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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Cell Dissolution in High-Pressure Foam Injection Molding: Towards a More Efficient Packing
Packing/holding stage as one of the most important stages during foam injection molding is often overlooked in the industry. It not only influences the part’s geometrical accuracy and stability, and the residual stress distribution but also has a significant impact on the production time, machine tonnage, etc. In this work, we attempted to predict the evolution of the cell size during packing using a previously developed model. The model predicted dissolution profile was then compared with measured cell size obtained from visualized high-pressure foam injection molding. Moreover, the use of the visualization mold granted us access to characterize the dissolution time for gate nucleated cells, thereby systematically study the efficiency of each individual packing parameters (i.e. gas concentration, packing pressure, and injection speed).
Inline Cross-Linking Degree Measurement in Continuous Vulcanization of Rubber
In the production of rubber profiles, there is a risk for the processor because measured values for the actual degree of cross-linking of the extrudates are only available with a time delay due to offline measuring methods. Therefore, the aim of this work is to develop an online method which provides the degree of crosslinking in a continuous extrusion and vulcanization process. Therefore, this paper shows how the degree of crosslinking can be determined by measuring the surface temperature drop and the eigenfrequency of the profile. On the one hand, the cooling rate on the surface of a heated extrudate is used to determine the core temperature. With the help of this core temperature, the degree of cross-linking in the core of a profile can be calculated. For this purpose, temperature measurements were carried out by varying the type of heating so that a homogeneous and inhomogeneous temperature distribution was present before the cooling process. On the other hand, the eigenfrequency of differently long vulcanized test specimens was determined with a laser vibrometer and compared with the cross-linking isotherms. Since the stiffness and thus the resonance frequency of the elastomer increases with the degree of crosslinking, a correlation was found. The investigations show a basic applicability of the presented methods for an inline measurement. Further investigations are necessary to prove the evidence of the presented correlations, so that a control loop for process optimization can be established.
Comparative Creep Evaluation of Polyacetal and Polyketone Resins
Failures occurred within threaded fasteners used in an outdoor industrial application. Specifically, cracking was observed within fasteners used to terminate a pipe conveying a gaseous chemical product. The parts had been installed leak free as verified through leak testing. However, failures occurred within some of the installations between four and five years, as identified by leakage of the gaseous project. A failure analysis identified that some of the fasteners had cracked through a mechanical short-term overload mechanism in which the stresses applied during installation exceeded the short-term strength of the material. Other parts, however, cracked through creep rupture, whereby the applied service stress exceeded the long-term strength of the material. In both cases, crack propagation and ultimate rupture was associated with the creep properties of the material. A material conversion was considered to increase the creep performance of the fasteners. This paper will review the testing performed to characterize and compare the creep performance of the incumbent and proposed materials.
Investigation of Influences on The Melting of Polyethylene and Polystyrene in a Co-Kneader
The co-kneader is well known for its superior mixing performance and its exact temperature control capabilities. Therefore, it is widely used in the polymer industry for the compounding of shear- and temperature-sensitive materials. In contrast to the considerable amount of scientific work that deals with investigation, modeling or simulation of the process behavior of single and twin screw extruders there are only few studies about the co-kneader. Due to increased quality requirements and the trend for cost reduction by process optimization, this is increasingly becoming a problem for plant construction and processing companies. To address this problem, experimental investigations of the melting behavior of polymer materials in the co-kneader were conducted. In order to determine the melting degree along the extruder length a special barrel was used which can be opened in axial direction. Based on the experimental results, a theoretical consideration for co-kneaders that are operated as plastification extruders is proposed. Therefore a disperse solid melting model is used. A comparison between simulated results and experimental data shows a descent agreement, when the point of melting initiation is estimated accurately.
Reproducibility Analysis of Fiber Length Measur ements During Processing With Twin Screw Extruders
The twin screw extruder is used for processing of plastics. One of the most important processing tasks is the preparation of plastics with fillers and reinforcing materials. For the processing of fibers various recommendations can be found. But in an industrial production, with the same specification and process parameters, the resulting fiber length may differ. These variations must be clearly defined and determined. While process deviations occur during compounding, measurement deviations can be detected in the fiber end length measurements. In order to evaluate the experimental investigations and to use it for model validations, the corresponding deviations must be known beforehand. Within this paper, a reproducibility study will be carried out to ensure the reliability of the experimental investigations. The aim of the work is to determine the fiber length degradation along the screw and their deviations. The investigations in this paper are showing that a producible fiber length reduction is possible.
