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Pretreatment of biomass is expected to improve the pulp properties and facilitate the main components in the raw materials to be better used. In this work, the refining energy consumption and properties of the poplar chemithermomechanical pulp (CTMP) from different autohydrolysis pretreatment intensities of wood chips were investigated, and the pulp bleaching ability was also studied. The results showed that the CTMP with autohydrolysis pretreatment at a severity factor of 3.47 could have a 26% energy reduction in pressurized refining, a 60% energy saving in PFI refining, and 44% and 46% increases in tensile and tear indices, respectively. Autohydrolysis pretreatment prior to pulping could result in CTMP with a higher water retention value, higher fines content, better strength properties, lower shives content, and lower bulk and ISO brightness after PFI refining. The brightness of CTMP can be improved by alkaline peroxide bleaching.

High-yield pulp (HYP) has various fractions, and they not only play an important role in the papermaking process but also affect paper properties. Hence, it is necessary to clarify the impact of different HYP fractions on paper formation and properties. In this study, the characteristics of poplar preconditioning followed by refining chemical treatment alkaline peroxide mechanical pulp fractions were determined, and their effects on paper formation and paper properties were investigated. The results show that the HYP fiber is not as flexible as the bleached wheat straw pulp fiber. Compared with the HYP long-fiber fraction, the short-fiber fraction can improve the formation index more favorably. It was also found that the long-fiber fraction can maintain the strength properties, while having a negligible effect on the light-scattering coefficient; on the contrary, the short-fiber fraction can improve the light-scattering coefficient effectively but reduces the strength properties.