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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Thermoforming Prototype Mold Evaluation using a CAE Software
The main objective of this project consisted on the development of a measure container prototype and its mold, using Computer-Aided Design (CAD) / Computer Aided Engineer (CAE) / Computer Aided Manufacture (CAM) tools, through a 3D program and a simulation software of the thermoforming process, to determine the geometry corrections in the part design. The part prototype was carried out by using the material deposition rapid prototyping (RP) technique and the mold prototype was carried out for the machine technique. To evaluate both prototypes, the results obtained in a thermoforming machine and in a simulation software were compared.
Processing Strategies for Rotational Molding of Integral Skin Polyethylene Foams
This paper focuses on the study of the single-shot rotational foam molding technology for producing integral skin polyethylene foams. In this context, parametric studies over the mold rotational speed and in-mold temperature transition have been conducted. In conjunction with the utilization of the particle size difference between foamable and non-foamable resins, it has been found that increased mold rotational speeds can significantly improve the crucial separation of the time of formation of the skin layer from that of the foam layer. The proposed processing strategies secure the formation of a distinct layer of solid skin surrounding the high quality foamed polyethylene core.
Experimental Study on the Mixing and Segregation of Granular Particles in Rotational Molding
The nature of powder flow and its effect on particle deposition in rotationally molded parts is studied in this work. Experiments were carried out to see the effects of various parameters such as powder characteristics and operating conditions on the deposition pattern. Models for cohesive forces were developed and their effects on particle movements were estimated. Results indicate that the polymeric powders are cohesive enough to prevent size segregation at room temperature. When heating, the particles become sticky and a relatively new phenomenon of cohesive segregation is seen.
Single Site Polyethylene Resins with Enhanced Processability for Rotational Molding Applications
The performance of a new generation of single site polyethylene resins is compared to that of conventional Ziegler-Natta (Z/N) resins. Results from rotational molding trials showed that under comparable molding conditions, the mechanical properties of parts produced from single-site resins superior to those of Z/N resins. Moreover, the densification of the single site resins is complete at significantly shorter residence time in the oven versus Z/N resins. The processing window is wider and shifted to lower temperatures for the single site resins compared to the Z/N resins. The enhanced densification arises from faster dissolution of bubbles formed during the heating cycle.
The Effect of Surface Tension on the Sintering of Polyethylene Copolymers and Blends in Rotational Molding
Polymer sintering is a formation of a homogenous melt through the coalescence of powder particles during the heating cycle of rotational molding. Although the importance of surface tension in rotational molding has been recognized as one of the most important controlling parameters, there is only limited information on the role of surface tension in rotational molding.The objective of this work was to develop an experimental technique for characterizing the surface tension of materials used in rotational molding. The effect of surface tension on sintering was investigated. This paper summarizes the results of the effect of surface tension on the rotomoldability of selected polyethylene copolymers and blends.
A Six Sigma" Approach to Process Optimization for the Rotational Molding Industry"
There is a consensus in the rotational molding and related industries that crosslinkable polyethylene (XLPE) is the choice material for gasoline-type reservoirs. Field failure of XLPE-based reservoirs is not common, and to resolve one such situation involving hydraulic fluid tanks, students of Pittsburg State University's plastics engineering technology program are utilizing the concepts of six sigma (DMAIC), define, measure, analyze, improve and control. In collaboration with the reservoir producing and user companies, the problem situation was defined; film products from the hydraulic fluid-XLPE tank interface clog up the fuel filter system and subsequently result in damaged pumps. Preliminary DSC (differential scanning calorimetry) measurements indicate similar thermal transition profiles for both film and tank materials, suggesting that the film is a plasticization rather than reaction product. Additional analysis of DSC, torque rheometry, rotational molding and solvent test data yield insightful information and the optimum processing parameters for improving and controlling XLPE hydraulic reservoir production.
Acetal Copolymer - A Potential Fuel Permeation Barrier for Rotationally Molded Fuel Tanks
Acetal copolymers can be rotationally molded into a wide variety of shapes and sizes, using conventional grinding and rotational molding equipment. Celcon® M15HP acetal copolymer is one such grade that was recently developed by Ticona to offer substantially improved physical, mechanical and thermal properties over general purpose grades of acetal copolymer. In particular, it exhibits higher tensile strength, flexural modulus, impact resistance, heat deflection, fatigue endurance, abrasion resistance and surface hardness.Because of its extremely low permeability to gasoline and alcohol, along with its excellent long-term chemical resistance and dimensional stability, acetal copolymer is currently being evaluated as a potential fuel permeation barrier to meet proposed CARB and EPA evaporative emissions regulations for small offroad engine and marine fuel tanks, which are found in numerous products manufactured by the Lawn & Garden, Outdoor Power Equipment, Recreation Vehicle and Marine industries. This paper will present some basic guidelines for the rotational molding of acetal copolymer, along with some techniques for data generation and analysis using six-sigma methodology, which have enabled us to optimize the rotational molding process around this material.
