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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A Closer Look at the Long-Chain Branch Formation in Ethylene Polymerization Using Metallocenes
Polymerization of ethylene using metallocene catalysts, particularly the constrained geometry catalysts (CGC), was studied. The main focus of the paper is on the control of chain microstructure in olefin polymerization using metallocene catalysts, particularly long chain branching in ethylene polymerization. Combined metallocene catalysts, consisting of CGC and a conventional metallocene catalyst, which only produces linear chains (linear catalyst), were used to manipulate long chain branching degree. The feasibility of this technique was verified using a mathematical model developed for the polymerization of ethylene in a semi-batch reactor using combined catalyst systems. Polymerization experiments were performed to verify the validity of the proposed technique and some of the modeling results. It was shown that by choosing a proper catalyst system and polymerization conditions chain microstructure could be tailor-made. Monte Carlo simulation was also used to study the structure and length of the branches in metallocene catalyzed ethylene polymerization. This information is essential for making any correlations between LCB degree and rheological properties.
Determination of Comonomer Distribution in Ethylene/?-Olefin Copolymers
Estimation of chemical composition distribution in ethylene/?-olefin copolymers using crystallization techniques is studied in this paper. Monte Carlo simulation was used to model the fractionation process in crystallization analysis fractionation (CRYSTAF). Five poly(ethylene/1-octene) samples synthesized with a single-site-type catalyst were used to verify the simulation results. It was proposed that the fractionation mechanism be controlled by the crystallization of the longest ethylene sequence in each chain. Good agreement between experimental and simulation results verified the validity of the proposed fractionation mechanism.
Evaluation of Thermal Environment in Plastic Injection Mold
Thermal deformation is one of the major problems that affects a product's quality in plastic injection molding. It is very important to have an accurate evaluation of the thermal environment surrounding the injection mold, especially in the case of high precision or large product molding. This paper proposes an evaluation method of thermal environment with a consideration of both the effect of the resin solidification process and the product's geometric shape. With this method, the validity of the thermal environment in different cooling designs is discussed using numerical analysis.
Vibration Welding of Dissimilar Nylons
Tensile strengths of linear vibration welds of nylons with different melting temperatures and glass contents were determined. Two different geometries were investigated: T-welds and a cylinder welded to a plaque. The study involved weld strengths for both homogeneous" welds where both components being welded were the same and for "heterogeneous" welds where the two components were made of nylons of different melt temperatures. It was determined based on the T-weld and the cylindrical-weld analysis that there is potential for dissimilar material weld combinations using vibration welding as the joining process. Relatively high weld strengths were obtained when PA 6 (and PA 66) was welded to the 3 different PPA's. For the short-glass-fiber materials one of the factors influencing weld strength was the difference in melt temperature between the two resins: greater difference in melt temperature resulting in lower weld strength. The long glass-fiber reinforced material which is predominantly PA 66 exhibited approximately the same weld strength regardless of the difference in melt temperature between it and the other nylon to which it was welded."
Development of an Extrusion System for Fine-Celled Foaming of Wood-Fiber Composites Using a Physical Blowing Agent
This paper presents an innovative design of a tandem extrusion system for fine-celled foaming of plastic/wood-fiber composites using a physical blowing agent (PBA). The plastic/wood-fiber composites utilize wood-fibers as reinforcing filler in the plastic matrix and are known to be advantageous over the neat plastics in terms of the materials cost and some improved mechanical properties such as stiffness and strength. However, these improvements are usually accompanied by sacrifices in the ductility and impact resistance. These shortcomings can be reduced by inducing fine-celled or microcellular foaming in these composites, thereby creating a new class of materials with unique properties. An innovative tandem extrusion system with continuous on-line moisture removal and PBA injection was successfully developed. The foamed composites, produced on the tandem extrusion system, were compared with those produced on a single extruder system, and demonstrated significant improvement in cell morphology, resulting from uniform mixing and effective moisture removal. The effects of both wood-fiber and PBA (CO2) content on the cell morphology and foam properties were studied. Increasing the CO2 content marginally improved the cell structure, whereas, increasing the wood-fiber content had an adverse affect. The effectiveness of a coupling agent was also evaluated. The cell morphology and foam properties showed improvement when the coupling agent was added.
An Experimental Investigation of the Plug Assist Thermoforming Process
This work investigates the influence of processing parameters on the properties of thermoformed polypropylene pots. Fourteen parameters were studied using a Design of Experiments methodology encompassing the polypropylene resin, extrusion parameters (Chill Roll Temperature and Line Speed) and thermoforming parameters including Plug Geometry, Plug Speed, Air Pressure and Sheet Temperature. The thermoformed pots were measured for wall thickness distribution, weight, and compression resistance. The force exerted on the plug during the forming cycle was also recorded, with a long-term goal of incorporating this data into a process control system for Plug Assist Thermoforming. Results show that the parameters associated with the plug have the greatest effect on the final pot quality.
