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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Pressure Regulation of the Extrusion Process
A self-regulating valve is placed between the extruder and die is to adjust the melt pressure and also reduce the amount of surging related to the screw beat in an extrusion process. The experimental results validate that there is a linear relationship between the control force and output melt pressure, and that the use of a self-regulating valve can significantly reduce the variation in output melt pressure compared to the conventional extrusion process. However, the results indicate that the specified control force and output melt pressure must be carefully selected in extrusion processes to prevent excessive increases in plastication pressure. Furthermore, the response time of the valve limits the dynamic performance of the system, and indicates the need for potential improvements in mechanical and control system designs.
Fracture Characteristics of CF and GF Reinforced PA6 Sandwich Moldings
The effects of interfacial shear stress between fiber and matrix, and fiber surface morphology on the fracture toughness of carbon fiber (CF) and glass fiber (GF) reinforced PA 6 sandwich composites are investigated in this study. Both fiber length distribution measurement and single edge notch bending fracture tests were carried out. 6 configurations were produced for this study, i.e. PA 6, composites reinforced with CF (CF/PA 6), composites reinforced with GF (GF/PA 6), GF and CF blend (GF/CF/PA 6) produced via conventional injection molding techniques, whereas the sandwich moldings CFPA 6 skin/GF-PA 6 core (CFs/GFc/PA6) and GF-PA 6 skin/CF-PA 6 core (CFs/CFc/PA6) which were produced using co-injection molding. As a result of rough CF surface, coupled with its capabilities to induce transcrystallinity in the matrix, CF/PA6 have higher interfacial shear stress, fracture toughness and fracture energy values compared to GF/PA 6 composites.. CF also tends to have a very low critical fiber length compared to GF. This is very obvious as the fracture toughness values of CF/PA6 were the highest among all composites. The GF/PA6 configuration was the second lowest, while PA 6 itself recorded the lowest fracture toughness values. Substantial retention of toughness is observed by blending both CF and GF together into GF/CF/PA6. Both CFs/GFc/PA 6 and GFs/CFc/PA 6 sandwich structures show nearly similar toughness values. This is due to the fact that both sandwich composites behave like laminates, i.e. GF/PA 6 and CF/PA 6 laminates combined into a single composite. As such, the superior properties of CF were not efficiently utilized. Fracture energy was calculated on the basis of Kc and Gc relation. CF/GF/PA 6 and GFs/CFc/PA 6 dominate the highest values of fracture energy. This is again attributed to the addition of CF into the sandwich composites.
Fabrication of Composite Pipe With Recycled Polycarbonate and Crushed FRP Products
Injection molding with recycled polycarbonate (PC) and crushed FRP products was fabricated and examined on tensile, flexural and Izod impact test. The specimen of composition filled with 5wt% of FRP and modifier had highest mechanical properties. The composite had approximate equivalent tensile strength and higher Izod notched impact value than that of standard rigid PVC. Composite pipe made of this composition was manufactured by using extrusion process. The composite pipe has extreme high flexibility because in 50% diameter reduction of lateral compression test no fracture ccurred. Consequently, the composite pipe can become substitute of PVC.
Effect of Loading Rate on Tear Resistance of LLDPE
It is known that mechanical properties of LLDPE films depend on the length of the short chain branches. However, it is often very difficult to differentiate this effect with the effect of other variables such as comonomer distribution and molecular weight distribution using standard test methods. Furthermore, the structure property relationships for copolymers with different length alpha olefins has not been clearly established. High rate tensile, high rate single edge notch tear, and the essential work of fracture method were used in this paper to differentiate the effect of short chain branch length using several well controlled samples. The crystal morphology of the samples at different stages of deformation were analyzed using DSC, AFM, and X-ray to explain the effect of short chain branch length. It was demonstrated that the tear resistance of LLDPE thin films produced with different length alpha olefins can be differentiated using strain hardening, tear energy, or essential work of fracture at high loading rate. A hypothesis is also proposed to explain the effect of short chain branch length on film tear resistance.
Mechanical Characteristics and Fractographic Analysis of Nanocomposites
In this study, the effect of the number and size of clusters on the fracture behavior of PP and TPO nanocomposites are investigated. The effect of the particle size distribution and injection molding flow profile are also discussed with respect to the effect of filler morphology on the tensile fracture toughness. Fracture pattern and fracture surface were examined by scanning electron microscopy (SEM). The morphological analysis of crack propagation path and the contribution of nanoparticles were studied by observing process zone formation during crack propagation. A schematic model of nanoparticle distribution in injection molded specimens is also proposed based on fractographic analysis.
