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Apparatus to measure the viscosity of toothpaste
Hello Chemist Corner.
I have just landed my first formulation chemist job at a small cosmetic company specializing in Oral Care. The company hasn’t had a designated cosmetic chemist before and have previously outsourced their testing. As such the first requirement of my job is setting up a cost-efficient lab that will allow me to undertake some preliminary accelerated testing on new toothpaste prototypes. Supposing new products meet these preliminary testing results they will then be validated at commercial testing labs, who have more advanced and precise apparatus.
I will be predominantly formulating toothpaste and one of the measurements I was wanting to use was viscosity. However upon researching the viscosity properties of Toothpaste i.e. plastic/pseudoplastic with high viscosity: ~ 100,000 cps it became evident that I would need quite advanced and expensive laboratory equipment, which is out of my allocating lab set up budget.
Therefore I am looking for some advice on a cheap apparatus/procedure that would be sufficient to test the viscosity of toothpaste (if it exists)? Or some advice on whether or not testing the viscosity is necessary for such preliminary testing of a product.
Thanks in advance
Ross
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5 Replies
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It would be simple to design a piece of kit to measure relative viscosity, but not actual values. EG a PTFE tube fitted with a plunger, you fill the tube with toothpaste and apply a known weight to the plunger, say a 500g mass, and measure the time taken to squeeze all the paste out via an orifice of say 5mm. Then compare that with commercial toothpastes. In this way you could duplicate the viscosity.
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like many other non-Newtonian liquids, toothpaste does not have a constant viscosity - the viscosity varies depending on the rate of shear applied to itthe cheapest equipment that can be used to make quantitative and meaningful measurements is a Brookfield RVT dial viscometer with a heliapath, or any fuctional equivalent -
3 basic tools for testing in any lab
Viscosity - need a brookfield or equivalent, or if you are making low viscosity products you can use a Ford cup (What they use in spray paint shops - advantage is that you can get it from a tool store, and they are cheap - disadvantage will be that they struggle over 2-3000cpspH meter - get those cheap enough off amazon
Something to measure SG. Pyconometer (basically a calibrated pot and lid is cheap and flexible- you’ll need to use it with a balance, but you should have one of those already
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Pretty much a variation of what @Belassi suggested:
A 50/60 ml syringe
saw the luer-lock connector off
drill a larger exit hole
make a suitable stands that holds it upright
place a weight to push the plunger down
Take the time it takes for toothpaste to be pushed out. -
Thanks for all the input guys it has been really helpful.
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