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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Morphology Development in PA6/PP System by Chaotic Mixing: Effect of Viscosity Ratio and Composition
Self similar mixing structures produced by chaotic mixing were utilized in this study to produce an array of mixing morphology, such as nested layers, elongated fibrils, droplets and their combinations in the blending of two immiscible polymers, polypropylene (PP) and polyamide-6 (PA6). Experiments were conducted in a specially designed batch chaotic mixer with PA6 as the continuous phase and the results were compared with those obtained in conventional batch mixing devices. The zero shear viscosity ratios were varied between 1 and 30, while the composition of PP phase was varied between 10 and 30wt%. It was found that repeated stretching and folding of the dispersed phase domains initially produced lamellar structures with much thinner layers and delayed the breakup process into fibrils and droplets. Consequently, domains much smaller than equilibrium sizes were obtained. The PP-domains were the smallest for a viscosity ratio of 1 and the largest for a viscosity ratio of 30, while the domain sizes increased with composition in all cases, purportedly through delayed breakup and increasing chances of coalescence.
In-Situ Compatibilization of PP/EPDM Blends during Ultrasound Aided Extrusion
Blends of isotactic polypropylene (iPP) and uncured ethylene-propylene diene rubber (EPDM) were treated by high intensity ultrasonic waves during extrusion. Die pressure and power consumption were measured. The effects of different gap sizes, blend ratios and number of ultrasonic horns were investigated. The rheological properties, morphology and mechanical properties of the blends with and without ultrasonic treatment were studied. In-situ compatibilization of the blends was observed as evident by their stable morphology after annealing and improved mechanical properties. The obtained results indicated that ultrasonic treatment induced the thermomechanical degradations and led to the possibility of enhanced molecular transport and chemical reactions at the interfaces. Processing conditions were established for enhanced in-situ compatibilization of the PP/EPDM blends.
Effect of High Intensity Ultrasonic Waves on Polypropylene, Polyamide 6 and Their Blends
The mechanical, rheological properties and morphology of polypropylene (PP), polyamide 6 (PA6) and their blends treated by high intensity ultrasound have been investigated. A lower head pressure and better mechanical properties are simultaneously achieved in the extrusion of these thermoplastics. A competition between the ultrasonically enhanced polycondensation reaction and degradation was observed for PA6. These enhanced polycondensation and degradation have a different mechanism than the thermally induced reaction. The better strength of ultrasonically treated PA6 is attributed to this reaction, leading to higher molecular weight, higher crystallinity and more uniform crystal size distribution. For PP, the degradation at high amplitude of ultrasound was observed. The mechanical properties of treated PP are maintained at low amplitude of ultrasound. For ultrasonically treated PP/PA6 blend, a competition between degradation and in-situ compatibilization was found. At a certain level of amplitude of ultrasound and a certain blend ratio, the tensile toughness and impact strength of treated blends were almost doubled, and a more stable morphology upon shearing and heating was observed.
Mechanical Properties and Morphology of Ternary PP/EPDM/PE Blends
The effect of high density polyethylene (PE) addition on the mechanical properties and morphology of polypropylene (PP) impact modified with ethylene-propylene- diene monomer (EPDM) has been studied. It was found that the modulus, tensile strength and impact resistance can be improved by PE addition. As predicted by the spreading coefficient, subinclusion morphologies where PE is encapsulated by the EPDM, were observed. The viscosity of the PE and its incorporation position along the twin-screw extruder was also found to play an important role on the final blend morphology and mechanical properties. The effect of the morphology on blends’ properties is discussed.
Influence of Ionomeric Compatibilizers on the Morphology and Properties of Amorphous Polyester/Polyamide Blends
The utilization of sulfonated polyester ionomers as minor component compatibilizers in blends of an amorphous polyester and polyamide was investigated. The blends were prepared using twin-screw extrusion and compared to solution blends to investigate the effect of elevated temperatures and shear mixing on blend miscibility and/or phase behavior. The thermal and mechanical properties of the blends were investigated using dynamic mechanical analysis (DMA) and tensile testing while the phase domain sizes of the solution blends with respect to ionomer content were studied using small angle light scattering (SALS) and phase contrast optical microscopy. Binary blends of the amorphous polyester and polyamide were immiscible with poor mechanical properties, while blends containing the polyester ionomer as a minor component compatibilizer showed a significant reduction in the dispersed domain sizes.
