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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Influence of Processing Conditions on Medical Material Degradation/Failures
In the medical packaging and devices industries, products are subjected to numerous converting and other downstream processing steps. For example, a vigorous drying step must be in place to minimize the reverse depolymerizing hydrolysis reaction before melt processing for condensation polymers. Another major downstream process for medical products is the sterilization. For medical devices, ionizing radiation has become increasingly popular. Of course the ionizing radiation which disrupts bio-macromolecular structures in bio-burdens can and frequently does damage polymer chains. In this presentation, we will report on case histories of processing modality and severity and their influence on material degradation and subsequent failures. In addition, situations where control limits can be created on manufacturing procedures can be put in place to prevent (minimize) failures due to processing degradation.
3-D Curing Simulation of Thick Thermoset Components
Thick components or sections such as ribs and bosses require a 3-D simulation to fully determine final properties due to the curing reaction and vitrification effects. A finite element simulation has been developed to model curing of thermoset parts, including compensation for diffusion control effects and varying boundary conditions. For diffusion control, the glass transition temperature (Tg) was related to conversion by the DiBenedetto equation. The simulation considers parts molded under realistic industrial processing conditions and has shown that non-uniform curing and thermal gradients occur during processing. These gradients depend on part geometry, cure kinetics, and processing conditions. This paper presents the models used, along with the results of the simulation applied to a sample geometry molded under various conditions.
Investigation of Rotational Moulding Characteristics and Mechanical Properties of Metallocene Polyethylene
Metallocene grades of polyethylene offer exciting opportunities for the rotational moulding industry. However, as they have only become commercially available in the last few years, their full potential has yet to be exploited. This paper reports on the results of an experimental investigation in which processing conditions are related to the microstructure and mechanical properties of three grades of metallocene polyethylene. The materials have been characterised by dynamic parallel plate rheological tests, NMR spectra and DMTA. The results obtained from equivalent standard grades of polyethylene are used as a basis for comparison. It is shown that the metallocene materials possess many rheological and physical properties that are desirable in rotational moulding. A detailed understanding of the unique nature of these materials is necessary in order to take full advantage of their properties in rotational moulding.
An Assessment of Weld Heterogeneities in PMMA Using Birefringence
This paper concentrates on the measurement of melt orientation of polymer chains and welding residual stress using birefringence. PMMA specimens were welded using four techniques, hot plate welding, laser welding, hot gas welding and ultrasonic welding. Measurements of birefringence made in transverse sections showed that levels of polymer chain orientation and some components of residual stress could be measured. These measurements were used as a basis for the assessment of heterogeneities introduced into PMMA during welding by the four techniques.
Foaming of Thermoplastic Elastomers with Water
We present results on foaming of a thermoplastic elastomer (TPE) using water as the physical blowing agent. The TPE is a blend of polypropylene and fully crosslinked EPDM rubber made by a dynamic vulcanization process. The influence of the blowing agent content, and the processing conditions on foam density, cell nucleation, and foam structure are discussed. A brief discussion about the similarities and the differences between foaming in homopolymers and in TPEs is also included.
Evaluation of Layer Spreading in Coextruded Structures via a Modular Die
Layer spreading in coextruded sheet structures remains a problem solved more often with art than with science. A modular die, i.e. a die with inserts for the entrance channel and for the manifold, was designed and evaluated for a range of entrance shapes, manifold shapes, and resins. The results from these experiments lead to an improved selection process for die designs for coextruded sheet.
Biaxial Test Method for Characterization of Fabric-Film Laminates Used in Scientific Balloons
Space Structures that require light-weight materials with sufficiently high strength and environmental endurance have been in increasing demand since the early 1980's. However, the biaxial behavior of these structural materials under pressurized loading, is rarely found in the literature. An experimental investigation was conducted to develop a test method and hardware to characterize the biaxial behavior of a fabric-film laminate intended for use as a structural envelope for large balloons. The material tested is a composite laminate of three layers. The three layers are: polyester-based woven fabric, 6 microns film of polyester (Mylar type A) and 6 microns film of linear low density polyethylene (LLDPE). The laminate structure provides high strength to weight ratio. In this study, a test technique has been developed to measure the biaxial response of the material to known stress ratios. The information gained from the test can be manipulated to estimate Poisson's ratio and the development of a material structural model.
