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 Cooling Systems in Injection Molds by an Easily Applicable Analytical Model
The production rate of injection-molded articles is determined by the cooling time of the polymer melt in the mold. By using state-of-the-art numerical software the mold design can be optimized in order to achieve fast cooling. However, the efforts required to apply this software do not always justify its use in dealing with the daily design problems. Taking the changing mold wall temperature into account a straightforward analytical procedure for optimizing the cooling channel lay-out for a thermoplastic resin has been developed. The equations in the model can be easily solved by means of a hand-held calculator, thus enabling quick estimates of the effect of relevant parameters on mold design. Results of numerous simulations and a worked-out example illustrate the application of the model which has led to good results in the practice.
Nucleation in Foam Extrusion
Nucleation results are presented for polyethylene sheet extrusion while using volatile carbon dioxide without any nucleating agent to study homogeneous nucleation. Since the extrusion pressure has to exceed the system pressure, mechanical superheat was calculated from the processing pressure. The experimental results show a different distribution from the conventional nucleation predictions, based on either chemical superheat or mechanical superheat. Also noted was the shear energy dependence. Various nucleation mechanisms are discussed to address the energy role played by shear in foam extrusion.
Modeling Flow-Induced Crystallization in Film Blowing
A mathematical model was developed for the simulation of film blowing including the effects of flow-induced crystallization, viscoelasticity, and film cooling. The microstructural model is based on the formulation of Doufas et al. Our model predicts the location of the freezeline naturally as a result of crystallization and the stresses at the frost line, which are closely related to the mechanical and physical film properties. Depending on the processing conditions, our model predicts uniaxial or biaxial film stretching.
Thermorheological Investigation of Entangled Branch Polybutadienes Having Different Architectures and Arm Lengths
Rheological behavior of entangled six-arm and eight-arm 1,4-polybutadiene melts of the types A3-A-A3 and A3-A- A2-A-A3 is investigated using low amplitude oscillatory shear and viscosity measurements. Experiments covered a time (frequency) and temperature range broad enough to characterize the complete relaxation spectrum. In oscillatory shear, three separate relaxation modes are identified. At high frequencies a maximum in the loss modulus is linked with segmental relaxation. At intermediate frequencies a new relaxation mode characteristic of the arms is observed. Finally, at low frequencies a terminal relaxation process is identified. This process is characterized by a lower plateau" modulus and is thought to reflect cross-bar reptation in an enlarged tube."
Prediction of Degradation of Polyethylene during Rotational Molding
During rotational molding the plastic is subjected to relatively high temperatures for long periods of time. This often causes degradation of the polymer at the inner surface of the molded article. The resulting degraded layer is responsible for the deterioration of the mechanical properties of the part. In practice, the optimum processing temperature and/or heating time must be obtained by means of an extensive molding and testing program. Moreover, as the degradability of polyethylene depends on many factors, such as the molecular structure of the material, the type and concentration of stabilizers and the thermal history experienced during processing, an optimization program that takes into account all these variables is very expensive and time consuming. In this work the degradation of polyethylene is studied using a technique widely used in the assessment of degradation resistance in the pipe industry - Oxygen Induction Time (OIT). The method enables the onset temperature of degradation to be identified using only a few milligrams of material. The data obtained from simple and quick experiments was used to produce an empirical model to predict the optimum inner air temperature for rotational molding of the materials. It is shown that whilst the maximum internal air temperature experienced during rotational molding is a good quality control parameter, there are many other important factors, such as the heating rate of the mold, the thickness of the mold material, etc.
Mixing Characteristics and Mechanical Properties of Polypropylene-Clay Composites
Polypropylene(PP)-clay composites were prepared by melt mixing in an intensive mixer. Three grades of PP's having different melt viscosities were employed to investigate the mixing characteristics of the composites with various clays which belong to organically modified montmorillonite(org-MMT). Depending on the matrix viscosity and nature of the organic layer in MMT, significant variations in the phase structure of the composites were found. In addition to the simple combination of PP and clay, modified PP's having various content of maleic anhydride were also incorporated. Major interest was focused on the effect of varying thermodynamic affinity between the components on the phase evolution and mechanical properties of the composites. Requirements for the effective dispersion of clay in the PP matrix are discussed in terms of both rheological effect and thermodynamic interaction.
