Mid Sweden University

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.