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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Comparison of Reactive Extrusion in Various Twin Screw Extruders and Their Roles on Mixing
A comparative modeling of distributive mixing has been investigated in intermeshing co-rotating, intermeshing counter-rotating and tangential counter-rotating modular twin screw extruders. This is based on the Spencer-Wiley premise of representing mixing through interfacial area increase and its relationship to shear strain of the various modular twin screw elements. It is necessary to develop flow analyses for different modular twin screw extrusion machines. We applied this analysis to understand the reactive extrusion process in various twin screw extruders. Our approach is to compute the development of interfacial area for composite modular twin screw extruders and an internal mixer, and a mixing index was determined for each processing device.
Comparison of Structure Development in Processing Syndiotactic and Isotactic Polypropylenes
We investigated the crystallization and orientation development in syndiotactic polypropylene (sPP) during various polymer processing operations and also compared the results with isotactic polypropylene (iPP). This was carried out in fiber spinning, tubular film extrusion and injection molding. Melt-spun sPP fibers exhibit Form I helical structure at low spinline stress levels and zig-zag all trans structure (Form III) at high stress levels. In tubular film extrusion, sPP exhibits Form I structure and the a-axis is preferentially oriented in the film normal direction. Injection-molded sPP samples exhibit very low frozen-in orientation levels due to its slow crystallization rate.
Comparison of Tensile Properties for PET and Acetal Specimens Using Two Different Tensile Testing Units
The compiled data are for unfilled acetal and filled polyethylene terephthalate (PET) specimens. Various sample sets were evaluated using the ASTM D 638-95 method, “Tensile Properties of Plastics.” These tensile data are used to evaluate material candidates for making molded parts. It is important to determine if the tensile data are the same or if they are different so that selections can be made without repeating the data collection each time a decision is required. Sample sets were evaluated using two different instruments—a SATEC and an Instron. These data were obtained over a number of years by different operators following an iterative approach. One sample set was molded from Delrin® 500*, a medium viscosity, acetal homopolymer (POM). The three addition sets were polyethylene terephthalate (PET) specimens molded from Rynite® SST 35,* Rynite® 545, and Ticona Celstran® PETGF 20-02.
A Comparison of the Axisymmetric and Planar Elongational Viscosities of a Polymer
The elongational viscosities of a low density polyethylene in axisymmetric and planar flows are compared. The experimental data on entrance pressure loss is matched with the corresponding finite element predictions to estimate the parameters in the elongational viscosity model proposed by Sarkar and Gupta. The entrance losses in the capillary and slit rheometers are used to predict the elongational viscosities for axisymmetric and planar flows respectively. The power-law region of the axisymmetric as well as planar elongational viscosity is found to follow the time-temperature superposition principle.
Comparison of the Experimentally Observed TSE Melting Lengths with those Predicted from Simple Plastic Energy Dissipation Compressive Experiments (Part I: Experimental)
In the last few years our group has demonstrated experimentally the dominant role which Plastic Energy Dissipation (PED) plays in the heating/melting of solid polymer (compacted) particulate beds in compounding processing equipment, such as twin screw extruders and counter-rotating continuous mixers/melters. We have also developed simple empirical methods of predicting the total axial distance in specific processing/compounding machines needed for melting as well as the melting rates, all based on the mechanical energy dissipated during solid particulate compression. This work explores how PED behavior of single-component polymers may affect the PED (and the melting) behavior of multi-component polymer blend.
Comparison of the Mechanical Performance and Crystallinity of Medium Density Polyethylene Films Manufactured on IBC and Conventional Blown Film Extrusion Lines
A range of films was manufactured from a medium density polyethylene (MDPE) resin of MFI 2.0 (g/10min) and density 0.94 g/cm 3 using a 75mm extruder fitted with a 290mm diameter Blown Film Die and a die gap of 0.9mm. The films were manufactured at different haul off rates and a constant blow up ratio of 1.24, using both conventional air ring and internal bubble cooling (IBC) systems. The line speed of the IBC extrusion line was approximately three times that of the conventional blown film line. Tensile analysis of the films at room temperature showed significant increase in break strength and break modulus in the machine direction for the IBC films, at all draw down ratios. Differential Scanning Calorimetric (DSC) analysis showed IBC quenched films to be more crystalline than the conventionally quenched blown films. The results also indicated the potential for significant down gauging of film thickness (by up to 25%), without reduction in film mechanical performance by using IBC systems in blown film extrusion processes.
