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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Optimization of Electrical Properties of Bipolar Plastes Out of Highly Filled Compounds: Investigations on Conditioning and Thermal-Mechanical Stress
To attain an optimal and efficient bipolar plate, the used material, a ternary compound consisting of polypropylene, graphite and carbon black, as well as the molding process have to be fathomed. Therefore, steps for conditioning the highly filled compound before injection molding are compiled and the behavior of the matrix material polypropylene during thermal-mechanical stresses was analyzed. On the one hand this paper shows the influence of pellet forms (different L/D ratios), moisture absorption and barrel temperature on the resulting electrical resistance of the bipolar plates. On the other hand the consequences of process temperatures above the recommended temperature range of polypropylene are investigated via the dedication of different amounts of a polypropylene-based heat stabilizer masterbatch and residence times.
Rapid Crack Propagation (RCP) Performance of Unimodal Medium Density Polyethylene (MDPE) Pipe
As polyethylene (PE) pipe is being employed across an ever-widening range of applications, its resistance to rapid crack propagation (RCP) is a primary consideration for designers and end users. Test methods for determining a pipe’s resistance to RCP are the ISO 13478 Full Scale (FS) test and the ISO 13477 Small Scale Steady State (S4) test. Because of availability, low cost, ease of installation, and low maintenance, medium density polyethylene (MDPE) has been a customary material of choice for gas distribution lines for several decades. Presented here are the results of an experimental study to characterize the RCP resistance of chromium catalyst based unimodal MDPE pipe of common sizes using both the FS and S4 tests. While the S4 test results suggest lower RCP performance, the FS test results for all pipes tested indicated very adequate RCP resistance for use in gas distribution lines. This difference is attributed to the fact that the current S4-to-FS correlation factor of 3.6 is not representative of many current generation PE pipes, and a factor of 4.5 is more appropriate. The correlation factor of 4.5 determined from the current study matches very well with previously published data from our laboratory.
New Approaches of 2D Recursive Least Squares System Identification for Batch Processes
For most model-based control algorithms, the control performance is heavily relied on the model accuracy. This paper presents two new Two Dimensional Recursive Least Squares (2DRLS) estimation approaches for batch process system identification, a time wise 2DRLS (t-2DRLS) and a batch wise 2DRLS (b-2DRLS). Both approaches use parameters information from previous batches. The difference between them is that the t-2DRLS uses intermediate computation information from last sampling period, while the b-2DRLS uses the information from last batch but the same sampling period. The proof of convergence of b-2DRLS is given in this paper. Furthermore, both approaches have been applied to injection molding, a typical batch process, to test the performance of the design. An adaptive control scheme has been adopted and the experimental results of injection packing pressure control verified the advantages of the proposed approaches over the traditional RLS.
Polymerization of Lactide to Polylactic Acid and Co-polymers of Polylactic Acid using High Viscosity Kneader Reactors
Polymerization of lactide to polylactic acid (PLA) can be performed using conventional reactor technology such as stirred tank reactors, but the conversion and/or final molecular weight may have to be controlled to a lower level. At higher conversion and/or molecular weight, the reaction mass will become very viscous, which limits the ability of conventional reactor technology to provide adequate mixing, minimize mass transfer effects on reaction kinetics, remove exothermic heat of reaction and ensure proper heat transfer in order to eliminate hotspots/thermal degradation. Kneader reactor technology has been used over 60 years in many high viscosity applications such as reactions and polymerization, devolatilization, and drying. This technology can handle the higher conversion and molecular weight polymerizations of lactide and other copolymers of lactide, while also providing the heat transfer required for proper temperature control. Using model kinetics and rheology data, a study was performed that shows the capability of kneader reactor technology for lactide polymerizations as well as other copolymers. Kneader reactor technology can also be used to remove the unconverted monomers from the polymer and expected results from the continuous operation of a polymerizer and finisher will be shown.
