an overview of #carrageenan. Apparently to gel it you heat it above 60° to dissolve it and then let it cool with potassium ions (for elastic gels) or calcium ions (for brittle gels). It seems like this might be better suited than alginate for #3D printing, since you could use a single nozzle that keeps the carrageenan solution hot to keep it from gelling. ι carrageenan gels made with calcium are #thixotropic, and used in toothpaste for this reason, as are κ carrageenan gels made with casein.
on 02015-08-15this lapsed Japanese patent from 2002 talks about making lime plaster (#slaked-lime) #materials sticky and #thixotropic by using 0.1%–5% #carrageenan (dry weight), which is apparently not as sticky as methylcellulose and won’t crack your plaster by absorbing water later. Some carrageenan molecules (κ and ι) gel with metal ions, while others don’t and are therefore more desirable for this. I'm surprised carrageenan will still gel in the insanely alkaline conditions found in lime plaster. It says you can use up to 4% or 5% (or sometimes as little as 2%) before it starts to shrink and crack as it dries. #patents
on 02015-08-15Galip Sarper Koçlar’s master’s thesis #paper on #gelcasting of #alumina #ceramics #materials with #gelatin and #carrageenan gum. He got best results with 5% by weight gelatin, or 1.7% by weight carrageenan, which resulted in significantly lower fired hardness but higher fired compressive strength than the gelatin, and all his trials were with 47–53% alumina, which reached 95.8% after firing at 1550°, and a bit of Dolapix dispersant. 17.5% linear shrinkage. In English, not Turkish, although it’s kind of broken English. The introduction has the best #survey of gelcasting I’ve found so far. Apparently #acrylamide (and, I guess, other similar binders) needs 30–60 minutes to gel in the mold. He also mentions existing “natural gelcasting” processes for technical ceramics using “starch, ovalbumin, chitosan, alginades [sic; should be #alginate], #gelatin, carragenan [sic] gum and [sic] etc.”, and agarose, with the disadvantage being lower green strength.
on 02015-08-15