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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Selectivity of Extensional Viscosity Measurement under Different Conditions – Melt Elongation Versus Converging Flow
Elongational viscosity becomes more and more important due to increasing processing velocities in industrial processing. For film blowing, blow moulding and spinning process it is inevitable to consider elongational properties. The most important requirements for industrial application areFast testing with easy useHigh selectivityElongation rates similar to processingOnline measurement.Several methods of measurement have been analyzed and some are introduced on the market but not under all aspects mentioned above.First an online elongational viscosity measurement on the basis of the so called “Rheotens” is presented in this work. This method of melt elongation is then compared with converging flow method (entrance pressure loss), were different calculations of elongational viscosity are used. Different lots of polyolefine types are selected for elongational viscosity measurement. The selectivity of both methods to material differences are compared discussing measurement uncertainty.
Low-Coherence Interferometry Applied to Uniaxial Elongational Rheometry
The relevance of transient uniaxial elongational viscosity determination of polymers to industrial processes such as film blowing and foam extrusion is now being well recognized. Elongational rheometry is also beginning to be well documented, but it remains a delicate measurement technique, with reliability of the equipment and reproducibility of the data still being of prime concern.Recent developments in experimental evaluation coupled with state-of-the art optical techniques extend a step further the capabilities of generating reliable response in elongation, especially for large Hencky strains where dimensions of the sample being stretched is subjected to uncertainty. This paper will review the current approaches used and present a new way of monitoring in real time the true elongational response of polymeric materials, which exhibits enhancement of both the accuracy and the rapidness of the data acquisition.
An Evaluation of Elongational Viscosity of Polyethylenes Obtained from a Semi-Hyperbolic Die
A semi-hyperbolic (SHPB) die attached to capillary rheometer has been proposed as a method to obtain extensional viscosity data for polymer melts at high extension rates and strains. There has been very little confirmation that data obtained from this type of device is a true measure of the extensional viscosity, ?e. Values of ?e+(transient extensional viscosity) were obtained on a Münstedt device for several polyethylenes (PE) at extension rates which overlapped with those obtained from a semi-hyperbolic die. For a highly branched PE the values obtained on a SHPB die were qualitatively in agreement with those from the extensional rheometer. However, for a linear and a sparsely branched PE the values were an order of magnitude higher than those obtained from the Münstedt device. A new analysis was carried out relating the pressure drop to the extensional viscosity which included a correction term for the variation of pressure along the die wall.
Investigation of the Predictive Capability of Advanced Differential Constitutive Equations for Polymer Melts under Different Flow Conditions
The predictive capabilities of three models (modified White-Metzner model, eXtended Pom-Pom model and newly proposed modification of the Leonov model) are tested for steady shear and uniaxial extensional flows of LDPE, mLLDPE and PVB melts. The input low-shear-rate viscosity data was measured on ARES Rheometrics parallel plate rheometer, whereas RH7-2 capillary rheometer was used for the determination of shear viscosity (capillary), first normal stress coefficient (slit die) and uniaxial elongational viscosity (Cogswell method). A newly proposed ‘effective entry length correction‘ has been applied to deal with all extensional viscosity data.
Ultrasonic and NIR Determination of Filler Concentration in Polymer Melt Flows in Extrusion
The work detailed here describes techniques for improving the accuracy of previous ultrasonic methods used in determining filler concentration (up to 20 wt.%) in polymer melt flows. Results from preliminary investigation into the application of in-line transmission Fourier Transform Near Infra red (FT-NIR) for determination of filler concentration real-time during processing is also presented.
Properties and Processing of Thermal Conductive Thermoplastics
The increase of at least 60 Vol.-% high thermal conductive filler in thermoplastics is an innovative approach for direct adjustment of a plastic part´s heat transfer. The filler content and high thermal conductivity affects directly the flow- and cooling-conditions during injection moulding. The paper presents basic influencing variables onto processing an part properties and shows new ideas for the construction and intelligent injection moulding processtechnology.
The Effect of PIB Molecular Weight on the Cling Characteristics of Polyethylene/PIB Films for Stretch and Cling Film Applications
The effect of molecular weight on the migratory characteristics of polyisobutylene (PIB) additive from the bulk to the surface of a range of mono-layer and multi-layer extruded polyethylene films was analysed by FTIR-ATR and peel cling analysis. Migration rates were shown to be higher for low molecular weight additive and cling strength increased as the PIB molecular weight increased.
