deltaH
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Problems with dissolving cotton
I am struggling to dissolve cotton wool by the method of Yan and Gao (2008). The free 'look inside' peak of that article gives the method and some background theory.
I cannot easily purchase PEG 2000 as the authors have used, however, by a stroke of luck, I do have an OTC laxative called Movicol that is
comprised of 95% PEG 3350 (Macrogol).
I have dissolved on a mass basis one sachet Movicol (13.8g) in 1.3l water, to which I then dissolved in 130g sodium hydroxide and poured the
resulting warm solution over 130g cotton wool (the white rolls one buys from personal care section at groceries) in a PP plastic container with closed
lid.
I set this aside to swell for 3 hours at RT as the authors have done. I noticed a slight yellowing of the cotton at the end of this, but not much of
anything else.
I then placed the closed container in the freezer overnight as the authors have done for 12h. The next day, I found the whole mass had frozen solid
and surprisingly was shrunken by about 20% in volume. I let it thaw as the authors had done and used a hand blender to try to break up the fibers as
it thawed, however, the fibers are still there, though maybe a little degraded.
I am not, however, obtaining a solution in the least 
Any ideas as to what I'm doing wrong?
UPDATE:
I am leaving it in the fridge for the day and will try a freeze-thaw cycle on the mass once again to see if that helps. Maybe the cellulose in cotton
fibers are simply sluggish.
[Edited on 31-8-2014 by deltaH]
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hissingnoise
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| Quote: | | Any ideas as to what I'm doing wrong? |
Using cottonwool rather than easily dissolved cellulose powder, possibly?
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deltaH
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I think you're right on the money hissingnoise.
I am wondering if I can degrade/alter the cotton wool somehow to help it work.
Perhaps baking the cotton wool with a loose fitting lid in the oven for a few hours before swelling?
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Paddywhacker
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Tissue paper might be a more useful source of cellulose. Pleas let us know how it works.
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deltaH
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I've repeated the freeze-thaw cycle and left the mass of cotton in the fridge for several hours in between, it looks promising at the moment,
definitely partially disintegrated and gelling up. I've decided to double up on the hydroxide-movicol solution because the gel fiber mass is
tremendously thick, so I'm at about 5% cotton at the moment. It mixes easily with a fork now. Gonna hit it with the blender a little later.
So tentatively, seems like cotton can be made to partially dissolve with multiple freeze-thaw cycles and multiple days of work with in-between
refrigeration.
While not super easy and not a pure solution, I'm actually quite excited about it.
Paddywhacker, thanks for the tissue paper suggestion, but I'm ultimately hoping to be targeting cotton rags, so need to get it to
work on very tough cellulose.
I'm just happy I might not need to bake it 
***************************************
Finally a breakthrough!
Doubling up on the solution helped a heck of a lot and so I had the brainwave that the solution is simply too saturated, so I doubled up again. It's
refrigerating now and work the remaining gelatinous clumps of cotton with a fork when done (my blender overheats but a fork does the job well).
So all in all, I used 5.2l water, 130g cotton wool, 500g sodium hydroxide and four sachets Movicol containing 52.5g PEG 3350
If I get a homogeneous solution, I'll post a photo.
****************************************
It's the next day and seems my excitement was premature. After a freeze-thaw and much mechanical mixing, even my dilute version still has fibres.
It's an optical illusion, while it appears much thinner, I think the fibers are merely well separated/suspended in the mass and so it gives the
illusion that it is dissolving.
I also think some is dissolving, but how much, it's hard to tell.
I've now added 130g urea in the hope that it would help as urea/hydroxide is a known powerful cellulose solvating agent combo. Normally, 13% urea and
7% sodium hydroxide is used, however, for my intended application, so much urea in the cellulose is unacceptable, so I am trying to see if 2.5% urea
in conjunction with the 1% PEG from Movicol could enhance it sufficiently.
I have the sinking feeling that perhaps there is a major error in this recipe, for example, perhaps it's supposed to be 10% PEG and not 1%.
