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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Engineering Properties and Structure
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.
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.
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.
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.
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.
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.
Superhydrophobic Encapsulants for FHE Devices
Flexible Hybrid Electronics (FHE) offer benefits for a wide range of applications, such as healthcare wearables, smart layer-based integrated sensor networks, soft robotics, and digital microcontroller circuits. It is critical to developing flexible and stretchable encapsulants for FHE devices to protect them from environmental conditions. Encapsulants for advanced FHE devices require innovative materials and processes to ensure the microchips' physical/chemical protection without compromising the stretch or flex characteristics. Consequently, this work is focused on developing a superhydrophobic (SH) coating that can be spray-coated on FHE device for encapsulation. The SH coating is based on commercial conformal acrylic resin with alkyl treated SiO2 nanoparticles that provide both the roughness and hydrophobic chemistry to be applied to alumina and treated polyimide. The resulted coatings possess low surface energy due to the formation of a micro/nano tailored hierarchical structure and hydrophobic moieties. The study investigates the durability of the superhydrophobic coatings using the Peel Test, Flexibility Test, Scratch Test, and Hardness Test on the two substrates. Experimental results indicated that the mechanical durability was improved when applying two coating layers with a mixing time of 1 hour first and then ¬Ω hour withstanding more than 8 peels. Furthermore, the aluminum and polyimide substrates' Scratching indicates that the coating peels off completely with Àú0.5 [N] andÀú4 [N], respectively. The Pencil hardness test results suggest that the polyimide substrate starts to fail at '5H' hardness, and the Alumina coating starts to fail at ‚ÄòH‚Äô hardness. The final coatings show good durability overall and long shelflife stability.
Improving the Hydrophobicity of Polymers through Surface Texturing
Introduction of surface textures has long been used to improve the hydrophobicity of solid materials. This study focusses on understanding the effects of various micro-texture geometries on the hydrophobicity of textured polymer surfaces. Square pillar, cylindrical, hemispherical and conical surface features, both protrusion and cavity, are considered in this study for two polymers. Employing the well-known models, the study shows that introducing textures on polymer surfaces generally increases the contact angle and, therefore, improves the hydrophobicity of polymers. The effect of surface texture on hydrophobicity significantly varies with texture geometry and dimension. The study provides useful guidelines for improving hydrophobicity of polymers by introducing textures on the surface.
Solid-State Shear Pulverization of Ultra-High Molecular Weight Polyethylene for Mechanical Recycling
Solid-State Sheer Pulverization (SSSP) is acontinuous processing technique in which low-temperature application of shear and compressive forces impart changes in structure and properties to different thermoplastics. In this paper, SSSP is applied to post-industrial ultra-high molecularweight polyethylene (UHMWPE) materials for a technical feasibility study of mechanical recycling of high-molecular weight, high-melt viscosity polymers. The SSSP process is able to effectively reduce the particle size while also mechanochemically enhance the crystallization behavior of the polymer.
Tensile Specimen Preparation Method Impacting Failure Behavior
Sample preparation for polymer testing is an overlooked portion of the test plan and execution. Thermoplastics and thermoset materials offer multiple methods to prepare samples: injection molding, CNC machining, waterjet cutting, die-cutting, and laser cutting are all used often. We test samples of a polycarbonate (PC) material in uniaxial tension and compare results for injection molded, machined, waterjet cut, and diecut samples. All but the diecut samples showed the same stress vs. strain response, though the waterjet samples failed at a significantly lower strain. The die-cut samples showed significant damage on the edge of the specimens, and had a lower yield stress. Careful selection of specimen preparation methods is important to a well-designed test plan.
Characterization of Impact Toughness of Thin Plastic Films
We investigate the role of film/dart friction on the results of dart impact test used to characterize toughness of plastic films against impact (biaxial loading) at a high speed (~3 m/s). Utilizing an instrumented dart impact (IDI) capability, impact tests were conducted for plastic films exhibiting a wide range of dart impact values under standard conditions. Steel and PTFE dart heads were used with the former representing a high-friction interaction and the latter a low-friction one at the film/dart interface. Our results indicate that differentiation between films on the basis of their measured impact toughness may change dramatically depending on friction. Load-displacement curves obtained from the IDI tests, a simplistic analysis of forces, failed samples, finite element simulations, and high-speed tensile tests help us rationalize our findings about the effect of friction on measured impact toughness of films.
