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Pharmaceutical Manufacturing and Packing Sourcer
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A knowledge of rheological behaviour is proving increasingly desirable for formulators of topical creams and lotions. For many personal care and pharmaceutical products rheology is a key determinant of processing characteristics such as pumping and filling behaviour, and also usage characteristics such as texture, 'pourability' and long-term storage stability. Whilst several sophisticated research rheometers are currently available to comprehensively characterise such products, simpler, cheaper and more abundant Brookfield-type viscometers are often overlooked as 'serious' tools for the formulator. This article will demonstrate a simple method that can be employed with such instruments to profile the flow behaviour of pharmaceutical emulsions.
By far the most common form of laboratory viscosity test involves running a defined viscometer fitted with a defined spindle at a defined motor speed and at a defined sample temperature. So a typical test method would then read: "Brookfield RVDVII+ viscometer, spindle 3 at 10rpm, 250C; record viscosity after 30s". Thus it is assumed that, as long as the method is adhered to, any two samples registering the same viscosities are rheologically similar. However, this is not necessarily true. Often two products that give similar single-point viscosity readings - for example 1,200mPa.s (1,200cP) with spindle 3 at 10rpm - will exhibit differing flow properties in the 'real world'. If you've ever over-ruled the results of a viscosity test because the appearance of the sample contradicted what the viscometer was telling you then you'll know what I mean. The visual assessment process - swirling, pouring or spooning for example - may impose completely different degrees of shear to the sample than those applied in the viscometer method. In a non-Newtonian fluid, that is, one whose viscosity is dependent upon the imposed shear rate, this will of course result in differing viscosities in effect in either situation.
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