Pyrolysis

Pyrolyis is a useful method for reproducibly degrading organic materials to produce volatile components. The combination of pyrolysis with the separating and identification capabilities of GC/MS provide a powerful analytical tool. In our laboratory, the pyrolysis can be carried out using two different experimental methods:

The simplest is an off-line pyrolysis at temperatures up to 600 C and samples up to 1 milligram. The condensates from this are taken up in a low-boiling solvent and analyzed immediately.

The second technique utilizes a CDS Pyroprobe with a platinum ribbon probe. This can be heated at controlled rates of 100 degrees/sec to 20,000 degrees/sec. The temperature range is 45 to 1500 C. The pyrolysis is usually carried out in helium, although at extra cost, any noncorrosive, nontoxic gas or mixture could be used. We normally use the Pyroprobe in conjunction with a Tekmar 5000 thermal desorption device which contains a cryofocusing unit to condense the volatiles produced before introduction into the GC. If very volatile products (boiling points below -10 C) are anticipated, then direct pyrolysis using the Pyroprobe would be used in order to analyze for the very volatile components.

APPLICATIONS

IDENTIFICATION OF POLYMERS

Pyrolysis routinely can be used to determine the composition of copolymer blends. This is especially useful in the case of polymers from mixed monomers such as methacrylate esters of more than one alcohol. In some cases that have been well studied, such as polyethylene and polypropylene, structural information about the polymer can be determined.

RUBBER ANALYSIS

Pyrolysis of hydrocarbon rubbers can provide information on the monomers used as well as many of the additive components. This is an important use of this technique, since infrared spectroscopy is limited by sample preparation difficulties when confronted by small rubber samples.

CROSSLINKED POLYMERS

Epoxies, polyimides, polyamides, phenolics. Pyrolysis on a microscale can provide important compositional information on these insoluble materials. These systems are typically filled with glass, metal, carbon, or mineral fiber, but pyrolysis readily separates the organic components from the reinforcement and generates molecular fragments from which we can derive the components of the thermoset.

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