Per Engstrand

Processing of wood-based microfibrillated cellulose and nanofibrillated cellulose, and applications relating to papermaking: a review

Abstract As an emerging cellulosic nanomaterial, microfibrillated cellulose (MFC) and nanofibrillated cellulose (NFC) have shown enormous potential in the forest products industry. The forest products industry and academia are working together to realise the possibilities of commercializing MFC and NFC. However, there are still needs to improve the processing, characterisation and material properties of nanocellulose in order to realise its full potential. The annual number of research publications and patents on nanocellulose with respect to manufacturing, properties and applications is now up in the thousands, so it is of the utmost importance to review articles that endeavour to research on this explosive topic of cellulose nanomaterials. This review examines the past and current situation of wood-based MFC and NFC in relation to its processing and applications relating to papermaking.

Determination of Charged Groups in Mechanical Pulp Fibres and Their Influence on Pulp Properties

Abstract The content of charged groups, i.e carboxylic and sulfonic acid groups in various kinds of mechanical pulp fibres has been investigated. Special emphasis has been given to the determination of the charged groups located at the fibre surfaces using a polyelectrolyte titration technique. The significance of these charged groups for some physical properties of the pulps has also been evaluated. The results suggest that it is feasible to determine the surface charges of the various kinds of mechanical pulp fibres by applying the polyelectrolyte titration technique. This study also indicates that fibre surface charges can serve as one of the basic chemical parameters to characterise fibre Surface properties, and that both total charged groups and surface charged groups are important for the physical properties of the pulps. 1Present address: Royal Institute of Technology, Department of Wood Chemistry, S-100 44 Stockholm, Sweden. 2Present address: Holmen Paper AB, Braviken Paper Mill, S-601 88 Norrkopi...

Fundamental understanding of pulp property development under different thermomechanical pulp refining conditions as observed by a new Simons’ staining method and SEM observation of the ultrastructure of fibre surfaces

Abstract The morphological and chemical characteristics of cell walls govern the response of wood fibre to mechanical pulping processes and thereby influence the energy efficiency of the process and determine most pulp and paper properties. A study has been carried out at the microstructural/ultrastructural level of fibre cell walls by means of a newly developed Simons’ staining (SS) method and scanning electron microscopy to characterize thermomechanical pulps (TMPs) produced under different refining conditions. The SS method allows assessment and quantification of pulp fibre development during the process in terms of cell wall delamination/internal fibrillation (D/IF) under different process conditions, and the degree of D/IF can be statistically evaluated for different TMP types. In focus was never-dried Norway spruce TMP from primary stage double-disc refining running in a full-scale mill, where specific refining energy was varied at different refining pressure levels. Improved energy efficiency was gained at the same tensile index level when applying high pressure (temperature). Under conditions of high pressure and refining energy, a significant enhancement of the degree of D/IF of pulp fibres was observed. The surface ultrastructure of these fibres exhibited an exposed S2 layer with long ribbon-type fibrillation compared to pulps produced with lower pressure and energy input. A given TMP type can be classified in the categories of high-severity and low-severity changes and quasi-untreated concerning the degree of D/IF of its fibres. The relative proportions of these are important for the development of pulp properties such as tensile strength. The presence of higher amounts of fibre fractions in the categories high D/IF and low D/IF will improve the tensile index of a TMP.

Paper strength improvement by inclusion of nano-ligno-cellulose to Chemi-thermomechanical pulp

Abstract So far, chemical pulp fibres have been utilized as conventional stock materials for nanocellulose production. The main aim of this work is to use stock materials from mechanical or chemi-thermomechanical pulping process to produce lignin containing nanofibres, which are referred to as nano-ligno-cellulose (NLC) in this study. The present study shows the influence on handsheets of chemi-thermomechanical pulp (CTMP) fibres blended with NLC. For comparison reasons, nanocellulose (NC) from bleached kraft pulp (BKP) was produced in a similar approach as NLC. Both the NLC and the NC were blended with their respective pulp fibres and their corresponding handsheets properties were evaluated with respect to sheet density. It was found that the handsheets of pulp fibres blended with NLC/NC improved the mechanical properties of handsheets with only a slight effect in relation to the sheet density. Improvements in strength properties of handsheets such as z-strength, tensile index, tear index, burst index, Emodulus, strain at break, tensile stiffness, air resistance were observed.