Modeling the Optimal Cellular Structure in Superior Insulating Microcellular and Nanocellular Foams
This work developed a mathematical model for the correlation between the cellular structure and the thermal conductivity of closed-cell microcellular and nanocellular insulation foams. Because convection is negligible in such confined structures, the model includes the contributions from thermal radiation and conduction through the solid and the gas. The conduction term included the effects of gas volume fraction, fraction of solid located in struts and cell walls and the Knudsen effect in the gas. The radiation term was determined by analyzing absorbing-scattering-reemitting radiative heat transfer based on Mie’s scattering theory, interference of propagating waves and tunneling of evanescent waves. Validated by the measured thermal conductivities in the literature, the model was used to predict the thermal conductivity of polystyrene (PS) poly(methyl methacrylate) (PMMA) foams at various volume expansion ratios and cell sizes. It was found that the radiative contribution plays a crucial role in nanocellular foam because of the thinner and highly transparent cell walls and struts. The balance between conduction and radiation leads to the optimal expansion ratio and the optimal cell size at which the thermal conductivity was minimized.
Influence of Twin Screw Configuration and Processing on Ketoprofen Dissolution in Polymer Blends
The solubility and dissolution enhancement of the poorly soluble drug ketoprofen (KTO) in polymer blends prepared by hot melt extrusion was studied using two different twin screw configurations while changing extrusion processing parameters. Soluplus and Kollidon SR blends were used as solid dispersion excipients. A design of experiments with three melt temperatures, three screw rotation speeds, and three fill factors was performed. Different characterization techniques such as differential scanning calorimetry (DSC), optical and polarized light microscopy, X-ray diffraction (XRD), solid-state nuclear magnetic resonance (ss-NMR), and dissolution testing were used. The results from DSC and XRD showed an amorphous solid solution. An optimal processing condition by twin screw extrusion was found for each screw configuration achieving more than 80% drug release in 8 hours.
Numerical and Experimental Studies on Warpage of Flat Panel Packages
This paper presents a study on flat-panel warpage deflection using experimental and numerical methods. The study was done for various silicon-die densities and panel thicknesses. The package was produced by compression molding, and the warpage was measured after the molding. The numerical warpage analyses were performed using both linear analysis and geometrically nonlinear analysis techniques. Comparison of the experimental and simulation results show that the geometric nonlinear warpage analysis produces results which better match the experimental results.
Understanding Cure, Mechanical Properties of Carbon Black Composites and Immiscible Polymer Blends
Carbon black filled immiscible polymer blends are specialty materials used for a variety of applications. The present work utilizes statistical approach to understand the controlling parameters of crosslinking and resulting mechanical properties in ethylene vinyl acetate copolymer (EVA)/acrylonitrile-butadiene copolymer (NBR)/carbon black (CB) conductive polymer composites. The influence of varying composition on material properties was investigated. Statistical analysis was used to model the overall crosslinking behavior and mechanical properties of the composites. Crosslinking in these composites seemed largely dominated by radical concentrations only. Mechanical properties were modeled well by degree of crosslinking and CB loading for the ranges of composition tested.
Modeling Fully Intermeshing Co-Rotating Twin-Screw Extruder Kneading-Blocks: Part A Conveying Characteristics
Twin-screw extrusion modeling is in most cases based on analytical approaches that are build on considerable geometric simplifications. These approaches give only rough estimations of the processing behavior. More accurate predictions generally require numerical methods with less drastic simplifications. In this work, we analyzed the pressure-throughput behavior in fully-intermeshing double-flighted kneading blocks. First, we conducted a dimensional analysis based on the Buckingham Π-theorem. Second, for each staggering angle, we determined the characteristic angular position that describes the mean throughput. Based on this position, a parametric design study was carried out by varying the identified dimensionless parameters. To solve the complex flow patterns, 3D CFD simulations were conducted. For each design point we evaluated the dimensionless drag flow-rate and the dimensionless dam-up pressure. As an addition to the two established dimensionless conveying parameters A1 and A2, we propose a novel conveying parameter A3. This new parameter simultaneously enables the description of conveying and non-conveying kneading discs. Our results offer considerably deeper insight into the conveying characteristics of kneading blocks. In addition, they can serve as foundation for screw design and process modeling. For a better understanding of the process, we additionally investigated the power consumption and viscous dissipation in Part B of this publication.
