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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Modeling Flexible Package/Granular Material Interation through Combination of Discrete Element Method (DEM) and Finite Element Method (FEM)
A variety of applications use flexible film for shipping solid granular materials. The film/packages must have sufficient toughness and/or strength to endure impact during shipping and handling. Package performance is commonly evaluated using a drop test typically from a certain height specified by ASTM and/or ISTA standards. One limitation of the drop test is that it can only qualitatively determine whether a package will survive. In order to better understand impact type loading which can lead to package failure, more quantitative information such as stresses/strains developed during the drop tests is required. We have developed a model to simulate drop tests of a flexible package containing solid particles. The model utilized some of the capabilities available in Abaqus software package, such as Abaqus/Explicit, Finite Element Method (FEM), and Discrete Element Method (DEM) to capture the interaction between the flexible package and a large amount of solid particles inside. Preliminary results compare well with drop tests carried out in our laboratory.
Flax Fiber-Polyamide 6 Composites via Solid-State Shear Pulverization: Expanding the Portfolio of Natural Fiber-Reinforced Thermoplastics
A chilled twin-screw extruder-based processing technique called solid-state shear pulverization (SSSP) explores an opportunity to create a new set of composites made from temperature-sensitive natural fibers and high-temperature melting thermoplastics. Model polyamide 6/ flax fiber composites produced with SSSP are compared to those made by conventional compounding methods. Mechanical property tests indicate that SSSP can defibrillate the flax into elementary fibers, which have superior specific mechanical properties, while retaining the fiber lengths above the critical values. SSSP can produce PA6/flax composites on an industrial scale without excessively degrading or damaging fibers.
Tecobax™ – A New Class of Non-softening Thermoplastic Polyurethanes for Medical Applications
Thermoplastic polyurethanes (TPUs) are a class of thermoplastic elastomers (TPEs) that are used in a variety of medical applications. Their characteristics including low temperature flexibility, excellent abrasion resistance, high tensile strength, good processing characteristics, and biocompatibility make them particularly attractive for medical applications by the device design engineers. In general current medical grade TPUs have the unique property of undergoing a reduction in flex modulus when placed in the body. This characteristic is referred to as “softening.” A new class of TPUs has been developed that retains many of the characteristics found attractive by designers but now offers the non-softening characteristic, broadening the design space for TPUs in medical devices. A non-softening TPU may be an attractive material for use in percutaneous interventional catheters where retention of stiffness is desired to enhance trackability and torqueability. Three grades of non-softening TPUs, covering low to mid durometers have been introduced into the market: Tecobax™ 25D, 40D, and 45D. The performance characteristics of these TPUs were measured and compared to other softening TPUs as well as non-softening TPEs. These materials maintain many of the typical TPU characteristics which make them widely used. For example, the 25D, 40D and 45D durometers have excellent tensile strengths and abrasion resistance. Softening characteristics were tested by comparing flexural modulus values at ambient conditions (22°C, 50% RH) to body conditions (100% RH, 37°C). The degree to which these new materials soften, especially in the harder grades, is significantly less than other TPUs but is comparable to non-softening TPEs. Torqueability at body conditions is also comparable to common non-softening TPEs. These materials also offer other unique characteristics which are of particular interest to the medical device community. For example, these materials have a high Vicat softening temperature; the 40D and 45D are above 100°C, resulting in compatibility with steam sterilization. In addition, these materials produce excellent quality extrusion components using standard extrusion equipment. Other unique characteristics and potential medical applications will be discussed.
