Abstract
We present a method which provides detailed insights to the dynamics of the water absorption process and water- paper interaction, based on transmittance measurements of ultrasonic beams. We found that the water absorption process of an uncoated paper- sheet comprises two consecutive time regimes. The underlying mechanism that governs the regimes’ shift is the combination of fibre surface modification by water and the recreation of the fibres lumen after wetting. In the first regime, water advances along the dry pore surface, which is hydro neutral, and the water forms a solid column inside the capillary (pore), while in the second regime, moving along the primed (wetted) surface of the capillary is a more favourable path as the surface becomes hydrophilic when wetted. Consequently, the water may not necessarily ¿ ll the entire capillary when the capillary expands in volume due to hydro- expansion and hence forms a hollow water column. We propose a model that enables us to determine/predict the depth of water absorption by the dry pore structure of the paper which is often the case for ink- paper interaction during printing. The results of our studies suggest that the depth of water penetration along the dry pore surfaces can very well be described by the Bosanquet model.
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