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.
The simultaneous effects of the incorporation of different types of fibers and of the presence of EPDM on the crystallization kinetics and thermodynamics of isotactic polypropylene are presented. The study is applied to the behavior of polypropylene matrix composites reinforced with glass, PET, aramidic and sisal fibers. The results obtained show that in all cases, either the fibers and the EPDM rubber behave as effective nucleant agents for the crystallization of polypropylene. A dramatic decrease of the half time of crystallization, t1/2, and an increase of the overall crystallization rate, Kn, are observed being the aramidic fibers the most effective. It is also reported that transcrystallinity takes places in all fibers being more evident with aramidic fibers in the neat PP matrix. Only a slight transcristallinity effect is detected when fibers were incorporated in the PP-EPDM matrix.
The effect of large strain, simple shear deformation induced by the Equal Channel Angular Extrusion (ECAE) process on semi-crystalline poly(ethylene terephthalate) (PET) and amorphous polycarbonate (PC) has been investigated. A through-thickness shear strain of approximately 190% after one ECAE pass is induced in the extrudates. Mechanical tests revealed that the extrudates are anisotropic, indicating that the process is capable of generating highly oriented microstructures. Improved fracture toughness can also be achieved via the ECAE process.
Real breakthroughs in strategy and business development come from looking beyond your in-kind competitors for a process view of customer-focused solutions. A company's basic operations are first level processes and cross over industry type. Best practices is the study of identifying the companies which have developed superior processes in product development, manufacturing, customer service and market segmentation regardless of the industry they are in. This paper discusses the benefits of the study of Best Practices in addition to competitive intelligence and benchmarking in business planning. Examples of companies in the plastic industry who have distinguished themselves by their best practices will be presented.
The effect of processing conditions on fiber length degradation was investigated in order to produce higher performance composites. For this aim, Nylon-6 was compounded with glass fibers in a twin screw extruder for various combinations of screw speed and feed rate. Collected samples were injection molded and izod impact and tensile strength tests were performed in order to observe the effects of fiber length on mechanical properties. Also, by using the extruded and injection molded samples, fiber length distribution curves for all experimental runs were obtained. Results show that when the shear rate is increased through the alteration of screw speed and feed rate the average fiber length decreases.
In-process monitoring of polymer melts is found to provide a fingerprint of the: • polymer (process-relevant polymer rheometry); • the process (injection pressure-time curves which reflect the material-machine-mould combination, including polymer batch to batch variation and machine dynamic repeatability); and • production trends, with 'process indices' offering an efficient basis for 100% automatic inspection, Statistical Process Control, and even insight into factory housekeeping. Specific pressure indices in an indentified low noise region of the primary injection stage of injection moulding have been found to provide a sensitive indicator of changes in a polymer, including batch to batch changes and process-induced changes, as such measurements are closely related to the rheology of the polymer melt. The same information has also been found to provide sensitive indications of variation in the processing operation for a given polymer-mould combination, and also consequently to allow meaningful statistical analysis of trends in the injection moulding process. Laboratory and factory data for raw material, process and production trend analysis (the latter involving data from substantial production runs) are presented.
Blends of conventional polypropylene (PP) and branched PP (bPP) enable PP to perform well in applications where extensional flow dominates, such as blow molding, thermoforming and foaming. Sag resistance tests shows a significant improvement in sag time of extruded sheet as the content of bPP increases, up to 30-wt.%. These blends (PP/bPP) show synergistic increases in melt tension while providing excellent processability by maintaining low viscosity.
This study examined the effects of injection molding conditions and critical design parameters on the filling, dimensional stability, and crystallization of syndiotactic polystyrene (sPS) parts. Part wall thickness was the primary factor affecting filling, shrinkage, and crystallization. While injection velocity was secondary influence during, mold temperature was the minor factor for crystallization and shrinkage. Melt temperature and gate dimensions had little or no effect on filling or part properties.
Experiments using a glass window extruder are presented. These provide direct observation of the different melting behavior among various polymers. Simulations performed using commercially available software showed good correlation with the observations. The data obtained provides valuable insight into the melting behavior which, can be used to evaluate and ultimately improve the capabilities of simulation software as well as screw designs.
A novel small scale (<30g of polymer) recirculating flow visualisation cell has been designed and built. The unit comprises a single screw extruder, gear pump and variable geometry inserts making a flow recirculation loop. The recirculation flow cell is capable of being used with a range of entry geometries, including abrupt entry and hyperbolic, with a polariscope for stress birefringence, and a CCD camera and image processing system for particle streak velocimetry. This new facility complements existing larger scale flow visualisation cells in our laboratory, fitted to a single screw extruder. Information from flows in both scales of flow cell are presented for an LDPE melt.
Reactive blends of styrene-maleic anhydride (SMAH) with polyethylene/methyl acrylate/glycidyl methacrylate (PE-F) and non-reactive blends of SMAH with polyethylene/methyl acrylate (PE-NF) were produced and characterized in terms of morphology and viscoelastic properties in order to understand the reaction characteristics between anhydride/epoxy functional groups. Storage modulus, G', loss modulus, G and complex viscosity ?* of reactive blends at 25 % and 50 % PE-F were higher than those of non-reactive ones. At 25 % PE-F a maximum in complex viscosity was obtained for the reactive blends. In morphological analysis the reactive blends showed finer morphology than the non-reactive ones."
The NIST Torsional Dilatometer measures simultaneously the torque, axial normal force and volume change in response to a torsional deformation. While the torque is a linear function of the angle of twist per unit of length, the normal force and volume change are effects of geometrical nonlinearities. In stress-relaxation experiments with an epoxy cylinder near its glass transition temperature, the torque and normal force decay monotonically, but the volume change associated with the torsion shows a significant non-monotonic decay at lower temperatures. The measurements are investigated with a series solution for torsion of an elastic, compressible material [Murnaghan, F.D. (1951) Finite Deformation of an Elastic Solid. Wiley, New York.].
