Mechanical particle coating using ethylcellulose nanoparticle agglomerates for preparing controlled release fine particles; effect of coating temperature on coating performance.

This study describes the effect of coating temperature on the performance of mechanical particle coating using ethylcellulose, which was done to produce controlled-release particles (diameters less than 100 µm) with different release rates. First, theophylline crystals were spheronized using a mechanical powder processor, yielding theophylline spheres (used as core particles). Second, ethylcellulose aqueous dispersion was powdered by spray-freeze drying to prepare colloidal agglomerates (used as coating powder). Finally, the spheres and agglomerates were mechanically mixed at various temperatures using the processor to produce composite particles. The ethylcellulose agglomerates were pulverized during processing to coat the theophylline spheres effectively. When the coating temperature was higher than the glass transition temperature (Tg) of ethylcellulose, the amount of coated polymer increased significantly due to plastics deformation, causing thickening of the coated layer. The porosity of the coated layer decreased upon coalescence of coated polymer particles due to plastic deformation, which prevented the appearance of cracks in the film during curing. Therefore, controlled-release fine particles with various release rates can be produced effectively by mechanical particle coating at temperatures higher than the Tg of the polymer.