<p>Plastic in general and 3d printer plastic specifically doesn't really melt so much as get softer in a range of temperatures (in a state refered to as &quot;plastic&quot; rather than liquid).  Below that range, it is a solid.  Above that range, it decomposes and ultimately burns.</p>
<p>If you want to make a solid block, you need to not only heat it to a specific temperature (which varies by plastic formulation), but also press it into a new shape.</p>

CC BY-SA 4.0
2021-12-26T01:20:50.393Z
2021-12-26T01:20:50.393Z
user10489
<p>PLA starts to char at about 220 °C. However, it also starts to soft at about 100 °C and becomes sloopy (and printable!) at 180 °C. Putting the oven to anything above 180 °C will, with the heating cycle an oven undergoes, result in air that is above the temperature it degrades into burning plastic.</p>
<p>keeping the temperature at or below 180 °C should prevent charring - you will have to take time though, as the plastic will flow only slowly on its own.</p>

CC BY-SA 4.0
2021-12-26T15:45:51.843Z
(Agree!) 20+ degree fluctuation on a consumer grade cooking oven is probably typical.  It's scary to put plastic in an oven under those conditions.
user10489
CC BY-SA 4.0
2021-12-27T19:04:11.383Z
I shall try again
AzulShiva
CC BY-SA 4.0
2021-12-26T09:53:50.853Z
2021-12-26T09:53:50.853Z
Trish
<p>Your kitchen oven is for food.  I'd strongly recommend using a different heating device for this.  Your oven probably has oils in it that are contaminating the plastic, and the plastic will make your later cooked-food contaminated.  I suggest cleaning your oven before cooking food, too.</p>
<p>Personally I've had good luck <strong>softening</strong> PLA with a hot air gun, essentially a workshop version of a hairdryer.  I've not tried forming it into shapes though.</p>
<p>I've been putting all my offcuts, bad prints, brims etc into a 2L icecream tub, and when its full of spidery bits, a 20 second heat with hot air shrivels it all down to 1/4 of the volume.</p>
<p>However I've not tried to make use of the resulting lump for anything.</p>

CC BY-SA 4.0
2021-12-26T01:49:06.963Z
2021-12-26T01:49:06.963Z
Criggie
<p>Every time I try melting a scrap piece of plastic it ends up turning brown, smelling, and smoking before even melting down completely. My entire home ends up filled with cancerous fumes and there's no way I'm baking any food in my oven ever again. I've tried different types of Nylon, ASA, and PLA and all of them turned brown before properly melting. I placed the scraps inside a glass jar inside an oven and tried both slowly increasing the temperature, and placing it into the preheated oven.</p>
<p>Absolutely disgusting.</p>
<p><a href="https://i.sstatic.net/TaFHz.jpg" rel="nofollow noreferrer" title="Glass jar with burnt melted plastic"><img src="https://i.sstatic.net/TaFHz.jpg" alt="Glass jar with burnt melted plastic" title="Glass jar with burnt melted plastic" /></a></p>
<p><a href="https://i.sstatic.net/0QNUQ.jpg" rel="nofollow noreferrer" title="Baking pan with burnt melted plastic"><img src="https://i.sstatic.net/0QNUQ.jpg" alt="Baking pan with burnt melted plastic" title="Baking pan with burnt melted plastic" /></a></p>
<p>I would like to melt it into blocks or cylinders or planes and further process it with my lathe, my CNC mill, bandsaw... whatever, like this guy: <div class="youtube-embed"><div>
                <iframe width="640px" height="395px" src="https://www.youtube.com/embed/G-HWrDMr0ks?start=0"></iframe>
            </div></div></p>

CC BY-SA 4.0
2021-12-25T18:19:48.137Z
What temperature are you using? You most certainly can't use a stovetop for this because it's not temperature-controlled. An oven is controlled, but not precisely, and might work if you set the temperature significantly below the print temperature for the material then only slowly raise it. Fortunately, at least for PLA, there should be minimal "cancerous fumes" (only possibly from pigments/additives; otherwise it's comparable to burning a pan full of corn).
R.. GitHub STOP HELPING ICE
CC BY-SA 4.0
2021-12-25T20:04:03.580Z
I wish to be able to explain why so many 3D printing folks are so obsessed with reusing scrap plastic. Processing of plastic needs precise temperatures, and high pressure. It would be beter to use your CNC and lathe with a more machineable material than molten / reprocessed crap plastic.
mguima
CC BY-SA 4.0
2021-12-25T20:35:42.587Z
PLA starts to melt at 100 °C, you sholdn't need more than 150 °C!
Trish
CC BY-SA 4.0
2021-12-26T01:36:55.073Z
@mguima: Probably because of ending up with so much of it and wanting something to do with it other than "throw it in the trash".
R.. GitHub STOP HELPING ICE
CC BY-SA 4.0
2021-12-26T20:07:28.323Z
air is needed to burn.  you can go a bit hotter with a controlled atmosphere - simplest form of which may be sealed chamber loaded with only plastic (your scraps and some virgin pellets)- may need to grind some scraps to size for better packing too... Connect such a chamber to a device similar to an extrusion head and press into recycled filament...
Abel
CC BY-SA 4.0
2021-12-26T21:00:04.883Z
With a controlled atmosphere, it won't burn *the same way*.  It'll still decompose, out gas toxic fumes, and carbonize.  It's better to just not let it get too hot.
user10489
CC BY-SA 4.0
2021-12-27T18:58:11.563Z
@R..GitHubSTOPHELPINGICE I put it in the oven. I just placed it on the stovetop to cool and to make the picture.
AzulShiva
CC BY-SA 4.0
2021-12-27T18:58:59.407Z
@Trish It will cristallize at 100 or 150 degrees. It actually hardens. It will only soften up around 200.
AzulShiva
CC BY-SA 4.0
2021-12-27T19:00:14.013Z
Unfortunately I don't have a grinder but I do have an entire 120 liter barrel filled with scraps. And that's only PLA.
AzulShiva
<recycling>
Melting 3D printed scraps: Burns up
AzulShiva
# Melting 3D printed scraps: Burns up

