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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The Effects of Nano-Clay on the Rheological Properties of Polylactic Acid
The rheological properties of polylactic acid (PLA) and its nano-composites with 3% and 6% montmorillonite (clay) are investigated using parallel plate rheometry. Frequency sweep experiments are performed at temperatures ranging from 160 to 185 ?. For all of the samples, as expected, both the storage modulus G' and the loss modulus G' decrease with increasing temperature. Master curves of G' and G' are successfully constructed for the neat PLA and its nano-composites, indicating the validity of the time-temperature superposition for these systems. Adding the clay filler increases the G' especially in the long term region as well as the dynamic viscosity, exhibiting reinforcement effects. This is consistent with the discrete relaxation spectra determined based on the dynamic shear data. Long chain modes are present in the composites, presumably coming from the interaction between the clay and the surrounding polymer chains.
Tensile Yield Stress Modeling of PTFE Paste Extrudates: Effect of Processing Conditions
The yield strength of extrudates of a Polytetrafluoroethylene (PTFE), extruded at different temperatures through dies of different reduction ratios, RR?(Db/Dd)2, was studied. The tensile experiments have been performed using the Sentmanat Extensional Rheometer (SER) at different temperatures and Hencky strain rates. The results showed that the yield strength increases with extrusion temperature and die reduction ratio and decreases with tensile temperature. An empirical model has been developed to predict yield stress as a function of processing conditions such as temperature and die reduction ratio, as well as tensile experiment parameters i.e. temperature and Hencky strain rate.
High Performance Inorganic Pigments: Complex Inorganic Colored Pigments
Color is as basic to people as emotions. When we are sad we feel blue, when we’re sick we look green and when we’re mad we are red under the collar. In fact, our use of color predates even modern humans.1 Scientists have discovered that humanities ancestors dispersed pigments with an abalone shell and quartz rock into natural resins to produce paints for body adornment and cave paintingsthe first DIY home improvement projects. Those earliest pigments were natural ochres. In the ongoing centuries we have expanded our palette of pigments to include synthetic pigments and organic chemistry based pigments. A special branch of this pigmentation are the Complex Inorganic Color Pigments (CICP)s.
Complex Inorganic Color Pigments provide highperformance color for the most demanding applications for plastics and polymers. CICPs can stand up to the most challenging and aggressive processing and applications. Recent advances have found that these pigments have properties that give them the ability to address regulatory requirements and give not only color, but also functional properties.
Cellulose Nanocrystals as Reinforcement in Glass Fiber/Epoxy Sheet Molding Compound Composites
Cellulose nanocrystals (CNC) are ideal candidates for reinforcement in polymers and polymer matrix composites due to their high specific modulus, and strength characteristics. In this study CNC are added as a filler in the epoxy resin and a sheet molding compound (SMC) manufacturing line is used to make glass fiber/CNC-epoxy composites. Freeze-dried CNC were first dispersed in the hardener via sonication, then the hardener-CNC suspension was mixed with the monomer to produce the resin for the SMC production. The tensile and flexural properties, the impact strength and the thermo-mechanical properties of the GF/CNCepoxy composites are determined as a function of the CNC content. The content GF content in the composites is determined using thermogravimetric analysis. In conclusion, it is found that there is an optimum CNC content for which there is enhancement of the mechanical properties of the SMC composites.
Mechanism of Cell Nucleation in High-Pressure Foam Injection Molding Followed by Precise Mold-Opening
In the present study, the mechanism of cell nucleation in high-pressure foam injection molding with high expansion was investigated. An in-situ visualization technique was used which enabled the monitoring of the entire process of cellular structure formation from the mold filling to the final nucleation stage. It was observed that the cells which were nucleated during mold filling, the so called gate-nucleated bubbles, remained in the melt/gas mixture after the mold filling stage was completed. These gate-nucleated bubbles led to the presence of large bubbles in the final molded part, which caused a reduction in the foam cell density (number of bubbles per unit volume) and a reduction in the uniformity of the cellular structure. A foam injection molding protocol based on the application of melt packing pressure was then proposed to remove the gate-nucleated bubbles. In this protocol, a high packing pressure is applied on the melt/gas mixture to re-dissolve gate-nucleated bubbles before the mold-opening stage. When the mold opens, new cells nucleate uniformly due to the rapid reduction of pressure. Also, a numerical simulation was performed, and a comparison with the experimental result was made.
