Polymer Degradation Mechanisms by Pyrolysis GC

Three mechanisms of polymer degradation by pyrolysis studied using pyrolysis GC unit.

Investigating Thermal Degradation Mechanisms of Polymers by Pyrolysis GC, Alltech Application Note PY001, September 21, 1998.

Polymers thermally degrade under pyrolysis conditions (inert atmosphere, high temperature) by one of three mechanisms depending on the type of polymer.

In depolymerization, the polymer is degraded to one or more monomers. An example of this is polystyrene which, degrades to produce styrene monomer.

In random scission, small fragments of varying chain lengths are produced. Polyethylene degrades by this mechanism.

Polyvinyl chloride degrades by a third mechanism, side group elimination occurs, resulting in a polyene macromolecule that ultimately forms aromatic compounds like benzene and naphthalene.

To study these degradation reactions, a pyrolysis/GC analysis was performed using an Alltech pyrola 2000 Pyrolyzer consisting of a Pyrolysing Inlet for GC (Part No. 56100) and the pyrola 2000 with Internal Valve (Part No. 56100).

Samples were heated to 700°C isothermally and pyrolyzed for 2 sec and chromatographed onto an AT-1 Capillary column (30m x 0.25mm x 0.25µm, Part No. 13638) with FID detection. The column temperature was held at 50°C for 2 min and raised to 300°C at 10°C/min with the detector at 325°C.

The pyrolysis of polystyrene produced peaks for benzene, toluene, styrene momonre, arylbenzene, a-methylstyrene, styrene dimmer and styrene trimer.

The pyrolysis of polyethylene produced a series of triplet peaks attributable to saturated molecules, molecules containing a double bond on one end and molecules containing two double bonds.

Pyrolysis of vinyl chloride produced peaks for benzene, toluene, styrene, 1-propynylbenzene, cyclopropyl(a)indene, cyclopentacycloheptene and biphenyl.