Mid Sweden University

Multiple image radiography (MIR) is an X-ray phase-contrast technique that enhances soft-tissuevisibility by rejecting Compton scatter and capturing absorption, refraction, and ultra-smallangle x-ray scattering (USAXS) signals. Conventional MIR workflows depend on normalizationbetween object and reference datasets and precise angular alignment, making them sensitive todrift and prone to artifacts such as banding. We present an improved analysis framework, MIR2,which eliminates normalization and alignment by independently analyzing object and referencedata and applying angular calibration based on the dynamical theory of diffraction. Like MIR, itemploys pixel-wise Gaussian fitting of angular intensity profiles, but the MIR2 pipeline is simpler,less error-prone, and more robust against alignment-related artifacts. Importantly, artifact suppression is achieved intrinsically, without relying on additional correction algorithms. MIR2 wasimplemented in Python and validated at the BMIT beamline (Canadian Light Source, 33.3 keV,Si(220) double-crystal monochromator) using both test objects (PMMA step wedge, layeredpaper) and in vivo imaging of a live anesthetized mouse lung. Across both studies, MIR2 producedmore stable and artifact-reduced images than MIR. The method simplifies analysis workflows andsupports streamlined application of MIR in biomedical and material imaging under dose-limitedconditions. 

Unlike fossil-based plastics, wood-based packaging materials can be produced in an eco-friendly manner using wood chip residuals from sawmills and pulpwood. To produce high-yield pulp like chemithermomechanical pulps (CTMPs) for paperboard and liquid packaging, it’s crucial to reduce the electric energy consumption during fiber separation. The ultimate objective is to revolutionize paperboard production by achieving a middle-layer CTMP process that consumes less than 200 kWh/t, significantly improving from the current 500-600 kWh/t energy demand.

Optimizing the CTMP impregnation process of sodium sulfite (Na2SO3) in wood chips is crucial for achieving uniform softening, ideally at the fiber level. The properties of the fibers are significantly affected by the content of lignin sulfonates within the walls of the fiber and the middle lamellae. In this study, we employed in-house developed X-ray fluorescence (XRF) techniques, validated by beamline measurements, to map the distribution of sulfonated lignin within fibers. It also seemed possible to enhance the surface area of lignin-rich pulp fibers while losing minimal bulk by refining them with well-optimized low consistency (LC) refining. We aim to achieve a highly efficient separation of coniferous wood fibers by co-optimizing the sulfonation and the temperature in the pre-heater and chip-refiner. Additionally, we explored how lignin's softening behavior and potential crosslinking influence subsequent unit operations, including pressing, peroxide bleaching, and drying, following the defibration process. In defibration during chip refining, the maximum softening of wood fibers is preferred to maximize fiber preservation and minimize energy consumption. However, optimizing the stiffness of finished pulp fibers is preferable to reduce bulk loss during paperboard production. It can strive to optimize processes to develop stronger, lighter, and more sustainable composite packaging materials. Reducing environmental impact and electric energy can help create a more sustainable future.

The transition toward renewable, fiber-based packaging requires an improved understandingof chemical modifications in high-yield pulps such as chemithermomechanical pulp (CTMP). Sulfonationuniformity is essential for the energy-efficient production of high-strength CTMP pulp. However,laboratory methods only measure total sulfur and cannot illustrate its distribution at the fiber level,which can be visualized using μ-XRF. In this work, we present a laboratory μ-XRF system developedat Mid Sweden University and assess its capability to detect light elements in CTMP paper handsheets.A 32 × 32 point grid scan (1.6 × 1.6mm2 field of view, 50 μm step, 300 s/point) successfully resolvedsulfur Kα (2.31 keV) and calcium Kα (3.69 keV) fluorescence without helium flushing. Comparativemeasurements at the Elettra synchrotron confirmed consistency of sulfur peak position and spatialdistribution, with higher spectral resolution and signal-to-noise ratio. Histogram analysis usingWassersteindistance metrics demonstrated close agreement between datasets despite differing acquisitionconditions. These results demonstrate that laboratory XRF can reproducibly detect and map sulfur inCTMP fibers under ambient conditions, providing a practical tool to complement synchrotron studiesand supporting the development of energy-efficient, fiber-based packaging materials.

High-yield pulping, such as Chemithermomechanical Pulp (CTMP), is critical in developing sustainable fiber-based packaging materials. Achieving uniform lignin sulfonation during the impregnation process is crucial for maintaining fiber stiffness, maximizing bulk, and optimizing energy efficiency. However, current impregnation techniques often result in uneven distribution of sulfite (-SO₃⁻), leading to variations in fiber properties and increased energy consumption during refining. The ultimate goal is to achieve a middle-layer CTMP process that consumes less than 200 kWh/t of energy, significantly reducing the current energy consumption of 500-600 kWh/t [1].

