The influence of carbohydrate nature and drying methods on the compaction properties and pore structure of new methyl methacrylate copolymers

Methyl methacrylate (MMA) copolymers have recently been proposed as an alternative in controlled-release matrix tablets. The aims of this study were to assess the potential value of these copolymers as direct compression excipients and to investigate relationships between the physical and structural properties of the polymers and the compression behaviour of the powders and the microstructural properties of the tablets. Copolymers were synthesised by free radical copolymerisation of MMA with starch or cellulose derivatives and were alternatively dried by oven or freeze-drying techniques. Thus, the present study focuses on the influence of the carbohydrate nature and the drying process on the mechanical and compaction properties of MMA copolymers. Particle size, shape and surface texture of the copolymers have been studied in detail and Heckel treatment has been chosen for discriminating the densification behaviour of powdered materials. Total pore volume and pore size distribution of MMA copolymer tablets were investigated with mercury porosimetry. Oven drying gave less porous particles with more homogenous surfaces than those freeze-dried. Differences in morphology between the MMA copolymers were demonstrated by increasing apparent particle densities, smaller flow rates and higher binding capacities for freeze-dried products. The porousness and mean pore radius of the tablets obtained from freeze-dried copolymers were higher than those of tablets obtained from oven-dried ones. (C) 2002 Elsevier Science B.V. All rights reserved.