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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Thick Composite Extrusion Process
Production of large thermoplastic composite products such as railroad cross ties, marine pilings and utility poles requires an extremely long cooling time. Undesirable internal shrinkage voids from the core of the extruded product create poor physical appearance and concern about the physical properties.Cross head extrusion allows the product to be cooled in layers, thereby reducing cooling time and internal imperfections. Elaborate internal core design increases the surface area for faster heat transfer, allowing for higher extrusion rates of the inline compounding extruders. Fusible polymers in the interfacing layers permit interlayer bonding. This bonding enhances shrinkage compression of the inner core. This internal compression will stiffen the resulting product.Additional cost savings can be achieved by using off-spec resins and low cost fillers at a high loading in the core. Twin-screw compounding extruders are well suited to accomplish this compounding step in line at low die pressures. The removal of volatiles by means of vacuum venting is essential to produce a solid profile.Cross head extrusion also allows the application of high performance weathering surfaces to enhance product performance. In the following paper, the thick composite extrusion process is demonstrated with the development of railroad ties as a replacement for conventional hardwood timbers.
Three Approaches in Utilizing High Power Diode Laser to Join Thermoplastics
As we enter the micro age, the new challenge in the plastics industry is to manufacture and assemble smaller and smaller parts. Standard joining methods, such as adhesives, fasteners, ultrasonic or vibration welding may no longer suffice.Conventional lasers, such as the CO2 and Nd:YAG, have developed into important tools for the metals industry but their use to the plastics industry is limited to the cutting and scribing of plastics. Diode lasers have a shorter wavelength and have now reached output powers that allow them to be used to produce a controlled melt, or welding, of thermoplastics. Weld lines as narrow 0.1 mm (0.004 in.) have been achieved using diode laser welding systems.This paper reviews the capabilities of the diode laser welding process, and expands on three methods of delivering the diode laser energy to the work piece.
Three-Dimensional Cae Analysis of Underfill Flow of Flip-Chips
This paper presents a true three-dimensional simulation of the underfill flow in the encapsulation of flip-chips. The SIMPLE-based finite volume method (FVM) is combined with the volume of fluid (VOF) method to solve the two-phase flow field and to track the advancement of the resin front during underfilling process. Since the underfill encapsulation is driven by the capillary force, the continuum surface force (CSF) model is employed in the present approach to calculate the surface tension at the resin front surface. In addition, the chemorheology of the encapsulant is also included to consider simultaneously the effects of temperature, shear-rate and degree-of-cure on the underfilling patterns. Several test examples with different dispensing locations or molding temperatures are analyzed to demonstrate the capabilities of the present approach.
Through-Transmission Infrared Welding (TTIR) - Filter Media
TTIR heating is more selective if filter media are used to remove unwanted light wavelengths from the spectrum of quartz-halogen lamps. Moving sheets of the non-absorbing polymer are excellent filters when interposed between the lamp and the workpieces. This paper describes an evaluation of different filter materials and filter thickness on heating selectivity and presents a method for quantifying filter performance for an acrylic to polycarbonate weld joint. Selectivity numbers (SNs) are defined here as the number of degrees of heating selectivity that are observed per second of heating. While the best filter material is another sheet of the non-absorbing polymer, some very good performance was seen for liquid filter media that are safe and easy to use. SNs greater than 4 are needed to achieve welds with minimal distortion and several liquid materials were found with SNs from 10 to 15°C/sec.
Tie Rod Strain Incorporated as Part of an Adaptive Process Monitoring Device
Introduction In today's industry, the number one priority is time. The faster a product reaches the market, the more profit a company can make. By utilizing a cavity pressure transducer in a mold, the quality of a finished part can be predicted. Based on this information, proper adjustments can be made to the process to correct quality issues and speed up rates of production. This works well, but an expensive transducer is required for each mold. With the aid of a newly redesigned device, it is believed that time and money can be saved in processing a product. Less scrap will also be generated by the implementation of such a monitoring device. This study is a continuation of previous research performed by Juraj Ulik, ANTEC 1999 and Scott M. Frantz, ANTEC 1993, which established that there is a relationship between tie rod bending and hold pressure. Previous research was hindered greatly by a transition noise" problem. The device has been redesigned to maximize the mechanical gain and minimize the amount of noise. Incorporating this tie rod device into an adaptive process monitoring system is the ultimate goal."
