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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The effect of particle size and shape of the nucleating agent on the foaming behavior of a styrene butadiene block copolymer
In this study the physical foaming of a styrene butadiene block copolymer (SBC) using different grades of mineral fillers as nucleating agent was examined. The aim was to determine, how the mean particle size and shape of the filler influence the foam morphology and the processing of styrene butadiene block copolymer foam. Therefore, several compounds were prepared with a twin screw extruder using calcium carbonate (CaCO3), talcum and glass bubble grades with distinct mean particle sizes. The different filler types were used to investigate the effect of the particle shape on the foam morphology of the SBC polymer. In this study spherical (glass bubbles), cubical (calcium carbonate) and plate-like (talcum) particle shapes were examined. All compounds were characterized with a cone plate rheometer to compare the influence of the different filler grades on the rheological properties. Their foaming behavior was investigated by using a single screw extruder with a screw diameter of 45 mm and supercritical CO2 as foaming agent. The different mineral fillers were compared, due to their effect on the maximum cell density, in terms of cell size and the foam density.
Tribological Investigations on PA46 Composites Filled with Different Shaped Silicates
Incorporation of diverse fillers in a polymer matrix can improve various physical and mechanical properties of the polymer. The influence of different filler types like structure modified organoclays (after incorporation existing in nanoscale) and silica sand on the tribological properties of Polyamide 46 (PA46) has been investigated. The composites and nanocomposites with 5 wt.% organoclay were prepared by melt compounding on a corotating twin screw extruder. The tribological measurements were carried out on a pin-on-disc type tribometer by pressing a flat pin of steel at predefined loads against a polymer disc sample rotating at a predefined velocity. The disc samples were prepared by compression molding. The surface of both steel and polymer samples was grinded and polished to attain a certain surface roughness. The wear properties were studied under dry sliding conditions and the coefficient of friction (COF) was measured also under oil lubricated conditions at different velocities and loads. The results showed that most of the PA46 composites can have better tribological properties than the unfilled polymer. A reduction in COF for most of the composites under dry sliding conditions could be observed. With increase in the normal load the specific wear rate and COF reduces. The influence of the shape and size of the silicate particles was also investigated. Tremendous improvement in the friction properties of one composite was observed under oil-lubricated conditions.
High Performance Thermoplastic Vulcanizates Based on Natural Rubber by Electron Induced Reactive Processing
Electron induced reactive processing (EIReP) – an eco-friendly and sustainable reactive processing method based on the use of high energy electrons - was used for cross-linking of the elastomeric domain during melt mixing in order to prepare natural rubber (NR) and polypropylene (PP) based thermoplastic vulcanizates (TPVs). The electron treatment with various absorbed dose values showed a prominent effect on mechanical, rheological, and morphological characteristics of the PP/NR TPV. SEM and TEM studies confirmed that these TPVs can exist across the co-continuous or discrete phase morphology. The maximum set of mechanical properties (tensile strength of 15 MPa and elongation at break of more than 500 %) were obtained at an absorbed dose of 100 kGy for a 50/50 blend ratio of NR and PP without any addition of compatibilizer or chemicals. At higher absorbed dose values the degradation of polypropylene showed a negative impact on the mechanical properties of the TPVs. Depending on the morphology and the results of tensile test a structure-property co-relationship is drawn on the basis of common phenomenological understanding of the TPVs.
The bending curvature of an elasto-viscoplastic beam under three-point flexion solicitation
The thermoplastic polymers have a very narrow range in which their behavior can be assumed to be elastic linear. When a thermoplastic is loaded, it rapidly exhibits a clear nonlinear behavior due to its viscous character, or to its plastic character or to both. However, the contribution of those two characters may be linear or nonlinear. The problem becomes more challenging when the material is subjected to a non-uniform stress field such us in the case of the flexion solicitation. In this case, the same material may have different behavior from one area to another according to the local stress state. The objective of this paper is to develop a rheological model to represent the behavior of an elastoviscoplastic and homogeneous beam, with straight and constant cross section, subjected to a three-point flexion solicitation. It is assumes the Bernoulli and Saint-Venant conditions are met in order for the strain field to be considered uni-dimensional. The work starts with the presentation of the analogical model followed by the mathematical formulation of the model established according to the elasticity, the viscoelasticity and the viscoplasticity laws. The aim of the work is to deal mainly with one specific geometrical parameter of the flexion which is the beam bending curvature. This parameter allows the determination of the deformation field and the stress field in the beam. It is found that in the elastoviscoplastic area of the beam the differential equation of the curvature requires numerical integration performed using the implicit Euler method. This theoretical modeling approach is supported by creep tests results carried out on samples of polyamide 66. The actual test results are qualitatively consistent with the predicted behavior of the rheological model.
