RHEOLOGICAL CHARACTERIZATION OF CONTROLLED-RHEOLOGY POLYPROPYLENES USING INTEGRAL CONSTITUTIVE-EQUATIONS

Controlled-theology polypropylene melts were prepared via molecular mo dification of a commercial polypropylene resin. A peroxide-initiated d egradation was performed, resulting in materials with different molecu lar weight distributions. These resins were subjected to theological c haracterization, and an integral constitutive equation of the K-BKZ ty pe was used to study the effect of molecular weight characteristics on their theological properties. Data for the linear viscoelastic spectr um and shear viscosities was used to obtain the model constants. The s ame constitutive equation has been used to predict the stress and Trou ton ratios for simple shear and simple elongational flows, thus giving a quantitative assessment of the viscoelastic character of the melts. The results show the effect of the molecular modification on the theo logical behavior of the melts. Polymers produced at higher peroxide co ncentrations exhibit reduced viscoelasticity manifested in less shear- and strain-thinning behavior. The present work clearly shows the pote ntial of integral constitutive equations in fitting and interpreting e xperimental data and, thus, giving a much better understanding of the theological behavior of commercial polymers. (C) 1996 John Wiley & Son s, Inc.