To Refine Mesh or Not to? An Innovative Mesh Generator for 3D Mold Filling Analysis
True three-dimensional (3D) mold-filling technique has been a research hotspot since 90s. Important and interesting 3D phenomena such as inertia, corner effect, splitting flow, as well as fiber orientation can only be captured by the true 3D approach. On the other hand, pre-processing of the geometry model before analysis is still a rate-determining step in a CAE analysis. Poor mesh distribution will lead to loss of resolution in the 3D solver; extensive meshing will lead to huge number of elements and long CPU time that is impractical for designers. In additional to these challenges, thin-wall structure of injection molded part will generate poor aspect-ratio 3D elements for most commercial mesh generators. Therefore, geometry modeling is even more crucial in 3D than the traditional 2.5D shell element approach. In this work, an innovative mesh generator is developed to relief the effort in 3D mesh generation. This approach combines the flexibility and robustness of non-structure tetra mesh and the good boundary-layer-resolution of prism mesh. Numerical experiments prove this new approach is promising for 3D mold filling analysis for thin-wall parts.
A Tough and Flexible Syndiotactic Polypropylene - Actylic System Made via in Situ Polymerization
Blends of syndiotactic polypropylene (sPP) with high molecular weight acrylic monomers were prepared by extrusion blending to obtain polymer/monomer (P/M) pellets. These pellets were then converted into sheet form using flat die extrusion. Sheets of P/M material were continuously thermally cured to high conversion. The effect of processing conditions on the behavior of the resulting uncured and cured sheets was investigated. The effect of the amount and composition of the monomer mix on the morphology and physical properties of the resulting cured sheets was studied. Processing conditions and compositions were identified which produced cured sheets showing reduced modulus and improved tensile properties, relative to sPP. The in situ polymerization produced a two-phase system with very small acrylic domains. Products with good clarity have been obtained.
Toughness Response of Amorphous (Co)Polyesters Using the Essential Work of Fracture Approach
The essential work of fracture (EWF) is an easy to perform approach to determine the plane stress fracture toughness of ductile polymeric sheets and films. Amorphous polyesters and copolyesters are the most suitable model materials for EWF studies as they undergo full ligament yielding prior to the subsequent necking+tearing process. This behavior allowed us to partition between the yielding- and necking-related EWF parameters. The EWF method was applied to study the fracture behavior of amorphous (co)polyesters as a function of external (testing-related) and internal (material-related) parameters. It was claimed that the yielding-related specific essential work of fracture term represents the inherent toughness of the materials accordingly. This material parameter is controlled by characteristics of the entanglement network which is in close analogy with the toughness response of chemically crosslinked rubbers.
A Tubular Melt Extrusion of Poly(Vinylidene Fluoride): Structure/Process/Property Behavior as a Function of Molecular Weight (Mw)
Five poly(vinylidene fluoride) (PVDF) resins, R1-R5, of narrow molecular weight distribution (ca. 2.0) but of different weight average molecular weights Mw’s (85 – 250 Kg/mol) were melt extruded in tubular film form with a blow up ratio (BUR) of unity. The objective was to produce a stacked lamella structure that could serve as a precursor for a later process step that converts this film into a microporous membrane. Four of the resins were in pure form R1-R4 whereas the fifth, R5, contained a small amount of plasticizer to facilitate processing due to its high molecular weight. Comparisons were made of how Mw influences film morphology under a given set of process conditions. WAXS systematically showed an increase in crystal orientation as Mw increased for fixed conditions. A Carreau-Yasuda fit of the melt rheological data provided a characteristic relaxation time and this variable was correlated to the respective morphologies produced. It was shown that nearly spherulitic-like textures could be induced with the lowest Mw material whereas highly concentrated fibril nucleated morphologies were promoted with the highest Mw under identical process conditions. It was demonstrated that by blending the resins, R2 & R4, the desired stacked lamellar structure could be fine tuned with regard to morphological features.
