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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Evaluation of the Impact and Tensile Properties of Virgin and Reground Delrin 500 Exposed to Nitric Acid
Izod and tensile testing has been used as a way to evaluate toughness in crystalline thermoplastics like Delrin®. As with many other ways to evaluate polymer properties, reproducibility is sensitive to sample handling, technique, and mechanical factors, as well as the variation in the polymer samples. The Delrin® 500 specimens were evaluated as-molded and then after various treatments. The treatments included exposure to varying nitric acid concentrations through smears on the samples or through complete sample submersion in acid. Reground sample blends were subjected to nitric acid smears while strained. These specimens were held under a 0.5% constant strain with nitric acid exposure for limited time. The Property Retention Index (PRI) format was used to compare the as-molded results to the after treatment results. The PRI was 0.70 for weight loss after submersion in 4.25% nitric acid after 312 hours of exposure. The PRI for the Izod impact was reduced to 0.21 in 4.25% nitric acid after 312 hours of exposure. The PRI never fell below 0.97 for the tensile specimens molded out of regrind. The observed trend in the tensile value is not a simple linear decrease with increasing regrind weight percent.
Evaluation of the Tensile Properties of PET before and after Chemical Exposure
The polyethylene terephthalate (PET) specimens were evaluated as molded and after various treatments. The PET polymers are known to undergo hydrolysis and thought to be sensitive to exposure to acid. The molded specimens were exposed to various chemicals including hydrocarbons, oils and greases and solutions of nitric acid. Chemicals were selected because of an opportunity for them to contact PET parts during assembly or as used in our applications. The molded samples were subjected to exposure for different periods. Exposure effects were monitored using the tensile strength at break data. The comparison of tensile strengths at break was done by using the Property Retention Index (PRI) per ASTM D 5870-95. Materials included: black DuPont™ Rynite® SST 35, black and grey DuPont™ Rynite® 545, and Ticona Celstran® PET GF20-02.
Evaluationof Melting Performance of a Co-Rotating Twin-Screw Extruder
A method is proposed to evaluate the melting performance of a corotating twin-screw extruder. The method involves model experiments whereby the polymer pellets (coated with blue pigment powder) are extruded using a screw configuration that only contains the functional zone (melting zone, kneading section) placed at the down-stream end of the screw. The polymer can flow out almost unrestricted through a large die opening. The extrudate contains a mixture of unmelted pellets in a colored melt: as soon as the polymer starts to melt, it turns blue; the polymer pellets that do not melt remain opaque. The extrudate is chopped off into samples that are cooled down and cut into thin slices, from which the unmelted fraction of polymer can be determined using image analysis. The data serve as a basis for the evaluation of the melting performance of a particular screw configuration.
The Evolution of Direct Extrusion Using High Speed Twin Screw Extruders
Historically, 95%+ of high speed twin screw extruders have been used to perform compounding, devolatilization and reactive extrusion operations with the end product being pellets, where dimensional stability is secondary to the mass transfer operations that occur in the twin screw extruder. Although high speed twin screw extruders have been used for many years to extrude products such as sheet, film, profile or fibers, it is only in the past 5 to 10 years that there has been a concerted development effort to perform direct extrusion from this device. The initial applications that utilized twin screw technology for direct extrusion, versus purchasing a pre-compounded material from a toll compounder for processing on a single screw extruder, were mandated, in desperation, for formulations that were adversely affected by the second heat and shear history inherent with the single screw extrusion step. Once the technical viability of direct extrusion was demonstrated, it became readily apparent to the marketplace that substantial cost savings were also possible using this technology. Additional benefits include the ability to adjust formulations in-line to accelerate development efforts, and to maintain a proprietary in-house manufacturing process. Some of the materials that have benefitted from direct extrusion include, but are not limited to, filled olefins, TPE/TPO/TPV’s, polyesters, PVB, woodfiber composites, adhesives, foamed polymers, nylons and degradable plastics.
Exfoliation of Polypropylene/Clay Nanocomposites under Electric Field
Polypropylene (PP) is known to form an exfoliated structure only when maleic anhydride functionalized polypropylene (MAPP) is added together. This can be easily achieved by melt processing, however, MAPP costs a lot as to prevent its commercial production.In this talk, we will present a novel approach to make exfoliated PP/clay nanocomposites without adding MAPP. PP/clay systems under large electric field do show the exfoliated structure, which is evidenced by rheometer and XRD. As applying electric field is a physical process, similar effect can be expected in other polymer systems that do not show exfoliated structure in a normal condition.
