Development of aromaticity in cellulosic chars

Cellulosic chars prepared at HTTs ranging up to 500°C contain aromatic structures as evidenced by the production of benzene polycarboxylic acid derivatives on permanganate oxidation. Analysis of these products indicates the concentration of the aromatic units and the degree of substitution of benzene polycarboxylic acids represents the extent of condensation or crosslinking of the structures. Further information on this subject is obtained by elemental composition of the char and the $\text{H}\text{C}$ ratio. These studies indicate a rapid weight loss and development of aromatic structures between 350 and 400°C, as the $\text{H}\text{C}$ ratio is gradually reduced from 1.5 to 0.7 and the aromatic carbon of the benzene polycarboxylic acids formed is increased to 2.5% of the carbon content of the original cellulose. Above 400°C the rate of weight loss is reduced with the formation of the “stable” char and the yield of the aromatic carbon remains constant. However, the aromatization process continues with rapid reduction in $\text{H}\text{C}$ ratio, due to the condensation and growth of the aromatic clusters as evidenced by the increased formation of the highly substituted benzene polycarboxylic acids. The presence of inorganic additives, representing flame retardants results in increased charring and enhancement of aromaticity and condensation.