The Effectiveness of SPETG as a Compatibilizer for PC/PETG Blends
The melt-mixed blends of an amorphous copolyester, poly(ethylene-co-cyclohexane 1,4-dimethanol terephthalate) (PETG) and the sulfonated analog of the copolyester (sPETG), with bisphenol-A polycarbonate (PC) were investigated over the entire composition range. Dynamic mechanical analysis (DMA) for the PC/PETG blends showed two, ?-relaxations, which coincided with the glass-transition temperatures of the two respective homopolymers. In contrast, the PC/sPETG blends displayed two ?-relaxations but with a shift of the PC ?- relaxation to lower temperatures. Unlike the PC/PETG blends, the tensile strain at break and yield stress for the PC/sPETG blends follows closely to a linear composition dependence due to greater interaction between the blend components. Analysis of the FT-IR spectra for the PC/sPETG blends indicates an interaction between the sulfonate group of sPETG and the carbonyl group on the PC backbone.
A Study on the Effects of Chaotic Mixer Design and Operating Conditions on the Development of Morphology in Immiscible Polymer Systems
Self-similar mixing structures, a novel feature of chaotic mixing, were utilized in this study to produce an array of mixing microstructures, such as nested layers, elongated fibrils, droplets and their combinations in the blending of two immiscible polymers, polypropylene (PP) and polyamide-6 (PA6). Simulations based on Newtonian flow model were used to compute the Poincaré maps and stretching distribution to determine the effect of shear gap and chaotic mixing parameter, such as angular displacement per period (?), on the degree of mixing produced in a batch chaotic mixing device. Experimental results at low mean shear rates, with PA6 as the continuous phase (90wt%), corroborate with the findings of simulation study.
Thermal and Rheological Properties of Novel Thermoplastic Polyimide Blends
We report the results of our preliminary studies on the thermal and rheological behavior of a new semicrystalline polyimide (PI) type R-BAPB and its miscibility with amorphous PI type R-BAPS having similar chemical structure to the former. To ensure miscibility of the above relatively viscous PI, a prepolymer prepared by melting dianhydride and diacetyl derivatives of aromatic diamine (BAPB type) was blended with thermoplastic R-BAPS at 50/50 and 70/30 wt % ratio. At the start of the chemical reaction, the resulting mixture was completely miscible with a low viscosity of about 50 Pa?s at 300°C that subsequently increased to about 3?104 Pa?s after 1 hr at 300°C. This mixture can provide new PI blends with better processability and thermal properties than a simple thermoplastic mixture of R-BAPS and R-BAPB having the same weight ratio.
Structure and Properties of New Polyimide Bonded Magnets with Enhanced Benefits
We report a new method for preparing thermally-stable and processable polyimide (PI)-bonded magnets via the chemical transformation of PI prepolymers (based on diacetyl derivatives of diamines and dianhydrides) filled with magnetic Nd-Fe-B alloy particles (75-100 ?m). The prepolymers with amorphous structure, after removing of up to 5% volatile, can be melted at 220±10°C to give a fluid with a very low viscosity of 15±5 Pa?s. This low viscosity of the prepolymer facilitates blending it with the magnetic particles at relatively high volume fractions up to 85 vol. %. The resulting PI-bonded magnets were found to exhibit excellent thermal stability, high storage modulus of 10 GPa at 400°C; and a 10% increase in energy product over that of commercially available bonded magnet materials.
