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Section 8 - How to obtain the best results
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 correspond-
ingly easy to find a suitable switch-off criterion.
Moisture content (%)
Time
Suitable time
for transfer
of the result
Result
Asymptote
Final value
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, continuous 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%).
Moisture content (%)
Time
Possible time
for transfer
of the result
Result
Asymptote
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