Expandable Foam from Amorphous Polyester Resin
A resilient foam that is both expandable and moldable was prepared from an amorphous polyester resin using a mixed blowing agent of a high-solubility compound and a low-permeability compound. The high-solubility compound permits a high degree of expansion, while the low-permeability compound renders secondary expandability. The polyester foam remedies the deficiencies of existing bead products. Polystyrene beads retain blowing agents but lack resilience. Polyolefin beads are resilient but do not retain blowing agent. The polyester foam board has a low thermal conductivity as well as excellent dynamic cushioning.
Experimental and Numerical Analysis of the Flow Imbalance in a Runner System
The flow of molten polymer in a multi-cavity injection mold is a complex fluid dynamics problem involving temperature- and shear-dependent viscosity and viscous heating. Recent work has shown that cavities are not filled evenly, even in a geometrically balanced runner. We investigated this phenomenon for two polymers (Nylon 6/6 and Acrylic) using the computational fluid dynamics (CFD) program FIDAP (Fluent Inc., Lebanon, NH), and compared the results with experimental measurements in a test mold. The results from the CFD model successfully capture the flow imbalance in the runner system for these polymers. The validated flow model can thus be used as a predictive tool to quickly evaluate the new runner system designs.
Experimental Evaluation of Composite-Concrete Interface Properties Using Sandwich Specimen
The experimental test results on the composite strengthened reinforced concrete beams showed that the failure of composite-concrete interface can originate from an existing concrete tensile crack at the interface. Due to the difference in the properties of the individual materials and due to practical conditions of loading, cracking of the composite-concrete interface involves mixed-mode of fracture effects. Fracture mechanics concept was used to design special types of sandwich specimen, in which a thin layer of composite is sandwiched between two parts of concrete. It is shown that the interface toughness as well as interface failure mode depend on composite type and combination of loading conditions.
Experimental Evaluation of Methods for Characterization of Power Output of High Power Ultrasonic Transducers
This paper reviews the evaluation of different techniques used to characterize the power output of high power ultrasonic transducers. Three laboratory measurement techniques were studied: 1) electrical, 2) calorimetric and 3) mechanical transmission line. The loads were theoretically modeled and their thermal, mechanical, and electrical losses were identified. It was found that the most accurate power measurement was based on multiplication of the measured voltage and current without the use of filters or methods that attempt to differentiate between stored and dissipated energy.
Experimental Studies in Gas-Assist Injection Molding to Investigate Residual Wall Thickness and Gloss Levels
Gas-assist injection molding allows designers the freedom to design plastic products that may be considered outside the realm of conventional injection molding. There are basically two design categories for the gas-assist injection molding technique: rod-shaped parts and panel-shaped parts. Rod-shaped parts have very thick cross-sections and include articles such as handles, armrests and structural components. Panel-shaped parts are large area moldings that utilize ribs with gas channels to improve part stiffness; automotive trim and business machine housings are in this category. This paper studies the residual wall thickness (RWT) of rod-shaped parts and gloss level variations of panel-shaped parts.
An Experimental Study of Antioxidants Effects on the Performance of Blow Molded HDPE Homopolymer Packagaing Containers
This research seeks to address the taste and odor problems that are currently being experienced in blow molded HDPE homopolymer packaging containers. Manufacturers of blow molded packaging containers have been experiencing odor and taste problems in their HDPE homopolymer products with antioxidant additives, especially in the water bottles. The scope of this research will be to determine the optimum idling time and antioxidant levels that will alleviate the taste and odor problems in water bottles. Odor and taste surveys as well as oxidative induction time tests will be used to characterize the performance of the tested blow molded products.
Experimental Study of Gas Penetration in the Gas-Assisted Injection Molding
Extensive studies were conducted to experimentally determine the effects of processing parameters on the gas penetration of the gas-assisted injection molding (GAIM) process. Experiments were performed in the mold having a standard tensile bar cavity with simultaneous measurements of the screw position, gas pressure, and pressures in the runner and cavity. Two Taguchi methods were applied in the study. The first method was used to determine the most important GAIM processing parameters affecting the gas penetration. In this case, various processing parameters, such as: shot size, gas delay and holding time, gas pressure, injection pressure, injection speed, mold and melt temperature were studied. The second method was used to elucidate a more detailed effect of the parameters on the gas penetration.
Experimental Study of LDPE Melting in a Twin Screw Extruder Using On-Line Visualization and Axial Pressure and Temperature Measurements
The melting of polymers in a twin-screw (T/S) extruder is an important operation in many industrial processes. Re-cent research by Shih, Gogos, Geng and others has identified the physical phenomena that take place during the phase transition. This paper describes an experimental study of Low Density Polyethylene (LDPE) melting in a co-rotating, intermeshing T/S extruder using on-line visualization and axial scanning of pressure and temperature techniques. The LDPE melting sequence observed included solid transport in a partially filled screw channel with conductive heating, compaction, pellet deformation, and viscous energy dissipation in the melt with un-melted solids. The effects of throughput (Q) and screw rotational speed (N) are examined. Low and high Q/N ratios have significantly different axial pressure profiles.
