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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Wood Plastics Composites Produced by Rotomolding
This study reports on the properties of wood plastic composites produced by rotomolding. As a special case, wood flour (maple) was dry-blended with linear low-density polyethylene (LLDPE) to produce composites up to 25%wt. From the samples produced, a complete characterization was performed including density, morphology, and mechanical properties (tensile and flexural). As expected, tensile and flexural moduli increased with wood content, while tensile strength and elongation at break decreased. The optimum wood content was found to be around 20%wt. for the range of conditions tested.
Effect of Cooling Rate and Mold Counter Pressure on the Crystallinity and Foaming Control in Microcellular Injection Molded Polypropylene Parts
The purpose of this study is to investigate Microcellular polymer injection molding, which is becoming increasingly popular in automotive, semiconductor, and industrial applications. While the technique has been widely successful using amorphous polymers, semi-crystalline polymers present new challenges not encountered during the processing of their amorphous counterparts. The polymer chains in a semi-crystalline material develop an organized crystal structure during the cooling stage. Crystal development generates two main issues for microcellular processing. First, the excess heat released during the crystal formation affects the expansion of the microcellular bubble causing unpredictable non-uniform growth. Second, the growth of the crystal structure within the polymer melt expels and displaces the supercritical fluid forcing the foaming to occur out at the edges of the part rather than uniformly through its core. This paper develops and explores strategies to control and overcome these problems.
The Effects of Gas Counter Pressure Combined with Dynamic Mold Temperature Control on the Skin Layer Thickness and Foaming Cell Size of Microcellular injection Molding
In this study, we developed a foaming control system using the Gas Counter Pressure (GCP) combined with Dynamic mold temperature control (DMTC) during the microcellular injection molding process and investigated its influence on part surface quality, skin layer thickness and foamed structure uniformity. The results show that under GCP control, part surface roughness for transparent polystyrene (PS) improved by 90%. When GCP increased, the skin thickness also increased and the weight reduction decreased. Applying mold temperature control alone with temperature at a high temperature near Tg, the surface roughness improved. Increasing mold temperature decreased the skin thickness; however, the cell size distribution became significantly non-uniform. It was found that rapid cooling speed is necessary for controlling the cell size and uniformity, with a 10°C/sec cooling rate alone, the average cell size decreased from 192.92 ?m to 84.97 ?m and uniformity was improved. We conclude that skin thickness, uniform cell size as well as good surface quality could be achieved efficiently by combining GCP and DMTC.
Preparation and Characterization of Poly(Lactic Acid)/Poly(Vinyl Alcohol) Blend
In this study, polymer blends based on poly(lactic acid) (PLA) and organic particles polyvinyl alcohol (PVOH) were prepared by melt mixing using a triple screw extruder. Phase morphology, thermal properties, dynamic mechanical properties and mechanical properties of the blends were investigated. Differential scanning calorimetry reveals that the addition of PVOH remarkably decrease the cold crystallization temperature and increase the degree of crystallinity of PLA/PVOH blends. Dynamic mechanical properties show that a general decrease of E? is observed with the addition of PVOH content, yet the loss tangent peaks broaden and slightly shift to higher temperature. From mechanical tests, it is found that tensile strength and the elongation at break decreased markedly with the addition of PVOH content, yet notched impact strength slightly increase.
True 3D Numerical Simulation in Compression Molding
The objective of this study is to develop a simulation tool of compression molding (CM) process to get a comprehensive understanding of the whole process. We primarily focused on numerical simulation of the flow during mold closure in compression molding process. The complex advancing flow front is simulated by means of novel moving mesh boundary technique to realize the effect of process conditions. The behavior of squish flow could be seen from the analysis. Furthermore, we also investigated the fiber orientation states in CM short-fiber-reinforced parts with rib geometry. By means of simulation tool, the distribution of fiber orientation can be tailored through the interpolation of fiber orientation tensor.
Synthesis and characterisation of PVA/SBMA crosslinked hydrogels with low fouling property
A novel zwitterionic poly(vinyl alcohol)/ sulfobetaine methacrylate (PVA/SBMA) cro-sslinked hydrogel was prepared by a two-step aqueous polymerization method, to improve the anti-protein fouling inadequacy of PVA hydrogels. Attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) and scanning electron microscope (SEM) were used to study the composition and microstructure of the hydrogel samples. The deswelling behaviors and adsorption of bovine serum albumin (BSA) on the prepared PVA/SBMA hydrogel were measured as a function of ionic strength. The results showed PVA/SBMA hydrogel significantly reduced protein adsorption.
Performance Comparison of selected Rapid Heat Cycle Molding Systems and Models for predicting Heating and Cooling Behavior
Rapid heat cycle molding (RHCM) continuously gains importance in achieving high grade polymer surface finishes. To examine the performance of selected RHCM systems, a new test mold, using two RHCM technologies, was used. The mold’s nozzle side is equipped with the areal heating and cooling technology BFMOLD®, which tempers a chamber below the cavity by using hot and cold water sequentially. A local electrical ceramic heating element (Ultramic™) is installed into the ejection side, 3 mm below the cavity surface. To examine the performance of both RHCM systems a central-composite Design of Experiments (DoE) was developed. Low and high temperatures of the RHCM systems were systematically varied within the DoE. The mold surface temperature responses on both, the moving and the fixed mold half, were transiently recorded using Type K thermocouples. Polynomial models and response surfaces for characterizing the heating and cooling performance of the used RHCM systems were obtained. These models allow the prediction of the heating rate as well as the cooling speed at arbitrary temperature levels of cooling- and heating-temperatures.
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.
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