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.
This paper focuses on gaining a fundamental understanding of the bubble growth and collapse phenomena occurring in a CBA-based foaming of plastics under atmospheric pressure. The behavior of CBA-blown bubbles exposed to various processing conditions was observed using a hot-stage optical microscope-based digital image processing system. A mathematical model that accounts for the effects of diffusion, surface tension, viscosity, and elasticity has been employed. It has been found that the processing temperature, diffusivity, and gas bulk concentration have dominant effects on the lifespan of CBA-blown bubbles.
The conditions that induce the bubble nucleation for the thermoplastic foam extrusion process in which physical foaming agents (PFA) are involved are obviously linked to the solubility parameters, i.e. temperature and pressure at a given PFA content, conditions that can be modified adding a nucleating agent. An in-line detection method based on ultrasonic sensors, sensitive to the onset of the phase separation, was used to investigate the influence of both talc and HFC-134a blowing agent concentrations on the nucleation cell density and degassing conditions for polystyrene foaming.
Most solubility data that is available has been determined by taking into account the swollen volume, which is estimated by the Sanchez-Lacombe (SL) equation of state (EOS). The swollen volume is typically determined with an interaction parameter that is chosen to minimize the differences between the experimentally measured and theoretically calculated solubility data.This paper presents a similar approach to ascertain the solubility based on the Simha-Somcynsky (SS) EOS. As a case example, we measured the apparent solubility of CO2 in a polystyrene melt at elevated pressure using a magnetic suspension balance. The solubilities determined by the two EOS were observed as being the same value below 1500 psi. When the pressure was above 1500 psi, the buoyancy effect was enhanced significantly because of the increased swollen volume and increased CO2 density. Consequently, the corrected solubilities that were determined by the two EOS at elevated pressures were observed to be different and the difference was 10% at 3000 psi.
The process of polymerization of syndiotactic polystyrene formed in presence of catalysts CpTiCl2(OC6H4Cl)/MAO was investigated. At the moment syndiotactic polystyrene is produced in pilot plant. The yield of syndiotactic polystyrene obtained in the reactor 240 dcm3 was about 7- 15 kg/charge. The molecular weight of syndiotactic polystyrene was about 200 000 g/mole and syndiatacticity about 96%. After process of synthesis composites based on syndiotactic polystyrene have been obtained. The powder of syndiotactic polystyrene has been granulated with stabilizers, and modifiers in twin-screw extruder with double degassing. Irganox 1076 have been used as the stabilizer. Syndiotactic polystyrene was reinforced by glass fiber or talc. Syndiotactic polystyrene was modified by polyoxyphenylene, linear polyethylene and hydrocarbon resin. The structure and physical and mechanical properties of composites were investigated.
The bulk isothermal crystallization kinetics and spherulite growth rate of a (1) metallocene polypropylene (m-PP) and metallocene propylene/ethylene copolymers (m-P/Es), (2) Ziegler-Natta polypropylene (ZN-PP) and Ziegler-Natta propylene/ethylene copolymers (ZN-P/Es), and (3) a new (n-PP) polypropylene and Development Performance Plastomers (DPPs) were studied. Crystallization half time (t1/2) and spherulite growth rate (G) as a function of melt crystallization temperature were analyzed for the three homopolymers and their corresponding copolymers containing 4, 8, and 13 mole % ethylene, respectively. With increasing ethylene content, all three polymer systems exhibited increased t1/2 and decreased G. At low comonomer contents, n-PP and DPPs exhibited slower t1/2s and Gs, however at high comonomer contents, m-PPs exhibited slower kinetic behavior.
The time-dependent elastic properties of a new Developmental Performance Elastomer (DPE) product family made with propylene-ethylene copolymers are investigated. These materials were previously referred to as new propylene-ethylene copolymers".Although these materials show some degree of permanent set upon initial tensile deformation the materials created as a result of a tensile "conditioning" process exhibit almost complete instantaneous strain recovery after a long period of stress relaxation. The stress relaxation behavior of the new DPE's are compared to that of elastomeric metallocene propylene-ethylene and ethylene-octene copolymers."
