Freeze-thaw repetition as an auxiliary method to promote efficient separation of hemicellulose from poplar
The application of the freeze-thaw repetition, as a pretreatment method in the hydrothermal treatment and green upgradation of poplar biomass has been investigated. The process was carried out at different freeze-thaw repetition (1 ~ 6 times) and freezing temperatures (-4℃ ~ -70℃). Poplar chips were freeze-thawed 4 times at -20℃, and then hydrolyzed by hot water for 1 h at 170℃, consequently a hemicellulose yield of 85.87 mg/g was obtained, showing an increase of 32.25% over that of untreated poplar chips. Besides, freeze-thaw repetition pretreatment resulted in lowered the molecular weight, and enhanced the concentration of monosaccharides. The morphology and chemical structure of all samples were also carefully addressed, indicating that freeze-thaw repetition could create irregular micro slit and pores, thus the fibers cell wall debris were increased, and significantly contributed to the dissolution rate of hemicellulose. This study demonstrates a feasible and effective strategy to predominately extract hemicellulose from raw biomass for promising biorefinery.