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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Plastics Processing: A Changing Environment
The U.S. plastics industry has been hit hard in the past three years. A number of factors have contributed to this changing environment, including globalization, recession and political uncertainty. The premise of this paper is: the market as we knew it in the late 1990s will never return. The world has changed, so has the plastics industry. The question to be addressed is: how can we prosper in this new environment?
On-Line Hybrid Model Based Tuning of Simulation Provides Soft Sensors for the Estimation of Sheet Temperature Distributions in Thermoforming
Some of the main problems to be solved when applying simulation to a process are the discrepancies between the predicted and measured parameters. This can be due to the fact that the actual operating conditions are different from the ones that were input into the simulation due to variations in material properties and errors in the assumptions for the simulation model. This work proposes a technique to tune the results of the simulation to the actual sensor outputs of the machine. The simulation can then be used as a generalized soft sensor for the process: Since the model of the simulation has been fitted to the actual process, the predictions of the simulation for non-readily accessible points will be that much closer to reality. A further advantage is that variations of the process are back-propagated to the input, so that faults that may appear in the system are presented as more easily interpretable variations of the input data.
The Science Based Optimization of Material Heating during Thermoforming Processes
In this paper, the optimized radiative heating of opaque thermoplastic sheet during thermoforming processes has been studied by using a newly developed modeling and optimization approach. The net radiation method has been employed to develop a comprehensive numerical code that can compute the total radiative heat and associated temperature developments locally on the thermoplastic sheet. The resultant simulation model can accommodate full non-symmetric zone heating situations and multi-layered forming materials. A coupled optimization package was then developed to obtain optimized heater pattern solutions that will lead to desired material temperatures during thermoforming processes. This is done by specifying a desired thermoplastic sheet temperature distribution and iteratively solving for the heater setting needed to obtain the desired results
Modeling of the Behavior of Semi-Crystalline Polypropylene at Elevated Strain Rate and Temperature
A non-linear viscoelastic model comprised of two components, a rubber-like hyperelastic component and a viscoelastic time-dependent relaxation spectrum was used to model the behavior of semi-crystalline PP at rates and temperatures close to that found in the thermoforming process. Temperature dependence was introduced through time-temperature-superposition (TTS) using WLF. The hyperelastic constants were identified from equibiaxial tensile experimental tests while the time-dependent relaxation spectrum was characterized through a temperature-frequency sweep analysis from a strain controlled DMTA test. Results show that the developed model is capable of simulating the behavior of semicrystalline PP fairly well.
Polymer-Polymeric Friction at Temperatures and Rates Simulating the Thermoforming Process
Plug assist thermoforming is one of the most important process variants for the thermoforming industry. The purpose of the plug assist is to pre-stretch the heated polymer sheet prior to the application of pressure and/or vacuum during the final part formation. Parametric studies performed on simulation models of the thermoforming process have shown friction between the polymer and the plug assist to be critical in predicting material distribution in the thermoformed part.This report presents the results of investigating the friction behaviour of a polymer to plug assist material at thermoforming conditions. A new measurement technique to determine friction coefficients will be shown and explained in detail. This technique allows the characterization of the friction coefficient as a function of temperature and rate and shows the sensitivity respectively.
Multiple Criteria Optimization Studies in In-Mold Coated Sheet Molding Compound (SMC)
Sheet Molding Compound (SMC) is a widely utilized material to manufacture automotive exterior body panels. Cycle time, dimensional consistency, and surface finish are among the most important aspects to consider in the production of SMC due to their impact in profit and quality. These performance measures often exhibit conflicting behavior i.e. lowering the cycle time might imply decreasing the part surface quality and/or achieving a lower overall part dimensional consistency. One must exercise especial care in identifying the best compromises between these performance measures (PMs) along with the processing conditions that result in these best compromises. This paper describes an application in SMC processing where the multiple criteria optimization problem is addressed by means of a non-parametric approach known as Data Envelopment Analysis.
Bluetooth Wireless Technology Enables New Applications
Bluetooth, the most widespread of the new wireless communications standards, enables electronic devices to talk amongst themselves. This capability has not only created the demand for many new electronic products, but has pushed value-added product development for plastics in the automotive, healthcare, appliance and computer accessories markets. This presentation will outline what the Bluetooth technology is, new applications, market projections, and considerations for designers as well as resin suppliers.
