Metrohm 895 Professional PVC Thermomat - Manual (Page 27)

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4 Operation
895 Professional PVC Thermomat
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4 Operation
4.1 Thermomat method
The determination of the thermostability of polyvinyl chloride according to
part 1 of DIN 53 381 is based on the fact that PVC decomposes at
increased temperatures by releasing HCl. The hydrochloric acid that is
formed is transferred into the measuring vessel with a gas flow (usually
N
2
) and absorbed there in the measuring solution (distilled water). The
progress of the decomposition is registered by measuring the conductivity.
The stability time and the induction time are determined.
The stability time is defined as the time until a conductivity difference of
50 µS/cm has been achieved.
The induction time is the time that is required to reach the break point
of the conductivity curve. This method is used for testing PVC at all stages
of fabrication and for testing stabilizers.