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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Preventing Squeeze-Out of Sealant during Hot Bar Sealing: Modeling and Experimental Insights
Excessive pressure and temperature during hot bar sealing can result in poor seals due to squeezing out of the sealant. A model is developed that shows the amount of squeeze-out increases with increasing seal bar pressure, seal temperature (by lowering the viscosity of the sealant), sealing dwell time, film thickness and decreasing seal bar width. Photomicrographs of the seal area reveal the change in sealant thickness near the edge of the seal area which correlates with the model predictions. The study shows that differences in rheological behavior of sealants, such as that between linear and branched polyolefins, can impact squeeze-out. Practical guidelines are proposed from the work to prevent problems associated with excessive squeeze flow.
Effect of Seal Process Parameters on Final Seal Strength Behavior for LLDPE
Heat sealing is joining two polymer surfaces while they are at least partially molten, by applying heat and pressure. The evolution of seal strength with seal process conditions was investigated in order to achieve high quality seals and high packaging production rates. This optimization of heat sealing process parameters (Time, Temperature and dwell time) in terms of seal strength was performed on a monolayer linear low-density polyethylene (LLDPE) film. Increasing dwell time enhanced seal strength, as expected, because of the more time available for diffusion. By increasing pressure, an increase in seal strength was observed; however, the effect of pressure was not as significant as the effect of dwell time. At very high pressure range, seal curves showed a narrower temperature window. Comparing dwell time and pressure effects, variation in dwell time had a larger effect than pressure on seal initiation temperature and plateau temperature broadness. The level of plateau seal strength changes slightly with process conditions. A 3D graph of process safety zones was introduced for seal strength in the range of heat seal process variables for the very first time.
Equipment and Material Considerations for Microcellular Foaming
Microcellular foaming processes are now proven technologies and integral part of the “mainstream” in polymer conversion operations. The present paper is a joint effort between two companies (Dow and Mucell) to address key aspects necessary to achieve a more efficient use of materials and resources via physical foaming. The paper reviews in detail all aspects that influence performance, paying special attention to the synergies that arise between hardware and material selection. A comparison of performance between chemical and physical blowing is analyzed, highlighting the advantages of microcellular foaming.
Predictive Analysis of Flexible Pouch Performance
The importance of flexible packaging is growing in the consumer products industry. This evolution in packaging is readily observable when walking down the food or cleaning products isle of the grocery store. As a packaging structure, however, flexibles pose a new and unique challenge to designers. Predictive computational methods, such as finite element analysis, can be broadly applied to the development of these packages, minimizing or eliminating the need to conduct trial and error development or testing. A total of six (6) case studies concerning flexible pouch simulation are presented in this paper, ranging from pouch formation, filling, heat seal strength and drop impact and tear-opening.
Machine Direction Orientation and its Effects on Multilayer Sealant Film
This study investigates the effects of machine direction orientation (MDO) on the performance of multilayer polyethylene sealant films. The study was designed to focus on how physical, sealant, and barrier properties of films, with varying core densities, would be modified after being MD stretched over a full range of possible draw ratios. Three layer linear low density polyethylene films were fabricated on a commercial-scale blown film line and were subsequently stretched on a machine direction orientation unit. Significant effects were seen in the areas of modulus, dart impact, haze, tear, heat seal, and barrier properties.
Adhering Flexo Inks to Flexible Packaging Substrates... The Surface Energy Solution
Flexographic ink systems cover a wide gamut - solvent-based, water-based, and ultraviolet-light cured. These system categories will include solvents, colorants, resins, additives, oligomers, monomers and other unique compounds. Each ink component influences the viscosity and surface energy of the ink and its relative adhesion to various substrates at different press speeds. Surface energy is the common denominator between ink and substrate, quantifying the disruption of intermolecular bonds that occurs when a surface is created and interfaced with. This presentation will discuss the components and viscosity impacts of inks, define the ideal surface energy calibrations between the different flexo ink systems and various substrates, explore ink-to-surface bonding dynamics, and provide surface treatment recommendations.