The Response of Highly Loaded Polylactic Acid Masterbatches Containing Pigmentary Titanium Dioxide
The use of bio-based polymers continues to gain commercial acceptability. With this growth, the need to impart opacity, whiteness, UV protection and printability to commercial articles is becoming more critical. Titanium dioxide (TiO2) is typically the pigment of choice to meet these criteria. While TiO2 is traditionally delivered as a highly loaded masterbatch, it is well known that many bio-based polymers are sensitive to masterbatch processing conditions. Understanding whether bio-based polymers are tolerant of the processing conditions used in high solids loading without significant performance degradation is the subject of this paper. Using polylactide (PLA) as a model system, the compounding performance of highly loaded TiO2-PLA masterbatches is discussed.
Floating/Swivel Top-Load Testing and Simulation - a Novel Approach for Evaluating Unit Load Stability at the Early Stage of Primary Package Development
A novel floating/swivel platen approach is proposed in this paper for primary package top-load evaluations. Different from the conventional fixed platen top-load practice, this approach, which frees the translational (floating) and rotational (swivel) degrees of the platens and designates them separately to the bottom and top platens, allows tests or simulations to predict the lateral instability of primary packages. The lateral instability of primary packages becomes increasingly crucial to the tray-based unit load stability with growing cost-saving efforts and design innovations from brand owners, design agencies and packaging suppliers. This study, through both lab testing and virtual computer simulation, has demonstrated that the proposed floating/swivel platen approach accurately captures the package top-load reduction induced by the package lateral instability, while the conventional fixed platen top- load practice dangerously over-predicts the package top-load by a factor of as high as 3.6, due to the suppression of the lateral instability by the fixed platens. Such an over-prediction could lead to unexpected damage to the primary packages and/or unit load collapse during storage and transportation. The proposed floating/swivel platen top-load approach is recommended for light- weighting and design innovation in the early package development stage.
Selective Localization of MWCNTS in Blends of Poly(Methyl Methacrylate) and Styrene-Acrylonitrile Copolymer
Multi-walled carbon nanotubes (MWCNTs) were introduced into poly(methyl methacrylate) (PMMA) and styrene-acrylonitrile copolymer (SAN) blends by melt mixing in an asymmetric mixer. A composition of 70 wt% of PMMA and 30 wt% of SAN was mixed to make a co-continuous morphology. Transmission electron microscopy images of ultra-microtomed samples (70 nm in thickness) showed selective localization of MWCNTs inside the percolated SAN polymer. The occurrence of the double percolation phenomenon resulted in lower electrical percolation thresholds of PMMA/SAN/MWCNT blends prepared at high temperatures. Dielectric spectroscopy indicated a higher electrical permittivity of samples that were molded at 260°C. Due to the higher affinity of MWCNTs to SAN, there was a migration of MWCNTs into the SAN phase during the melt processing.
Cyclic Olefin Copolymer Foams Part 1: Solubility Measurement of CO2 in Cyclic Olefin Copolymer and Preliminary Foaming Study
Cyclic olefin copolymers (COCs) is a novel engineering plastic with excellent thermal and mechanical properties which make them viable alternative to polyolefins. In this study, the solubility of supercritical carbon dioxide (CO2) in COC (Topas 6017) was measured at temperature from 453.15 to 493.15 K and pressure up to 17 MPa by a modified pressure decay system which can be operated in high temperature environment. The volumetric expansion of polymer caused by the dissolved CO2 were calculated by using the Sanchez-Lacombe equation of state (SL EoS) and these volume data were used to correct the apparent solubility data. The results demonstrated that solubility of CO2 in COC increased with the elevated pressure and decreased with the elevated temperature. SL EoS can correlated the solubility within 6% average relative deviation by introducing a temperature dependent interaction parameter. Moreover the COC foams were prepared by using pressure quench process and some preliminary results were obtained.
