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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Electrical Resistivities and Internal Structures of Multiwall Nanotube-Polypropylene Composites Produced with a Continuous Chaotic Blender
A continuous chaotic blender (CCB) has been used in prior work to produce alternating polymer layers with thicknesses below 100 nm, volumetrically align and localize nanoplatelets in multilayers, and assemble carbon black particles into conducting networks. In consideration of the nanoscale dimensions of these novel structured materials, similar processing methods have been applied in this paper to produce electrically conducting networks from a masterbatch of polypropylene (PP) and multiwall nanotubes (MWNTs). Nanocomposites were extruded as films in a continuous, industrially relevant process. Percolation was obtained at the minimum composition considered of 1 wt%. Structure in the nanocomposite films is related to processing conditions and electrical resistivities.
A 3-D Numerical Study on Injection Molding Filling
This paper presents the development of a threedimensional (3-D) injection molding filling simulation using different algorithms and finite element types. Two numerical models, the mixed model and the equal-order model, were used to solve the Stokes equations with three different tetrahedral elements (Taylor–Hood, MINI, and equal-order). The control volume scheme with the tetrahedral finite element mesh was used for tracking advancing melt fronts. The numerical simulation was validated for the mold filling of a precision optical lens. The numerical simulation agreed very well with the experimental results. As a new application area, a two-step, macro-micro filling approach was adopted for the filling analysis of a part with a micro-surface feature to handle both macro and micro dimensions while avoiding an excessive number of elements. Comparison between the numerical predictions and experimental data suggests that the flow velocity and heat transfer coefficient on the mold surface plays an important role in determining the flow behavior and penetration length within the micro feature.
Failure of a 100 Tonne Fibreglass Storage Tank
A chemical storage tank holding nearly 100 tonnes of hot fluid failed suddenly in August 2003, after about 2 years from installation, and about 18 months actual use. Nobody was injured, but the flood caused substantial damage to the surrounding equipment. Inspection indicated that the failure started at a pipe outlet at the base, with delamination of the GRP wall. Analysis showed the wall to be too thin to support the load from the contents, and that failure was inevitable. Other design defects included poorly positioned piping and a badly designed bund wall, which contributed to the accident. The polyester resin matrix was totally inadequate to resist anticipated content temperature approaching and sometimes exceeding 90 C.
Failure of a Nylon Bridge Bearing
Nylon is widely used as a bearing material, and many different grades have been developed for specific applications. Self-lubricated nylon is a robust grade which has found use in heavy duty bearings such as those used in swing bridges. The case study describes the failure of a bridge bearing, which was replaced owing to excessive deck movement .The steel pin on which the nylon sleeve bearing operated was found to be severely worn, while the sleeve was intact, but heavily contaminated. Sand had become embedded in the nylon surface and acted abrasively against the steel when the bearing moved. The nylon sleeve was at the limit of its specification, and a superior grade chosen for replacement.
Failure Analysis of Polypropylene Block Copolymer Welded Joints
Failure behavior of polypropylene block copolymer welded joints was investigated. Double V welded joints were performed using an automated hot gas welding machine, which is able to independently control welding parameters leading to reproducible welded joints. Uniaxial tensile tests and fracture mechanics experiments were carried out. From these results and complementary FEM analysis, the quality of welding rods and welding interfaces were assessed. By using different specimen configurations and optical microscopy the damage zones generated during mechanical solicitation of the joints were investigated. Welded joints coming up from three hot gas temperatures in the range of 230 to 260°C were analyzed.
Injection Molded, Electrically-Conductive Polyethylene in Electromagnetic Interference (EMI/RFI) Applications: A REACH-RS, K-12 Summer Project
REACH-RS (Research & Education Academy for Coaching/Mentoring High School – Rising Stars) introduces K-12 participants to the needs for enhanced inter-personal skills and technical proficiency in the areas of nanomaterials, multifunctional materials and processing through a series of in-lab assignments. In this project, a group of K-12 students in collaboration with PSU undergraduates injection molded blends of HDPE and carbon black, and tested the resultant ASTM-type, test bars for electrical conductivity, flammability resistance and mechanical properties. The generated stress-strain, electrical and flammability data were analyzed, and correlated to electromagnetic interference (EMI/RFI) applications.
Structure and Properties of Partially Shrunk Oriented Polyethylene Films
In the present study morphology and properties of partly shrunk linear low density polyethylene (LLDPE) biaxially oriented films were studied. It is shown that the mechanical properties of the films as function of the thermal shrinkage behave differently in machine (MD) and transverse (TD) directions. A correlation between mechanical properties and orientation factors determined by Fourier Transform Infra-Red spectroscopy (FTIR) was found. On the basis of the thermal shrinkage behavior of the films as a function of temperature, the molecular orientation during double bubble process was explained in term of superposition of different orientation stages.
Investigation of the Electrically Conductive Acrylonitrile Butadiene Rubber
The electrically conductive acrylonitrile butadiene rubbers (NBR) containing a carbon black as a conductive additive were prepared to investigate electrical and mechanical properties in this study. We considered the effects of conductive carbon black loading and various temperatures on conductivity, acrylonitrile contents, crosslinking density of vulcanizates, and the existence of a plasticizer. The change in electrical conductivity with different amounts of carbon black of NBRs showed that there is a certain critical point which produces a significant decrease in electrical resistivity (increase in conductivity). The mechanical properties like tensile strength, elongation to break, and surface hardness of vulcanized NBRs were determined. We found that the percolation threshold region was 5 phr CB in the NBR/CB composites. It means that there are formed continuous electrical paths which are attributed conductive carbon black in the NBR/CB vulcanizates.
Effects of CO2 and Talc Contents on Recyclable HMS PP Foaming
Recyclable high-melt-strength (HMS) PP has been introduced as an alternative choice to replace crosslinked material in a tandem foaming extrusion process. A filamentary die was selected to promote the optimum processing condition. The cell nucleation and volume expansion behaviors have been investigated as a function of the aspects of die temperature, CO2 content, and talc content. The results exhibited a significant relationship between the processing parameters and foaming behaviors. Low density (i.e., 12~14 fold), fine-celled (i.e., 107-109 cells/cm3) PP foams were successfully produced using a small amount of talc (i.e., 0.8 wt%) and 5 wt% CO2.
Reducing Resin Waste by Optimizing Polymer Process and Machine Design
Polymer processing and converting operations, whether they relate to extrusion coating, blown film extrusion, producing sheets for thermoforming or manufacturing finished articles by injection molding, generally involve some amount of resin waste. A total conversion of the resin into an article of desired quality is an exception rather than a rule.As material costs constitute the bulk of the total costs associated with any product, the aim should be to keep the resin waste as low as possible. With the quality of the product depending largely on the machine and processing parameters, one of the easiest and most effective methods of reducing polymer waste is to optimize the design of the converting machinery at the design stage before they are built as well as optimization of processing conditions.With the illustration of several examples representative of blown film extrusion, flat film extrusion, extrusion coating, blow molding and pelletization process, this paper demonstrates how by applying this strategy resin waste could be reduced.
Low Rate Plastic Component Breakage - A Case Study
In assembly processes, occasionally a plastic component mysteriously" breaks at a rate of two percent or less. Successful diagnosis of this type of low rate breakage depends on not only skillful laboratory work but also careful observation of failed samples. In addition it is useful to observe and understand the relevant assembly process because the interaction between the plastic component in question and surrounding components may be the key factor in its breakage. Solution to this type of low rate breakage typically starts with identification of the crack initiation site. Examples of the diagnosis and verification of low rate plastic component breakage are given in this paper."
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.
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