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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Numerical and Experimental Analysis of Infill Rate on the Mechanical Properties of Fused Deposition Modelling Polylactic Acid Parts
Material characterization of 3D printed PLA parts with different infill rates was performed by standard tensile tests. Three-dimensional finite element simulations of the tensile tests were also performed. For the simulations, a method for reconstructing the CAD model of the printed parts with different infill rates was proposed and numerical simulations were conducted on the reconstructed models. A reasonable prediction of the experiments in terms of material behavior and the stress-strain characteristics for infill rate of 100% is obtained from the numerical analysis. Discrepancies between the numerical predictions and experimental results especially in the plastic deformation region for other infill rates are discussed in the paper.
Polycarbonate Filled with Hybrid Conductive Fillers for Bipolar Plate Application
Conductive polymer composites (CPCs) of polycarbonate (PC) filled with carbon fiber (CF), carbon nanotube (CNT), graphite (Gr), and their double and triple hybrids were prepared using solution casting method followed by compression molding. The through-plane electrical conductivity of CPCs filled with single and hybrid fillers were investigated. The results showed that the percolation thresholds for the PC-CNT and PC-CF was ~1 wt.% and ~10 wt. %, respectively, while no clear threshold was found for PC-Gr composites. Addition of 3-5 wt.% CNT improved the conductivity of PC-CF and PC-Gr systems up to 6 orders of magnitude. The results of hybrid CPCs filled with all three fillers (with constant total loading of 63 wt.%) indicated that the best conductivity result is achieved when the CF and CNT loadings were near their percolation thresholds. Therefore, a triple filler system of 3 wt.% CNT, 10 wt.% CF and 50 wt.% Gr resulted in a composite with the highest through-plane conductivity (12.81 S.cm-1), surpassing the reported values in the literature, and a step forward toward meeting the US Department of Energy criterion for the electrical conductivity required for bipolar plates of fuel cells.
A Composition-Morphology Mapping of Particle-Filled Polymer Blends up to High Fill Fraction
This study explores the effects of particulate filler on the morphology of two immiscible high-molecular-weight thermoplastic polymers across a wide range of composition. Blends of polyisobutylene (PIB) and polyethylene oxide (PEO) with silica particle loadings of up to 30 vol% were studied. The silica particles have a strong affinity for PEO, and hence the effects of particles on the morphology depend on whether or not there is sufficient PEO to engulf the particles. We observe two morphologies that are qualitatively different from those seen in particle-free polymer blends: one in which particles are bonded together by small menisci of PEO, and the other in which a highly-filled particles-in-PEO phase percolates throughout the sample. Other morphologies in filled blends resemble droplet-matrix or cocontinuous morphologies in corresponding unfilled blends. Overall, particles have major effects on the morphology when the polymer preferred by the particles (PEO) is in a minority, but only modest effects when the preferred polymer is in a majority.
Fundamentals of Twin-Screw Compounding: Kneading Block Performance Characteristics
The co-rotating fully intermeshing twin-screw extruder has evolved significantly in the 60 years since it was commercialized in 1957. While this equipment might be considered a “mature” technology, it has not experienced a decline in new developments as might be expected, but rather a significant number of advancements. The technology continues to evolve. For example in the last 20 years several significant developments have been introduced. These include a) the implementation of high torque (power) designs, b) the use of increased screw rpm in conjunction with high torque for improved operating flexibility and productivity, and c) a breakthrough technology for feeding difficult to handle low bulk density materials. However, one area of twinscrew technology that has not evolved as much is screw elements geometry. Conveying elements and kneading blocks have remained essentially the same since the original Erdmenger design patents filed in the late 1940’s and early 1950’s. In spite of their longevity in the market, there are still unknown qualitative as well as quantitative operational characteristics. This paper will focus on kneading blocks, specifically looking at some significant aspects related to performance. These include pressure generation as a function of 1) absolute pressure, 2) disc profile (2-lobe vs, 3-lobe), 3) disc width, 4) disc stagger angle, and 5) material viscosity.
