SPE Library
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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Conference Proceedings
A Predictive Melting Model for Polymer Particulates in Co-Rotating Twin Screw Extruders
A predictive melting model for polymer particulates in co-rotating twin screw extruders (Co-TSEs) is proposed. The proposed model starts with the solids conveying section where discrete mechanics is used to describe the movement and deformation of solid particulate assemblies. The interparticle forces can be estimated based on the screw geometry, processing conditions, and material properties. These forces are the sources of two important melting mechanisms: the Frictional Energy Dissipation (FED) and the Plastic Energy Dissipation (PED). The model also considers the role of barrel heating in creating a layer of preformed melt". The existence of preformed melt changes the conveying properties of solid particulates dramatically. Finally the model considers the important heat generating term the Viscous Energy Dissipation (VED) whose onset coincides with the creation of a fraction of molten polymer generated by any of the above mechanisms."
Quantification of Calibration Drift for the TC Probe Thermal Effusivity and Conductivity Instrument
The Pyris TC Probe requires calibration with characterized standards to relate instrument response to effusivity and/or thermal conductivity. This study was under taken to determine the magnitude of any drift in calibration that occurred over time. Drift could occur due to uptake of water in the sensor's insulation or surface wear. Three calibration standards of known effusivity values were used to calibrate the instrument at 4 test times from 6 to 30 seconds. Several standards were tested during a period of 64 days with each of the calibration files. Of the 120 tests conducted, only 2 results varied more than 4%, indicating excellent stability.
Large, Structural, Class A" Thermoplastic Automotive Part Production without Painting"
The Valyi surface finishing/compression molding process (SFC) has successfully been used to produce large structural panels with Class A finishing under low pressure. The material used in the SFC process must meet certain performance requirements in order to fully exploit the capability of the process. This paper compares the mechanical properties and rheological properties of short and long glass and carbon fiber reinforced materials. The Long fiber reinforced PP resins show enhanced stiffness and impact strength. Degradation of surface appearance due to long fiber read through is an issue to be addressed in future work.
A New Method for Determining the Thermal Conductivity of Polymeric Samples through the Melt
Understanding thermal behavior of molten polymers is critical to many different resin molding processes. The objective of this study was to investigate the adaptation of the Transient Plane Source (TPS) thermal analysis method for evaluating polymer feedstock raw materials in pellet form through the melt. A new sample holder was designed to accommodate the logistics of the experiment. Two sets of polymer raw materials were evaluated, one a random copolymer polypropylene with no filler and the other a polypropylene backbone modified with rubbers and mineral fillers. Thermal conductivity results for each sample were obtained at five temperatures, 250°C, 200°C, 150°C, 100°C and 50°C. Each sample was tested in triplicate to identify the precision of the TPS technique under each condition. The results of this study were correlated to thermal conductivity results obtained on the same samples by ASTM testing method D5930-97[1], using the transient line-source (TLS) technique.
Plastic Energy Dissipation (PED) a Major Contributor to Melting of Polymers in Polymer Compounding Equipment
Polymer processing equipment, batch or continuous, provides for some or all of the following mechanisms for the heating and melting of polymer particulates: Conductive Heating, Interparticle Friction Energy Dissipation (FED), Plastic Energy Dissipation from each deforming solid particulate (PED) and Viscous Energy Dissipation (VED) arising from the flow of the viscous polymer melts. Experimental evidence generated in our laboratories where PED was evaluated with individual solid polymer cylindrical samples and inside compounding equipment, such as Co-TSEs, indicates that PED arising from the irreversible deformation applied by the compounding equipment on solid particulates is often orders higher in magnitude than other heating/melting mechanisms.
Microfoams of Polycarbonate Have High Impact Properties
Customary polycarbonate (PC) with a relatively small amount of polypropylene (PP) between 0,5 and 5 weight-% has been processed into blends and determined in extensive tests. An increase in low-temperature impact strength was shown: the impact resistance values of pure PC determined in Izod-tests could be improved by the factor 5 by adding 3 weight-% of PP. As a reason for the extremely high impact properties an special morphology of this group of blends could be stated. Because of the incompatibility of both blend partners in connection with remarkably different thermal dilatation factors concerning a common processing, fine-dispersed PP particles are created in the PC-matrix, which are surrounded by cavities. If favourable geometrical conditions of this cavity morphology (diameters, distances and so on) are present, shear mechanisms of deformation and stop processes of cracks are facilitated, which restrain or decelerate a crack propagation at a sudden load.