A Geometry-Based Model for Determining the Filling Time in Resin Transfer Molding Process
A geometry-based model is developed for determining the fill time in resin transfer molding process. In this model, the preforms are assumed to be thin flat with isotropic and orthotropic permeabilities. The in-plane shape of the preform is arbitrary. The location of the vents, the maximum flow length, and the time required to fill the mold are calculated applying analytical solutions. The variety of preforms and processing conditions are used to verify the model. The mold filling time calculated by the model was in good agreement with those obtained using the C-MOLD filling simulation. Saving in the computational time was the key advantage of this model.
A Rapid Method for Prediction of the Vent Locations in Resin Transfer Molding Process
A model is developed for predicting the location of the vents in isotropic RTM molds of various geometries. The preforms may contain holes and/or impermeable inserts. The location of the vents required to avoid trapping air bubbles are determined using neural network and geometric-based solutions. The neural network was trained with data obtained from simulation and actual molding experimentation. For a number of test cases, the performance of the method is compared to the prediction of vent locations obtained using a commercial mold filling simulation. It was found that the proposed method can predict vent locations with a good accuracy as compared to the filling simulation results. Applying the neural networks reduced the amount of computational time in comparison to the simulation methods.
Structure-Property Relationships for Propylene/?-Olefin Copolymers: Effect of Short Branch Length
A single active-site-type catalyst was supported onto silica and used to produce propylene/ a-olefin copolymers with high isotacticity and high molecular weight. The effects of different reaction conditions such as temperature, pressure and hydrogen content on structural properties were investigated. Several comonomers with varying length and bulkiness such as hexene, decene, octene, dodecene, hexadecene, eicosene, and styrene were copolymerized with propylene. With the knowledge of the reactivity ratios and the effect of different reaction parameters on polymer microstructure, copolymers with the same level of comonomer content and similar molecular weight were made with different comonomer types. The produced copolymers were analyzed for their structural and rheological properties using GPC, DSC, CRYSTAF, NMR and RMS. Thus, the isolated effects of comonomer type (length and bulkiness) on structural and rheological properties were studied and correlated.
Morphology Control of Ternary Polymer Blends Using Interfacial Tension
Morphological studies for various ternary polymer blends were performed. The blends were prepared using a Haake batch mixer and analyzed using SEM and TEM. Interfacial tensions and spreading coefficients were used for predicting the blending morphology, and the predicted morphology was compared to the experimental results. The interfacial tensions were calculated from surface tensions at 20°C, and the temperature dependence of the surface tension and a harmonic mean equation were also used. All blending systems chosen in this experimental work were expected to have a minor component (B or C) encapsulated by the second component (C or B) in the matrix (A). It was found that many ternary blends (PC/PMMA/PE, PMMA/SAN/PBT, PBT/SAN/PC, etc) agree with the predicted morphology. However, some blending systems show an opposite encapsulation behavior (SAN/PC/PMMA) or a complex blending behavior (PP/PC/SAN).
New Compatibilizers for Styrenic/Olefinic Blends
Styrenic block copolymers (SBC's) are increasingly being used as compatibilizers (interfacial agents) in polystyrene and polyolefin blends with either virgin and/ or recycled resins. Many technical articles and patents on blends of styrenic and olefinic polymers indicate that styrenic block copolymers and more specifically styrene-butadiene- styrene copolymers function as compatibilizers. This paper reports the effectiveness of new block copolymers to compatibilize styrenics and polyolefins. In addition, a comparison of physical properties of blends using new block copolymers is made to those currently used in the industry.
An Experimental Investigation of the Effect of Polymer Processing Additives (PPA) on the Melting and Gel Formation Mechanisms in a Single Screw Extruder
Much work has been published showing how the addition of a polymer processing aid (PPA) has improved the processing characteristics on the single screw extruder. This paper will give insight on how the PPA affects a single screw extruder. Solids conveying, melting, and melt conveying were experimentally studied to determine how the PPA affected these important processes during extrusion leading to improvements in the melt quality.
