Mid Sweden University

There is a growing demand for the utilization of sustainable materials, such as cellulose-based alternatives, over fossil-based materials. However, the inherent drawbacks of cellulosic materials, such as extremely low wet strength and resistance to moisture, need significant improvements. Moreover, several of the commercially available wet-strength chemicals and hydrophobic agents for cellulosic material treatment are toxic or fossil-based (e.g., epichlorohydrin and fluorocarbons). Herein, we present an eco-friendly, high-yield, industrially relevant, and scalable method inspired by birch bark for fabricating hydrophobic and strong cellulosic materials. This was accomplished by combining simple surface modification of cellulosic fibers in water using colloidal particles of betulin, an abundant triterpene extracted from birch bark, with sustainable chemical engineering (e.g., lignin modification and hot-pressing). This led to a transformative process that not only altered the morphology of the cellulosic materials into a more dense and compact structure but also made them hydrophobic (contact angles of up to >130°) with the betulin particles undergoing polymorphic transformations from prismatic crystals (betulin III) to orthorhombic whiskers (betulin I). Significant synergistic effects are observed, resulting in a remarkable increase in wet strength (>1400%) of the produced hydrophobic cellulosic materials.

In the pulp and paper industry, about 5 Mt/y chemithermomechanical pulp (CTMP) are produced globally from softwood chips for production of carton board grades. For tailor making CTMP for this purpose, wood chips are impregnated with aqueous sodium sulphite for sulphonation of the wood lignin. When lignin is sulphonated, the defibration of wood into pulp becomes more selective, resulting in enhanced pulp properties. On a microscopic fibre scale, however, one could strongly assume that the sulphonation of the wood structure is very uneven due to its macroscale size of wood chips. If this is the case and the sulphonation could be done significantly more evenly, the CTMP process could be more efficient and produce pulp even better suited for carton boards. Therefore, the present study aimed to develop a technique based on X-ray fluorescence microscopy imaging (µXRF) for quantifying the sulphur distribution on CTMP wood fibres. Firstly, the feasibility of µXRF imaging for sulphur homogeneity measurements in wood fibres needs investigation. Therefore, clarification of which spatial and spectral resolution that allows visualization of sulphur impregnation into single wood fibres is needed. Measurements of single fibre imaging were carried out at the Argonne National Laboratory’s Advanced Photon Source (APS) synchrotron facility. With a synchrotron beam using one micrometre scanning step, images of elemental mapping are acquired from CTMP samples diluted with non-sulphonated pulp under specified conditions. Since the measurements show significant differences between sulphonated and non-sulphonated fibres, and a significant peak concentration in the shell of the sulphonated fibres, the proposed technique is found to be feasible. The required spatial resolution of the µXRF imaging for an on-site CTMP sulphur homogeneity measurement setup is about 15 µm, and the homogeneity measured along the fibre shells is suggested to be used as the CTMP sulphonation measurement parameter.

Most of the earlier proposed ways to reduce energy con-sumption in high consistency refining requires operating at a small disc gap. However, a small gap is often associated with a severe fiber length reduction and often lead to unsta-ble refining and a small operational window. To address these issues, the idea of utilizing abrasive segments surfaces is here revisited. Abrasive refiner segments, consisting of abrasive surfaces in combinations with traditional bars and grooves or flat abrasive surfaces without any bars or grooves, were evaluated in both pilot and mill scale. From the trials it could be concluded, that particularly stable refin-ing was achieved with less power variations compared to when using standard segments, even when refining at very small disc gaps. The lw-mean fiber length of the pulps was not reduced or only slightly reduced, even when refining at very small disc gaps. Tensile index could be increased more efficiently or equally efficient as when using standard seg-ments. Improved energy efficiency could be achieved when combining the abrasive surface with high intensity treat-ment.

An underestimated problem in the rapidly growing CTMP industry is uneven sulphonation. Optimizing the unit operations before chip refining, chip washing, steaming, impregnation, and preheating improves efficiency, provides smoother fiber properties, and reduces the cost of certain properties in the final product. Impregnation is crucial to the CTMP quality, and a further improvement in its smoothness requires a careful study of the optimization of pulpwood chipping and the chipping process with reduction technology at sawmills. The CTMP system, however, is difficult to optimize due to the lack of rapid measurement methods for determining the smoothness of the impregnation at the fiber level. The ability to study how the processing system can be optimized requires a robust method of measuring the degree of sulphonation at the fiber level. It is possible to study CTMP's degree of sulphonation at the fiber level by measuring the distribution of elemental sulphur and counterions of the sulphonate groups, such as sodium or calcium. Thus, we are developing an XRF (x-ray fluorescence) technology based on scanning imaging and energy-resolved X-ray spectrum from a collimated X-ray source. The measurement technology is developed so that it can be used in pulp industry laboratories.

