Guar 2

[queiry]

From what I've read, guar is a natural polymer. I want to use it in a solution (mostly sugar and guar) to mix into sand to form a crust (after drying).

I heard that citric acid should be added. I have two questions:
- how much citric acid needs to be added?
- what is the purpose of citric acid? (to depolymerize partially? to better dissolve?)

I would appreciate any pearls of wisdom...

Thanks!

 

[Compositepro]

Guar is a water soluable polymer that is used as a thickener. Changing the pH of the water causes the guar to gel because the surface hydroxyl groups of the polymer are altered so that the molecules stick to each other by hydrogen bonding. The reaction is reverseable. Carbopol is a synthetic acrylic water soluable polymer and they have good literaure on how it works.

 

[queiry]

Thanks for the help, much appreciated.

Any idea what amounts of citric acid would be required?

We're testing guar because it's more water-soluble than starch, and it's cheap. Is Carbopol as cheap as starch or guar?

Thanks again.

 

[Demon3]

I have used Guar as a thickening agent and it is effective and cheap but is attacked on storage in solution by microbes and you get a terrible rotting smell. I therefore advise either using a preservative (possible safety issues with skin contact) or a synthetic polymer that bugs don't attack (I have used Viscalex & Rheovis many years ago)

 

[queiry]

Thanks for the info.

For lab tests, guar's microbial degradation can be addressed by making smaller (fresh) batches as I go.

For commercial applications, the tote would typically only be used once, so perhaps vacuum-sealing it (or with N2) will prevent the microbes from wreaking havoc. But if the tote is used for more than one application, the preservative you suggested would be necessary.

That being said, one of the attractive features of the end-product is its biodegradability, so a preservative would make it less appealing.

The major ingredient is sugar, so regardless of whether I use a synthetic polymer as a guar substitute, I still have to worry about microbial degradation.

Sorry for the lengthy reply, just brain-storming...

PS (to anyone): Does anyone have a ball-park idea of what concentration of citric acid I need to add to the guar mixture, or which pH I need to aim for?

 

[Demon3]

Hello,

I see your point if you have sugar there. For me the guar worked fine as a thickening agent with no added citric acid. I don't think that is key to the thickening effect. Citric acid is used as a mild preservative so that may be why you were advised to add it.

E.g.

http://www.absoluteastronomy.com/encyclopedia/c/ci/citric_acid.htm