Mastodawn

(My dumb ass forgot to tag)

Hello Fediverse, I have a bit of a technical question about the chemistry of resins, drying oils and their polymerisation. Related to an ink-making project of mine, I'll tell more about that later. The thing is, I am *absolutely not* a chemist, so I turn to the Internet with the hope of finding the knowledge I am lacking! I explain more in the following thread, thanks in advance for reading and feel free to answer in either French or English.

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#chemistry #ink

So, I'm a pen and paper lover, and I wanted to make a durable ink of (most importantly) open composition, preferably plant-based. Resins and drying oils have caught my interest for two reasons : the firsts have an ability to set quickly, however they remain soluble in their solvent, the others… well, *dry* (although they actually cross-link) in a longer period of time (about a week for raw flaxseed oil, can be brought to under a day). Let me get into a few details here.

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Resins, at least natural ones, are essentially made of two compounds : long, acyclic chains or carbons, and another cyclic aliphatic, with several cycles, both compounds bearing a carboxylic (R-C(O)OH) and a few alcohol (R-OH) groups. When the solvent evaporates, intermolecular forces make the resin set, and the whole thing may take years to cure, if untreated.

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Drying oils are made of unsaturated fats. The more double bonds they have, the more “drying” they are.

I am not sure what happens with the double bonds, however dioxygen from the air will create a hydroperoxyde (R-O-OH) that will allow the cross-linking of two carbon chains as an ether (R1-O-R2) and release water. Siccatives (metallic soaps) catalyse these reactions, and interestingly, they can also catalyse the polymerisation of resins (this time, through esterification).

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Now that all this is said, I believe it would be… *mechanically* beneficial to use both resin and oil, for flow at first, then for the plasticity of the dried ink film. But anyway, if I want rapid setting, I will need resin, and if I want curing, I will need the addition of siccatives. However, contrary to drying oils, resins molecules all have oxygen atoms in carboxylic and alcohol groups.

(Question coming, finally!)

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So my question is : *in solvent* (I think I'll use ethanol) and with the addition of a siccative, should the molecules of resin cross-link? And if so, can the reaction be prevented by the addition of an antioxydant (say, eugenol)?

Thanks again for your time.

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(What would be a long thread without a post scriptum?)

PS : It is going to be an artistic, small scale and artisanal process, so I do not expect to get an exact theory and there will be a lot of testing to get the recipe right, but I would like to confirm that my expectations are correct, otherwise… well, if it dries in the pot, it is not going to work!

Also, I'm a very *safety first* person, so I will be careful.

PS 2 (last one I promise) : I do know how to make ink and I did make some, however I the only recipes I know of are either for printing, use animal glue (China ink), are not as durable as I would like (saponified resin), or they… *destroy* paper over time (iron-gall ink).

Rolf Steinort (314.8 ppm)May 20

@machinart The oxygen in the resin will not interact with the double bonds in the oils. That is done only by O2 and some other not so common oxidisers.
An antioxidant will not help in any way. Could even prevent the curing.

@rstein Thank you for your answers! Out of curiosity, may I ask what these “not so common oxidisers” are? And, as I asked in another answer, if the antioxidant is volatile enough to evaporate with the solvent, it won't prevent the curing?

Rolf Steinort (314.8 ppm)May 20

@machinart If you keep the air out and the ethanol in with a tight lid your ink will keep for some time. Linseed oil is stable in a closed bottle, but not for years.

Getzler Lab at KenyonCollege May 19

@machinart in general, reaction rates decrease when the reactants are diluted, so putting your compounds in ethanol should slow the rate of intermolecular (cross linking) reactions. If you’re not storing for years on end, I don’t think adding an antioxidant (sacrificial reductant) is needed. And, if you did add it and it was effective, you’d then need to get it all to oxidize before your oil/resin could start to react

𝓙. 𝓜.May 20

@machinart to add to this explanation by @GetzlerChem: in keeping it dilute, the cross-linking should not happen in significant amounts. During drying, as the solvent seeps in to the air, that's when things become more concentrated, and the cross-linking is more likely to happen. The oxygen atoms in alcohols and acids are tied up, so to speak, and would not cross-link the unsaturated stuff in your linseed oil. (The mechanism is chemically similar to how oils like olive oil become rancid.)

I presume you already know the folowing, but just in case you do not: linseed oil can heat up as it sets (the polymerization/cross-linking is exothermic), so be very careful.

@GetzlerChem & @tpfto, thank you for your answers! And yes, I am aware of the heat problem, but a safety reminder is always welcome.

However, you seem to talk mostly of resin to fat linking, is it the same for resin to resin?

Also, about the antioxidant : some will be present anyway, as eugenol is also a preservative (and clove oil has a lovely smell) but if it is volatile enough to evaporate with the solvent, it won't prevent the ink to cure once applied, right?

Getzler Lab at KenyonCollege May 21

@machinart @tpfto the relationship between concentration & rate is general & true for either monomer. crosslinking follows slightly different dynamics as it forms a gel rather than a chain. in terms of runaway heating (aka autoacceleration or Trommsdorff-Norish effect), keeping the bulk monomer dilute will avoid it. antioxidant will, eventually, all react with oxygen. with a bp of 254 °C, I don't think eugenol evaporates quickly. we can just detect the odor at very low levels

𝓙. 𝓜.May 21

@machinart I do not have a handbook on hand, but https://www.scentree.co/en/Eugenol.html claims that eugenol's vapor pressure is low (which is what you're usually more concerned with at temperatures far away from the boiling point). (Of course, because of all the other stuff mixed with the eugenol, the vapor pressure will be even lower; generally mixtures will exhibit lower vapor pressures compared to individual components.) The thing will heat up as it sets (and the original solvent vaporizes out), as you already know, so cure the thing in a well-ventilated place, and certainly far away from anything combustible. Good luck! (cc. @GetzlerChem)

ScenTree - Eugenol (CAS N° 97-53-0)

Eugenol (CAS N° 97-53-0) is an ingredient used in perfumes. Discover all about its exploitation, its smell, and its regulation with ScenTree !

@tpfto @GetzlerChem That is all very interesting, now I believe I have enough information to devise test protocols. It might take some time, but that's a good step forward. Once again, thank you very much!

Getzler Lab at KenyonCollege May 21

@machinart @tpfto my pleasure! Have fun! I’d love to see pics of the experiments!

@GetzlerChem Sure! I will post updates when I can on this account, and someday (I hope) I will have my own website, where I will be able to put more details. Anyway, I'll think about you ^^