Blends of developmental performance elastomers (DPE), produced by INSITE™ technology, and polypropylene exhibit a superior balance of flexibility and heat resistance. These blends provide a new family of flexible TPO that can be engineered to meet performance requirements of many applications. Generalized blend design strategies for flexible TPO based on thermodynamic considerations are reviewed. Thermal, dynamic mechanical and tensile properties of the blends will be presented. The utility and potential applications of these blends will be highlighted.
Fibers made with novel propylene based polymers produced with INSITE™ technology from The Dow Chemical Company have been shown to offer distinctive processing, mechanical, and thermal characteristics. These unusual properties were attributed to differences in structure as measured by a variety of methods. The performance capabilities of these new fibers have been shown to offer properties previously unavailable with homopolymer polypropylene fiber and Ziegler-Natta polyethylene fiber. As a result, these novel propylenebased polymers were shown to expand the product offering capabilities of current fiber conversion technology.
The pressure drop rate is one of the most important parameters used to control the cell density of foams for a given processing pressure, temperature, nucleating agent content, and blowing agent content. In this paper, we concentrate on the experimental and theoretical analysis of the pressure drop behaviors in an experimental foaming simulation system using a visualization window. Both CO2 and N2 were used in the experiments and the simulation. It was observed that the maximum pressure drop rates obtained were 2.5 GPa/s and 0.4 GPa/s for CO2 and N2, respectively. Some simulation results at high-pressure drop rates are also shown.
This presentation will cover recent advances on selected inorganic and organic micron or sub micron fillers, which in addition to their primary functionality of modifying bulk mechanical properties provide also unique secondary functionalities. Inorganic particles (e.g. surface coated CaCO3) dispersed in polyolefins and organic particles (e.g. polystyrene with or without adhesion promoters) particles dispersed in polypropylene may promote the formation of micro/nano porous structures by post extrusion stretching of flat precursor films. The effects of filler concentration and process conditions on the resulting morphology and properties are discussed with applications in separation membranes and water breathable films.
Using Sanchez-Lacombe Theory, we have calculated the solubility and spinodal surfaces for solutions of inert gases dissolving in thermoplastics. The gas solubility surfaces are compared to known experimental data and can be used for simulating the kinetic path of foaming on the pressure-temperature plane in batch or continuous extrusion processes. Relations of experimental data of cell density and the pressure superheat are studied and are compared with the classic nucleation theory. A critical superheat surface is suggested for explaining the gap between theoretically predicted and experimental measured nucleation rates.
Microcellular processing techniques have been applied at a experimental level to both extrusion and injection molding plastics processing, using wood fiber as a reinforcing filler. The focus of the current research is the investigations of these processes using chemical foaming agents and comparative studies of physico-mechanical properties of materials. Results of using different chemical foaming agents (endothermic and exothermic), the variation of their content for producing wood fiber-polypropylene microfoamed composites and the effect of a coupling agent on the composites are presented. Microcells morphology, cell size, shape and distribution were investigated using scanning electron micrographs.
Shrinkage predictions from a commercial simulation package were compared with shrinkage of parts molded from neat and glass-filled grades of polycarbonate, poly(butylene terephthalate) (PBT), polyamide-6, and polyamide-6,6 various over a range of processing conditions. For both the neat and filled materials, the simulations overpredicted in-flow shrinkage and cross-flow shrinkage near the gate. Cross-flow shrinkage at the end of fill was underpredicted for glass-filled materials, did not correlate with values predicted for neat materials. The validation of shrinkage prediction for thin walled parts was also done using PC+PET blends.
The polystyrene specimens were foamed under various foaming temperatures and decompression rates, and the equivalency of decompression time that can obtain from decompression rate and foaming temperature about cell density was examined. As results, it was found that cell density has time and temperature dependence that cell density increases with a decrease in decompression time and foaming temperature, and cell density decrease with an increase in decompression time and foaming temperature. And it was found that the time-temperature equivalency seems to be held to the decompression time and foaming temperature, which affect cell density.
