bluuebunny/crossref_metadata_2025_split huggingface dataset:
Plasticating single‐screw extrusion of amorphous polymers: Development of a mathematical model and comparison with experiment
Authors: Han Chang Dae , Lee Kee Yoon , Wheeler Norton C. 
Published: April 2004

AbstractA mathematical model was developed for plasticating single‐screw extrusion of amorphous polymers. We considered a standard metering screw design. By introducing a ‘critical flow temperature’ (Tcf), below which an amorphous polymer may be regarded as a ‘rubber‐like’ solid, we modified the Lee‐Han melting model, which had been developed earlier for the extrusion of crystalline polymers, to model the flow of an amorphous polymer in the screw channel. Tcf is de facto a temperature equivalent to the melting point of a crystalline polymer. The introduction of Tcf was necessary for defining the interface between the solid bed and the melt pool, and between the solid bed and thin melt films surrounding the solid bed. We found from numerical simulations that (1) when the Tcf was assumed to be close to its glass transition temperature (Tg), the viscosity of the polymer became so high that no numerical solutions of the system of equations could be obtained, and (2) when the value of Tcf was assumed to be much higher than Tg, the extrusion pressure did not develop inside the screw channel. Thus, an optimum modeling value of Tcf appears to exist, enabling us to predict pressure profiles along the extruder axis. We found that for both polystyrene and polycarbonate, Tcf lies about 55°C above their respective Tgs. In carrying out the numerical simulation we employed (1) the WLF equation to describe the temperature dependence of the shear modulus of the bulk solid bed at temperatures between Tg and Tcf, (2) the WLF equation to describe the temperature dependence of the viscosity of molten polymer at temperatures between Tcf and Tg + 100°C, (3) the Arrhenius relationship to describe the temperature dependence of the viscosity of molten polymer at temperatures above Tg + 100°C, and (4) the truncated power‐law model to describe the shear‐rate dependence of the viscosity of molten polymer. We have shown that the Tg of an amorphous polymer cannot be regarded as being equal to the Tm of a crystalline polymer, because the viscosities of an amorphous polymer at or near its Tg are too large to flow like a crystalline polymer above its Tm. Also conducted was an experimental study for polystyrene and polycarbonate, using both a standard metering screw and a barrier screw design having a length‐to‐diameter ratio of 24. For the study, nine pressure transducers were mounted on the barrel along the extruder axis, and the pressure signal patterns and axial pressure profiles were measured at various screw speeds, throughputs, and head pressures. In addition to significantly higher rates, we found that the barrier screw design gives rise to much more stable pressure signals, thus minimizing surging, than the metering screw design. The experimentally measured axial pressure profiles were compared with prediction.
An extrusion system for the processing of microcellular polymer sheets: Shaping and cell growth control
Authors: Baldwin Daniel F. , Park Chul B. , Suh Nam P. 
Published: April 2004

AbstractA new processing system for the extrusion of microcellular polymer sheets is presented. Specifically, the detailed design of a shaping and cell growth control system is discussed in the context of an overall extrusion system design with particular emphasis on the system level functional requirements of cell nucleation, cell growth, and shaping. The principle of the basic extrusion system design is to shape a nucleated polymer/gas solution flow under pressure and accurate temperature control. In this way, the initial cell growth is controlled so as to prevent degradation of the nucleated cell density during shaping. Two foaming die designs for satisfying the initial shaping and cell growth requirements are presented. Critical experiments are then presented which verified the concept of shaping a nucleated polymer/gas solution. Moreover, these experiments demonstrated the feasibility of the overall microcellular polymer sheet extrusion system design.
A microcellular processing study of poly(ethylene terephthalate) in the amorphous and semicrystalline states. Part II: Cell growth and process design
Authors: Baldwin Daniel F. , Park Chul B. , Suh Nam P. 
Published: April 2004

AbstractMicrocellular semicrystalline polymers such as poly(ethylene terephthalate) show great promise for engineering applications because of their unique properties, particularly at higher densities. Recent studies have shown that some high density microcellular polymers have longer fatigue lives and/or equivalent strengths relative to the neat polymer. Relatively few microcellular processing studies of semicrystalline polymers have been presented. In general, semicrystalline polymers are relatively difficult to microcellular process compared to amorphous polymers. In this paper, the microcellular processing of poly(ethylene terephthalate) in the amorphous and semicrystalline states is studied in order to quantify the processing differences. Particular emphasis is given to the cell growth stage of microcellular processing comparing the processing characteristics of semicrystalline and amorphous PET. Based on the results of this study, a number of critical process parameters are identified. Another goal of this analysis is to derive robust microcellular process design strategies for the amorphous and semicrystalline materials. Process design strategies are given for both semicrystalline and amorphous PET.
Online pattern‐based part quality monitoring of the injection molding process
Authors: Woll Suzanne L. B. , Cooper Douglas J. , Souder Blair V. 
Published: April 2004