Twin Screw Extrusion Guidelines for Compounding Nanocomposites
Nancomposite polymer compounds are poised to have a significant impact on the reinforced polymer market. A relatively small loading of properly dispersed treated clay can yield substantial improvement in a polymer's thermal, mechanical and barrier properties, as well as flame resistance, and abrasion resistance. Until recently, most nanocomposite development has focused on determining proper treatment for the clay to make it more compatible with the base polymer and thus improve the ease with which it can be dispersed. However, increasingly more effort has been extended to development of a direct compounding production methodology that will effectively disperse and exfoliate the clay. Of course, clay preparation is still extremely important, but proper design and operation of the compounding system is critical. This presentation will review the design flexibility associated with co-rotating twin-screw extruders and discuss key unit operations necessary to obtain well dispersed clay.
Twin Screw Extrusion of Polyurethane Nanocomposites
Triton Systems, Inc., has fabricated polymer layered silicate nanocomposites excellent dispersion of layered nanosilicates within a wide range of thermoplastics through inorganic surface chemical modification and polymer processing. These materials, including those with polyamides, polyolefins, polyesters, and polyurethanes result in dramatic improvements in mechanical, flammability, and gas barrier properties, while maintaining processibility for extrusion, injection molding, and blown film applications. This study aims to investigate the effects processing parameters have on thermoplastic polyurethane-nanocomposites. The optimization of the processing temperature, shear, and nanosilicate loading level results in materials with superior mechanical strength, toughness, solvent resistance, and hydrolytic stability.
Twin-Sheet Thermoforming of Dissimilar Materials
The effects of material properties in the simultaneous twin-sheet thermoforming of dissimilar materials were evaluated using a selection of 1 mm thick sheets and a test mold. Forming of dissimilar sheets required major modifications to parameters recommended for similar sheets. For this system, increasing the sheet temperature provided the greatest improvement in seal strength. Mold temperature had little effect of seal strength whereas air temperature and pressure had no processing window. The seal strength was sensitive to the solubility parameter mismatch and difference between sheet temperature and critical transition temperature. When the former was large and latter was small, seal strength was inadequate. Of the materials used in this study, polycarbonate and ABS exhibited the highest seal strengths.
Twin-Sheet Thermoforming of Elastomers
In this study, the use of elastomeric materials for simultaneous twin-sheet thermoforming was investigated. While formability depended on the particular elastomers, a polyether polyurethane formed relatively easily whereas an elastomeric polyester blend apparently required higher sheet temperatures than could be obtained with this equipment. The seal strength of the polyurethane was a function of the seal width. Narrower seals permitted greater shear flow while compressive forces dominated in wider seals. Shear flow produced high seal strengths. Increasing the sheet temperature only improved the seal strength when the compression was the primary interfacial force.
Two in One, Inline Compounding and Injection Molding
Direct compounding combines the continuous preparatory process with the cyclic, or discontinuous, injection-molding process. Everything involved in turning the individual components (polymer, colorizer, fillers, and so on) into a homogen melt takes place in a single heat. The co-rotating, intermeshing twin-screw extruder is never shut down during production, so the quality of the melt at the machine's nozzle always remains consistent. The constancy of the recipe is sustained for all individual components by a continuously operating gravimetric feeding system. This one heat" process allows better material properties for a substantial lower price."
Ultra High Shear Rates and Their Effect on the Physical Properties of an Injection Molded Part
The objective of this experiment was to determine how ultra high shear rates affected the physical properties of polycarbonate and polypropylene. To accomplish this, three different runner inserts will be utilized. The three inserts vary the time that the plastic is sheared, and the plastic's shear rate. Parts were then molded using the three different inserts. Finally, tensile data was collected to determine the effects of ultra high shear rates and shear times on injection molded parts. The data was not what was expected. The higher shear rates increased the ultimate elongation and the modulus due to cross-linking in the plastic as it cooled.