Understanding of the Failure Mechanism of Stress Corrosion Cracking by SEM Analysis
Stress corrosion cracking (SCC) results from strongly coupled electro-chemical and thermo-mechanical processes, and this cracking is sensitive to material composition and morphology. There are four stages of SCC such as initiation, individual SC crack propagation, many crack interactions and clusters of crack formation, and finally crack or cluster instability and dynamic growth leading to the ultimate failure. In this paper the mechanism of SCC is investigated by the observation of SCC surface using a scanning electron microscope (SEM). Thermodynamic model of SCC propagation and statistical modeling of SCC initiation based on chemical degradation has been proposed before by the authors. The model predicts a change of the mechanisms of crack growth from chemically driven to mechanical stress control propagation. This prediction is validated by fractographic observations. It provides important information on the change of SCC propagation mechanism by the variation of micro-morphology and striation on the fracture surface. The duration of chemically driven stage of SCC and transition to stress controlled propagation depend on temperature and stress.
Injection Molding Simulation in Dealing with Part Quality Variance and Correlation Study
Utilizing the injection molding simulation, this paper illustrates a methodology of dealing with manufacturing variance occurring in molded parts. For the simulation, the manufacturing variance is deliberately induced by a small change in processing condition variables, which consequently causes a variation in the rheological properties of the polymer melt entering into cavity. By comparing the simulation results with previously published experimental results, an attempt is made to statistically validate this methodology. In doing so, the effect of different switchover methods during the injection stage is comparatively evaluated. The part weight and dimensions are chosen as the quality characteristics. This study also investigates correlations between part weight and dimensions, as well as between the predictions and the experiments of an actual molding trial.
Integrative Simulation: Prediction of Mechanical Parts Properties Based on the Simulation of Local Inner Parts Properties
Inner parts properties strongly affect the global mechanical behavior of molded semi-crystalline parts. During the last years an IKV research group tried to bridge the gap between simulation of inner properties and structural analysis. By a self-developed software to simulate inner properties arising during injection molding and programmed subroutines for Abaqus a so-called integrative simulation was realized. Results of this simulation chain will be presented and discussed focusing on a plastics pipe fitting made out of polypropylene.
The Affect of Accelerated Aging and Physical Aging on Molecular Weight in Medical Polymers
Shelf life is an important quality for medical components. It is uncertain at what point physical aging affects the chemical resistance of medical components. The breakdown of chemical resistance in the polymer can result in adverse effects in the field.As a polymer ages there is usually a reduction in molecular weight, which can lead to greater susceptibility to chemical attack. The objective of this research is to attempt to draw correlations between accelerated aging at elevated temperatures and room temperature aging to better identify when molecular weight reduction and increases susceptibility to chemical attack occurs.
Microcellular Injection Molding Compared to Conventional Injection Molding
This paper will show how the microcellular injection molding process compares to conventional injection molding for an injection molded part with tight tolerances. A critical part from a laser printer was used as an example in the study. The part was first injection molded using the conventional injection molding process then analyzed using the microcellular injection molding process. The Moldflow® injection molding simulation software was able to accurately predict the part warpage which agreed well with the real injection molded part. The predicted part warpage in microcellular injection molding process was better than in the conventional injection molding process.
Increasing the Surface Quality of Foamed Injection Molded Parts
Besides a lot of positive aspects of foam injection molding (FIM), the achievable surface qualities are rather poor in many cases. Occurring silver streaks, melt eruptions and cold-displaced polymer melt areas cause more uneven and non-uniform part surfaces in comparison to conventional injection molding. That is the reason why foamed parts are often excluded as visually exposed parts. A comprehensive understanding of the effects arising during the filling phase establishes new possibilities to increase the surface qualities in foam injection molding. New research shows that different process variants of FIM such as breathing" molds gas-counterpressure structured and coated cavity surfaces can increase the surface quality effectively."
Molecular Structure and Rheology Relationship of Polyethylenes
The structure-rheology relationship is investigated in three polyethylenes namely high density polyethylene (HDPE), a metallocene linear low density polyethylene with no chain branching (mLLDPE) and a metallocene polyethylene containing long chain branching (mLLDPE-LCB). Shear and extensional rheology measurements were carried out in the linear viscoelastic regime and correlated to the molecular weight, molecular weight distribution and long chain branching. Shear rheology showed that HDPE exhibits a viscosity profile whereby the Newtonian behavior is not completely attained as shown by the slope of the storage modulus in the terminal region. mLLDPE was found to possess the longest and well-defined Newtonian region and the highest transition to the non-Newtonian region. In the presence of long chain branching (LCB), the terminal region is not apparent while the onset of shear thinning is decreased. Such behavior can be related to the effects of MWD and LCB and was corroborated using extensional viscosity measurements, which showed slight deviation from the LVE envelope for broader molecular weight distribution and strain hardening in the presence of long chain branching.