Friction and Wear Behavior of Expanded Perlite Filled Polyproylene Composites
Tribological properties of perlite filled polypropylene (PP) composites were studied using a pin-on-disc tribometer. The influence of the filler content, particle size and the normal load on the specific wear rate and the coefficient of friction (COF) were analyzed under dry sliding conditions. The results indicate that increase in normal load reduces the COF and the wear rate by all filler loading. Larger particles and lower filler content reduce the specific wear rate while there is almost no influence on COF. The COF of PP-perlite composites exhibit good wear resistance and low coefficient of friction by a filler loading of 5 wt.% with larger particles.
On Process-Morphology of Semicrystalline Poly (Ether-Block-Amide) PEBAX® Therrmoplastic Elastomers Using A Micro Injection Molding Process
Polymer melts under micro injection molding process experience high shear rates and high thermal gradients, resulting in some unique morphology features. This paper examined the morphology of Pebax 7233 SA01 under designed experimental conditions. With measurement by cavity pressure and temperature (PT) sensors, shear rates and thermal gradients were quantitatively evaluated and related to morphology evolution. Unique spherulites were formed beside the skin layer, having a much larger size than its adjacent larger while the central region had no visible structure. Their formation, and the related thermomechanical history, were examined.
Verfication of Rheological Mixing Rules to the Application of Masterbatches
Polymer flow behavior is influenced by the rheology of additives such as colors, fibers or fillers. To prevent expensive and time consuming material testing after compounding, mixing models have been developed to estimate the resulting viscosity. In this investigation, three different mixing models were applied to the mixture of masterbatches including different colors and carbon black. The prediction of the three mixing models were compared to the measured viscosity of the compounded mixture. The results suggest significant predictive capability of the mixture rheology, but not sufficient to identify the ratio of the constituent materials given rheological data of a compounded material.
Mold Design for Microinjection Molding of Deformable Membrane Mirrors
Experimental and numerical simulations were carried out to produce a deformable membrane mirror (DMM) with micro-features. A commercial CAE analysis program (Moldex3D-R10) was used to simulate the polymer melt flow inside the mold cavity during the microinjection molding process. The Moldex3D simulations and experimental results are compared. Different micro-feature thicknesses result in different flow behaviors. A mold insert was designed and fabricated. A microinjection molding machine was used to mold the part using COC-Topas-5013S.
Influence of Process Parameters on Edge Replication Quality of Lab-On-A-Chip Micro Fluidic Systems Geometries
The growing demand to manufacture, with high accuracy, structures enabling transportation, treatments and measurements of minuscule biomedical samples on polymer substrates is pushing the process capability of technologies such as injection molding to their limits. To characterize and asses the replication quality of molded micro-features on cyclic olefin copolymer (COC) a tool insert collecting critical channel cross sections was manufactured. The master was made by UV lithography and subsequent nickel electroplating. Effect of packing phase parameters (packing time, packing pressure) and mold temperature were investigated. Moreover, consequences of different positions, directions and nominal channels width were considered. Edge replication quality was quantitatively characterized, analyzing calibrated scanning electron microscope (SEM) images with a digital imaging processing software. Results showed better replication fidelity mainly influenced by the higher mold temperature and also by higher packing pressure, whereas poor edges quality was observed for the smallest replicated test structures.