Comparison of the Mechanical Properties of a Wood-Fibre and a MDF Polymer Composite
Natural fibres at levels up to 20% have been used for years as fillers to improve the rigidity of polymers. In the past five years up to 60% wood sawdust has been used in a rapidly increasing wood polymer composite market, particularly in the US. A series of composites, using spruce sawdust and MDF sawdust at different levels, with three polypropylenes, have been produced using a single-screw extruder and an injection moulder. The impact energy, tensile and flexural strengths of these composites were measured. The results show significant differences between the impact, tensile and flexural strengths from two types of wood as well as the type of polypropylene.
The Complex Effects of Long Chain Branching on the Blown Film Performance of LLDPE Resins
Long chain branching (LCB) has long been recognized as an important molecular parameter that significantly influences both processing and property performance of polymers. In this study, we report on the effects of LCB on the blown film processing and performance behavior of both narrow and broad molecular weight distribution (MWD), linear-low density polyethylene (LLDPE) resins. The LCB was introduced by peroxide addition and by varying the finishing stabilization additives. The results showed that while improvements in some processing characteristics were observed with LCB addition, this generally came at the expense of physical properties. Thus, in contrast to the general belief in the literature, we contend that LCB addition in LLDPE type film resins involves a trade-off in improved processing at the expense of film properties.
Composite Films of Polypropylene from Post-Consumer Plastics Waste to Substitute Cellulose Paper
The aim of this work is to obtain composite films of polypropylene (PP) to substitute paper. The plastic component is PP from mineral water bottle (PPb) collected from municipal plastic waste (MPW) and the filler component is CaCO3. Composite films with weight ratio of PPb and CaCO3 (70:30) were prepared. These films were surface treated by corone discharge. Preliminary results have shown a good printability with pencil and pen ink on these films without treating and an improved printability with ink jet after surface treatment. These films were then compared to cellulose paper by physico-chemical characterizations.
Computer Aided Optimization of Extrusion Dies
In an extrusion process polymer is melted and conveyed through the extrusion die. In the die the form of the melt is converted from a cylindrical into a requested cross-section of the profile. The primary objective of the rheological design of extrusion dies in polymer processing is to obtain an even melt velocity distribution at the outlet of the die. For a given complex cross-section of a profile, yet no procedure is known to calculate or predict the die flow channel geometry with respect to an even velocity profile at the outlet. By designing a complex profile extrusion die an iterative process has to be performed to optimize the flow channel.In this paper a new calculation method is presented which uses a combination of the Finite-Element-Analysis (FEA) and the 'network-theory'. With the aid of this method it is possible to accelerate the iterative optimization process for the design of profile extrusion dies. Furthermore, this method is combined with an optimization scheme based on the evolution strategy. The result is an algorithm to optimize the flow channels in extrusion dies automatically.
Computer Simulations of Crack Formation and Propagation in Two Phase Polymeric Materials
We have used computer simulations to study the phenomena of crack formation and propagation in two-phase polymeric materials. The simulated materials are subjected to constant-force tensile stress resulting in deformation. We use computer graphics to create animations of the cracking phenomena.We are trying to answer the key question where the cracks form: inside the flexible matrix, inside the rigid phase, or at the interface. Computer simulations provide answers to this and other questions which cannot be answered by conducting experiments.The results obtained guide us in the creation of real materials with improved mechanical properties.
Concurrent Engineering Based Mold Development
In the “mold development” designation it is comprehended a process composed by the (sub)processes of the mold specification, contracting, design, planning, manufacturing, “in-field” service, etc. By the Concurrent Engineering (CE) principle, all these processes are performed simultaneously (with higher or lower degree) which reduces the mold development time, through the minimization of changes in the mold subprocesses procedures.The CE principles imply application of teamwork. These teams are composed by experts from different functional areas (for specific mold development subprocesses).It is presented a CE model based upon mold development processes to fulfill the increasing needs of design and mold making industry.
Constitutive Modeling of Crystallizable Shape Memory Polymers
Shape memory polymers are novel materials that can be easily formed into complex shapes, retaining memory of their original shape even after undergoing large deformations. In this paper, we develop constitutive equations to model the thermo-mechanical behavior of crystallizable shape memory polymers. This is done using a framework that was developed recently for studying crystallization in polymers (,). The constitutive equations are formulated in a full thermodynamic framework using the notion of multiple natural configurations. Here, we outline the main components of such a model and investigate its response for a crystallizable shape memory polymer undergoing a typical thermo-mechanical cycle. The results of the model compare favorably with experimental observations.
