SPE Library

This study investigated the effect of surface modification of nanoclays on the compatibility of Maleic Anhydride-grafted polypropylene (PP-g-MA)/poly (ethylene oxide) (PEO) blends. Rheological testing confirmed the network formation of nanaoclays of all types. SEM confirmed the emulsifying role of nanoclays by reducing the PEO domain size. For the case of using dialkyl (C18)-modified nanoclays, mechanical testing showed that the elastic modulus and the toughness were respectively improved by 20% and 55% compared to unfilled samples.

Three major polyethylene (PE) engineering plastics, linear-low-density (LLDPE), low-density (LDPE) and high- density (HDPE) are studied in capillary flow. The purpose is to find experimentally and predict numerically their flow behaviour, namely the pressure drop in flow through tapered dies. This behavior is related to their individual rheological and flow properties. Using a series of capillary dies having different diameters D and length-to-diameter L/D ratios, a full rheological characterization has been carried out, and the experimental data have been fitted with the viscoelastic K-BKZ/PSM model. The branched LDPE has a strong pressure-dependence of viscosity, with a pressure-dependent coefficient ?p. For the linear LLDPE and HDPE melts, the pressure-dependence of viscosity is weak, but slip at the wall is strong and affects their flow behaviour. Thermal effects due to viscous dissipation are included but are rather mild. It is found that the viscoelastic simulations are capable of reproducing the experimental data well, in the whole range of apparent shear rates and L/D ratios.

The miscibility between drug indomethacin and excipient Eudragit® E PO were extensively characterized by rheological and thermal analysis. The evolution of glass transition temperature and activation energy with indomethacin concentration indicates the existence of overall positive deviation which represents anti-plasticization effect. The rheological analysis is in agreement with the thermal analysis, and both methods indicate that the miscibility between them is very good for indomethacin concentrations up to 60~70%.

In this study, thermal and rheological properties of polyamide 6 (PA6), poly (m-xylene adipamide) (MXD6) and their commercial nanocomposites (4 wt.% clay) were studied. Dynamic rheological experiments were carried out for both neat resins and corresponding nanocomposites at different temperatures. Rheological measurements were conducted using a strain-controlled rheometer. Crystallinity and thermal transitions of the materials are established via both DSC and XRD techniques. Oxygen transmission rates were also measured and normalized by the films thickness.

The aim of this study is to increase the complex viscosity of low viscous polyamide 66 (PA 66) by means of a chain extension process. The technical goal of the process is to extrude thick-walled pipes from chain extended PA 66 without the appearance of sagging problems. The influence of styrene maleic anhydride (SMA) and epoxide (EP) on chain extension of PA 66 were studied using a co-rotating twin- screw extruder. To evaluate the coupling effects of the different extenders on PA 66, the rheological and mechanical properties of the chain extended PA 66 were investigated. The extruded pipes, obtained from chain extended PA 66, featured a considerably improved wall-thickness distribution.

The continuous demand of high performance materials with key properties requires the optimization of polymerization and post-reactor treatment processes. A multiscale characterization approach including techniques such as rheology, fractionation and NMR has proven to be essential to understand the links between polymerization conditions, molecular structural properties and end performance. Rheology is a preferred candidate for analytical characterization, since its use provides combined knowledge on molecular characteristics and processability. A key parameter for the performance of materials during processing is the so-called LCB. Rheology, in particular methods exploring the longest relaxation mechanisms, is known to provide a significant insight into the type and amount of longer chains incorporated during polymerization. Most of the existing rheological parameters used by Industry and Academia, to correlate molecular structure and processability, are based on techniques that are often time consuming and which, for most of the cases, are only applicable to a given class of materials. The increasing need to reduce “time to market” requires the development of more sophisticated and efficient characterization tools. The combination of different non-linear viscoelastic methods presented within this work will provide further insight into the links between molecular structural properties and polymerization conditions. The use of the Large Amplitude Oscillatory Shear (LAOS) together with uniaxial extensional flow measurements can bring new understanding on the nature of the non-linear viscoelastic response of LCB materials and its correlation with molecular characteristics.

A multivariate sensor is designed with a piezoelectric ring and an infrared detector for measurement of melt pressure and temperature. The infrared detector includes a thermistor for measurement of the mold temperature. The polymer melt velocity is estimated by inspecting the transient melt temperature signal. The melt viscosity is then estimated from rheological models as the slope of the melt pressure relative to the melt velocity. Experiments confirm the validity of the approach.

Block copolymers are materials with many applications in the field of thermoplastic elastomers. Their properties can be further improved by the addition of nanoclays. However, the morphological and rheological properties of these hybrid materials are not very well known. In this work, the effects of clay concentration on the evolution of morphology of two block copolymers, (SEBS and SEBS-MA), presenting an aligned cylindrical morphology, when submitted to elongational flows was studied. The elongational test was performed using a Sentmanat elongational rheometer and the morphology of the clay-containing block copolymers was studied using small angle x-ray scattering (SAXS) and transmission electron microscopy (TEM).

