Structural characterization of alkali lignins from sugar beet pulp

Six alkali lignin fractions were extracted from sugar beet pulp with 2% NaO H at 45 degrees for 0.5, 1, 2, 3, 4, and 5 h, respectively. The yields of t otal and pure lignin fractions, LA, were 4.07-7.63% and 2.90-5.85%, respect ively, during the increase of alkali treatment time from 0.5 to 5 h. The ch emical tend physico-chemical properties of the pure lignins were studied by nitrobenzene oxidation, and UV-, FT-IR- and C-13-NMR spectroscopy. All iso lated pure lignin fractions (LA) contained rather low amounts of bound neut ral polysaccharides (0.92-1.80%) and pectic substances (2.15-2.75%). The mo lecular-average weights ranged between 1970-2120 Da. The lignin fraction, i solated with 2% NaOH at 45 degrees for 0.5 h, is mainly composed of beta-O- 4 ether bonds. The less common beta-beta, beta-5, 5-5', and beta-1 carbon-c arbon linkages in the lignin structural units are also present. Further stu dies indicated that p-coumaric acids are esterified to lignin at the side c hains, while ferulic acids are both esterified and etherified to lignin sid e chains. The results also showed that the lignins are strongly linked to g alacturonic acids by esterification.