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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Simulation of Squeezing Flow during Hot Embossing of Polymer Microstructures
In this paper, numerical simulation of the hot embossing process with non-isothermal embossing conditions (i.e. the initial temperature of the polymer substrate is the room temperature) was carried out to observe the flow patterns of thin PMMA films into micro cavities. Different thicknesses of PMMA films, from 1 ?m to 400 ?m, were used in the simulation. It was found that, as the thickness of the PMMA film reduced the filling mechanism varied. For PMMA films with a thickness above 100 ?m, the polymer flow climbed along the wall of the heated die, and then compressed downward and squeezed outward. In contrast, for a smaller thickness of less than 50 ?m, the flow was uniform and the wall climbing flow was absent. This size effect was explained using the temperature distribution of the polymer substrate during the embossing process. For a thickness above 100 ?m, the high temperature zone was localized in the vicinity of the die wall, and consequently localized wall climbing flow resulted.
Modeling of a Microfluidic Analog of the Four-Roll Mill for Materials Characterization
The fluid dynamics of channel geometries for liquid state materials characterization in microfluidic devices are investigated. A pressure driven microchannel device is sought that has an adjustable flow type, approximating the function of the four-roll mill. In particular, classes of channel flows in which the full range of linear flows (extension, shear and rotation) can be approximated in the neighborhood surrounding a stagnation point are investigated using finite element flow simulation and flow classification criteria. A class of flow geometries is identified which makes use of opposing, laterally offset fluid streams that produce a stagnation point in the center of the geometry.
A Rheological Model for Quantitative Prediction of Die Swell: Effect of Shear Rate and Temperature
During the last three decades a progress has been made in modeling of the die swell by the introduction of the so-called first normal stress difference and shear stress. Initially developed by Tanner, the model has undergone several improvements or alterations, leading to the development of new formulations. The purpose of the present investigation is to review the formulation of the die swell models proposed by Tanner, Bagley and Duffy, Mendelson and Finger, White and Roman, Vinogradov and Malkin, Macosko and Kumar et al. Next, an alternative formulation is proposed, which does not appear to exhibit mathematical defects, and an attempt is made to explore its modeling performance by comparing the predictions with the experiments of low density polyethylene, polypropylene and polystyrene under a steady shear mode over the wide range of shear rates and processing temperatures.
Modeling Free Boundary Flows in Wire Coating and Pipe Extrusion
In wire coating, polymer melt is extruded through an annular die and then drawn onto a wire, with a vacuum applied to the inner annular surface. In pipe extrusion, the annular extrudate is pressed into a sizing sleeve, sometimes using a positive pressure applied to the inner annular surface. For both flows, there is an annular free boundary flow between the die and a radial constraint. The similarity between these two flows suggests that these could be modeled similarly. These flows also resemble tubular film blowing, for which solutions exist. Here, a numerical solution for an upper convected Maxwell (UCM) fluid is developed. Solutions and examplees are presented in ways most helpful to practitioners saddled with designing process equipment and predicting operating parameters.
Flow Simulation for Polymer Melt under Disentanglement Conditions.
We determine and solve numerically the flow equations for melts submitted to conditions of disentanglement, i.e. combining pressure flow, from the feed end, and drag flow, both cross-rotational and oscillatory. We calculate the value of pressure, shear stress and viscosity along the flow path, for a given throughput and temperature, as the melt is moved through an annular gap of constant thickness.We compare solutions for various conditions of flow: pure extrusion, with no inner shaft motion, and extrusion with drag, either pure cross-rotational flow or combined rotation and oscillation at given frequency and strain % amplitude. The simulation predicts the total torque requirement for a given throughput and desired degree of disentanglement.
Morphology-Rheology Relationships in Coalescence of Polypropylene Droplets in Polyamide 6-Polypropylene Blends Induced by Simple Shear Flows
A mechanistic model for coalescence was developed by considering ballistic approximation for the kinetics of approach of the droplets. The collision frequency was corrected to take into account hydrodynamic interactions and the effects of drainage between partially mobile interfaces. A semi-quantitative agreement was observed between the model and the experimental results obtained using isotactic polypropylene (PP) and polyamide-6 (PA6) blends sheared in a cone and plate rheometer at low shear sates (0.1 s-1). Model predictions were combined with the phenomenological model of Lee and Park and predictions of the rheological behavior of the blend during coalescence were obtained.
Correlation between Material Structure, Processing Conditions and Optical Properties of PP Cast Films
Polypropylene (PP) homopolymer and ethylene/propylene random copolymer (EP random copolymer) formulated with and without antiblocking additives were extruded to cast films in a high speed extrusion process. The extrusion was performed with an industrial scale extruder equipped with a soft box. For comparison purposes two different soft box conditions were used. The films were analyzed for their optical properties haze and clarity. To establish structure-property relationships a comprehensive surface roughness characterization was performed applying atomic force microscopy (AFM). In addition, high resolution AFM and small angle X-ray scattering (SAXS) analysis were done to obtain morphological information of the film surface and the bulk on a nanometer length scale. The measurements revealed a good correlation between surface roughness parameters and optical properties. A significant effect of polymer processing additives on the surface and the optical properties of PP cast films was obtained. However, material structures and soft box processing conditions were shown to have effects on the film properties. High resolution morphological analysis revealed similar crystalline structures at the film surface and within the bulk of the investigated homo- and copolymer PP cast films.
