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Conference Proceedings

Draping Simulation of Thermoplastic Prepregs with Special Focus on the Non-Linear Bending Stiffness
Patrick M. Mabry, Steffen Ropers, Tim A. Osswald, Annegret Mallach, May 2015

Draping simulation tools improve virtual prototyping for Fiber Reinforced Plastics (FRP) by eliminating a costly trial and error development process. While the mechanical in-plane properties, i.e. tensional and shearing behavior, of FRP are widely studied, the out-of-plane bending is not well understood. The bending stiffness of a thermoplastic pre-preg was determined in dependency of temperature, fabric orientation and bending length, using a modified cantilever test. Simulation tools were used to validate the results. As the thermoplastic matrix and textile matrix interactions were expected to have a significant influence on the bending behavior, DMA was performed to account for viscoelastic effects during deformation.

Fiber Orientation in Injection Molded Long Carbon Fiber Thermoplastic Composites
Jin Wang, Ba Nghiep Nguyen, Raj N. Mathur, Bhisham Sharma, Michael D. Sangid, Franco Costa, Xiaoshi Jin, Charles L. Tucker, Leonard S. Fifield, May 2015

A set of edge-gated and center-gated plaques were injection molded with long carbon fiber-reinforced thermoplastic composites, and the fiber orientation was measured at different locations of the plaques. Autodesk Simulation Moldflow Insight (ASMI) software was used to simulate the injection molding of these plaques and to predict the fiber orientation, using the Anisotropic Rotary Diffusion and the Reduced Strain Closure models. The phenomenological parameters of the orientation models were carefully identified by fitting to the measured orientation data. The fiber orientation predictions show very good agreement with the experimental data.

Bismaleimide and Boron Nitride Composites: Thermal Conductivity and Dielectric Strength Characterization
Nathan Warner, Andres Garcia, Mickey Richarson, Hugo Diaz, Nandika D?Souza, Luu Nguyen, May 2015

Hexagonal boron nitride (h-BN) nano-particle composites were prepared with Bismaleimide (BMI) resin and low concentrations of filler to compare their thermal and mechanical properties. Silver was used as a filler to increase the thermal conductivity and to see the effect in the dielectric strength. Thermal conductivity values in the axial and radial direction were measured. The dielectric strength, dielectric constant, and the Tg were compared and analyzed among the different concentrations and particles sizes of the BN in the BMI resin. The thermal conductivity values increase as the concentration of the h-BN particles increase, and the axial and radial thermal conductivity gradient increases as the concentration increases due to the orientation of the particles as they become more closely packed. The Tg has remained constant among the different h-BN particle sizes. The dielectric strength shows improvement with the boron nitride particles as filler. Silver decreases the dielectric strength considerably. A Nova NanoSEM was used to precisely analyze the orientation and dispersion of the h-BN particles.

Mechanical and Thermal Properties of Coaxial Electrspun Fibers Mesh of PCL-PBAT
Syed Hussain R. Rizvi, Yoni Mercier, Thunyatorn Pukkrueapun, Nandika D?Souza, May 2015

Physical morphology, mechanical and thermal properties of potential drug delivery devices and scaffold structures were examined. PCL and PBAT were selected because of their biodegradable and biocompatible nature. Properties of electrospun single component PCL and PBAT meshes were compared with coaxial fibers of PCL as a sheath material and PBAT as core. DMA test results indicate that the stiffness of the coaxial fiber sample has increased significantly diminishing the flexibility of the mesh. DMA results also reinforced that the strength of the coaxial fibers increases many fold as compared to individual fibers spun.

Methodology for Quasi-Viscoelastic Simulation of Polymer Gears Made from Peek Using ANSYS?
Neil P. Doll, Anthony J. Verdesca, Eduardo Bastos, Tim A. Osswald, Rod Kleiss, May 2015

Beginning in June 2014, a small group of students at the Polymer Engineering Center at the University of Wisconsin-Madison collaborated with Kleiss Gears, Inc. in an effort to provide a fundamental understanding of the viscoelastic behavior of high-speed polymer gearing in heavy-duty applications. The project has the following ongoing objectives: material characterization, injection molding simulation, thermal-mechanical simulation, and experimental validation. The goal of this paper is to present the first look at a methodology for creating a robust viscoelastic material model that can be utilized by ANSYS? for precise simulation of thermal and mechanical behavior in polymer gears made from polyetheretherketone (PEEK).

