Some physical properties of acetosolv lignins from bagasse

Acetosolv-solubilized lignins were characterized by their solubility in different organic solvents, Fourier transform infrared, ¹³C-NMR, UV, gel permeation chromatography, differential scanning calorimetry, and thermogravimetric analysis. Solvents having a solubility parameter in the range of 10-12.7 and a hydrogen-bonding parameter in the range of 3.6-5 were considered good solvents for acetosolv lignins. Fourier transform infrared spectra of the lignins were typical for lignins containing p-hydroxy phenylpropane (H), guaiacyl (G), and syringyl (S) units. The lignins contained more conjugated and fewer nonconjugated C==O groups, and the guaiacyl groups were etherified and condensed. ¹³C-NMR confirmed partial acetylation of the lignins and the presence of β-O-4 and β-5 linkages. Acetosolv lignins also showed the typical UV spectrum of annual plants. The effects of the acetic acid concentration and pulping time on the molecular weights of the lignins were explained with the presieving and condensation concepts. The thermal behavior of the acetosolv lignins was also studied.