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Effect of Mixer Type on Exfoliation of Polypropylene Nanocomposites
Polypropylene/organoclay nanocomposites have been prepared by melt blending in five different mixers: an internal mixer, two lab-scale, co-rotating vertical twin-screw mixers, a 30 mm co-rotating twin-screw extruder, and a multilayer extrusion system. The effectiveness of these mixers toward the dispersion of the clay into the polymer matrix was evaluated by TEM, X-ray diffraction, and melt rheology. Mechanical properties and coefficients of linear thermal expansion (CLTE) were also evaluated for these blends. The vertical twin-screw mixer at lower shear rate appears to provide the best mixing in terms of dispersion efficiency and modulus improvement. The combination of shear rate and residence time in the mixer is discussed in order to rationalize our results.
Interfacial Tension Effects in Ternary Biphasic Blends
It has been long recognized that properties of multiphase polymer systems are strongly dependent upon supramolecular structure. Examples of controlling supramolecular structure for property enhancement during fabrication include (a) control of molecular orientation and/or crystallization, and (b) establishing optimum morphology in multiphase polymer systems.Interfacial tension strongly influences multiphase polymer blend morphology, and compatablizers are frequently employed to manage interfacial tension in order to encourage the formation of a specifically desired morphology. Interfacial tension has also been found to affect the flow stability of certain multilayer flows.This paper will discus interfacial tension effects in ternary biphasic blends of bisphenol-A polycarbonate, poly(methyl methacrylate), and poly(vinylidene fluoride). PMMA and PVdF are thermodynamically miscible and form one phase of the biphasic blend. The Imbedded Fiber Retraction method was used to probe interfacial tension of the blends with polycarbonate. The interfacial tension function was found to be non-linear with respect to PMMA/PVdF phase composition, and this result will be rationalized by applying surface thermodynamic theory.
Effects of Supercritical CO2 on the Interfacial Reaction of Maleic Anhydride Functionalized Polyethene and Polyamide-6
Reactive extrusion of maleic anhydride functionalized polyethylene (PE-MA) and amine-terminated polyamide-6 (PA-6) was carried out in a twin-screw extruder with the injection of supercritical CO2 (scCO2). The extent of the interfacial reaction was quantified by measuring the amount of unreacted maleic anhydride (MA) by means of FTIR. It was found that the final MA conversion increases with CO2 concentration. The increase of MA conversion was explained from the mechanism of interfacial reactions between two melt phases. Dissolution of CO2 into polymer melts increases the free volume, thus enhancing the segmental chain mobility, promoting the reorientation of chain configuration and facilitating contact of reactive functional groups. It was also found that, with the increase of polyamide-6 content in the blend, the effect of CO2 on the MA conversion is less pronounced. At high concentration of polyamide-6 (70%), the MA conversion is very high (80 %) even without using CO2 and injection of CO2 into the polymer melts seems to have no effect on the MA conversion. This is most likely due to the development of a cross-linked interfacial region or the saturation of copolymers at the interface.
Effects of Supercritical CO2 on the Interfacial Tension between Ps and LDPE Melts
In this study, the effect of supercritical CO2 (scCO2) on the interfacial tension between polystyrene (PS) and low density polyethylene (LDPE) was studied using the pendant drop method at temperatures from 200 to 240 °C and CO2 pressures up to 18 MPa. The LDPE melt was prepared in a high pressure optical cell and the PS pendant drop was injected into the LDPE melt with a special high pressure syringe. The interfacial tension measurement was taken after saturation of CO2 into both polymer melts. It was found that the interfacial tension between PS and LDPE decreases by as much as 30% at CO2 pressures just above its critical pressure. Further increase of CO2 pressure seems to have small effect on the interfacial tension.
