Pakistan Journal of Pharmaceutical Sciences Vol. 18, No.3, July 2005, pp.25-38 THE INFLUENCE OF DIFFERENT PLASTICIZERS ON SOME PHYSICAL AND MECHANICAL PROPERTIES OF HYDROXYPROPYL METHYLCELLULOSE FREE FILMS HAJI BAIE SARINGAT, KHALID IBRAHIM ALFADOL AND GUL MAJID KHAN* School of Pharmaceutical Science, Universiti Sains Malaysia, Pulau Pinang, Malaysia *Department of Pharmaceutics, Faculty of Pharmacy, Gomal University, Dera Ismail Khan, NWFP, Pakistan Coating has been widely used in pharmaceutical manufacture either as non-functional or a functional entity. The objectives of the present study were to investigate the effect of plasticizers such as PEG400, PEG1000 and triacetin on mechanical properties, glass transition temperature and water vapor transmission of free films prepared from HPMC and/or HPMC:PVA blends, to develop suitable coating system for tablets, and to determine the release profiles of the coated tablets. The tensile strength of plasticized HPMC films was generally lower than that of control HPMC film and could be attributed to increased crystallinity and segmental chain mobility of HPMC. This effect increased as the concentration of plasticizer increased. Generally the addition of both grades of polyethylene glycol (PEG400 & PEG1000) increased the moisture permeability of HPMC films but the films containing triacetin provided a more rigid barrier to moisture compared to unplasticized HPMC films. The dissolution profiles of paracetamol tablets coated with 7% w/v HPMC coating-solutions containing PEG400, PEG1000 and triacetin, and those containing PEG400 & PVA together showed that HPMC had weak water resistance. The presence of PEG400 and 1000 in HPMC films further weakened its resistance to solubility while the presence of triacetin caused a little increase in HPMC water resistance. From the results it was concluded that HPMC at 7%w/w concentration was suitable for film-coating intended for non-functional coating. Presence of the PEG 400, PEG1000 and triacetin as well as the presence of PVA and PEG400 together improved the coating properties of HPMC films and made it more suitable as a non-functional coating material. Keywords: Plasticizers, hydroxypropyl, methylcellulose, tablet coating. INTRODUCTION Coating has been widely used in pharmaceutical manufacture either as non-functional or a functional entity. The non-functional coating is utilized to improve appearance or mask undesirable taste/odor and to provide additional protection whereas the functional coating is aimed at modifying release pattern of the drug. Both natural and synthetic materials have been used for coating. Sugar and film coating are the two most common types used in pharmaceutical manufacturing. The tablet dosage form is the most common dosage form to be coated. During a film coating process, we must convert a liquid into an essentially dry solid. Dry films are those that resist blocking when two coated surfaces (e.g. two coated tablets) are brought into contact for two seconds under a pressure of 20psi. Such block resistance occurs when the viscosity of the coating exceeds 107 Pa.s (Burrell, 1962). A viscosity conducive to such blocking occurs when a coating is exposed to temperatures that exceed its glass transition temperature (T g ) by approximately 20˚C (William et al., 1955). If the temperature of a product (during the coating process or storage of the coated product) exceeds the glass transition temperature of the modified polymer by more than 20˚C, tackiness becomes a problem. The presence of plasticizer and retained solvent may reduce the glass transition temperature of the polymer well below the normal value for the polymer. When forming coatings from polymeric solutions, we are essentially converting a viscous liquid into a visco-elastic solid passing through various stages, comprising of: 1 Initial rapid evaporation of solvent from the atomized droplets of coating liquid cause an increase in polymer concentration and a contraction in volume of the droplets. 2 Further loss of solvent from the film at a slower rate which is now controlled by the rate of diffusion of solvent through the polymer matrix. 3 Immobilization of the polymer molecules at the solidification point, further solvent loss from the film at a very much-reduced rate and concurrent formation of shrinkage stresses within the film as a result of constrain imposed by the immobility of polymer molecules and the adhesion of coating to substrate. According to Banker (1966) there are two sets of forces in film forming process; one operates between the film forming polymer molecules (cohesion force) and the other between the film and substrate (adhesion force). The degree of cohesion in film structure is fundamental to film properties. In order to obtain high levels of cohesion, it is necessary that the cohesive (autoadhesive) strength of the Corresponding author: E-mail: rgulmajeed@yahoo.com