Some melt flow properties of polypropylene

Abstract

The ability to express laboratory melt flow data in generalized terms serves both the fabricator and the resin producer: the fabricator can reduce the relations to the particular conditions of his process; the resin producer can assess the effect of polymer composition and structure on melt flow properties. An empirical method of correlating and generalizing laboratory capillary viscometer data has been developed which allows prediction of pressure–output relations for any cylindrical orifice. It is based on the Rabinowitsch and Bagley methods of calculating the correct shear rate and shear stress. The pressure drop across a die is made up of two terms, the entry pressure and the land pressure. Each is a function of the shear rate, but only the latter is a function of the die dimensions. Six key rheological parameters are developed, using polypropylene as an illustrative example. The effect of molecular weight and molecular weight distribution of polypropylene on the parameters is shown. In addition, some examples of practical uses of the generalized formulations are given. In the examples, the shear rate range of 10–1000 sec.−1 is covered, although the method could be applied to any experimentally attainable shear rates.