Durability of Cellulose Nanomaterials under Industry Relevant Shear Stresses
The effects of high-shear flow on cellulose nanocrystals (CNCs) were studied to characterize potential impacts of industrial processing on these materials. A microcapillary rheometer was employed to study the rheological characteristics ofaqueous CNC suspensions at concentrations ranging from 1.5 wt% to 12.1 wt%.Increased cellulose content in the suspensions produced increased viscosities. A Sisko model was successfully fit to the data which display high shear Newtonian plateaus. Shear rate sweeps at these concentrations failed tofullyreduce to a master curve. Furthermore, repeated testing of the same sample volume at nearly 800000 s-1led to a permanent decrease in viscosityfor all samples.Atomic Force Microscopy (AFM) probed CNC morphology to observe any changes in the CNC dimensions which may have contributed to this phenomenon. AFM resultsindicate significant decreases in both height and length of the CNCsafter repeated testing at high shear rates.
Effect of Coating Anisotropy on Scratch Behavior
Three-dimensional finite element method (FEM) modeling has been carried out in this study to investigatethe scratch-induced surface deformation and damage mechanisms in composite coatings applied on polymer substrate. Composite coating systems with anisotropic properties and variation in thicknessare considered in the numerical framework to study the influence of coating anisotropy and layer thickness on scratch behavior. The results show that coating anisotropysignificantly affectsthe scratch resistance of coating systems. Implications of the numerical findings on scratch resistance of coating systems are discussed.
Effect of Long-Chain Branching on Scratch Behavior of Polypropylene
The effect of long-chain branching (LCB) on scratch behavior of polypropylene (PP) was investigated. In this study, the model LCB PP samples were modified viareactive extrusion process by incorporating increasing amount of polyfunctional monomerin PP. Small amplitude oscillatory shear results show that LCB level in PP increases with increasing polyfunctional monomer introduced. Moreover, increasing LCB content slightly improves the tensile strength of PP. ASTM D7027/ISO19252 standard scratch test was employed to determine the scratch resistance of the model LCB PPs. It is found that incorporation of LCB delays the onset of fish-scale formation.
Fabrication of Multifunctional PVDF/MWCNT Nanofibrous Membrane via Electrospinning for Membrane Bioreactors
Nanofibrous membranes in membrane technology applications for water and wastewater treatment have gained interests among researchers because of their high mechanical and chemical resistances. In this study, Polyvinylidene fluoride (PVDF) nanofibrous membranes were prepared by electrospinning method with 20 wt% PVDF solution. The effects of processing parameters including flow rate, applied voltage, tip-to-collector distance and presence of multiwalled carbon nanotube (MWCNT) on fibers morphology were observed using scanning electron microscopy. The changes of fiber diameters, pore size, and membrane porosity were investigated to investigate the characteristics of nanofibers as a function of processing parameters. The modified membranes with MWCNT were characterized with contact angle analyses and water filtration tests to evaluate the performance of the membranes.
Optical 3D Metrology the Ultimate Biomechanics Tool
3D Digital Image Correlation (DIC) provides the ability to measure non-contact 3D coordinates, displacements and strains of materials and structures. Although widely accepted in mechanical engineering and materials engineering, this tool as yet to prove its capability within the biomechanics industry with soft tissues, bones and most medical-specific materials. Known for its unique capability to be used for rapid full-field measurements from material characterization to full component testing, providing the equivalent of the results of over 10,000 contiguous strain gauges or displacement sensors, this technique is now recognized and certified (NIST, Boeing...) as equivalent to standard mechanical testing tools in the aerospace and automotive industries. 3D DIC is used across industries for improving the quality and the accuracy of the data collected to best understand mechanical behaviors of components or validate FEA models. This work focuses on the integration of the DIC technology with load frame such as Instron, MTS and Zwick for simple coupon testing of soft tissues, implants and prostheses. It was shown that DIC could in fact provide a more flexible measurement platform with capabilities for any coupon size, very small to large strains with a single instrument as well as multi-axial data in every direction for each and every one of the biomechanics applications evaluated.
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