Abstract: The wheat straw was pretreated by steam explosion and ethanol cooking to investigate the changes of chemical composition and morphology structure. The wheat straw were firstly steam explored under 1.75 MPa pressure for 3.5 min, then treated by 55% ethanol at 170℃ for 30 min with a 1:5 solid to liquid ratio (g:mL). The hemicellulose content of the treated product was 89%, and the lignin content was decreased to 42.16%. The morphology structures of the treated wheat straw were analyzed by FT-IR, Fiber Fester and SEM. The results showed that the hemicelluloses were degraded significantly and the ester linkages were also destroyed after steam explosion, but only tiny degradation of cellulose was observed. For the fiber morphology, the average length of steam explored pulp was significantly decreased. However, the average width of the steam explored pulp were increased. After the ethanol pretreatment, there is no negative impact on the average fiber length, but a lower average width was observed. After this two-step pretreatment, a fluffier wheat straw was obtained and very few fragments were attached to the fiber surface.

Key words: steam explosion, ethanol pretreatment, wheat straw, fiber morphology