Mechanical and adhesive properties of cellulosic film coats containing polymeric additives

The effects of some polymeric additives, i.e. corn starch (CS) and magnesium stearate (MS), on mechanical properties (tensile strength, modulus of elasticity, and elongation at break) and adhesive toughness of hydroxypropyl methylcellulose (HPMC) and ethylcellulose (EC) film coats were investigated. The free and in situ films containing 10 and 20% additives by weight of polymer were prepared by spray method. The mechanical properties of both HPMC and EC free films decreased as the concentration of additives was increased because of the lower stiffening effect brought about by hydrodynamic or reinforcing effect. However, adhesive toughness of in situ films was found to increase for HPMC whereas that of EC films decreased with the increasing concentration of polymeric additives. Such contradictory results between these two film forming polymers may be attributed to the net result of the opposite effects between interference of film-tablet interfacial bonds and the reduction of mechanical properties. The former seemed to be preferential in the case of EC films, while the latter predominated for HPMC films. Such conclusions were supported by the FTIR results, in which the polymer-additive interaction was found for EC. Increase in concentration of polymeric additives resulted in the decrease in mechanical properties of free films whereas the adhesive toughness of in situ films may be influenced by either the interference of film-tablet interfacial bonds or the significant reduction of mechanical properties.