Sustainable Design for the Direct Fabrication and Highly Versatile Functionalization of Nanocelluloses

Abstract This study describes a novel sustainable concept for the scalable direct fabrication and functionalization of nanocellulose from wood pulp with reduced energy consumption. A central concept is the use of metal‐free small organic molecules as mediators and catalysts for the production and subsequent versatile surface engineering of the cellulosic nanomaterials via organocatalysis and click chemistry. Here, “organoclick” chemistry enables the selective functionalization of nanocelluloses with different organic molecules as well as the binding of palladium ions or nanoparticles. The nanocellulosic material is also shown to function as a sustainable support for heterogeneous catalysis in modern organic synthesis (e.g., Suzuki cross‐coupling transformations in water). The reported strategy not only addresses obstacles and challenges for the future utilization of nanocellulose (e.g., low moisture resistance, the need for green chemistry, and energy‐intensive production) but also enables new applications for nanocellulosic materials in different areas.

Properties of wood chips for thermomechanical pulp (TMP) production as a function of spout angle

Abstract Spruce wood chips were produced under well-controlled conditions in a laboratory wood chipper at spout angles of 30°, 40°, and 50° at a cutting rate of 20 m s-1 and with a nominal chip length of 25 mm. The chips were then refined under thermomechanical pulp (TMP) conditions in a pilot refiner plant. The pulp properties such as freeness, average fiber length, and shives content were determined and evaluated as a function of specific energy consumption. For a first stage refining and for a freeness value of 350 ml, a decrease in specific electrical energy consumption could be achieved by performing the wood chipping at a spout angle of 50° as compared to 30° which is the spout angle commonly used. A patent application regarding this method has been filed and is pending. It is realized that a freeness value is not directly indicative of any quality measure, such as, for example tensile index and light scattering coefficient but the obtained results can be interpreted to be promising. Further studies are needed regarding the impact of the modified chipping process.

Refiner bleaching in a peroxide-based ATMP process compared with conventional bleaching

Abstract The aim of this study was to compare refiner bleaching with conventional laboratory bleaching by means of hydrogen peroxide and magnesium hydroxide. Refiner bleaching in this study was a part of the ATMP (advanced thermo mechanical pulping) process, in which bleaching chemicals are added to the first stage refiner. Unbleached reference pulp which underwent similar mechanical treatment as refiner bleached pulp was used for laboratory bleaching. Bleaching efficiency was found to be almost equal for pilot scale refiner bleaching and conventional laboratory bleaching. A brightness increase of 10 ISO% was reached with addition of 26 kg t-1 hydrogen peroxide leading to a final brightness of 66 ISO% using both methods. Slightly more COD (52 kg t-1 compared with 46 kg t-1) was generated in refiner bleaching compared with conventional laboratory bleaching to equal brightness with the same chemicals added.

Dewatering properties of low grammage handsheets of softwood kraft pulps modified to minimize the need for refining

Abstract Previous paper (Rahman et al. 2017) showed that the yield of softwood kraft pulp increased by the addition of either polysulfide or sodium borohydride because of higher hemicellulose retention. An increase in hemicellulose content can make dewatering more difficult as WRV of the pulp increases, but instead, an overall increase in pulp yield could improve dewatering as a sheet of a certain weight will contain fewer fibres, giving a more open sheet structure. It was therefore of interest to measure the dewatering properties of low grammage handsheets (20 g/m2) under conditions mimicking the tissue paper machine dewatering processes, and sheet strength properties, WRV, °SR and fibre dimensions were also studied. The results showed that the positive influence of overall yield increase dominated over the negative influence of an increase in hemicellulose content on the dewatering properties, particularly at lower refining energy levels. Moreover, higher yield and higher hemicellulose content pulps had a higher tensile index at the same dryness. A given tensile index was achieved with less refining energy. The results indicate that increased yield and hemicellulose content by modification of the kraft pulping process will result in a pulp with a potential to improve tissue paper quality.

Effects of chip pretreatment and feeding segments on specific energy and pulp quality in TMP production

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 effect of increased pulp yield using additives in the softwood kraft cook on the physical properties of low-grammage handsheets

The effect of increasing the pulp yield by the addition of sodium borohydride (NaBH4) or polysulfide (PS) in softwood kraft cooking, i.e. enhancing the retention of glucomannan, on the physical pro ...