Modeling Fully Intermeshing Co-Rotating Twin-Screw Extruder Kneading-Blocks: Part B Power Consumption
Modeling twin-screw extrusion is commonly based on significant geometric simplifications such as the representation of the flow domain as flat channels. Furthermore, the prediction of the conveying characteristics and power demand of kneading blocks is typically based on their approximation as conveying elements. Considering the accurate flow geometry of fully intermeshing co-rotating twin-screw extrusion kneading blocks we analyzed the power characteristics by means of three-dimensional numerical simulations for Newtonian flow. Therefor we first conducted a dimensional analysis to identify the dimensionless characteristic influencing parameters. Next, we derived novel dimensionless power parameters and then conducted a parametric design study. Our proposed power parameters are capable to simultaneously cover conveying and non-conveying screw elements. The results provide new insights in the power characteristics of kneading blocks and are fundamental for screw design, screw simulation, and scale-up. In Part A.  of this work we focused on the conveying parameters.
Spreading Coefficient: A Simple Tool for Predicting Failure in Adhesives
A thermodynamic theory was applied to predict compatibility between a completely biobased epoxy adhesive and substrate. Single lap shear strength samples were also prepared to confirm the correlation. Using this theory, equations were defined that could predict the type of failure and the failure strengths observed.
Optimizing Film Bending Stiffness and Coefficient of Friction for High Speed Converting
Thin polymer films with high Coefficient of Friction (COF) often perform poorly on packaging lines due to their tendency to buckle or elongate under stress. Film buckling, leads to inconsistent package dimensions and other flaws. Lowering the film’s COF by addition of slip agents reduces drag or unbalanced forces during converting can improve the packages’ dimensional consistency. However, since friction can never be eliminated, reducing COF offers limited utility. Improving the film’s buckling resistance by increasing bending stiffness may be a practical, complimentary strategy to resolve film buckling. A better understanding of the combined effects of film COF and bending stiffness can help manufacturers optimize multilayer films without increasing gauge or sacrificing key performance criteria. The purpose of this study was to evaluate the combined effects of bending stiffness and COF on the convert-ability of films in vertical form-fill-seal pouch (VFFS) lines. Specifically, we examined dimensional changes in VFFS pouches made using similar films with variable bending stiffness and COF values. The results suggest that films with the right balance of high bending stiffness and low COF exhibit less buckling and are less prone to tracking, bunching or slipping issues in VFFS conversions. A proposed mechanism is provided to explain how high COF and low bending can lead to unbalanced forces in the film and inconsistent dimensions in the finished package.
The Use of Diblock Carbon Nanotubes to Increase Fracture Toughness at Immiscble Blend Interfaces
An asymmetric double cantilever beam (ADCB) test was used to determine the ability of carbon nanotubes with varying chemistry along their length, i.e. diblock nanotubes, to strengthen the polystyrene/poly(methyl methacrylate) (PS/PMMA) interface. PS molecules were grafted primarily to one of the blocks to cause that block to migrate to the PS phase since otherwise both blocks would prefer to reside in PMMA. Fracture toughnesses increased monotonically with increasing diblock carbon nanotube concentration and maximum values were similar to that for block copolymer reinforced interfaces while single-chemistry nanotubes showed no reinforcing effect. However, the abrupt increase in fracture toughness with added compatibilizer indicative of a transition to crazing was not found consistent with nanotubes suppressing crazing in homopolymers. Significant aggregation was visibly present, which likely reduced the interfacial thickness toughening possible.
