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...

Microporous 'functionalised' calcium carbonate (FCC) has potential for use as a carrier for the controlled release of 'actives', by permeation and diffusion. We have investigated the nature of the FCC surface and the mechanism of adsorption of two typical actives, namely the anti-inflammatory drug aspirin and the flavour compound vanillin, from chloroform and aqueous ethanolic solutions. There is indirect evidence from the quantitative perturbation of Tóth isotherms that their adsorption is hindered by a stagnant diffusion layer of water trapped in the microporosity of the FCC. To complement previous studies of the surface of FCC, it was also tested with the cationic probe benzyltrimethylammonium bromide and the anionic probe sodium 2-naphthalenesulphonate. Experimental procedures were validated by comparison with adsorption onto ground calcium carbonate and high surface area talc.

No abstract

This work addresses two continuing fallacies in the interpretation of percolation characteristics of porous solids. The first is that the first derivative (slope) of the intrusion characteristic of the non-wetting fluid or drainage characteristic of the wetting fluid corresponds to the void size distribution, and the second is that the sizes of all voids can be measured. The fallacies are illustrated with the aid of the PoreXpert ® inverse modelling package. A new void analysis method is then described, which is an add-on to the inverse modelling package and addresses the second fallacy. It is applied to three widely contrasting and challenging porous media. The first comprises two fine-grain graphites for use in the next-generation nuclear reactors. Their larger void sizes were measured by mercury intrusion, and the smallest by using a grand canonical Monte Carlo interpretation of surface area measurement down to nanometre scale. The second application is to the mercury intrusion of a series of mixtures of ground calcium carbonate with powdered microporous calcium carbonate known as functionalised calcium carbonate (FCC). The third is the water retention/drainage characteristic of a soil sample which undergoes naturally occurring hydrophilic/hydrophobic transitions. The first-derivative approximation is shown to be reasonable in the interpretation of the mercury intrusion porosimetry of the two graphites, which differ only at low mercury intrusion