After all, urea is normally used at 13% strength with sodium hydroxide and here the authors have replaced it with PEG being also a hydrogen bond
acceptor, but surely it can't be over a factor ten more effective than urea?
[Edited on 1-9-2014 by deltaH]
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deltaH
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Apologies for the double post, but some useful info:
I'm found a useful thesis on dissolving cellulose in hydroxide/urea systems that contains some great additional info.
9% Sodium hydroxide solutions can only dissolve cellulose with a degree of polymerisation less than 200. This is very low, comparable to very old
paper or cellulose that has been purposefully cracked or degraded, for example enzymatically.
Most commercial wood pulps have DPs of 800+ while cotton fibers are usually in the thousands.
7% sodium hydroxide + 12% urea is stronger and can dissolve cellulose up to a DP of 700, still a little short for fresh paper and original cotton
linters, but should work for aged paper.
The only reasonably foolproof version of this type of cellulose solvent system is lithium hydroxide 4.2% and urea 12%. This can dissolve cellulose up
to a degree of polymerisation of 2500, but honestly, having to use a lithium defeats the practicality of this system.
Attachment: dissolving cellulose thesis.pdf (5.7MB)
This file has been downloaded 868 times
[Edited on 1-9-2014 by deltaH]
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Zyklon-A
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See this thread for information on making mono-crystalline cellulose from cotton balls, rags or any cotton source, and dilute hydrochloric acid.
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deltaH
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Thanks Zyklon for the suggestion... sounds great.
They affected the degradation at 85C for 1.5h, so by a rough rule of thumb, the RT version should work in 4-8 days if one were to bucket chemistry
this. Furthermore, if one is going the RT route, one could easily use HCl out of the bottle. That should speed things up significantly.
It has also got me thinking that if acid hydrolysis is so easy and effective, the base version might work too, i.e. perhaps simply cooking up the
cotton in 9% NaOH for a couple of hours before doing the refrigeration step is the way to go or else leaving it to soak for a week before
refrigerating etc, plus NaOH solutions don't generate noxious fumes.
This would save having to wash the cotton of acid and deal with the wash water and so make me VERY happy, but if all else fails, I have a plan B now
thanks to you.
[Edited on 1-9-2014 by deltaH]
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PHILOU Zrealone
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@DeltaH
You could also use cupro-ammoniacal mix (CuO or Cu(OH)2 with concentrated NH3 solution) or even better cupro-ethylendiamine mix (CuO/Cu(OH)2 with
H2N-CH2-CH2-NH2) to dissolve cellulose.
BTW thank you for the Movicol info...I was precisely looking for a PEG source (solvent for easy and high yielding nitrocarbon synthesis (SN) from R-X
and NaNO2 (X= Cl, Br or I))
PH Z (PHILOU Zrealone)
"Physic is all what never works; Chemistry is all what stinks and explodes!"-"Life that deadly disease, sexually transmitted."(W.Allen)
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deltaH
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Greatest of pleasures PHILOU, it's lovely to hear that you found it useful for something else. Movicol, not just for explosive
poop... 
Thank you for the cuproamine suggestion... unfortunately I need a white product. A couple of reviews I've read mention that zinc amines also work,
though they don't discuss specifics... which makes me question just how well they work.
That said, I am reasonably satisfied with the route of acid degredation (recommended by Zyklon-A) followed by caustic only for
dissolution and this is what I am working on now. I don't yet have anything to report for the moment because I am trying the room temperature version
of the acid degradation, which by my estimate will take about 5 days to complete.
I cannot find any literature evidence for the base catalysed hydrolysis of cellulose, leading me to doubt it's efficacy (in contrast there are tons of
literature on the acid catalysed hydrolysis of cellulose).
According to literature, acid degradation can produce microcrystalline cellulose from cotton lint and rags with a DP of less than 200, which is the
cuttoff for cellulose dissolution in 9% NaOH only (no urea) by the thesis I attached above, so I should be ok, touch wood...
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