I need to use a custom part inside high vacuum (cryo vacuum), for example as a shadow mask. If PLA/ABS are not volatile, I could just print the part I need.
The question is, are ABS or PLA too volatile to be used in cryo vacuum chambers?
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Sign up to join this communityI need to use a custom part inside high vacuum (cryo vacuum), for example as a shadow mask. If PLA/ABS are not volatile, I could just print the part I need.
The question is, are ABS or PLA too volatile to be used in cryo vacuum chambers?
It is unlikely polymers will be an issue, but the additives used may pose problems. Polymers should have negligible volatility due to their long chain nature. Polymer additives may still pose an issue. You may need to test any particular filament material to ensure it meets your needs.
Polymers do not behave like small molecules in terms of mobility. Whereas some small molecules are relatively free to leave the bulk at any temperature due to the nature of neighbor-neighbor bonding, the polymer molecules of interest have purely covalent bonding along their backbones. For a molecule to leave the bulk and enter a gas phase, not only does the molecule have to mechanically disentangle from its neighbors, the entire chain must simultaneously defeat secondary bonding along its entire length, which can be many thousands of atoms long. While it is possible for chains to disentangle, that only occurs above the glass transition temperature, or $T_g$, of the polymer in question. Above the $T_g$ is when reptation - relative, cooperative chain motion - becomes possible. Reptation time is inversely proportional to temperature, as noted in the Wikipedia article.
As a result, polymers should have negligible volatility, especially below their glass transition temperatures. The lowest $T_g$ is of the butadiene rubber in the ABS copolymer (acrylonitrile-butadiene-styrene), at about $-90\ \textrm{°C}$. The styrene has a $T_g$ of about $105\ \textrm{°C}$. Because ABS is a block or graft copolymer, meaning the different components reside on the same chain, the molecules are effectively "locked in" below the $T_g$ of the styrene component. PLA, or poly(lactic acid), typically has a $T_g$ of about $60\ \textrm{°C}$. If your cryo chamber is below these temperatures then the molecules have virtually no freedom to move relative to one another, let alone leave the bulk. Note that this is not a guarantee due to the stochastic nature of kinetics, and the dearth of studies on polymer volatility.
What you more likely need to be worried about are polymer modifiers:
all of which are small molecules. Some of these are almost certainly present in printed polymers due to the special requirements of printing. Diluents are likely in some filament-printer systems to achieve optimal high-resolution flow. Compatibilizers are unlikely in "pure" ABS and PLA, but are possible depending on the specifics of the filament material. Trace solvents are possible especially if the filament is of low quality. Additionally, some forms of PLA are mildly hydrophilic, and may absorb water. Drying printed PLA may be useful.