A Continuum Model for Flow Induced Crystallization in Polymers
In this paper, we present a new continuum framework to formulate models to study flow induced crystallization in polymers. The models are developed in a general thermo-mechanical setting and are able to incorporate the main features of the crystallization process. A consistent framework is developed to model the transition from a fluid like behavior to a solid like behavior. The anisotropy of the crystalline phase is included in the model and depends on the deformation in the melt. Particular models are generated by choosing specific forms for the internal energy, entropy and the rate of dissipation. Equations governing the evolution of the natural configurations and the rate of crystallization are obtained by maximizing the rate of dissipation. The initiation criterion, marking the onset of crystallization, arises naturally in this setting in terms of the thermodynamic functions. The model is used to simulate bi-axial extension in a polymer film that is undergoing crystallization.
On the Inherent Stability of a Dynamic, Pressure Controlled Injection Molding Process to Material Variations
Dynamic feed is the injection molding process whereby the machine's polymeric flow is attenuated by a series of independent valves that are placed in a hot runner manifold just prior to each cavities entry gate. Each valve is controlled dynamically, in real time, to follow a pre-programmed pressure profile using feedback from a pressure transducer located downstream. The advantages of having control over each cavity (or open/close sequencing along with pressure profiling) are many. Parts of widely varying fill needs can each have a tailor made pressure profile specific to the needs of that particular part geometry. Strikingly dissimilar parts can be made in a single shot that would not be possible on a conventionally equipped machine. Watkins and Hume have discussed the primary advantages of this technology previously, they focused on the particular advantages of using the technique with modular tooling1. Kazmer discussed the process in detail5. Of concern in this work is the inherent stability of the dynamic feed process and the apparent potential for increased process variation due to anticipated material variations2.
The Role of Melt Dynamics in Shear-Enhanced Crystallization of Isotactic Polypropylene
Processing flows are known to accelerate polymer crystallization kinetics, strongly altering the orientation distribution of the crystallites and producing dramatic changes in material properties. Our research probes the molecular level processes that give rise to these effects. To clarify the role of macromolecular relaxation, we investigate the effects of shear history on the crystallization of isotactic polypropylenes. A unique apparatus enables us to subject a subcooled melt to precisely controlled intervals of shear at stress levels similar to those encountered in industrial processes.(1) Brief intervals of shear enhance the rate of subsequent crystallization by orders of magnitude. Previous rheo-optical experiments have indicated that the creation of long-lived, oriented structures during flow is controlled by the dynamics of the melt.(2) We present polarimetry and synchrotron wide-angle x-ray diffraction (WAXD) data obtained during and after shear of an iPP believed to contain chains with long branches. Results suggest that shearing near the nominal melting temperature induces the formation of a slow relaxing species that templates subsequent oriented crystal growth, emphasizing the importance of rheology to shear-enhanced crystallization.
Snap-Fit Performance as Predicted by Three Rapid Prototyping Techniques
This research involves the area of rapid prototyping (RP) and a new concept called functional prototyping. The overall goal of this project was to determine if current rapid prototyping methods allow for the prediction of the mechanical performance of a molded snap-fit. The Rapid Prototyping methods that were evaluated are Fused Deposition Modeling (FDM), Selective Laser Sintering (SLS), and machining plastic from stock shape. The results show that machining is the best method to use for functional testing, followed by SLS, and FDM. An attempt to ratio the results using the modulus of elasticity and yield strength are not quite satisfactory. But it can still be used for the rough estimation. Each of the prototypes types has its own tendency to deviate from the actual value.
