Plasticization of cellulose ethers used in the film coating of tablets

Abstract

plasticizer/polymer interactions have been studied by measuring the intrinsic viscosities of both ethyl cellulose and hydroxypropyl methylcellulose in a series of dialkyl phthalates and in a series of liquid glycols respectively. A correlation was found between the intrinsic viscosity of the polymer/plasticizer solutions and the tensile strength, elongation at rupture and work done in stressing to failure of cast films-the mechanical properties being at a minimum when the intrinsic viscosity was at a maximum. This correlation held only within a homologous series of plasticizers and none was found for plasticizers of different structures. A relationship was found between the lowering of a calculated glass transition temperature of hydroxypropyl methylcellulose in the presence of the plasticizers propylene glycol, polyethylene glycol 200 and glycerol and the intrinsic viscosity of the corresponding solutions-the higher the viscosity the greater the lowering of the transition temperature.Film formers such as the cellulpse ethers, ethyl cellulose and hydroxypropyl methylcellulose are now used extensively in the film coating of solid dosage forms. Plasticizers are often added to these polymers in order to change their physical properties and enhance their film forming characteristics. To be effective a plasticizer must interpose itself between the polymer chains and interact with the forces holding the chains together thereby extending and softening the polymer matrix. A very convenient way of assessing the degree of plasticizer/poiymer interaction is to measure the intrinsic viscosity of the polymer dissolved in the plasticizer. In this work these measurements have been made for ethyl cellulose and hydroxypropyl methyl cellulose in a series of liquid plasticizers and correlated with both glass transition temperatures and the mechanical properties of free films. M A T E R I A L S A N D M E T H O D SThe two polymers used were ethyl cellulose (Grade N50, Hercules Powder Co. Ltd., U.S.A.) and hydroxypropyl methylcellulose U.S.P. (Pharmacoat 606, Shinetsu Chemical Co. Ltd., Japan). Dimethyl phthalate, diethyl phthalate, dibutyl phthalate and dioctyl phthalate were used as plasticizers for the ethyl cellulose; ethylene glycol, diethylene glycol, triethylene glycol, the polyethylene glycols 200, 300, 400, 600, 1O00, 4OO0, 6000, propylene glycol, dipropylene glycol and glycerol were used as plasticizers for the hydroxypropyl methylcellulose.~ * Correspondence. t While it is realised that ethylene glycol, diethylene glycol, triethylene glycol and dipropylene glycol would not normally be used in the film coating of solid dosage forms because of their toxicity, they have been included In this study in order to examine the effect of plasticizer molecular weight.Intrinsic viscosities of the polymers were determined by measuring the viscosity of the plasticizer (where liquid) and a solution of known concentration of the polymer (usually between 0.1 and 0.5% w/w) using a 'U' tube viscometer and substituting these values in the equa...

The effect of plasticizer type and concentration on the incidence of bridging of intagliations on film-coated tablets

“…1 are similar in shape to those reported for the same system showing the effect of plasticizer concentration on the glass transition temperature (Entwistle & Rowe 1979). There are, however, two anomalies: firstly, the rank order of plasticizer efficiency predicted by Entwistle & Rowe (1979) on the basis of decrease in glass transition temperature was propylene glycol > polyethylene glycol 200 > glycerol, and secondly, the difference in efficiency between glycerol and the other two plasticizers used in this study is greater than would be anticipated on the basis of this glass transition curve for theglycerol. The first of these discrepancies is probably due to the fact that the glass transition curves were calculated from a knowledge of the physical properties of the materials and the data used for polyethylene glycol 200 were averaged figures from manufacturer's literature.…”

“…1. These results lend further support both to the concept of residual stresses in the film being the cause of bridging of the intagliations and to the adoption of a fundamental thermodynamic approach to the choice of plasticizers as advocated by Entwistle & Rowe (1979).…”

“…The second could well be due to plasticizer loss during the coating process. Since loss is dependent on thevolatility of the plasticizer, its interaction with the polymer and its diffusivity through the polymer matrix, it would beexpected that glycerol, with its low molecular weight and poor interaction with hydroxypropyl methylcellulose (as determined from intrinsic viscosity measurements- Entwistle & Rowe 1979). would be lost more readily than the other two plasticizers.…”

Enhanced Controlled Release of Loratadine From the Ethylene-vinyl Acetate Matrix Containing Plasticizer

“…The plasticizer will interpose itself between the polymer chains and interact with the forces held together by extending, and softening the polymer matrix (Entwistle and Rowe 1979). The plasticizer reduces the brittleness, improves flow and imparts flexibility.…”

Enhanced transdermal controlled delivery of glimepiride from the ethylene-vinyl acetate matrix

“…The plasticizer will interpose itself between the polymer chains and interact with the forces held together by extending and softening the polymer matrix (Entwistle & Rowe, 1979). The plasticizer reduces the brittleness, improves flow, imparts flexibility, and increases the toughness, strength, tear resistance, and impact resistance of the polymer.…”