Achieving Rapid Absorption and Extensive Liquid Uptake Capacity in Porous Structures by Decoupling Capillarity and Permeability: Nanoporous Modified Calcium Carbonate, 2006 TAPPI Advanced Coating Fundamentals Symposium

A special rapidly absorbing porous structure with a high absorption capacity is illustrated using a pigment designed to allow decoupling of the capillarity from the permeability of the packed medium. The new pigment morphology, based on natural ground calcium carbonate (gcc) with special surface structure modifications, is contrasted with standard gcc by using consolidated tablet blocks made from a suspension of the pigment and chosen mixtures thereof. The blocks are characterised after drying by mercury porosimetry, and the absorption dynamic of a selected liquid is studied. It is clear that using a self-assembly method of discrete pore structures provides a much faster absorption rate and a liquid capacity for up to 10 times more fluid than a conventional homogeneously distributed pore concept. These properties are advantageous for many types of liquid uptake requirements, including digital printing, for both oil-based and water-based inks. The combination of nano- surface features and pores (intraparticle voids) on an otherwise micro-particle provides a combination of two discrete pore networks which allow the driving force associated with the nano- features and the permeability of the bulk (interparticle voids) to be separated. In such unique discrete network systems, the mercury intrusion curve provides a separable analysis of permeability and capillarity in respect to the inflection point of the cumulative intrusion curve. The discrete decoupled properties each follow the absorption behaviour predicted by previous modelling using discrete pore and throat size distributions [1]. The absorption driving force is shown to be determined by the proportion of fine pores present up to a size equal to a Bosanquet inertially-defined optimum within the timescale of absorption. Combining the wetting force, from the capillarity-controlled fine pore structure, with the experimental resistance of the sample, consisting of the assembly of particles, it is possible to predict the trends in absorption dynamic of the sample using the pore and throat model Pore-Cor, a software product name of the Environmental and Fluid Modelling Group, University of Plymouth, Devon PL4 8AA, U.K (later referred to as the network model).