Temperature Modeling For a Multivariate Injection Molding Sensor
An infrared temperature sensor is detailed using a thermopile with an incorporated thermistor into a standard Dynisco snout. A testing apparatus was built to measure the temperature of various heated polymers, with sapphire and zinc selenide windows of varying thickness. Simulation was also developed to determine the heat transfer from the hot polymer to the thermopile including transmission, absorption and reflectance. The results indicate that a combination scattering, emitting, and absorbing effect is occurring regarding the transfer of infrared radiation to the thermopile. This effect can be calculated, and lead to accurate prediction of melt temperature.
Melt Flow Simulation of an Injection Molding Cavity For Validation of a Multivariate Sensor
Utilizing mold filling simulation to validate a multivariate molding sensor is described. The multivariate sensor uses an infrared thermopile for temperature measurement and a piezoelectric ring for measuring pressure. A zinc selenide window is used in order to transmit melt radiation, pressure, and prevent leakage. Velocity is estimated based on the rise time of the melt temperature signal. Viscosity is estimated using the pressure and velocity based on constitutive rheological models. Results indicate that the frozen layer thickness is significant in estimating the shear rates and viscosity, but an accuracy of ±5% can be obtained across a wide range of processes.
Improved Exfoliation and Dispersion of Nano-clays in Nylon 6 Using Supercritical Carbon Dioxide
The use of supercritical carbon dioxide (scCO2) as a processing aid to help exfoliate nanoclays and improve their dispersion after melt blending in polymer matrices has been reported in the literature. Previous work has focused on nonpolar polymers such as polypropylene. In this work, the supercritical aided melt blending method was applied to a Nylon 6/ organoclay composite system with favorable organoclay/polymer interactions. Transmission electron microscopy (TEM), rheological results, and tensile tests are provided to investigate the effect of processing with scCO2 on the final composite properties and morphology. It was found that the scCO2 aided method improved the composite properties compared to reported twin screw results in literature. At 7.6 wt% the modulus is observed to reach about 4.75 GPa which is one of the highest increases (~1.7 GPa) reported for these materials at intermediate concentrations. We note that beyond 7.6 wt% the improvement due to scCO2 processing only matches that of direct blending. It is possible that with the use of a twin screw extruder, or reduction in processing steps, the modulus would continue to increase.
FEM Simulation of Brittle Damage Features Developed during Scratch
Brittle damage features, such as crazing and cracking, formed on polymer surfaces during scratch are to be avoided if at all possible. Successful simulation of the evolution of these deformation processes would allow for deciphering the fundamental mechanics involved and for establishing correlation between the material/surface properties and the brittle damage features induced during scratch. In this work, attempts are made to simulate microcrack formation in the scratch groove. The FEM simulation results show good agreement with experimental observation reported in the literature.
Synergistic Effect of Hybrid Fillers on Thermal Conductivity and Mechanical Property of PA6 Composites
In order to obtain high thermally conductive composites and research the synergistic effect of the hybrid fillers on the properties of the composites, three kinds of PA6 composites were prepared by melting blend with one, two or three kinds of AlN, SiC and BN fillers. The microstructure, crystal behavior, thermal conductivity and mechanical property of the composites were characterized by SEM, DSC, DSC combined with LFA, and electronic tensile testing machine separately. The AlN, BN and SiC fillers were almost homogeneously dispersed in PA6. The addition of BN fillers promoted the generation of ? crystal form of PA6. The hybrid fillers had obviously synergistic effect on thermal conductivity of the composites, specially the AlN and BN. However, the tensile strength of PA6/SiC was the highest among the composites.
Design and Fabrication of Polymer/Ceramic Scaffolds for Bone Tissue Engineering
Bone tissue engineering is a rapidly developing field, and seeks to offer an alternative treatment for bone defects by restoring and maintaining the function of bone tissue. One of the most established approaches is using polymer scaffolds seeded with osteoblast and other growth factors to speed the body’s natural healing processes, decreasing rehabilitation time for patients. The biomimetic design of the scaffolds will need to replicate the structural and mechanical properties of the tissue and be stiff enough to withstand immediate weight bearing. The effectiveness of this approach is determined by examining the properties of the scaffold including porosity, interconnectivity, and mechanical properties. The goal of this study is to create viable polymer/ceramic scaffolds through melt processing of polycaprolactone (PCL) and poly(ethylene oxide) (PEO), combined with hydroxyapatite (HA) and salt (NaCl), followed by porogen leaching. The effects of polymer ratio, ceramic and salt content, and the pressure applied during the fabrication process have been examined in this study. These results will be used to create a factorial design of experiments (DOE) to determine the optimal scaffold fabrication parameters.