Crystallization and Foaming Behavior of Polypropylene with a Crystal-Nucleating Agent
Raymond K. Chu, Lun Howe Mark, Chul. B. Park, May 2015

The manufacture of polymeric foams with high cell densities with injection molding is of great interest to industry, primarily because of the flexibility and cost-effectiveness of the technology. Nonetheless, achieving high cell density foams with foam injection molding is inherently challenging due to process constraints. In our earlier work [1], we showed that by controlling the cooling and crystallization time within the mold cavity, foams with cell densities as high as 1010 cells/cm3 were attainable. In this work, we investigated the use of a crystal-nucleating agent in controlling the crystallization behaviors of the polypropylene and studied its influence on the foaming behavior during foam injection molding.

Developing Three-Dimensional Carbon Scaffold Anodes from Polyacrylonitrile for Microbial Fuel Cells
Han-Xiong Huang, Ya-Qiong Wang, May 2015

Novel three-dimensional (3D) open-celled carbon scaffolds (CS and CS-GR) anodes were prepared by carbonizing the microcellular polyacrylonitrile (PAN) and PAN/graphite composites (PAN-GR), which were obtained by means of foaming via using supercritical carbon dioxide as physical foaming agent. Both anodes were assembled in microbial fuel cells (MFCs) based on Escherichia coli (E. coli). The improved performance for the CS anode is ascribed to remained ?C=N group resulting in considerably improved hydrophilicity and biocompatibility after carbonization and the 3D open-celled scaffold structure contributing to the substrate transfer and internal colonization of E. coli bacteria. Meanwhile, the superior performance for the CS-GR anode is mainly attributed to increased specific surface area and active reaction area resulting from the addition of graphite. This work provides an effective method to develop a 3D open-celled biocompatible CS-GR anode, which facilitates the extracellular electron transfer for high-performance MFCs that are promising for practical applications on a large scale.

Fibrinogen Protein Binding Evaluation of Eastman Tritantm Copolyesters and Other Polymers for Medical Applications
Yubiao Liu, Mechi Jackson, Mark Barbour, May 2015

Medical devices in contact with blood require engineering plastics with reduced or negligible thrombosis or blood clotting properties. Other than the blood itself and the flow rate, the material is one of the most important variables affecting blood coagulation. A relatively new family of engineering plastics is Eastman TritanTM copolyester, which offers significant advantages to the medical industry due to excellent optical clarity before and after radiation sterilization, toughness, and chemical resistance to a variety of medical disinfectants and oncology drugs. In this paper, we describe a fibrinogen ELISA testing protocol that was developed to evaluate the fibrinogen binding behavior of various commonly used plastics including Tritan copolyesters. Surface-adsorbed fibrinogen directs cell adhesion and therefore plays a crucial role in thrombosis formation. These studies illustrate that Tritan MX731 and MX711 copolyesters exhibit low fibrinogen adsorption, indicating potential for reduced thrombosis compared to other engineering plastics.

Enhanced Foaming Ability through Microstructure Control of Polymer Blends
Ali Rizvi, Chul. B. Park, May 2015

The effect of the dispersed phase morphology on the foaming ability of a blend of polyethylene (PE) and polypropylene (PP) is investigated. Two blends of PE/PP are prepared, one with the PP phase exhibiting spherical domains and the other with the PP phase exhibiting fibrillar domains. The morphological features of the PE/spherical-PP and PE/fibrillar-PP are identified using SEM. Batch foaming is conducted to show the effect of the blend morphology on the foaming ability. Measurements of the uniaxial extensional viscosity of the two types of blends are made. The crystallization kinetics is investigated using small amplitude oscillatory shear test. Changes in foaming ability are explained in terms of the differences in extensional viscosity and crystallization kinetics.

Visualization of Cell-Growth Induced Fiber Orientation in Polymer Composite Foams
Amir Ameli, Vahid Shaayegan, Chul. B. Park, May 2015

In conductive polymer composites (CPCs), the alignment of fibers play a key role in determining the functional properties such as electrical conductivity, thermal conductivity, electromagnetic interference shielding, and dielectric behavior. However, in CPC foams, the evolution of fiber alignment caused by cell growth is not well understood. In this work, the interactions between carbon fibers (CF) and growing cells were in-situ visualized in a high-pressure foam injection molding process using polystyrene (PS)/CF as a model material system. The carbon fiber content, foam processing conditions, and visualization set-up were identified in a way that the interactions between individual fibers and cells can be captured. The results clearly demonstrate that the fibers in the vicinity of cell nuclei exhibit both translational and rotational movements upon the growth of the cells and the degree of rotation is a function of the cell size, initial fiber angle, and its distance from the cell nucleus. The results of this work provide a better understanding of the mechanisms by which foaming influences the functionalities of CPC foams and gives insight into the development of new orientation models that can accommodate foaming effects.