Control of State Parameters in Blow Moulding
The blow moulding industry has achieved a good understanding of the process, which has been in large scale operation since the 1960's. Consequently, control of machine settings such as heater band temperatures, die gap position, die and mould temperatures is quite advanced. However, to date, little work has been done to address the control of state parameters describing material behaviour during processing, such as parison weight and temperature distribution. Control of state parameters is essential as material property changes, environmental factors and machine operating drifts can significantly change the dynamic operating point of the machine.
Controlling Warpage for the Decorating and Assembly of Plastic Parts
Nothing is more frustrating to decorators and assemblers of plastic parts that attempting to perform these functions with parts that are warped and out of specification. Injection molding is the process used to produce the bulk of these parts. There are three principal causes of warpage in injection molded parts: differential shrinkage, internal stresses and distortion resulting from ejection of the part from mold. Often, two or three of these conditions exist simultaneously, thereby complicating the solution significantly. This paper discusses the causes of these conditions and the means to control them through design.
Cooperative Development of Moulds and Parts
With the emergence of today’s new geography model, where the omnipresent electronic place coexists with the physical one, the challenge is now to take advantage of the available technology to build and coordinate efficient and innovative business relationships, in order to draw strengths from the diverse and worldwide distributed knowledge, experience, expertise and competencies.In July 1998, an international consortium was established between three SME’s, two research and development institutes and one governmental organization. Six organizations from four different countries (Portugal, Germany, Mexico and People’s Republic of China) united by a shared goal: the development of the project “Round the Clock – 24 Hours Collaborative Product Development Work”.The basic idea, behind the project conceptualization was to take advantage of the time gap between the several organizations located in different time zones, for the establishment of a continuous non-stop product development cycle at a planetary scale based on the suitable use of a communication platform and coherently supported by an efficient work methodology.
Copolymers of Ethylene and a Highly Branched Unsaturated Comonomer
The diversity of possible structures in copolymers of ethylene and a wide variety of comonomers provides an interesting field for research.Low-density polyethylene exhibits special properties not yet surpassed by other polymers such as linear low-density polyethylene.In this work, a highly branched unsaturated comonomer (HBU) was synthesized and copolymerized with ethylene by using Et(Flu)2ZrCl2/MAO catalyst system. Reactions were performed in a 500ml autoclave equipped with mechanical stirrer. Toluene and MAO were added to the reactor under nitrogen atmosphere. Ethylene was introduced until constant pressure of 2 bar at 90°C. Catalyst activity and polyethylene characteristics were evaluated and compared to LDPE. The results showed that the catalyst activities for the copolymerization were surprisingly higher when compared to the homopolymerization of ethylene and in the same order of magnitude of the copolymerization with 1-octene.
Correlation of Processing Temperature, Density Gradients, and Mechanical Properties in a Molded Polyurethane Foam System
Polyurethane foam is often molded directly in place as a thermal or vibration insulator, energy absorbing material, or core material for a sandwich structure. A smooth thin skin forms between the mold and the interior cellular structure of the foam. A non-uniform microstructure is often visible when foam cross-sections are examined, resulting in density variations throughout the foam. This paper investigates the effect of processing temperature on the average density, density gradient, compressive modulus, and compressive strength, for a free rise, water blown polyurethane foam system molded in aluminum cylinders. Resulting properties are also compared to reference samples that have a uniform density. It is shown that the processing temperature has a significant effect on the foam density and density gradient. This density gradient, as well as the presence of the skin, affect the compressive modulus but have minimal effect on the compressive strength.
The Cost of Tolerances in Injection Molded Parts
Specifying realistic tolerances that insure form, fit or function is one of the most overlooked areas in product development. All too often, tolerance specifications are missing, vague, and unrealistic. This and the subsequent 'variances' can lead to higher than necessary manufacturing costs, poor market acceptance and product liability exposure.This paper will examine the cost, quality and time-to-market implications of injection molded part tolerances and how to improve the tolerance specification and implementation process. The primary focus will be on the obvious - dimensional tolerances, but we will also look at the impact of visual specification tolerances and mechanical requirement tolerances.
Coupled Rheological and Mechanical Design of Stackable Spiral Dies
In recent years, the use of stackable spiral (pancake") dies in blown film extrusion has been continuously growing. One main disadvantage of this die design is the susceptibility to mechanical die deflections resulting from melt pressure which can lead to a poor melt distribution or leakage problems. In this paper a flow simulation model will be presented that is able to calculate the melt velocity and pressure distribution in the spiral section. Additionally a mechanical simulation model has been derived that can calculate the deflection of the die plates for a given pressure load. Because of the mutual influence of melt flow and die deflection the two models are coupled and iteratively solved. The impact of the die deflection on the melt distribution and experimental results will be shown."
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