Junk_Enginerd
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Tried to make Sodium Alginate(from kelp) and Calcium alginate, but something's wrong
It'd be great if someone could point to where I'm making a mistake... I'm doing a thing where Calcium alginate gel(spheres) might be a useful thing. I
realized I had a little bag of "Irish moss"(I think it's actually kelp, don't know why it's called moss), used for beer brewing clarification, at home
and thought it'd be interesting to synthesize calcium alginate from this. It didn't turn out very well, and I'm clueless about what might be wrong.
I tried to do some research but couldn't find much useful information, so I thought "how complicated can it be?" and decided to do some freestyle
chemistry. I at least found that alginate is the salt of Alginic Acid, so I'd have to react it with a base.
First I soaked the "Irish moss", maybe a table spoon of it, in 200 ml of cold water. I left it like that for an hour or so. Not much happened, except
it got rehydrated basically.
Then I heated it to boiling, and a very viscous slime started forming, as expected.
I added some NaOH, maybe 10 g, reasoning that's the obvious candidate to form a sodium salt of alginate. The slime started thinning out immediately. I
took this as a good sign of a soluble salt forming. I left it simmering like this for a couple of hours.
The solution was a warm brown color at this point.
I read somewhere that purification can be troublesome as there will be a significant amount of what's basically cellulose slime, which will
mercilessly clog everything. To try and handle this I diluted the solution with more water, to a total volume of about 1000 ml.
I then filtered it through a standard coffee filter. This took several hours. It got all particulates and crud out, but the solution was still quite
strongly colored.
Apparently sodium alginate is soluble in pretty much only water, so I decided to crash it with alcohol. First I boiled it back down to 200 ish ml.
Then I poured it hot into 400 ml of chilled ethanol. This immediately precipitated a large amount of fine white gel-like substance. I took this as a
good indication that I indeed had sodium alginate in there.
I then painstakingly filtered it again, which left me with a filter full of white gooey stuff. The drained liquid was discarded.
Then I poured boiling hot water into the filter, which seemed to efficiently dissolve the mass. Good sign!
I felt pretty happy with the expected purity of this solution. Still slightly pale yellow colored, but not too bad for a freestyling novice!
I boiled it down again to about 200 ml, which is the point I started noting that I'd get small amounts of gel like precipitation when it cooled down,
so i figured it was close to maximum concentration.
The real test here was to make the Calcium Alginate from this solution. This is supposedly done by dripping the sodium alginate solution into a
Calcium Chloride solution.
In my first attempt I used a solution at maximum concentration, just an open jar of at some point solid calcium chloride that had liquefied due to
moisture. This didn't go well since the sodium alginate solution was strongly buoyant, and quickly settled on the surface before it had time to react,
and it just turned into a mess.
I diluted the calcium chloride solution until the two solutions were roughly the same density and tried again, injecting the sodium alginate solution
into the diluted calcium chloride solution with a syringe, regulating the flow so that it formed hovering ~3-4 mm blobs.
I then left it to react in peace for about an hour, since I understand it takes time for the reaction to complete due to skin formation on the blobs.
But the result of this reaction was a little disappointing. I was expecting mostly transparent, squishy hydrogel blobs. What I instead found was...
well, it was some type of gel, but it wasn't really coherent and homogenous. The "blobs" easily fall apart, and parts of them seem a little crusty.
When I tried rinsing the blobs in clean water, they basically fell apart and dispersed into something reminiscent of snowflakes. The result was
similar to what's happened when I inject sodium silicate into calcium chloride to get a silicate gel.
Any insights, ideas, or suggestions to what went wrong?
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karlos³
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When I form them, its really imporant to let them harden in the CaCl2 solution for an hour or better two.
The drops need to be evenly formed and the solution needs to be stirred.
Then you'll get ideal round spheres.
At least with bought sodium alginate this works as it should.
verrückt und wissenschaftlich
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Junk_Enginerd
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Ah okay, that's great info. So I might not have waited long enough then. And I assume any stirring will have to be done veeery carefully?
Have you ever seen any "crustyness" happening? That's what I'm most confused by. Is it just NaCl which is to be expected? Why is it not dissolving
away? Is it a contaminant?
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unionised
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Did you do anything to remove sodium carbonate from your alginate solution?
Could CaCO3 be a problem here?
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Junk_Enginerd
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I guess maybe you mean NaOH? But I suppose it doesn't make much difference.
I didn't do anything specifically to remove the sodium hydroxide, but I figured it would precipitate to a much lesser degree than the
alginate when I crashed it into ethanol.
Looking at sodium hydroxide now it seems reasonably soluble in ethanol, so I suppose I would have discarded it when I filtered out the precipitated
alginate after the ethanol crash?
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