Characteristics of pharmaceutical grade phyllosilicate compacts.

The purpose of this paper was to determine the possible employment of three groups of phyllosilicates (two smectites, three palygorskites, and two sepiolites) as direct-compression tablet excipients. Compact lots of each material were obtained after application of three different compression loads and the elastic recoveries and tensile strengths of each lot were then determined. The results showed that, in comparison with laminar minerals (smectite samples), fibrous minerals (palygorskites and sepiolites) were found to have lower elastic recovery, regardless of the compression load. Almost all elastic recovery happened immediately after the ejection of the compacts. Then, and at least during the next 24 hr, smectite compacts maintained their dimensions without any significant variation, whereas fibrous compacts tended to continue increasing slightly their dimensions. On the other hand, compacts made with laminar particles had higher mechanical strength than those made with fibrous particles, except for one sepiolite sample in which the strength was similar. Both particle morphologies and the presence or absence of hydration water molecules were taken into account in order to explain these differences. According to the compact properties measured, at least two of the noncommercial samples (smectite from Gádor, Spain, and sepiolite from Vicálvaro, Spain) would be useful as direct-compression tablet excipients.