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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Modeling Polymer Failure under Creep Loading through Simulation of Crack Growth
Plastics used for structural applications are often subjected to creep loading and component lifetime will be limited by crack propagation. A finite element model of crack growth in plastics subjected to creep loading is developed. The model is comprised of a viscoplastic model of the bulk material and a cohesive zone model for tracking crack growth. Model parameters are found by curve fit to experimental data for polyethylene sheet samples. Model predictions for creep behavior and time to failure under creep loading conditions are compared to published data for HDPE. The model predicts the trends observed in the published data.
Processing of Biomass Fillers and Reinforcements at Entitled Capacity on Co-Rotating Twin Screw Extruders
Polymers are increasingly being combined with renewable biomass fillers and reinforcements to improve product performance, reduce cost, reduce product density, improve aesthetics and/or reduce the carbon footprint typically associated with plastics. The use of renewable materials for fillers and reinforcements in plastics has existed for several decades, however, their acceptance is rapidly expanding due to increasing plastics costs and environmental concerns. Unfortunately, a common property most of these materials share - sensitivity to heat and shear, limits their availability to be mass produced in an efficient manner in order to be cost competitive with commodity plastics and thermoplastic composites. However, a better understanding of the physical mechanisms that contribute to the onset of thermal degradation and of the technologies available to prevent such can enable significant capacity enhancements when processing biocomposites using co-rotating twin screw extruders. Another characteristic of many of these materials is that they possess a low bulk density, making them difficult to transport into the extruder at a high throughput. Technologies have recently emerged that can effectively improve the conveying efficiency of “difficult-to-feed” fillers and reinforcements.
Residual Stress Analysis of Compression-Molded Poly(Ether Ether Ketone) Cylindrical Parts
Cylindrical parts were compression-molded using polyetheretherketone (PEEK) fine powder. Post-molding thermal stress relief was executed through systematic variations in time and temperature cycles. Following stress relief, washers were cut from the cylindrical stock shapes and used in the analysis of residual stress. Quantitative determination of the residual stresses along the circumferential direction was carried out based on displacement data obtained by a ring slitting and layer removal method. Thermal and morphological properties of the material were characterized, and their relationship with the residual stress distribution in the material is discussed.
Chemical Resistance of Pigments in a Plastic Substrate
Plastics are used in numerous applications where they come into contact with acids, bases and chlorine containing chemicals, for example common bleach. These include packaging of all sorts, home and garden uses, and building and construction applications, for example. Chromatic pigments used to color these polyolefins may or may not be durable over time depending upon how the chemical penetrates the substrate and how resistant the pigments are to the chemical agent. One application of particular interest is also what colorants can be used in conjunction with recreational pools and pool chemicals. This paper will present data on the color change of pigments exposed in such situations. Emphasis will be on polyolefins, but data from synthetic fiber testing can also be illuminating. An attempt will be made to understand the results on the basis of pigment chemistry, concentration, and particle size.
Understanding Processability of PA11 via Rheology
Polymers are continuously being introduced in applications where metals have been traditionally utilized. For example, PA11 is now being used in the oil and gas industry in underwater flexible pipelines. There are some challenges that are presented when using these nontraditional materials of construction, and likewise, there are interesting challenges that arise during processing. Due to molecular weight growth from shearing and thermal history, the rheological behavior of this resin is a function of time. The molecular weight increase leads to viscosity increase, which reduces sag after extrusion, but hinders flow inside the die. These competing mechanisms must be controlled during processing. This experimental study will help in the understanding of the rheological changes during processing by showing the influence of time, temperature, thermal history and moisture content on the rheology of PA11. Modeling the change in viscosity, which affects production parameters and throughput in extrusion processes, is part of the future work of this study. Beside the temperature-shifting factor, the thermal history and moisture content were identified as playing a critical role in processing tuning. Conventional shear thinning models fail to predict the behavior of this type of material. It is necessary to investigate modeling strategies to assess the appropriate processing conditions of PA11.
