In order to destroy the natural anti-degradation barrier, promote efficient conversion efficiency and utilization of woody biomass, finally select a suitable heat pretreatment method.

Taking oak as the research object, the physical properties and lignocellulose content of oak treated by high-temperature steam, solid-state steam explosion and extrusion were determined by mass method/volume method and Van Soest method, and its functional groups and relative crystallinity of cellulose were analyzed by Fourier transform infrared spectroscopy and X- ray diffraction.

The extrusion treatment could significantly change the morphology of oak, the water-holding capacity and specific porosity were 3.2 times and 4.71 times higher than that of untreated wood, respectively, and the volumetric weight was reduced to 1/4 of untreated wood. All heat pretreatments significantly reduced the content of lignocellulose in oak. Lignocellulose content was significantly reduced after extrusion. The contents of cellulose, hemicellulose and lignin were reduced by 22.60%, 15.85% and 7.9% respectively compared with control group. Fourier transform infrared spectroscopy (FT-IR) showed that all the heat pretreatment oak had wood characteristic functional groups, and the ratio of I₈₉₈/I_{1 509} increased significantly after extrusion, indicating that cellulose was enriched. After different heat pretreatments, the wood still had typical cellulose X- ray diffraction characteristics, and the peak shape of crystal structure did not changed, but the intensity was weakened. The relative crystallinity increased after different heat pretreatments, and the relative crystallinity increased significantly after solid-state steam explosion treatment and extrusion treatment, which indicated that the cellulose in the crystallization area was more exposed.

The extrusion treatment can significantly change the physical properties of oak, reduce the lignocellulose content and expose the cellulose in the crystallization zone, which is beneficial to the conversion efficiency and utilization of woody biomass.