Effects of Holding Pressure & Process Temperatures on the Mechanical Properties of Moulded Metallic Parts
Metal injection moulding is gaining more and more importance over the time and needs more research to be done to understand the sensitivity of process to different process parameters. The current paper makes an attempt to better understand the effects of holding pressure and process temperatures on the moulded metallic parts. Stainless steel 316L is used in the investigation to produce the specimen by metal injection moulding (MIM) and multiple analyses were carried out on samples produced with different combinations of holding pressure, mould temperature and melt temperature. Finally, the parts were characterized to investigate mechanical properties like density, ultimate tensile strength, shrinkage etc. The results are discussed in the paper. The main conclusion from this study is unlike plastic moulding, the tensile properties of MIM parts doesn’t vary based on the flow direction of the melt, and tensile properties are sensitive to holding pressure and process temperatures. In order to achieve higher tensile strength, higher holding pressure is required. It was also observed that the samples shrunk more in thickness than in the width and length.
Design of an Innovate and Recycle Float-Valve System by Using CAD/CAE/LCA Tools
Due to the growing worldwide interest in tasks such as environment preservation and recycling, a model of float-valve system for domestic water tanks has been proposed. It considers in its design, the use of an urban waste product such as PET bottles, as the floating device of the mentioned mechanism, having as main idea to contribute with environment care. If the new design is compared with known commercial models, it could be considered as innovative due the reutilization of plastics wastes. At the same time, the system functionality is preserved, and the final parts are easy to fabricate at low cost. Also, the estimation of the Life Cycle Assessment (LCA) for the system shows that the proposed design could be catalogued as environmental friendly.
Design of an Isolated Runners Mould by Using CAD/CAE Tools
The main objective of this work was to compare the advantages and disadvantages of using an isolated runner mould comparing with hot and cold runner moulds. It was used CAD and CAE software for the representation of the mould. The isolated and hot runner’s moulds showed advantages regarding volumetric and lineal shrinkages and sink marks of the injected part and there is not loss of material after each cycle by solidification of the sprue and runners when it is compared with the cold runners. The isolated runner mould is less expensive than a hot runner mould.
In Mold Coating of Thermoplastic Parts: Electrical Conductivity Versus Injection Pressure
In Mold Coating (IMC) has been applied to Sheet Molding Compound (SMC) as an environmentally friendly alternative to make the surface conductive; for subsequent electrostatic painting operations. Due to its successful application to exterior body panels made from compression molded SMC, the application of In Mold Coating for injection molded thermoplastic parts is being developed. In order to make the coating conductive, the filler used in IMC is carbon black (CB). However, the injection pressure needed to coat the part is significantly affected by the amount of CB in the coating material. Predicting injection pressures for IMC of thermoplastic parts is more critical than for IMC of SMC. To predict the coating pressures we need to measure the effect of CB on the IMC viscosity. In the present work, we studied the effect of CB on electrical conductivity and viscosity. The pressures needed for coating a typical IMC part with the required conductivity level are estimated.
Morphology and Thermal Behavior of Nylon-6/Clay Nanocomposites Synthesized by In-Situ Solution Polymerization of Caprolactam
A novel in-situ anionic polymerization method for preparation of nylon-6/clay nanocomposites in N- methylpyrollidone is explored. Anionic solution polymerization of caprolactam was performed in the presence of montmorillonite clay. The product was obtained as granules. The morphology of the nanocomposites was studied by using X-ray Diffraction (XRD) technique and Scanning Electron Microscopy (SEM). Differential scanning calorimeter (DSC), was used to study the composites transition temperatures and melting behavior. The presence of clay broadens the melting and crystallization peaks and shifts the glass transition temperature and melting point to higher temperature.
The Effects of Turbulent Flow on Cooling Effeciency in Injection Molding
Cooling plays an important role in injection molding process. A well designed cooling system can effectively shorten cycle time and improve product quality as well. Nowadays, three dimensional cooling analysis has been applied in injection molding simulation. With this function, a complex cooling system design can be validated with its efficiency prior to actual manufacturing. However, the current simulation tool is not perfect yet since it does not consider turbulent flow and pipe surface roughness effect. In the current study, a latest simulation tool was applied which can predict the turbulent flow effect on cooling. Two cooling systems (conventional and conformal) were designed and simulated. The results were compared to each other which are helpful at the design stage in an injection molding cooling system.