Nonlinear Rheological Behavior of LDPE Melt during Capillary Extrusion under Vibration Force Field
In order to study the rheological behavior of polymer on vibration force field, a new capillary dynamic rheometer has been successfully developed by us for the vibration extrusion experiments of polymer melts. In this paper the measuring principles for the capillary rheological behavior of polymer melts under vibration force field will be introduced. By the experiment study of low-density polyethylene (LDPE), it has been discovered that melt viscosity and extrusion swelling ratio nonlinearly changed with the frequency and amplitude of vibration sources. The viscosity of the LDPE melt, the swelling ratio and unstable flow of LDPE decreased during capillary extrusion under vibration force field, and had a minimum with vibration frequency's change. It has great significance to the researches on dynamic extrusion and injection processing of polymer materials.
Rapid Prototype Tooling for Injection Molding Microfluidic Components Using Photodefinable SU-8 Epoxy
A rapid method for fabricating an injection molding tool using current MEMS processing is presented. The process was used to fabricate micro fluidic channels in a plastic substrate with depths of 27 µm. The tool was made using a photosensitive SU-8 epoxy on silicon. Two polymers were successfully used for injection molding the channels, clear rigid polycarbonate and opaque flexible polypropylene. Tool fabrication time was approximately 30 minutes and survived, 22 shots for polypropylene and 8 shots for polycarbonate. Deformities of the channels were observed in both plastics. Channel height was increased by 2-3 µm due to a ridge that was formed from shear forces generated between the walls. The channel width shrunk approximately 7.9% maximum for polypropylene.
Controlling Injection Phase/Packing Phase Switchover Using an Ultrasonic Sensor
An ultrasonic transducer was installed on an injection mold such that a sound pulse would strike a surface of the mold cavity and reflect back to the transducer. A change in the intensity of reflected echoes indicates the presence of polymer at the point where the sound pulse strikes the cavity surface. Detection of the arrival of the polymer at a specific position in the mold cavity is then used to identify the end of the injection phase in a similar fashion to the current cavity pressure based technique. Two important advantages of this technique are that the transducer can be mounted on the external surface of many molds, allowing an installation that requires no machining of the mold and the technique directly senses the position of the polymer in the mold cavity.
Overmolding-Stack-Mold Technology - An Innovative Concept in Multi Component Injection Molding with Many Advantages for the Molder
Turning a part of the mold is the classical, most widely used, method of transporting preforms in multiple component engineering molds. Up until now, turning was carried out exclusively with vertical turntables which were mounted on the moving machine platen and which have a horizontal turning axis. However, because the machine has to provide turning space according to the diagonals of the mold, the problem of a very large machine clamping unit is encountered. In addition to the turning space, a high clamping force is needed for the injection of preform and finished part in one cycle. This situation looks much more advantageous if the over-molding-stack mold system is linked with a horizontal turning device. This process has been developed by Ferromatik Milacron in close co-operation with Foboha GmbH Formenbau, Haslach.
Weathering Effects on Mechanical Properties of Recycled HDPE Based Plastic Lumber
Commingled recycled plastic lumber (RPL) decking was exposed to the environment for eleven years. The weathering effect is examined by performing mechanical property tests on the full size deck boards before and after the exposure. Flexural tests on the weathered deck boards were conducted with the exposed side and the unexposed side tested in tension. The flexural properties after weathering are compared to the original flexural properties. These data show the effect of weathering on recycled high-density polyethylene based RPL. A life cycle cost analysis (LCCA) is also presented to compare the cost of a wood deck versus an all RPL deck. The purchase, maintenance, and disposal costs are included.
Investigation of the Change in Mechanical Properties of Concrete Mixed with Styrene Beads
Judicial mixture of industrial material to produce new properties not inherent in each individual micro constituent has been the subject of an intense scientific and engineering investigation. One such material is a concrete based mixed with styrene (poly-concrete) to change a selected physical and mechanical properties with a reduction in weight. Poly-concrete not only can be used in the construction industries it is also used in plastics industries as well. The need to corrugated materials for production of thermoforming mold has been well sited in the technical literature. Such a material can provide thermoformer with the ability to produce a rapid prototype molds, or molds requires a deep draw ratio at a fraction of cost of more conventional materials. At the present time corrugated aluminum is considered the only material with such a property available in the market. The cost of the corrugated aluminum prohibits more common application of this material in thermoforming industry. The purpose of this study is to investigate the difference between selected properties of traditional concrete as compared to concrete mixed with various amount of expanded polystyrene beads. The investigation was involved with preparation of a concrete mixed with various amounts of expanded Styrofoam beads for evaluation. Five samples of each mixture were produced to the dimensions specified by a predesigned specification. Common concrete mixture as specified by the American Concrete Society was used. A proper curing-time was given to the samples to achieve the optimum mechanical properties. The verification of the uniformity and integrity of the sample was investigated using an imaging system and optical microscope. The result was evaluated using three-point- bending, compression, and impact tests. The expected result was used to establish a correlation between the selected mechanical properties and as a function of the physical composition of the material.