Flexible Bio-Degradable Packaging - Strategic IP Insights
Hundreds of patents and scientific papers are published every year in the field of packaging. With innovation beyond the core i.e packaging gaining the limelight, we thought that a strategic IP insights study would be interesting. Further, we know for a fact that “the technologies of tomorrow lie as of now in the patent databases of the world.” The objective of our study was to find out the innovative market players in this technology area. Intellectual Property that these players hold is taken as a measure of their technological prowess in this particular area. We have used Patents and Scientific articles to point out the innovative and technologically advanced market players. Further, the study also reveals the technology as an understandable taxonomy, and the in-depth categorization of patents in this domain. Other topics covered include key universities, companies and market players in this area. We sincerely believe that the findings of our study will help researchers understand the technology space, the white spaces & where technology is headed; the deal makers can identify the acquisition targets; IP licensing professionals can understand their potential buyers & the market; C-level executives & strategy executives can make crucial business decisions etc
Flow Length Analysis of Micro Parts in Optical Polymers
Micro injection molding is a prevalent mass production technology in the manufacturing of micro parts. Applications of micro parts range from high technology devices to daily consumer goods. In order to meet the requirements of challenging micro parts, it is crucial to investigate the filling behavior of chosen polymers in micro injection molding of small scaled parts with a high surface-area-to-volume ratio. This investigation focuses on mold design, mold manufacture and particularly injection molding of thin, flat optical micro parts with high surface-area-to-volume ratio; for simplification, a spiral part geometry was chosen. The analysis of the micro molded parts comprises the achievable flow length as well as the overall quality and the melt front within the variation of processing parameters.
Case Study: The Root Cause of Failure of an EPS Foam Coffee Cup
This study was carried out to determine the root cause of failure of a coffee cup resulting in serious personal injury. Billions of disposable coffee cups are used annually around the world. Most of the cups are molded using expandable polystyrene (EPS). EPS is a very complex material with many structural variables that affect the strength of molded parts. Lab testing and computer FEA analyses of the most common cup designs reveal that cups having a flared rim design are least robust and are thus most likely to fail during human interaction (e.g., lidding and holding/squeezing) compared with cups having a straight rim design.
Moisture Determination of Specialty Resins Using Relative Humidity Sensor Technology; A Solvent-Free Alternative to Karl Fischer Titration
The Health Care industry has increased its needs for specialized devices over the past decade, which has led to a new frontier of resin and polymer development designed to keep the quality of care high while minimizing cost. With these goals in mind, the resins being used for medical devices are scrutinized more thoroughly than other resins that require less regulatory compliance. The development of an alternative to Karl Fischer moisture analyzer, which uses a relative humidity (RH) sensor for quantifying water content has been achieved, and can be used for moisture specific analysis of medical device grade resins. The results between the two methods of detection of H2O content in TPU strongly correlate with the KF, with the KF measuring an average of 62ppm of water in the resin and the RH sensor instrument measuring 65ppm.
A Hybrid Approach for Prediction of Sheet Formation in Twin Sheet Extrusion Blow Molding (TSEBM) Process
The sheet formation is the most critical stage in the Twin Sheet Extrusion Blow Molding (TSEBM) process, as the final dimensions of the blow molded part is directly related the initial extrudate sheet shape. A better understanding of the sheet swell/sag phenomena will ultimately lead to improvements in the prediction of the extrusion process, such as the optimization of both die design and processing parameters. Consequently, the development of a robust 2.5D numerical simulation tool of sheet formation in TSEBM process remains a challenging task, in order to achieve a prescribed accuracy with an optimal computational time, especially when it comes to industrial production rates featuring high Weissenberg numbers. The numerical validation, in terms of length and width distribution of the extruded sheet, is performed by comparing predicted solutions to experimental measurements obtained with different flow rates, die gap opening and extrusion time.
New Stainless Mold Base Steel with High Machinability and Improved Thermal Conductivity
An injection mold is designed to contain the polymer melt within the mold, efficiently transfer the thermal energy from the hot polymer to the cooler mold steel to provide uniform plastic parts, and eject the plastic part. In order to fulfil these primary functions, there are some main requirements for mold bases: • High machinability to provide both high productivity and longer tool life (cost reduction) • High and consistent mechanical strength and hardness • Good thermal properties to facilitate the removal of heat energy through cooling. • Good corrosion resistance to ensure mold durability and reduce maintenance costs. INDUSTEEL ArcelorMittal has developed an original patented free machining martensitic stainless steel: SUPERPLAST® Stainless (SPS). In this paper hardness and microstructure uniformity, high feed milling performance and thermal conductivity of the new grade and standard grade AISI 420FM (2085) will be compared.
Notes on Characterization of Natural Fiber Polypropylene Composites
Injection molding simulation of natural fiber thermoplastic composites NFTC requires material full characterization of the following parameter: density, thermal expansion, viscosity, (Pressure- Volume- Temperature) PVT-behavior, thermal conductivity, thermal degradation, polymer structure, specific heat and dynamic mechanical properties. The effect of fiber type (regenerated cellulose, sisal, hemp, wood fiber, wheat straw and kenaf), fiber content (10 and 30 wt.-%) and fiber length (0.5 and 1.5 mm for cellulose) on the mentioned material parameter as well as on their processing behavior during injection in a spiral mold was characterized. Compound viscosity and fiber type/ size were correlated. Other auxiliary results are found in this study concerning the constancy of fiber content along the injected products and the pore formation due to the inevitable gas evolution from the natural fibers.
