The process is generally to apply a sodium bisulphate solution, allow the water to evaporate leaving the fabric impregnated with the dry(ish)
bisulphate (hydrate), and then heat the item which results in severe attack to the cellulose.
I'd like to find a substance that behaves identically, but is not hygroscopic. Reason being that the sodium bisulphate absorbs so much water that, in
the interim, the fabric is damp feeling and floppy and it makes it hard to work with. Any ideas?
I tried citric and oxalic acid on a lark - they do not have any appreciable action on the cellulose. Things like DAP (diammonium phosphate) seem like
they might be promising, but are still at least slightly hygroscopic. DJF90 - 25-7-2012 at 02:21
I suppose thats a fair answer... ... but I should have mentioned that the "dry"
nature of the bisulphate process is important.
The entire issue is that I need to handle the item between the time that the bisulphate/whatever has dried and the time that the heat is applied to
"activate" it. If there is any sigificant moisture (like there is with bisulphate) its impossible to handle, too floppy.Lambda-Eyde - 25-7-2012 at 06:25
Maybe potassium bisulfate would be less hygroscopic?Si-Sa-Sulfur - 25-7-2012 at 15:28
Assuming you need an acid for the staining, I don't think you'll be able to find a non-hygroscopic staining agent.
The acid group almost assures a hygroscopic nature, and certainly a very heavily hydrophilic one. The best you can get is mildly-hygroscopic, at least
with the "mineral" acids.
If I were you I'd give the DAP a try.
[Edited on 25-7-2012 by Si-Sa-Sulfur]amaurer - 25-7-2012 at 15:53
Not for the staining, I'm actually after the embrittlement that allows area to be cracked/washed away. Its for making irregular holes in the fabric
without taking time to cut each one out.DJF90 - 25-7-2012 at 22:43
I reckon lambda-eyde might be onto something with his suggestion...amaurer - 26-7-2012 at 07:14
Is there any measurement of hygroscopy so I could compare the two?AJKOER - 26-7-2012 at 09:19
Try Tetra-amminecopper(II) sulfate, [Cu(NH3)4(H2O)n]SO4. It is a blue solid hydrate reputedly related to Schweizer's reagent, tetra-amminediaquacopper
dihydroxide, [Cu(NH3)4(H2O)2](OH)2, which exists in aqueous solutions only (hence not the answer), that is capable of dissolving cellulose fibers.
On heating Tetra-amminecopper(II) sulfate, any hydrolysis that occurs within the hydrated salt could yield Schweizer's reagent and H2SO4, both of
which attack cellulose.
[Edited on 26-7-2012 by AJKOER]woelen - 26-7-2012 at 09:48
Potassium bisulfate is not an option. I have both the sodium salt and the potassium salt. The latter is MUCH more hygroscopic, it becomes wet in plain
air, not just humid.Si-Sa-Sulfur - 26-7-2012 at 09:50
Not for the staining, I'm actually after the embrittlement that allows area to be cracked/washed away. Its for making irregular holes in the fabric
without taking time to cut each one out.
If the embrittling must be done with an acid, the hygrophillic nature of acid groups will still get you. Same thing with basic compounds.
Some ionic liquids are able to dissolve cellulose. The copper ammonia complex already mentioned in this thread will also dissolve cellulose, but it's
also hydroscopic.liquidlightning - 26-7-2012 at 09:55
Zinc chloride maybe? Although that too is hygroscopic...bahamuth - 26-7-2012 at 10:11
Perhaps a dry conversion of a bicarbonate salt to carbonate may be doable, given that carbonate is strong enough to chew through cellulose which i am
not sure it does...
liquidlightning - 26-7-2012 at 11:13
So, we need something that is non-hygroscopic, hydrate, and corrosive to cellulose. Melts at a low temp, etches fabric, then dries due to water of
hydration evaporating. I can't think of anything that fits the bill.amaurer - 26-7-2012 at 12:08
Yeah maybe its a tall order. It doesn't need to melt, really.
The way the process works now is that the sodium bisulphate is dissolved in water (often with a thickener like xantham gum to prevent running) and
then applied to the fabric to be removed. Then its allowed to dry, presumably leaving the sodium bisulphate hydrate inside the fabric.
It can stay like that nearly indefinitely without issue, except for the fact that the moisture trapped by the bisulphate will make even the stiffest
fabrics feel damp and floppy.
Then heating past ~250F causes the bisulphate to attack the fabric.
I'm not really sure chemically how that last step works. I assume, perhaps, that the water from the hydrate a requirement for the bisulphate to act
on the cellulose? or is the bisulphate itself melting (I think the MP of the hydrate is quite low) and reacts without water?
[Edited on 26-7-2012 by amaurer]liquidlightning - 26-7-2012 at 14:15
Hydrates will sometimes dissolve in their own water of hydration at even fairly low temps, like 35-40C. They don't exactly "melt" per se.
Sodium Bisulfate monohydrate "melts" at 58.5C
Anhydrous melts at 315C.
Besides, why does it matter if it is hygroscopic? Aren't you supposed to thoroughly wash after the process is done? I mean, what happens if it starts
to rain and you have bisulphate/other corrosive substance in your clothes.
[Edited on 26-7-2012 by liquidlightning]
[Edited on 26-7-2012 by liquidlightning]amaurer - 26-7-2012 at 14:20
Its just a handling issue. By the time you'd be wearing it yes it'd be washed and bisulphate free. But while you're working with the fabric prior to
washing the moisture content is problemmatic.liquidlightning - 26-7-2012 at 14:41
As far as I know, solids won't react the way you want, it needs to be dissolved, or molten. That's just as far as I know though, might be something
out there.amaurer - 26-7-2012 at 14:44
Well I'm no chemist but thats my understanding as well. I do know that the process still works even if I get it as dry as possible... for example,
putting the fabric under silica gel, or in the oven at 170F, for several hours gets rid of the damp behavior but it will return in short order if left
in the air.
But the cellulose burns out fine even when as "dry" as I can get it.
[Edited on 26-7-2012 by amaurer]liquidlightning - 26-7-2012 at 20:20
Water of hydration remains at 170C. amaurer - 26-7-2012 at 21:50
I don't doubt it. Maybe its also deliquescent too? Its holding a lot of moisture beyond the hydrate, for sure.
