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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Crack Initiation in Pipe Grade Polyethylene
Crack initiation in pipe grade polyethylene is studied using a circular notch specimen (CNS) under constant load. The specimen geometry and loading conditions are selected in a way that the crack becomes unstable and leads to almost instant fracture after initiation. Therefore the time of crack initiation practically coincides with easily recorded time to failure. The crack initiation takes place within a process zone (PZ) coplanar with the notch and extending from the front of the notch. Two sub-zones are distinguished within PZ. The first, located in the frontal part of PZ comprises of a planar set of micro cavities within a thin strip of material coplanar with the notch. The second, constituting the rest of PZ, consists of micro fibers and membranes resulting from cold drawing of the material between the cavities. With time creep & degradation of micro fibers and membranes leads to crack initiation. Results of experimental observation and an approach to modeling of crack initiation in CNS are reported.
Material Development on Polyester Compositions with Improved Flowability
Polyesters are widely used in automotive and electrical industry parts due to their excellent electrical, mechanical and molding properties. However, as the industry is driving/evolving towards miniaturization of parts it is a challenge to develop polyester compositions with high flow properties in order to fill the thin wall molds/parts. Furthermore, flow improvement is more challenging in filled polyester compositions as these have substantially higher viscosity than corresponding neat polyesters. Polyester modification in compounding, molding, and extrusion stage is an easy, economically viable and flexible route than corresponding modification in reactor stage. In the present study, we discuss the development of new high flow polyester compositions using extrusion process and flow additives. The correlation between standard viscosity measurements and molding properties in thin wall molds is also discussed.
Effect of Localized Orientation and Anisotropy with Melt Manipulation during Polymer Processing on Mechanical Part Properties
This study investigates the effect of localized final molecular orientation and anisotropy on mechanical part properties with melt manipulation during polymer processing. The localized final molecular orientation and morphology are indicative of the resultant product response and typically resulted in improved mechanical properties with an increase in tensile strength for the material investigated, polystyrene. In general, specimens with high levels of retardation distributed more uniformly along the gage length exhibited higher tensile strengths. he specimens tested in tension tended to fail in the gage section end opposite the gate with the lowest molecular orientation. To elicit the ultimate tensile strength of the higher oriented sections, miniature specimens were machined from molded specimens of varying molecular weight uniformly along the gage length and tested. This paper discusses the results of the investigation along with future directions of study.
Crystallization Enhancement of Poly(L-Lactide) by Carbon Nanotubes
In this work, we started the preparation of multiwalled carbon nanotubes (MWNTs) by the CVD method. Following surface modifications, MWNTs were grafted with poly(L-lactide) to obtain poly(L-lactide)-grafted MWNTs (or MWNTs-g-PLLA). Prior to investigation on whether the MWNTs-g-PLLA could be an effective reinforcement for the semicrystalline, biocompatible and biodegradable PLLA, we investigated the effects of MWNTs on the crystallization of PLLA in the nanocomposites (PLLA/MWNTs-g-PLLA) using differential scanning calorimetry (DSC). The MWNTs was found to significantly enhance the crystallization of PLLA.
Plastic Contact Mechanics and its Impact on DEM Simulations of Solds Transport in Extruders
Research work using the Distinct Element Method (DEM) has identified the potential of a discrete approach for more accurately modeling the motion of plastics solids within a single-screw extruder. Experiments of HDPE particles contacting a steel anvil showed a velocity dependency in their impact behavior, which becomes an important consideration when selecting an appropriate force-displacement model for DEM simulations. In addition, Experimental trials have been conducted to examine the bulk motion of solids within an actual single-screw extruder at different screw speeds and barrel temperatures. The implications of velocity-dependency in the contact-displacement models were subsequently examined in 3-D, non-isothermal DEM simulations of the solids-inflow and solids-conveying zones of a single-screw extruder.
The Effects of Mold Closing Speeds and Positions on the Pinch-Off Strength of an Extrusion Blow Molded Bottle
This study will show the effects of mold closing speed and position on the pinch-off strength of an extrusion blow molded bottle. It is important to have an optimal mold closing speed and position so the pinch-off strength is most advantageous to the part integrity. Today, the industry uses past knowledge to process the pinch-off strength. The study will add more scientific knowledge to the industry and improve overall pinch-off strengths. This is needed because simply relying on past experience may not help in new and more difficult situations. Data acquired from the study will give the necessary results to optimize the mold closing speed, position, and pinch-off strength on an extrusion blow molded bottle.It was found that the slower mold closing speed and larger mold closing position created the greatest pinch-off strength and thickness.