AbstractThe quality of injection molded parts is currently monitored in the plant using techniques that focus on the statistical analysis of discrete data and, in particular, peak values. This paper presents an alternative online technique for part quality monitoring that focuses on the analysis of complete data patterns. Specifically, this paper discusses the application of artificial neural networks (ANNs) as part quality monitoring tools. The method of approach is to train a back propagation network (BPN) to associate part quality with the corresponding data pattern produced during injection. In Part I of this work, the data pattern consists of a series of discrete values and the part quality measure is defined as part weight. In Part II, the data pattern is the measurement profile observed from a pressure sensor placed in the mold cavity and the part quality measure is defined as part length. Results show that ANNs are successful in predicting part quality based on data patterns when an entire sensor profile is analyzed. Furthermore, demonstrations show that the approach is superior in predicting part quality when compared to statistical techniques now widely practiced by the injection molding process industry.
The development of flow instabilities during the injection molding of multicomponent resins
Authors: Hobbs S. Y. 
Published: April 2004

AbstractIn this study, several blends of BPA polycarbonate and acrylonitrile/butadiene/styrene (ABS) resins having different gloss levels and microscopic surface roughness values were injection molded over a range of injection rates. Changes in surface appearance were monitored by visual observation, optical microscopy, and electron microscopy. The onset of unstable flow was marked by the development of regularly spaced surface patches on the molded parts. The surface irregularities were found to be strikingly similar to those produced by dragging crosslinked rubbers across hard surfaces. It was observed that blends having higher surface roughness values had lower coefficients of friction and exhibited unstable flow at lower stresses than compositions with smoother surfaces. The data were used to quantify the rheological parameters and surface characteristics defining an acceptable molding envelope for these materials.
Melt blends of αSAN with a phenoxy
Authors: Kim Byung Kyu , Choi Chi Hoon 
Published: April 2004

AbstractMelt blends of poly(α‐methyl styrene‐co‐acrylonitrile) (αSAN) with a phenoxy were prepared using a Brabender Plasticorder. Morphological, thermal, rheological, and mechanical properties of the blends were studied. DSC (differential scanning calorimetry) measurements showed two Tg (glass transition temperature) of the blends. Tg of αSAN decreased by 5 to 7°C, whereas that of phenoxy increased slightly. Melt viscosity measured using an RDS (Rheometrics dynamic spectrometer) showed a small negative and relatively large positive deviation in αSAN‐ and phenoxy‐rich blends, respectively. Transverse views of SEM (scanning electron microscopy) micrographs of the fractured surfaces again showed two phases, regardless of composition. Traces of full‐out upon fracture were seen in αSAN‐rich but not in phenoxy‐rich blends, indicating stronger interfacial adhesion in phenoxy‐rich blends. Longitudinal views of the SEM micrographs showed highly elongated structure of disperse phases (30 to 70% of phenoxy), especially when phenoxy forms dispersed phase, resulting in finer and well developed phenoxy fibrils. Tensile modulus and strengths showed a negative deviation in αSAN and positive deviation (strength) or additivity (modulus) in phenoxy‐rich blends.
Prediction of optimal preform thickness distribution in blow molding
Authors: Lee D. K. , Soh S. K. 
Published: April 2004

AbstractA finite element optimization method is presented that determines the optimal thickness profile of a preform for a blow‐molded part having the required wall thickness distribution. The optimization method is based on a method of feasible directions and the design variables are thicknesses of finite elements. The step size is determined by using a Brent 1‐dimensional minimization method. Two methods for determining feasible directions are compared. A finite element model is formulated based on the thin membrane approximation, which relates the preform wall thickness distribution to the wall thickness distribution in the blow‐molded part. Triangular or conical frustra elements are used to describe deformed shapes of the preform for 2‐dimensional axisymmetric deformations. An incompressible nonlinear elastic constitutive model describes the material response. The accuracy of the finite element model used is evaluated by comparing the model predictions to published experimental data and computer simulations.
Basic studies of blow molding of talc‐thermoplastic compounds
Authors: Suh Chang Ho , White James L. 
Published: April 2004

AbstractAn experimental study of the blow molding of talc‐polyethylene and talc‐polypropylene compounds is presented. These compounds are found not to exhibit zero shear viscosity but rather yield stresses, below which there is no flow. The annular swell of the compositions is greatly reduced compared to the neat thermoplastics, but extrusion sag is minimized. Blow molded bottles of talc‐thermoplastic compounds were found to have much greater thickness uniformity than blow molded neat polyolefins. The talc particles were determined, by X‐ray diffraction, to be oriented with the flake surfaces parallel to the mold surface or equivalently to the bottle surface.
Reactive processing of thermoset/thermoplastic blends: A potential for injection molding
Authors: Fujiwara Hiroaki , Kim Bong Sup , Inoue Takashi 
Published: April 2004

