| Molecular structure of various petroleum-based pitch precursors were determined by a combination of standard characterization techniques. Pitch precursors contains many different but chemically similar molecules with various degrees of aromaticity and alkyl substitutions. Representative structures were identified by using parameters such as number average molecular weight (Mn), carbon to hydrogen (C/H) ratio, and aromaticity (Af ).; Oxidative stabilization process was studied in detail using a Thermogravimetric Analyzer (TGA), NMR, and Infra-Red Spectroscopy (IR), and Electron Microprobe. Low stabilization temperatures below 240°C favors a reaction-limited oxygen uptake kinetics and higher temperatures above 270°C favors a diffusion-limited kinetics. At low temperatures, oxygen reacts with the as-spun fibers to form products that are chemically attached to the pitch molecules (uptake). At high temperatures, oxygen atoms attack the pitch molecules breaking carbon-carbon bonds to form gaseous by-products (burnoff). Burnoff kinetics can be modeled closely by both a homogenous decomposition and surface dependent oxidation. A theoretical calculations of both the steady state and non-steady state kinetics of an unreacted shrinking core model were performed.; Co-pyrolysis studies of pitch/polymer blends were used to investigate possible interactions between them. Two polymers emerged as candidate to modify fiber transverse microstructure. Poly(vinyl alcohol) (PVA) and poly(ethylene oxide) (PEO) provide substantial improvement in pitch char yield. Cross-linking reactions were supplied by the relative abundance of oxygen atoms in the polymers. In addition, decomposing PVA polymer afforded a highly reactive carbon backbone. |
