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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Analytical Methodologies Employed in a Comprehensive FDA Food Contact Compliance Investigation: Analyses for Residual Monomers, Resin Oligomers, Additives and Modifiers in Several Food Simulating Solv
FDA mandates and product stewardship concerns have given rise to challenging analytical problems. This is evident when considering the potential migration of constituents of a polymer formulation intended for food contact applications. Residual monomers, resin oligomers, additives and modifiers must all be considered in the evaluation of potential human health impact. In this paper we present a series of analytical methodologies that address these concerns. Liquid and gas chromatography and mass spectroscopy are used to quantitate the migration of a number of representative compounds from polymeric formulations intended for food contact applications.
Effect of Layered Silicates on Thermal Characteristics of Polycarbonate Nanocomposites
Differential Scanning Calorimetry (DSC) and Thermo-Gravimetric Analysis (TGA) were used to investigate the thermal properties of polycarbonate (PC)-layered silicate nanocomposites. The type of clays used in this study include phosphonium exchanged montmorillonites as well as synthetic clays which contained C18-alkyl side chains with or without additional tethering amino- or epoxy-groups. Effects of clay contents on the glass transition temperature (Tg) and thermal stability of PC were determined. DSC results indicated that synthetic clays had little effect on the Tg of PC; however, a very slight decrease in Tg was noted in those nanocomposites filled with phosphonium exchanged montmorillonites compared to that of the pure PC. In addition to Tg, an endotherm at about 50°C was also evident in DSC obtained for the synthetic clay filled nanocomposites. TGA results revealed that the presence of synthetic clays caused a significant reduction in the thermal stability of PC. Nanocomposites filled with 7.5 and 10 % of C18-synthetic clay also exhibited a two-step thermal degradation. The second step occurred at a temperature slightly higher than the onset degradation temperature observed in pure PC. Phosphonium exchanged montmorillonites provided better thermal stability for PC than the synthetic clays; a slight increase in the onset temperature of thermal degradation over that of the pure PC was evidenced.
Mechanical Performance of Polyamides with Influence of Moisture and Temperature-Accurate Evaluation and Better Understanding
The wide use of thermoplastics has put higher demands on designers to conduct more accurate and increasingly sophisticated analysis of materials in order to ensure the performance of the molded parts under the end-use conditions characterized by varying humidity, temperature, and dynamic load or deformation. One of the key aspects in thermoplastic analysis is to apply correct material property parameters obtained using standard testing procedures and under end-use conditions. Previously we reported to SPE (AnTec'97, AnTec'98, and RETEC/ASTM'99) the short- and long-term mechanical properties of polyamides (nylon) with time and temperature effects under dry-as-molded conditions. The current paper focuses on the two of the most influential factors on polyamides' properties and performance - moisture and temperature. The tensile properties of conditioned polyamides were obtained from -40°C to 150°C, and the moisture content in the sample was examined immediately after test to ensure that the change in material properties is accurately reflected. The results provided critical understanding on the impact of moisture and temperature on polyamides strength and ductility. The findings in this investigation will enable engineers and product developers to successfully design and evaluate the performance of injection molded nylon parts under end-use conditions.
Defect Analysis and High Density Polyethylene Pipe Durability
Engineering thermoplastics, in particular polyolefins such as special grades of high density polyethylene, are gaining importance in high pressure pipe applications such as gas and water supply systems. To ensure proper performance of such pipes over the required lifetime, durability analyses are needed to adequately account for the effects of loading, time, temperature, and especially the occurrence of defect particles in the pipe, such as gel particles, contaminants, process residues etc. The objectives of this work are to characterize the defect particles in HDPE pipes, examine their origins, and correlate with the long-term performance of pipes. The results indicate that the lifetime of these pipes under hydrostatic test conditions may be more sensitive to the rigidity and interfacial adhesion of defect particles than purely the size of defect particles.
Automatic Cooling Channels Layout of Straight Cooling Pipes in Injection Molding
This paper deals with method of automatically arranging cooling channels, which are composed of linear-shaped cooling pipes, in an injection mold. For this study, an autonomous design methodology to automatically arrange curved cooling pipes was suggested and its efficacy was confirmed. This method will be expanded in this paper so as to be applied to a cooling channel with a combination of straight cooling pipes. Then, the method will be examined through a series of numerical experiments. In this study, straight cooling pipes are expressed by arranging in a straight line, lengthwise, a plural number of heat-absorbing elements. A cooling channel is composed of a combination of those pipes. To achieve the desired temperature distribution on the mold cavity surface, the arrangement of the cooling channel is searched through autonomous movement of cooling pipes. This movement will be achieved through translational motion, and expansion/contraction to satisfy the two constraints, the straight shape of cooling pipes and the maintenance of their interconnected relationship.