Recently, a novel family of processable rigid-rod polyphenylenes with outstanding mechanical properties was introduced (Parmax® SRPs). These materials possess strength and stiffness superior to other thermoplastics while retaining reasonable notched Izod values (65 J/m). To understand this better, the mechanical behavior of these materials, focusing on fundamental fracture mechanisms, was investigated. The materials appear to generate weak crazes at crack tips combined with a multiplanar step-deflection mechanism for crazing/cracking behavior during the crack propagation stage.
The presence of fibre/matrix interfaces strongly influences the overall mechanical properties of composites. This paper reports investigations on the fabrication process and tensile behaviour of weft-knitted thermoplastic composites by combining micro-braiding and compression moulding techniques. Aramid/Nylon66 (AF/PA66) microbraid yarns (MB) were produced using a tubular braiding machine and these MB yarns were subsequently used to produce weft-knitted fabrics having 1×1 rib architecture. Three types of MB hybrid knitted composites were fabricated and tensile test was conducted to evaluate tensile properties. Properties were also compared with those of the Aramid/Epoxy and Aramid/Nylon filmstacked knitted composites. Cross-sectional observations on the selected AF/PA66 MB hybrid knitted specimens by optical microscopy have confirmed that moulding condition at 290°C under 2 MPa for 20 minutes was ideal for achieving better matrix fusion and improved state of resin impregnation. The overall changes in the mechanical properties were found to be broadly related to several factors such as, continuity of reinforcing fibres in the knitted preforms, processing techniques and parameters, pre-tensioning prior to consolidation and the fibre/matrix interfacial adhesion.
Improved heat resistance, chemical resistance and mechanical properties have been consistently demanded for ABS polymers to widen its application. To improve heat resistance of ABS several approaches have been taken. From the industrial point of view, one of the most useful approach is to prepare copolymers of poly (?- methylstyrene-co-acrylonirile) (MSAN) or poly (styrene-co-maleimide) (SMI) and to blend with grafted ABS (g-ABS).In this study, the miscibility and mechanical properties of the MSAN/SMI blends were investigated which contained various kind of styrene copolymers such as a styrene-coacrylonitrile with controlled AN content, styreneco- maleicanhydride and styrene-co-acrylic polymer. The MSAN/SMI blends samples were prepared using a twin screw extruder.Miscibility was investigated from Dynamic mechanical thermal analysis (DMTA) and differential scanning calorimetry (DSC). Mechanical property was investigated by measuring the tensile elongation and impact strength.
Solid-state shear pulverization (SSSP) has been shown to achieve compatibilization of immiscible polymer blends by the in situ formation of block copolymer resulting from coupling of polymer radicals made via low levels chain scission. Here we describe the impacts of microscopic dispersion of a blend prior to SSSP, processing aids (trace levels of polyethylene wax), and various SSSP process parameters on the ability to achieve intimate mixing as well as compatibilization. These studies also reveal that optimization of SSSP of polymer blends can result from focusing on only several of the many SSSP processing variables.
Polymer blends can be obtained from two-phase polymer particles synthesized by seeded emulsion polymerization, whose properties depend on their particle morphology. Here, a mathematical simulator is presented to predict the development of particle morphology during the seeded stage and after the reaction (aging period). Two experimental systems previously reported showing as the only difference the type of initiator used (AIBN or KPS) were simulated, as an example, and an acceptable agreement between predictions and experimental morphologies was obtained.
Polymer blends were prepared with ultrasonic assisted mixing in an internal mixer. The influence of the ultrasonic irradiation time, blend ratio, and rotor speed on the mechanical properties of the polymer blends was carefully examined. The morphology of the polymer blends was examined under scanning electron microscope for domain-size measurements. Also, for confirmation of the mechanical properties, we performed the impact and tensile test. The effect of the ultrasonic irradiation on the polymer blends morphology was investigated. It was observed that the most significant reduction of domain-size occurred at an increase of ultrasonic irradiation time.As a result, mechanical properties of polymer blends prepared by ultrasonic assisted mixing were extraordinarily increased with sonication time compared to the polymer blends prepared by simple mixing. And the important relationship between ultrasonic irradiation time and mechanical properties was revealed.
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Brown, H. L. and Jones, D. H. 2016, May.
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ANTEC 2016 - Indianapolis, Indiana, USA May 23-25, 2016. [On-line].
Society of Plastics Engineers
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