Ultrasonic Characterization Performed during Chemical Foaming of Cross-Linked Polyolefins
Injection molding of cross-linked low density foams made from poly(ethylene-co-octene) resins results from simultaneous reactions occurring during the process. The ultrasonic quasi-static technique (no flow) can mimic adequately the conditions prevailing during the molding process (pressure, temperature, time). In this work, compounds prepared from resins with different MFIs are investigated, exhibiting the influence of the degree of cross-linking on the CBA decomposition, as well as the effect of viscosity on the degassing conditions. Experiments demonstrate the complexity of CBA decomposition and of gas molecules diffusion in the polymer matrix.
Ultrasonic Riveting and Hot-Air-Sticking of Fibre-Reinforced Thermoplastics
Mechanical fastening, e.g. screwing or riveting, or thermal joining techniques like ultrasonic riveting or hot-air-sticking, are used to join thermoplastic composites and metallic structures.This paper compares the experimental results of ultrasonic riveting and hot-air sticking of fiber-reinforced polypropylene (PP-GM30, PP-LGF40) and polyamide6 (PA6-GF30) with steel. The influence of glass fiber volume fraction on process stability and on the tensile strength of the joint are evaluated from micrographs and X-ray photographs. The influence of the thermoplastic matrix material and the glass fiber length on the wear of the sonotrode during ultrasonic riveting is investigated based on SEM-micrographs and surface roughness measurements.
An Ultrasonic Spectroscopic Evaluation of the Ring Opening Metathesis Polymerization of Dicyclopentadiene
Characterization of reaction kinetics and degree of polymerization can be difficult in some polymer systems. In this work, an in-situ ultrasonic spectroscopy technique is used to study the ring-opening metathesis polymerization (ROMP) of dicyclopentadiene (DCPD) by bis(tricyclohexylphosphine)benzylidene ruthenium (IV) dichloride (1). Pulse echo ultrasonic spectroscopy employing a 20 MHz transducer is used to measure reaction kinetics of the polymerizing media. By designing a reaction cell with a flexible PET window, the change in both density and velocity can be simultaneously monitored. The technique is evaluated by comparison to FTIR analysis of a model system.
Ultrasonic Tests to Monitor Cure of Dicyclopentadiene (DCPD) for Use in Reactive Rotational Moulding
Ultrasound can be used to measure viscosity by analysis of signal velocity and attenuation. This work looks at exploiting change in signal properties to monitor viscosity during cure in reactive rotational moulding (RRM). Results from off-line tests on dicyclopentadiene DCPD show a rise in ultrasonic velocity, and a decrease in relative attenuation during cure, associated with mechanical property changes owing to increased cross-linking. Variations in velocity and attenuation can be used to predict important stages in polymer development. This technique is non-intrusive; a single transducer is mounted on the mould exterior. Pulse-echo measurements are made, allowing additional estimation of part thickness.
Ultrasonic Weld Shear Strength of Mineral Filled and Glass Fiber Reinforced Polypropylene Blends
A study was conducted to determine the effects of inorganic fillers and reinforcements type and concentrations on the joint strength of ultrasonically welded polypropylene. An ultrasonic welding test specimen was designed with the goal of producing shear failure at the welded joint during tensile testing. Twelve formulations of neat, mineral filled, and glass reinforced polypropylene, each at different additive concentration levels, were prepared, injection molded, ultrasonically welded, and tested. The formulations were also evaluated for inherent bulk material shear strength. It was found that the ultrasonically welded joint shear strength reached a maximum at an additive concentration of approximately 30% by weight for all three additive types studied. It was also found that the mineral filled formulations had ultrasonically welded joint shear strengths that were approximately equal to or slightly more than the estimated shear strength of the bulk material, while the glass reinforced formulations had ultrasonically welded joint shear strengths approximately 50% less than that of the bulk material.
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