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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Deformation and Yielding in Blown Oriented Polystyrene Films
Shear bands were generated in polystyrene upon melt extrusion and film blowing. These bands consisted of two sets with an intersection angle ranging from approximately 36 to 65 degrees. The definition, morphology and intersection angle of the bands varied with film processing conditions. The widely distributed bands are indicative of shear yielding rather than viscoelastic flow that could govern the later stages of film formation. Upon further deformation, new shear bands were generated with the band morphology varied with the draw ratios introduced in film blowing. The bands were fine and diffusive for films with high draw ratios. They were large and localized for that of low draw ratios.
Failure of Thermoplastic Tanks
Thermoplastic sheet polypropylene and PVDC is widely used in corrosion-resistant tanks for storage of fluids, including dangerous chemicals. We report the failure of one such PP tank used to store 40% caustic soda. A weld failed in a full tank 3 months after installation, causing damage to property but no personal injury. The detailed investigation revealed that the basic design was faulty, the tank being built like a barrel rather than like a dam. The excessive hoop stress from the hydrostatic pressure caused the failure of two welds. Other tanks made in the same way were inspected and corrective action taken. Such tanks should be built to the German standard DVS 2205.
Solvent Welding of Abs and Hips-A Case Study in Methylene Chloride Substitution
An investigation was conducted to evaluate replacements for methylene chloride in the solvent welding of an acrylonitrile-butadiene-styrene system (ABS) and a high-impact polystyrene (HIPS). Fourteen candidate solvents were experimentally considered. These were divided into three general categories: traditional, green and clean." A relative hazard rating was assigned to each solvent by taking the maximum concentration that the solvent could keep in equilibrium in a specified air space and dividing this value by the threshold limit value (TLV). Solvent welding was tested in both bond-in-tension and single-lap shear geometries. Parameters affecting resultant bond strength that were quantified included time polymer in contact with solvent time after surfaces joined temperature (pre- and post-bonding) contact pressure and vacuum."
Product Positioning in the INSITE* Technology Process
Over the last ten years Dow Chemical has been developing INSITE* technology using Speed" based principles to insure speedier development and faster revenue growth. One of the principles we have been using relates to using marketing to position our products to the various audiences required for a successful launch: our customers our competitors and our people. In general positioning products is not well understood in our company but it is critical to help shape people's perceptions of what is possible how this product relates to other products and what the value of the product is to the marketplace. By positioning INSITE technology and delivering new products to the marketplace Dow's image as a technology leader has been enhanced. The INSITE technology capability continues to encompass more opportunity and the credibility of the technology and products Dow launches grows. The process to establish a positioning and new product delivery are key elements to maximize the value not only of consumer products but also even differentiated commodities. Positioning is a key element in Dow's drive to launch INSITE technology and maximize value of the subsequent product lines."
The Role of Testing in the Failure Analysis of Plastics
Failure analysis (FA) of products and materials always requires careful observation of the general circumstances involved. The product failure analyst never overlooks external causes or environmental effects. All FA also requires a healthy dose of common sense and a 'Sherlock Holmes' investigatory sense. However, specialized material and product tests are also essential components of successful FA including: material mechanical properties, tests for composition and uniformity, residual stress tests, tests for contamination, identification and quantification of residual solvents, microstructural examination, and many more. An overview of general FA techniques will be presented, followed by specific examples of plastic FA. These specific examples will be discussed in detail, with special emphasis on the key findings derived from specialized laboratory testing. Examples will include plastic piping systems, consumer products, industrial equipment, and sporting equipment. Techniques discussed will include residual solvent identification by GC/MS, various spectroscopic techniques, optical and electron microscopy, thermal analysis, and mechanical properties testing.
Interfacial Tension, Phase Inversion and Co-Continuity in Poly(L-Lactide)/Polystyrene Blends
In this work blends of poly(L-lactide) (PLA) and polystyrene (PS) were investigated. The breaking thread method was used to measure the interfacial tension between poly(L-lactide) and polystyrene at 200°C. The complex viscosity and the storage modulus of the pure components were measured as a function of the frequency. L-PLA/PS blends were prepared by melt mixing the polymers in a Brabender mixer and the level of continuity has been investigated. The interfacial tension was found to be about 9.1 mN/m, whereas the phase inversion was determined to a PS concentration higher than 60%.