Measuring a Company's Performance: Economic Value Added in Comparison with Traditional Performance Measures
The choice of a suitable indicator for measuring a company's performance is one of the most widely discussed areas in today's corporate management circles. This paper attempts to analyse a company's performance through different indicators. The case study presented in this paper reveals that value-based measures represented by Economic Value Added (EVA) should have a commanding role in corporate management strategy, and traditional income measures should act as a facilitator for providing supporting information.
Preventing Failure by Design: A Case Study in the Development of a Medical Device
Preventing failure in a plastic medical device requires a thorough understanding of the key fitness for use criteria. This paper explores a case study of copolyester resin development for a device requiring clarity, toughness, chemical resistance, solvent bonding, printability, and ethylene oxide and gamma sterilization. Analyses included molecular weight, modulated DSC, fractography and functional testing.
Development of an Environmentally Friendly Solventless Process for Electronic Prepregs
The most common commercial processes for manufacturing pre-pregs for electronic boards use solvent-based resin systems. Solvents are environmentally unfriendly and contribute to voids in the pre-preg and laminate. The resin impregnation process is done in an open resin bath. This low-pressure impregnation is conducent to voids in the prepregs. Voids cause product variability, which is a major source of scrap in board shops. To eliminate the above mentioned drawbacks, a solventless process, based on the concept of injection pultrusion, is developed. The impregnation is done in a die under pressure to minimize voids.In previous work, chemo-rheological and kinetic measurements were used to identify a potential epoxy-based resin system. In addition, flow visualization using model fluids was used to establish the basic flow mechanism. Here, we use the previous results to develop a mathematical model for the B-staging process. Based on the mathematical model, three potential alternatives to produce prepreg are developed and analyzed. A prototype B-staging die is built and used to verify the mathematical model. The result shows that the model agrees well with the experimental data for low pulling speed and slightly under predicts the high pulling speed runs.
Investigation of Electron Beam Curing of Bismaleimide (BMI) and BMI/NVP Resins
Electron beam curing of a 4,4’-Bismaleimidodiphenyl-methane (BMPM) / BMI-1,3-tolyl / o,o’-diallylbisphenol A (DABPA) based BMI system, and the mixture of the above BMI resin with N-vinylpyrrolidone (NVP) is investigated to build the relationship of temperature rise, dosage and dosage rate and corresponding cure extents. The cure kinetics and effect of initiator on cure reactions are also carried out. Low intensity E-beam exposure cannot initiate BMI polymerization but high intensity E-beam exposure gives high reaction yield due to high temperature rise, which induced thermal curing. However, BMI/NVP systems can be initiated easily by low intensity E-beam exposure without thermal curing being induced. According to FT-IR measurements, 70% reaction conversion of BMI/NVP can be achieved by 200 kGy dosage exposure at 10 kGy per pass with the temperature rise no more than 50°C. The product having a Tg of 180°C can be obtained.
Numerical Simulation of the Curing Reaction during Pultrusion Processes with a Diffusion Controlled Model
A numerical simulation of the pultrusion process was developed. The material properties were determined experimentally and fitt to a numerical diffusion controlled curing model. The DiBenedetto equation was used to calculate the instantaneous glass transition temperature during the curing process. The simulation determines the expected temperatures and degrees of cure throughout the part, in response to varied processing conditions. The primary application of the simulation is the pultrusion process and part design as well as testing the effect of new unsaturated polyester resins during processing.
Developing Time-Temperature-Transformation Diagrams for Unsaturated Polyesters Using DSC Data
A general concept of time-temperature-transformation (TTT) diagrams was numerically established to portray the effects of processing conditions during the curing of unsaturated polyester resins. The isothermal curing curves and the vitrification line were constructed based on a numerical procedure to model the curing of an unsaturated polyester resin. Isothermal and dynamic DSC modes were used to obtain the experimental data. A non-linear least squares Levenberg-Marquardt algorithm was used to fit the reaction rates with an autocatalytic kinetic model with diffusion effects. The DiBenedetto equation (1987) was utilized to correlate the degree of curing and glass transition temperature to model the diffusion-limited part of the reaction. The fitted model shows a good agreement between the experimental DSC scans and the predicted reaction rates. The numerical TTT diagram can be utilized during process design and optimization, since most of the curing behavior is represented in the diagram.