Compatibilization of Nylon 6 Nanocomposites/ABS Blends Using Functionalized Metallocene Polyolefin Elastomer
The impact behaviors of nanoclay filled Nylon 6 (Nano-Nylon 6) blended with poly (acrylonitirile-butadiene-styrene) terpolymers (ABS) prepared through a twin screw mixing process were investigated here using metallocene polyethylene grafted maleic anhydride (POE-g-MA) as compatibilizer. It is found that impact strength increases slightly for Nano-Nylon 6/ABS blend system with the addition of compatibilizer, but increases remarkably for the conventional Nylon 6/ABS case. These discrepancies could be attributed to a different degree of available reaction sites from amine group on Nano-Nylon 6 and Nylon 6.
Compatibilisation Studies of Blends of Nylon 6 with Metallocene Linear Low-Density Polyethylenes
Polymer blends of polyamides and polyethylenes are immiscible and highly incompatible. These blends are characterised by high interfacial tension, a two-phase morphology and poor physical characteristics due to reduced interaction across the phase boundaries. The compatibilising agent, maleic anhydride-grafted-LLDPE, is physically miscible with the polyethylene phase and has a chemical functionality with the polyamide phase. The use of a new generation mLLDPE (ENGAGE ™ by Dupont) was studied to investigate its suitability as a modifier for the polyamide grade. The influence of the composition of the blends and the effect of the addition of the compatibiliser were both investigated for their effect on the mechanical properties. Increased mLLDPE content was shown to slightly decrease the impact values but significantly increase the modulus values. The addition of the compatibiliser improved the properties of the blends.
Nano-Composites Derived from Melt Mixing a Thermotropic Liquid Crystalline Polyester and Zinc Sulfonated Polystyrene Ionomers
A nanocomposite consisting of rectangular prism-shaped liquid crystalline polymer nano-crystals dispersed in a thermoplastic polymer matrix was produced by melt mixing blends of a thermotropic liquid crystalline polyester (TLCP) and the zinc salt of lightly sulfonated polystyrene ionomers at 300 °C. The conversion of a macroscopically dispersed LCP phase to nano-particles during melt mixing was analyzed directly by torque measurements during melt-mixing and indirectly by wide angle X-ray diffraction and transmission electron microscopy of the resulting blends. Salts other than zinc did not induce the formation of the TLCP nano-particles, so it appears that the formation of the nano-crystals involved a specific interaction of the zinc sulfonate groups with the TLCP. The specific nature of the interaction, e.g., physical or chemical is not yet known.
New Miscible Blends of Nylon 6 and Polyhydroxyaminoether Resins
Nylon 6 (PA-6) was found to form fairly miscible blends with certain types of polyhydroxyaminoether (PHAE) resins as evidenced by microscopy and DSC techniques. Such miscibility between a nylon and a non-nylon polymer is rather rare and novel. However, the observed miscibility and phase behavior was found to depend on both the nylon and the PHAE resin structures. For PA-6, the miscibility was found to occur only when the PHAE contained sufficient amounts of resorcinol moieties and ethanol amine moieties. Other nylons such as PA-66, PA-6I/6T, PA-MXD6 and PA-12 showed an increasing tendency for phase separation and immiscibility.
In Situ Block Copolymer Formation during Solid-State Shear Pulverization: An Explanation for Blend Compatibilization via Interpolymer Radical Reactions
Interpolymer radical coupling leading to block copolymer formation is demonstrated for the first time in the solid state and in the absence of diffusion using solid-state shear pulverization. Fluorescence-detection gel permeation chromatography detected interpolymer reaction in high-molecular weight polystyrene (PS)/pyrene-labeled PS and high-MW poly(methyl methacrylate) (PMMA)/pyrene-labeled PS blends. Proof of interpolymer radical coupling supports prior pulverization studies demonstrating compatibilization, i.e., stability of dispersed-phase to long-time annealing, of PS/high density polyethylene and PS/PMMA blends.
Compatibilization of PC-SAN Blends by Ultrasound-Assisted Melt Mixing
In this study, high intensity ultrasound was employed to induce mechano-chemical degradation during melt processing of polymeric materials. It was expected that generation of macroradicals in polymer mixture can lead to in-situ copolymer formation by their mutual combination, which should be an efficient path to compatibilize immiscible polymer blends and stabilize their phase morphology in the absence of other chemical agents.Ultrasound-aided degradation of PC and SAN was practiced during melt processing of the polymer in a sonicated mixer. We investigated the changes in the morphology of PC/SAN blends for various viscosity ratios of PC and SAN and improvement of mechanical properties of sonicated blends was evaluated.
