THERMAL AND MECHANICAL CHARACTERIZATION OF CELLULOSE-ACETATE PHTHALATE FILMS FOR PHARMACEUTICAL TABLET COATING - EFFECT OF HUMIDITY DURING MEASUREMENTS

Films from a polymer used in pharmaceutical coating (cellulose acetate phthalate) were analyzed by thermomechanical techniques including dyn amic mechanical thermal analysis (DMTA) and tensile tests. Emphasis,va s placed on relative humidity (RH) at the measurement site (as opposed to storage or conditioning RH). The films were plasticized with eithe r triethyl citrate or diethyl phthalate. The results show that the fil ms respond rapidly to changes in the environmental humidity. This in t urn influences the data obtained from DMTA and tensile testing; thus, good control of the humidity is essential. Absorption isotherms have b een obtained for the two types of films, and the results were interpre ted in terms of the equilibrium moisture content which is determined b y the polar nature of the plasticizer This factor must be considered w hen formulating a film composition because moisture can, apart from it s influence on mechanical proper-ties, also speed the chemical degrada tion processes. When the stability of a film composition during storag e is studied the actual measurements on the films should prefer ably b e done at 0% RH, irrespective of the storage RH. At 0% RH, the mechani cal testing results will reflect the chemical stability correctly, wit hout interference from plasticizing effect of absorbed water A functio nality test for films has been suggested: DMTA under isothermal condit ions using either step or continuous humidity scans. Isothermal dynami c humidity scans on the DMTA were performed for the first time, and th e utility of these measurements is discussed.