Knowledge-Based Support for the Designer regarding Injection-molded Part Design
CAD-Systems have become a standard tool for the development process. Due to the extensive possibilities of modern CAD-software, the classic approach turns into a more dynamic one. This opens up the possibility to take into consideration influences from the production and computation at an early stage of the design process. This paper presents a methodological approach to ensure a design for injection-molded parts. An important goal is the realization of a knowledge based assessment of manufacturing possibilities and the preselection of materials for a safe and objective product planning. Furthermore, the project objectives for the acceleration of the design of molded parts through the reduction of unnecessary optimization steps according to the usage of knowledge based systems.
Mechanical Characterization and Fractography of PC, ABS and PMMA – A Comparison of Tensile, Impact and ESC Fracture Surfaces
This work presents an effort to document and describe fracture surfaces for three commercially available amorphous polymers (PC, PMMA and ABS) each subjected to tension, impact and environmental stress cracking (ESC). We present mechanical properties as well as microscopic characterization at low and high magnification to distinguish between slow tensile loading, fast impact loading, and environmentally assisted creep failure mechanisms. Chemical surface analysis of select fracture surfaces was also performed to evaluate its utility as a failure analysis technique for identifying ESC failure. The fractographic atlas presented herein serves to assist others in identifying topographical fracture surface features and crack growth mechanisms of failed plastic components, and more accurately distinguish between pure mechanical failure and ESC-generated fracture, where possible.
Optimizing 3D Printed Components: A Methodological Approach to Assessing Print Parameters on Tensile Properties
Additive manufacturing provides the designer with more freedom, but at the cost of higher complexity when optimizing the design for additive manufacturing. Any 3D printing process or machine has easily over 100 unique variables and settings, and understanding their effects on the performance of the produced part is equally unique to the specific process. To achieve optimal design for additive manufacturing (DFAM), one must explore the trends and interactions present in these processes. Here we demonstrate an empirical method utilizing a statistical design of experiment technique and standardized mechanical testing which ultimately exposes trends and variable interactions specific to our selected additive manufacturing process.
Macromolecular Structure-Property Relationship for Impact Strength and Hardness of Polydimethylsiloxane (PDMS) Blends
In this study, Polydimethylsiloxane (PDMS) with varying crosslinking densities were fabricated by vacuum assisted bubble free casting of PDMS followed by heat treatment. Shore A hardness tests and impact tests were performed to evaluate the hardness and maximum impact strength of PDMS. PDMS with varying mix ratios of 5:1, 10:1, 15:1 wt/wt silicone resin to curing agent were fabricated for instrumented drop weight impact testing and hardness testing. Fourier transform infrared (FTIR) spectroscopic analysis revealed that there is a strong correlation between impact strength and hardness with respect to molecular dipole moments of Silicone-Oxygen-Silicone (Si-O-Si) bonds. It was also determined that there is an inverse correlation between dipole moments of Oxygen - Hydrogen (O-H) bonds with respect to impact strength and hardness of PDMS.
Evaluation of the Mechanical and Morphological Characteristics of PLA-Lignin, PLA-Tannin and PLA-CNF Composites
PLA has now attained significant utility in the plastics and manufacturing sector. It high stiffness, strength and bio-degradability has made it an attractive option for in many applications including additive manufacturing. This paper presents the modification in properties of neat PLA with the addition of Lignin, Tannin and Carbon Nanofibers fabricated via high shear twin screw compounding. Lignin and Tannin were chosen as completely bio-based fillers and Carbon Nanofibers were chosen for their high performance and modest expense as compared with other carbon based nano-materials. Detailed morphological evaluation of the composites is also presented.
Bio-Inspired Textured Composite Surfaces with Increased Hydrophobicity
Texturing composite surfaces in the past employed techniques such as photolithography, laser sintering and plasma etching. However, these techniques pose to be very complex in nature. In this paper, we present a method to texture composite surface without the need for using such complex surface texturing methods. The textured samples were fabricated by taking advantage of the fiber de-bonding and pull out process. Varying fiber volume fractions of carbon fibers were melt blended with Thermoplastic Polyurethane matrix followed by cutting to expose the fibers from the matrix surface. The TPU composite had shown a 23% improvement in the contact angle.
