The oxidative stabilization and carbonization of a synthetic mesophase pitch, part I: The oxidative stabilization process

Abstract

The transformation of mesophase pitch to an ordered carbon by high-temperature heat treatment in an inert atmosphere must be preceded by a suitable period of thermosetting or oxidative stabilization. The chemical process of oxidative stabilization is not well characterized, although research has clearly indicated that the oxidation history of the mesophase has a profound impact on the mechanical qualities of the resultant carbon product. In this study, we oxidized samples of a commercially available, synthetic mesophase pitch to determine the effect of different time/temperature profiles of oxidation on the quantity and type of introduced functionality. Fourier transform infrared spectroscopy (FT-IR) was used to characterize and quantify oxygen functionality present in this oxidized pitch. The oxidation process was characterized by periods of weight gain and weight loss. It was concluded that weight gain during oxidation involves the loss of aliphatic content in the pitch, with a concurrent increase in oxygen content as predominately ester and anhydride functionality. Weight loss is characterized by a loss of aromatic carbon content from the pitch and a further increase in the relative oxygen content in the pitch. It was discovered that changing the time/temperature profile of oxidation affects the pitch primarily via the degree of weight gain and weight loss experienced, rather than through the introduction of specific functionality with weight gain dominating at lower oxidation temperatures and shorter time periods, and weight loss dominating at higher temperatures and longer periods of oxidation. We conclude by suggesting mechanisms of derivatization to explain the oxidative stabilization of this synthetic, naphthalene-derived mesophase pitch in an oxygen-rich atmosphere.