The Effect of Blend Ratio on the Properties of Syndiotactic and Isotactic Polymer Blends
Isotactic polypropylene and syndiotactic polypropylene were random blended and injection molded in various ratios. The blends produced mechanical properties that varied blend composition. Blends with increased i-PP content had higher crystallinity in the isotactic phase, and so exhibited higher moduli and yield strengths and elongation and lower impact properties. As the percent s-PP was increased, overall crystallinity decreased and the impact behavior improved. Since increasing the back pressure during molding enhanced isotactic crystallinity at the expense of syndiotactic, the blends became more rigid. Best clarity was observed in blends with high s-PP contents and lower back pressure.
The Effect of Plastication Variables on Melt Temperature
The affect of back pressure, screw speed, and injection rate on melt temperature of three materials was examined using full factorial designs of experiment. The most significant factor affecting melt temperature of polypropylene and impact modified polystyrene was the screw speed. With these materials, the injection rate also influenced melt temperature, but back pressure and interactions between the primary factors had only minor or insignificant effects. The melt temperature was raised by shear on the polymer and increased soak time. In contrast, the melt temperature of polycarbonate was not significantly affected by back pressure or screw speed; injection rate was not be examined.
Using Process Monitoring as a Method of Preventative Maintenance for Check Ring Wear during Injection Molding
An advantage of collecting process information, after qualifying parts from an injection molding process, is that trends and indicators can be identified that allow you to reject bad parts before they are ejected from the mold. In a similar fashion, it is believed that relationships between some of these indicators can be used to detect long-term deterioration of some elements of the molding process. This study developed a model using a regression analysis that can be used in the monitoring process to identify early indicators of check ring wear, which is a common maintenance item in injection molding.
Crystallization Kinetics of Poly(Ethylene Terephthalate) Based Ionomer Nanocomposite Materials
Cloisite 30A and sodium montmorillonite clays have been added to poly (ethylene terephthalate) and 2, 6, and 10 mol% sulfonated poly (ethylene terephthalate) ionomers in 1,1,1,3,3,3-hexafluoro-2-propanol to form solvent cast nanocomposite materials. Differential scanning calorimetry (DSC) was used to compare and observe differences in crystallization temperatures as well as rates of crystallization for each polymer-clay system. Analysis shows that addition of the clays into poly (ethylene terephthatlate) and sulfonated poly (ethelyene terephthalate) 2 and 6 mol% ionomers increases the crystallization temperatures and decreases crystallization half-times.
The Effects of Regrind Loading Levels and Heat History on the Properties of Selected Engineering Polymers
This study examined the effect regrind levels and heat history on the mechanical properties of polycarbonate. Increasing regrind content and heat history produced no significant change in the tensile and flexural moduli and yield strength of polycarbonate. The Izod impact properties were not greatly affected when the regrind levels were increased, but decreased severely after the fourth heat history. Comparable decreases in transfer (fill) pressure suggest that the molecular weight was reduced. While mixing the single-heat-history regrind with virgin resin produced cloudy samples, increasing the number of thermal cycles caused discoloration of the material.
The Effect of Pack and Hold Parameters on Part Cooling in Injection Molding
This study examined the effects of packing and holding conditions on the cooling of an injection molded part. Increasing packing of molded parts initially resulted in lower surface temperatures of the ejected parts. However, the introduction of more melt into the part increased the overall part temperature, thereby reducing the cooling rate. Thus, highly packed parts exhibited higher surface temperatures at long cooling times. For amorphous materials, the part surface temperature was less dependent on packing pressure. Air gaps measured at part ejection suggested that the time of part surface to mold wall contact was less than five seconds.
The Sensitivity of Notch Radius on the Izod Impact Strength of Polycarbonate and the Effects of Blending with ABS
The notch radius affects the crack propagation rate through polycarbonate upon instantaneous impact loading. The relationship between notch radius and impact strength has been shown to be directly related. Depending on the notch radius, the failures will be either ductile or brittle. Notch sensitivity is a function of impact force divided by the area of the radius. Small radii have less area than a larger radii, thus, an equal force will affect the smaller radii to the greatest degree. Notch radii vary between 0.005 and 1.000 inches. Additionally, ABS, which is not notch sensitive, is added to determine its affect.
Properties of Nanofiber Reinforced Polymer Composites with Intercalated Copper Particles
Polyethylene and Acrylate-Styrene-Acrylonitrile were mixed with carbon nanofibers and copper particles. The composites were mixed with high shear conditions to break-up nanofiber agglomerates and disperse copper. The thermo-physical, electrical and mechanical properties of the composites were analyzed. Electrical measurements showed a drop in resistivity as function of nanofiber concentration. Crystallization temperature of PE composites was not altered; glass transition temperature of ASA was altered. Dynamic mechanical studies showed increases in stiffness for both systems.
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