Permeability and mechanical properties of a new polymer: cellulose hydrogen phthalate

Films prepared from a new pH-dependent polymer, cellulose hydrogen phthalate (CHP), containing different proportions of plasticizers, were studied to evaluate their possible application to produce retard coated dosage forms. Neat CHP films were brittle and broke easily upon handling, therefore plasticizers were needed to improve the mechanical properties. Dibutyl phthalate, a hydrophobic plasticizer, was found to be an ineffective plasticizer since it did not improve the mechanical properties. However, glycerol, a hydrophilic plasticizer, was shown to be effective. These results were confirmed by differential scanning calorimetry analysis of the various plasticized CHP films. Permeability studies using theophylline as a model drug revealed that increasing the concentration of the hydrophilic plasticizer in the film enhanced the permeation rate and reduced the time lag, whereas the concentration of the hydrophobic plasticizer did not affect significantly either the permeation rate or the time lag. CHP films plasticized with glycerol could therefore be used in coating processes for the design of gastro-resistant delivery dosage forms.