effect of polymer grade and plasticizer molecular weights on viscoelastic behavior of coating solutions

film coating solutions containing different grades of hpmc (e5, e15 and e50) with and without polyethylene glycol (with various molecular weights) were examined by an oscillatory method, using haake cv 100 rheometer. fundamental rheological parameters (?, g? and g² ) were measured over the frequency range from 0.04 to 2 hz. the variation with frequency of the loss tangent (a ratio of viscous to elastic contribution) provides a useful parameter for the characterization of pharmaceutical products. magnitudes of the loss tangent are discussed with relation to coating solutions made by different grades of polymers and plasticizers.