Direct Particle Level Simulation Coupled with the Folgar-Tucker Rsc Model to Predict Fiber Orientation in Injection Molding of Long Glass Fiber Reinforced Thermoplastics
Polymer Engineering Center at the University of Wisconsin-Madison has developed a particle level simulation model to predict fiber motion at industry relevant fiber concentrations. The model provides a solution to study fiber alignment for long and short fiber-reinforced thermoplastics at the particle level by accounting for all relevant effects, including fiber-fiber interactions. This simulation couples with the Reduced Strain Closure (RSC) Folgar-Tucker model to describe the orientation evolution and interaction coefficients for fibers placed in a simple shear flow. In this work, the process is outlined and the results are compared to existing models for predicting interaction coefficients. Results are then compared to those obtained through injection molding experiments of long glass fiber-reinforced polypropylene. A new relationship between fiber aspect ratio and volume fraction will then be proposed.
Crystallographic Matching Effect in Self-Induced Nanohybrid Shish-Kebab Structure of Poly(E-Caprolactone)
The shish-kebab structure has been investigated for many years and it has been widely applied in many field, while the formation mechanism is attracting researcher. In this study, different electrospun poly(e-caprolactone) (PCL) fibers were applied as shish material in the self-induced crystallization and two different self-induced crystal structure were obtained. By comparing with the surface crystalline structure, it seems that the self-induced nanohybrid shish-kebab (SINSK) structure follows a crystallographic matching mechanism in the crystallization process. The PCL fibers with different internal crystalline structure led to different induced crystal lamellae morphology. This study might helps people to screen the materials for formation of SINSK structure.
Study of Residence Time Distribution for a Blown Film Line Using Inline UV-VIS Spectroscopy and Optical Imaging on a Film Bubble
Residence time distribution (RTD) in an extruder has been studied extensively, but not many experiments have focused on the RTD in an extrusion based production process, such as a blown film line. Two inline methods on the film bubble, i.e., UV-Vis spectroscopy and optical imaging, were verified to measure the RTD in a lab scale blown film line using copper phthalocyanine tracer pulses. Both methods measured similar RTD results and can be used for research and troubleshooting of the blown film line. A full factorial design of experiments was also conducted to study the effects of rate, blow up ratio, tracer type, and tracer concentration on the measured RTD by UV-vis spectroscopy. The results showed that rate was the strongest factor for the RTD in the blown film line (as expected), blow up ratio had no effect, and tracer type and tracer concentration has some minor effects.
Relationship of Shear History, Morphology – Microstructure and Mechanical Properties of Micro Injection Molded Parts
The relationship of shear history, morphology-microstructure and mechanical properties of the micro-scale parts was investigated based on the polypropylene parts with thickness 0.2mm and 0.5mm molded under varied injection speed. Shear rate was analyzed using Moldflow. 0.5 mm parts showed skin-core structure in the thickness direction with imperfect shish-kebab structure appeared in the transition layer between skin layer and core layer, however, the transition layer of 0.2 mm parts shows columnar crystal. The whole shear level in shear history increased with injection speed increasing for all the parts with two thicknesses. The ratio of skin layer of 0.5 mm parts decreased as the injection speed increased, which result in the decreasing of yield stress, modulus, breaking strength and elongation at break. The ratio of skin layer of 0.2 mm parts increased with injection speed increasing, and results in increasing of yield stress, modulus and breaking strength, and decreasing of elongation at break.
Simulation of Cell Growth in High-Pressure Foam Injection Molding
In this work, the prediction of final cell size of high-pressure foam injection molded parts has been attempted. An in-situ visualization technique was used to capture real-time cell growth data from high-pressure foam injection molding experiments conducted with PS and CO2. The simulated cell growth profile was compared with experimental measurements. For the PS/CO2 system, quantitative agreement (over 80%) between predicted and measured growth profile were achieved. With the validated simulation, the effect of cooling history on final cell size and cell size distribution was investigated. It is shown that in high-pressure foam injection during which all the gate nucleated cells are dissolved, final morphology is characterized by having large cells in the center and smaller cells near the skin.