Novel Polycarbonate/SEBS-g-MA Blend for FDM-Type 3D Printing
The field of Additive Manufacturing (also known as 3D printing) is growing at an accelerating rate. Currently, 3D printing platforms based on fused deposition modeling (FDM) technology are practically ubiquitous. Relying mainly on mainstream thermoplastics such as acrylonitrile butadiene styrene (ABS), polycarbonate (PC), and polylactic acid (PLA) as feedstock, the applicability of this 3D printing method is limited due to the physical properties of said polymeric materials. The work presented here is an example of the development of a new polymer blend system for FDM –type 3D printing. Here we have created a rubberized PC blend which has physical properties differing from the PC base resin An overview of materials development activities for material extrusion 3D printing based on FDM technology performed at the W.M. Keck Center for 3D Innovation is discussed where we have created several polymer composites and polymer blends with physical properties differing from the state of the art, while maintaining compatibility with commercially available capital equipment.
An Approach to Decomposition of Deformation from a Molding Simulation
In an injection molding simulation of plastic parts, shrinkage and warpage information are of importance. Usually, the total deformation with respect to the baseline design is obtained and shrinkage and warpage are not distinctly defined. In this paper, a methodology is developed to decompose the total deformation obtained from a molding simulation into its shrinkage and warpage components. Mathematical basis for the decomposition is also described. Examples are shown to depict the shrinkage and warpage quantities and verify the methodology. Section analyses are also carried out to quantify the contribution of shrinkage and warpage to the total deformation.
Impact Properties Analysis of Rotationally Molded Polyethylene and Polypropylene for a Wide Range of Temperatures
Rotational molding is an established and growing manufacturing method for large, hollow plastic components. In this work the impact properties of rotationally molded Polyethylene (PE) and Polypropylene (PP) were tested at temperature in the range of -40 ºC to 30 ºC. Dynamic mechanical thermal analysis (DMTA) was performed to analyse the measured impact properties of PP and PE plastics. For PP, a very good relationship was found between peak impact strength and the loss modulus curve obtained in DMTA analysis. A relationship between density, ? peak height and peak impact strength was found for PE which is different from previous findings in the literature. It is concluded that further work should focus on developing an understanding of the PE material’s microstructure in order to more fully understand its impact properties.
Capillary Coextrusion: A New Process for Creating Small-Scale Coextruded Films
Coextrusion is an important method for making barrier and optical products at large scale. In these multilayer polymer films, adhesion is critical for performance, yet is difficult to predict by small scale experiments. Past work has shown vast differences between bilayers produced in coextrusion (continuous process) versus lamination (batch, quiescent process). In this work, a small scale coextruder die is designed and attached to a dual-bore capillary rheometer. Model films are quickly produced for adhesion testing, with adhesion showing a strong dependence on residence time.
Mastering Plasma & Flame Surface Treating Technologies to Improve Adhesion
In-line surface treatment technologies are used in the plastics industry to clean, micro-etch and functionalize surfaces to promote adhesion, improve quality and increase productivity. For some applications surface treatment is a requirement for adhesion success, for others it eliminates the need for expensive & specialty coating formulations, and in all cases it provides a safeguard against materials which may exhibit inconsistent surface energy. Examples are found in the automotive, medical, decorating, marking, assembly, film extruding & converting, folding carton, pipe, cable and other markets where surfaces need assistance in bonding with coatings. This paper will share laboratory trial data on the impact of surface treatment on a variety of materials with results measured in dyne level, polarity and surface free energy. It also addresses adhesion basics, how to select the right technology for your application, and how to implement blown arc air plasma, blown ion air plasma, variable chemistry plasma and high velocity flame plasma treaters for optimum results.
Ionomers as Smart Vapor Barriers for Building Applications
A “smart vapor barrier” is a material whose moisture vapor permeance changes as a function of relative humidity, preferably with the permeance increasing with increasing relative humidity. Sodium ionomers are capable of behaving as smart vapor barriers at suitably high extents of neutralization. This unique property is accentuated even further when the sodium ionomers are modified with fatty acid salts. The smart vapor barrier properties of the ionomers compare favorably to commercially-available polyamide film used for this application (as measured by ASTM E96 Procedure A and B testing). Modified permeance testing at extremely high relative humidities indicates that the permeability advantage of ionomer films over the commercially-available polyamide film is extended even further, which is desired for this application.