Compatibilization of Poly(Phenylene Ether) and Polyamide-6 Blends by Functionalized Polystyrenes
In this paper the compatibilizing effect of a polystyrene which was synthesized via controlled free radical polymerization and endcapped with an epoxy function in the immiscible blends of PPO and PA-6 was investigated. The properties being examined were notched Izod impact and tensile of injection molded parts. Tensile properties during exposure in a xenon arc weatherometer under exterior automotive conditions per SAE J1960 were investigated. The morphology was examined by scanning electron microscope. Results had shown that mechanical properties improved with addition of this functionalized compatibilizer. Blends of PPO/PA-6,6 and PPO/PA-6 were also compared.
A New Insturment to Monitor the True Stress-True Strain-Birefringence Behavior during Multiaxial Deformation and Annealing of PET Films
With the recent and very fast developments in the polymer processing techniques, which led to very fast and highly productive production lines, the need for fast measurement and monitoring techniques has grown greatly. Knowing that, the off-line or after-the-fact characterization techniques are unable to track the very fast structural changes in the polymeric materials under processing, the demand for on-line fast measurements is increasing. One of the most useful techniques for characterizing the orientation and crystallization of the macromolecules is the birefringence where, optical properties depend on the molecular structure and strong birefringence can be observed if highly polarizable bonds (multiple bonds) are present and if, during processing, they adopt a preferred orientation. We have developed real-time spectral birefringence measurements systems to monitor true stress-true strain-birefringence behavior during multiaxial deformation and annealing of polymer films. The system is able to track the orientation, crystallization and developed stresses in the films in order to facilitate better understanding for the processing-structure relationships in polymeric materials.
Uniaxial Stretching of PLA Using Fully Automated On-Line Birefringence Coupled with True Stress - True Strain Measurement - Part I: Stretching Rate Effects
The effect of deformation rate on fundamental deformation-structure relationships in melt cast amorphous Poly(lactic acid) (PLA) films was investigated using a stretch birefringence apparatus that allows for direct measurement of true stress, true strain, and birefringence. Crystalline phase behavior was elucidated with WAXD and DSC. Relationships between stress, strain, and birefringence are strongly affected by stretching rate. The effect of stretching rates on the molecular mechanisms of uniaxial deformation in rubbery state PLA films and its affect on the various levels of structure are elucidated in this study.
Uniaxial Extension of PLA Using Fully Automated On-Line Birefringence Coupled with True Stress - True Strain Measurement - Part II: Temperature Effects
The effect of temperature on the fundamental deformation-structure relationships in amorphous Poly(lactic acid) (PLA) melt cast films was investigated using a stretch birefringence apparatus that allows for direct measurement of true stress, true strain, and birefringence. The crystalline phase behavior was elucidated with WAXD and DSC. The relationships between stress, strain, and birefringence, and structure are strongly affected by the stretching temperature. The effects of temperature on molecular mechanisms of this deformation and structural development are elucidated in this study.
Drop Retraction Methods to Measure Interfacial Tension between Compatibilized Blends
Surface-active compatibilizers, commonly used to facilitate blending of immiscible polymers, are known to lower the interfacial tension between the immiscible polymers. Here we seek to measure the equilibrium interfacial tension of compatibilized polymer interfaces using the Imbedded Fiber Retraction Method and the Deformed Drop Retraction Method. These methods, popular for measuring the interfacial tension of uncompatibilized interfaces, are shown to give anomalous results for compatibilized interfaces. Both these methods use the kinetics of interfacial evolution to obtain interfacial tension. We employ computational fluid mechanical simulations to demonstrate that this interfacial evolution causes the local concentration of compatibilizer on the interface to deviate from the equilibrium value, leading to gradients in interfacial tension along the interface. These gradients appear to be the main reason for the errors in interfacial tension measurements noted experimentally.
