A Simplified Model of Moisture Transport in Hydrophilic Porous Media With Applications to Pharmaceutical Tablets

Moisture Transport Coefficients Determination on a Model Pharmaceutical Tablet

In this work, a novel methodology to determine moisture transport coefficients for MMC PH101 tablets is presented. Absolute permeability, moisture diffusion, moisture transfer, and water vapor permeability coefficients were estimated on compressed powder tablets produced with different compression pressures (20 MPa to 200 MPa with an interval of 20 MPa). The ASTM D6539 standard test was used to measure the absolute permeability. The moisture transfer coefficient was determined from measured absolute permeability. The moisture diffusion coefficient was obtained with the tablet average pore radius, which was determined with the water droplet penetration method. Descriptive and phenomenological models derived from the measurements were confronted with existing and adopted models, and a good agreement was found. The obtained models are of the function of the microstructural properties of the tablet (average pore radius and average porosity). The tablet average porosity was found to be the principal parameter that governs the behavior of the moisture transport coefficients. The findings of this study might be applicable to obtain a series of input parameters for modelling software, such as COMSOL Multiphysics®, to infer delamination, sticking, and failure propensity from the effect of moisture.

Understanding and Modeling the Liquid Uptake in Porous Compacted Powder Preparations

Porous solid materials commonly undergo coating processes during their manufacture, where liquids are put in contact with solids for different purposes. The study of liquid penetration in porous substrates is a process of high relevance in activities in several industries. In particular, powder detergents are subject to coating with surfactants that will boost their performance, although this may affect the flowability and even cause caking of the particulate material, which can be detrimental to consumer acceptance. Here we present a methodology to make compacted preparations of powders relevant to detergent making and evaluate the internal structure of such porous substrates by means of X-ray microcomputed tomography. Liquid penetration in the preparation and the total mass uptake of fluid were monitored by a gravimetric technique based on a modified Wilhelmy plate method consisting of consecutive cycles. Taking into account the geometry of the system, two models were proposed to describe the liquid uptake based on the process being driven by mass (model 1) or pressure (model 2) gradients. A comparison between both from statistical and physical points of view led to the conclusion that the latter was more appropriate for describing the process and retrieving values of the permeability of the solid between 0.03 × 10^-12 and 0.95 × 10^-12 m². Finally, with the parameters retrieved from model 2, the force balance observed throughout the experiment was simulated satisfactorily.