Mid Sweden University

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.