Chain Extension of Virgin and Recycled Poly(Ethylene Terephthalate): Rapid Estimate of Molecular Weight Increase
This work is concerned with the determination of changes in molar masses of virgin and recycled PET resulting from the action of a chain extender additive compounded in a laboratory internal mixer, based on the processing data provided by the mixer, without further analysis. Results obtained show that the additive increases the molecular weight of both, virgin and recycled PET. Actual values depend on the amount of additive used and processing conditions. The additive tested is more efficient increasing the molar mass of the virgin versus the recycled resin (more additive is needed to obtain the same relative increase).
Effect of Loading Level and Granulometry on PHB/Begetal Fiber Eco-Composites
The present work is concerned with the preparation and characterization of composites of poly(3- hydroxibutirate) (PHB) and vegetal fiber from the mesocarp of the babaçu palm tree fruit. Composites with 5, 10 and 20% micronized babaçu fibers of two different granulometries were prepared in an internal mixer, and characterized by melt flow rate (ASTM D1238) and optical microscopy. Results indicate that the PHB is thermally unstable at all admissible processing conditions, and that partial degradation of the matrix in the resulting composites must be taken into consideration. On the other hand, the analysis of low-magnification optical microscopy images showed that excellent dispersion was obtained for all loadings and particle sizes tested.
Developing Polymer/Ceramic Scaffolds via Thermally Induced Phase Separation for Bone Tissue Engineering
Biodegradable polymers are used to fabricate porous scaffolds for tissue engineering. Among different scaffold fabrication techniques, thermally induced phase separation (TIPS) is valuable because of producing highly porous scaffolds with interconnected structures. The effect of adding hydroxyapatite (HA) to poly (lactic-co-glycolic acid) (PLGA) scaffolds as well as other TIPS parameters was investigated in this study. The ultimate goal is to fabricate porous scaffolds that are mechanically functional, while they provide the desired porosity and pore interconnectivity for cell migration, cell growth, and transport of oxygen and nutrients.
Study of Morphology on Microcellular Injection Molded Scaffolds for Tissue Engineering
In this research, injection molding was combined with a novel material combination, supercritical fluid processing, and particulate leaching techniques to produce highly porous and interconnected structures that have the potential to act as scaffolds for tissue engineering applications. The foamed structures, molded with Poly(?-caprolactone) (PCL) and Poly(ethylene oxide) (PEO) with salt as the particulate, were processed without the aid of organic solvents, which can be detrimental to tissue growth. The pore size in the scaffolds is controlled by salt particulates and interconnectivity is achieved by the cocontinuous blending morphology of biodegradable PCL matrix with water-soluble PEO. Nitrogen (N2) at the supercritical state is used to serve as a plasticizer, thereby imparting moldability of blends even with an ultra high salt particulate content, and allows the use of low processing temperatures. Interconnected pores of ~200 ?m in diameter and porosities of ~72% are reported and discussed.
Improving Cellular Structure of Microcellular Polystyrene Foams with Injection-Compression Molding
The rectangular foamed polystyrene plates were molded using microcellular injection-compression molding (MICM) and standard microcellular injection molding (without compression, MIM). The cellular structures of both MICM and MIM samples were investigated. The results showed the compression can further change the cellular structure formed in the injection stage of MICM. Taking 4 mm-thick sample as an example, the thicknesses of the outer zone, where irregular striations-shaped cells dominated, decreased about 25% at different positions along the melt flow direction. In the inner zone dominated by ellipsoidal cells, the cell size distributions at different positions, especially near the sprue, became narrow. Finally, a cellular development mechanism in the compression stage of MICM was proposed. The narrow cell diameter distribution in the inner zone resulted from the collapse of some small cells and decrease of some large cells.
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