Matrix tablets of carrageenans. I. A compaction study.

Carrageenans can be used as excipients for controlled-release tablets. The aim of this study was to determine their compaction and consolidation behavior to prove their usefulness for tableting. The Carr indices of the three carrangeenans, two kappa-carrageenans(Gelcarin GP-812 NF and GP-911 NF) and one tau-carrageenan (Gelcarin GP-379 NF), indicate that the materials are free flowing. They are polymers in the rubbery state. Their glass transition-temperature is about 0 degree C analyzed by differential scanning calorimetry (DSC). The powders were analyzed regarding their compression behavior using an eccentric tableting machine. From data obtained during one compaction cycle, porosity-pressure and pressure-time plots were made. Compaction behavior is evaluated by fitting the pressure-time function to the pressure-time plot and by fitting the Heckel function to the porosity-pressure plot. The polymers show "viscoelastic" tableting behavior. Several additional tableting parameters were analyzed for strengthening the results obtained, namely, maximum work, maximum power, and the time between maximum upper punch force and maximum displacement of the upper punch. The crushing strength of the tablets is high; therefore, the carrageenans are able to form strong compacts. However, they remain in the rubbery state, as shown by thermomechanical analysis. In addition, elastic recovery is regarded at several times after ejection. Finally, after 10 days, it is about 30% as determined from the minimum of tablet height during the compression cycle. These results indicate that the carrageenans are suitable tableting excipients for controlled-release tablets. They show good compactibility and good consolidation behavior. Strong compacts with a high elastic recovery are formed; this means that the materials are able to embed drugs softly. Only a little stress and strain remains in the tablet. All three carrageenans show similar tableting behavior, and a flexible dosage form design is possible.