Comparison of organosolv and hydrotropic pretreatments of eucalyptus for enhancing enzymatic saccharification

•Hydrotropic method could dramatically remove lignin from fiber surface and fiber cell wall.•Effect of organosolv pretreatment on reducing cellulose crystallinity was notable.•Water treatment without addition chemicals was able to displace the lignin on fiber surface.•Cellulase adsorption capacity of hydrotropic pretreated substrates was better.•Hydrotropic lignin contains more phenolic group and syringyl unit than organosolv lignin. The objective of this study was to investigate the effects of organosolv and hydrotropic pretreatments on improving enzymatic hydrolysis of eucalyptus. The chemical composition of the fiber surface was analyzed using X-ray photoelectron spectroscopy (XPS) to determine the surface characteristics of pretreated eucalyptus. Other than the significant decrease of surface coverage by lignin, hydrotropic pretreatment was more effective in removing the lignin and xylose from fiber cell walls than organosolv pretreatment. The restriction of acetyl and phenolic groups in pretreated substrates was typically eliminated by hydrotropic pretreatments. Moreover, fiber structure and morphology after pretreatments were more suitable for enzymatic hydrolysis. Cellulase adsorption capacity was notably improved by hydrotropic pretreatment, which indicating the better enzyme accessibility of cellulose in pretreated substrates. Eventually, higher glucose yield was obtained with hydrotropic pretreatment. In addition, the precipitated lignin as an important by-product of pretreatments was characterized by Fourier transforms infrared spectroscopy (FTIR) also.