Physicochemical and structural characterization of alkali soluble lignins from oil palm trunk and empty fruit-bunch fibers.
Six alkali soluble lignin fractions were extracted from the cell wall materials of oil palm trunk and empty fruit-bunch (EFB) fibers with 5% NaOH, 10% NaOH, and 24% KOH/2% H(3)BO(3). All of the lignin fractions contained rather low amounts of associated neutral sugars (0.8-1.2%) and uronic acids (1.1-2.0%). The lignin fractions isolated with 5% NaOH from the lignified palm trunk and EFB fibers gave a relatively higher degree of polymerization as shown by weight-average molecular weights ranging between 2620 and 2840, whereas the lignin fractions isolated with 10% NaOH and 24% KOH/2% H(3)BO(3) from the partially delignified palm trunk and EFB fibers showed a relatively lower degree of polymerization, as shown by weight-average molecular weights ranging between 1750 and 1980. The results obtained by alkaline nitrobenzene oxidation showed that all of the lignin preparations contained a high proportion of noncondensed syringyl units with small amounts of noncondensed guaiacyl and fewer p-hydroxyphenyl units. The lignin fraction extracted with 5% NaOH from the lignified EFB fiber was mainly composed of beta-O-4 ether-linked units. Small amounts of 5-5', beta-5, and beta-beta' carbon-carbon linkages were also found to be present between the lignin structural units. Further studies showed that uronic, p-hydroxybenzoic, and ferulic acids in the cell walls of palm fibers were esterified to lignin.
Sun
R
R
The BioComposites Centre, University of Wales, Bangor LL57 2UW, United Kingdom.
Fang
J M
JM
Tomkinson
J
J
Bolton
J
J
D000468:Alkalies / Q000737:chemistry; D008031:Lignin / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D013056:Spectrophotometry, Ultraviolet; D017550:Spectroscopy, Fourier Transform Infrared; D014197:Trees / Q000737:chemistry*
D000468:Alkalies; D008031:Lignin