Modelling of Bubble Formation in Rotational Molding
Polymer sintering and heat transfer are fundamental phenomena in rotational molding. In the heating stage of the molding cycle, the powder particles melt, adhere to each other and sinter. During this stage, pockets of air are entrapped between the particles and form bubbles. This work aims at determining the relative effects of material properties and molding temperature on the initial sintering and bubble formation in rotational molding. The molding temperature varies strongly with the oven temperature and molded part thickness, and is determined using a lumped parameters heat transfer model (Gogos et al., 1998). The initial sintering of powder is predicted using a two-particle sintering model (Pokluda et al, 1997). The sintering model is used together with the heat transfer model to predict the level of sintering reached when an additional powder layer adheres to the melt and thus entraps air pockets which in turn will form bubbles. Results show that the initial size of the bubbles formed does not vary significantly when changing molding conditions. The polymer rheological properties seem to dominate the bubble formation process. Further results will be compared with experimental work.
A Study of the Deterioration in the Mechanical Performance of Polymers Used in Multilayer Fuel Lines with Immersion in a Standard Automotive Test Fuel
Many multilayer fuel line structures are currently being developed for use in fuel handling systems in an effort to comply with pending legislation regarding reduced vapor emissions. This study examines the changes in the mechanical properties and glass transition temperatures (Tg) of the polymers used in multilayer tubes such as conductive Nylons, barrier layer materials including Fluoropolymers, and tie layers with immersion in the standard test fuel Fuel C at 25°C. The changes in Tg, percentage mass uptake, swelling, mechanical properties such as tensile, flexural and impact were determined for different immersion times. The results show that a significant deterioration in the mechanical performance of many of these polymers was recorded. A corresponding decrease in Tg with increasing immersion time in the test fuel was observed.
Pressure Build-Up in a Staggered Pin Compounding System
Pultrusion compounding is a widely used technique for mixing polymer with continuous reinforcement. It often involves pulling glass roving over staggered pins immersed in a pool of liquid polymer. This causes polymer pressure to build-up in a wedge-shaped region located between the roving and pin. This pressure drives polymer into the roving. To study this pressure build-up, roving was pulled over an instrumented pin placed in a silicon oil pool. A hole in the pin allows pressure to be measured at various locations in the wedge as a function of pulling speed, oil viscosity, and inlet tension. These parameters are lumped together with the roving width to form a dimensionless group called the lubrication number. Initial studies using impermeable tape showed that for lubrication values above 0.0001, the maximum pressure was equal to its theoretical value of tension divided by the product of tape width and pin radius. For permeable roving the maximum pressure was significantly less than that value. Models for pulling force as a function of process parameters have also been developed and validated.
Optimizing Welding Temperature of Semi-Crystalline Thermoplastics-Memory Effects of Nylon
Previously we reported*1 to SPE'99 on the basic principles for optimization of the vibration welding process and presented an analysis of the weld-melt temperature kinetics for linear vibration welding. For this investigation we used the advanced Thermovision 900® infrared measurement system*2 for comprehensive, real-time analysis and thermal imaging. Under optimized processing conditions for vibration (linear and orbital) and hot-plate welding technologies, the tensile strength of welded nylon 6 butt joints is equal to or 14% higher than the tensile strength of the base polymer (matrix). For optimized vibration welding conditions, the maximum temperatures of the weld-melt (in inter-phase) were significantly above (85 - 90 °C) the melt point of the welded nylon 6 and nylon 66 (Tm = 223 °C and 261 °C, respectively). For PP based plastics, J. Vetter and G. W. Ehrenstein observed*3 an increase in the maximum temperature in the weld-melt / in weld inter-phase of not more than 10 °C above the melting point ( Tmp ). In their report to SPE'99, the authors discussed the results of the physical modeling for semi-crystalline HDPE, showing the values of maximum temperatures in the weld inter-phase above 250 °C compared to melting point (Tmp = 126 °C). Ch. Bonten presented*4 to SPE'99 his analysis on the mechanisms active in weld interface of semi-crystalline thermoplastics (HDPE and cross-linked polyethylene PE-X). Mechanical performance of welded joints was affected by crystallization across the boundary layer and weld-melt temperature kinetics (above melting point Tmp). For a better understanding of the role and influence of the temperature of the melt (in injection molding) and weld-melt (in welding) on mechanical performance of semi-crystalline molded (welded) thermoplastics, we performed a comparative study for nylon 6 and nylon 66 (non-filled and fiber-glass reinforced) plastics. Mechanical performance of injection molded and welded nylon was evaluated using static (tens
Thermoforming Simulation and Experimental Validation on a Bass Boat Hull
An integrated thermoforming simulation of a HDPE bass boat hull was performed. The part is fabricated by Pelican International. The sheet heating, forming and cooling stages were sequentially analysed in order to predict the sheet sag and temperature as well as the final part wall thickness distribution. Sheet heating includes radiation from the oven banks combined with air convection. The viscoelastic deformation of the polymer under gravity load was modelled in order to predict sheet sag in the oven. The effect of the sheet sag, for a long part (3 m), on the sheet deformation during the forming stage could then be predicted. The part thickness was measured with a magnetic sensor. These experimental values were then compared with the prediction. Good agreement between predicted and measured wall thickness distribution was found.