Orientation Measurements Online
Orientation of polymers enhances many of their properties, particularly mechanical, impact, barrier and optical etc.. Orientation processes all involve extrusion prior to deformation and can generally be classified into three categories: fibers, films, and parts (sheets, bottles, rods, ...). The knowledge of the polymer orientation produced by the different processes is critical for establishing the process conditions and the final properties of the oriented polymer. There is a long history of investigations of orientation in polymers, mainly from off-line measurements, involving techniques such as birefringence, infrared spectroscopy, X-ray scattering, Raman, NMR, fluorescence, ultrasonic etc. In this presentation, we will focus on techniques which are or could be used for on-line monitoring of orientation processes. These include birefringence, spectroscopy, fluorescence and ultrasonic.
Process Monitoring Using UV-VIS Spectroscopy
The paper describes process monitoring applications by spectroscopic methods for polymer/additive analysis, polymer melt analysis, additive quantitation, QA/QC purposes, on-line compositional polymer analysis, in-situ reaction monitoring (cure kinetics, polymerisation, color designation, molecular interactions, monitoring of extrusion processes, real-time measurements and use of fiber optics. In particular, the current status of on-line multicomponent additive analysis in the polymer melt by means of UV-VIS spectroscopy will be illustrated.
Color Stable, Glass Filled Thermoplastic Polyesters
Color stability is a general term which can be manifest in several ways, for example, color consistency over the course of a run, color stability on UV exposure, color stability on processing, chemical exposure or color stability of the final article at elevated temperature. Materials with enhanced capability of the latter type are positioned in applications where sustained high temperatures would rapidly discolor conventional thermoplastics or thermosets. This paper will discuss the variables that control heat aged color stability in ignition resistant and non-ignition resistant glass filled thermoplastic polyesters.
Effects of Processing Conditions on Extruded Polystyrene Sheet Feedstock Quality
This work investigates the influence of various extrusion parameters on the physical properties of rubber modified polystyrene sheets. The extrusion parameters under consideration are melt temperature, chill-roll temperature, line speed and sheet thickness. Optimum extrusion conditions for producing polystyrene sheet feedstock are discussed.
Viscoelastic Stress Calculation in Multilayer Coextrusion Dies
Calculation of transient viscoelastic stresses in a coextrusion die is performed using the modified Leonov constitutive equation and the deformation rate field from finite element simulations. It is shown that a heuristic criterion based on the difference of normal stress differences across the layer interfaces may be used to potentially detect the onset of interfacial instabilities. Finally, it is shown how this criterion may be incorporated into current design practices to optimize resin selection and die design in order to eliminate interfacial instabilities.
Dynamic Vulcanization of Elastomers in Polypropylene Blends
The use of innovative crosslinking agents for the preparation of thermoplastic vulcanizates (TPVs) is investigated. In this preliminary study, the most common TPVs systems, based on polypropylene (iPP) and rubber ethylene-propylene-diene terpolymer (EPDM) blends, are studied. Typical vulcanization agents, such as sulfur, phenolic resins and peroxides do not permit to crosslink saturated elastomers and, furthermore, give rise to dynamic vulcanization of the polyolefins. For this reason, the main goal of the present study is to investigate a new vulcanization agent for elastomeric matrices. This agent is based on azide derivative, 1,3-bis sulphonyl azide benzene that, for the specific behavior of the sulphonyl azide group, allows its interaction with the C-H bonds of the elastomeric phase and of the polyolefin. The study includes the dynamic vulcanization of PP-EPDM blends and their rheological, mechanical and thermal characterization. A comparison with traditional blends prepared with sulfur as vulcanization agent is also presented.
Effects of Fibers on the Crystallization of Polypropylene in Binary and Ternary Composites
The simultaneous effects of the incorporation of different types of fibers and of the presence of EPDM on the crystallization kinetics and thermodynamics of isotactic polypropylene are presented. The study is applied to the behavior of polypropylene matrix composites reinforced with glass, PET, aramidic and sisal fibers. The results obtained show that in all cases, either the fibers and the EPDM rubber behave as effective nucleant agents for the crystallization of polypropylene. A dramatic decrease of the half time of crystallization, t1/2, and an increase of the overall crystallization rate, Kn, are observed being the aramidic fibers the most effective. It is also reported that transcrystallinity takes places in all fibers being more evident with aramidic fibers in the neat PP matrix. Only a slight transcristallinity effect is detected when fibers were incorporated in the PP-EPDM matrix.
