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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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.
Undercutting Mold Performance: Ejection Wear
During mold design, most consideration given to wear in the ejector system is focused on metal-to-metal interfaces. Specifically, attention is paid to the wear between the pins, sleeves, blades, and the bores through which they pass. This research focused on wear that occurred on the metal core during ejection of glass filled plastic parts. This phenomenon has been largely undocumented, and was, in some cases, found to be aggressive. Certain tool steels and copper alloys with hard coatings were shown to be significantly more resistant to this type of wear than others. In addition, product geometry appeared to play a role in the wear process.
Upgrading Recycled Waste Stream Polyethylene by Modification with Nanoscale Clay Hybrids
Recycled polyethylene (RPE) - clay hybrids (RPECHs) were prepared by melt mixing of RPE with modified montmorillonite clay using maleic anhydride grafted polyethylene oligomer (PE-MA) as a compatibilizer. Electron microscopy and X-ray diffractometry revealed that dispersion of hydrophilic clay in the highly hydrophobic polyethylene matrix increased with increasing PE-MA content. The highly dispersed RPECH nanocomposites provide substantially enhanced mechanical properties over neat RPE. The results of experimental parametric studies are reported and applied to new value-added applications for this inexpensive and plentiful polymer resource.
Use of Fitments on Stand-Up Pouches for Liquids
Over the past ten years, there has not only been a growth but also an evolution in the use of cap fitments on flexible packages around the world.In Japan and South America, and to a lesser extent in Europe, the stand-up pouch for liquids, both with, and without, fitment has been used for a number of years as a primary package. In the U S, there has been limited use, and primarily as a “refill” package for a rigid container.A lot of fitment applications started out as pre-made pouches that where then filled on fill/seal equipment. That is currently still true in the limited applications in the US. However, for a number of years, form-fill seal equipment has been used extensively in other countries. This paper will focus on the form-fill-seal application.
The Use of FTIR/ATR to Investigate the Migration of Polyisobutylene in Polyethylene for Cling Film Applications
A range of LLDPE films with polyisobutylene (PIB) content from 2%-8% was manufactured using a Killion cast film extrusion system. The films were aged at 25, 35 and 45°C for up 28 days, to enable tack (cling) development. FTIR/ATR analysis was used to investigate the surface migration of PIB. The results were confirmed by mechanical tack (cling) analysis and these showed increased migration rates with increasing PIB concentration, ageing and storage temperature.A second series of films with 8% PIB content were manufactured from a range of LLDPE's. FTIR/ATR, DSC and mechanical tack analysis were used to investigate the relationship between polymer properties and migration rates. The study established that crystallinity was the most influential factor governing PIB migration and this could be related to polymer density. Co-monomer type was found not to be a factor influencing migration of PIB.
The Use of FTIR-ATR to Investigate the Migration of Automotive Fuel Components in High Barrier Materials used in Fuel Line Applications
A Perkin Elmer Fourier Transform Infra-Red (FTIR) spectrometer with a variable temperature Attenuated Total Reflectance (ATR) attachment was used to investigate the migration of fuel components in a series of fluoropolymer, polyester and polyamide based films at various temperatures. Diffusion of the fuel components in these films was investigated by monitoring the changes in peak height of the infrared spectrum at particular wavenumbers, specific to the individual fuel components. The results show that fuel component migration increases significantly with progressive increase in temperature. The results also show that the diffusion rates increase significantly at temperatures above the glass transition temperature (Tg) of the particular polymer. The diffusion results are similar to those obtained using other techniques such as gravimetric and dynamic permeation techniques, which involve a much more prolonged analysis regime.
The Use of Polymer Processing Additives to Improve Melt Processing of m-LLDPE Extrusion
There is a large body of work showing that the addition of polymer processing additives (PPAs) results in an improvement in the processing performance of polymers. Some of the processing improvements that have been observed include a reduction in melt fracture, pressure, die build-up, and gels along with an increased processing window and improved surface finishes. Previous papers have shown the addition of a PPA has reduced many types of gels that result from cross-linking, oxidization, and unmelted material. This paper will investigate the reduction of unmelt gels seen with the addition of PPA to a polyolefin plastomer (POP) and will infer the mechanism of how the coating of the PPA on the extrusion barrel reduces the unmelt gels. In addition to the mechanism this paper will evaluate the different methods of adding the PPA to the extrusion system.
The Use of Three-Dimensional Computation Fluid Dynamics in the Design of Profile Dies
Efficient fully three-dimensional, non-Newtonian flow algorithms have been available for several years to aid in the design of flat extrusion dies . However, there are few tools available, which can be used in a practical way by an engineer tasked with designing a complex profile die in a reasonable period of time. This paper demonstrates through an actual example how the efficient use of 3-D CFD algorithms and automatic finite element mesh generators can be used to eliminate much of the cut and try" from profile die design. The effect of die swell on the profile shape downstream of the die exit is also examined."
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