Use of Temperature-Modulated and Step-Scan DSC and DMA to Study Curing in an Epoxy Composite
Prepregs of an amine-rich mixture of the tetrafunctional epoxy tetraglycidyl 4,4-diaminodiphenyl methane (TGDDM) and the tetrafunctional amine 4,4'-diaminodiphenylsulfone (DDS) were characterized with temperature-modulated DSC (TMDSC) as well as dynamic mechanical analysis (DMA). The baseline shift of the glass transition was separated from the curing exotherm by using temperature-modulated and step scan DSC temperature scans. Likewise, the baseline shift in heat capacity due to vitrification was isolated using TMDSC isotherms. Using the TMDSC glass transition temperature, degree of conversion, and vitrification results, combined with the gelation data generated from DMA, a time-temperature-transformation (TTT) diagram was constructed, providing information necessary for optimization of industrial processing of the epoxy prepreg. Thus, effects of storage, preprocessing, and postprocessing on the overall curing process are taken into account.
Characterization of Adhesive Failure and Modeling for Dynamic Analysis
One of the ways of increasing fuel efficiency of a typical automobile is to reduce its overall weight. To this extent, plastics, especially fiber reinforced plastics are finding an increasing role as automotive structural components. The automotive structural systems made up of these structural fiber reinforced plastic components, should satisfy the needs in terms of safety, strength, NVH and durability, in addition to being affordable, manufacturable with desired fit and finish and recyclable. In general, structural components made up of fiber reinforced plastics are adhesively bonded together to form structural systems, capable of carrying automotive structural loads under static and dynamic conditions. Fiber reinforced plastics and the adhesive used to bond them to form a structure are inherently viscoelastic in behavior. It is imperative therefore, to understand the behavior of these adhesively bonded fiber reinforced plastic components, in terms of their load carrying capacity at different temperatures and different load or strain rates. One of the key factors in this understanding is to characterize the adhesive failure itself at different temperatures and different strain rates of loading. The present paper is an attempt to present some results from an ongoing research work on fiber reinforced adhesively bonded large injection molded thermoplastic automotive structural systems. In particular the paper presents the results from the test methodology and the mathematical models used to characterize the failure mechanics of adhesively bonded automotive body sections, at different temperatures and different load or strain rates.
360 Degree Competitive Intelligence A Full Circle" Perspective of the Competitive Environment"
A competitive intelligence methodology has been developed which ensures an actionable customer focus is reflected in an assessment of the competitive arena. This is accomplished by combining the classic top down" or Industry analysis of a competitor (or group of competitors) with a "bottoms up" view from the customer perspective. The Industry approach assesses factors such as external environment market position technology supply chain issues and corporate culture among others identifying strengths weaknesses and apparent strategy. The Customer view obtained by in depth field interviews provides insights into unmet needs emerging trends and supplier performance against the strategy. The result is an externally focused actionable plan. This paper will detail the combined methodologies employed and the value added obtained by a review of case studies."
Experiments on the Induction Welding of Thermoplastics
Because of the increasing use of thermoplastics and thermoplastic composites in load-bearing applications, welding methods are becoming important for part cost reduction. Welding requires the melting of the surfaces to be joined, followed by a solidification of the interfacial molten layers under pressure. Many welding techniques using different means for heating the joint interface are available [1]. One such versatile technique is induction welding, in which the surfaces to be joined are brought to the melting temperature" by induction heating a specially made gasket placed in the joint interface. Applications of this technique include welding of hot-water kettle housings and the welding of high-pressure water tanks. This process is not well understood. In this paper tensile tests on induction butt-welds of amorphous and semicrystalline materials are used to characterize achievable weld strengths. Microscopy is used to correlate the strengths achieved with the morphology of the failure surface."
High Carbon Fly Ash/Mixed Thermoplastic Aggregate for Use in Lightweight Concrete
Synthetic lightweight aggregate has been produced by melt compounding high concentrations of high carbon fly ash into various thermoplastic binders. The composite material is being developed as a synthetic lightweight aggregate for use in applications such as lightweight concrete. In this study, a series of lightweight aggregates have been produced using several fly ash concentrations, and several different thermoplastic binders. The synthetic aggregates have been produced using flexible thermoplastic binders, rigid thermoplastic binders, and a mixed thermoplastic binder formulation. The physical properties of the melt compounded aggregate materials have been evaluated in an effort to determine the relationship between variables, such as the binder stiffness, and the aggregate stiffness. Lightweight concrete test samples have also been prepared and evaluated. The results of the study show that the lightweight aggregate properties are influenced by both the fly ash concentration and the thermoplastic binder composition. However, the effect that the thermoplastic binder has on the physical properties of the aggregate becomes less significant at high fly ash concentrations. At fly ash concentrations of 80%, the physical properties of the aggregate are fairly insensitive" to the composition of the thermoplastic binder. The aggregates produced using a mixed plastic composition had properties that were quite similar to those produced using the individual (control) thermoplastic binders indicating that low value mixed plastic waste may be a candidate binder material for the polymer bound fly ash aggregate."