Oxygen Barrier Enhancement of PET by Blending with an Aromatic Polyamide
The improvement of oxygen-barrier properties of poly(ethylene terephthalate) (PET) by blending with an aromatic polyamide (MXD6I) based on poly(m-xylylene adipamide) (MXD6) in which 12 mol% of isophthalamide was replaced with adipamide, was examined. The sequentially biaxially oriented blends containing 10 wt% MXD6I had significantly reduced oxygen permeability of PET by a factor of about 3 when tested at 43% relative humidity. Enhanced barrier arose from increased tortuosity of the diffusion pathway provided by the oriented, flat MXD6I platelets of high aspect ratio, which was confirmed by atomic force microscopy.
Unique Antiblocks for High Clarity Polyethylene Film
Our research shows that an excellent balance of haze, gloss, polymer color and antiblocking properties in PE film can be achieved with unique new antiblocks derived from a special class of diatomaceous earth (DE). Of particular interest is DE derived from MELASIRA diatoms (derived from fresh water), which show consistent size and shape, as distinguished from other ore bodies of greatly varying shapes. When this DE is fluxed, milled and classified, unique and outstanding new antiblocks are achieved which create PE film with superior color, gloss, and haze compared to using other DE and natural silica antiblocks.Details of the experiments and property measurements are discussed, and show unique enhancements of these new antiblocks in color, haze, gloss and antiblocking performance in LDPE, LLDPE, and metallocene LLDPE.
Welding of Recycled Thermoplastic Lumber for Structural Components
This paper reviews experimental work on welding of reinforced recycled thermoplastic lumber for the fabrication of structural components. Recently the use of thermoplastic lumber has become more accepted due to the materials longevity. However, because of extrusion difficulties, such as shrinkage holes and long cooling times, plastic lumber has not been widely used for structural components, such as pilings and supports. In order to solve some of these issues, it has been proposed to extrude standard, relatively small cross sectional components, such as 2x4 and 2x6, and join these components into larger structural components, such as 6x6 to 10x10 or engineering components such as I-beams. This work evaluated a wide range of welding processes, including; hot plate, vibration, IR and non-contact hot plate welding as well as adhesive bonding. Star design of experiments was conducted for each process and relevant parameters. Process optimization was preformed for each process in order to minimize cycle time and maximize weld strength. In addition, flexural tests of selected samples were performed. It was found that welding could produce joints as strong and as stiff as the base material.
Effect of Paint Over Spray for Vibration and Ultrasonic Welding Processes
Thermoplastic Olefin (TPO) has been commonly used for automotive interior parts. TPO material used for this study was a Polypropylene (PP) and Polyethylene (PE) copolymer for better impact resistance and it contained 20% of talc. Considering the facts that PP and PE are semi-crystalline thermoplastics with high molecular weights, and that it contains rubbery contents and talc, weldability of the material needed to be carefully evaluated. Especially for the ultrasonic welding process utilizing 40 - 60 microns of ultrasonic vibration amplitude for welding, these could affect the material weldability significantly.Additionally during manufacturing processes, the paint over-spray (undesired painting at the weld joint area) is sometimes unavoidable. Specific effects of the paint layers on the welding processes have been investigated. To investigate the effects effectively, the processes have been fully optimized by through Design of Experimentation (DOE).
Vibration Welding Polypropylene-Based Nanocomposites
Nanocomposite materials present interesting mechanical properties due to the high surface area to volume ratio of the dispersed reinforcement. The vibration weldability of these new composites has not yet been reported in the open literature. This research examines the effect of the vibration welding parameters of weld pressure and target meltdown on the strength of butt welds made from two polypropylene-based nanocomposites. The results of unreinforced polypropylene are shown for reference. The nanocomposites were made by melt compounding two levels of organoclay with polypropylene. All welded assemblies were assessed by tensile testing. The results show that 3-6% of organoclay causes a significant decrease in weld strength.
Microstructure of Polyamide-6 Vibration Welded Joints
The microstructure and morphology of the Heat Affected Zone (HAZ) of vibration welded joints of polyamide-6 were studied using Polarized light microscopy (PLM), Fourier Transform infrared (FTIR) microspectrometry and scanning electron microscopy (SEM). PLM images showed existence of two distinct HAZ layers: an inner layer (HAZ-I) with small spherulites and an outer deformed layer (HAZ-II) adjacent to the bulk zone. The thickness of the HAZ-I and HAZ-II layers and the size of spherulites in HAZ-I depended significantly on the welding pressure. The microstructure study suggests that HAZ-I originates from molten fluid film and HAZ-II mainly consists of deformed crystallites. Etched HAZ surfaces also showed clear distinction between the two HAZ layers. Birefringence measurements showed that HAZ-I is more highly oriented than HAZ-II. HAZs obtained under high pressure retain higher molecular orientation than those obtained under low pressure. FTIR results show that the ?-crystal phase content of HAZ-I is higher than that of HAZ-II and higher welding pressure induces more ?-crystal phase.
