This thixotropic effect is rare, but it could affect drastically process and trouble also accuracy of viscosity control.Ģ.2 Viscometer choice, which technology to choose?ĭue to historical standard methods or easy to use justification, many types of viscometers were developed and used to control viscosity measurement. Time is the third variable to control for several types of products, because viscosity has tendency to decrease when the shearing is longer than if it is short. This induces to use defined or standard geometry where this parameter is well-known like cone-plate, coaxial cylinder systems. Speed or shear rate is the major parameter which influence the viscosity of formulated products, that are non-Newtonian fluids. Even the increasing of temperature will give lower viscosity values, it is recommended to compare samples’ viscosities or to be in accordance with standard values. Temperature, because according to the chemical formulation of sample, the temperature could affect the viscosity value.
The most important factors to know or control are the following: Of course, some standards in place or product constraints – available volume, test temperature, product type – will require the use of identical or use versatile instruments that will adapt to most of the stated conditions.Ģ Viscosity Measurement 2.1 Which parameter is important to do one right viscosity measurement?Īs viscosity is not a constant physical value to measure, therefore it is important to know the varying parameters which could influence this value during a quality measurement. The more information that accompanies the viscosity value provided, the more it is easy to refer to it to make a measurement in the closest conditions with its own means. This requires a precise and clear dialogue on the measures established by each other. This very frequent and quite legitimate question has its source in the notion of rheological behavior, which we will deal with in the second chapter. Why don’t I find the same viscosity value as my supplier? What information should I communicate around this viscosity value? Specify the standard used where measurement conditions will help to dialogue between services, with your customers and your suppliers. Why do I need the viscosity value? Meet a standard, check the stability of the product quality, validate an industrial process, innovate, provide a specification to a customer.ĭefining the purpose of this measure is the first step.ĭoes the temperature at which I am measuring reflect the time I want characterize? it is very important to be as close as possible to what the product undergoes in its life cycle.ĭo the quantified results of this measure allow me to identify discrepancies that I judge between two products? The precision of a measurement is not enough to make it relevant. The answer to this question raises other questions: It is therefore important to clearly define what information you want to collect before embarking on a measure of “viscosity” that could prove difficult or unnecessary to better qualify your product.ġ.2 Is the measure of the defined viscosity relevant? In the field of polymers, there are other viscosity values such as specific viscosity, intrinsic viscosity, and relative viscosity, which make it possible to calculate the average viscous molar mass of these polymers in solution. s (1 mPa.s = 20☌ water viscosity) or Poise or cPoise. It can consider the rheological behavior of the product, which gives it an absolute character.
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It is expressed in Stokes, cStokes or cm2/s.ĭynamic viscosity h (Eta) qualifies most formulated products it is free from the effect of density and is most measured with rotary instruments. Kinematic viscosity n (nu), resulting from a flow time measurement, takes account of gravity and concerns rather less viscous fluids and simple rheological behavior: Newtonian fluids. This frequently asked question deserves clarification as there are several viscosity values to qualify a product: 1 Viscosity Defined 1.1 What is the viscosity of my product?
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