A Technique for Absolute Biaxial Birefringence Measurements and its Applications
In this study, we discuss the applications of a birefringence technique for on-line or off-line quantitative measurement of biaxial orientation in transparent films, sheets, bottles, etc. Absolute values of biaxial birefringence are measured in two directions using a technique based on an incident multi-wavelength double beam and a photodiode array assembly, combined with in-house developed software. Both machine and transverse direction birefringences (relative to the normal direction) are measured simultaneously. Film and sheet of different thicknesses were tested and birefringence values from 0.0005 to 0.25 were measured. The technique was tested on different materials and under different conditions and its applications, particularly for online monitoring of biaxial orientation processes, are discussed.
Processing of Intractable Polymers Using High-Pressure Carbon Dioxide.
A modified extrusion system is used to process a variety of polymers (HDPE, LDPE, FEP, PTFE, s-PS) in the presence of high-pressure CO2. The extruder’s design includes a modified feed section that allows a given mass of polymer to interact with CO2 prior to the extrusion process. This alternative design provides a new and easy route to melt process high melt viscosity polymers of commercial importance such as PTFE, FEP and s-PS. The inherent shear mixing and the presence of CO2 allow for a specific control over the extrudate morphology. Some of the relevant parameters in the process are analyzed and related to the nucleation and plasticization effects brought about by the presence of CO2.
Prediction of the Melting Temperature of Polymers
A generalized equation is introduced to clarify conceptual definitions of copolymer melting temperatures. This treatment incorporates the effects of comonomer volume, crystal length, folding surface free energy and enthalpy of fusion, when comonomers are excluded from the crystallite lattice. Both the Gibbs- Thomson Equation for homopolymers and a modified application to copolymers have also been derived from the proposed equation as two special cases. The equation satisfactorily evaluates the melting temperatures of linear polyethylene homopolymers (including paraffins) and various ?-alkene-ethylene copolymers.
The Effect of Shear-Induced Migration of Conductive Fillers on Conductivity of Injection Molded Articles
Conductive filler particles tend to migrate in nonuniform shear fields such as during mold filling from the regions of high shear stress to low shear stress leading to the loss of conductivity in polymeric articles. In this work, the effect of conductive filler migration on surface and volume conductivity was investigated in conductive compounds of polystyrene and polypropylene and carbon black. Injection molded articles with mean particle concentration of ?c and 3.5?c, where ?c is the percolation threshold, showed volume conductivity values of respectively 10-18 and 10-4 S-cm, while compression molded specimens with same composition offered volume conductivity of 10-4 S-cm. Removal of surface layers from injection molded specimens by excimer laser ablation technique restored the conductivity to 10-4 S-cm. The extent of migration was evaluated in terms of the thickness of polymer layers removed from the surface, which depended on the type of polymer used.
UV Degradation of Recycled Photo-Degraded Polymers
The ultraviolet (UV) degradation of molded bars containing recycled polymer has been studied to determine whether products of photo-degradation act as pro-degradants. Recyclate that had been photo-degraded prior to recycling was mixed with virgin granules to mold new bars. Bars were also prepared from a mixture of virgin polymer with recyclate that had not been photo-degraded.Bars made from blends of virgin and recycled polymer were photo-degraded in the laboratory. For exposures of less than a month, the mechanical properties of both polystyrene and polypropylene were inferior when previously photo-degraded material was included. After extended exposure, the effect of including photo-degraded material diminished but by this time, the properties of the materials were unacceptable.
Polymer/Clay Nanocomposite Foams Prepared by CO2
Polymeric foams are widely used in many applications. In this study, we prepared polymer/clay nanocomposite foams using carbon dioxide as the foaming agent. The effect of clay dispersion (intercalation vs. exfoliation), clay concentration and types of polymers on foam morphology were investigated. It was found that clay nanoparticles serve as an efficient nucleation agent. The nucleation efficiency is affected by both clay dispersion and polymer-clay-CO2 interaction. By controlling nanocomposite composition and foaming conditions, PMMA nanocomposite foams with cell size as small as ~0.4 ?m and cell density as high as ~1012 cells/cc can be produced. These foams exhibit good combination of stiffness, toughness, weight saving and dimension stability. In addition, PLGA nanocomposites foams were also prepared and they can be used for tissue engineering scaffolds.
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