EFFECT OF ISOLATION PROCEDURE ON MOLECULAR-WEIGHT DISTRIBUTION OF WHEAT-STRAW LIGNINS

Neutral detergent fiber (NDF) of wheat straw (WS) was ball-milled for 7, 14, 21, and 28 days in a porcelain rotary ball-mill and hydrolyzed by a cellulase for 4 days, and the residue was used for lignin extraction by either dioxane or 1 M NaOH. The effects of ball-milling duration (BMD) and extraction procedure on lignin yield and its high-performance size exclusion chromatography (HPSEC) features were examined in this study. Optimal BMD was 14 days, at which 80% and 100% of the permanganate lignin has been extracted by the dioxane and alkali systems, respectively. At a BMD of 14 days, carbohydrate content was 6% and 15% of the alkali lignin (AL) and dioxane lignin (DL), respectively. By increasing the BMD, there was an increase in the proportion of the high molecular weight fraction residing in the 23-130-kDa range of the ALs, reaching 26% of the total AL at a BMD of 28 days. At 100% yield of the permanganate lignin, 75% of the lignin molecules resided in the range 1.6-23 kDa, the entire lignin having a weight-average molecular weight (MWBAR) of 17.6 kDa and a dispersivity of 2.29. Ball-milling in a porcelain rotary BM for prolonged periods did not cause a subdivision of the lignin molecules.