Simulation of Droplet Breakup Using a Lattice Boltzmann Method
Droplet breakup in homogeneous shear flow at super critical Capillary numbers and a viscosity ratio of unity is studied using a lattice Boltzmann method. We find that the total number of child drops that form from an isolated super critical drop scales according to a power law relation (n = 3.5). The child drops that form are all below critical, but not wholly uniform in size, and the distribution appears to be log-normal at high drop numbers. It is also found that for large ratios of the Capillary number to its critical value, the total strain required to break up a drop into N sub-critical entities tends to a constant value.
Drop Breakup Mechanisms in Polymer-Polymer Systems
The deformation and breakup of a single viscoelastic polymer drop inside a viscoelastic polymer matrix at high temperatures under simple shear was visualized in a specially designed transparent Couette mixer. The polymer systems studied were polyethylene matrix/polycarbonate drop (PE/PC) with viscosity ratios between 2 and 8. Aside from the “erosion” mechanism, which has already been reported (1, 2), three other distinct breakup modes were observed: (a) “parallel breakup” – the drop breaks after being stretched into a thin sheet or sausage parallel to the flow direction; (b) “tip streaming” – streams of small droplets are released from the tips of a pointed drop in the flow direction; and (c) “perpendicular breakup” – the drop breaks after being elongated in the vorticity direction.
Polymer Dispersion Visualization in a Couette Flow Cell
Dispersion mechanisms in high viscosity ratio polystyrene/polyethylene (PS/PE) and ethylene propylene rubber/polypropylene (EPR/PP) systems under relatively high shear rates and temperatures up to 230°C have been investigated in a transparent Couette setup. Through the in situ visualization, two non-Newtonian breakup mechanisms were revealed. The first one was the droplet elongation perpendicular to the flow direction followed by droplet shattering when the ends of the elongated droplets get slightly off axis with the stationary plane. The initial elongation has been associated to elastic normal force buildup in the droplet. The second non-Newtonian mechanism consisted in erosion at the drop surface.
Time-Scales of Coalescence in Polymer Processing: Study on Polypropylene/Polyamide-6 Blends
The effects of shearing time, volume fraction, shear rate, and viscosity ratio on coalescence of isotactic polypropylene (PP) and polyamide-6 (PA6) blends were studied in simple shear flow. A simple model for coalescence developed to provide characteristic times in coalescence in polymer processing operations was used to analyze experimental results. The pre-coalescence droplet morphology was created by melt blending the polymers in a twin-screw extruder at several compositions and was subjected to a simple shear flow in a cone and plate rheometer at low shear rates (0.1 and 0.5 s-1). The rheological data was analyzed after removing the effects of viscosity mismatch to leave only the interfacial effects on coalescence.
Morphology Transitions in Multilayer Polymer Melts Due to Growth and Interaction of Holes
Chaotic advection has been used in prior work to create melts containing a large numbers of very thin individual layers among polymer components. Morphology changes in the layers occurred due to hole growth and interaction. Because the process was amenable to control, a wide variety of blend morphologies were obtained in extrusions. Modeling of these morphological transitions has been carried out with the aim of improving process control in envisioned smart blending machines where blend morphology can be specified via a computer keyboard. The lattice Boltzmann method (LBM) was used to study the interactive growth of various hole patterns in layers in a periodic three-dimensional domain. It was demonstrated computationally that hole growth can lead to numerous thin and oriented fibers, single and dual phase continuous morphologies, and very fine droplets. The advantages of obtaining these and other structures via controllable multilayer formation and breakup are discussed.
