The SPE Library contains thousands of papers, presentations, journal briefs and recorded webinars from the best minds in the Plastics Industry. Spanning almost two decades, this collection of published research and development work in polymer science and plastics technology is a wealth of knowledge and information for anyone involved in plastics.
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Role of Nano-Particles on Crystalline Orientation in Polypropylene/Clay Nanocomposite Films
Preferential orientation of the polypropylene (PP) crystalline phase is investigated in polypropylene/clay nanocomposite (PPCN) films. Clay loading and degree of dispersion within the matrix are used to determine the role of nanoparticles on orientation.The PPCN films have been characterized using MDSC, XRD, FTIR, DMA, and tensile testing. Based on XRD measurements, there is evidence of matrix orientation, while FTIR shows no preferential orientation of the matrix. Mechanical analysis of films produced at low screw speeds and containing a high clay content exhibit higher moduli and lower elongation. DMA results also suggest that clay particles are aligned orthogonal to the orientation axis. While these results suggest that there may be preferential orientation in the films, further analysis must be performed to differentiate matrix alignment imposed by nanoparticles from shear-induced orientation (as a result of film extrusion).
Modeling Cell Nucleation during Microcellular Injection Molding
This paper presents a numerical simulation to predict nucleation and cell growth through the injection molding process. The model presented is based on a coupled solidification-nucleation process that considers mold and melt temperature, injection pressure, and material properties. Comparison of numerical prediction to experimental results was excellent at the center of the part, but under-predicted the cell size toward its outer surface. From numerical simulation, the influence of varying processing conditions on the cell structure is quantified.
Electrically Activated Polypropylene/Clay Nanocomposites
Polypropylene(PP)/clay nanocomposites under electric field was reported to show an exfoliated structure without any compatibilizer such as maleic anhydride functionalized polypropylene(MAPP). We could regulate the degree of dispersion and exfoliation of materials by controlling the amount of clay loading, the strength of electric field, the time exposed to electric field, etc. However, a new design concept is required for a continuous production of PP/clay nanocomposites under electric field.In this talk, we will present a novel method to continuously produce PP/clay nanocomposites using electric melt pipe equipped on a twin-screw extruder. Rheological and XRD measurements guide the degree of exfoliation and the improved properties of PP/clay nanocomposites. As applying the electric field is a physical process, the approach can be easily extended to make other polymer/clay nanocomposites.
Effect of Mixing Element in a Single Screw Extruder on the Microstructure of Polypropylene/Montmorillonite Nanocomposites
Polypropylene/organic-montmorillonite nanocomposites (in pellet form) prepared by using an industrial-scale twin screw extruder were extruded into ribbons by using an industrial-scale single screw extruder equipped with a screw involving different screw elements. Different type and intensity of mixing screw elements, including a fluted mixing element, pin mixing element, and chaos screw, and the Kenics static mixer, were used. The basal spacing of silicates in the nanocomposites was measured by X-ray diffraction. The morphology of the nanocomposites was observed by transmission electron microscopy. It has been demonstrated that the changes of the microstructure of nanocomposites occur after processed using a single screw extruder. Moreover, chaotic mixing is favorable for making polymer chains intercalate into the silicate interlayers and to obtain exfoliated nanocomposites.
Carbon Nanotube Nucleation of Polypropylene Crystals
Non-isothermal and isothermal crystallization experiments were performed on polypropylene mixed with carbon nanotubes. Mixing of the nanotubes with the polymer was accomplished by adding the nanotubes to a decalin solution that contained dissolved polypropylene, followed by evaporation of the solvent. Nanotubes promoted growth of the less-preferred beta form of crystalline polypropylene at the expense of the alpha form. In the case of non-isothermal crystallization, the total amount of crystalline material in the sample was the same for the filled and unfilled materials. However, for isothermal crystallization experiments, the percent crystallinity in the filled materials was slightly higher. Most importantly, the rate of crystallization was substantially higher in the filled system.
Effect of Organoclay Structure on the Rheology and Crystallization Behavior of In-Situ Polymerized PA6 Nanocomposites
PA-6 Nanocomposites containing nanometer-scale, finely dispersed silicate platelets (‘nanoclays’) have been prepared via in-situ polymerization of caprolactam with various types of organoclays. Depending on the chemical structure of the organoclay, a covalently tethered, a nontethered or a weakly tethered PA-6 Nanocomposite was obtained. While all the nanoclays showed a consistent nucleation effect on the PA-6 crystallization, the tethered nanocomposites showed a slower rate of crystallization than standard PA-6 or the non-tethered systems. The melt rheology at low shear rates reflected the clear effects of the tethering in causing a significantly higher melt viscosity and slower relaxation relative to standard PA-6.
Synthesis and Characterization of Hierarchical Structure in Supercritical CO2-Fabricated Composites
This paper illustrates the fabrication of two unique nanocomposite materials. These composites are synthesized via a supercritical CO2-assisted process similar to a rim and rtm technique. The use of SC CO2 in the fabrication of fiber-reinforced composites allows for the templated deposition of resin into the fiber’s crystal structure. Utilizing SC CO2 in the synthesis of intercalated silicate nano-composites significantly lowers viscosity and allows for synthesis of nanocomposites containing saturated levels (>40%) of organically modified layered silicates (OMLS).
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.
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