Two-Dimensional Slip-Flow Model of Rotational Molding
A new slip-flow model is developed to simplify and to overcome the current numerical difficulties of two-dimensional rotomolding model in predicting the internal air temperature inside the mold during the rotomolding process. The lumped-parameter system and coincident node technique have been incorporated with the Galerkin finite element method to address these rotomolding problems. This proposed methodology allows macroscopic multi-layered deposition" of heating polymer powder onto the mold surface in order to account for the complex thermal interactions between the internal air and its surroundings (mold and polymer). A semi-implicit method is applied to deal with the overall internal air temperature inside the mold. The predicted results agree with the available experimental data for rotomolded parts of cross sectional thicknesses up to 12 mm."
Computer Simulation of the Effect of Coefficient of Friction in Plug Assist Thermoforming
In plug assist thermoforming, surface friction strongly affects the final part thickness distribution. This work investigates the effect of plug material, plug temperature, and sheet temperature on coefficient of friction between the plug and sheet. Three different plug materials (epoxy syntactic, engineering thermoplastic nonsyntactic and engineering thermoplastic syntactic) with a range of friction coefficients were investigated for thermoforming polypropylene sheet. The coefficient of friction was assessed using simulation software (T-SIM®). Coefficient of friction values were varied in the simulation software until the thickness distribution predicted by simulation was similar to that obtained experimentally.
Development of a Measurement Technique for Tailored Material Characterization and Validation of Thermoforming Simulation
For thermoforming simulation a measurement technique was developed to enable material characterization. A holistic approach was chosen to measure material parameters and the coefficient of friction. An improved “reverse-engineering” algorithm generates the material data.This paper explains the measurement devices and emphasizes the importance of the coefficient of friction. While static and dynamic friction occur in the thermoforming process, for simulation a “mixed” coefficient is used. As an example PET and ABS are investigated.
Optimization of Acrylic Capped ABS Coextruded Systems for Sheet Applications
There is a need for high quality, high gloss, scratch resistant, weatherable Acrylonitrile-Butadiene-Styrene (ABS) sheet for exterior applications. This sheet can be obtained by co-extruding a thin capstock layer of a weather resistant and weather protective acrylic resin over an ABS substrate. This paper discusses the key parameters for the design of this sheet. It is intended to be an aid for sheet converters and those specifying weatherable coextruded sheet. The Dow Chemical Company and Atofina Chemicals, Inc. have combined their materials expertise to manufacture and test the sheet structures presented in this paper.
Rapid Thermal Response (RTR) Hot Embossing of Micro-Structures
Although hot embossing is gaining popularity in the replication of micro-structures, it needs a breakthrough improvement on cycle time reduction before it can become a mass-production process. Previously, the authors developed a Rapid Thermal Response (RTR) molding process for enhancing the quality of conventionally molded parts. In the current study, this technology was adopted to hot embossing micro-structures. In the paper, RTR hot embossing machine setup and mold construction were described, and the results of fatigue test and RTR embossing were presented. Microstructures with characteristic dimension of 2?m were successfully replicated with substantially reduced cycle time. The fatigue test result indicated that this embossing technology is durable and reliable for microscale feature replication.
Neuronal Networks Application for Characterization of Softened Polymers
Recent progress in computer-aided polymer processing analysis demonstrates the need for accurate description of the material behavior under the conjugated effect of applied stress and temperature. In this work, we are interested in the characterization of circular thermoplastic membranes, ABS and HIPS thermoforming grade, under biaxial deformation using the bubble inflation technique. Hyperelastic (Mooney-Rivlin, Ogden) models are considered. First, the governing equations for the inflation of a flat circular membrane are solved using a dynamic finite element model (triangular membrane elements), and there after, a neuronal algorithm is employed to determine the materials constants. Moreover, the influence of the Mooney-Rivlin and Ogden constitutive models on the thickness and the stress distribution in the thermoforming sheet are analysed.
Development of Rapid Heating and Uniformly Pressing System for Micro Hot Embossing
Hot embossing is an effective method for transferring micro-features in mold to plastic film or plates. Improving uniformity of pressure and reducing cycle time are constant challenges with MEMS or NEMS applications. This paper reports development of a rapid heating and uniformly pressing system for micro hot embossing. Direct fluids are used as working media. The seal film/mold/substrate stack is placed in a closed chamber. Then the fluid is introduced into the chamber for heating and pressing the stack. Micro patterns in the mold can be successfully replicated onto the substrate. Perfectly uniform embossing pressure throughout whole area can be achieved. The cycle time is less than 30 seconds.