Fabrication of Interconnected Porous Poly(Lactic Acid) Scaffolds Based on Dynamic Elongational Flow Procedure, Batch Foaming and Particulate Leaching
This study reports a highly porous interconnected poly(lactic acid) (PLA) scaffold fabrication method, which utilized self-developed vane extruder melt blending followed by supercritical carbon dioxide (Sc-CO2) foaming and particulate leaching. PLA as polymer matrix was blended with polyvinyl alcohol (PVA) and NaCl particles via vane extruder, which generates global dynamic elongational flow. Then, the prepared blends were foamed by Sc-CO2 followed by leaching the porogens. It was found that most NaCl particles could preserve their original size after vane extruder blending and the macropore density and size can be tuned by modifying the salt concentration and particle size. The scaffolds prepared using this approach could achieve a porosity up to 93% with well interconnected porous structure.
Modeling of the Fiber Orientation in Polymer/Fiber Composite Foams
The electrical conductivity of conductive fiber/polymer composites is highly affected by the alignment of the fibers, as well as the fiber-to-fiber distance and contacts. While the formation and growth of gaseous cells result in the translational and rotational displacement of the fibers in foamed conductive polymer composites, the mechanism of the cell/fiber interaction and the effective parameters on the fiber movement is not fully understood. In this research, we propose a geometrical model to predict the behavior of carbon fibers at close vicinity of a growing cell. The predicted results were then validated using experimental data, obtained from the foam injection molding of polystyrene/carbon fiber composites. The model predictions were in good agreement with the experimental observation. The parametric analysis using the model revealed that cell size, and cell-fiber distance greatly influenced the rotational displacements of the fibers around the growing cells. It was also found that the cell growth induces a nonuniform degree of re-orientation on the fibers in its vicinity.
Study on high-performance of WPC
The global environment problem is a very serious problem, especially the global warming issue. In order to prevent this phenomenon continues to deteriorate, WPC (wood plastic composite) can be used as a new kind of composite to solve this problem. However, as an industrial high-quality material, WPC still has a lot of problems at present. For example, WPC material has poor toughness and low izod impact strength. Based on the above two problems, in this study, a lot of research and some new technologies are used to improve the performance of WPC. In order to improve the toughness of WPC, we use wood particles having different lengths to make WPC, through tensile test, it is shows that the shorter length of the particles will lead the better toughness of WPC. On the other hand, surface modification technology is also used as a way to changing the WPC’s toughness. For improving impact strength of WPC, we mix microparticle and dispersant of wood with WPC. For high tensile modulus of WPC, we make the shape of wood likes fiber. Finally, conductivity and incombustibility of WPC have been evaluated in this research.
The Importance of Inflow Conditions on the Simulation of Extrusion of Thermally Sensitve Material
Simulating flow through the simplest components for use in extrusion still requires accurately representing the inflow conditions of that particular component. Due to the many different stages a polymer experiences through the extrusion process, capturing proper inflow conditions still remains a challenge. The goal of this study was to demonstrate the importance of proper setup of inflow conditions and material parameters to detect problematic regions for thermally sensitive materials within a simple symmetric adapter flow channel. The studied showed mimicking the outflow of material from the screws in a counter rotating twin screw extruder is the most significant factor to accomplishing this task. This work used an imbalanced inflow and a helical inflow condition to predict high residence time regions. These factors must be considered carefully when simulating any part of the extrusion process.
Preparation of PPC/PS/PTFE Composites with in-Situ Fibrillated PTFE Nanofibrillar Network and Their Supercritical Carbon Dioxide Extrusion Foaming Properties
In this work, polystyrene (PS) and polytetrafluoroethylene (PTFE) were compounded with poly(propylene carbonate) (PPC) via a triple-screw extruder to prepare multiphase composites that possess special properties and to improve the extrusion foaming ability of PPC. It was found that PS was immiscible with PPC and formed dispersion phase, and PTFE were in-situ fibrillated into nanofibrillar network within PPC/PS matrix. The introduction of rigid PS domains and PTFE nanofibrils showed remarkable effects on the properties of PPC. Compared with neat PPC, PPC/PS/PTFE composites had 1576% higher initial viscosity. Moreover, the physical network formed by PTFE nanofibrils effectively prevented the shear-thinning behavior of the polymer matrix. Significant influence of PTFE on the cell morphology was found in the extrusion foaming process. The cell density of PPC/PS/PTFE foams was four orders of magnitude higher than PPC foams.
