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A Comparative Study of the Melting and Crystallization Behavior for a Metallocene and a Narrow Fraction of Ziegler-Natta Isotactic Polypropylene
A comparative study of the melting and crystallization behavior is carried out between a metallocene type isotactic polypropylene and a narrow fraction of a Ziegler-Natta type with the same average defect content. At any crystallization temperature the melting temperature of the Ziegler fraction is ~ 3.5 °C higher than the metallocene. This difference is associated with the thicker lamellae thicknesses found in the fraction. The lamellae thicknesses were obtained by AFM, TEM and SAXS and good agreement was obtained between these techniques. The difference in thicknesses is interpreted as a consequence of a sustained heterogeneity of the intermolecular defect composition distribution in the Ziegler fraction even after fractionation. A second source for this difference could be a different partitioning of the defects present in the metallocene and in the fraction between the crystalline and the non crystalline phases. The product of the interfacial free energies obtained from nucleation theory, is very similar for both isotactic polypropylenes.
Processability and Mechanical Properties of Metallocenic s-PP/Conventional i-PP Blends
Polypropylene with especial properties can be obtained by metallocenic catalysts, which represented the beginning of a new era in the polyolefins technology. In this context, some properties and principally some applications of sindyotatic polypropylene (s-PP) have not been well investigated. In this work, the influence of the metallocenic s-PP addition on the processability and on the mechanical properties of isotatic polypropylene (i-PP) was evaluated. It was observed that an increasing addition of s-PP promoted better processabilility, with an increasing in the impact strength. It was also verified a decreasing in the crystallinity of the blends, resulting in a decreasing in the stress at yield and module.
Interfacial Tensions in Polyolefin Blends
The interfacial tension between immiscible polymers is difficult to measure due to the high viscosity of molten polymers. Additionally, the lack of optical contrast that exists between two molten polyolefins renders conventional optical methods impractical. Small-amplitude oscillatory shear flow provides an indirect technique for measuring the interfacial stress between immiscible polyolefin binary blends. Based on the model of Palierne, the interfacial contribution to the measured rheological response is governed by the ratio of the interfacial tension to the average radius of the dispersed droplets. In this work we have investigated the use of amplitude oscillatory shear measurements to determine the interfacial tension in binary blends of immiscible polyolefins. The two-dimensional droplet morphology in each blend was characterized using tapping-phase AFM. True dispersion phase radii were obtained after converting the measured two-dimensional size distributions to three-dimensional size distributions through the linear transformation method of Schwartz-Saltykov. Results of measured interfacial tensions in various polyolefin blends are reported. The interfacial tension of a PP/EP blend thus obtained was in agreement with the value calculated from the SANS measurement.
Rheological Properties of in situ Organic Composites
A study to evaluate the rheological properties of organic in situ short polymer fibres (poly(butylene terephtalate) (PBT))/high density polyethylene (HDPE) and high density polyethylene/poly(ethylene-co-vinyl acetate) (HDPE/EVA9) composites has been carried out. The in situ compatibilization of the HDPE/EVA9/PBT systems with the Bu2SnO catalyst was performed. The different systems were melt blended in a twin screw extruder, drawn at the die exit and cooled. The results indicate that it is possible to produce such composites using reactive extrusion for compatibilization and post extrusion drawing to control the aspect ratio of the PBT fibres. Morphological analysis allowed evaluation of parameters such as draw ratio, PBT concentration and compatibilization on the size and shape of the fibrils. Their influence on the solid rheological behaviour is discussed.
Anisotropic Properties of Injection-Molded Short-Fiber Thermoplastics
As plastics are reinforced with short fibers to increase stiffness and strength and to reduce shrinkage and thermal expansion, fiber motion controlled by the developing flow field during molding leads to a layered microstructure characterized by different fiber orientations through the thickness. The anisotropy of material properties is determined by the fiber orientation and the thickness of each layer which depends on the gating configuration, the part geometry, the rheological properties, and the processing conditions. In this paper we report the directional elastic properties in plaques injection molded with glass fiber reinforced polycarbonate (PC), polybutyleneterephthalate (PBT), and polyamide (PA). Anisotropy plus fiber content and length strongly govern the thermomechanical properties of fiber-reinforced products, which are essential for performing CAE analyses of short-fiber-filled parts.
