The influences of hydroxyl groups on the compactness of lignin adsorption layer and the mechanism were studied when lignin was adsorbed on the solid-liquid interface.By the acetylized modification of alkali lignin (AL)

the acetylized alkali lignin (ACAL) was obtained

of which the quantity of hydroxyl groups got a significant reduction from 1.80 to 0.06 mmol/g.The compactness differences between the AL and ACAL monolayer adsorption films on the gold in solution conditions were studied by the quartz crystal microbalance with dissipation (QCM-D)

and the differences of the multilayer adsorption films built up with poly-(diallydimethyl ammoniumchloride) (PDAC) in dryness condition were studied by the combination of UV-Vis spectroscopy (UV) and atomic force microscopy (AFM).Both the monolayer and multilayer adsorption results show that the hydroxyl groups can reduce the compactness of the lignin adsorption layer.The infrared spectroscopy (IR) shows that the main aromatic peak of AL shifts to lower wave numbers in ACAL

which provides direct evidence for the enhancement of - interactions between the aromatic nucleus.It can be explained that the existence of the hydroxyl groups goes against the coplanar formation of the aromatic nucleus in lignin.The reduction of the hydroxyl groups can enhance the coplanarity of the aromatic nucleus

which makes a contribution to the increase of the compactness of lignin adsorption layers.