Controlled Foaming of Polystyrene/MWCNT by Carbon Dioxide
Sai Wang, Amir Ameli, Yasamin Kazemi, Kejing Yu, Chul. B. Park, Hani Naguib, May 2015

The ability to prepare various foams with a fixed relative density or a fixed cell size opens the possibility for decoupling the effects of cell size and cell density on the properties of foams, especially electrical conductivity. In this work, the PS/MWCNT composite foams were selected as a model system and various foamed samples were prepared by one step batch process with supercritical carbon dioxide (scCO2). Processing conditions were determined to produce polystyrene (PS)/multi-walled carbon nanotube (MWCNTs) composite foams that have the same relative density with significantly different cell sizes. Different cellular structures were achieved by controlling the saturation temperature, pressure, and time. The microcellular structure and relative density of PS-MWCNT nanocomposites were then characterized. Around the relative density of 0.48, the cell size varied from 4.5 -103 ?m.

From Nano-Structured iPP Formation to Nano-Cellular iPP Foam
Mehdi Saniei, Amir Ameli, Minh Phoung Tran, Chul. B. Park, May 2015

Nanocellular foams of isotactic polypropylene (iPP) containing clarifying agent were prepared through batch foaming process with supercritical carbon dioxide (CO2). Clarifying agent, Millad NX8000, which has been introduced as a new generation of sorbitol derivatives to enhance the clarity of PP, was used to promote cell nucleation. The samples of iPP/sorbitol were prepared using twin-screw micro-compounder. Thermo-gravimetric analysis (TGA) was performed to assess the thermal degradation status of the materials during processing and characterization tests. Crystallization behavior of neat iPP and iPP/sorbitol was studied using differential scanning calorimetry and polarized optical microscopy. Cellular structure of the foams was also characterized. Depending on the foaming condition, foam structure was obtained in both micro and nano scales. Nanocellular foams with a cell density of ~1015 cells/cm3 was achieved by controlling crystallization kinetic of iPP in the presence of sorbitol. An optimum foaming temperature was found wherein the smallest cell size with highest cell density could be produced.

Uniaxial Strain Effects on the Percolatoin Threshold of Fibers in Polymer Composites: A Monte Carlo Simulation
Eunse Chang, Amir Ameli, Lun Howe Mark, Chul. B. Park, May 2015

In this research, a Monte Carlo model is built to examine the effects of compressive and tensile strains on the percolation threshold of fibers in polymer composites. Uniaxial strain was applied in the vertical direction in a system containing fibers with an aspect ratio of 10. The strain effect was modeled by introducing its corresponding alignment effect on the fibers. The critical volume fraction èc was then analyzed in both normal direction (vertical, èc?) and parallel direction (planar, èc?) to that of the cross-section plain. The results showed that the introduction of fiber alignment, caused by strain changed both the èc? and èc?, albeit with different trends. With the increase of tensile strain, èc? reached a minimum value first before starting to rise, while èc? continuously increased. On the other hand, under compression, with the increase of strain, èc? showed a minimal behavior before rise while èc? always increased. The results of this study confirm that the percolation threshold in a particular direction of interest can be decreased via a proper choice of applied strain.

Surface Quality of Parts Manufactured Using Selective Laser Sintering
Sean A. Petzold, Jonathan Smet, Tim A. Osswald, May 2015

Surface quality remains one of the biggest problems when manufacturing products using selective laser sintering (SLS). Several experiments were performed using different SLS input variables in order to manufacture samples with different surface characteristics. The effect of virgin or recycled powder, the laser power utilized, and the roller speed were studied and related to surface defects. An Alicona metrology system, with a 4th axis for rotating and imaging tools system was utilized to analyze samples. The three main quantities investigated were average surface roughness, root mean square roughness and ratio of areas. Bearing area curves were also examined.

A Fracture Mechancis Approach to Service Life Prediction of Hdpe Fusion Joints in Nuclear Applications
Prabhat Krishnaswamy, May 2015

Limiting failure mode for long term performance of High Density Polyethylene (HDPE) pressure piping is slow crack growth (SCG), which is governed by the sustained stress levels (pressure and axial loads), and increases exponentially with elevated temperatures. Preliminary findings indicated the much lower resistance to SCG exhibited by HDPE butt-fusion pipe joints when compared to the parent pipe material. The integrity of HDPE pipe joints and the critical flaw size evaluation has now become a focus for the nuclear industry, regulators, and the plastic pipe industry. The ASME Boiler and Pressure Vessel Code Committee Sections III, IX, and XI address the use of HDPE piping in nuclear safety related applications. This current study is a summary of the findings till date on the crack driving force (Stress Intensity Factor), material fracture resistance (SCG tests on butt-fusion pipe joint materials), and service life prediction models for critical flaw size determination.
see attached

