I am making a salt scrub for hair and am adding rice vinegar, as you know there is a chemical reaction that dissolves the salt. As this is a cosmetic product I require the astringent and degreasing properties of the vinegar but would like to keep the scrubbing and exfoliating properties of the salt for at least 6 months. What can I do to achieve such a goal? Thanks
First of all, I am not a cosmetic chemist, so take my remarks for what they are worth.
Because vinegar is mostly water, and because salt dissolves in water, that is what is happening. There is no "chemical reaction" as such.
You can add salt until no more will dissolve to make a supersaturated solution or a paste, if you like. You could add a nonsolvent to the vinegar to reduce the solubility, something like a glycol or glycerin. You may also find that a paste is likely to set up and become more of a cake than to remain fluid. If so, you would probably need other ingredients to maintain the thickness and flowability. To make it shelf stable, you would likely have to add other ingredients as well. You have not said whether you intend this for personal use or to be offered for sale.
If you are holding this out to the general public, you must take care, however, in using only ingredients that are generally regarded as safe (GRAS). In this regard, there are very few "secrets" in the personal care industry as all must stick with GRAS ingredients. Otherwise, the burden of proving that your compound is safe is on you, and you better have deep pockets to do the work and to settle the lawsuits. In short, if there is an existing product that is roughly what you are trying to do, then get it and find or figure out how it is made.
A quick look on-line for an apple cider vinegar salt scrub reveals these ingredients:
What is the purpose of the salt as you envision it? To act as an abrasive? If so, use a abrasive mineral that is not soluble in a dilute acid.