Biodegradable Plasticizers for Polylactic Acid
Poly(lactic acid) [PLA] is a well known biodegradable polymer which has been used in drug delivery systems, surgical repair systems such as sutures and bone fracture fixation pins and screws. PLA is biocompatible, has a high tensile strength, and has a high elastic modulus[1,2]. However, one drawback of PLA is the low elongation at break due to a brittle fracture while under tensile and bending loads. The elongation at break of PLA is typically 3 - 5 percent. The reason for this brittle behavior is due to physical aging which occurs during storage at room temperature and has been studied extensively. Plasticization is a common technique used to increase the ductility of a brittle polymer. In the case of PLA a suitable plasticizer must be miscible with PLA so as to decrease the glass transition temperature, as well as be biodegradable and nontoxic so as to provide a useful biodegradable blend. The advantages of the plasticization are low cost, ease of processing, and the ability to alter the properties of the blends by varying the amount of plasticizer. Use of a functionalized plasticizer can be more desirable such that a chemical bond is formed with the PLA polymer thereby preventing loss of the plasticizer through migration.
An Assessment of Dynamic Feed Control in Modular Tooling
An experimental investigation of the inter-cavity dependencies of a modular tool using Dynamic Feed control is presented. The results showed that part weight and overall part dimension are controlled by the individual command pressure to each cavity and the material's melt temperature. The weight and dimensions of a particular cavity appear independent of the control pressures set to fill the other cavity inserts. This was demonstrated to the extent that weight and dimension showed independence from a deliberate short shot condition in the hardest to fill part. There may be a minor synergistic effect of adjacent cavity pressure and the shorting part but this would need to be confirmed with additional experimentation. Once initially stabilized both traditional machine velocity control and Dynamic Feed weight variations were in the range of +/- 0.025% or less.
Effects of Antiblocking Agents on Polyethylene Crystallization in Bulk and in Dilute Solution
The effects of antiblocking agents on the crystallization process of linear-low density polyethylene were investigated in dilute solution and in bulk. It was found that the type of antiblock has a more profound influence on crystallization than does macromolecular architecture. Silica was not found to have appreciable influence on the crystallization process either in bulk or in dilute solution. Talc, however, affected the crystallization process in both phases: in dilute solution, it decreased the apparent homopolymer fraction in TREF, and in bulk, it elevated the onset of crystallization and reduced the rate of nucleation, as monitored by DSC and DMA.
Re-Engineering of an Epoxy Matrix for Composite Water Ski Fabrication
Changes in resin chemistry have a significant effect on the manufacturing parameters and mechanical properties of composite systems. A customized resin was developed for the fabrication of a water ski, which conformed to the initial manufacturing parameters of the commercial resin system. The curing properties of the resins were investigated and laminates were taken from skis to compare resistance to high temperature deformation using stress relaxation experiments. Also, real-time strain measurement systems were built and tested on skis made with both resins. Results showed that the stiffness increased under a 3-point bending load and stiffness was maintained at higher temperatures with the customized resin system.
Investigation of Non-Thermal Effects Produced by Ultrasonic Heating on Curing of Two-Part Epoxy Adhesive
Rapid curing of structural adhesives by ultrasonic heating has been demonstrated successfully in recent work. Therefore, it is important to examine whether ultrasound would induce non-thermal effects that accelerate the reaction rate of the adhesive. In this paper, Differential Scanning Calorimeter was used to carry out thermal analysis of the reaction kinetics of a two-part structural epoxy adhesive. A chemical model based on a four-parametric semi-empirical equation was developed to distinguish the non-thermal effects from ultrasonic vibration from the thermal effects resulting from ultrasonic heating. It was found that the non-thermal effects was more significant at the beginning of the curing process but it gradually diminished as the heating time was increased. The conversion of the epoxy adhesive produced by ultrasonic curing at 50 seconds was almost three times higher than that obtained by thermal heating.
Modeling of Ultrasonic Forced Wetting Process by Dimensional Analysis
Wetting of liquids on solid surfaces is very important for many applications including adhesive bonding. Ultrasonic forced wetting has been shown to reduce the contact angle of liquids on solid surface. The application of hydrodynamic analysis to model the process is difficult because of the well-known stress singularity that arises at the liquid/solid contact line. In this paper, dimensional analysis was utilized to establish a semi-empirical dimensionless equation for the prediction of the ultrasonic forced wetting process. Experimental data of dynamic contact angles of three liquids vibrated at different frequencies and amplitudes were produced. By correlating the dynamic contact angle with liquid properties, geometric parameters, ultrasonic vibration parameters, gravity, and thermal effects caused by viscous heating, it was shown that a dimensionless equation can be developed to predict the dynamic contact angle of liquids under ultrasonic forced wetting.
Physical Modeling of Elastomer Extrusion Using the Visioplasticity Method
The visioplastic method is often used to model material flow for the deformation of metals. The method provides qualitative and quantitative data on material flow such as strain, strain rate and velocity throughout the flow regime. Data obtained is used to evaluate die design, troubleshoot processing problems or evaluate results of computer modeling software. The present study applies this method to the extrusion of elastomeric profiles. An advantage with elastomers is that the actual polymer being studied can be modeled directly. A general discussion of the visioplastic method is provided along with results from the evaluation of selected die geometries.
