High Brightness Mechanical Pulp from Eucalyptus Planted Trees

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The mechanical pulp yield is about 85 to 95% of the original wood, compared with around 45 to 55% for chemical pulp. Hardwood mechanical pulp has the desirable properties of low cost, high opacity and good printing quality due to its high bulk, high smoothness, resiliency, and good ink absorption. Hardwood mechanical pulp tends to have shorter fibers, higher light-scattering coefficient and lower strength value. Eucalyptus plantation tree is a common tropical hardwood species and is used for the production of lower yield chemical pulps such as kraft pulps. It is believed, however, that Eucalyptus mechanical pulp is said to be not suitable for the production of graphical paper grades because of its low initial brightness and limited bleachability. Alkaline peroxide mechanical pulping（APMP） and thermomechanical pulping（APTMP） add caustic soda, hydrogen peroxide, and stabilizers to soften and brighten wood chips prior to refining in a disc refiner. The chip pretreatment facility uses a screw feeder device to apply mechanical compression on wood chips and squeezed out the detrimental substances for bleaching. The facility also partially destroys wood matrix of chips allowing for easier fiber separation and reduced refining energy. In our study, APMP and APTMP methods were applied to Eucalyptus-globulus planted trees by pilot plant tests and significant benefits were obtained in bleachability improvement. Eucalyptus APMP reached 87% ISO brightness that exceeded 80% ISO brightness of aspen APMP.