Sandwich Injection Molding - Core Breakthrough and Flow Imbalance Studies
We presented numerical simulations concerning two important defects encountered in the sandwich molding process: the core breakthrough in a thin-walled part and the flow imbalance in a multi-cavity mold. The part thickness largely determines how far the skin melt front advance before breakthrough happens. This limits the size of the part and the maximum core ratio. The skin and core advancement in the multi-cavity system is complex due to the temperature imbalance and pressure resistance variation encountered in the runner. An understanding of the melt flow mechanism through simulation is helpful for the part designer to fully utilize the benefits of the sandwich molding process.
Transformation of Measured Viscosity Data of Special Plastic Materials Into Moldflow Software
Special applications in plastic engineering require new different polymers. Therefore new polymers and additives are constantly being developed. A lot of these special polymers are not available in databases and cannot be used in simulation software. But it is becoming more and more important to know as much as possible about polymers in order to avoid problems in product development and the manufacturing process. So the polymers have to be tested. This paper shows a possibility of measuring points of flow curves and transforming them into a mathematic model to do molding simulation with the specific material afterwards.
Role of Simulation in Analyzing Root Cause Failure
Understanding root cause failure mechanisms for plastic packaging is becoming more important. This need has become critical due to new packaging materials, faster production speeds, lighter weight packages, creative designs and challenging product formulations. Often there is a need find and eliminate the cause for failure and come up with a more robust package. Replicating and analyzing failures via simulation can provide rapid feedback and optimal solutions in a shorter time frame than traditional methodologies. This paper looks at some of the common failure mechanisms and not so common analysis and detection procedures. Practical case study examples will be presented.
A Study of Rolling Resistance of Electrospun Polymer Fabrics
Rolling resistance contributes to 6-10% of the overall fuel consumption of vehicles. Little is understood on the relationship between rolling resistance and surface characteristics such as adhesion, surface asperities and topology. In this study, we evaluate the rolling resistance using a free oscillation of a pendulum. Different substrate materials such as asphalt, rubber, wood, high-density polyethylene (HDPE), nylon, polycaprolactone (PCL) and poly(vinylidene fluoride) (PVDF) were tested by a laboratory fabricated pendulum steel roller. The damping factor is examined using an envelope analysis technique based on Hilbert transform methodology. The rolling resistance is found to depend on viscoelastic properties, adhesion and surface characteristics. The damping factor is the highest for asphalt and the second highest for rubber. The damping factor of electrospun polymer fabrics lies somewhere in between those pertaining to asphalt and more rigid substrates such as steel and copper
Key figures for describing and comparing the energy consumption of injection molding processes
This paper deals with energy consumption data for a broad variety of injection molded parts. An analysis shows that key figures can be derived for comparison and reference purposes and allow the evaluation of the energy efficiency in a part dependent production process. The key figures comprise material properties and part geometries to build a focus relative to these particular part characteristics independent of category or application. This approach goes beyond the widely applied method of examining a machine specific energy consumption data. A significant potential of energy reduction for most analyzed injection molding processes is expected.
Microcellular injection molding of in-situ modified Poly(Ethylene Terephthalate) with supercritical nitrogen
The microcellular injection molding (commercially known as MuCell) of in-situ polymerization-modified PET (m-PET) was performed using supercritical nitrogen as the physical blowing agent. Based on design of experiment (DOE) matrices, the influence of operating conditions on mechanical properties of molded samples were studied systematically for two kinds of m-PETs, namely, n-m-PET and m-m-PET synthesized using pentaerythritol (PENTA) and pyromellitic dianhydride (PMDA) as modifying monomers, respectively. The optimal conditions for injection molding were obtained by analyzing the signal-to-noise (S/N) ratio of the tensile strength of the molded samples. The specific mechanical properties, especially the impact strength, of the microcellular samples under these conditions increased significantly. Scanning electron microscope (SEM) analyses showed a uniform cell structure in the molded specimens with an average cell size of around 35 ?m. The m-m-PET modified with PMDA generated a slightly finer cell structure and a higher cell density than the n-m-PET.
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