Critical Factors Affecting the Use of Finite Element Analysis for Rotomolded Parts
Computer aided engineering (CAE) technologies, such as finite element analysis (FEA) of stresses offers the capability to optimize and validate engineering designs within a virtual environment, enabling potential problems to be highlighted and development time to be decreased. FEA has been used widely in the rotomolding industry, although it does not always appear to give an accurate prediction of behavior in the field. This paper examines several aspects with the aim of ensuring better correlation between FEA and actual part performance. Aspects considered include: Is Young’s Modulus representative of real stiffness? How important is Poisson’s Ratio? What is the effect of wall thickness variation in moldings?
4 Case Studies to Discover the Possible Automotive Applications of Glass Beads
Solid glass beads can be used in a lot of different thermoplastics in order to improve the following properties : scratch and abrasion résistances, dimensional stability, processing, ... The goal of this presentation is to show, with 4 case studies in automotive, the advantages given by the introduction of solid glass beads in different resins. The 4 case studies are : Mix of glass in Nylon compound in order to improve surface properties. Filler Pp compound with glass beads to improve scratch resistance Advantages to use glass beads in styrenic resins New solid glass bead grade to improve PC properties General conclusion will finish this presentation.
Limitations & Level of Accuracy of Tests for Rotomolding Powders
The rotomolding industry commonly uses two connected tests to assess the quality of plastic powders: Dry Flow and Bulk Density. Industry-specific test methods are available for both parameters. Repeated measurements were carried out on five different rotomolding powders, in order to assess the influence of the various equipment and environmental parameters that are thought to affect the test. This enabled estimates to be made of the limits for the accuracy and repeatability that are achievable practically. The results obtained from the Dry Flow test suffer from significantly higher variance than those obtained from the Bulk Density test.
Effects of Temperature and Viscoelasticity on Film Die Flow Uniformity
This study shows the effect of die temperature distribution and resin viscoelacticity on the flow uniformity in a film die. The magnitude of the thermal affects can be significant enough to mask other rheological effects. Computational Fluid Dynamics (CFD) simulations predictions using temperature-dependent viscosity models and gradients in the die wall temperature boundary conditions agreed well with the experimental measurements of flow uniformity. When the die wall is more uniformly heated, the flow uniformity is improved in both the measurements and simulations, although the simulations showed more deviation from the experimental results as the elasticity and shear thinning of the resins increased.
Unique Rheological Properties of Polymer Melts with Flexible Nanofibers
Rheological response under elongational flow is studied using polymer melts with polymeric fine fibers composed of poly(butylene terephthalate) PBT and poly(4-methyl-1-pentene) PMP. Both fibers are prepared by hot-stretching of the blends with isotactic polypropylene PP or poly(L-lactic acid) PLA. The samples with 1 wt% of PBT fibers whose diameters are smaller than 1 µm show marked strain-hardening in elongational stress. On the contrary, the sample with PMP fibers with a diameter of approximately 2 ?m shows no strain-hardening, although the measured elongational stress is significantly higher than that calculated from the linear viscoelastic properties.
A Study on Void Formation in the Residual Wall Thickness of a Curved Area during Fluid-Assisted Injection Molding
We analyzed the different effects on the formation of void in a residual’s wall thickness during fluid-assisted injection molding where water and silicone oil that had different thermal properties were used. For this, we conducted heat transfer analysis and injection molding analysis. We confirmed that void formation occurred due to the distribution of the temperature and volumetric shrinkage in the direction of the residual wall thickness in a curved area with a hollow section. We also found that void formation in the curved area decreased in case of using silicone oil compared to using water from simulation and experiment.
Viscoelastic Models with Logarithmic Strains
Analysis of 3-D viscoelastic flows is of a particular interest in polymer processing. Classical approaches rely on the Finger tensor and its inverse for strain evaluation. In this paper, we present a general Maxwell model with a logarithmic tensor for strain determination. Since the logarithmic strain provides a better representation of the state of straining of the material, the resulting constitutive model is expected to have a number of advantages including more uniform straining in different directions and extended linear behavior towards moderate deformations. Model testing on simple shear with only two material constants demonstrated simultaneous prediction of shear thinning and first and second normal stress differences.
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