Optimizing the fiber property distribution could increase the pulp properties as well as the process efficiency of chemimechanical pulps (CMP/CTMP). This can only be achieved with a better understanding of how evenly distributed sulphonate concentrations are between the individual CTMP fibres. Given that the quality of wood chips varies with the chipping methods used in pulpwood processing and sawmill processing, as well as with the chip screening system, it is a challenge to develop an impregnation process that ensures even distribution of sodium sulphite (Na2SO3) in the liquid used to impregnate the chemimechanical pulp (CMP/CTMP). Therefore, the distribution of sulphonate groups within wood chips and individual fibers must be measured at the microscale level. On a micro level, the degree of unevenness, ie, the amount of fiber sulphonation and softening before defibration, cannot be determined due to the use of excessively robust or complex processing methods. By having it, we could better understand how sulphonation occurs before defibration, so we could improve impregnation. Developing a laboratory-scale miniaturized energy dispersive X-ray fluorescence (ED-XRF) method that measures sulfur distribution at the fiber level can enable us to study the influence of impregnation on improving processes.

This work presents a hypothesis of how steam flow effect the chip flow in the Double disc (DD) refiner and test it with a numerical simulation. DD refiners are often considered one of the most energy efficient refiner models. However, feeding chips into these machines is not as easy as feeding single disc refiners due to the rotating geometries. It is our belief that to increase energy efficiency in refining we need to increase also the production rates. The authors have previously noticed that in a standard DD rotor, steam flowed both in the same direction as the flow of woodchips and in the opposite direction. It is our hypothesis that backwards flowing steam in and in close proximity to the critical transition from the non-rotating geometry to the rotating geometry is negative for the material flow. To evaluate the hypothesis a new rotor was designed to eliminate the backwards flow. The authors have previously presented a two way coupled multiphase model with steam flow modeled with Computational Fluid Dynamics and wood chips modeled as groups of connected spherical particles with Discrete Element Method with a momentum exchange model. This model was utilized to model the flow of steam and woodchips in a DD under normal operational parameters, with the conventional rotor and with the new rotor. The throughput of wood chips was evaluated and normalized with regards to the chip flow to the refiner. The flow was considerable more stable in the new rotor, the throughput was close to 100 % for the observed time window, and the steam flow was more uniform. The results of the simulation supports the hypothesis. The next step in the research would be to test the new rotor in full scale operation.

The project goal was to efficiently separate spruce fibers with preserved fiber stiffness and a low content of unsepa-rated fibers (shive content max~1%) using minimal amounts of electricity. The project tested process variants based on the .HT-CTMP-process concept. Above room temperature, the mechanical properties of water saturated wood are pri-marily determined by the lignin, which softens with increas-ing temperature and water content. The lignin is not evenly distributed in the wood structure, and the pattern of fiber separation in wood will therefore to a large extent be de-pendent on the properties of the lignin. The relative softening temperature increases with increasing strain rate. In me-chanical defibration at temperatures below the lignin soften-ing temperature, a large proportion of the fibers will frac-ture across the fiber direction. At elevated temperatures, above the lignin softening interval, an increasing proportion of the fibers will be separated in the middle lamella along the fiber axis, i.e. with a higher fiber separation selectivity. Sulfonation of wood reduces the degree of crosslinking in lignin and increases the charge. The structural change makes the wood softer at a certain temperature. In a pilot trial Norway spruce (Picea abies (L.) Karst.) chips were re-fined at 130, 160 or 180 degrees C after impregnation with 25 or 50 kg/ton sodium sulfite in a pH range from 4,5 to 12. The temperature was the most important factor affecting the shives/energy relation. The sulfite charge and the pH-level also affect the results, but less than the temperature within the evaluated range. The results show there is a potential to produce pulps with a shive content of about 1% using less than 200 kWh/ton at 180 °C in the pre-heater and inlet of the refiner. Producing a high yield, fiber material with pre-served fiber dimensions and low content of shives using a few hundred kWh/ton opens for new opportunities both in paper and board production, but also in new applications where the bonding between fibers is achieved by other means than in traditional paper and paperboard products. 

The aim of this work was to study the effects of a mild dosage of sodium sulfite in chip impregnation at diffen temperatures during atmospheric preheating and during refining for production of TMP for printing papers usi high intensity double disk refining. Two trials were performed in the 800 bdt/day double disc line at I Braviken paper mill (Holmen Paper AB, Sweden) using Norway spruce chips. During the trials, chips w( impregnated in an Impressafiner where chips were preheated at 1.8 bar(g) for a few seconds and th compressed before impregnation. During impregnation, sodium sulfite was added to chips at pH 9 in dosages 0.6 or 1.2%. Reference pulps without addition of sulfite were also produced. In the first trial, the effect different temperatures and retention times (80°C for 6 minutes vs. 96°C for 9 minutes) in the atmosphe preheating bin following impregnation was evaluated both with and without the addition of 1.2% sodium sulf In the second trial, the effect of different refining temperatures (refiner house pressures of 4.6 or 6.4 bar(g), 1 or 167°C) was evaluated with different additions of sodium sulfite (0.0, 0.6 or 1,2%) during impregnation. The results from the two trials showed that the increase in refiner house pressure increased the tensile index pulps both with and without addition of sodium sulfite, when compared at certain SEC. However, the increase preheater bin temperature and retention time did not increase the tensile index of pulps but rather led to a sm reduction in tensile index when combined with an addition of 1.2% sodium sulfite. The two different methc used to increase the temperature in the system led to different effects in the disc gap at certain SEC. The disc j temperature was increased by both methods but disc gap was only reduced at certain SEC when the refini temperature was increased by increasing the refiner housing pressure. The difference in the effect on the disc j may hold the answer to the different effects seen in tensile index.