Effects of Small Range Color (Pigment) Concentration Levels on Plastic Injection Molded Parts
Color (pigment) concentration levels play a great role in changing the mechanical properties of an injection molded part. Higher concentration levels result in failure during the use of the parts . A general rule of thumb for concentration levels are between 3 to 5% or 5 to 10% is being used across different industries to achieve the required color. The above concentration levels are considered as small range in this manuscript. It is observed during the tensile test conducted on injection molded plastic parts that the small range of concentration levels has an impact on a few mechanical properties including strain at yield and strain at failure. There is no impact on tensile strength, Young's modulus and Poisson's ratio. Hence Product Designers need to assess the impact of these small concentration levels with respect to the base resin and need to specify the acceptable concentration levels in their product drawings or in product specification documents. It is equally important for the molders to verify these concentration levels during molding process.
An Investigation of Real-Time Monitoring of Shear Induced Cavity Filling Imbalances during Polymer Injection Molding
Since the beginning of injection molding industry development, multi-cavity molding has been widely utilized to increase manufacturing efficiency, save time and reduce costs. As a result, geometrically balanced mold cavities and runner systems have become industry standards for injection molding. Some seemingly balanced designs, however, still provide imbalanced cavity filling results. The reason for the imbalanced filling is due to the shearing between the lamellae of the molten polymer as it is injected through the runner system and into the mold cavities. The current investigation includes visual studies of how the shearing of the polymer through the runner systems affects the mold filling in real time. In order to develop a deeper understanding of the shear induced imbalances in injection molding, a custom built mold incorporating transparent mold inserts and runner systems was used. Polymers were injection molded into different types of cavities and the cavity filling was documented in real time via a high-speed camera. With this study, there is a potential to find and/or verify methods to mitigate the non-uniform behavior of molten polymers undergoing shear thinning or shear heating, especially since the imbalances have the potential to alter properties of the finished products.
Dynamic Solubility of Carbon Dioxide in Polypropylene Melt
A testing method has been developed to measure the dynamic solubility of polymer/gas mixtures at high pressures and a wide range of melt temperatures. This method utilizes tandem extruders equipped with a highpressure optical slit cell; a camera; a set of pressure transducers; and a metering valve for back-pressure control. This in-line visualization system provides a direct way to investigate the dynamic solubility within a wide range of processing conditions (i.e, melt pressure, melt temperature, gas content, and flow rate). The measurements were carried out for various amounts of CO2 dissolved into branched polypropylene (PP) melt at two different temperatures. The dynamic solubility was estimated based on the degassing pressure when the second phase starts to nucleate. The experimental results showed that the dynamic solubility of carbon dioxide in PP melt increased with system pressure but decreased with melt temperature. It was also found that a higher flow rate, which corresponds to a higher shear rate, decreased the dynamic solubility of CO2 in branched PP.
Measuring the Interlayer Fracture Resistance of FDM Printed Thermoplastics
With increasing structural and functional applications of 3D printed materials, their mechanical performance is highly demanded. So far, stress- and strain-based experiments have been used to characterize the mechanical properties of fused deposition modeled (FDM) samples. In this work, a fracture-mechanics-based methodology was developed to characterize the interlayer adhesion of FDM 3D printed materials. Double cantilever beam (DCB) specimens were designed and printed with a precrack set at the interface of the layers. The DCB samples were tested in mode I loading and the load displacement curves were obtained. Critical stress intensity factor was found using the DCB loading data coupled with a finite element model. The critical strain energy release rate, Gc was also calculated using the finite element model data and the elastic properties, obtained by the tensile test of FDM 3D printed samples. The results of this work demonstrates a methodology that can be implemented to measure the interlayer fracture resistance of FDM printed materials.
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