8.08.2020

How to make crystalline nanocellulose with phosphoric acid

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10mL (or more) 85% Phosphoric acid
1 cotton ball (0.5g)
Glass beaker

*edit this produces regenerated not nano cellulose*
Place the cotton ball into the phosphoric acid in the beaker.  It helps if the cotton ball is shredded into fine pieces by hand so it stirs in well.
Get the beaker hot to the touch (45-65c) and stir constantly (with a glass rod or porcelain spoon)
In about an hour you should have a clear liquid.
 Add about 10x volume (100mL) of distilled water (or any water will probably work)  stir.  You should notice a white milk.  If you get clumps you have a problem.  You want a perfect white milky suspension.
 Centrifuge this down.  discard supernatant.  Mix in new water and centrifuge again.  Keep doing this step until the pH is neutral after you resuspend, about 5-6 times.  Resuspend all pellets in around 10ml of water and transfer to beaker to homogenize or sonicate.
You can sonicate  or homogenize the sample to get the nanocrystals to disperse.  A commercial blender might also work, especially if surfactant such as lecithin is used to help.  Also something like nano hydroxyapatite may also help.
Dry to a powder if desired by placing in an open dish and putting a fan blowing on it.  A final centrifugation might be helpful before doing this.  When dry grind to a fine powder in a mortar and pestle.
A final treatment with hydrogen peroxide might help break up the crystals/fibers even finer.  After peroxidation dry by fan, and grind to a fine powder in mortar and pestle.

Method adapted from here:
https://www.intechopen.com/books/cellulose-fundamental-aspects-and-current-trends/crystalline-nanocellulose-preparation-modification-and-properties

Removed steps:
 dialyze to neutral pH.  This is putting the solution in this tube (cut a ft long piece and tie off one end, place the liquid in, then tie off the other end and place in a big beaker of water) and letting the hydrogen ions (acid) diffuse out into the liquid it is sitting in.  Heat may be added to speed up the process.

Phosphoric acid papers, might not want to dissolve
https://www.researchgate.net/profile/Amanda_Melo5/post/Relation_between_Crystallinity_Chemical_Resistance2/attachment/5d0e6edccfe4a7968dad7df4/AS%3A772656076959744%401561226972222/download/13.+2012_Espinosa_Isolation+of+Thermally+Stable+Cellulose+Nanocrystals+by+Phosphoric.pdf

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5746556/ 
 dissolving then regenerating actually produces regenerated cellulose, not nano-crystals, but still nano scale shperes
https://www.sciencedirect.com/science/article/abs/pii/S0141813020335716
amorphous with low crystallinity and good at stabilization of emulsification.
 https://pubmed.ncbi.nlm.nih.gov/24279285/
 temp and time degree of polymerization (higher is better in mcc for tableting)
https://www.sciencedirect.com/science/article/abs/pii/S0144861715000867
 regenerated cellulose and nano hydroxyapatite
https://pubmed.ncbi.nlm.nih.gov/29498222/

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