To improve process efficiency and create stronger, lightweight paperboards, gaining a deeper understanding of sulfonation at the microscale is essential. This study uses Synchrotron-based X-ray Fluorescence (XRF) techniques to analyze sulfur distribution in CTMP fibers with high spatial resolution (10–15 µm). By mapping sulfonate content at the fiber level, we aim to enhance impregnation strategies and ensure a more homogeneous sulfonation process. Our research has been validated at beamline facilities such as APS (USA) [2], Elettra (Italy), and Diamond (Oxford, UK), providing new insights into how sulfonate ions (-SO₃⁻) integrate into lignin structures, which directly influences fiber softening and defibration efficiency.

We propose a refined impregnation approach that minimizes sulfite dosage while maintaining optimal fiber properties, ultimately reducing energy consumption in refining. By incorporating Synchrotron XRF analysis, we can assess the uniformity of sulfonation in wood chips in real-time, improving fiber separation and enhancing material performance. 

These advancements support the development of high-strength, lightweight packaging materials while promoting a more energy-efficient and eco-friendly pulping process. This study demonstrates the potential of advanced X-ray characterization techniques in optimizing the processing of fiber-based materials, bridging the gap between fundamental research and industrial applications. The findings contribute to the ongoing transition from fossil-based to sustainable, bio-based packaging solutions, aligning with global environmental goals.

REFERENCES 

[1]                Persson, E., Norgren, S., Engstrand, P., Johansson, M., & Edlund, H. [2019]: Spruce HT-CTMP revisited – A high yield, energy efficient pulp for future products,11 FMPRS Conference, Norrköping, Sweden.

[2]                Norlin, B., An, S., Granfeldt, T., Krapohl, D., Lai, B., Rahman, H., Zeeshan, F., & Engstrand, P. [2023]: Visualization of sulfur on single fiber level for pulping industry, Journal of Instrumentation, vol. 18: 01.

Global environmental campaigns emphasize the need to understand better how renewable raw materials can be utilized effectively. There is a notable trend towards replacing fossil-based materials with fiber-based alternatives across various packaging applications. Solid and lightweight composite packaging structures can be produced in an environmentally friendly and energy-efficient way. In recent years, wood fibers have gained popularity as a packaging material. High-yield pulps, such as CTMP (Chemithermomechanical pulp), which achieves a 95% yield, are increasingly used in packaging. Worldwide, 5-10 Mt/y of CTMP are produced from softwood and hardwood chips for paperboard manufacturing. During tailor-making CTMP, wood chips are impregnated with aqueous sodium sulfite (Na2SO3) to sulfonate the wood's lignin. This sulfonation (-SO3-) softens the wood chips, enabling more selective defibration into the pulp. As a result, the pulp properties, including the bulk and strength characteristics of the final packaging, are enhanced. Several factors influence the quality of wood chips, including the chipping method used for pulpwood, sawmill chipping practices, and the chip screening system. Developing an impregnation technology that ensures an even distribution of sodium sulfite (Na2SO3) can be challenging. It is essential to measure the distribution of sulfonate groups in individual fibers and wood chips at a micro-scale; however, existing processing methods often need to be more robust and complex, making this difficult. If better measurement techniques were available, we could understand how sulfonation operates before defibration, improving the impregnation process. Sulfur impregnation can be studied using spatial and spectral resolutions to investigate the degree of sulfonation at the microscale. Therefore, we propose creating a laboratory-scale miniaturized X-ray fluorescence (XRF) scanner to measure sulfur distribution in wood chips on-site. We aim to minimize differences in sulfonate content between fibers, allowing us to reduce the dosage of sulfite (SO32-) needed for fiber separation and, consequently, lower the overall electrical energy used in chip refining. Research facilities, including APS beamline in the United States, Elettra beamlines in Italy, and Diamond light source in Oxford, United Kingdom, have validated X-ray fluorescence (XRF) techniques developed in-house. These techniques enable the measurement of sulfonated lignin distribution, providing a more detailed understanding of distribution within and between individual fibers. To ensure the homogeneity of sulfur distribution required for CTMP, we typically need a spatial resolution of 10-15 μm. We have developed our methodology based on this spatial resolution, which informs us about homogeneity. Our research has shown that sulfonation at the fiber surface is the most effective process parameter. Therefore, it is crucial to understand how sulfonate ions (-SO3-) are integrated into the structure of lignin in wood fibers, as this knowledge could be vital for developing future products and processes of high-strength packaging.

Uniform sulfonation using Na₂SO₃ is critical in chemithermomechanical pulp (CTMP) productionfor ensuring efficient processing and high product quality. However, achieving even distributionof sulfonate groups (–SO₃⁻) across wood fibers is challenging due to variability in wood chip size.To investigate sulfur(S) at the microscale, we developed a cost-effective X-ray fluorescence (XRF)imaging system utilizing polycapillary focusing optics. This setup enables high-resolution elementalmapping, achieving a spot size of ˜15 μm and spatial resolution of 15–20 μm, as confirmed witha chromium test pattern. A 3D-printed sealed chamber enables helium flushing, significantly enhancingthe detection of low atomic number elements, particularly sodium (Na). XRF imaging ofCTMP sheets reveals the distribution contours of S along individual wood fibers. This method offersa practical tool for evaluating and optimizing sulfonation uniformity during fiber impregnation inindustrial CTMP processes.

