DYNAMIC SURFACE-TENSION STUDIES OF HYDROXYPROPYLMETHYLCELLULOSE FILM-COATING SOLUTIONS

Film coating of pharmaceuticals involves interfacial interactions base d on adhesion and spreading of the polymer over the substrate surface. The surface tension of the polymer solution will have a major influen ce on these interfacial events. It is known that solutions of macromol ecules exhibit surface ageing; however, data are not available concern ing the dynamic surface tension (DST) of such systems in the first few seconds of surface formation. In this study, the DST of hydroxypropyl methylcellulose (HPMC) has been measured using a maximum bubble pressu re method. It was found that, at all concentrations, the DST was highe r than the equilibrium surface tension, but that at concentrations abo ve 6% (w/w) this difference was much greater. This can be related to d ifficulties in film coating which can occur with more concentrated sol utions. It was shown that additions of additives, such as poly(ethylen e) glycol or lactose, had a detrimental impact on DST for the high-con centration solutions only. These data provide an improved understandin g of the film coating process and give a route by which film-coating f ormulations may be optimised. Copyright (C) 1996 Elsevier Science B.V.