Mid Sweden University

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.