Biomass chars of pectin and cotton wood (Populus deltoides) were prepared by using a heating rate of about 1 degreesC/s, peak pyrolysis temperatures of 400-800 degreesC, and residence times of 10-60 min at peak temperatures. Char samples were pyrolyzed in a helium atmosphere using a thermogravimetric analyzer (TGA). Oxidation reactivity measurements of the same char samples in the TGA were collected after converting the helium atmosphere to an oxygen containing atmosphere. Reactivities were measured using an isothermal method at various reaction temperatures from 400 to 700 degreesC and oxygen concentrations of 2-21%. Oxidation kinetic parameters such as apparent reaction order and apparent activation energies were obtained. Scanning electron microscopy (SEM) was employed to study morphological and structural development in the char samples as a function of heat treatment temperature. An interesting morphological development on the surface of the char was observed by SEM, which showed evolution of vesicle formation and whisker growth as heat treatment temperatures increased. Its implication on char reactivity is discussed. Preliminary results showed decreasing reactivity with increasing peak heat treatment temperatures. Char reactivity was affected more by the heat treatment temperature than by the hold times (10-60 min). (C) 2004 Elsevier Ltd. All rights reserved.