Effect of Nanoparticles and Processing Conditions on the Development of Structural Hierarchy in Injection Molded Nylon Composites
Preliminary studies on the basic structure developed in nylon 6 and its blends with nanoparticles are presented. The melting transition and crystallization behavior of compression molded nylon 6 and its nanocomposites are investigated using DSC and WAXD techniques. The structural hierarchy developed along and across the flow direction is also addressed using optical microscopy. Polarized optical microscopy revealed that the presence of nanoparticles causes significant enhancement of the preferential orientation through the thickness direction of the molded parts even at mold temperatures very close to the melting temperature.
Efficient Injection Molding Workcells: The Case for Remote Integration
Today's competitive business environment requires companies to embark on continuous improvement projects aimed at dealing with plant inefficiencies and new product introductions. Almost every company is unsatisfied with the slow rate of implementation and unsatisfied with bottom line results. How do you ensure that your new system integration will not fall into the same trap? Once the plastic part is designed, the task of creating a cell to manufacture it is too often considered to be a mere formality. It is more than a simple matter of buying the pieces of individual equipment, positioning them on the floor, connecting them to the services and pressing GO" to start. In fact there are critical cell design choices and decisions to be made even before designing the plastic part which are crucial to the ultimate success of the project. A world class injection molding cell requires a well thought out plan detailed engineering design of the system including all the auxiliaries and finally rigorous testing of all the components and their interaction. The focus of this paper will be on the system integration which can be loosely defined as the physical placement/connection of the equipment as well as the performance testing and validation."
Reinforcement of Thermoplastics Using Microcomposite Fillers
Thermoset recyclate fillers are considered as microcomposite reinforcements for polymers. Emphasis is given to glass fibre-reinforced phenolic and polyester waste products as functional fillers for polypropylene, where with appropriate surface modification, significant enhancement in mechanical properties can be achieved. In this respect, the role of a two component treatment package is discussed, in terms of fibre-matrix interfacial bonding, the effect on properties of the host polypropylene matrix, and the failure mechanism induced. Novel integrated compounding technology is described for the cost-effective preparation of polymer composites, containing thermoset recyclate fillers.
Real Time Development of Stress and Birefringence in PET during Uniaxial Stretching as Detected by Spectral Birefringence Technique
The birefringence and stress development of PET films has been measured by our new stretching system that couples the Spectral Birefringence Technique with the stress strain measurements. The tensile stretching machine which is specifically designed such that both clamps of the samples move away from each other. This allows for keeping the midsection of the sample stationary. The birefringence and width of the sample is measured at this location. The width of the sample is measured using laser micrometer through which true strain is obtained real time. It has been found that the birefringence development starts before strain-hardening point. The system is fast enough to follow the deformation at high rates of strains. The increased strain rates results in higher birefringence levels through all stages of deformation
Effects of Biaxial Stretch Ratio and Stretch Mode: The Evolution of on Structural Hierarchy in Polylactic Acid
A series of stretch modes: uniaxial free width (UFW) stretching, uniaxial constant width (UCW) stretching, simultaneous equall biaxial(SEB) stretching and sequential equally biaxial (SEQEB) stretching, were applied to cast amorphous films of PLA in order to investigate the effect of processing on the structure and properties. It is found that UFW stretching leads to higher crystallinity. SEQEB stretching is found to induce very high stress during this resulted in higher crystallinity development in the sequentially stretched films as compared to simultaneously stretched ones of comparable stretch ratios. This was attributed to the increased efficiency of strain induced crystallization in the sequential deformation mode stemming from the first stretching stage.
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