The influence of plasticizers in film coating formulations on the adhesive properties of an acrylic resin copolymer was determined using the butt adhesion technique. Hydrophilic and hydrophobic plasticizing agents were incorporated into aqueous dispersions of Eudragit(R) L 30 D-55 and coated onto hydrophilic and hydrophobic tablet compacts. Using data obtained from a Chatillon digital force gauge attached to a motorized test stand, force-deflection profiles, similar to stress-strain curves generated in the tensile testing of free films, were constructed and the force of adhesion, elongation at adhesive failure, and adhesive toughness were determined. Plasticizer concentration and plasticizer type were found to influence the adhesive properties-of the acrylic polymer. An increase in adhesive toughness was found when the concentration of triethyl citrate (TEC) in the coating formulation was increased from 20 to 30%, which was attributed to an increase in the elasticity of the film and a decrease in the internal stresses within the polymer. Films containing water soluble plasticizers were found to adhere more strongly to the tablet compacts than the water insoluble agents, due to more effective disruption of the intermolecular attractions between the polymer chains. Adhesion of the polymer to tablet compacts was found to be significantly influenced by the hydrophobicity of the tablet surface when the water soluble plasticizers were incorporated into the film coating, whereas no significant differences in the adhesive properties were found when the polymer was plasticized with water insoluble agents. Aging of the film-coated tablets resulted in a decrease in adhesive toughness, irrespective of the environmental storage condition. (C) 1997 Elsevier Science B.V.