Development of Thermoplastic Polyurethane Electrolytes and Their Ionic Conductivity
The ionic conductivity of linear segmented thermoplastic polyurethane (TPU) in-situ reacted with alkali metal salts as well as their blends of TPU and modified polysiloxane is investigated. The relationship between ion conductivity and cationic size in TPU electrolytes is discussed with different salts. We focused on investigating two particular types of salts such as LiClO4 and KI. Differential scanning calorimeter (DSC) and Fourier transform infra-red (FTIR) spectroscopy was used to determine the interaction of salts with TPU. The temperature dependency of TPU electrolytes is also studied by using the modified LCR meter.
Injector Technology for the Water Injection Technique (WIT)
The water injector is the centerpiece of the complete system configuration for the water injection technique. For a stable and reproducible process cycle, a well operating injector system is one of the basic demands. It is still unclear how the injector design effects the stability of the process and important part properties. Thus, different injector concepts have been developed and evaluated practically with different polymers. The first results presented in this paper suggest, that the injector orifice diameter and the ambient shape of the injector closure cap influence directly the part quality and the process stability.
Prediction of Temperature, Viscosity and Shear Stress during Steady State of Vibation Welding of Polyamide-6
A simple model was developed for the steady state phase of the vibration welding process using the lubrication approximation. The model predicts temperature and pressure at the interface, molten fluid film thickness, shear stress and shear rate as functions of weld pressure, amplitude, frequency, and penetration velocity. The melt viscosity was estimated, using the penetration velocity obtained from meltdown velocity, since data for melt viscosity of polyamide-6 at vibration molding conditions were not available. The model predicts temperature at the interface in a reasonable range, 7-37°C above the melting peak temperature. The overall predictions of the model are reasonable and they should be helpful in optimization of vibration welding process parameters.
Sacrificial Mold Embossing for High Density, High Aspect Ratio Micro/Nano Structures
An unconventional embossing method is evaluated in which de-embossing is avoided to prevent the deformation or damage of the polymer microstructure on the substrate due to one or more of the following issues involved in hot embossing process: higher feature density, higher aspect ratio, bad surface quality and under-cuts. In this study, a PDMS mold is used to transfer a SU-8 structure to a water-soluble polymeric stamp under low pressure and low temperature, which is used as the rigid tool in the following hot embossing and can be reused by being dissolved in water, an environmentally benign solvent. This method has potential uses in the replication of high aspect ratio microstructure on polymeric materials that cannot be easily achieved using other methods.
Carbon-Filled Polymer Composite Bipolar Plates for Proton Exchange Membrane Fuel Cells (PEMFCS)
Carbon-filled epoxy composites were developed as potential materials of bipolar plates in proton exchange membrane fuel cells (PEMFCs). The synergistic effect of combining graphite and carbon black on conductivity of composites was investigated. All composites provided much higher in-plane electrical conductivity than the Department of Energy (DOE) target value of 100 S/cm, although through-plane conductivity was measured to be about 50 S/cm. The chemical stability of these materials was checked by using acid reflux in boiling aqueous sulfuric acid solution with a pH of 2. The thermal properties of these composites was investigated through DSC and TGA.
A Study of Ethylene Co-Vinyl Alcohol (EVOH) / Montmorillonite Layered Silicate Interactions
A series of poly (ethylene co-vinyl alcohol) (EVOH) / montmorillonite layered silicate (MLS) nanocomposites were processed using a mini-extruder and evaluated by xray diffraction, transmission electron microscopy (TEM) and thermal analysis to determine the polymer/MLS interactions and morphologies. The nanocomposite materials were produced using different concentrations of MLS (3, 10 and 15% by weight) and EVOH that were equilibrated to 95% humidity and to dry conditions prior to processing. Most samples displayed an intercalated morphology with no significant changes with the presence of moisture.
Synthesis and Characterization of PMMA/Silica Nanocomposites
Thermal stability and mechanical properties of polymeric nanocomposites consisting of functionalized silica nano-particles (average diameter 75nm) embedded in polymethyl methacrylate (PMMA), with and without surface grafting of PMMA, were studied. Results from differential scanning calorimetry show an increase of Tg upon the introduction of the nano-particles, however, only to a limited extent. Similar results were observed in dynamic mechanic thermal analysis. The storage modulus also showed a slight increase less than 5%. Samples with PMMA grafted particles synthesized via in-situ polymerization in supercritical CO2 did not show an anticipated drastic improvement. This may result from the plasticizing effect of the stabilizer used the dispersion polymerization.
Optimization of Acrylic Components in Extruded Rigid PVC
In this study the effect of acrylic-based components, including process aids (PPA), on the rheological properties of rigid PVC formulation is investigated. A statistically designed experiment was set up to cover the effect of composition on the melt viscosity and the melt strength of the compound as a function of temperature. The effect of the acrylic components was studied in relation to the rheological properties such as capillary rheometry and melt strength. In the absence of an acrylic process aid, the PVC compound showed a loss of adhesion at the wall caused by a change in the microstructure and characterized by pressure oscillations and a dip in the melt strength trace. As the temperature is increased, the slippage appears to be minimized and the head pressure stabilized.
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