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A portion of hemicelluloses and acetic acid can be pre-extracted with dilute sulfuric acid prior to the aspen chemithermomechanical pulp process. The streams collected from the second press-impregnation stage after acid pre-extraction contain a significant amount of acid pre-extracted hemicelluloses. Most of the total sugars obtained from the pressate were xylan, in which xylan was further hydrolyzed to sugar monomers under the acid pre-extraction condition. To fully understand the characteristics of hemicelluloses yielded prior to pulping, the pre-extracted hemicelluloses were separated and characterized by FT-IR, (1)H NMR, and thermogravimetric analysis in this study. Most of the FT-IR bonds from the hemicelluloses agreed well with the other two spectra of birch xylan and CA0050 xylan, except a new absorption at 1734 cm(-1) contributed to acetyl groups. The hemicelluloses obtained from acid pre-extraction began to decompose significantly at about 225 °C, slightly lower in comparison with organosolv and alkaline hemicelluloses reported in the literature.

Pre-extraction of hemicelluloses prior to pulping and conversion of the extracted hemicelluloses to other byproducts will provide additional revenue to the traditional pulp and paper industry. The effect of hemicelluloses pre-extraction with dilute sulfuric acid on the properties and bleachability of aspen (Populus tremuloides) chemithermomechanical pulp (CTMP) was investigated. The acid pre-extraction significantly reduced refining energy consumption to a given freeness. However, at the same freeness, the acid pre-extraction resulted in the reduction of bulk, tensile index, and zero-span breaking length, fewer long fibers and more fines, but an increase of the Scott bond strength. Alkaline peroxide bleaching can compensate the strength loss, but the bleachability of pulps with acid pre-extraction was lower than that of the control.

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