Investigation of Pitch Stabilisation Using Pyrolysis-gas Chromatography-mass Spectrometry

Oxidative stabilisation of mesophase pitch is well known to severely limit the dimensions of artifacts formed from it or, for slightly larger artifacts, to be time-consuming and costly (Gallego, Edie, Nysten, Issi, Treleaven, and Deshpande, 2000). Control and understanding of this step is of very great interest in the production of highly oriented graphitisable material as it could lead to a dramatic reduction in production costs. The mechanism of such stabilisation is thought to involve oxygen cross-linking but its exact nature is still not fully understood (Drbohlav and Stevenson, 1995). Analytical pyrolysis methods such as pyrolysisgas chromatography-mass spectrometry (Py-GC-MS) are ideal for investigating the structure of macromolecular polymeric materials (Jones, Ross and Williams, 2006). Strong inferences regarding pitch structure and composition can be drawn from the identification and quantification of hydrocarbon fragments evolved during pyrolysis of pitch. Py-GC-MS is therefore ideally suited to identification of structural changes occurring in the pitch during oxidative stabilisation. In addition, the use of reactive gas Py-GC-MS offers a method for performing oxidative stabilisation of the pitch on an analytical scale. A series of oxygen-treated mesophase pitch samples with a range of potentials for stabilisation following further heat treatment (as demonstrated by softening point behavior) have been characterised using Py-GC-MS. This technique was used to identify and quantify volatile species evolved upon pyrolysis of the series of samples. Identification of the oxygen containing fragments has shed light on the nature of the oxygen functionality within the oxygen-treated pitch and therefore helped to elucidate the mechanism of the stabilisation process.