Effect of Disperse Phase Structure on the Optical Properties of Multicomponent PP Blends
Shipments of plastic packaging materials have strongly increased in recent years. A major reason for the rapid growth of plastics is the versatility of these materials. Blending is a powerful method to create materials with enhanced properties at competitive costs. PP based blends are very promising in these area. This work presents results obtained for ternary blends of polypropylene, linear low-density polyethylene and different ethylene-propylene rubbers. The effect of elastomer viscosity and co-monomer content, blend composition on the phase morphology and optical properties were studied. The particle size distribution of the dispersed phase was studied by TEM. The crystalline structure of the PP matrix was analyzed by DSC and WAXS. Transparency was studied by measuring the light transmitted through specimens of blends placed between polarizers.
Incidence of the Stereoregularity on the Crystalline Modifications of Isotactic Polypropylenes Synthesized with Metallocene Catalysts
Polypropylene metallocene technology has been growing very fast in the last years. Polypropylene produced in this way is expected to provide competitive properties over the conventional Ziegler-Natta products. This work shows the effect of the regioirregularities content of metallocene based Polypropylene on the % ?-modification of samples isothermally crystallized at different temperatures. The regioirregularities content was determined by 13CNMR and the molecular weights by SEC. The proportion of the different crystalline modifications was determined by WAXS. The thermal behavior of the isothermally crystallized samples was analyzed by DSC. Supermolecular morphologies were observed by Polarized Light Microscopy.
The Use of Benchmarking as a Design Tool
Benchmarking can be used as a design tool during product development. When used as a design aid, benchmarking reduces costs, increases design reliability, limits liability exposure, and reduces time to market. Benchmarking, typically delegated to a quality function, when integrated into development, reduces design time and cost. Benchmarking is used to establish product critical, major and minor characteristics, and allows design comparison to competitive products. The best of the best" elements from products can be incorporated into the design thus avoiding any mistakes made during the first generation and by competitors in subsequent product. Likewise "worst of the worst" elements can be avoided in new and next generation products thus gaining time money and more profit for the manufacturing sector."
Development of Impact Modified Engineering Polyester Resins for Automotive Applications
Polyethylene terephthalate (PET) has been successfully used as a fiber, packaging and film material for many years. PET compounds have also been used successfully for injection molding. The use of engineering thermoplastics in the automotive industry continues to expand. A current trend is to replace traditional body panel materials such as metal and SMC with engineering thermoplastics that can be injection molded. The use of the injection molding process to make body panels can save manufacturing time and reduce labor cost. The part made from engineering thermoplastics has to meet the same stringent requirements as traditional materials, including strength, toughness, dimensional stability, weather resistance, and chemical resistance. Recently, Ticona has worked with automotive companies to develop impact modified and reinforced engineering polyester resins to meet these requirements. An early developmental product, Impet® EKX-182, was successfully used in molding the structural body of Chrysler's Composite Concept Vehicle. This material has a good balance of strength and toughness, heat resistance, weatherability and cost effectiveness. Additional application opportunities led to the development of Impet® EKX-215 which has improved strength and toughness. Recently, we have developed a higher modulus, high impact strength material, Impet® EKX-221. In this presentation, we will review the development of these PET based engineering resins. Structure property relationships will also be discussed.
Energy Absorption in Foam Filled Glass Fiber Reinforced Plastic Sections with Light Metal Reinforcement
The automobile industry is seeing an increased need for the application of plastics and their derivatives in various forms such as fiber reinforced plastics, in the design and manufacture of various automotive structural components, to reduce weight, cost and improve fuel efficiency. A lot of effort is being directed at the development of structural plastics, to meet specific automotive requirements such as stiffness, safety management, strength, durability, environmental standards and recyclability. This paper presents the effect of foam filling on the energy absorption during impact, of typical automotive body sections made up of fiber reinforced thermoplastic material with or without metallic reinforcements. In particular the study compares energy absorption characteristics during impact of typical automotive sections made of fiber reinforced thermoplastic materials without foam filling, with foam filling, with foam and some light metallic reinforcements. An attempt is also made to present results on such energy absorption at varying temperature conditions such as low temperature, ambient and elevated temperatures. In all cases it is found that the inclusion of foam and some lightweight material reinforcement enhances not only the structural integrity of fiber reinforced plastic sections but also improves significantly the energy absorption of such material systems under impact.