A New Class of Epoxy Thermosets
SBM, PolyStyrene-block-1,4-polyButadiene-block-polyMethylMethacrylate, is a new family of block copolymers offering an original way to modify polymer materials performances. Blended with a polymer compatible with one block, SBM disperses readily and imposes a structuration to the host matrix. This organization imparts unique combinations of properties, such as impact strength, high rigidity and transparency. This stands both for thermoplastics and thermosets. Here nanostructured thermosets are presented. These supramolecular architectures yield significant toughness improvements while preserving the optical transparency of the material.
An Investigation into Fracture Toughness Testing of Dental Luting Cements Using Various Methods
Various types of luting cements are used for fixation in dentistry. Failure through fracture is a significant issue with these materials. Several fracture toughness tests have been developed to characterise dental luting cements. Among them are the Chevron-Notch Short-Rod and Mixed-Mode Sandwich tests. In this study these two techniques are applied to a dental luting cement and from the results of the testing, conclusions are drawn on what they can determine regarding a material's properties.
Characterisation of the Fracture Toughness of Acrylic Bone Cement Containing Nanoparticles using the Chevron Notch Short Rod Technique
Chevron Notch Short Rod (CNSR) bone cement samples containing silicate clay nanoparticles were prepared and mechanically tested and their fracture toughness properties determined. Acrylic bone cement samples without the nanoparticles were also tested as a control and a reduction in the derived KIC for acrylic based nanocomposite structure was found to exist. The CNSR technique has been shown to be an appropriate test method to characterise the fracture toughness of nanocomposite structures.
Mechanical and Thermal Characterization for Sterilized Medical Elastomers
We have applied thermal, mechanical, and rheological techniques in the product development for medical elastomers with success. In this presentation, examples of actual product application will be used to illustrate the utility of these techniques and to demonstrate the derived information that was used in developing successful elastomeric related medical products.
Epoxy + Montmorillonite Nanocomposite: Effects of Water, Ultrasound, and Stoichiometry on Aggregates
The effect of controlled water addition to the development of random aggregates of alkonium ion substituted montmorillonite clay in epoxy was studied based on changes to the hardener mix ratio, clay composition, and ultrasonic treatment before cure. The effects on the glass transition temperature and microhardness were determined. The introduction of water before ultrasonic mixing altered the apparent size of the treated clay aggregates observed in these mixtures after cure. The clay aggregates also appeared to change the location and the distribution of water-induced microcracks in the cured nanocomposites. This information was used to develop a technique to remove aggregates without causing microcracks.
Development of a New Solution to Vary the Thickness of the Parison over its Circumference While It Is Extracted
Complex blow molded parts afford not only a variation of the thickness of the parison in axial direction but also in circumference direction to end up in the desired optimal thickness distribution in the final part. Integrating a partial multi-walled Flex Ring into a blow molding die allows to alter the local flow channel geometry. While deforming the Flex Ring its geometry alters gradually, so no dead spots are created. As additionally the deformation of the Flex Ring keeps within its linear elastic range the deformation can be repeated for every cycle. The principle of the technology will be explained and potential solutions of the new technology will be discussed.
Preform Optimization Using Non-Linear Finite Element Simulations
Non-linear finite element simulations of the blow molding and thermoforming processes have been used to provide accurate predictions of the material thinning. However, this powerful simulation tool has provided limited assistance to the design and optimization of the wall thickness distribution of preforms used in injection blow molding. Trial-and-error methods are often used in design. This paper presents a technique that converts finite element analysis of the injection blow molding process into a design/optimization tool. A systematic optimization technique for preform design that uses an iterative series of non-linear finite element simulations will be described. The series of simulations converges on a preform wall thickness distribution that will result in a specified thickness distribution in the blow molded product. This design technique is especially effective for non-circular or irregular shaped products.
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