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APPLICATION NOTE:
Yield Point Determination -
a Critical Discussion of
Different Methods
Eva-Maria Kutschmann
Gebrüder HAAKE GmbH, Dieselstrasse 4, D-76227 Karlsruhe
ABSTRACT
In many practical applications the yield point of a product is
of interest. Methods and possibilities on different
instruments are discussed and compared presenting
practical examples of food and cosmetic products.
INTRODUCTION
In a simple definition the yield point is the minimum stress
that is required to make a material flow. If it exists at all, it
is still in the discussion stage. Some people argue that it is
only a question of observation time. If you wait millions of
years you can even see mountains flow. But this point of
view is not relevant for our daily work, thus we are going to
discuss acceptable time scales when we talk about yield
values
1
.
In general, cosmetic and pharmaceutical formulations, such as O/W or W/O-emulsions, show plastic flow
behaviour. In order to characterize the product quality the yield point is used as an important criteria. New product
formulations are developed with respect to the final use of the product, to its typical application and the
consumer’s expectations
2
In the food industry the yield value is very important for a product’s stability. For example, a salad dressing should
not show phase separation or sedimentation of solid ingredients such as herbs and spices
3
.
The engineers responsible for the processing technologies must know the rheological behaviour of the products.
Depending on the yield stress, different filling and packing machines are used; the final products are sold in
bottles, tins, boxes, tubes or other special containers.
Last but not least there is nowadays an increasing interest in being able to empty containers completely before
the packing material is recycled. Here the yield value is important information for the recycling company.
TYPICAL YIELD VALUES
The following table shows some typical
yield values for well known every day
products:
Table 1: Typical Yield Values
© 2006 Rheology Solutions Pty Ltd
(1)
Solutions for Chemical & Allied Industries - Application Note: Yield Point Determination - a Critical Discussion of Different Methods
RHEO303-SK
Substance
Yield Point
Body Lotion
2-10
Pa
Skin Creme
20-50
Pa
Ketchup
15-20
Pa
Mayonnaise
20-30
Pa
