Nordic Paper (Sweden)

Increased wood softening and refining intensity have earlier been utilized to improve refining efficiency in mechanical pulping. We have evaluated a combination of increased softening by low dose sulphite chip pretreatment and increased intensity by feeding segment design in a TMP line for production of high quality printing papers.

Abstract Increased wood softening and refining intensity have earlier been utilized to improve refining efficiency in mechanical pulping. We have evaluated a combination of increased softening by low dose sulphite chip pretreatment and increased intensity by feeding segment design in a TMP line for production of high quality printing papers. Norway spruce wood chips were preheated, compressed in an Impressafiner and impregnated with water or sodium sulphite solutions (Na2SO3 charges 3.6 and 7.2 kg/t). Chips were refined in two parallel 68” double disc refiners using two different refining conditions: standard bidirectional segments at normal production rate (9 t/h) and feeding segments at increased production rate (11.1–12.1 t/h). The feeding segments enabled a 30 % increase in production rate. Refining with feeding segments at 12.1 t/h production rate combined with chip pretreatment with 3.6 kg/t sodium sulphite reduced the specific energy 360 kWh/t (19 %) compared to refining with standard segments and no pretreatment. Pulp properties were similar for the two configurations. The combination of feeding segments and chip pretreatment with water reduced the specific energy 180 kWh/t (9 %). Implementation of most of the technology presented has reduced the electrical energy use for the mill by approximately 80 GWh/year.

The aim of this investigation was to find new approaches to evaluate the performance of low-consistency refiners. Data from a paper mill producing TMP from Norway spruce was used in order to find a possible way to calculate the power split between the zones in a TwinFlo refiner. An assumption of equal amount of fibres captured between overlapping bars was found successful in order to develop equations for the power split. The equations predicted equal power in both zones at equal disc gaps. The power was found to increase approximately linearly with decreasing disc gap over the range, 0.1-0.2 mm. The power split was essential to know for calculating refining intensities expressed as specific edge load and forces on fibres in the two zones. The reduction in fibre length was about 5% at 0.17 mm disc gap or at 0.03 N forces on fibres or at 0.7 J/m specific edge load. Disc gap, forces on fibres and specific edge load was found to predict fibre shortening approximately equally upon changes in power and flow rate through the refiner.

Inkjet printing is a non impact printing method that deposits a limited amount of ink onto the paper surface. To improve runnabillity and printability the demands on papers ability to rapidly absorb the fluid and make the colorants stay on the surface increase. These demands get more pronounced as the technology develops and the print speed significantly increases.The quality of a printed image is strongly influenced by the physical and the chemical interactions between the ink and the paper. Some print quality parameters can be measured objectively by physical measurements using instruments. Subjective print quality evaluation involves human judgments of the final print.In this article, the print quality on commercial papers as well as on trial papers with different amounts of salt for surface fixation has been studied. The printouts have been made with a desktop printer that uses pigmented inks. The print quality measurements have been both objective measurements such as print density and line quality and subjective image evaluation using a test panel in a perceptual study. The perceptual study focused on detail reproduction, and efforts were made to separate the influence of the print density from the edge definition on the detail reproduction. The study confirms the influence of ink and paper interaction on print quality and the relation to different levels of surface fixation.

This paper discusses how the properties of dry handsheets from two different mechanical pulps and one chemithermomechanical pulp and their respective long fibre fractions depend on the level of dryness to which the sheets are pressed at high temperature. Sheets were pressed and dried to different dryness levels at 400 kPa and 93 degrees C in a modified Rapid Kothen dryer. Prior to testing of the physical properties, the sheets were dried without pressure at, room temperature to full dryness and kept in a conditioning room. This was performed with the aim of evaluating the consolidation and development of final strength properties with respect to dryness after a press section in a paper machine.The most interesting finding from these trials was that the increase in density and strength were far from linear with increased press dryness, especially for the long fibre fractions when looking at the Z-strength development. There was a distinct inflection of the curve when the sheets reached a press dryness level of some 50%. The most important dryness interval for internal strength development was found between 50 and 80%.The fact that most paper and board machines press the sheet to only some 50% dryness, before feeding it into the drying section, implies that much of the inherent strength potential of mechanical pulps may be unexploited. Further research on pressing to higher dryness levels will in the future be continued at FSCN at Mid Sweden University.

Article The behavior of chromophoric structures in softwood mechanical pulp on bleaching with alkaline hydrogen peroxide was published on August 1, 2006 in the journal Nordic Pulp & Paper Research Journal (volume 21, issue 3).

Traditional seasoning of wood chips normally results in significant yield losses and brightness reduction due to the uncontrolled action of microorganisms. Techniques for reduction of the amount of wood extractives with minimal yield and brightness loss are therefore of interest for the pulp and paper industry. To study a biotechnological approach for reduction of wood extractives, wood chips from sapwood of Scots pine (Pinus sylvestris) and Norway spruce (Picea abies) were treated with a commercial albino strain of the sap stain fungus Ophiostoma piliferum. During 2 weeks of controlled seasoning, the content of wood extractives decreased by approximately 40% for Scots pine and 25% for Norway spruce, where the triglyceride contents were degraded to a greater degree. Thermomechanical pulps were produced from untreated and pretreated pine chips. The properties of these pulps and corresponding laboratory sheets were investigated. The pretreated pulps showed less shortened fibers, lower amounts of triglycerides, and enhanced strength properties. The mechanisms behind these effects are discussed. Furthermore, the ability of the albino Ophiostoma piliferum to displace mould growth from wood chips was investigated in a series of experiments. It was concluded that the fungus should preferably be inoculated on fresh chips in order to repress mould growth.