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Autohydrolysis with different severity factors was performed on poplar wood chips prior to pulping, and the wettability, absorbility and the following impregnation of NaOH solution for the poplar wood chips were then investigated. The results showed that after autohydrolysis pretreatment the porosity, shrinkage and fiber saturation point (FSP) of the poplar wood chips were increased, while the surface contact angle decreased as the severity factor was increased. The autohydrolyzed chips absorbed more NaOH in impregnation that resulted in a low NaOH concentration in the bulk impregnation liquor (i.e., the impregnation liquor outside wood chips), while the concentration in the entrapped liquor (i.e., the impregnation liquor inside wood chips) was increased. Autohydrolysis substantially improved the effectiveness of alkali impregnation.

Some of the dissolved and colloidal substances (DCS) such as extractives and pectic acids have great negative influence through the whole papermaking process, and their control and understanding would benefit the production, especially in the mills with closed water system. In this work, the DCS from the alkaline peroxide bleaching of poplar chemi-thermomechanical pulp (CTMP) with partial substituting MgO for NaOH were analyzed. The results showed that the amount, pH value, lignin content, conductivity, and cationic demand (CD) of the DCS decreased with increasing substitution percentage of MgO for NaOH. The methyl tert-butyl ether (MTBE) extractives were characterized by a gas chromatograph coupled to a mass spectrometry (GC-MS). The substitution of MgO for NaOH in the bleaching process improves the bulk, light-scattering coefficient, and opacity of the bleached poplar CTMP, reduces the pulp brightness, and decreases the tensile and burst indices.