Thermal Degradation of Hydrolyzed and Oxidized Lignins

Abstract

The infrared spectra of lignin treated with hydrochloric acid and peroxyacetic acid is investigated. The hydrolysed lignin spectra show a high intensity phenolic OH band at 1375 cm⁻¹ and a decrease in the intensities of CH vibration of methoxyl group at 2920–2810 cm⁻¹ and of the linkage (β–O–4 linkage) at 1120 cm⁻¹.

In contrast, the intensity of methoxy group band increases in the case of lignin treated with peroxyacetic acid. This treatment increases also the intensity of the C=O band at 1710 cm⁻¹. The intensity of C=C of aromatic ring band at 1605 and1505 cm⁻¹ is highly affected by the treatment of lignin with peroxyacetic acid, it decreases with large value than in case of lignin treated with HCl.

The thermal behavior of these types of lignin has also been studied. The initial and char temperatures of lignin were determined to be 280 and 700°C respectively for unreacted lignin while were 265and 550; 220 and 580°C for lignins treated with hydrochloric and peroxyacetic acid respectively. The rate constants of the mass loss of untreated, hydrolysed and oxidized lignins were found to be 0.05, 0.045 and 0.044 min⁻¹ respectively.