3. Sulfur homogeneity mapping in 2D and 3D can improve packaging paper strength

Sodium sulfite is commonly used for impregnating wood chips prior to refining when producing high-yield pulps such as CTMP. The impregnation process should ideally result in evenly sulfonated lignin, i.e. similar concentrations of sulfite (SO3 ^2-) ions in all parts of each wood chip. Sulfonated lignin is known to swell the fiber wall, which is beneficial for developing higher joint-strength between fibers. In reality, even sulfonation is not easy to achieve considering variations in wood chip size, density, quality, etc. Being able to trace where the sulfite ions end up in the wood or fiber structure can therefore be a key to both process and product development in the future. Synchrotron measurements can provide an understanding of the sulfur distribution both inside single wood fibers and on a larger scale between wood fibers. There is little knowledge of wood fiber nanostructures in 3 dimensions, although some interesting research has been conducted recently [1]. We have compared these measurements with 2D synchrotron XRF mappings [2]. The 3D material mapping provide insight on a sub-fiber level, but the 2D mapping technique might be preferable when studying sulfur distributions due to the highly uneven sulfur content observed. We can probably learn more about the development of fiber-joint-strength and strength uniformity in products by characterizing the distribution of sulfur on sub-fiber level. This paper discusses feasible future measurement strategies.

[1] Fernando, D., et.al, Sci Rep 13, 2350 (2023). DOI: 101038/s41598-023-29113-x

[2] Norlin, B., et.al, JINST 18 C01012. DOI: 10.1088/1748-0221/18/01/C01012