After 500 °C, the thermal deposition temperature of all the cellulosic samples leveled off, and a slow thermal degradation profile was attained. This can be accredited to the further carbonization of polysaccharide chains initiated by the cleavage of C–C and C–H bonds. According to Figure 6, it is interesting to note that the sulfated-CNCH2SO4 possesses the highest residues (black char) at 600 °C as compared to that of other cellulosic sample. This behavior was attributed to that the sulfate groups in the CNCH2SO4 tend to play the role of flame retardant by promoting the dehydration reactions, which is conducive to the production of anhydrocellulose and leads to its decomposition to carbonaceous residues, as reported by other authors as Mohamed and his group . Moreover, the CNCH2SO4 product with the acid sulfate group might be decomposed by more pathways by the action of acid, and, eventually, the intermediate products obtained, which could be further decomposed into the char residue, were more complex compared to the cellulose with acid content. Therefore, it is expected that char yield of neutralized CNCH2SO4 (6.57%) is remarkably lower than sulfated CNCH2SO4 (17.4%), considering the lack of remnant surface sulfate in the CNCH2SO4. It is quite interesting to note that the char level of neutralized CNCH2SO4 and CNCCr(NO3)3 (6.57%–9.03%) was much lower than native cellulose (10.2%). The decreased char residue for the nanocellulose sample may be mostly related to the increased split hydrogen bonds and/or due to the absence of non-cellulosic components in the treated nanocellulose after hydrolysis treatment . Furthermore, the presence of alkaline ions with highly polar field might act as the catalyst for complete degradation of glycosidic linkages via the hemolytic mechanism, which resulted in the decrement of char yield .