Best Practices: Looking beyond Benchmarking to Develop Your Business Strategy
Real breakthroughs in strategy and business development come from looking beyond your in-kind competitors for a process view of customer-focused solutions. A company's basic operations are first level processes and cross over industry type. Best practices is the study of identifying the companies which have developed superior processes in product development, manufacturing, customer service and market segmentation regardless of the industry they are in. This paper discusses the benefits of the study of Best Practices in addition to competitive intelligence and benchmarking in business planning. Examples of companies in the plastic industry who have distinguished themselves by their best practices will be presented.
Effects of Twin Screw Compounding Conditions on the Mechanical Properties of Nylon-6/Glass Fiber Composites
The effect of processing conditions on fiber length degradation was investigated in order to produce higher performance composites. For this aim, Nylon-6 was compounded with glass fibers in a twin screw extruder for various combinations of screw speed and feed rate. Collected samples were injection molded and izod impact and tensile strength tests were performed in order to observe the effects of fiber length on mechanical properties. Also, by using the extruded and injection molded samples, fiber length distribution curves for all experimental runs were obtained. Results show that when the shear rate is increased through the alteration of screw speed and feed rate the average fiber length decreases.
Polymer Raw Material, Process and Production Fingerprints in Injection Moulding
In-process monitoring of polymer melts is found to provide a fingerprint of the: • polymer (process-relevant polymer rheometry); • the process (injection pressure-time curves which reflect the material-machine-mould combination, including polymer batch to batch variation and machine dynamic repeatability); and • production trends, with 'process indices' offering an efficient basis for 100% automatic inspection, Statistical Process Control, and even insight into factory housekeeping. Specific pressure indices in an indentified low noise region of the primary injection stage of injection moulding have been found to provide a sensitive indicator of changes in a polymer, including batch to batch changes and process-induced changes, as such measurements are closely related to the rheology of the polymer melt. The same information has also been found to provide sensitive indications of variation in the processing operation for a given polymer-mould combination, and also consequently to allow meaningful statistical analysis of trends in the injection moulding process. Laboratory and factory data for raw material, process and production trend analysis (the latter involving data from substantial production runs) are presented.
A Three-Dimensional Analysis of Coextrusion in a Single Manifold Flat Die
The coextrusion of two polymers through a single manifold flat die is examined. The three components of velocity and the pressure are determined in each layer along with the interface between the layers. It is shown that even when the viscosity ratio is one (i.e., single layer), flat layers" entering the die will not remain flat but will be distorted by the die. For coextrusion of two polymers the distortion of the interface profile at the exit of the die and thus the uniformity of the layers depends upon the viscosity and flow rate ratios of the two polymers as well as the geometry of the die."
Design for Rotational Molding
This paper will cover the details of piece part design particular to the rotational molding process. Ribs, bosses, wall thicknesses, parallel walls, internal and external corners, openings, draft angles and undercuts will be discussed. Joining features, such as inserts, hinges and molded-in threads, will also be reviewed.
Designing for the Process? (Design Details to Avoid)
At first glance the Rotomold process is a fairly simple one. Its capabilities are exiting and have opened new avenues for creative industrial designs including complex shapes and rugged structural parts. Successful Rotomolded designs can be obtained by keeping a few guidelines in mind from concept through to product generation. This portion of the program will cover the areas that need to be considered during the design process. Items to be highlighted are basic design guidelines, features that can compromise, complicate and delay a project and what to ask a molder about specific designs.
Novel Small and Large Scale Flow Visualisation of Polymer Melts
A novel small scale (<30g of polymer) recirculating flow visualisation cell has been designed and built. The unit comprises a single screw extruder, gear pump and variable geometry inserts making a flow recirculation loop. The recirculation flow cell is capable of being used with a range of entry geometries, including abrupt entry and hyperbolic, with a polariscope for stress birefringence, and a CCD camera and image processing system for particle streak velocimetry. This new facility complements existing larger scale flow visualisation cells in our laboratory, fitted to a single screw extruder. Information from flows in both scales of flow cell are presented for an LDPE melt.
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