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Polyacrylonitrile fibers were heat‐treated in air, and a series of stretching experiments were conducted in different temperature zones. The effects of tension on the microstructure of the heat‐treated fibers and the tensile strength of the resultant carbon fibers were investigated. The results show the variations in morphological characteristics affected by stretching were different as stabilization proceeded. A possible mechanism of tension on cyclization and, thus, stabilization was elucidated. During stabilization, tension at low temperatures led to a great increase in the tensile strength of the carbon fibers, whereas tension at high temperatures resulted in only small improvement in the tensile strength of the carbon fibers. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1029–1034, 2005

Polyacrylonitrile copolymer fibers have been heated in air to different maximum heat treatment temperatures (MHTT) from 190 to 270°C. The functionalities of C, O, and N in the precursors were determined by X‐ray photoelectron spectroscopy. The intensity of the C1s spectra line 286.8ev, which is identified as C‐O and C = N functionalities, was found to initially increase and suddenly decrease above 230°C. Additionally, the significant broadening of the N1s spectra line was also observed at the same MHTT. It is suggested that some oxygen was incorporated into the six‐member heterocyclic structures that formed by cyclization of nitrile groups and transformed into pyrrole‐type structures by the elimination of carbon monoxide. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1705–1709, 2004

Carbon aerogels were prepared by sol-gel polymerization of phenolic novolak and furfural followed by supercritical drying and pyrolysis. The porosity and morphologies of carbon aerogels were characterized by nitrogen adsorption, apparent density, He- pycnometer method, and transmission electronic microscopy (TEM). Effect of ratios of phenolic novolak to furfural (Ra) and total concentration of reactants (C) in sol-gel step on porosity and morphologies of carbon aerogels was investigated. The carbon aerogels synthesized are rich in meso- and macropores. The Ra determines the cross-linking density of polymers, thereby the compatibility of the polymers, and ultimately the shrinkage of gels in the drying and pyrolysis. The network sizes and the porosity of organic and carbon aerogels are mainly determined by Ra. The C has no effect on volume shrinkage of gels in drying and pyrolysis and has only dilute effect in determining bulk density of organic and carbon aerogels, and ultimately the porosity of carbon aerogels. Conversion of mesopores to micro- and macropores is observed, which is related to combination of C and Ra, and determines the partition of micro-, meso- and macropores.