notice, drain-pipes also degrade in time.

Now, i don’t know if you have any experience on this, but do you think it will be an issue? I mean, i think it would be fine if it only turned slightly yellow, but the windows shouldn’t start falling apart all of a sudden. I guess the windows aren’t under that much stress, since they are stationary? Of course, i should probably factor in wind, which could cause some stress. I don’t know much about hydrolysis, but i will look into it.
Do you know of any plastic that won’t run into such issues?
I was thinking something like PC, even though it isn’t THAT widely available.
I must say, this forum has given invaluable info, thanks so far!

Maybe not melting it down is a way to go, but just reshaping it. Slice a PET bottle in half and iron it flat like a wrinked shirt – this way you don’t have to hit the perfect melting point, no grinding, no extrusion, so you can work with PET easily and the transparency should stay the same.

Yes PP degrades from UV light and heat <both found in a greenhouse. PET degrades from hydrolysis, which in a greenhouse is assisted by condensation. They will both wear down slowly and loose their rigidity, but they might still be see-through.

I would like it to be as easy as possible, so i can have more people involved in the project so your info about PET is valuable 🙂
Doesnt PP degrade in sunlight though? It would kinda be an issue if it has to be windows… Or maybe it’s not that big of an issue?

Hej @emil-b

Waterbottles is mainly PET, which is possible to recycle. However PET has a very high melting temperature and you have to hit the right temperature within +/- 5 degrees or you will have problems. – in other words, it’s very difficult to work with.

I would recommend trying polypropylene (PP), you’ll find it in all see-through food-products, i.e. grape-trays, tomato-trays etc.
You can recognize it by being almost clear, but slightly opaque. It very easy to source and easy to work with. Even without a fine polished mold you will still get plenty of light through – on this i have personal experience as i am working with recycling PP and MDPE at the moment.

last document is a pdf instructions to make it

aaaaaand here


and here

I think this is the best solution

Okay, this is actually really interesting, never considered something that simple! As it will be used for aquaponics, do you have any ideas about the insulation properties? Also, it will be mounted on the frame of an old greenery, so would have to think about how to fit it 🙂 But very cool nonetheless

Hej @davidpaag, nice to see a fellow Dane in here 🙂

At least it’s a pretty flat mold, since it’s a pane, so there aren’t any nooks and crannies that can make it difficult.
Do you by chance have any recommendations on which plastic to use? I was hoping to be able to use something like waterbottles, if i can ind a good source for it

Hej @emil-b

If you melt it at the proper temperature, the clarity should stay somewhat the same. The trick to get clarity is a very fine polished mold.