Experimental Study of Prepreg Bonded Single-Lap Composite Joint
Neat resin bonded single-lap composite joint has been extensively used in composite structures. Lower strength and longer fabrication time have been identified as technical barriers in practice. In order to increase the joint strength and reduce the fabrication time, two types of prepreg composites were used to bond composite single-lap joints. Test specimens were prepared per ASTM D 3165-95 standard. Accelerated conditioning was conducted to investigate the environmental resistance of specimens. The shear strength of various specimens was obtained using tension tests. Compared to control specimens, prepreg bonded samples exhibit higher tensile strength, higher environmental resistance, and shorter fabrication time.
Experiments and Simulations with Barrier Screws
Experiments were performed using four different industrial sized extruder barrier screws extruding two different polyethylene resins, 0.3 MI LDPE and 1.0 MI LLDPE, at two motor speeds. The data collected from these experiments consist of readings of pressure along the axis of the screw, exiting pressure, melt temperature, and output. The extruder motor load, screw speed and barrel temperature settings were also recorded. Experimental measurements are compared to computer simulation results from a flexible extrusion simulation approach which uses relatively simple models for pumping, heat transfer, and melting functions. The calculations are coupled through an iterative process, and are based on a number of assumptions. Reasonable agreement is found between experimental and predicted melt pressures.
Extensional and Shear Rheology of Reactively Extruded Polyethylenes
In this study, the rheological characterization in extension and in shear of melts of reactively extruded low-density and linear low-density polyethylenes was carried out. The polyethylenes were extruded with peroxide, in one case, and with peroxide and diethylmaleate, in the other, using a co-rotating twin-screw extruder. A capillary rheometer with cylindrical and converging dies was employed to obtain the shear and extensional viscosities at 200 °C. The Cogswell, Binding and Mackay-Astarita models were used to estimate the extensional viscosity of the materials. An increase in both the shear and extensional viscosities was obtained due to the presence of long branches produced by the modification processes.
Extensional Rheology of Polypropylene and its Effect on Foaming of Thermoplastic Elastomers
Extensional viscosity of several polypropylene polymers and their blends was measured and compared to the relative foamability of thermoplastic elastomers (TPEs) containing these polymers. Both linear isotactic polypropylenes and branched polypropylenes were considered for this work. The extensional viscosity is measured using an RME Extensional Rheometer at various strain rates. The TPE foam is characterized based on density and cell size distribution. A small amount of branched polymer substituted for linear polymer was found to lead to improved foamability of the TPE. Results of this study will aid in the understanding of the foaming process in TPEs.
Extruder Output-Pressure Relationships for Power Law Fluids Including Leakage Flow
In order to predict output for screw extruders it is useful to have relationships of output versus pressure for various degrees of shear thinning. These relationships can be determined using numerical techniques and are usually graphically presented in dimensionless form. Various workers have presented such dimensionless graphs.It is well know that leakage flow, the flow between the flight tip and barrel, can significantly affect output and power consumption. A finite difference program was developed that accurately calculates the effect of leakage flow on output and power consumption. When the flight clearance is made dimensionless with respect to the flight height the family of output-pressure- clearance curves can be used for extruders of any diameter; in fact, creating universal output-pressure- clearance curves. This paper will present data of two different size extruders on output vs. pressure and energy efficiency vs. pressure. The utility of the information presented will be demonstrated with actual examples.
Extrusion Blow Mold Simulation Software Verification of Pinch-Off Design Parameters
The design of the pinch-off in extrusion blow mold ing has relied on past experience, company recommendation guidelines, and material supplier guidelines. This experiment was implemented to determine if simulation software could be used effectively to design a functional pinch-off design before any steel is cut. Actual bottle measurements from a Design of Experiment (DOE) (1) were contrasted to the results of the simulation software to determine the accuracy of the simulation. The actual DOE that the software was compared to is a three level DOE. The DOE was used to determine the processing parameters and flash pocket depth that produces the strongest weld line strength. The specimens collected from the DOE were tested for tensile strength and impact strength.
Failure Analysis and Redesign of a Polycarbonate Spring
An integrated approach is advocated for failure prevention of plastic products by optimising: material selection, design, processing and mould construction. The redesign of a plastic spring for a positioning device, using a buckled strip, illustrates this approach.The initial design suffered from mistakes:A low molecular PC was selected for obtaining short cycle times.The transverse deflection of the spring was too high.The mould was not tapered and caused scratches on the surface.Unlocking the positioning device caused very high bending stresses.By combining mechanical engineering, polymer engineering and practical knowledge about mould design and injection moulding, a reliable spring was redesigned.
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