Infrared Spectra of Lignin and Related Compounds. II. Conifer Lignin and Model Compounds^1,2

Abstract

The infrared spectra of conifer lignin model compounds and degradation products were determined, and characteristic frequencies of carbonyl groups, ethylenic double bonds, aromatic rings, and hydroxyl groups are presented. These results are applied to lignins isolated from five different coniferous genera. The functional groups occurring in the lignin molecule are discussed and related to the mode of isolation.

TGA-FTIR Analysis of Torrefaction of Lignocellulosic Components (cellulose, xylan, lignin) in Isothermal Conditions over a Wide Range of Time Durations

“…Most studies assign this peak and the peak at 1131 cm -1 in LS to aromatic C-H in-plane deformation in S units in hardwood and G units in softwood, respectively. However, some investigators have proposed that these absorptions may be due to some other ether-type linkages (Briggs et al 1957;Hergert 1960). This study suggests that both types of vibrations contribute to this peak.…”

“…3), which is indicative of dehydration and dehydrogenation reactions. This is also evidenced by the drastic decline in the absorptions at 1082 and 1026 cm -1 (C-O stretch in secondary and primary alcohols, respectively) (Hergert 1960;Nada et al 1998). Peaks at 1743 (C=O) and 766 cm -1 (O-C=O in-plane deformation) exhibited characteristics of esters and decreased with increasing temperature.…”

“…The decomposition of the side groups caused the aromatic out-of-plane C-H deformation vibrations in 1,3,4-trisubstituted benzenes at 857 and 810 cm -1 (Hergert 1960;Boeriu et al 2004) to decrease. Changes within the aromatic ring took place, as evidenced by the decrease in intensity of aromatic skeletal vibrations at 1592 and 1506 cm -1 .…”

Characterization of aspen exploded wood lignin

“…This indicates the presence of unconjugated ketone and/or aldehyde groups as well as carboxyl ester groups in aspen EXWL. In the spectra of lignin preparations including MWL and solvolysis lignins, the bands observed at 1710-1750 cm-' are attributed to unconjugated carboxyl ester groups (6,13) or unconjugated aliphaticor P-ketone groups (12,(14)(15)(16)(17)(18). It should be noted that in the reported lignin spectra the bands due to conjugated carbonyl groups are observed at 1660-1670cm-' whereas only background absorption was detected in this region of the spectrum of EXWL.…”

Investigating the Usability of Alkali Lignin as an Additive in Polysulfone Ultrafiltration Membranes

“…3. Lignin from wood, grass, and biomass sources has characteristic peaks at around 1600 cm -1 and 1750 cm -1 due to aromatic stretching and the vibration of unsaturated carbonyls (C=O), respectively (Hergert 1960;Lisperguer et al 2009;Zhou et al 2011;Vilakati et al 2012). This peak was not present in the spectra before or after post-treatment with sodium hydroxide.…”