The Effect of Molding Condition on Interfacial Mechanical and Morphological Properties of Film Insert Injection Molded PP-Film/PP Matrix
The effects of barrel temperature and injection rate on the interfacial mechanical and morphological properties of film-insert injection-molded PP-film/PP matrix were investigated. In high barrel temperature and injection rate, film did not peel from the injected PP. In this situation, the surface of the film was found to have melted by the heat of injected PP, which resulted in higher crystallinity of PP film near the interface. On the other hand, in low barrel temperature and injection rate, the film peeled from the substrate. In this situation, crystallinity of the surface of the film was found to be low because the heat of the injected PP did not affect the film.
Analysis of Residual Stress in Hot Plate Welded Polycarbonate
The analysis of thermally induced residual stresses has gained a lot of importance because residual stresses are known to affect the strength, fatigue life and chemical resistance of a welded component. In this paper, the effects of annealing on residual stresses in hot-plate welded polycarbonate (LEXAN) samples were studied. The GE solvent stress analysis test provided a quantitative means for determining the stress levels in the samples. Temperature distribution along the length of the welded samples was measured as a function of time using thermocouples. A simple model for predicting the residual stresses in hot plate welded PC samples was developed. Our results showed that the residual stress in non-annealed samples were in the range of 10.5-12 MPa.
Interfacial Properties of Film-Insert Injection Molded Polyethylene-Film/Polyethylene Matrix
This study involves the investigation of interfacial adhesion strength between a polyethylene (PE) film and a PE substrate fused together by means of film-insert injection molding technique. 180° peel tests were done and the barrel temperature was found to have a significant influence on the adhesion strength, whereby if the melt temperature is sufficiently high, adhesion strength is comparable to, if not stronger than, the film. Several models were used to pinpoint the region of the load-displacement curve that could denote the true peel strength.
Experimental Study and Modeling of Bond Formation between ABS Filaments in the FDM Process
The application of Fused Deposition Modeling (FDM), a plastic based rapid prototyping technique, has been limited due to poor bonding between the filaments forming the parts. This study focuses on understanding the bonding mechanism and its dependence on processing parameters. The bond quality was experimentally assessed based on the growth of the neck formed between adjacent filaments and their failure under flexural loading. We present two thermally driven models which describe the formation of bonds due to sintering and molecular diffusion. Experimental results suggest that the diffusion model is more appropriate for this application.
HDPE Effects on the Heat-Sealing Properties of LLDPE
Heat sealing properties of Linear Low Density Polyethylene (LLDPE) blend with varying proportions of High Density Polyethylene (HDPE) was investigated. Heat sealing properties of LLDPE namely, heat seal strength and hot tack strength are evaluated as a function of HDPE content in the binary blends. To elucidate their relevance, the thermal behaviour obtained by Differential Scanning Calorimetry (DSC) is correlated to these heat sealing properties. Keeping the process variables of seal pressure and dwell time constant, experimental results indicate that HDPE induced pronounced changes on the heat sealing ability of LLDPE.
Experiments in Hot Plate Welding of Polypropylene Nanocomposite
Clay-based nanocomposites have recently attracted attention in many industries due to their high specific strength, modulus and low permeability. A typical nanocomposite plastic has only about 3 to 6 percent by weight nanoclay, where after being purified and surface-treated they are mixed with pure resins to produce polymeric nanocomposites. As the usage of these nanocomposites increases in industry, knowledge of its weldability becomes important. The hot plate weldability of three specific Polypropylene nanocomposites with 0wt%, 3wt% and 6wt% nanoclay was investigated. A three factors (heating temperature, welding time and welding pressure), two level design of experiments (DOE) was used to screen welding parameters and obtain near optimum welding conditions. The maximum joint strength was found to be 94%, 79% and 62% of the bulk strength for 0wt%, 3wt% and 6wt% nanoclay samples, respectively. While increasing nanoclay levels in the composite improved the bulk material strength, it reduced the weld strength significantly.
Ultrasonic Treatment of Advanced Thermoset Composites
This paper reviews experimental work on ultrasonic treatment of advanced thermoset composites. It has been proposed that treating these composites with high power ultrasonics (~10-50 W) may cause a decrease in void content without adverse effects, such as premature partial curing or a degradation of mechanical properties. Samples of advanced composites were treated with ultrasonic energy at various travel speeds, amplitudes, force, orientations of the horn to the surface and number of pregregs plies treated at once. Significant heating was observed but there was no evidence that the treatment had any adverse effects. It was seen that the treatment reduced the overall thickness of the samples, implying that the void content was decreased. In addition, there was evidence that ultrasonic treatment slightly increased the stiffness and short beam shear strength of the samples.
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