Flow behavior in a corotating twin‐screw extruder of pure polymers and blends: Characterization by fluorescence monitoring technique

The objective of this work was to investigate the flow behavior of pure polymers and blends, especially miscible polymer/polymer systems, in a corotating twin‐screw extruder (TSE) using an online fluorescence monitoring device. An immiscible blend was also studied for the sake of comparison. The fluorescence signal was obtained by using synthesized fluorescence tracers added to the melt at very low concentrations. These tracers consisted of two styrene‐maleic anhydride copolymers (SMA) labeled with anthracene. The investigated blends were SMA8 (8 wt % of MA in SMA)/polystyrene (PS), SMA14 (14 wt % of MA in SMA)/styrene acrylonitrile copolymer (SAN), and poly(methyl methacrylate) (PMMA)/ethyl acrylate‐methyl methacrylate copolymer (PMMAEA). The residence time distribution (RTD), the mean residence time (t ), the dimensionless variance (σ_θ²), the Peclet number (Pe) and the fluorescence peak intensity distribution of pure polymers and binary polymer systems were investigated and interpreted in terms of polymers rheological properties. It was observed that polymers presenting higher viscosity or higher pressure showed longer residence time. A difference in behavior was also observed for the RTD of miscible and immiscible blends. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Three‐site mechanism and molecular weight: Time dependency in liquid propylene batch polymerization using a MgCl2‐supported Ziegler‐Natta catalyst

This article demonstrates that the molecular weight of propylene homopolymer decreases with time, and that the molecular weight distribution (MWD) narrows when a highly active MgCl₂‐supported catalyst is used in a liquid pool polymerization at constant H₂ concentration and temperature. To track the change in molecular weight and its distribution during polymerization, small portions of homo polymer samples were taken during the reaction. These samples were analyzed by Cross Fractionation Chromatograph (CFC), and the resulting data were treated with a three‐site model. These analyses clearly showed that the high molecular weight fraction of the distribution decreases as a function of time. At the same time, the MWD narrows because the weight‐average molecular weight decreases faster than the number‐average molecular weight. A probable mechanism based on the reaction of an external donor with AlEt₃ is proposed to explain these phenomena. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 1035–1047, 2001