Influence of Long-Term Annealing on Residual Stress Distribution and Quasi-Brittle Failure Properties of Talcum Reinforced Pipe Grade Polyproyplene
In this study a polypropylene material with talcum reinforcement used for sewer pipes has been subjected to an annealing procedure at 80°C, roughly 60°C above the actual application temperature, in air for a time period of 18 months. As expected, examination of the material showed no significant decrease in mechanical or fracture mechanical properties due to the temperature exposure. However, samples stored at higher temperature showed better resistance against quasi-brittle failure in fatigue tests compared to unconditioned samples. This could mainly be attributed to the decrease of residual stress in the pipe wall. Even though pipes have been annealed for very long times above Tg, residual stress could not be totally relaxed within 18 months.
Cocontinuous Conductive Polymer Composites with Interfacial Graphene
Interfacial localization of graphene in the cocontinuous polymer blends is shown to be effective in stabilizing the cocontinuous morphology and increasing the conductivity with a lower electrical percolation threshold. We created polylactic acid (PLA) and polystyrene (PS) cocontinuous blends filled with thermally reduced graphene oxide (r-GO) jammed at the interface. The resulting conductive composites show dramatically improved conductivity at low filler loadings and an ultralow percolation threshold of 0.028 vol%. We found that r-GO transfers from the PLA phase to the interface during melt compounding and forms a spanning 3D network during annealing, which effective suppresses the coarsening of the cocontinuous structure. Our study demonstrated that the 3D r-GO network significantly increases the conductivity and the storage modulus of the melt blends.
Use of Decahydrodecaborate as Flame Retardants in Coatings
As the need to protect the environment continues to increase, there is a growing demand for non-halogenated flame retardants. Two different decaborate compounds were combined with triphenylphosphine oxide into polyurethane and characterized. The thermal stability and the potential flame retardancy of the new materials were tested via thermogravimetric analysis and cone calorimetry. The cone test provided heat release rates and smoke release rates. Per the results of these tests the combination of the new decaborate, and triphenylphosphine oxide showed potential for flame retardancy at minimal amounts of flame retardant.
Validation of Residence Stress Distribution Approach Using 1-D Computer Simulations
The compounding process in the twin-screw extruder (TSE) comprises the dispersive and distributive mixing. Dispersive mixing has been the primary agent that influences the mixing of polymer melt in the TSE. It has been difficult to predict the dispersive mixing in the TSE due to the complex flows that develop in the TSE. The Residence Stress Distribution (RSD) approach has been used to quantify the amount of polymer melt that experiences a particular amount of stress, when processed in a co-rotating twin screw extruder. In order to predict the stress history developed in the twin-screw extruder, the percent break up of CAMES (Calibrated Micro Encapsulated Sensor) beads have been used. Percent Break up (%BU) values obtained across an operating condition domain are used to generate a predictive equation using JMP statistical software, in order to express % BU as a function of screw speed (N) and specific throughput (Q/N). In order to provide an insight into the RSD results, a 1-Dimensional Twin Screw Extrusion software called Ludovic is used. Based on the screw geometry and operating conditions, Ludovic simulates a set of results such as the temperature, viscosity and shear rate experienced by the polymer melt in the extruder. These results have helped understand the percent break up results obtained from the RSD experiments. An independent validation of the Residence Revolution Distribution (RRD) and Residence Volume Distribution (RVD) has been performed using the computer simulations.
High Performance Polymers for Medical Device Applications
EVONIK is a technology leader for high-performance polyamides, EVONIK’s current portfolio of specialty polyamides include PA12, PEBA (flexible polyamide), bio-based polyamides, transparent polyamides, and polyphthalamide materials for the medical sector. From catheters and balloons to diagnostic equipment and surgical instrumentation, VESTAMID® Care and TROGAMID® Care are well established. EVONIK offers flexibility in the design and manufacturing through our new Bonding VESTAMID® Care and TROGAMID® Care grade polymers. EVONIK’s VESTAKEEP® Care PEEK materials are used in temporary contact and instrument applications, while VESTAKEEP® PEEK i-Grades are used for permanent implant applications. From spine and sports medicine, to drug delivery devices and heart valve applications, new compounds of VESTAKEEP® PEEK are designed to meet the specific application needs and performance demands of medical sector.
