EVOLUTION OF THE MOLECULAR WEIGHT DISTRIBUTION AND LINEAR VISCOELASTIC RHEOLOGICAL PROPERTIES DURING THE REACTIVE EXTRUSION OF POLYPROPYLENE

摘要

Homogeneous and nonhomogeneous reactive extrusion of polypropylene is modeled using random chain scission statistics coupled with the double reptation mixing rule. In this manner, the evolution of both the molecular weight distribution and the linear viscoelastic material properties is quantitatively predicted for the reactive extrusion-pelletization process. Dispersion in the level of random chain scission has little impact on the MFI for a given average level of chain scission; however, dispersion does generate a marked increase in the recoverable compliance (melt elasticity) relative to the ideal homogeneous random chain scission case. Methods to quantitatively determine the degree of cracking dispersion in processing equipment are identified. Quality control issues such as blending materials of known linear viscoelastic properties to obtain a desired property set is considered in the context of known empirical relations consistent with the double reptation model. Simple mixing rules for the melt flow index and the steady-state recoverable compliance involving only single component MFI and J(e) information are derived. (C) 1995 John Wiley and Sons, Inc. [References: 42]