In this work the detailed morphology of poly(lactic acid)/ poly (butylene adipate-co-terephthalate) has been carried out for the first time. The morphology of PLA/PBAT blends with different compositions was studied and limits of the co-continuity region were determined using rheological measurements and image analysis. Particle size analysis and breaking thread experiments showed that PLA/PBAT is a very low interfacial tension polymer blend. Moreover, composites of PLA/PBAT/spherical silica particles were prepared and the localization of silica particles in this blend was studied.

Liquid Crystal Polymers (LCPs) are advanced high temperature processing polymers with unique physical properties. It contains rigid rod like molecules, which exhibit structural orientation during the flow process at one or two dimensional level. Rheological behaviour of unfilled LCPs and filled (glass fibre) LCPs were characterized with ARES and Capillary rheometer at low and high shear rates. The complex viscosities (h*) as well as shear viscosities (h) showed a typical shear- thinning behaviour. LCPs exhibit anomalous rheological behaviour with shear and temperature. Viscosity reduced at low shear rate region because of the tumbling nature of rod like molecules. The abnormal temperature dependence of the viscosities can be explained by the transition of anisotropic rod-like molecules to isotropic molecules with increase in temperature. In steady shear flow, it was observed that rotational transformation occur from direction of flow to surface direction, which leads to first negative normal stress difference (N1) with shear rate. Stress relaxation conducted after cessation of shear flow to prove the molecular dynamics. Multiple overshoot observed due to tumbling, which was varying with temperature and shear rate.

In this study, a numerical stability analysis of the film blowing process is performed considering non- isothermal processing conditions, non-Newtonian behavior of the polymer and physically limiting criteria (maximum tensile and/or hoop stress) in order to investigate the complex relationship between processing conditions (internal bubble pressure, heat transfer coefficient, mass flow rate, cooling air temperature, melt/die temperature), material parameters (extensional viscosity, rupture stress, Newtonian viscosity, flow activation energy, power law index) and film blowing stability.

Reactive modification of linear PP by radical mediated grafting in the melt state is investigated as a means of increasing its melt strength, thus resulting in improved foam processing characteristics. A tri-functional coagent, triallyl trimesate (TAM) is used to introduce long chain branching to the linear PP homopolymer. Rheological characterization is conducted to relate the rheological properties to the modified PP chain architecture. The foaming behaviour of the linear and branched PPs is investigated using a batch foaming apparatus with N2 as a blowing agent.

The purpose of this study is to investigate the rheological behavior of Polystyrene melt with dissolved SCF of nitrogen during Microcellular Injection Molding process applied with Gas Counter Pressure (GCP) technology; also, rheological behavior is compared with independent theoretical simulation using moldex3D. A slit cavity is designed to measure the pressure drop of polystyrene mixed with 0.4wt% supercritical nitrogen fluid under different mould temperatures (185°C, 195°C, and 205°C), injection speeds (5, 10, and 15 mm/s) as well as counter pressures (0, 150, 300 bars). It was found that the melt viscosity is reduced by up to 30% when GCP is increased from 50 to 150 bar as compared to conventional injection molding. The simulation results of pressure history well agrees with the experiments and provide a theoretical point of view on process design.

This work presents a systematic analysis on the capillary rheology of polystyrene melts under high shear rates ranging from 103 to 106 s-1. The precise Bagley correction was achieved by means of the enhanced exit pressure technique. The end pressure drop was found to predominate over the Bagley-corrected capillary pressure drop in the high shear rate range. Furthermore, the dissipation heating, pressure dependence, and compressibility effects were quantitatively evaluated. Results implied that the apparent nonlinearity of the Bagley-corrected capillary pressure drop versus apparent shear rate profile, which occurred at the shear rates of above 105 s-1, mainly resulted from the dissipation heating. In the shear rate ranges investigated, the corrected rheological behavior could be adequately described by the power law.

The mechanical properties of fiber reinforced materials are highly dependent on fiber orientation generated within the composite during molding operations. Rheologically obtained parameters for fiber suspensions are applied to current models to predict fiber orientation in complex geometries independent of experimental considerations. This method provides an a priori pathway to determine fiber orientation based solely on rheological testing of the suspension and independent of the mold geometry. Furthermore, predictions for fiber orientation are carried out using the traditional rigid fiber Folgar-Tucker model as well as the semi-flexible Bead-Rod model which allows for the inclusion of fiber bending to be taken into account often witnessed in long-glass fiber (LGF) systems. Computations for fiber orientation are performed for center-gated disks and predictions with the two above models are compared to experimental data.