Die Balancing: Coupling Flow Simulation, Shape Deformation, & Optimization
The current work demonstrates a novel automatic approach for the die balancing process. The algorithm involves flow simulation through computational fluid dynamics (CFD) and shape change via automatic shape deformation (ASD) to minimize the flow non-uniformity at the die exit. Taking a spiral mandrel die as an example, the combined use of ASD with CFD is highlighted. Using this approach, one baseline simulation was manually set up and two more simulations were automatically created study the effects of helical angle. In the example studied, it was found that changing the helical angle from 315° to 405° had a minor effect on the flow uniformity.
Application of Neural Networks in Prediction of the Microstructure and Mechanical Properties of Microcellular Injection Molded Polyamide Nanocomposites
Back-propagation artificial neural network (ANN) models were constructed to predict the microstructure and mechanical properties of the microcellular injection molded polyamide nanocomposites. Key parameters that affect the evolution of the microstructure, i.e. supercritical content, melt temperature, shot size, melt plastication pressures and injection speed are selected as the artificial neural network inputs, and the outputs are the microstructure defined as the cell size, Weight reduction, and mechanical properties . The results revealed that ANN model offer a favorable method in the optimum design of the nanocomposites and process improvement. This work enhances the systematic understanding of parameters in the optimum design of the nanocomposites and process improvement.
A New Approach for Temperature Measurement Inside an Injection Molding Tool
In the context of lightweight construction and miniaturization, especially in the automotive industry, direct encapsulation of electrical components in injection molded parts gains further in importance. In particular with regard to the processing of temperature sensitive semiconductor devices specific knowledge on the thermal load is required for product-life estimation. In consequence of its mounting points and mass-to-melt-ratio, standard temperature probes are suitable only to a limited extent for this kind of measurement.As this paper shows, semiconductor diodes are well capable of measuring the time-dependent temperature inside an injection molding tool because of their electrothermal properties. During the investigation probes with an edge length less than 200 ?m have been mounted in the cavity of the tool. Due to the low heat capacity of the probe the temperature of the melt is unaffected by its presence and the thermal signal is registered with almost no delay. Using the method presented, the thermal load of directly encapsulated electrical devices can be measured. In particular the thermal degradation of semiconductors can be estimated.
Virtual Simulation of Top Load Performance of Plastic Bottles
A novel analytical computational model was developed to predict Top Load and Side Load performance of light weighted water bottle containers. This approach involves, simulating reheat stretch blow molding of PET containers using Virtual Prototyping™ software to predict the material thickness distribution of the blow molded container and associated mechanical properties derived from estimating the degree of stretch and orientation of different sections of the container. These parameters serve as inputs for Finite Element Analysis involving highly non-linear deformation of the containers under various types of loading. A predictive curve was established to determine the degree of light weighting that can be achieved for a 500mL water bottle by plotting the Top Load Strength as a function of container Sidewall Thickness. The Top Load performance for an empty 14g container was predicted to be about 47 N (10.5 lbs) compared to 86 N (19 lbs) for a 17g bottle and 61 N (14 lbs) for 15g bottle. This analysis has been proven to be effective and accurate for performance analysis without expensive prototyping of the container design and allows a wider number of sample designs and light-weighting options to be explored in a limited amount of time.
Effect of Screw Geometries on Extrusion of Wood-HDPE Blends
This paper investigates the effect of three screw geometries on the extrusion characteristics of 0%, 25%, 36% and 50% wood-filled HDPE blends in a single screw extruder. From the three screw geometries, the effects of feed depths, the compression ratios, and the metering depths were compared. The characteristics included output, pressures and melting profiles. It was found that, due to its partially filled phenomenon, the solid conveying section dominates the extrusion behaviour of the wood-filled resins. A modified solid conveying model based on viscosity was presented, and the solid conveying angles calculated.
Optimization and Analysis of Variability in Injection Molding
Injection Molding (IM) is the most important process for mass-producing plastic products. The difficulty of optimizing an IM process is that the performance measures (PMs), usually show conflicting behavior. The aim of this work is to demonstrate a method utilizing CAE, statistical testing, artificial neural networks (ANNs), and data envelopment analysis (DEA) to find the best compromises between multiple PMs and their variability. Two case studies are presented. A case study based on a virtual part is presented in detail in order to illustrate this method. The second case study is experimentally based, using the American Society of Testing Materials (ASTM) mold, to illustrate how this approach applies when only experimental results are available.
In-Mold Coating for Thermoplastic Parts: Modeling, Rheology and Apparent Slip
In-mold coating (IMC) is carried out by injecting a liquid low viscosity thermoset material onto the surface of the thermoplastic substrate while it is still in the mold. A computer code based on the Control Volume based Finite Element Method (CV/FEM) has been developed to predict the fill pattern and pressure distribution during the coating flow using the Sisko viscosity model and taking apparent slip into account during. Both these factors lead to a better prediction of pressure distribution. The rheological parameters and the apparent slip parameter are ascertained by using a slit rheometer. Simulation and rheology results are presented in this paper.