Pitfalls of MFI Targeting in the Specification of Golf Ball Thermoplastic Polyurethane Cover Layers
Shane R. Parnell, May 2015

Injection moldable thermoplastic polyurethanes (TPUs) have been used in golf ball cover layers since the 1980s and can provide an attractive combination of formulation flexibility, performance, ease of processing, and overall lower cost when compared to cast thermoset polyurethane and polyurethane-urea systems. In developing raw material specifications for TPU and in their polymerization at the material supplier, melt flow index (MFI) is often used as a means to target certain processing and property requirements. However, using MFI as the only metric for quantifying a given TPU formulation can lead to problems as it does not capture polymerization and thermal history dependent structural variations inherent to these materials. In this study, final golf ball performance attributes, mechanical properties, thermal properties, dynamic mechanical properties, and dynamic rheological properties of two batches of TPU with identical composition and MFI were compared and contrasted. The results will be used to illustrate why TPU copolymer segmental structure and both temperature and time dependent morphology are important in the processing characteristics and properties of these versatile materials.

Isothermal Crystallization Behavior of Poly(Lactic Acid)/Cellulose Nanofiber Composites with Presence of CO2
WeiDan Ding, Raymond K. Chu, Chul. B. Park, Mohini Sain, May 2015

The isothermal melt crystallization behavior of poly(lactic acid) (PLA)/cellulose nanofiber (CNF) at atmospheric pressure and two CO2 pressures was investigated using regular and high-pressure differential scanning calorimeters (DSC). The DSC analysis and polarized optical microscope (POM) result indicated that CNFs acted as crystal nucleating agents and accelerated the crystallization kinetics by providing more nuclei and decreasing the crystallization half-time. It was found that the crystallization kinetics of PLA materials was changed depending on the crystallization temperature, CNF content, and CO2 pressure. During isothermal process, the crystallization kinetic constant, k, increased with temperature up to a critical isothermal temperature before decreased; increasing CO2 pressure accelerated the crystallization kinetics of PLA at temperatures below 110 øC, but depressed at higher temperatures. The highest crystallinity was achieved at 15 bar.

Combinatorial Effects of Kneading Elements on Mixing in Twin-Screw Compounding
Graeme M. Fukuda, Ben Dryer, Jake Webb, David I. Bigio, Mark D. Wetzel, Paul Andersen, May 2015

Modularity in the design of screw configurations is one of the most advantageous characteristics in twin-screw extrusion. In the compounding of polymers and solid additives, various mixing section geometries are used to distribute and disperse the minor phase within the polymer matrix. Thus, quantitative determination of the mixing efficiency of a particular screw configuration can greatly improve final product quality. Kneading blocks are the standard screw elements used to perform the mixing operation. This paper will discuss the mixing performance of various kneading blocks with regards to paddle size, mixing section length, and positioning. Mixing will be characterized through a design of experiment approach and the evaluation of the residence stress distribution for a range of operating conditions.

Injection Molding of Nano-Features ? A Study on Filling and Birefringence
Srini Vaddiraju, Nikhil Vasudeo, John Cadotte, Aravind Rammohan, May 2015

The ability of the polymer melt to enter into the micro- or nano-structures is a crucial factor for successful molding operations and their final usability. When molding a rectangular plate with nano-features on top of it, it was observed that the nano-features are filled completely, away from the fan gate and only partially filled near the gate. A fundamental understanding based hypothesis driven approach helps to understand and solve the non-uniform filling behavior and leverage existing commercial modeling tools effectively. Based on the hypothesis, recommendations were made for further experimental studies, which showed a significant improvement in the filling of the nano-features completely throughout the part. Further studies focused on reducing the non-uniform birefringence by optimizing the gate design, using Moldflow? and Abaqus?.

Effect of Thin Walling and Foaming on TPO Part Performance
Jason R. Fincher, May 2015

Two prominent strategies for decreasing injection molded part weight are thin walling of solid parts and foaming parts via supercritical fluids or chemical blowing agents. These strategies not only affect part weight but also mechanical performance. Advanced Composites has evaluated the effect of both of these strategies on part performance in a laboratory plaque study. Part density and weight were measured along with tensile, flexural, and notched impact properties. In the case of wall thickness reduction, the decrease in stiffness was more substantial than the reduction in weight on a percentage basis. Injection foaming resulted in a greater percentage of impact reduction than weight reduction but demonstrated advantages in flexural stiffness. These findings have ramifications for both part design and material selection.

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