Cold sodium hydroxide/urea based pretreatment of bamboo for bioethanol production: Characterization of the cellulose rich fraction

Bamboo (Neosinocalamus affinis) was subjected to successive pretreatments to isolate cellulose rich fractions for further utilization. In this study, the ball-milled bamboo underwent ultrasound treatment in ethanol solution at 20 °C for 0, 5, 15, 35, and 50 min, respectively. Then the samples were dissolved with 7% NaOH/12% urea solutions at −12 °C, followed by successive extractions with dioxane, ethanol, and dimethyl sulfoxide (DMSO). The yields of the obtained cellulose rich fractions ranged from 75.1 to 77.7%. In addition, the structural features of the cellulose rich fractions and the original ball-milled sample were comparatively characterized with a set of spectroscopy and wet chemistry methods including FT-IR, CP/MAS 13C NMR, XRD, SEM, sugar analysis, etc. The results showed that the successive pretreatments resulted in partial removal of carbohydrates and lignin. The lignin released during the pretreatments could facilitate the removal of lignin, which was mainly composed of G and S types. The removal of acetyl groups suggested a decrease of the satirical barrier of enzyme absorption to cellulose. The cellulose rich fractions appeared looser and exhibited more internal surfaces compared to the ball-milled sample. The changes of chemical structures and morphology of the treated sample suggested that the cold sodium hydroxide/urea based pretreatments effectively disrupted the recalcitrance of bamboo, generating highly reactive cellulosic materials for enzymatic hydrolysis to produce bioethanol.