Laminar Morphology of Extruded HDPE/PA-6 Blends Controlled by Flow Fields
Ribbons were extruded from two high-density polyethylene (HDPE)/polyamide-6 (PA-6) blends with different melt shear viscosity ratios (VRs) of PA-6 to HDPE. Three different screw configurations, one metering and two mixing screws, and three screw speeds were evaluated to investigated their effects on the morphology of extruded ribbons. The scanning electron microscopy (SEM) observation showed that the blends with different VRs need different screw shearing intensity to yield a thin, overlapping, and discontinuous laminar PA-6 phase, which results in enhancing permeability barrier properties. The screw speed also played a distinct role in controlling the morphology of the blend. By controlling the flow fields, through appropriately combining the screw configuration with screw speed in this study, a well-developed laminar PA-6 phase with an aspect ratio of about 100 was obtained.
Interfacial Chemistry and Morphology of Blends of Polybutyleneterephthalate and Epoxide-Containing Rubber
Of the various ways in which polybutyleneterephthalate (PBT) can be toughened, the addition of epoxidecontaining rubbers is one of the most effective. The interfacial chemistry (dissolution and fractionation experiments) and morphology (transmission electron microscopy) development in blends of PBT with ethylene-(methyl acrylate)-(glycidyl methacrylate) rubber (E-MA-GMA) has been studied as a function of the mixing time for batch kneaders and of the length along the axis of a co-rotating twin-screw extruder. First, a physics-controlled mixing regime occurs with a very fast dispersion of the rubber to the ?m level. Subsequently, a chemistry-controlled regime occurs, where the interfacial area is covered with PBT/E-MA-GMA graft copolymer, which prevents coalescence and, thus, results in further refinement of the morphology to sub-?m level. The occurrence of cross-linking of the rubber phase in some cases limits optimum blend dispersion.
Interfacial Area and Rheological Measurements of Cocontinuous Poly(Ethylene Oxide)/Polystyrene Blends
Blends of poly(ethylene oxide) and polystyrene were analyzed using scanning electron microscopy with image analysis and rheological measurements to determine the region of cocontinuity. Local maxima in the amount of interface in the blends and in the elastic modulus at low frequency correspond to the boundaries of the region of cocontinuity. Annealing of the samples caused some blends near the boundaries of the region of cocontinuity to break up into dispersed morphologies, while other blends remained cocontinuous, despite dramatic increases in the size scale.
Morphological Phase Behavior of PMMA and PC in PMMA/PC Binary and PP/PMMA/PC Ternary Blends
The morphological phase behavior of polycarbonate and poly(methyl methacrylate) was studied in PMMA/PC binary and PP/PMMA/PC ternary blends prepared in a Haake batch mixer. Even though extensive research on the PMMA/PC blends has been performed, the miscibility between two polymers has not been clearly understood to date. The phase separation between two polymers has been consistently observed specifically the blends were prepared in molten state. In this paper, immiscible and miscible PMMA/PC phases were observed in PMMA/PC binary blends and PP/PMMA/PC ternary blends, respectively. Therefore, effects of the PP-matrix on the PMMA/PC miscibility were proposed in this study. In order to clarify the effects of the PP-matrix, various analyzing techniques including NMR, GPC, ICP and SEM were utilized. It was also found that the miscibility of PMMA and PC is highly affected by the processing parameters such as mixing temperature and mixing time in the presence of the PPmatrix.
Blends of Ethylene-Methyl Acrylate-Acrylic Acid Terpolymers with Ethylene-Acrylic Acid Copolymers
The effect of methyl acrylate composition in ethylene-methyl acrylate-acrylic acid (E-MA-AA) terpolymers and acrylic acid content in ethylene-acrylic acid (E-AA) copolymers was investigated in blends of these two materials. The E-MA-AA terpolymer with 8 mole percent methyl acrylate was not miscible with any E-AA material no matter what the AA content, while the terpolymer with only 2 mole percent methyl acrylate was miscible, at least to some extent, with the E-AA copolymer at high acrylic acid contents. For the E-AA polymer material with the highest acid content, there was a synergistic effect for some properties at low E-MA-AA contents; the tensile strength was 10% higher than the value for the E-AA copolymer, even though the E-AA copolymer was much more stiff.
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