The Role of Interfacial Slip in Melt Rheology of Immiscible Polymer Blends
A number of researchers have reported an anomalous lowering of viscosity in immiscible polymer blends. Slip at the interfaces between the polymers has been proposed to explain these observations. Because of the complex morphology developed in melt blends it is difficult to test the slip hypothesis. However, using layer multiplication dies in coextrusion, two or more polymers can be alternatively combined into hundreds or even thousands of continuous layers generating a large amount of well-defined interfacial area. Polypropylene (PP) and polystyrene (PS) with closely matched viscosity were blended in a twin screw extruder and also coextruded into 2, 32, 128 alternating layers. The steady shear and dynamic shear viscosity of the blends was first measured in a capillary rheometer and a rotational shear rheometer using parallel plates geometry. While the steady shear viscosity of the blends was lower than that of both homopolymers, the dynamic shear viscosity of the blends was the same as that of the homopolymers. The pressure drop of the coextruded multilayer melts through a slit die was lower than that of both homopolymers and decreased with an increase in the number of layers. From these results an interfacial slip viscosity was estimated. Addition of diblock copolymer was able to suppress interfacial slip.
Polyamides 4.10 and 4.12: Potentially New Engineering Plastics
The 1,4-diaminobutane based polyamides 4.8, 4.10 and 4.12 were synthesized and characterized. For comparison, some 1,6-diaminohexane based counterparts were studied as well. PA 4.12, and in particular PA 4.10, proved to have a very beneficial combination of high Tm, high crystallization rate and excellent physical properties, like a relatively low moisture absorption and accordingly good mechanical properties after conditioning. Further, PA 4.12 proved to exhibit an excellent zinkchloride resistance. First indications were obtained, that for aliphatic polyamide isomers, containing 16 carbon atoms in the repeating unit, the melting points are related to the number of ways to make an energetically favourable chain fold upon crystallization: isomers having two possible ways of chain folding have Tm's which are 13-15 °C lower than isomers having only one possible way of chain folding upon crystallization.
The Challenges Facing CAE of Injection Molding as We Enter the Next Millennium
By the end of the 1980s, everyone interested in injection molding had read of the wonders of flow analysis, and of its fabulous capabilities. Since then, nearly everyone engaged in molding projects is likely to have had at least some degree of involvement in one or more applications of molding analysis. As we enter the next millenium, the utility of these techniques is generally accepted. However, the application of CAE technology in the molding industry is still confined to only a small fraction of molding projects. This paper examines the challenges that need to be met to expand CAE of Injection Molding to its full potential in the 22nd century.
Intermittent Extrusion Blow Molding Using a Reciprocating Screw
The intermittent type of extrusion blow molding is different from continuous blow molding in that it is not a continuous cycle. An intermittent blow molder can be very useful when processing plastics that have a low melt strength, like Polycarbonate. This project began with the donation of a partially finished prototype of a continuous blow molder. This blow molder will use a reciprocating screw injection unit that had been donated. The hydraulic pumps, the clamping system and the frame are still part of the design. This paper will discuss the design and construction of this intermittent extrusion blow molder that will be used in the Penn State University's plastics processing lab in Erie, Pennsylvania.
Sequential Valve Gating for Thin Wall Injection Molding Comparison between Experimental Results and Filling Software
The objective of this study was to investigate the sequential and concurrent filling patterns of a U-shaped thin walled cavity and to evaluate the weld line location, shifting of weld line location and retention of weld line strength. The experimental results were also compared with the predicted results obtained from a computer filling simulation software. The opening of the gates was sequenced to achieve the desired fill pattern, thereby eliminating hesitation effects which cause the flow front freeze-off and also to control the wall thickness to flow length ratio. The paper discusses the effect of critical processing parameters that affect the shifting of weld line location such as, fill pressure, fill time and gate opening-closing time.
