Sciencemadness Discussion Board

Need Help: Polymer Chemistry, Surfactants and Inerts

MineMan - 24-10-2018 at 17:08

Hello fellow scientist! I need your help!

I am working on making 3D printing filaments with a high amount of inert metal particles (SS and Copper mainly) for special projects. I have already invested in an extruder and melting pot and have made various filaments that contain 80 percent metal. But the filaments are too brittle to be fed reliably through an extruder system of the printer....

Upon examination of the filament it is clear the reason for the brittleness is porosity. Its true you don't know what you don't know, and I thought it would just be as simple as trying different polymers to see which could hold the most metal content while retaining most of it's plastic properties... I think this is too simple.

After researching Metal Injection Molding it seems that small amounts of surfacants and lubricants are added into the polymer to eliminate the porosity, and increase the binding between the metal particles and polymers...

I don't even know where to start here because most of this information seems propitiatory, so my questions are?

How do I determine the best binder/polymer to hold inert materials (metal powders)? Is this based on the original flexibility of the polymer without any inerts? Elongation percent at breakage?? Smoothness?

In the world of thousands of reagents, based on chemistry and not luck, how do I pick an appropriate surfactant and lubricant?

I should say that the metal powder I am using is 625 mesh... the same used in metal injection molding feedstock. I don't need my filament to be optimized... I just need it to work, and any guidance on how I can take the guesswork out of this and replace it with science is appreciated!!

A large chemical company has a filament that has 80 percent metal powder while being flexible enough that it can even be wrapped around pulleys!!

Mine does not have to be perfect, it just has to work, as I need to use metal powders that they do not offer...



[Edited on 25-10-2018 by MineMan]

gatosgr - 25-10-2018 at 12:57

What kind of plastic? You can modify the metal particles since they are oxidized and can react with many groups, a surfactant would work only partially.

[Edited on 25-10-2018 by gatosgr]

MineMan - 28-10-2018 at 12:06

Gatosgr! Thank you for the reply! Specifically thermo plastics that are readily available and mostly amorphous (warps less than crystalline).

For example PLA and TPU.... I am lookig at other [plastics and can PM you more info..

What do you mean by modifying the metal particles? Small quantity experiments show that a Surfactant does indeed help with uniform mixing, but decreases the the amount of strain the plastic breaks under during bending.

I would like to try a plasticizer other than PEG... but I don't know what method is used to match specific plastizers with specific polymers...

The EM folks have good experience with plasticizing... but those are crystalline materials...

I just don't know what I don't know

andy1988 - 28-10-2018 at 14:00

Quote: Originally posted by MineMan  
I am working on making 3D printing filaments with a high amount of inert metal particles (SS and Copper mainly) for special projects. I have already invested in an extruder and melting pot and have made various filaments that contain 80 percent metal. But the filaments are too brittle to be fed reliably through an extruder system of the printer....

Upon examination of the filament it is clear the reason for the brittleness is porosity. Its true you don't know what you don't know, and I thought it would just be as simple as trying different polymers to see which could hold the most metal content while retaining most of it's plastic properties... I think this is too simple.

You are trying to maximize magnetic permeability & magnetic saturation? For the magnetic core of a solenoid? I've looked into this problem before, but was going for the tuna-can mixing method route, and pouring it into a mold. Cool you bought an extruder to make filament.

See this study from 1996 funded by the U.S. Office of Naval Research Relative Magnetic Permeability of Polymeric Composites with Hybrid Particulate Fillers.

PLA has an issue with adsorbing moisture, maybe this is causing the porosity you're observing? PLA has a lower deformation temperature compared to alternatives as well... and electric motors can get hot.

With all this metal added, it is very abrasive on the extruder. Consider looking into additives which minimize that abrasion and extend the lifespan of the extruder screw/barrel/die. Talc was one such additive IIRC, mentioned on an article somewhere on ptoline.com

Now, extruders are not really one size fits all... you may find a different design and/or running parameters may help improve/resolve your issue... all sorts of things you can look into such as screw flight, venting, adjustment for the viscosity of the polymer, and surging. Some useful info on this website/forum. EDIT: Then again, many of these adjustments may be just to optimize throughput and energy efficiency... I am no expert.
Quote: Originally posted by MineMan  

I would like to try a plasticizer other than PEG... but I don't know what method is used to match specific plastizers with specific polymers...

Literature search. Something along the lines of, e.g. "PLA plasticizer review". Maybe "compounding". You'll see the melt window, decomposition temperature, and other details depending on % plasticizer added. I've found often times the best information is buried in very expensive books. If you're asking about an analytical method instead of interpreting empirical results I have no idea either. I believe I did see an analytical overview somewhere but I couldn't find it at a glance in my bookmarks.

Hopefully others can help with your other chemistry questions... but I would expect the problem has already been well investigated and published in literature somewhere (but probably not with your plastic/plasticizer/%metal of choice). If you're going to make a lot, I do recommend you look into a biodegradable plastic and biodegradable plasticizer. I am thinking this is more a rheology/process issue and not a surfactant issue? Sorry I don't have more specific answers. I am no expert, just an amateur.

A photo or two of your experiments would be neat to see :-)

[Edited on 29-10-2018 by andy1988]

DrP - 13-11-2018 at 07:05

How is this progressing Mine Man? Have you found a polymer that works well yet?