Mapping absorbency in cellulosic fibres with iron tracers

Understanding water absorbency in paper is challenging as fibre swelling and out-of-plane deformation occur simultaneously during liquid imbibition. Liquid absorption is commonly accessed by gravimetric tests, which provides limited information on the local spatial and temporal distribution of fluid in the substrate. In this work, we developed iron tracers to map liquid imbibition in paper by in situ precipitation of iron oxide nanoparticles during passage of the wetting front. The iron oxide tracers were found to be robustly attached to the cellulosic fibres. After liquid absorption tests, absorbency was investigated by mapping the distribution of iron in 3D using X-ray micro-computed tomography (mu CT) and in 2D using energy-dispersive X-ray spectroscopy. We demonstrate a difference in tracer distribution between the wetting front and the fully saturated region supporting that imbibition proceeds in two phases, i.e. liquid percolation through the cell wall initially prior to filling of the external pore spaces. Critically, we demonstrate that these iron tracers enhance image contrast and allow for new imaging modalities in mu CT for fibre networks.

Automated summary

Understanding water absorbency in paper is challenging due to the simultaneous occurrence of fibre swelling and out-of-plane deformation during liquid imbibition. In this study, we developed iron tracers to map liquid imbibition in paper by precipitating iron oxide nanoparticles during wetting. The iron tracers were found to be firmly attached to the cellulose fibers. Through X-ray micro-computed tomography (μCT) and energy-dispersive X-ray spectroscopy, we demonstrated the distribution of iron in 3D and 2D, and also showed that these iron tracers enhance image contrast and allow for new imaging modalities in μCT for fiber networks.