Characterization and degradation of lignin from steam explosion of pine and corn stalk lignin: the role of superoxide ion and ozone

Steam explosion of corn stalk in the presence of 3% sulphuric acid at 200°C for 5 min gave the highest recovery of lignin. Lignin has Mw = 2640 and Mz = 93,994. In the UV spectrum absorptions at lambda = 231 and 280 nm were recorded. 1H NMR spectrum of lignin showed signals attributable to cinnamaldehyde units, guaiacyl units, and syringyl units. Syringyl and guaiacyl units are in 1:1 ratio. 13C NMR spectrum showed signals for guaiacyl, syringyl, and p-hydroxyphenyl units. The spectrum shoed a prevalence of guaiacyl units. The 13C NMR spectrum is in agreement with the presence of cinnamic untis. The same characterization was performed on lignin from pine. The irradiation of lignin from pine from steam explosione process in the presence of oxygen, in conditions described for the formation of superoxide ion, for different irradiation time was followed isolating the lignin and determining the average molecular weight. The experiments showed that, until 8 h irradiation, Mn decreases, while Mw and Mz increases. After 8 h irradiation an inverse behaviour was observed, with an increase of Mn and a decrease of Mw and Mz. These results are in agreement with an initial polymerization process followed by a photoinduced degradation. Ozonization was carried out in acetonitrile-methanol solution. The reaction showed a zero-order knetics. After 50 min the average molecular weight of lignin is the half. The reaction mixture was analyzed by using GC-MS. Oxalic acid was determined.