Development of High Density Syntactic TPU Foam by Incorporation of Expancel through Extrusion
Extrusion was used to produce thermoplastic polyurethane foams using Expancel microspheres as a blowing agent. Few studies have looked into syntactic thermoplastic polyurethane foams by extrusion, making it a topic worth exploring. The density of the foams is reported in terms of cell size and cell density using 0.05wt%, 0.1wt%, 0.3wt%, 0.4wt%, 0.5wt%, 0.8wt%, and 1wt% of Expancel. The resulting foams were characterized mechanically in terms of tensile modulus. In general, specific gravity and tensile modulus decrease with increasing addition of foaming agent.
Selective Laser Sintering Processing Behavior of Polyamide Powders
Selective laser sintering (SLS) is a rapid developing additive manufacturing process. It produces parts by selectively sintering powder together in a layer-by-layer mode. SLS processing behavior were investigated with a desktop printer for commercial polyamide/carbon black (PA/CB) powders and a fabricated PA12/silica nanocomposite powder. By systematically increasing thermal and laser energy received by powder, low laser power (2 W) was sufficient for successfully sintering PA11/CB, PA12/CB and PA12/silica powders. PA11/CB exhibited a wider processing window for part bed temperature than PA12/CB. Printed PA11/CB parts yielded well and elongated up to 65%, while PA12/CB parts broke before yielding. Both were of ultimate tensile strength above 50 MPa. An in-house prepared PA12/silica nanocomposite powder tolerated higher bed temperature than powder without silica in it. Incorporation of silica nanoparticles into SLS powder brought comparable tensile strength and elongation at break to parts printed without silica in the powder while tensile modulus was noticeably increased. Finally, DSC is a useful tool to evaluate degree of powder melting during SLS.
New Developments in Polymers for Medical Device Housings
Trinseo LLC has long served the medical device market with a wide range of PC, PC/ABS and ABS grades, including glass-filled and ignition-resistant (IR) materials. In order to continue to meet the more demanding performance requirements for engineering plastics in medical device housings, Trinseo has developed a number of new PC compounds (HB and V-0) that can tolerate multiple cleanings using aggressive disinfectants in both hospital and home environments. This chemical resistance requirement for equipment housings is due to the necessity of reducing the incidence of hospital acquired infections (HAI’s) that are the cause of billions of dollars in health care costs and many thousands of deaths annually. We will review these new chemical resistant materials, discuss the mechanism of how they work, and discuss their performance attributes and breadth of applications that they are suited for. These grades exhibit a superior combination of toughness and easy processing, excellent color stability as well as excellent durability.
Numerical Simulation of Discontinuous Slow Crack Growth of Semi-Elliptical Surface Crack in Polyethylene Based on Crack Layer Theory
For the structural application of engineering thermoplastics, the knowledge of failure modes depending on their service conditions is essential. The most prevalent failure mode is brittle fracture followed by the slow crack growth (SCG) initiated by surface flaws. In that the general geometry of the surface flaws is semi-elliptical, it is vital to investigate the SCG aspects from such kind of shape. The simple strategy which has been employed to predict the crack growth aspect is an application of conventional law, Paris-Erdogan relationship. The approach is regarded as quite simple since only stress intensity factor (SIF) is needed for a crack driving force term. However, through this empirical relationship, the SCG in engineering thermoplastics cannot be properly modeled. For example, in case of the high-density polyethylene (HDPE), frequently used for water transportation pipelines, the crack usually propagates discontinuously. It arises from the existence of a significant damaged zone in front of the main crack tip, which is normally observed in engineering thermoplastics. Thus, adopting one linear elastic fracture mechanics (LEFM) parameter may not reflect the severe damage zone. To handle this feature properly, a theoretical approach with a reflection of such energy dissipation is necessary. In this study, the crack layer (CL) theory was employed to simulate the discontinuous SCG of semi-elliptical surface crack in HDPE plate with finite thickness. The existing 1-dimensional CL theory was expanded to the semi-elliptical crack growth.
