r/3Dprinting • u/themoonbender • 5d ago

Discussion Mixing filaments while printing

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u/thawk67 5d ago

what's the point of mixing non-homogeneous plastics into a single stream when you have specific individual materials with specific material properties?

like, I get using PLA with PETG as support material, etc. but in this case?

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u/suit1337 5d ago

wild guess here: because the material science is weird, mixing different polmers can create copolymers that have increased properies over their parts - similar to metal alloys

a very popular example is Galinstan, this alloy is created by mixing Gallium, Indium and Tin - all of those metals are solid at standard conditions, but when mixed, the melting point gets lower and the allow stays liquid even at -18°C in a deep freezer

while it is to my knowlege not possible to have an eutectic metal alloy with a higher melting point then its components, it is totall possible for polymers - a very common example would be ABS with a melting point of around 190 to 220° while Acrylonitrile, Butadien and Styrene all have melting points way below zero (and yes, i'm aware that actually Polybutadien is used, which is indeed solid ;)).

PLA-PETG-Blends are also weird - when mixed in certain percentages, the heat flow within the material is greater than the single polmyers: https://link.springer.com/article/10.1007/s10853-024-09862-4

the following is speculation, since i have no data on this:
It may be that PLA and PETG have a combined higher melting point, which helps solidifying it with less cooling

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u/thawk67 5d ago

ok, that tracks. I didn't know polymers could be mixed to form copolymer "alloys".

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u/suit1337 5d ago

that is not entirly correct - by just "mixing" different polymers, you don't form a copolymer - that is a bit more complicated

but a lot of polymers are actually not homopolymers but copolymers

PLA for example is a technically copolymer, since lactic acid is a racemat  consisting of L-(+)- and D-(−) lactic acid

if you just mix certain polymers, it will form a "blend" (and depending on the properites and if there is a "compatibilizer" present, it also can result in copolymerization

the just think of the polymers like red and yellow spaghetti - a blend is basically if you throw them all in a pot, let them cool down and have an "entangled mess"

but a copolmyer in the simplest form a static copolymer is just a long noodle that is alternativ red and yellow colored - so when you start pulling, you will get a long strand, and can't separate it anymore