Chemistry Forums for Students > Undergraduate General Chemistry Forum

Behaviour of molten metal interacting with polylactic acid

(1/5) > >>

tunkor:
Hello all!

I am kinda shooting in the dark here. I'm a mechanical engineering student with very little knowledge of chemistry. I'm trying to figure out a proces for casting a 3d printed model by directly pouring molten iron (1400C) on top of it.

The model is coated by a ceramic coating and put in a sand container. The molten metal 'interacts' with the PLA model by melting and evaporating(?) the PLA. The metal will take the shape of the 3D printed model inside the ceramic coating shell, leaving a casted product. I have done a few tests which came out decent, I am however eager to know about what exactly happens when these two materials (fluid metal, and PLA) interact with eachother.

What happens to the PLA, how fast does this happen, what kind of rest products are left behind, how much gas does the PLA produce? Information like this would be useful for me to know, to maybe screen for other printing materials other than PLA. I'm basically trying to analytically see what happens with the material.

For example, I want as little gas production from the material, because this gas needs to leave via the ceramic coating. So if I can screen a material beforehand this would be useful.

Would anyone know how I can figure this out, maybe some useful online tools/databases/literature?

I hope I am asking this in the right place!

Thanks in advance.

Kind regards.

Borek:
By the look of it I would expect decomposition to a mixture of gases (CO, CO2, ethylene, water, some of them at these temperatures would immediately burn on contact with air), and perhaps some elemental carbon (which can easily dissolve in the iron). Assuming simple decomposition to CO2 and ethylene simple stoichiometry is all you need to calculate amounts.

The exact outcome is insanely difficult to predict, this is one of these cases where the experimental approach is the only viable way of getting into details.

Enthalpy:
This process uses a foam traditionally, polystyrene foam. It works because the same volume holds little foam mass or much iron mass. Polystyrene leaves uncontrolled dirty things (mostly carbon) whose small proportion in iron is tolerable.

I can't tell if the same is done with plain polymer like PLA nor if it can succeed.

* The amount of PLA needs much heat to decompose, possibly more than hot iron brings.
* The decomposition of PLA would leave a huge amount of carbon. Probably, iron can't fill the mold, but if iron achieves to decompose the PLA, too much carbon in iron will spoil its properties.It that process already used? What lets you suppose that the dirty things will escape through the ceramic?

What the reaction is: mainly a pyrolysis, which is a pedant word for "makes a bunch of unknown dirty things". The big heat breaks all big molecules, the atoms rearrange in small molecules and often in graphite. From the C3H4O2 period, 2×CO may escape and possibly carry some hydrogen away. From the remaining C, some may leave as small hydrocarbons, but I suppose some remains as graphite.

By the way, pyrolysis products are always a bit toxic. Nothing tragic, but better do it outside, or in a well ventilated area, without making a chicha of it. If this shall become a regular activity, you need some protective measures.

Borek:

--- Quote from: Enthalpy on March 24, 2020, 06:47:26 PM ---It that process already used?
--- End quote ---


--- Quote from: tunkor on March 24, 2020, 06:08:25 AM ---I have done a few tests which came out decent
--- End quote ---

tunkor:

--- Quote from: Enthalpy on March 24, 2020, 06:47:26 PM ---This process uses a foam traditionally, polystyrene foam. It works because the same volume holds little foam mass or much iron mass. Polystyrene leaves uncontrolled dirty things (mostly carbon) whose small proportion in iron is tolerable.

I can't tell if the same is done with plain polymer like PLA nor if it can succeed.

* The amount of PLA needs much heat to decompose, possibly more than hot iron brings.
* The decomposition of PLA would leave a huge amount of carbon. Probably, iron can't fill the mold, but if iron achieves to decompose the PLA, too much carbon in iron will spoil its properties.It that process already used? What lets you suppose that the dirty things will escape through the ceramic?

What the reaction is: mainly a pyrolysis, which is a pedant word for "makes a bunch of unknown dirty things". The big heat breaks all big molecules, the atoms rearrange in small molecules and often in graphite. From the C3H4O2 period, 2×CO may escape and possibly carry some hydrogen away. From the remaining C, some may leave as small hydrocarbons, but I suppose some remains as graphite.

By the way, pyrolysis products are always a bit toxic. Nothing tragic, but better do it outside, or in a well ventilated area, without making a chicha of it. If this shall become a regular activity, you need some protective measures.

--- End quote ---

The lost foam proces is what I'm 'copying' from. I am using a PLA which has a foaming additive to it, achieving very low weight printed parts. This was kinda the basis for starting this experiment, because the total density of the part can come pretty close to what a foam model would be. The difference being that the PLA model is mostly hollow, whereas the foam is homogeneous. This brings a difference in how the metal will fill the void (like the metal flowing too fast), but that's another story I am trying to experiment with.

How much energy does it take te decompose PLA compared to PS? Is this what activation energy means? How much carbon does PLA leave compared to PS?

I tried a few tests, but haven't checked the casted part for any properties (but this is in the works). The parts were pretty small and simple (a rounded off cube) but mostly casted fine, some parts did not fill up nicely. But I will be testing new PLA models soon which hopefully have even less mass which has to be burned.

By the way thank you so much for taking the time to reply, I really appreciate it!

Navigation

[0] Message Index

[#] Next page