Microstructural changes of phenolic resin during pyrolysis

After curing, phenol-formaldehyde resins were postcured at 230 degreesC in air for 32 h and then carbonized and graphitized from 300 to 2400 degreesC. Thermal fragmentation and condensation of the polymer structure occurred a bove 300 degreesC. The crystal size of the cured phenolic resins decreased with the temperature increase. Above 600 degreesC the original resin struct ures disappeared completely. Below 1000 degreesC the stack size (L-c) and c rystal size (L-a) were small. Above 1000 degreesC the L-c increased with th e increasing treatment temperature. The carbonized and graphitized resins w ere characterized using Raman spectroscopy. Below 400 degreesC there were n o carbon structures in the Raman spectra analysis. Above 500 degreesC the G and D bands appeared. The frequency of the G band of all carbonized and gr aphitized samples shifted to 1600 cm(-1) from the 1582 cm(-1) of graphite. The D band shifted to 1330 cm(-1) from the 1357 cm(-1) of the imperfect car bon. The carbonized and graphitized phenolic resins could not be considered as truly glassy or amorphous carbon materials because they had some degree of order in the basal plane. However, the crystal size was very small even at 2400 degreesC. (C) 2001 John Wiley & Sons, Inc.