NIST develops Standard Reference Materials for calibration, quality assurance and research into improved measurements. Two fluid standards are being developed to exhibit shear thinning and normal stresses typical of polymeric fluids. SRM 2490 is a solution of polyisobutylene dissolved in 2,6,10,14-tetramethylpentadecane. At this time, SRM 2491 is expected to be a poly(dimethylsiloxane) melt, giving less temperature dependence than SRM 2490. NIST will certify linear viscoelastic behavior and the shear-rate dependence of the viscosity and first normal stress difference at 0 °C, 25 °C and 50 °C. A round robin with the fluids will investigate variability in rheological measurements. We report progress on the project.
The initiation, growth and final failure of a craze at the site of a flaw is known to precede slow crack growth under low constant load in polyethylene pipe. Most established slow crack growth tests rely on being able to generate high constraint at the crack tip in order to promote damage and micro-voiding. However, for recently developed PE80 and PE100 type grades of polyethylene, such methods cannot achieve constrained brittle fracture due to extensive crack tip blunting and the formation of large crack tip craze zones, thus invalidating the use of a conventional fracture mechanics analysis. An experimental method is described here wherein deep notched tensile specimens are used to analyse craze behaviour in tough polyethylenes under plane strain conditions. Under constant load conditions, stress - time characteristics of the craze provide good discrimination between various grades within acceptable times. Under constant speed conditions, traction - separation properties of the craze have been measured directly, yielding a rate and temperature dependent work of separation(?) which may be thought of as equivalent to Gc. Rate dependent trends in ? distinguish well between the grades allowing assessment of long term properties. The intrinsic physical justification of the method lies in the measurement and analysis of separation properties locally at the craze interface. A cohesive zone modelling technique using the 'Finite Volume' method is introduced indicating how the results may be applied to the prediction of slow crack growth in other geometries.
Mold designers and mold builders know many different ways to solve mold problems.. Yet a surprising number of our colleagues have not yet used the wide variety of proven mold steel on offer in to-day's market place. This paper reviews the range of available grades of steel; it cites examples of mold problems that have been solved by selecting better and more appropriate alloys; it lists the worldwide availability of innovative mold steels, and finally, it shows that better steel adds value to a mold at very modest cost.
The melt compounding route is a powerful approach in the preparation of polymer-clay nanocomposites as existing technologies can be utilized and easily scaled to commercial quantities. Polymer-clay nanocomposites have been developed via melt compounding. Dramatic increases are exhibited in heat distortion, stiffness, and barrier properties compared to the neat resin. Other benefits include low specific gravity, processing ease, surface appearance, etc.
Haze is a cosmetic defect that occasionally appears on injection molded part surfaces. This defect is especially noticeable in dark colored, high gloss parts. A study was performed to identify and understand the underlying causes of surface haze formation in unfilled PP/PMMA alloys. Four different Polypropylene resins with varying amounts of PMMA were evaluated. The formation of haze was found to correlate with the amount of PMMA included in the formulation and the melt elasticity as indicated by tan ? at low frequency.
It has been known for many years that both types of acetal plastic are susceptible to oxidative attack, or stress corrosion cracking (SCC) when in contact with chlorine. It was thought that high levels (>30ppm) of free chlorine in cold water are needed to initiate attack, so that acetal injection moulded fittings could be used quite safely in potable water supplies where free chlorine levels are very much lower (<1 ppm). The case study to be described here of a fracture in a water supply which caused substantial damage, indicates that attack probably can occur at such levels, especially if the fittings exhibit extensive weld lines near stressed zones. High chlorine concentrations can arise due to chlorine surges in the water supply, especially when the water company overdoses the supply after a major leak.
The molecular structure of randomly branched polymers is understood using percolation theory. Once the chain length between branch points and the extent of reaction relative to the gel point are specified by synthesis, both the molecular structure and the linear viscoelastic response can be determined using simple models. We demonstrate these ideas using randomly branched polymers with known chain lengths between branch points. Then we exploit this finding to characterize the chain length between branch points for polyethylenes from knowledge of their weight-average molecular weight and zero-shear-rate viscosity.
This paper presents a finite element algorithm for solving gas-assisted injection molding problems. The solution of the three-dimensional (3D) equations modeling the momentum, mass and energy conservation is coupled with two front-tracking equations, which are solved for the polymer/air and gas/polymer interfaces. The performances of the proposed procedure are quantified by solving the gas-assisted injection problem on a thin plate with a rib. Solutions are shown for different ratios polymer/gas injected. The effect of the melt temperature, gas pressure and gas injection delay, on the solution behavior is also investigated. The approach is then applied to a thick 3D part.
This paper presents a finite element algorithm for solving polymer injection molding problems. The methodology consists in solving for the three-dimensional (3D) equations modeling the momentum, mass and energy conservation. The packing and cooling stages of the injection molding process are modeled by including the compressibility effects. The procedure is aimed by problems in which three-dimensional effects are important but is also effective for thin parts. The performances of the proposed approach are quantified for the injection of a thin plate for which experimental data are available. The procedure is then applied to a thick 3D part. The method results in accurate solutions and it proves to be a useful tool to quantify the solution behavior on cases otherwise difficult to investigate.
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Brown, H. L. and Jones, D. H. 2016, May.
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ANTEC 2016 - Indianapolis, Indiana, USA May 23-25, 2016. [On-line].
Society of Plastics Engineers
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