Mid Sweden University

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.

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.

Minimizing the fiber property distribution would have the potential to improve the pulp properties and the process efficiency of chemimechanical pulp. To achieve this, it is essential to improve the level of knowledge of how evenly distributed the sulfonate concentration is between the individual chemimechanical pulp fibers. Due to the variation in quality between pulpwood and sawmill chips, as well as the on-chip screening method, it is difficult to develop an impregnation system that ensures the even distribution of sodium sulfite (Na2SO3) impregnation liquid. It is, therefore, crucial to measure the distribution of sulfonate groups within wood chips and fibers on a microscale. Typically, the degree of unevenness, i.e., the amount of fiber sulfonation and softening prior to defibration, is unknown on a microlevel due to excessively robust or complex processing methods. The degree of sulfonation at the fiber level can be determined by measuring the distribution of elemental sulfur and counterions of sulfonate groups, such as sodium or calcium. A miniaturized energy-dispersive X-ray fluorescence (ED-XRF) method has been developed to address this issue, enabling the analysis of sulfur distributions. It is effective enough to be applied to industrial laboratories for further development, i.e., improved image resolution and measurement time. 

The manufacturing of CTMP has a significant role in producing sustainable packaging products. But the strategy to improve the impregnation technology is still challenging due to the uneven distribution of Na2SO3. Our aim was to investigate the oxidation states of Sulphonate present in our handmade paper samples which consist of different CTMP percentages. Therefore, XANES measurements were done to investigate the oxidation states and XRF measurements were done to see the presence of other elements. XRF mapping was also done to know the distribution of Na in the samples.

A large amount of contaminated cellulose and wood fibers were emitted directly onto the seabed by the pulp and paper industry before the year of 1970. This fiber-rich sediment contains concentrations of hazardous substances that cause environmental problems. Mercury (Hg) in the fiber sediment is a worldwide threat because it can bioaccumulate in the aquatic ecosystem and eventually affect human health. X-ray fluorescence (XRF) analysis is anelemental analysis method for earth materials, which is rapid and requires minimal sample preparation. However, for in-situ XRF analyses, constraints in the measurement conditions will strongly affect the measurement sensitivity and accuracy, such as the scattered background and the water content surrounding the sample. In this work, we showed that applying an X-ray beam filter foil, optimized by using the material absorption edge, can improve the sensitivity of the XRF spectrometer system for Hg determination. Furthermore, the influence of water content in XRF measurement for Hg contamination analysis was investigated. The attenuation coefficient in water was determined by simulation of water layer with varying thickness using a Monte Carlo simulation code. The measured intensity for Hg was decreased exponentially asthe water thickness increase, as expected. We propose a method to correct the attenuation in water with XRF analysis and we expect that these findings can contribute to an accurate in-situ Hg detection experiment.

To improve the competitive advantages of pulp fibre based materials such as tissue and packaging products over the fossil-based products, it is of key importance to improve the knowledge of the selectivity of the cooking process. There is also demand to expand the fundamental scientific understanding of pulp and paper manufacturing systems because of growing demand for replacing plastics. However, it is challenged to improve the selectivity of the cooking process by optimizing unit operation such as impregnation, cooking and refining. For pulp production based on chips regardless of chemical (kraft or sulphite) or high-yield (chemimechanical or semi-chemical pulp) pulping process, the efficiency of the impregnation is always crucial. To improve impregnation uniformity, we need to study how even distribution of lignin releases down to fibre level via easily impregnated wood chips. It can be achieved, using classic measures such as; equalized hydroxide ion concentration, increased initial sulphide ion concentration, low sodium ion concentration and low boiling temperature combined with the oxidative and reductive environment to understand how the chemicals quickly enter and distribute in the chips. However, we have studied the uniformity of impregnation at fibre level by the possibility of accurately measuring S and Na content by collimating the X-ray beam into a ~200 µm spot in diameter using energy-dispersive X-ray fluorescence (ED-XRF) spectrometry. In addition, we have also studied improved impregnation by selective cooking systems for sulphate pulp in oxidative (polysulfide) and reductive (sodium borohydride, NaBH4) environments. Our aim is to develop standard measurement methods to improve the smoothness of fibre properties for tissue and packaging products to reach the sustainable development goal (SDG) stated by the UN at target 9.5 “Enhance research and upgrade industrial technologies”.

Discharge of waste water from pulp and paper industries has led to environmental impact in the formation of sediment layers, so called fiber banks, on the coast of Västernorrland and Norrbotten counties in Sweden. These fiber banks are thick underwater deposits which are highly contaminated with some toxic metals such as Al, Cr, Fe, Cu, Zn, As, Pb, Hg. These metals can lead to several consequences for the environment, thus ultimately having harmful effects on living organisms. Our purpose is to study several of these toxic metals and analyze the concentration level by using portable X-ray Fluorescence (pXRF) spectrometry for rapid sample characterization of wet samples. Field analyses are highly affected by moisture and it is difficult to obtain measurement accuracy. Therefore, moisture tests were performed by air drying samples at room temperature from 0 to 24 h. Some of the samples were oven dried for 48 h at 950 C, dried, grinded and turned into pellets and performed laboratory measurements to compare results with field measurements. Our aim is to provide an improved state of facts for decision makers to prevent and reduce marine pollution and to protect and restore ecosystems in order to avoid significant adverse impacts, and take actions for their restoration in order to achieve healthy and productive oceans. A future outcome is to reach the sustainable development goal (SDG) stated by the UN at target 14.1 and 14.2 “Life below water”.