On another discussion group someone asked how to determine the correct viscosity range and spindle for your formulas. Specifically, they wanted to know what parameters go into making a viscosity range and picking a spindle.
Viscosity factors to consider
The key things to consider when picking a spindle and speed.
1. Target viscosity of the product. This is more dependent on the marketing of the product than the formulating. Body wash/shampoo have viscosity ranges from 5000 – 20,000 cps. But lotions, gels, and other products vary. If you haven’t set a target viscosity find a competitive product that looks like what you want.
2. Middle of the range. Get spindle/speed combination that puts target viscosity at middle of the range. A Brookfield viscometer has a range from 0 to 100 (at least the old analog ones did) which was then multiplied by a factor depending on spindle & speed. Ideally, you want to use a spindle and speed that gives a reading of 50.
3. Use “drilling” viscometer for non-Newtonian fluids. Since some products get thinner as you apply a force (e.g. creams & gels) you need a movable viscometer so the reading is more reflective of the static product. Brookfield calls this type of viscometer a Heliopath. Typically, you use T-bar spindles for these products.
Do you have any other tips for taking viscosity? Leave a comment below.