A new concept for both furnish composition and z-directional furnish arrangement involving the interaction between specific thermo-mechanical pulp fractions (TMP), nanofibrillated cellulose (NFC) and clay in oriented layered laboratory sheets is presented. Used separately, NFC improves the strength properties of paper while fillers enhance the optical properties. Synergy effects of clay-NFC interactions are assessed. The study comprises a structural assessment, including laser profilometry, scanning electron microscopy (SEM) and field-emission (FE)-SEM analyses. In addition, optical and strength properties are assessed. It is demonstrated that a potential reduction of strength properties caused by filler addition may be counteracted by appropriate NFC addition to specific layers in the zdirection. Based on an estimation of an overall quality index considering five variables, it is concluded that the best sheet construction is obtained when placing the fillers in surface layers with the TMP accept fraction and the NFC in the centre of the sheets together with the refined TMP reject fraction.
SUMMARY:Pilot scale refining of White spruce using a modified TMP refining process (ATMP -Advanced Thermomechanical Pulp) was studied. ATMP combines selective wood disintegration by mechanical pretreatment and refining at elevated intensity with chemical treatment after defibration (in this study hydrogen peroxide, alone and in combination with alkali).The electrical energy efficiency and pulp quality using ATMP were evaluated and compared to a conventional TMP process. One goal was to retain the combination of optical properties and strength of typical TMP. Fibre properties (structural dimensions, external and internal fibre development) as well as the amount of split fibres resulting from TMP and ATMP processes were compared.The results indicate an electrical energy efficiency improvement potential of 0.65 MWh/odt (34%) at tensile index 30 N.m/g of ATMP compared to reference TMP. All ATMP pulps retained their TMP character, i.e. the relationships between light scattering coefficient, density, elongation properties and strength that are important for printing paper. ATMP had a significantly lower content of shives and higher external and internal fibre development compared to TMP at equal energy application. The long fibre fraction of ATMP also contained significantly higher amount of split fibres. The brightness of ATMP produced with addition of hydrogen peroxide (28 kg/odt) and magnesium hydroxide (14 kg/odt) was 14 ISO % higher compared to TMP.
The correlation between the fibre flexibility and cross-sectional area moment of inertia of thermomechanical pulp fibres was investigated. The main effects of refining were found to be internal fibrillation, external fibrillation, and fibre shortening. Internal fibrillation increases fibre flexibility and fibre collapsibility, improving fibre-to-fibre contact in a paper sheet. The raw materials used were pulps produced from six different Norway spruce logs and six different Scots pine logs, chosen in a manner that allowed variation of fibre wall thickness and fibril angle independently. Each wood sample was refined in four stages using a pressurized 12″ Sprout Waldron single disc refiner. Fibre flexibility was assessed by FiberMaster bendability measurements. Fibre bendability was measured on the +48 Bauer McNett fractions of the twelve 2nd, 3rd, and 4th stage thermomechanical pulps (TMP). The fibre cross-sectional samples were imaged using scanning electron microscopy (SEM). An image analysis method to calculate the area moment of inertia of each fibre using numerical integration was developed. Fiber bendability increased with specific energy consumption for both wood species (spruce and pine) from the 2nd refining stage to the fourth refining stage. Spruce had a higher rate of bendability increase than pine upon refining. It was expected that fibres with a low area moment of inertia would result in higher bendability, but no such correlation was found for either spruce or pine. Fibre bendability increased with internal fibrillation, as assessed from Simons staining. These results imply that local damage of the fibre wall such as delaminations, kinks, and compressions was the main effect in increasing the flexibility through refining of TMP.
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