High Temperature Flexible PPS Products for Harsh Environments
There has been an increasing interest for high temperature flexible materials for growing market applications, such as deep ocean extraction in oil and gas industry, and under the hood fuel handling in automotive industry. This trend has prompted the search for a material that can operate above 130 °C and often in harsh chemical environment. A series of flexible polyphenylene sulfide (PPS) products were developed to enable high temperature tubing/piping applications in oil & gas and automotive industry. These new flexible PPS materials demonstrated superior heat resistance up to 165 °C and low temperature impact resistance down to -40°C. The flexible PPS materials also showed excellent chemical resistance to fuels, oils and variety of automotive fluids. More importantly, these material can be processed into parts, tubes, pipes, tanks, wires, films and sheets using injection molding, extrusion, blow molding and wire coating.
Thickness Measurement Methods Aiding Lightweighting of PET Bottles
The aim of lightweighting PET bottles is to reduce waste in material use by optimizing the design and manufacture process. Efficient lightweighting development requires adapting robust techniques for thickness measurements. Knowledge of the final thickness distribution at different locations of the bottle is essential for identifying critical locations that could be modified in the preform or mold. X-ray tomography, IR-based thickness measurements, and Hall Effect techniques have been demonstrated as nondestructive tools for thickness measurement. Some methods are slow or expensive. Here, a low cost method for thickness measurement of PET bottles based on cross section measurement also was demonstrated using an optical scanner.
Lightweight Polypropylene-Carbon Nanotube Foams with Low Filler Content, High Permittivity and Low Dielectric Loss for Charge Storage Applications
Microcellular polypropylene-multiwalled carbon nanotube (MWCNT) composites with low filler content exhibiting high dielectric permittivity, and low dielectric loss are reported. Nanocomposites were prepared by melt compounding and foamed using supercritical carbon dioxide in a batch process. The introduction of cellular structure decreased the dielectric loss of the nanocomposites up to five orders of magnitude, while the decrease in dielectric permittivity was only 2-4 times. Thus, microcellular composites containing only ~ 0.34 vol.% MWCNT presented a frequency-independent high dielectric permittivity (~ 30) and very low dielectric loss (~ 0.06). The improvement in dielectric loss was explained in terms of the formation of effective nano-capacitors caused by foaming action (biaxial stretching and uniaxial compression) and volume exclusion. The results of this work reveal that high dielectric nanocomposites can be developed using foaming technologies for charge storage applications.
An Innovative Method to Increase the Charge Storage Capability of Polymer Nanocomposites
Microcellular polypropylene-multiwalled carbon nanotube (PP-MWCNT) composites exhibiting high dielectric permittivity and low dielectric loss at low MWCNT content are reported. Nanocomposites were foamed using N2 in injection molding process. The electrical and dielectric performances of the foamed samples are compared against those of compressionmolded and injection-molded solids. In addition to 35% density reduction, the introduction of cellular structure provided a unique arrangement of MWCNTs around cells favorable to enhancing the dielectric properties. Therefore, foams containing 1.25 vol.% MWCNT presented a dielectric permittivity of ?'=68.3 and a dielectric loss of tan ? =0.05, highly superior to those of the compression-molded (?'=14.1 and tan ?=0.39) and injection-molded (?'=17.8 and tan ?=0.04) solids. The results of this work reveal that high performance dielectric polymer nanocomposites can be developed using foaming technologies for charge storage applications.
One-Step Nanocellular Foaming of Clarified Polypropylene Using Supercritical CO2
Nanocellular foams of clarified isotactic polypropylene (iPP+clarifying agent) were prepared through one-step batch foaming process with supercritical carbon dioxide (CO2). Clarifying agent, Millad NX8000, was used in order to promote cell nucleation. Clarified iPP was prepared using twin-screw microcompounder. Crystallization behavior of iPP and clarified iPP was studied using DSC. Cellular structure of the foam was also characterized. Depending on the foaming condition, foam structure was obtained in both micro and nano scales. Nanocellular foams with the cell size distribution of 33-260 nm and cell density of about 1014 cells/cm3 was achieved by controlling the size of the crystals within iPP. An optimum foaming temperature was found wherein the smallest cell size with highest cell density could be produced.
