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Engineering Properties and Structure
Scratch & Fracture Behavior Of Talc-Reinforced Polypropylene
Thermoplastic polyolefins (TPOs) have been widely utilized in a variety of automotive applications. Most importantly, the TPOs used in interior and exterior parts in automotive applications require aesthetics and good mechanical properties simultaneously. Among many of the inorganic fillers, talc is an inexpensive and natural mineral, which has the platelet structure with individual layers holding together by week Vander Waals forces. This distinct layer structure can be delaminated at low shear forces to easily disperse in TPOs. Additionally, the talc particle size can be manipulated by the various micronizing processes. In this research, talc-reinforced polypropylene (PP) systems as a set of model systems have been chosen to investigate how the particle size and surface treatment of talc influence the TPO fundamental scratch and fracture behaviors.
The Toughening Of Highly Crosslinked Epoxy Networks Using Core-Shell Rubber Particles
This work explores the effect of core shell rubber (CSR) addition on the resulting properties of a highly crosslinked bi-component epoxy resin blend. The effects of network structure and topology are explored and related to the efficacy of CSR as a toughener for rigid, high-Tg polymer networks. A combination of thermal, spectral, and mechanical testing shows that excellent toughness enhancement can indeed still be achieved, despite a modest reduction in flexural properties for a high glass transition temperature (~259°C) network.
Fem Modeling On Scratch Behavior Of Micro-Patterned Polymer Surfaces
Polymers are inherently scratch sensitive due to their soft nature. Utilizing patterned surfaces while retaining transparency is a viable strategy to achieve better scratch performance. In this paper, we model the scratch behavior of micro-patterned surfaces using FEM simulation by employing a powerful coupled Eulerian-Lagrangian approach. The effect of two different pattern types on scratch behavior is studied and validated with available experimental results. Results suggest the significance of patterned surface topology in improving scratch performance.
Thermal & Rheological Characterization Of Two High Density Polyethylene Grades
Presently, polymers such as high density polyethylene(HDPE) are utilized for an extensive array of applications because of their low weight, economical production, and exceptional physical and chemical properties. Thermal analysis and rheological measurements are the ideal techniques for characterizing the material properties of polymers. This paper employs thermo-gravimetric analysis (TGA), differential scanning calorimetry (DSC), and capillary rheometry to collate the contrasting nature of two HDPE resins. These resins will be referred to as HDPE A and HDPE C and are similar to two resins (Sample A and Sample C) included in a previous publication  that focused on blow molding parison sag and swell. TGA was used to investigate the thermal stability of these polymeric materials, as they were ultimately decomposed inside a furnace. DSC was conducted to examine the thermal transition behaviors of the polymers. Capillary rheometry was run to construct shear viscosity and extrudate swell versus shear rate data through single and twin bore configurations under varying temperatures. These measurements were conducted under testing conditions that are representative of industrial processes, such as extrusion blow molding. HDPE C was found to exhibit greater extrudate swell than HDPE A, as measured by capillary rheology measurements, and these data correspond to the earlier published results that Sample C exhibited greater parison diameter, thickness, and weight swell than Sample A as measured with a lab scale extruder.
Effect Of Plasticizer Content In EPDM On Ex-Situ Wear Test After High Pressure Hydrogen Exposure
In high pressure hydrogen environment, elastomeric seals undergo degradation of mechanical properties and wear problems. Especially, wear of elastomeric seals causes failure of sealing system. Therefore, developing the material with good mechanical properties and wear resistance is important. In this study, five ethylenepropylene-diene-monomer (EPDM) with different content of plasticizer were prepared to investigate the effect of plasticizer on their tribological properties after the specimens were exposed to high pressure hydrogen.
Stress Corrosion Crack Growth Of High Density Polyethylene With Cracked Round Bar Specimen In Chlorine Medium
In this study, the stress corrosion crack (SCC) growth model for the cracked round bar (CRB) specimen was developed. The axisymmetric crack layer (CL) theory for simulating the slow crack growth (SCG) behavior of CRB specimen was modified to consider the chemical degradation due to diffused aggressive environment. The diffusion of oxidative fluid into the process zone (PZ) in radial direction is considered. Also, the chemical degradation kinetics of PZ materials due to the oxidation were modeled. The proposed model was shown that the discontinuous SCG behavior and the deteriorative effect from the chemicals were successfully simulated.
Deformation Mechanisms Of Toughened Poly(Lactic Acid) Using Novel Additives
Poly(lactic acid) (PLA) is certified biodegradable under specific composting conditions, but its inherent brittleness limits usefulness in commercial applications. In this study, novel additives were supplied by TRuCapSol for twin-screw melt compounding and injection molding with general purpose PLA resin. These additives were received in powder form and investigated for their ability to improve the tensile toughness. We compared our blends to several commercially available toughened PLA blends. The inherent micro-deformations of PLA were amplified by the novel additive and resulted in improved ductility. Therefore, the potential for the development of blends that enhances the toughness and increase the rate of biodegradation of PLA has been demonstrated.
In-Depth Rheological Study Of Acrylic Processing Aids For Rigid Pvc Applications
Acrylic processing aids are used widely in rigid Polyvinyl Chloride (PVC) applications. Key functions of processing aids in terms of processing and performance are discussed in the paper. Effect of molecular weight of acrylic processing aids on their functions are studied. Additionally, effect of processing conditions, such as temperature and shear on fusion characteristics of PVC formulations, are investigated. Shear rate in the processing was varied by means of rotor speed in torque rheometer. Processing aids of wide molecular weight range are evaluated in the study. It was observed that relatively lower molecular weight processing aids have different response to change in shear and temperature than higher molecular weight processing aids. Depending upon fusion conditions PVC formulations can yield either single or double fusion peak. Generally, it was considered that ultra-high molecular weight processing aids yield double fusion peak, however, it was demonstrated in the studies that it is not true. Fusion conditions, temperature, and shear are the main driving forces of fusion dynamics, resulting in either single of double fusion peak. Melt viscosity and shear thinning properties are also examined. Relatively lower molecular weight processing aids showed higher shear thinning behavior.
Reheat Injection Stretch Blow Molded Bottles Of High-Density Polyethylene Blended With Cyclc Olefin Copolymer To Improve Processing, Properties And Sustainability
Cyclic olefin copolymers (COC) provide manufacturers and converters with an opportunity to create thin, stiff, high performance polyolefin packaging products. COC provides an unexpected, but essential benefit that enables the manufacture of high-density polyethylene (HDPE) containers by reheat injection stretch blow molding. COC has good dimensional stability and excellent heat resistance, minimizes distortion of PE exposed to thermal and mechanical stresses.
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.
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.
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