Nanocomposites from Lignin-Containing Cellulose Nanocrystals and Poly(Lactic Acid)
Utilizing lignin-containing cellulose nanocrystals (HLCNCs) as reinforcing agents to poly(lactic acid) (PLA) for nanocomposites was studied for the first time. The PLA/HLCNCs nanocomposites were prepared by extrusion and injection molding. The freeze-dried HLCNCs showed micron scale agglomerates. As indicated by the water contact angle measurements, the HLCNCs were more hydrophobic than dealkaline lignin and traditional, lignin-free CNCs derived from high cellulose content wood pulp. Thermogravimetric analysis (TGA) showed that the HLCNCs started to degrade at about 300°C. The thermal stability of nanocomposites was slightly lower than neat PLA. The Young’s modulus of nanocomposites containing 1%, 2% and 5% CNCs was improved by 21.0%, 18.4% and 17.7%, respectively, while the strain at break was improved by 73.2%, 63.4%, and 54.9% compared to neat PLA. The nanocomposites (PLA/2%HLCNC) exhibited increased microductility and plastic deformation over neat PLA during tensile test. No statistically significant changes in the tensile strength were found with HLCNC addition. The results provide some practical and fundamental insight of PLA/HLCNCs nanocomposites to be used for flexible packaging films. Future work to improve the dispersion of HLCNCs in the PLA matrix as well as in the CNC drying approach is suggested.
Polyhedral Oligomeric Silesquioxane Based Flame Retardant for Acrylic
With glass being heavy, expensive, and fairly brittle there is a market for flame-retardant acrylic (PMMA). Acrylic has optimal transparency, mechanical properties, and cost of production; therefore, adding flame retardant capabilities would be valuable for glass replacement applications. Blends of monomer and polymer PMMA, a unique nanostructured chemical Polyhedral Oligomeric Silesquioxane (POSS), and 9,10-Dihydro-9-oxa-10-phosphaphenanthrene 10-Oxide (DOPO) were prepared to obtain transparent flame retardant acrylic. The results show that the synergistic additives had significant effect on the flame retardancy of the acrylic, with minor effect on optical and mechanical properties.
The Rheology of Concentrated Slurries: Experimental Evaluation and the Effects on Polymer Processing
Highly filled polymer compounds can present processing challenges, including high screw shaft torque, energy consumption, die pressure and melt temperature rise. Previous theoretical development and experimental evaluations of highly filled polymer melts showed that the rheology can be described with a percolation model [1-4]. This paper re-evaluates a batch mixer characterization method used to measure the effects of filler concentration on melt processing. The experimental results are compared with capillary rheometer measurements using several low-density polyethylene resins, calcium carbonate and titanium dioxide. The theoretical treatment of the rheology as a particulate percolating system with power-law behavior is used to analyze rheometer and batch mixer data. The effects of resin molecular weight, filler type and size on rheology and melt processing are described.
Direct Measurement of Thermal Conductivity Components in Rigid Foams
In order to maintain desired properties of insulating products, while also complying with ever-increasing regulatory pressure on blowing agents, emphasis of academic and private sector foams research has shifted to minimizing the radiative and solid conduction components of heat transfer in rigid closed-cell foams. Although methods and equipment for measuring total thermal conductivity of low density, insulating rigid polymeric foams are well established , and there are theoretical models [4 - 6] for estimating individual contribution of each heat transfer mode, experimental methods for direct measurement of the latter are lacking. In this paper, we offer a method for measurement of individual heat transfer modes (conductivity through solid, conductivity through gas, and radiative transfer) in rigid, low density polymeric foams by employing measurements in ambient atmosphere and in vacuum, as well as specific specimen preparation.