Self-Assembly of Chromophoric Arrays on Conducting Polymers
The study of self-assembled mono- and multilayers has advanced rapidly in recent years. One promising area that has received little attention to date is the assembly of molecular devices" on the surface of electrically conducting polymers. We previously developed an effective coating procedure for attachment of various alkane thiols to the surface of thin films of polyaniline polypyrrole polythiophene and poly(ethylenedioxy-thiophene) which were electrochemically grown on indium-tin oxide-coated (ITO) glass plates. Similarly alkane thiols that are derivatized at the terminal end with a porphyrin also assemble on polymer surfaces. The use of porphyrins containing an acetylene "handle" trans to the thiol enables the sequential attachment of additional porphyrin units leading to oligomeric arrays. Similar arrays can be constructed on polystyrene resins. This is useful for preparing larger quantities of the oligomers for characterization and for optimizing the solid-phase reaction parameters. If necessary chromophores can be assembled on the polystyrene resins and then transferred to other polymers that might be sensitive to some of the reactions used in the synthesis of arrays."
Advances in Modular Tool Design Coupled with the in Mold Process Control of Dynamic Feed Provides Lower Tooling Costs, Shorter Lead Times, High Level Part Quality and Improved Machine Utilization
The concept of modular tooling offers many advantages to the molder. Shorter lead-times on tooling, lower tooling costs, and better operational efficiency are all benefits which can be realized with the modular tooling concept. Complex part geometries often have limited the use and value of modular tooling. With an advanced modular tool design complex geometries requiring slides and lifters can now be successfully produced in modular tools. One of the limitations of modular tooling has also been that of molding differing size and geometry's of parts within the same frame. By incorporating the Dynamic system this is no longer a limitation. Dynamic Feed is a leading edge technology, which provides real time closed loop pressure control to each cavity independently. Thus Dynamic Feed allows each cavity to have its own injection and pack pressure profile, providing tight dimensional control to each part regardless of the cavity mix. Advanced Modular Tool designs combined with Dynamic Feed carry modular tool molding to the next level of dimensional control and versatility.
Fiberoptic Evanescent Wave Spectroscopy(FEWS) for the Real Time Investigation of Diffusion Processes in Amorphous Polymers: The Use of AgClBr Infrared Fibers for Studying the Penetration of Water & Or
Advanced optical methods have already been used for the investigation of the mechanisms of diffusion in amorphous polymers. In this work Fiber Optic Evanescent Wave Spectroscopy has been used for the real time investigation of diffusion processes in glassy polymers. Unclad AgClBr fibers of diameter 0.9 mm were dip coated by polystyrene layers of thickness 1-30 ?m. The transmission of the fibers in the mid - IR was measured using by a Fourier Transform Infrared (FTIR) spectrometer. The penetration of liquids into these layers gave rise to significant changes in the measured spectrum. These changes were used for diffusion studies in situ. The sensitivity of the method was sufficient for studying the penetration of small concentrations (up to 5 ppm) of organic liquids through polymer layers. It must to be emphasized that the cylindrical symmetry of our fibers render them especially suitable for the diffusion study and allows to obviate the difficulties caused by end effects. Fickian and non-Fickian cases were observed and the mathematical model of the process was proposed.
Investigating the Effect of Coupling Agent on the Structural Properties of Glass Fiber Reinforced HDPE
Plastic lumber used to be a poorly regarded material. In the past decade advances in processing and materials have allowed plastic lumber to become a competitive material in the construction industry.1 This study evaluates the effectiveness of three coupling agents on the properties of glass fiber filled HDPE lumber. The coupling agents to be studied are titanate, zirconate and silane. Test samples will be manufactured from compounds that utilize various concentrations of coupling agent. They will be tested for flexural and tensile modulus and impact strength. The results will be compared to data gathered from samples made with the industry standard silane loading and sample with no coupling agent.
Building Soft Tooling Molds Using Rapid Prototyping and Different Methods of Construction in a University Environment
The objective of this investigation is to determine an optimal and efficient method of building soft tooling molds for injection molding in a university environment. The procedure for this investigation will involve using rapid prototype models and different methods of construction. Because the soft tooling will be intended for universal use between multiple university injection molding machines, the molds will be designed for direct use with a small machine or as a cavity for a large insert mold. Each construction method will be evaluated on multiple properties, such as cost, production time, surface finish, quantity of parts, and thermal conductivity.
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