Effect of slight chemical modification on the pyrolysis behavior of cellulose fibers

Partially carboxymethylated cellulose (CMC) was subjected to thermal decomposition to observe the effect of low degree of acidic substitution on the pyrolysis mechanisms of cellulose. The impact of Zn2+ and Ca2+ ions introduced into CMC and untreated cotton fibers was also studied. Simultaneous thermogravimetry/mass spectrometry was applied to monitor the thermal decomposition of the samples in inert atmosphere. The detailed analysis of the volatile products has been carried out by pyrolysis–gas chromatography/mass spectrometry. concluded that a low degree of carboxymethyl (CM) substitution (DS = 0.05) results in significant changes in the thermal properties of cellulose. The decomposition of the carbohydrate chains is promoted by the scission of the thermally less stable CM substituents leading to levoglucosan evolution at lower temperature. The gas evolution and the char formation are enhanced while the yield of the high molecular mass products is reduced. Zn2+ ions have similar effects on the original and carboxymethylated cellulose. The decomposition shifts to lower temperature and the char formation is promoted. The quantity of calcium present in the samples has great effect on the charring processes. The higher loading of Ca2+ ions present in CMC increases the char yield, while the smaller amount of Ca2+ ions has slight effect on the thermal behavior of the original cellulose. A hydroxylactone compound, 1-hydroxy-3,6-dioxabicyclo[3.2.1]octan-2-one is increased significantly, while levoglucosan and 2-hydroxymethyl-5-hydroxy-2,3-dihydro-(4H)pyran-4-one are reduced in the pyrograms of cation-containing samples.