Morphology and Mechanical Properties of Polylactic Acid/Cellulose Nanofiber Composite Foams
This paper investigates the foaming behaviors of polylactic acid (PLA)/cellulose nanofiber composites and the mechanical properties of the composites and their foams. The composites were fabricated by mixing PLA and nanofibers in a solvent with different fiber contents, followed by drying and hot pressing into test specimens. The composites were then foamed via a batch foaming process with CO2 as a blowing agent at different foaming conditions. The effect of nanofiber content on the cell morphology of PLA was studied. The impact strength and thermo-mechanical properties of PLA composites and their foams were also investigated.
Performance Attributes of Thermoplastic Polyurethane Golf Ball Covers
Injection moldable thermoplastic elastomers (TPE) have been used in golf ball constructions since the 1960s. They provide an attractive combination of performance, processability, and cost when compared to thermoset materials. In particular, ionomer based TPEs are well suited for use in golf ball cover layers as they exhibit attractive properties such as high rebound resilience, good durability, excellent UV stability, and hydrophobicity. However, in multilayer golf ball constructions where the goal is maximum performance, thermoplastic polyurethanes (TPU) are better suited for use as cover materials. In this study, the thermal properties, mechanical properties, dynamic mechanical-thermal properties, and final golf ball performance attributes of a polyether based TPU were characterized and compared to a relevant ionomer based golf ball cover composition.
CPVC Sprinkler Pipe in Contact with Suspected off-Ratio Urethane Foams
This paper discusses failures in a residential fire sprinkler system using CPVC pipe surrounded by sprayed urethane foam insulation. The pipe had multiple circumferential cracks. The external surface had a brown coloration in cracked areas. Chemical analysis showed presence of chemicals in the polymer consistent with components that may have been present in the foam. These chemicals had solubility parameters and boiling temperatures consistent with causation of Environmental Stress Cracking of CPVC. Accelerated exposure of strained CPVC pipe sections to three of these chemicals showed rapid formation of suspected environmental stress cracks.
Feasibility of Double Melting Peak Generation for Expanded Thermoplastic Polyurethane Bead Foams
This study investigated the effects of dissolved CO2 on the crystallization of hard segment (HS) to generate double crystal melting peak for expanded thermoplastic polyurethane (ETPU) bead foam manufacturing. The double crystal melting peak is generated while annealing at elevated temperatures in a autoclave-based ETPU foaming process. The influence of saturation temperature, time, and pressure on the generation of double melting peak structure in TPU was investigated. It was observed that higher saturation temperature assisted in the improvement in the size and perfection of the smaller HS crystals and resulted in formation of double melting peak close to the melting point of TPU. However, the saturation pressure was the most critical parameter to enhance the double melting peak. Furthermore, in the presence of dissolved CO2, the saturation temperature required to generate the double melting peak in the TPU decreased significantly due to the plasticization effect of CO2. The longer saturation time increased the amount of perfected HS crystals with a high melting temperature.
Experiments with Hot Tool Joining of Thermoplastics to Metal
With the requirements for increasing fuel efficiency of automobiles lightening of structures would require joining of dissimilar materials like metals to plastics. In this study, thermoplastics were joined to metal using a heated tool. The metal substrate was textured with a fine knurl pattern and heated for a preset time by pressing it against a hot tool that was kept at a high temperature. Then the metal part and hot plate were retracted, and the cool thermoplastic sheet was pressed against the hot metal surface for a preset time. The hot metal would then melt the thermoplastic surface resulting in flow and wetting and joining of the parts together. Increasing the heating time generally increased the joint strength until an optimum was reached. HDPE to steel joints were slightly stronger and more consistent than HDPE to aluminum joints. For a fixed heating time, the PC and HDPE steel joints were stronger than PP and acrylic to steel joints.