Melt Drawing of LDPE/Thermoplastic Starch Blends
In this work, the influence of thermoplastic starch (TPS) composition, processing conditions and the hot stretch ratio (HSR) on the morphology of LDPE/TPS blends were studied. Blends were prepared in one- and two-step processes. Both series of blends were drawn at different HSR at the exit of the die. The morphology of blends was quantified using a novel methodology, which allows a more precise evaluation of the particle volume. Blends prepared in the one-step process showed increased levels of anisotropy as a consequence of a combination of coalescence and particle deformation during melt drawing. Conversely, TPS particles of reprocessed blends showed no-coalescence and a low degree of deformation.
Evaluation of New Insulation Materials for Heater Bands
The performance of standard mica heater bands, mineral heater bands, and heater bands containing new inorganic insulation materials were compared. The overall performance of the inorganic and mineral insulation was far better than that of standard mica insulation. Inorganic-insulated heater bands generally provided faster response, better stability, and lower power consumption than a standard mineral-filled band. Although high water retention in experimental binders led to premature heater band failure, optimized inorganic binders gave better high temperature performance than organic binders. Finally, a combination of inorganic insulating materials produced the best overall results.
A Predictive Melting Model for Polymer Particulates in Co-Rotating Twin Screw Extruders
A predictive melting model for polymer particulates in co-rotating twin screw extruders (Co-TSEs) is proposed. The proposed model starts with the solids conveying section where discrete mechanics is used to describe the movement and deformation of solid particulate assemblies. The interparticle forces can be estimated based on the screw geometry, processing conditions, and material properties. These forces are the sources of two important melting mechanisms: the Frictional Energy Dissipation (FED) and the Plastic Energy Dissipation (PED). The model also considers the role of barrel heating in creating a layer of preformed melt". The existence of preformed melt changes the conveying properties of solid particulates dramatically. Finally the model considers the important heat generating term the Viscous Energy Dissipation (VED) whose onset coincides with the creation of a fraction of molten polymer generated by any of the above mechanisms."
Quantification of Calibration Drift for the TC Probe Thermal Effusivity and Conductivity Instrument
The Pyris TC Probe requires calibration with characterized standards to relate instrument response to effusivity and/or thermal conductivity. This study was under taken to determine the magnitude of any drift in calibration that occurred over time. Drift could occur due to uptake of water in the sensor's insulation or surface wear. Three calibration standards of known effusivity values were used to calibrate the instrument at 4 test times from 6 to 30 seconds. Several standards were tested during a period of 64 days with each of the calibration files. Of the 120 tests conducted, only 2 results varied more than 4%, indicating excellent stability.
Large, Structural, Class A" Thermoplastic Automotive Part Production without Painting"
The Valyi surface finishing/compression molding process (SFC) has successfully been used to produce large structural panels with Class A finishing under low pressure. The material used in the SFC process must meet certain performance requirements in order to fully exploit the capability of the process. This paper compares the mechanical properties and rheological properties of short and long glass and carbon fiber reinforced materials. The Long fiber reinforced PP resins show enhanced stiffness and impact strength. Degradation of surface appearance due to long fiber read through is an issue to be addressed in future work.
A New Method for Determining the Thermal Conductivity of Polymeric Samples through the Melt
Understanding thermal behavior of molten polymers is critical to many different resin molding processes. The objective of this study was to investigate the adaptation of the Transient Plane Source (TPS) thermal analysis method for evaluating polymer feedstock raw materials in pellet form through the melt. A new sample holder was designed to accommodate the logistics of the experiment. Two sets of polymer raw materials were evaluated, one a random copolymer polypropylene with no filler and the other a polypropylene backbone modified with rubbers and mineral fillers. Thermal conductivity results for each sample were obtained at five temperatures, 250°C, 200°C, 150°C, 100°C and 50°C. Each sample was tested in triplicate to identify the precision of the TPS technique under each condition. The results of this study were correlated to thermal conductivity results obtained on the same samples by ASTM testing method D5930-97, using the transient line-source (TLS) technique.
Plastic Energy Dissipation (PED) a Major Contributor to Melting of Polymers in Polymer Compounding Equipment
Polymer processing equipment, batch or continuous, provides for some or all of the following mechanisms for the heating and melting of polymer particulates: Conductive Heating, Interparticle Friction Energy Dissipation (FED), Plastic Energy Dissipation from each deforming solid particulate (PED) and Viscous Energy Dissipation (VED) arising from the flow of the viscous polymer melts. Experimental evidence generated in our laboratories where PED was evaluated with individual solid polymer cylindrical samples and inside compounding equipment, such as Co-TSEs, indicates that PED arising from the irreversible deformation applied by the compounding equipment on solid particulates is often orders higher in magnitude than other heating/melting mechanisms.
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