Diffusion and Tortuosity in Porous Functionalized Calcium Carbonate

Abstract

Calcium carbonate can be "functionalized" by use of etching agents such as phosphoric acid to create inter-and intraparticle porosity with a range of morphologies. Functionalized calcium carbonate has potential for use as a carrier for the delayed release of actives, such as drugs, plant protection chemicals, and food additives such as flavors. The drug or flavor is released slowly by permeation and diffusion. In order to measure the effective rate of diffusion within a range of morphologies, and hence gain insights into the optimum mode of functionalization, the diffusion of vanillin in ethanol is reported. Effective diffusion coefficients D′ were measured in a flow cell connected to a high performance liquid chromatograph (HPLC). Samples were also subjected to mercury intrusion porosimetry. The resulting percolation characteristics were inverse modeled using the PoreXpert package to generate representative void structures with estimated tortuosities. It is shown that the primary particle size of a sample was a better predictor of D′ calculated from the experimental diffusion curves, and also of the porosity-scaled tortuosity values, than the porosity or surface area. There was also a correlation between intraparticle tortuosity, scaled by porosity, and diffusion coefficient. The approach is validated by experimental evidence from this and related studies. ■ INTRODUCTION"Functionalized" calcium carbonate (FCC) is produced by etching calcium carbonate particles and reprecipitating modified surface structure with in situ or externally supplied CO 2 in the form of carbonic acid. To facilitate the in situ production of CO 2 , acids such as phosphoric acid can be used, resulting in a mixed mineral morphology. Variations in the etching process produce a range of morphologies with recrystallized surfaces, consisting of incorporated hydroxyapatite (HAP) in the case of phosphoric acid, which are dual porous (i.e., inter-and intraparticle porosity).FCCs are proving to have a wide range of novel applications. In particular, they are being proposed as an excipient and a pharmaceutical ingredient, 1,2 because the porous nature of calcium carbonate offers a good stability of the ingredients, slow biodegradability, is easily produced, tasteless, stable, and biocompatible. 3−6 The use of HAP as a drug carrier has also been discussed in the literature. 7−12 FCC offers benefits over HAP because the current commercial methods used to produce HAP give a low yield mixed with several phases, so that the product is expensive and suitable only for small-scale and timeconsuming production. 13 Adjustments to the FCC production process can be used to produce a wide range of different morphologies, and raise the possibility of tailoring the void structures of the particles to provide controlled release delivery vehicles for actives across many fields, including drugs and flavors. (The term "active" encompasses active ingredients, active constituents, and bulk actives.) However, such tailoring can only be fully optimized by a fundamental ch...

Microfluidic Lateral Flow Cytochrome P450 Assay on a Novel Printed Functionalized Calcium Carbonate‐Based Platform for Rapid Screening of Human Xenobiotic Metabolism

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Petrographic and Petrophysical Characterization of Detrital Reservoir Rocks for CO2 Geological Storage (Utrillas and Escucha Sandstones, Northern Spain)

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Improved Interpretation of Mercury Intrusion and Soil Water Retention Percolation Characteristics by Inverse Modelling and Void Cluster Analysis

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