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How to obtain the best results - Section 8
8.6 Analysis of the drying profile
In the first type, the drying profile is asymptotic. The amount of moisture lost assumes a constant value and no longer
changes after long drying times. With this drying profile, repeatable determinations of the moisture content are always
simple.
The measurement result then corresponds exactly to the constant value of the asymptote. It is also correspondingly
easy to find a suitable switch-off criterion.
In the second type, drying runs quickly at the start and then flattens out. The moisture content never assumes a
constant value. The causes of such a drying profile can be as follows:
The sample exhibits thermal decomposition,
the decomposition products vaporize and the
sample continuously loses weight. Fats, oils,
plasticizers or other volatile components can
lead to superimposed profiles owing to their
slower vaporization than water. The difficult to
volatilize components lead to a slow, continu-
ous decrease in weight.
Measurement results of such a drying profile
can be optimized:
Lowering the temperature can slow down the decomposition reaction.
The selection of a suitable switch-off criterion can allow recognition of the end of the analysis at the desired break
point of the drying curve.
The selection of a constant drying time often provides good measurement results.
Keep the initial weight of the sample constant (
+10%....+20%).
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