Characteristics of pharmaceutical grade phyllosilicate powders

The purpose of this paper was to evaluate the possible use of three types of pharmaceutical grades of phyllosilicates as pharmaceutical excipients. Seven samples (two smectites, three palygorskites, and two sepiolites) were studied. A complete mineralogical and chemical characterization of each material was made and powder texture was established by image analysis of scanning electron micrographs. Powder flow properties were then determined and the influence of textural characteristics on powder rheology and particle packing was assessed. Mineral contents were adequate for the sepiolites (> 90% of main mineral) and smectites (78 and 95%), but should be improved on the palygorskite samples (around 50% of main mineral in two of the studied samples). According to the textural characterization, the samples presented almost equal size distributions, but exhibited two different morphologies (i.e., laminar for smectites and fibrous for sepiolites and palygorskites). Both sepiolites possessed high flowability, whereas this factor varied from medium to low in the other materials. The compressibility of smectites was adequate, whereas that of palygorskites was high and that of the sepiolites was low. All of the samples studied would be useful as solid dosage form excipients (some samples would require improvement of their flow properties or treatment to reduce the amount of mineral impurities).