The Evaluation of Two Pyrolyzers for the Analysis of Insoluble Polymers

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Abstract
Two devices were evaluated in the pyrolysis-gas chromatographic analysis of a linear polyethylene standard. The Chemical Data Systems Coil Probe, a pulse-type pyrolyzer, and the Du Pont 950 Thermogravimetric Analyzer, a continuous heat-type unit, were studied. The latter was connected to the gas chromatograph using an interface designed to allow on-column collection of pyrolyzates. It was found that the coil probe yields reproducible results in the analysis of linear polyethylene, and the distribution of pyrolysis products obtained is essentially unaffected by changes in heating rate, time, and final heating temperature, provided these parameters are above certain experimentally determined values. This behavior may be explained by the action of the quartz tube sample holder as a heat transfer barrier between the heating coil and the sample. Large size samples enhance the formation of secondary products. The most serious shortcoming of the device is the difficulty involved in quantitating sample size. It was further found that the proposed thermogravimetric analysis-gas chromatography interface had only limited use-fulness because of back-diffusion. Condensation in the transport lines and formation of secondary products presented some problems. The results were reproducible and product distribution was not effected by changing heating rate and sample size. Isothermal operation of the thermal balance yielded satisfactory results and shortened the analysis time considerably.

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