Unlike fossil-based plastics, wood-based packaging materials can be produced eco-friendly by using residuals from wooden houses, such as wood chips from sawmills and pulpwood from well-managed growing forests in northern Europe. The use of these woodchips to produce chemithermomechanical pulps (CTMP) paperboard and liquid packaging requires a reduction in electric energy consumption during fiber separation, since the content of lignin sulfonate within fiber walls and mid-lamellae affects fiber properties. As a result, it is imperative to optimize the impregnation methodology of sodium sulfite in wood chips to achieve evenly distributed softening properties preferably at the level of individual fibers. The long-term goal is to understand how to produce paperboard middle layer CTMP at less than 200 kWh/t rather than the present 500-600 kWh/t [1]. By using XRF (X-ray Fluorescence) techniques developed in-house and validated by beamline measurements, we have been able to determine how the sulfonated lignin is distributed both on individual fibers and between the fibers [2]. It also seems possible to enhance the surface area of lignin-rich pulp fibers while losing minimal bulk by refining them by means of well optimized low consistency refining. We have aimed to achieve extremely efficient separation of coniferous wood fibers by co-optimizing the sulfonation and the temperature in pre-heater and chip-refiner. Furthermore, we have studied the influence of lignin softening behavior and possible crosslinking after defibration i.e., in following unit operations as pressing, peroxide bleaching and drying. In defibration during chip refining, the maximum softening of wood fibers is preferred to maximize fiber preservation and minimize energy consumption. However, it is preferable to maximize the stiffness of finished pulp fibers to reduce bulk loss during paperboard production. We believe that strong and lightweight composite packaging structures can be manufactured in an environmentally friendly and low-energy-consuming manner.

REFERENCES 

[1]               Persson, E., Norgren, S., Engstrand, P., Johansson, M., & Edlund, H. [2019]: Spruce HT-CTMP revisited – A high yield, energy efficient pulp for future products,11 FMPRS Conference, Norrköping, Sweden.

[2]               Norlin, B., An, S., Granfeldt, T., Krapohl, D., Lai, B., Rahman, H., Zeeshan, F., & Engstrand, P. [2023]: Visualization of sulfur on single fiber level for pulping industry, Journal of Instrumentation, vol. 18: 01.

A strong and lightweight composite packaging structure can be produced in an environmentally friendly and energy-efficient manner. It is necessary to develop methods for producing lighter, higher-quality paperboard with better strength and stiffness while retaining the same brightness. Energy efficiency is important when producing chemthermomechanical pulps (CTMP). The CTMP for paperboard should be designed to retain maximum bulk, therefor it is imperative to avoid unnecessary reductions in softening temperature when improving fiber stiffness. Optimizing the impregnation methodology of sodium sulfite (Na2SO3) in wood chips requires equally distributing softening properties across fibers. Wood fiber softening determines the efficiency of fiber separation during chip refining. Sulfonated lignin in the fiber walls and mid-lamellae determines the softening properties of these structures, as well as promoting stronger joint connections between fibers. However, evenly distributed sulfonation is difficult to achieve due to wood chips' differences in size, density, and quality. To determine how sulfonated lignin is distributed within and between individual fibers, we have employed XRF (X-ray fluorescence) techniques developed in-house and validated by beamline. Using our synchrotron measurements at APS, USA, we can gain a better understanding of sulfur distribution within and between wood fibers. As shown in the CTMP samples on images, there is an uneven distribution of sulfur between fibers. Typically, CTMP sulfur homogeneity inspections require spatial resolutions of 10µm-15µm. The methodology is developed based on the resolution containing homogeneity information. We believe that even the sulfonation along the fiber shell is the most favorable process parameter to extract. Identifying where the sulfonate ions (-SO3-) end up in the lignin of the wood fiber structure may therefore be an important element of future process and product development. We can, however, learn more about the development of fiber-joint strength and strength uniformity in products by characterizing sulfur distribution at the sub fiber level.

An X-ray based quality inspection method for paperboard was implemented and tested as a fast and non-destructive alternative to the burnout method. An argument against X-ray imaging for inspection of paper and paperboard has been that X-ray absorption is low in paper. To overcome this limitation, we used phase-contrast X-ray imaging (PCXI), which gives higher contrast than conventional attenuation-based imaging for low-absorbing materials such as paper. The suggested PCXI method was applied to previously prepared and quality rated samples using the burnout method. A strong similarity between the burnout images and the PCXI images was observed. In conclusion, further development of the phase-contrast X-ray method would provide an interesting option for replacing or complementing the standard burnout method.