(Asked by: username_0 on 2021-12-25)

Every time I try melting a scrap piece of plastic it ends up turning brown, smelling, and smoking before even melting down completely. My entire home ends up filled with cancerous fumes and there's no way I'm baking any food in my oven ever again. I've tried different types of Nylon, ASA, and PLA and all of them turned brown before properly melting. I placed the scraps inside a glass jar inside an oven and tried both slowly increasing the temperature, and placing it into the preheated oven.

Absolutely disgusting.

[![Glass jar with burnt melted plastic](https://i.sstatic.net/TaFHz.jpg "Glass jar with burnt melted plastic")](https://i.sstatic.net/TaFHz.jpg "Glass jar with burnt melted plastic")

[![Baking pan with burnt melted plastic](https://i.sstatic.net/0QNUQ.jpg "Baking pan with burnt melted plastic")](https://i.sstatic.net/0QNUQ.jpg "Baking pan with burnt melted plastic")

I would like to melt it into blocks or cylinders or planes and further process it with my lathe, my CNC mill, bandsaw... whatever, like this guy:

**Tags:** recycling
> **Comments:**
> **username_1**: What temperature are you using? You most certainly can't use a stovetop for this because it's not temperature-controlled. An oven is controlled, but not precisely, and might work if you set the temperature significantly below the print temperature for the material then only slowly raise it. Fortunately, at least for PLA, there should be minimal "cancerous fumes" (only possibly from pigments/additives; otherwise it's comparable to burning a pan full of corn).  
> **username_2**: I wish to be able to explain why so many 3D printing folks are so obsessed with reusing scrap plastic. Processing of plastic needs precise temperatures, and high pressure. It would be beter to use your CNC and lathe with a more machineable material than molten / reprocessed crap plastic.  
> **username_3**: PLA starts to melt at 100 °C, you sholdn't need more than 150 °C!  
> **username_1**: @mguima: Probably because of ending up with so much of it and wanting something to do with it other than "throw it in the trash".  
> **username_4**: air is needed to burn.  you can go a bit hotter with a controlled atmosphere - simplest form of which may be sealed chamber loaded with only plastic (your scraps and some virgin pellets)- may need to grind some scraps to size for better packing too... Connect such a chamber to a device similar to an extrusion head and press into recycled filament...  
> **username_5**: With a controlled atmosphere, it won't burn *the same way*.  It'll still decompose, out gas toxic fumes, and carbonize.  It's better to just not let it get too hot.  
> **username_0**: @R..GitHubSTOPHELPINGICE I put it in the oven. I just placed it on the stovetop to cool and to make the picture.  
> **username_0**: @Trish It will cristallize at 100 or 150 degrees. It actually hardens. It will only soften up around 200.  
> **username_0**: Unfortunately I don't have a grinder but I do have an entire 120 liter barrel filled with scraps. And that's only PLA.  

---

## 3 answers

### Answer by username_5 on 2021-12-26. Score: 2

Plastic in general and 3d printer plastic specifically doesn't really melt so much as get softer in a range of temperatures (in a state refered to as "plastic" rather than liquid). Below that range, it is a solid. Above that range, it decomposes and ultimately burns.

If you want to make a solid block, you need to not only heat it to a specific temperature (which varies by plastic formulation), but also press it into a new shape.


---

### Answer by username_3 on 2021-12-26. Score: 2

PLA starts to char at about 220 °C. However, it also starts to soft at about 100 °C and becomes sloopy (and printable!) at 180 °C. Putting the oven to anything above 180 °C will, with the heating cycle an oven undergoes, result in air that is above the temperature it degrades into burning plastic.

keeping the temperature at or below 180 °C should prevent charring - you will have to take time though, as the plastic will flow only slowly on its own.

> **Comments:**
> **username_5**: (Agree!) 20+ degree fluctuation on a consumer grade cooking oven is probably typical.  It's scary to put plastic in an oven under those conditions.  
> **username_0**: I shall try again  

---

### Answer by username_6 on 2021-12-26. Score: 1

Your kitchen oven is for food. I'd strongly recommend using a different heating device for this. Your oven probably has oils in it that are contaminating the plastic, and the plastic will make your later cooked-food contaminated. I suggest cleaning your oven before cooking food, too.

Personally I've had good luck **softening** PLA with a hot air gun, essentially a workshop version of a hairdryer. I've not tried forming it into shapes though.

I've been putting all my offcuts, bad prints, brims etc into a 2L icecream tub, and when its full of spidery bits, a 20 second heat with hot air shrivels it all down to 1/4 of the volume.

However I've not tried to make use of the resulting lump for anything.


---

