Valérie Meyer

Energy reduction of refining by cellulases.

Abstract The effect of three different commercial cellulase treatments applied on softwood bleached kraft pulp before the refining step was studied. Disc refining was applied under similar conditions as usual in paper mills. Two cellulase treatments allowed an energy saving of 20% to reach a given drainage index or breaking length. Water retention value (WRV), which characterizes the water absorption inside the fibre wall, was increased by the cellulase treatment. However, tear index losses were observed upon enzyme treatment. The third cellulase did not have an impact either on any parameters of the refining or on the pulp properties, except WRV. Viscosity measurements showed that the two first cellulases have strong endoglucanase activities but are lacking exoglucanase activities. Probably, endoglucanase activity weakens the fibre structure by generation of weak points or kinks. This hypothesis would explain the important cutting and fibrillation phenomena observed in the case of these two cellulases. It can be concluded that cellulase treatment could save 20% of electrical energy needed for refining, i.e., 50 kWh t-1, if a paper quality with a high tensile resistance but lowered tear strength is acceptable.

Laccase/HBT and laccase-CBM/HBT treatment of softwood kraft pulp: impact on pulp bleachability and physical properties.

Pycnoporus cinnabarinus laccase and a chimeric laccase-CBM were applied in softwood kraft pulp biobleaching in the presence of 1-hydroxybenzotriazole (HBT). The presence of CBM could enhance the laccase biobleaching potential as a decrease in the enzymatic charge and chlorine dioxide consumption, as well as an increase in pulp brightness were observed. Laccase/HBT treatment could be improved by increasing oxygen pressure from 1 to 3bar and pulp consistency from 5% to 10%. Conversely, under the same conditions, no improvement of laccase-CBM/HBT treatment was observed, indicating a different behavior of both systems. However, laccase-CBM/HBT treatment led to a better preservation of pulp properties. This effect was probably due to fiber surface modifications involving the action of the CBM. Transmission electron microscopy examination of pulp fibers indicated a retention of laccase-CBM inside the pulp fibers due to CBM binding and an increased external microfibrillation of the fibers due to enzymatic treatments.

Mechanisms of TMP peroxide bleaching using Mg-based alkalis

Abstract The driving force for pulp and paper industry is to develop new technologies with less impact to the environment. In this context, the successful approach in the present paper was the substitution of sodium hydroxide during peroxide bleaching of thermomechanical pulp (TMP) by magnesium hydroxide or magnesium carbonate. Looking at brightening development, thioacidolysis showed that Mg-based processes eliminated less coniferaldehydes than NaOH-based bleaching. Moreover, 19F NMR analysis showed slightly more residual quinone in lignin isolated from NaOH-based bleached pulp than lignin extracted after Mg-based bleaching. Replacing NaOH by Mg-based compounds affected the strength properties of the paper: tensile index was 10% lower than conventional bleached paper, probably due to Mg2+ adsorption on the acid groups of fibers. However, the brightness reversion of Mg-based bleached paper decreased by about two ISO points during photoageing under sunlight. X-ray photoelectron spectroscopy supported the conclusion that Mg-based bleaching caused less re-deposition of lignin and extractives onto the fiber surface compared to the conventional process resulting in less light-induced yellowing.

Combination of twin-screw extruder and homogenizer to produce high-quality nanofibrillated cellulose with low energy consumption

The commercialization of cellulose nanofibrils (CNF) is limited due to the high energy consumed during production. Twin-screw extrusion has recently been employed for the energy-efficient production of CNF with high solid content, but the method requires several passes. Cellulose nanofibrils have been produced by using both a twin-screw extruder and a homogenizer. Some combinations require a fewer number of passes thereby using less energy, while maintaining the desired CNF quality. The morphology and quality of CNF were characterized by optical microscopy, MorFi analysis, and with a recently developed quality index. The combination of one pass through the twin-screw extruder and two passes through the homogenizer decreases energy consumption by 45%. These CNF have a similar quality to CNF produced after five passes through the homogenizer alone.