A Rheological Model for Thermoplastic Resins Melt
A new rheological model of polymer melt was developed to describe viscosity-shear rate curves utilizing a four parameters equation based on Guassian processes approach for regression description of melt properties. Four parameters of the model (Newtonian viscosity at “zero” shear rate, viscosity and shear rate at inflection point, and dispersion of the rate of change of the viscosity) were found to be a function of polymer chain structure, molecular weight and temperature. The model provides precision description in a wide range of conditions of shear deformation of the polymer melts, solutions, blends and alloys.
Experiments in Micro-Welding of Polycarbonate with Laser Diodes
Polymer use in micro-devices, especially in the medical industry has been rapidly increasing. During assembly of micro-devices it is desirable to produce weld joints that are about 100 ?m in width. This paper reviews the use of fiber coupled laser diodes in conjunction with special lenses to produce spot sizes between 25 and 50 ?m in diameter for through transmission infrared welding technique. Studies were completed to evaluate the effect of travel speed, power density and pressure on weld quality for polycarbonate and polystyrene. It was found that process parameters are extremely critical in producing consistent welds. In addition, new testing techniques had to be developed to allow quantitative measurements to be made on weld strength due to relatively small weld area. Micrographs of the resulting welds revealed evidence of ablation at high heat inputs. Finite element analysis of the mechanical tests showed that the localized weld strength approached the yield strength of polycarbonate.
Modeling Heat Flow for a Moving Heat Source to Describe Scan Micro-Laser Welding
Polymer use in micro-devices, especially in the medical industry has been rapidly increasing. During assembly of micro-devices it is desirable to produce weld joints that are about 100 ?m in width. This paper reviews the modeling of heat flow during through transmission infrared micro-welding of plastic using fiber coupled laser diodes. Two models were used to predict temperature distributions within welded samples. Both models were based on a moving heat source and moving coordinate system. For the simpler model a moving point heat source was used and for the more complex model a Gaussian distributed heat source was used. It was found that the distributed model can accurately predict temperature fields in plastic laser welds for all ranges of the parameters evaluated. However, the point heat source model was only able to accurately predict temperature fields with a relatively small laser focal spot (25 ?m). In addition it was found that for micro-welding of plastics, when the dimensionless distribution parameter is less than two, a point heat source model predicts similar widths to those predicted by a distributed heat source model.
Measurement of Residual Stresses in Clearwelds Using Photoelasticity
Residual stresses are detrimental to a plastic joint for a number of reasons. They lead to reduced strength and fatigue life in joints, act as stress concentrators and cause crazing, cracking when exposed to solvents. In this paper, the residual stresses in Clearweld® joints were measured using photoelasticity. This interference based technique was used in conjunction with a stress separation algorithm to quantify the maximum residual stress level and the stress distribution in the weld region. Also, the effects of process parameters like welding speed, power and ink solvents on residual stresses were evaluated. The GE solvent test was also employed for comparison with the photoelasticity results. A comparison of the residual stresses between various joining processes was also made.
Diode Laser Characterization and Measurement of Optical Properties of Polycarbonate and High-Density Polyethylene
In recent years, the use of high power diode lasers for through transmission laser welding (TTLW) of thermoplastics has increased rapidly due to the many advantages that they provide, mainly their compact size and low cost. The diode laser output can affect the heating rate and uniformity, making it important to characterize the diode laser in any welding application. In this study, diode laser bar characterization included measurement of the power efficiency, beam shape, and intensity distribution. Those measurements were performed with and without a proprietary fiber bundle provided by Branson Ultrasonics, which improved the uniformity of power intensity. In TTLW laser beam reflection, absorption and scattering as it passes through the transparent part affects the power that reaches the weld interface. Therefore, it was important to study the transmittance and reflectance of polycarbonate and high-density polyethylene. The effects of thickness and beam incident angle on transmittance and reflectance were also measured.
Applications of Polymers in Cement-Based Structural Materials
Cement-based materials are widely used in the civil infrastructure. Polymers as admixtures can improve the properties, particularly in relation to water absorption reduction, toughness enhancement, vibration damping and increase of the bond strength of cement to reinforcements. Polymeric admixtures include particles, short fibers and organic liquids. Latex in the form of an aqueous particle dispersion is most common. Other than being used as admixtures, polymers are used as partial replacement of fine aggregate, for coating, sealing and repairing concrete and for coating steel reinforcing bars for corrosion protection.
Hydrosilylation of Polypropylene through Reactive Extrusion
Hydrosilylation of terminal double bonds in polypropylene (PP) was investigated in a twin-screw extruder. This process involved two steps: i) peroxide initiated degradation, which leads to the formation of terminal double bonds and ii) the addition of siloxane compound to such bonds. FTIR was used to follow the terminal double bond formation and siloxane incorporation. The shear viscosity at different temperatures and the contact angle of the hydrosilylated PP were evaluated. The reaction was found to decrease viscosity and to improve hydrophobicity.
