EPR Investigations of the Effects of Inorganic Additives on the Charring and Char/Air Interactions of Cellulose

EPR (electron paramagnetic resonance) behaviors of cellulose chars during exposure to air at room temperature strongly depend on the identities of any inorganic additives and on the charring temperature. The air exposure of low-temperature (300−400 °C) cellulose/alkali carbonate chars or alkali bicarbonate chars appears to involve two different chemical processes, the production and annihilation of free radicals. The “new” radicals formed during air exposure have larger g-values than those generated by pyrolysis. In contrast, the corresponding low-temperature chars of pure cellulose and cellulose/NaCl show only an apparently small, slow decrease in radical concentration upon air exposure. For the high-temperature (>400 °C) chars of cellulose and cellulose/additive mixtures used in this study, air exposure is accompanied by a large reduction in apparent radical concentration. However, this decrease is found to depend dramatically on the presence of water in the exposure environment. Adding Na2CO3 into the ...