Modeling of In-Mold Coating for Resin Transfer Molding
Closed mold reactive liquid composite molding processes such as resin transfer molding (RTM) and any of its variations such as vacuum-assisted resin transfer molding (VARTM), Seemann Composite Resin Infusion Molding Process (SCRIMP), etc, are environmentally friendly alternatives to open mold processes, which have been traditionally employed to form large composite parts. However, in most cases, in order to improve and/or protect the part surfaces, gel coating is required. The gel coat is applied with the mold open, which releases harmful volatile organic compounds (VOCs) to the environment, partially compromising the benefits of the closed mold processes. In-mold coating (IMC) is an attractive alternative to gel coating to eliminate VOCs. IMC is a coating operation performed by injecting a coating material onto the surface of the substrate with the mold closed. The coating flows by compressing the substrate under pressure. In the present work, we develop mathematical models to predict the filling and packing stages of IMC for RTM substrates. These models include the effect of the compressibility of the substrate and mold.
Modeling the Vulcanization Process of High Consistency Rubber and Liquid Silicone Rubber
A kinetic model of the vulcanization process of high consistency rubber (HCR) and liquid silicone rubber (LSR) was developed. The exothermal vulcanization process was measured with a differential scanning calorimeter. Viscosity was measured with a cone and plate rheometer. A computer program fit coefficients to the experimental data. Values for activation energy and fitted rate coefficient were found using both nth order polynomial and autocatalytic models. A kinetic model of vulcanization will help manufacturers understand and optimize their production processes.
Effect of Dual-Initiator and Promoter on Low Temperature Cure of UP Resins
In low temperature composite manufacturing processes, a major concern for material suppliers and fabricators is how to control the resin gel time and cure time and how to achieve a high final conversion with low residual volatile organic chemicals. In this study, a cobalt promoter catalyzed dual-initiator system is used to control the reaction rate and resin conversion of unsaturated polyester (UP) resins. A mechanistic kinetic model is developed to predict the reaction kinetics with dual initiators. This model can be utilized to simulate both isothermal and dynamic reaction rate and conversion profiles. It can also be used to predict the effect of promoter contents on UP resins cured at low temperatures.
Study of Mixtures of Different Fibers in Sheet Molding Compound (SMC)
The automotive industry requires parts with high strength and low weight, and if the application requires it, surface quality. These requirements have led to investigate the use of carbon fibers as a reinforcement alternative to the widely used glass fibers. Our previous studies compared the performance of glass and carbon fibers in unsaturated polyester based sheet molding compounds (SMC) for non-structural applications. These showed that there are compromises between the performance of physical properties, cost (incurred by adding the more expensive carbon fibers), and consistency (i.e. variability). In this work, we investigated the effect on physical properties of SMC structural parts when there is a mixture of carbon and glass fibers. Special considerations in the analysis and the implementation of these experiments are discussed.
Preparation and Characterization of Biphenyl Epoxy Nanocomposites via Pre-Intercalated Phenolic Hardener
Polymer-layered silicate nanocomposites(PLSN) as nanometer scale reinforcements offers an interesting alternative for the modification of polymer matrix properties with really great improvements in their mechanical, thermal and physical properties. The biphenyl epoxy(BPE)-phenol aralkyl novolac (so called xylok resin, XK)-montmorillonite (MMT) hybrid PLSN were newly synthesized via indirect melt process using pre-intercalated XK-MMT PLSN to avoid the fatal disadvantages of storage stability in conventionally synthesized epoxy PLSN due to the reaction between the epoxy resins and the organic group in the MMT. This storage stability is one of the important properties for the commercial uses such as epoxy molding compounds (EMC). To develop a novel formulations for the semiconductor packaging which have the good storage stability, we prepared pre-intercalated XK-MMT PLSN as the first step, and then we synthesized BPE-XK-MMT PLSN using these pre-intercalated XK-MMT PLSN. In this work we studied the effects of the MMT with different organic groups. Also we investigated the evidences of the power ultrasonication effects on the nano-scale structure. The x-ray diffractometer results shows the intercalated or exfoliated PLSN which were characterized by conducting differential scanning calorimeter, dynamic mechanical analyzer, thermo gravimetric analyzer, universal testing machine, and impedance analyzer. Moreover we could figure out the optimum contents of the MMT from the agglomeration due to the higher loading of the MMT.
Characterisation of Reactive Extruded Recycled Poly(Ethylene Terephthalate)
Recycled poly(ethylene terephthalate) (R-PET) was chain extended with pyromellitic dianhydride (PMDA) in an industrial scale twin-screw reactive extrusion system. Reactive extruded recycled poly(ethylene terephthalate) (RER-PET) samples at different PMDA concentrations were characterised in terms of rheological properties; thermal transitions and crystallinity. The results confirm the increase in molecular weight with an increase of PMDA concentration, and the formation of branching at concentrations above 0.25 wt.% PMDA. Structural changes due to PMDA addition affect the Tm, Tc and the crystallinity; however, no significant change was observed for the Tg.
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