The Compression of Spheres Coated with an Aqueous Ethylcellulose Dispersion

Tablets were compressed from commercial samples of Sugar Spheres NF, Sucrose NF, Corn Starch NF, as well as ground spheres and a physical mixture of ground sucrose plus cornstarch. Additional tablets were compressed from spheres that had been coated with a water-soluble cellulosic polymer solution followed by an aqueous ethylcellulose dispersion. Tableting parameters measured “in-die” included work of compression, peak offset time, tablet density, and Young's modulus. Following ejection, tensile strength was determined under diametrical loading. Dissolution of a marker contained in the water-soluble layer was determined for both compressed and uncompressed spheres. Porosities at peak pressure and peak offset times or tensile strength as functions of peak pressure did not differ between tablets compressed from pristine spheres or from ground spheres. Tablets compressed from spheres had higher values for porosity, tensile strength, and peak offset time than those compressed from sucrose or the sucrose:starch mixture. Values for work of compression were higher for tablets compressed from pristine spheres or from starch. This was attributed to the work required for particle deformation and for breaking of the spheres. The greatest elastic recovery during decompression was observed for tablets compressed from pristine spheres or starch. More brittle behavior was observed for tablets compressed from sucrose or the sucrose:starch mixture. Tablets compressed from ground spheres were more brittle than those compressed from the pristine spheres, indicating an effect due to grinding. Most mechanical properties of tablets compressed from the coated spheres were comparable to those of tablets compressed from uncoated spheres. An exception was diametric strain for tablets compressed from spheres coated with the aqueous ethylcellulose dispersion. These values increased since the plasticized ethylcellulose allowed greater distortion of the tablet before failure occurred. The dye marker was released more rapidly from tablets compressed from spheres coated with the aqueous ethylcellulose dispersion than from comparable uncompressed spheres. At both the 5% and 10% coating levels, spheres coated with the aqueous ethylcellulose dispersion fused into nondisintegrating matrices during compression. Little difference in release rates was seen between the two tablets.