Engine Cooling Performance Optimization Using a CFD Guided Design Modification of a Centrifugal Plastic Fan
Large scale computational fluid dynamics (CFD) models, typically consisting of 100 thousands of cells, are used in the design process of plastic components. Readily available hardware and software have made it possible to simulate a system as a whole and determine the contribution and effect of each component onto the overall performance. The CFD tools are used primarily to guide making modifications to achieve better performance and to execute smarter validation test, thus eliminating unnecessary preliminary models. This paper presents a CFD guided case study on performance optimization, conducted on a centrifugal fan used in the cooling of a tractor engine.
Application of Internet and Web Technologies for Management of Molding Know-How
This paper presents the latest development of a Web-based Knowledge Management System (KMS) for injection molding. This system is aimed at helping any knowledge-intensive organization in the molding industry to create, capture, manage, and share engineering data and know-how related to plastics part design and manufacturing (Molding Intelligence"). The KMS is implemented within the framework of the Internet and Web technologies to facilitate ease of use global and instant information access and dissemination and collaboration among geographically dispersed team members."
Blow and Injection Molding Process Set-Ups Play a Key Role in Stress Crack Resistance for PET Bottles for Carbonated Beverages
This paper discusses the role of injection and blow molding set-up in reducing the bottles' vulnerability to stress cracking; an aspect often ignored in traditional training on stress crack prevention. Case studies, involving process optimization for stress crack resistance, illustrate typical key process variables affecting stress cracking including interactions with injection molding variables. Examples show how to strike a balance between the demands of stress cracking performance and performance of other key areas. It comments on the relationship between stress crack resistance and properties such as material distribution and base clearance (the gap between the injection gate and the bottom of the bottle).
Understanding the Effects of Weathering Variables on Plastics Using Fractional Factorial Experiments
Sophistication of experimental designs for weathering research testing continues to evolve. The majority of current weathering experiments utilize simple designs which change few variables at a time. These types of weathering experiments require more trials and result in more cost and less information than approaches using Fractional Factorials." Conducting "Fractional Factorial" experiments before using traditional approaches focuses weathering research on the significant and important variables effecting material performance. This paper presents a methodology for applying "Screening Fractional Factorial" approaches to material performance research. This paper includes a case study and examples of weathering data."
Edge Effects in Film Casting of Molten Polymers
In most analyses of the film casting process, edge effects such as necking in and edge beading are usually neglected. In this work, we investigated the significance of these effects and their dependence on the rheological properties of the melts, the draw ratio, and the extrusion rate. Two linear low-density polyethylene melts and a low-density polyethylene melt were considered. The rheological behaviors of these melts were characterized under shear and elongational flows. Streamlines from the die exit to the chill roll, velocity profiles, film tension, neck-in profiles, thickness profile of the solidified film, and edge bead thickness profile were examined.
Solution of Inverse Thermoforming Problems Using Finite Element Simulation
Finite element simulation of thermoforming can provide highly accurate predictions of final part thickness. The majority of these simulations have been for isothermal situations. Similar calculations can also be performed for non-isothermal processing conditions, provided suitable temperature dependent material properties are available for the polymer of interest. For these simulations, it is assumed that the initial sheet temperature is known and does not change significantly during forming. In this paper sample results are presented for the so-called inverse thermoforming problem, where an initial temperature distribution is sought that will result in a specific final thickness distribution. Thus, a finite element simulation is combined with an iterative algorithm to obtain inverse solutions for a simple axisymmetric thermoformed part. In this example, the required initial temperature distributions that result in a uniform final thickness, are determined for a deeply drawn part. It is shown that the calculated results are quite sensitive to perturbations in the specified initial temperature profile and thus the practical application of optimal temperature distributions may require high precision thermal sensors and controls.