Effects of Material and Processing Conditions on the Shrinkage of an Injection Molded Liquid Silicone Rubber Part
An injection molded liquid silicone rubber (LSR) part was investigated for better understanding of how material properties, typical processing conditions, and packing affect shrinkage. This work showed no direct correlation between material durometer and shrinkage. In-flow shrinkage was greater than cross-flow shrinkage, but the diametric shrinkage was twice the in-flow shrinkage. Small (1%) increases in shot size significantly reduced shrinkage, whereas injection velocity and cure time had no direct effect on shrinkage. Packing of LSR parts is possible, with higher pack pressures and shorter pack times decreasing shrinkage. As expected, higher mold temperatures produced greater shrinkage, but this effect was offset by packing of the part near the gate.
Effect of Screw Speed on Polyethylene-Calcium Carbonate Composites Produced Using Twin and Quad Screw Extruders
The effect of ultra high screw speed on mixing was investigated using polyethylene microcomposites with 1 wt% calcium carbonate compounded on novel twin and quad screw extruders. The screws had similar designs and the screw speeds were 300 to 2000 rpm. Extruder type influenced the effects screw speed had on extruder residence time, melt temperature, drive torque, and head pressure. Parallel plate rheology indicated significant chain scission of the polymers and better filler dispersion at higher screw speeds of 900 and 1500 rpm, especially with the quad screw extruder. In the quad screw extruder, the lower melt temperatures and greater shear allowed better mixing at higher screw speeds than the twin screw extruder. The level of mixing in the quad screw extruder also depended on resin viscosity.
A Preliminary Study on the Performance of Additive Manufacturing Tooling for Injection Molding
Tooling for injection molding is expensive and the time it takes to manufacture a tool is also a concern, especially for companies who are on a tight production schedule. The introduction of Additive Manufacturing (AM) tooling for injection molding is an attractive option for cutting cost and time for not only prototype designs, but also for short production runs. The objective of this research is a preliminary study on two AM tooling questions: How long will the plastic tool survive, and will the parts look similar to the parts produced from a traditional steel tool? In this paper, we compare the mechanical integrity of ribs of different aspect ratio (length to thickness), both experimentally and via computer simulation. We show that there is good agreement between both. The rib with the larger aspect ratio (10 to 1) breaks as predicted by the simulation and the one with the smaller ratio (5 to 1) survives several moldings as expected. In the second case, if the cycle time is adjusted to allow the mold to cool down between cycles, the rib survived a large number of moldings. The effect of tool wall thickness under different packing pressures is also evaluated.
Characterization of Slow Crack Growth Resistance of Polyethylene Pipe Grades with Cyclic Cracked round Bar (CRB) Test in Correlation to Strain Hardening (SH) Test
Several test methods have been developed to determine slow crack growth (SCG) resistance of modern polyethylene (PE) pipe materials. Unfortunately, most of these test methods exceed practical time frames and take unfeasible time to reach brittle failure at standard test conditions. Therefore new acceleration methods for a reliable and quick material ranking are required. The Cyclic Cracked Round Bar (CRB) Test and the Strain Hardening (SH) Test are two of these recently developed standard test methods with a significant expediting of testing time. This study summarizes quite a few results of the Cyclic CRB test and compares them with results from Strain Hardening (SH) test to demonstrate the correlation between these two test methods and to highlight the advantages of the Cyclic CRB Test.
Crosslinking Polyethylene Resins via E-Beam Irradiation
In this work, the crosslinking of various thin polyethylene films via electron beam exposure in an inert environment was studied. Increasing Melt Flow Index and polymer density both decreased the insoluble gel fraction resulting from irradiation at a dosage of 800 kGy. The effect of adding low levels of two different polyfunctional monomers was also examined. Trimethylolpropane triacrylate (TMPTA) was found to decrease the dosage necessary to initiate gel formation, and gave higher gel fractions at lower dosages, but showed little effect at higher dosages. A low molecular weight polybutadiene (PBd) resin showed little effect on gel fraction as compared to the neat resin controls.
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