Modelling and Experimental Characterization of Unsaturated Flow in Absorbent and Swelling Porous Media: Material Characterization

A comprehensive experimental protocol is presented for the characterization of physico-chemical and morphological properties of absorbent hygiene products (AHPs), composite materials, mainly made of super absorbent polymer (SAP) granules blended with cellulose fibres (fluff). The protocol is based on a combination of experimental methods for the characterization of the material properties varying SAP/fluff ratio (SFR): absorption rate, porosity, hydraulic conductivity, retention model and swelling. Major findings were that: (1) liquid absorption rate by the SAP particles was nonlinear; (2) the hydraulic conductivity could be expressed as a function of the porosity of the composite medium for any sample and liquid uptake; and (3) the retention model showed moderate variability with SFR, in the range investigated. Experimental results have been used to determine the constitutive equations for the multiphase flow model developed in the literature (Diersch et al. in Theory Transp Porous Media 83:437-464, 2010. https://doi.org/10.1007/s11242-009-9454-6) for the prediction of the performance of AHPs during cycles of imbibition and drainage (Chem Eng Sci 224:115765, 2020. https://doi.org/10.1016/j.ces.2020.115765).