Polypropylene Crystallization in Bulk during an Extrusion Process: Effect of Molecular Weight and Supercritical Carbon Dioxide
Through in-situ visualization, the crystallization behavior of two grades of polypropylene (PP) with medium and high melt flow index was investigated during an extrusion process in the absence and presence of the supercritical carbon dioxide. In all experiments conducted in this study, the crystalline phase (i.e., crystallite) was visualized in the melt during continues process by decreasing the processing temperatures. However, the crystallization onset and the crystallites’ morphologies vary from one condition to another depending on the material molecular weight and the presence of the gas. In the absence of blowing agent, effect of processing conditions (i.e., temperature profile, and flow rate) on the crystallization was studied. It was observed that increasing the flow rate didn’t show any significant changes on the crystallization onset for the lower molecular weight PP. On the other hand, the crystallization onset was shifted to a higher temperature profile for PP with higher molecular weight. The results indicate that the flow-induced crystallization (FIC) is more active in PP with higher molecular weight. In the presence of supercritical CO2, the onset of crystallization was lowered for both PPs studied here mostly due to the CO2 plasticization effect. However, this temperature depression was more pronounced in the higher molecular weight PP than that of lower molecular weight PP, suggesting that carbon dioxide also hinders the effect of FIC.
Metal Replacement with Specialty Thermoplastic Solutions in Heat-Sensitive Automotive Applications
Automotive OEMs are facing immediate and continuous short- and mid-term targets to improve fuel economy. Light-weighting and energy efficiency are key enablers to reach these targets. Light-weighting primarily involves implementing material solutions with an appropriate performance/weight ratio for an application, without compromising quality and costs. Energy efficiency mainly comes from power-train innovations, including electrification of the car, with innovations in electronics (LED, power electronics, alternative energy, etc.) translated to automotive uses. Specialty thermoplastics have a key role to play in this respect. This paper/presentation from PolyOne will describe how thermally conductive thermoplastics can help achieve these targets, specifically in heat-sensitive automotive applications - from the fundamentals of thermal management and the corresponding material properties, to a case study of metal replacement in automotive LED lighting applications.
Importance of Application Representative Sealant Test Methods
Polyethylene (PE) based sealants are an integral part of the food packaging industry. Their use in packaging ranges from simple multi-layer PE film configurations to complex multi-polymer laminate structures. There is a constant drive to develop sealant resins that offer an improved balance of properties in terms of ease of processing, excellent sealant and physical properties. When developing new sealant resins, it is also essential that the performance be characterized by test methods relevant to converters and end-users. This study assesses the sealant performance of various PE resins in the context of molecular architecture, sealant performance test methods, and application specific packaging fabrication conditions.
Simulation of Single Fiber Motion and its Application to Short Fiber Orientation Predictions in Composites Processing
A simulation-based approach is presented to predict the motion of a single fiber or a set of fibers in a viscous fluid with application to short fiber composites processing. This model is developed specifically to reconsider basic assumptions made in Jeffery’s model published in 1922 which forms the basis for nearly all polymer processing fiber orientation prediction today. Our approach computes the velocities in the fluid domain surrounding a fiber, and the fiber motion is determined to zero the forces and torques on the moving fiber. A numerical integration method is then used to determine the fiber’s position and orientation as a function of time. This approach is used to better understand the effect of fiber shape, far-field boundary condition, velocity profile, and neighboring fibers on fiber orientation. Special attention is given to the effect each of these have on recent observations that current fiber orientation models based on Jeffery’s equation tend to over-predict the rate of fiber alignment.
Review of Analytical Models of Anisotropy-Induce Spring Forward Effect via FEA Simulation and an Experimental Study
The increase of residual stresses during the phase change of thermoset fiber-reinforced composites causes unintended situations. A specific situation of interest is the angular distortion in curved fiber-reinforced thermoset parts, also referred to as the spring-forward effect or anisotropy induced curvature change. It has been identified that conventional analytical models deviate from experimental results when changing the part thickness. Therefore, it is of interest to study the effect of thickness variation on the final angle change. Some of these models neglect the effect of phase change in the distortion. This research relates the current scope of analytical and experimental models to predict spring-forward effect. It is necessary to extend the current models to involve the cure time-temperature-diagram (TTT) of thermoset resins.
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