Effects of Varying Strand Length on Shielding Properties of Conductive Elastomers in Near-and Far-Field Experiments
A new study examined the effects of varying the strand length of extruded conductive thermoplastic elastomer (TPE) pellets on the shielding efficacy of plaques molded of the material in both near- and far-field experiments. Results indicated that longer strand lengths yielded parts with higher shielding efficacy but at a cost of higher durometer and modulus. Data also indicated that far-field results were consistently higher than near-field values for the same materials and frequencies.
Effects of Processing Conditions on the Failure Mode of an Aliphatic Polyketone Terpolymer
The yield and failure response of an aliphatic polyketone terpolymer subjected to multi-axial stress states has been studied, with a focus on the effects of processing conditions on the failure mode. Testing has been performed on anisotropic hollow cylindrical samples of this semi-crystalline thermoplastic material. Samples were processed under 5 different extrusion conditions. It was found that the cooling rate has some effect on the failure mode, while the rate of extrusion is less significant. Possible processing effects that may account for the differences in behavior include residual stress, amorphous orientation, or crystal morphology.
Toughness Enhancement through Conversion of Cyclic Polybutylene Terephthalate to Linear PBT
The fracture toughness of macrocyclic polybutylene terephthalate (simple ring molecules) and linear PBT is correlated with the size of the plastic zone at the crack tip, which is inversely related to the yield stress. Macrocyclic PBT (c-PBT) molecules have a lower melt viscosity than linear molecules of comparable molecular weight, making them easier to process. However, the cyclic molecules are highly crystalline, with a high yield stress, and consequently a lower toughness. A ten-minute heat treatment in the melt opens the rings, and allows molecular entanglement, causing lower crystallinity of the solid polymer, and increased toughness. Therefore, control of the molecular structure of PBT provides a polymer with low viscosity that can be toughened by an easy heat treatment.
Effects of PP-MMA Alloy and Impact Modification on Weathering Performance of Polypropylene
The weathering performance of polypropylene and a novel polypropylene/acrylic alloy with and without impact modifier was investigated. Accelerated weathering testing was completed using Xenon Arc Weather-ometer. Surface cosmetics (gloss and color change), microscopy, and FTIR were used to characterize the surface and bulk properties after exposure to accelerated weathering. Dramatic improvements in weathering performance were observed through the addition of propylene/acrylic alloys and a proprietary impact modifier to the base polypropylene homopolymer. The individual significance of the propylene/acrylic and the impact modifier on weathering performance were similar. The benefit observed with weathering when combining the propylene/acrylic alloy and proprietary impact modifier was additive with respect to weathering performance.
Prediction of the Weld Lines in Injection Molding Process Using Neural Networks
A model is developed for the prediction of the weld lines in injection molding process. The position of the weld lines in a multigate cavity system, with holes and/or inserts in the part, are predicted using a neural network-based back propagation algorithm. The neural network was trained with data obtained from simulation and actual molding experimentation. For a number of test cases, the performance of the method is investigated on comparing predicted weld lines with those obtained using a complete mold filling simulation. It was found that the proposed method can predict the position of the weld lines with a good accuracy as compared to the filling simulation. Applying the neural networks reduced the amount of computational time and eliminated the pre/post processing time as compared to simulation methods.
The Effects of Mold Filling on Living Hinge Performance
Filling characteristics of polypropylene living hinges and their performance were compared in order to create a model that will predict the quality of living hinges. In this study, three filling characteristics correlated to hinge quality: melt front advancement, skin orientation, and hinge fill time percentage. First, the melt front advancement; should be parallel to the axis of hinge rotation and free from discontinuities. Then, the skin orientation must be perpendicular to the hinge's axis of rotation. Finally, the most critical parameter was the hinge fill time as a percentage of the fill time for the part.
Applications of Gas-Assisted Injection Molding and Injection/Compression Molding in Thinwall Molding
Gas-assisted injection molding (GAIM) and injection/compression molding (ICM) processes are studied and compared with the injection molding (IM) process for thinwall applications (also called thinwall molding). In this paper, analysts for these three processes arc carried out. A cellular phone part will be used as an example. Analysis results will be reported and comparisons of these three processes will be made. Injection pressure, clamp force and deformation will be used to evaluate these processes. Injection pressure and clamp force reduction in the GAIM and ICM processes and their effectiveness in packing will be emphasized.
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