The Thought Emporium on youtube made a video about weaving fibers made from the chitin, obtained from waste arthropod exoskeletons, e.g. shrimp and crab shells. I shared it with a friend and they didn't like the presenter's style, so here is a text summary. It's also a summary for me, because I don't remember all that many exact process details after watching a 16 minute video.
To make chitosan: reduce crustacean shells to very small pieces, perhaps powder, and cover with 10% solution of HCl. Stir for several hours (with heat?). Filter out solids and rinse. Cover solids in 10% solution of NaOH. Heat at 90 C for 2 hours. Filter out solids and rinse. Cover in 45% NaOH. Boil vigorously for 3 hours, topping off with water to maintain coverage. Strain and rinse. Now you have chitosan.
To make chitosan threads: Dissolve in vinegar. The mixture thickens a lot and will need to be stirred for a day for full incorporation. You'll only get about 3% chitosan by weight into your solvent, but you need more like an 11% solution for making threads. Heat the dilute solution to 65 C with stirring overnight (for 16 hours? until the solution reduces to a 1/4 of its initial volume?) to drive off water. You'll have a thick brown jelly now. Chitosan is soluble in the vinegar (and other acids), but not in bases, so to form fibers, extrude the jelly solution into NaOH and you get coagulation or some similar effect. Pull the coagulated thread from the extrusion syringe, through te NaOH bath, and then through a water bath to rinse, then hang to dry. Thinner extrusions will be less brittle. You might be able to loop the thread around a sequence of rollers with gradually increasing speeds to pull the thread thinner.
The lab hopes to put acetyl groups back on the chitosan threads at some point, turning the chitosan back into chitin, to make the threads more generally insoluble.
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