Measurement of Residual Stresses in Laser Welded Polycarbonate Using Photoelasticity
Residual stresses are detrimental to the strength of plastic joints. They lead to reduced strength and fatigue life in joints, act as stress concentrators and cause crazing and cracking when parts are exposed to solvents. In this paper, photoelasticity is used to measure the residual stresses in laser welded polycarbonate. Photoelasticity, an interference based technique, was used in conjunction with a stress separation algorithm to quantify these stresses along and perpendicular to the weld line. The GE solvent test was also employed to serve as a comparison to the photoelasticity results. A comparison of the residual stresses between laser welded samples and hotplate welded samples have also been made.
Effect of Polypropylene Rheology on the Vibration Welding Process
Vibration welding is a joining technique to assembly thermoplastic components. Meltdown-time profiles and assessment of weld microstructure are commonly used to characterize the behavior of polymers during vibration welding. The aim of this work is to establish relationships between the rheological properties of molten polymers and their meltdown rate during vibration welding. Two polypropylene homopolymers with different molecular weights resulting in different rheological properties were studied. Vibration welding was carried out using a butt-weld geometry and meltdown-time profiles were measured. Significant discrepancies between experimental results and theoretical predictions based on the simple model developed by Stokes suggest the presence of significant elastic effects.
Real Time Temperature Measurement of Nylon 66 Butt-Joints during Vibration Welding
Modeling the vibration welding process requires accurate knowledge of the melt temperature at the interface. Due to technical difficulties related to the very small molten film thickness, little work has been done to date on measuring the weld temperature under real time conditions. This paper presents a novel technique for measuring the weld temperature in real time. It involves inserting a 25 ?m thermocouple into one of the welding parts in close proximity to the weld zone. During vibration welding, the thermocouple works its way to the weld interface and records the melt temperature. The experimental data from vibration welding nylon 66 butt joints indicate that the melt temperature at the weld interface is within 15°C of the onset of polymer melting. The temperatures measured in the solid phase prior to entering the melt film are consistent with theoretical models for heat conduction into solid plates.
Heated Tool Welding of Thermoplastic Polyolefin (TPO)
This study focused on the weldability of two specific thermoplastic polyolefins (TPO-A and TPO-B) using heated tool welding. A three-factor (heating temperature, heating time, and welding pressure) and three-level design matrix was used to perform the welding. Two statistical methods, three-factor two-level design of experiments (DOE) and Box Behnken method, were used to analyze the weld results. In addition, vibration welding of these TPOs was also used to compare the weldability. For heated tool welding, the maximum joint strength was 88% of the bulk strength for TPO-A and 76% of the bulk strength for TPOB. For vibration welding, the maximum joint strength was 65% for TPO-A and 56% for TPO-B. While heated tool welding provided stronger joints compared to vibration welding, it had a longer cycle time. The two statistical methods provided similar results indicating that the simple three-factor two-level design of experiments was a valid screening method for heated tool welding of TPO.
The Effects of Weld Geometry and Glass-Fiber Orientation on the Mechanical Performance of Joints – Part II: Kinetics of Glass-Fiber Orientation and Mechanical Performance
The mechanical performance of injection molded short glass-fiber reinforced thermoplastic components is anisotropic and is highly dependent on the fiber orientation and distribution. Similarly, the bulk and short and long-term mechanical performance at the weld is influenced by these fibers and the specific welding technology used as related to melt-pool formation.The purpose of this analysis is to show:the short-fiber orientation (analytical and simulation data) and distribution at the pre-welded bead, ribs and wall areas;advantages of SigmaSoft injection molding simulation software, which utilizes full three dimensional fiber representation of any molded part;the mechanical performance of welds with optimized geometry (US Patent 6,447,866).Findings on the mechanical performance of butt-joints with different designs and localized geometry will help designers and technicians with plastic part design optimization. In a previous ANTEC paper (Part I), we related these findings to the kinetics of welds and part design issues for straight and T-type butt-joints.
Optimized Rheology and Density of Polyolefin Elastomers for Clarified Polypropylene Applications
Polyolefin elastomers based on metallocene technology are excellent impact modifiers for polypropylene. This study looks at how density and melt rheology of polyolefin elastomers affect clarity and impact performance of clarified polypropylenes with 2, 10, and 35 MFR. Optimum clarity and improved impact performance are achieved by matching rheology and density of polyolefin elastomers with polypropylene.
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