Chemical changes within solids during liquid hot water pretreatment of wood

The chemical properties of willow were studied following liquid hot water pretreatment. Three different temperatures of liquid hot water pretreatment were used (160, 180, and 200 °C) for periods of 30, 60, 120, and 240 min. The contents of extractives, lignin, holocellulose, glucose, and xylose was determined. Compared with the original sample, the results indicated that lignin and extractives content increased after pretreatment. Further, the content of xylose decreased significantly with increasing pretreatment time for all three temperatures. The highest glucose content was obtained under the conditions of 180 °C for 240 min. In addition, a significant correlation was found between the content of xylose in the solid fraction and the severity factor of treatment. To determine the changes in cellulose crystallinity, the total crystallinity index (TCI) and the lateral order index (LOI) were calculated from the Fourier-transform infrared spectroscopy spectra of cellulose. An increase in both of these structural characteristics was observed at all experimental temperatures.