Mechanical Properties of Rice Hull / Polypropylene Composites
This study attempted to improve the mechanical properties – and impact resistance, in particular – of rice hull/polypropylene composites with the aid of styrene-ethylene/ butylene-styrene (SEBS) and maleated styrene-ethylene/ butylene-styrene (SEBS-MA). The results suggested that both types of additives increased the impact strength of the composites significantly as their content was increased, but only SEBS-MA improved the tensile and flexural strength of the composites. The results also indicated that the SEBS-MA composites consistently showed better mechanical properties – strength and modulus in both tensile and flexural tests and impact strength – than the SEBS counterparts at a given content of additives.
Web-Based Navigating System for Conceptual Design of Plastic Parts
The object of enterprises management is to obtain the competition advantage by better efficiency, quality, innovation, and customer responds. As such, most enterprises implement the product life management (PLM) system to assist design and development, however, the interaction between PLM and CAD is mainly for viewing purpose. Therefore, this research is to develop a web-based conceptual design navigating system which can provide standard and automatic component to shorten the process of conceptual design by seamlessly integrating with CAD system. Furthermore, this system can greatly help the inexperienced designer and provide the collaborative environment of designing process.
Structure and Properties of Thin-Wall Molded with Micro Surface Features
Injection molding of thin-wall parts with micro-scale grooves of polypropylene (PP) and cycloolefin copolymer (COC) were performed to clarify the processability and surface structure of the molded products. Effects of cavity thickness and process conditions on processability and structure of the molded products were evaluated. The replication property and optical anisotropy of molded products were analyzed by polariscope, polarizing microscope, SEM, and confocal laser scanning microscope. The optical anisotropy in the vicinity of the gate was higher than that of any other position, and the optical anisotropy increased with a decrease in cavity thickness. The replication property in the vicinity of the gate also was higher than that of the flow end, and the replication ratio was slightly increased with increasing mold temperature. It was found that the replication properties were correlated closely with skin-shear thickness inside products.
Micro-Scale Disk in Ultra Miniature Injection Molding
Precision micromolding of polypropylene (PP), polyoxymethylene (POM) and polycarbonate (PC) were performed to develop a micro-scale miniature disk and to clarify the mechanism of structure development in micromolded products. Especially effects of process condition and cavity thickness on processability and structure formation in micromolding were evaluated. The processability and high-structures of molded products were also analyzed by polariscope, birefringence, and AFM measurements. In case of PC micro-disk, the molecular orientation in the vicinity of the gate was higher than that of any other position. Birefringence increased with decreasing cavity thickness. Furthermore it was found that the resin flow became unstable in the cavity thickness of 0.1 mm. The molecular orientation of PP products also showed the similar tendency as the case of PC, where birefringences in the vicinity of the gate were higher than any other position.
Modeling of Deformation Processes in Vacuum Thermoforming of a Pre-Stretched Sheet
Modeling of deformation processes in vacuum thermoforming for a preliminary stretched thermoplastic sheet (plug-assist vacuum thermoforming) is investigated in this paper. The model can be used for production of polymeric articles with minor wall-thickness variation. A nonlinear rheological model is implemented for developing the process model. It describes deformation process of a pre-stretched sheet at any phase of vacuum thermoforming process. This process is described by a set of deformation processes that each on them is specified by an appropriate boundary conditions. For model validation, a comparative analysis of the theoretical and experimental data is presented. The wall-thickness distributions obtained from modeling results corresponded well with experiments. The satisfactory result establishes a method for prediction and enhancement of the final products quality in criterion of wall-thickness distribution.
Investigation of Re-Crystallization of Injection Molded TPO Unpainted Plaques
Thermoplastic olefins (TPO) are widely used in the automotive industry as painted exterior plastic parts such as fascias and bumpers. The overall production process includes injection molding of parts, surface treatment, painting and finally baking at 120°C for 30 min. During the injection process, residual stresses are generated by chain orientation and thermal gradients. After the paint process, more stresses and deformations are added. This work focuses mainly on baking conditions and the micro-structural changes as a source of final surface defects. As a first step, we used DSC to simulate the baking process and study the effect of injection molding and baking conditions on unpainted samples. By controlling the scanning rates and the residence time within the DSC furnace, this alternative technique can reveal some interesting results. Samples were also annealed in an oven in the same conditions then analyzed by DSC. The results of both approaches are compared and discussed.
The Effect of Cooling Air Aerodynamics on Bubble Instability in Blown Film
A numerical analysis using a renormalization group (RNG), k-? model and Fluent software was performed to predict the static pressure distribution around the bubble as well as the flow field of cooling air in the film blowing process. Bubble instabilities were experimentally studied using an in-line scanning camera system developed in our laboratory. The combination of experimental measurements and numerical analysis indicated that different bubble shapes led by various cooling rate produced significant differences in dynamics of bubble instability. When the gradient of static pressure along the axis of the bubble is minimized, the stability of the bubble increases.
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