Analysis of Adhesive Properties of Different Engineering Thermoplastics to Elastomers by a Two-Shot Injection Molding Process
The objective of this research was to study the adhesion between a core (hard) material and skin (soft) material mainly used for the interior applications in automotive industry, using the two-shot injection molding process. Two different groups of materials were tested for the adhesive bond strength. In the first group, filled polypropylene (PP) and two thermoplastic polyolefins (TPO) were tested with two thermoplastic elastomers (TPE). In the second group, polycarbonate (PC), acrylonitrile butadiene styrene (ABS), and PC+ABS alloy were tested with thermoplastic polyurethane (TPU). Since many current applications involve the use of an elastomeric material as a skin material for a hard material, this research will provide some guideline for materials to be used, part design, process parameters, adhesive joint design, and post conditioning.
Kinetic Welding of Plastic Parts
Typical consumer products cannot be produced as a single part. Most items require the manufacturing of multiple parts followed by an assembly procedure. Assembly methods vary depending on the nature of the parts and their end uses. Typical assembly methods utilize bosses with nuts and bolts, snap fits, ultrasonic or spin welding and press fits. This report addresses tests undertaken on a variety of plastics, to determine the viability of the patented kinetic weld process invented at Bell Labs, the research and development arm of Lucent Technologies. In order to develop design guidelines for kinetic welding it is necessary to test a wide range of materials with different pin and boss combinations. The first series of tests were performed with welds of three different materials at three different assembly pressures and two geometric configurations. It was found that materials with relatively higher impact strengths tend to perform better than less resilient ones. It was also found that numerical design guidelines were important in optimizing the dimensions of the pin, boss and weld so as to have equalized stress throughout the part.
Ultrasonic Heating and Hardening of Hot Melt Adhesive
The application of hot melt adhesives is based on heating the adhesive from solid state to liquid state for wetting, and cooling back to its solid state to develop cohesive and adhesive strength. Conventional hot melt adhesive application methods use a separate heat source to melt the adhesive and apply it onto one of the substrates. Frequently, the adhesive cools while the second substrate is brought into contact with it resulting in inadequate wetting. With ultrasonic vibration, viscoelastic internal heating of the adhesive is used to melt it and to aid in wetting of the pre-placed hot melt adhesive film on the surfaces of both substrates. In this work, a conventional 40 kHz ultrasonic welder was used to heat a coated hot melt adhesive film in a laminate. The effects of the processing parameters of heating time, vibration amplitude, heating pressure, and hold pressure on bond performance were studied. It was found that the holding pressure plays an important role in sealing and bonding performance. Through the use of ultrasonic vibration it was possible to produce high quality seals in very short cycle times of less than 7 seconds.
Laser Transmission Welding of Semi-Crystalline Thermoplastics-Part I: Optical Characterization of Nylon-Based Plastics
Optimization of welding for thermoplastic parts strongly depends on the material properties, part design, as well as the welding operating technology conditions. Laser transmission welding requires preferential deposition of energy and subsequent melting of the material in the interfacial zone. This is optimized when the laser beam is transmitted through the transparent part and absorbed by the adjoining part to be welded. Energy deposition can be controlled to some extent by adjusting laser parameters (power, choice of beam focussing optics, sweep rate etc.) The thermoplastic material properties may have the greater influence and need to be characterized for optimum material selection. Commercial nylon type materials cover a large array of compositions, which may affect the welding process. To guide selection of nylon based plastics for a range of applications we have measured the influence of specific factors such as fiber-glass, mineral filler, impact modifier content, additives, and color versions on the Near InfraRed (NIR) transmission properties. In a following paper (Part II)a1 we have related these findings to the mechanical performance of shear and butt joints produced under various laser welding technology conditions (laser beam power, welding speed, laser beam/spot diameter, clamp pressure, plastic color, etc.). Comprehensive results of this evaluation will assist designers and technologists in thermoplastics selection for laser welding applications. The purpose of this report is to increase the understanding of the plastics engineering community regarding the usefulness and possible applicability of laser transmission welding (LTW) technology for nylon made components.
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