During the last decades, the food, pharmaceutical and many other industries have seen several changes in packaging technology and applications because of new consumer demands and market trends. These drivers can be summarized as requirements for high quality, freshness and extended shelf-life of products, with easy-to-use and resistant packaging made with lighter, cheaper and recyclable materials. On the other hand, public demand and awareness for food safety has become a significant concern. This has even intensified on the recent regular outbreak of Listeria and Salmonella bacteria in various area of the world, following the consumption of contaminated meat and cheese products. The outbreak has prompted the public awareness to question food quality in stores and technological solutions that could prevent contamination and/or alert consumers may provide better public protection. Finally, the global market for materials and films used in packaging is very large. When decomposed into various segments such as controlled, active, and smart or barrier packaging, the volumes used and annual growth rates are significant in addition to other concerns such as sustainability. The performance of polymer films and multilayer packages are the result of the microstructure that is imparted to the material as a result of complex interactions between the resin and the thermo- mechanical history that it experiences during processing. This microstructure is strongly influenced by molecular parameters of the resins used (molecular weight, molecular weight distribution, branching, co-monomer type and content, etc.), their layout in multilayer structures and the additives used as well as the rheological, thermodynamic, thermal properties and the crystallization kinetics under the processing conditions. In the past, most of the studies were directed to the improvement of structural properties of films and multilayer structures (mainly mechanical: strength, tear, toughness etc...) and muc

Thermal issues associated with polymer melt extrusion are complex. The process efficiency associated with melting and conveying polymers using a rotating screw inside a barrel is highly dependent upon the frictional, thermal and rheological properties of the polymer, the selected screw geometry, and designated extruder operating conditions including machine set temperatures and screw speed. Melting of the polymer is attained through a combination of thermal conduction and viscous shearing. This process is energy intensive but optimisation cannot be simply indicated by the energy used per kilogram of product. The quality of the extrudate is also of paramount importance. Melt quality can be defined in terms of the value and homogeneity of melt temperature. In this work, in- process monitoring techniques incorporating thermocouple grid sensors, infra-red thermometers and an energy meter have enabled real-time characterisation of thermal dynamics in single screw extrusion, for a 63.5mm diameter extruder. Operation of this extruder has also been simulated using commercial CAE software. Two commercial grades of polyethylene have been investigated using three extruder screw geometries at different extrusion operating conditions to gather evidence relating to process thermal efficiency. Extruder screw geometry, screw rotation speed, extruder set temperatures and material properties were each found to have a significant effect on the thermal homogeneity of the melt and on process energy consumed.

Blends of poly(lactic acid) (PLA) and poly[(butylene succinate)-co-adipate] (PBSA) were prepared using a twin screw extruder. The morphology of the blends was examined using scanning electron microscopy (SEM). Elongational flow properties of the blends and pure components were studied. A strong strain hardening behavior was observed for PLA/PBSA blends, in which PBSA forms the continuous phase (PBSA wt% ? 50). The results of tensile test showed that even for blends containing only 10wt% PBSA, elongation at break increased significantly. By the addition of PBSA to PLA, a transition from brittle behavior (observed for pure PLA) to ductile behavior was observed.

The rheological properties of complex fluids has been one of the interesting research subject due to the macroscopic behaviour (namely shear thinning and shear thickening) exhibited when they are subject to shear force. All concentrated suspensions under right conditions can exhibit the non-Newtonian flow behaviour, however, the required conditions and the underlying mechanism are not well understood in literature. To this respect, this study systematically investigates the effects of physicochemical parameters on the flow behavior of colloidal nanoparticle suspension (CNS) to shed a light on the mechanism behind the shear thickening behavior of CNS. We have also presented the outcomes of experimental studies of CNS with a low particle volume fraction, and anisotropic and flocculated microstructures through measuring their viscosity and electrical resistance under various shear forces together with utilizing several relevant characterization methods (i.e., Dynamic Light Scattering, Transmission Electron Microscopy and Capacitance Measurement). It is observed that studied CNS display shear thickening/thinning flow behavior depending on their microstructure forms due to the interaction forces among particles and associated changes in floc sizes, which are controlled by the shear induced hydrodynamical forces. The detailed valuation of the experimental results indicates that the shear thickening phenomena in low volume fraction, anisotropic and flocculated systems is mainly attributed to the increase in the total surface area and the effective volume fraction of particles due to both hydrodynamic and interparticle forces.

The challenges materials processing and compounding face nowadays are related not only with the design and control of better and more efficient machines but, essentially, with the manipulation of the molecular structure of the materials, with a view to obtaining innovative high performing products. Extruders are a fundamental part of any extrusion process and intermeshing co-rotating twin-screw extruders, in particular, have special application niches, being the equipment of choice for blending and compounding operations, mainly because of their good distributive and dispersive mixing capabilities. In fact, they are used in most important modern polymer applications such as compounding of filled polymer systems and masterbatches, polymer melt homogenization, polymer modification and the polymer blending. Very often, the last two operations involve, apart from polymer processing, chemical reactions, classical examples of which are the peroxide induced degradation of polypropylene to prepare grades with controlled rheology, and the grafting of maleic anhydride onto polyolefins to improve their compatibility with other polymers. Although these are widespread value-added processes in the polymer industry, there is often a gap in the fundamental knowledge of the properties and physical and chemical composition of the materials being processed during the extrusion process because the extruders are “black boxes” in which the properties of the initial materials, as well as those of the final product, are known, but not the kinetics of the transformation process. This poses severe limitations to current operations because without this knowledge any optimization effort of material structure and/or properties is done by trial- and-error and, thus, is very time consuming and offers no guarantees that the final product is, in fact, optimal. In this work, we present a review of recent developments in on-line sensors that allow for the monitoring of the rheological, chemical and s