Thermal Ageing Performance of Polyolefins under Different Temperatures
Heat stability of polyolefin materials is of great interest as the need for long lifetimes is expected for certain applications. Accelerated tests are often used where materials are tested under elevated temperatures, in which unrealistic degradation may occur. This paper aims to demonstrate the importance of choosing adequate temperatures for accelerated ageing test. Also, a nondestructive surface chemistry tracking method is employed to provide insight into degradation as a fast and convenient alternative to mechanical testing. A comparison is made between the two tracking metric results under different temperatures, which revealed the importance of selecting an adequate ageing temperature for comparing materials with different melting temperatures. Above the polymer melting temperature the decrease in crystallinity allows more oxygen to diffuse into the polymer and may cause unrealistic failure, resulting in invalid comparisons under high testing temperatures.
Influence of Water Exposure on Scratch-Induced Deformation in Polyurethane Elastomers
The scratch performance of a series of cast polyurethane elastomers (CPU) upon exposure to water is investigated. Four different kinds of CPU were chosen and their scratch performances were compared in dry and water-saturated conditions. The CPU model systems were synthesized containing the same isocyanate and chain extender, 4,4'-methylene diphenyl diisocyanate (MDI) and 1,4-butane diol (BDO), to form the same type of hard segment, with four different soft segments (polyols): polytetramethylene ether glycol (PT), polycaprolactone (PC), ethylene oxide and propylene oxide based polyether polyol (PET) and adipic anhydride based polyester polyol (PES). Scratch tests were carried out according to the ASTM D7027/ISO 19252 standard. Results indicate the changes in scratch performance are closely correlated with the variations in coefficient of friction, tensile true stressstrain behavior as well as dynamic mechanical behavior of all the CPU model systems upon water exposure. Fundamental structure-property relationships of CPU affected by water content are discussed.
Using Micronized Recycled Tire Rubbers in Thermoplastic Polyolefins as a Value-Enhanced Solution to Sustainability
Thermoplastic elastomers (TPE) including thermoplastic polyolefins (TPO) and thermoplastic vulcanizates (TPV) are promising elastomeric materials for automotive applications such as headlight surrounds, bumper covers, door gaskets, etc. TPEs offer a combination of great thermoplastic processability and outstanding rubbery properties, however, the process of recycling scrap and post-consumer products and reprocessing them into useful products have always been challenging. In addition, tire rubbers have been one of the most problematic sources to recycle, due to their large volume and durability. Innovative and effective methods are critical to reuse the recycled tire rubbers in value-added products other than their traditional use for fuel values. In this study, micron-size rubber powders (MRPs) were fabricated from recycled truck tires in large volume, and used as fillers for the twin screw extruder (TSE) compounding of recycled TPOs. TPO was chosen as the base resin for compounding because of its excellent reprocessability, good compatibility with the micron-size tire rubbers, and reasonable low cost. A compatibilizer was studied to enhance the uniform incorporation of micro-size rubber powders into the base resins and improve the overall performance of the compounds in a cost-effective way. The chemical structure of the recycled TPOs was confirmed by FTIR, and the thermal stability and compositional analysis of the recycled tire rubbers were characterized by TGA. The physical and mechanical properties (hardness, MFI, tensile, Izod impact, etc) were extensively tested to study the overall performance of the compounds. The surface details of injection molded parts are studied and improved for automotive and commodity applications.
Rheological Properties of Polyethylene Blend with Poor Mixing
The effect of mixing condition on flow instability at capillary extrusion was studied using linear low-density polyethylene (LLDPE) blends. Two types of LLDPE with different molecular weights were blended by various mixing devices and conditions. It was found that the onset of flow instability is sensitive to the mixing method even though their linear viscoelastic properties are almost identical. The blend obtained by poor mixing conditions shows shark-skin failure even at a low shear stress, although the blend prepared by intensive mixing provides smooth surface at the same shear stress. This is attributed to the low onset shear stress of shark-skin failure for the blend prepared by poor mixing. Furthermore, a blend by poor mixing is found to show a significantly low value of the maximum draw ratio at hot-stretching. The result suggests the existence of mechanically-weak points, which leads to cohesive failure at strand surface by the abrupt stretching at the die exit, i.e., the shark-skin failure.
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