Structural features and changes of lignocellulosic biomass during thermochemical pretreatments: A synchrotron X-ray scattering study on photoperiod-sensitive sorghum

► WAXD and SAXS were used to study biomass structural changes during various pretreatments. ► The outside rind had oriented crystal peaks. ► The crystalline structures of the inner pith and leaf were less ordered. ► A smooth pore-boundary surface structure of cellulose was noted by SAXS results after acid pretreatment. ► Alkali pretreatment transformed part of cellulose to a more stable form and increased the crystal size. Fundamental understanding of the structural changes during pretreatment of lignocellulosic biomass could lead to improved processes and cost reductions for bioethanol production. Synchrotron wide-angle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS) were used to study the structures of different parts of photoperiod-sensitive sorghum and structural changes during various pretreatments. WAXD study showed that the PS sorghum rind had oriented crystal peaks and the highest degree of crystallinity, whereas the crystalline structures of the inner pith and leaf were less ordered. Orientation distribution of cellulose changed during pretreatments. Crystalline cellulose was degraded partially by acid pretreatment and a smooth pore-boundary surface structure of cellulose was noted by SAXS. Alkali pretreatment transformed part of the cellulose to a more stable form and increased the crystal size of cellulose. The study provides information on a large length scale to understand how structure changes with different pretreatments.