Identification of Swelling cause on Rubber Gaskets

Detta är en Master-uppsats från KTH/Skolan för kemivetenskap (CHE)

Sammanfattning:

The aim of this master thesis was to develop an analysis method which identifies the swelling cause of EPDM rubber gaskets. The method shall facilitate failure investigation of rubber gaskets used in plate heat exchangers which require both determinations of volatile and involatile compounds as well as polar and non-polar compounds. To achieve this goal a combination analysis method of Headspace Gas chromatography Mass spectrometry (GC-MS) and liquid-liquid extraction Fourier Transform Infrared spectroscopy (FT-IR) was chosen. Three extraction fluids were tested to extract the compounds from the EPDM rubber: tetrahydrofuran, 2-propanol and supercritical carbon dioxide. The analysis method was first tested on EPDM rubber samples swelled in four known solvents with different volatility and polarity (hexane, acetic acid, 1-octanol and pentadecane). Then it was tested on EPDM rubber samples swelled in three different mixtures of these four solvents and finally on two EPDM gaskets, swelled by unknown media, that were being assessed in an actual failure investigations.

The analysis method was successful in identifying compounds which caused EPDM rubber gaskets to swell but not in a way as it was supposed to. The FT-IR analysis could not be used to identify compounds in a mixture because the spectra of mixtures are very difficult to analyze. However the FT-IR results complimented the results from the GC-MS analysis which due to a poor search database was not good enough to determine the exact composition of the swelling agents by itself. The liquid extraction also gave useful information about how much swelling agents that were absorbed by the EPDM gasket. Tetrahydrofuran and 2-propanol were the most effective for extraction of the solvents. However, supercritical carbon dioxide was very good for selective extraction of non-polar compounds.

The method detected both polar and non-polar compounds but non-polar compounds with low boiling point were not detected. It did not interact strongly enough with the GC-column used in this trials, because the polarity of the column was not sufficient. The method detects both volatile and involatile compounds. But to be sure that all volatile swelling agents were detected a special sample handling technique must be developed.

To improve the analysis method it is suggested that the method is developed so that only GC-MS analysis is needed. This is accomplished by further GC-MS analysis with other GC-columns and better search databases. It is also suggested that the method is developed so that it is not only a qualitative analysis method but also a quantitative analysis method.  In that way it can be used as a much more effective tool during failure investigations.

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