Scratch Behavior of Polyrotaxane-Modified Poly(methylmethacrylate)
The role of polyrotaxane (PR) on the scratch behavior of poly(methylmethacrylate) (PMMA) was investigated. PR is a necklace-like supramolecule with rings threaded onto a linear backbone chain that is capped by bulky end groups. Cyclodextrin (CD) serves as the ring structure and it can be functionalized to induce specific interactions with the hosting polymer matrix and achieve improved mechanical properties. The CD structure in PR contains polycaprolactone (PCL) grafted chains, which are partially modified with a methacrylate functional group. The effect of PR on the scratch resistance of PMMA was investigated by varying the PR concentration. The findings suggest that the methacrylate functional group in PR enhances the compatibility with PMMA, leading to an increase in tensile strength and reduction in scratch coefficient of friction, which accounts for an improvement in scratch resistance by over 100%.
Wetting Characteristics of Microstructures on Injection Molded Parts
The generation of micro-structures on plastic part surfaces has been a topic of great interest due to the potential applications in a wide range of fields such as optical, medical, and electronics. These microstructures modify the wetting properties allowing the creation of superhydrophobic surfaces. Accurate surface replication is essential to achieve consistent and repeatable wetting properties. In this work, micro-structures were generated on steel inserts using a femtosecond laser and then replicated by injection molding on polypropylene and polylactic acid. Experiments were performed for each polymer to determine the effects of mold temperature, texture orientation, and measurement location on the replicated structures’ height and the contact angle. The experimental results show that the orientation of the drop and the mold temperature have significant effects on both the contact angle and height of the micro-structures.
Optimization of Double-Lip Cooling Rings in Blown Film Extrusion Considering the Coanda-Effect
In blown film extrusion, heat dissipation is usually achieved by convection, using double-lip cooling rings. To maximize the heat dissipation, a narrow cooling air flow at the film bubble is essential. However, the cooling air flow is influenced by the so-called “Coanda-effect”, which describes the adhesion of a flowing medium to a surface. If the cooling air adheres at the cooling ring lip, this can lead to a dead zone in the flow field, which reduces the convective heat extraction and thus the mass throughput. Up to now, this effect has been almost unexplored in blown film extrusion, so that the IKV is investigating this effect for the first time in real flow experiments. The aim is to find out, whether the effect depends on the process parameters and the die lip design, so that this knowledge can be used in the future to optimize cooling rings. First investigations show a great potential for an optimization: Only by adjusting the die lip geometry higher mass throughputs are possible at equal energy inputs.
Adhesive Resin Technology for Oriented Multilayer Films
Multilayer films are widely used in flexible packaging to provide an optimum balance of performance and cost. Orientation in the semi-solid state via tenter frame, double bubble and machine direction orientation processes enhances barrier and mechanical properties and offers a means towards light weighting packaging structures. Interlayer adhesion of coextruded films, however, substantially decreases during orientation as generation of new interfacial area decreases bond density and chain segments are stressed. A heuristic model is proposed that provides insight into how changes during orientation in chain segment penetration, entanglement, orientation and density affects peel strength. Examples are provided that use these insights to design novel tie resins with improved performance.
Transparent Layered Composite for Protective Eyewear Applications
Sapphire and polycarbonate are commonly used for transparent ballistic applications. This work focuses on the application of eyewear protection with the requirement of maintaining a thin profile. In this work, the properties of the two materials are combined in layered composites with two different material thickness configurations. The lamination process of the two materials is investigated to achieve appropriate adhesion and maintain acceptable light transmission. The ballistic properties of the laminates were observed with a qualitative analysis focusing on delamination upon impact.
Optimization of Ethylene Acrylic Acid and Low Density Polyethylene Blend in Tie-Layer
Ethylene acrylic acid copolymer (EAA) is widely used as tie-layer in multilayer film structures containing aluminum foil. EAA provides adhesion between foil and rest of the film structure. It can be used in pure or blending with low density polyethylene (LDPE) ordinarily in the range from 20 to 50%. However, this common practice of blending does not always work perfectly. From time to time, a clear film becomes hazed. The adhesion can deteriorate as well. This study focuses on examining the mechanism behind high haze and poor adhesion in LDPE and EAA blends and factors for optimization. The results from this study indicate that miscibility not viscosity mismatch is the dominant factor affecting the blending of EAA and LDPE. Low acid content EAA in general is more compatible with LDPE than high acid content EAA. Processing parameters, such as rotation per minute and temperature of an extruder, can also effectively change the properties of the blend.
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