AbstractPoly(2,6‐dimethyl‐1,4‐phenylene ether) (PPE) is an engineering plastic with high heat distortion temperature. Melt processing of neat PPE is usually accompanied with thermal degradation. The degradation problem is solved by blending with polystyrene to reduce the processing temperature. We propose an alternative using triallylisocyanurate (TAIC). TAIC is a low viscosity liquid that can be cured by peroxide, e.g. α,α′‐bis(t‐butylperoxy‐m‐isopropyl)benzene (PBP), to provide a thermoset. The PPE/TAIC mixture was shown to have the upper critical solution temperature (UCST) type phase behavior. At the single‐phase regime above UCST and below the cure temperature (∼180°C for PBP), the mixture had a low viscosity, less viscous than a conventional thermoplastic such as PC and PP. That is, a nice window for injection molding was available, e.g., at 100°C to 160°C for a 50/50 blend. After injecting into a hot mold set at cure temperature, the blend cured in a short time (∼80% conversion in 5 min). Then the molded and partly cured material kept its shape and dimensions during post‐cure in a hot chamber at higher temperature (e.g. 250°C). Using transmission electron microscopy and dynamic mechanical analyses, it was shown that the cured blend had a bicontinuous two‐phase structure with periodic spacings of ∼30 nm, suggesting a structure formation via a spinodal decomposition driven by the increase in molecular weight of TAIC during cure. The cured material showed excellent flexural strength and high chemical resistance.
Interphase and compatibilization of polymer blends
Authors: Ajji Abdellah , Utracki L. A. 
Published: April 2004

AbstractPolymer blends are mixtures of at least two polymers and/or copolymers comprising more than 2 wt% of each macromolecular component. Most blends are immiscible, and need to be compatibilized. The compatibilization must not only ensure improvement in performance, but it must be reproducible, insensitive to forming stresses and repeated processing. This review on compatibilization of polymer blends is prepared in three parts: (i) description of the interface/interphase; (ii) compatibilization by addition of a copolymer (with a special emphasis on the use of block copolymers); and (iii) reactive compatibilization.
Microstructural characterization of polymer blends
Authors: Vesely D. 
Published: April 2004

AbstractMicroscopy techniques for direct visualization of phases in polymer blends are reviewed. Light microscopy is suitable for immiscible blends and contrast techniques include polarized light, phase contrast, differential interference contrast, and fluorescence. Each technique has an application for a particular polymer system. Scanning electron microscopy is used for study of surface morphology and contrast can be enhanced by electron beam damage or by chemical etching. Cutting often provides sufficient contrast, but surface preparation by fracture or by solvent extraction must be used with caution. Surface carbon replica is a good alternative that provides better resolution and contrast. A new technique of selective swelling will be discussed. Transmission electron microscopy has very good resolution and can thus be used for the study of very fine dispersion in miscible blends. Contrast can be enhanced electronically or by staining of pre‐irradiated samples. It will be shown that the latter, together with mass loss measurements, can provide some new and unique information on the polymer blend system. Crystallographic studies are limited by the beam damage. It is nevertheless possible with some specialized techniques (STEM and microdiffraction) to obtain several dark field images and diffraction patterns from one area of highly beam sensitive polymers.
Polymer blends with a crystallizable diblock copolymer: Thermal properties and phase behavior
Authors: Kammer H. W. , Kummerloewe C. 
Published: April 2004

AbstractWe report on the thermal behavior of polymer blends comprising a block copolymer and random copolymers of styrene and acrylonitrile (SAN). The block copolymer constituents are ε‐caprolactone (CL) and a carbonate. Melting as well as crystallization behavior of the blocks are strongly influenced by addition of amorphous SAN, which is miscible only with PCL block. Blends under discussion can undergo different phase changes as macro‐ and microphase separation and crystallization. Hence, morphology formation is controlled by different transitions and even a cooperative interplay between them. Phase behavior of the blends is discussed and correlated with results of morphological studies.
Prediction of dispersed phase drop diameter in polymer blends: The effect of elasticity
Authors: Ghodgaonkar Parag G. , Sundararaj Uttandaraman 
Published: April 2004

AbstractThis paper discusses the prediction of the dispersed phase drop diameter in polymer blends considering the viscoelastic properties of polymers. The prediction is based on a simple force proportionality. Polymers are viscoelastic, and thus the elasticity of the matrix and the elasticity of the dispersed phase affect the drop size. The forces that deform a polymer droplet in a polymer matrix are the shear forces, ηmγ, and the matrix first normal stress, T11,m. This deformation is resisted by the interfacial forces, 2 Γ/D and the drop's first normal stress, T11,d. As a first approximation, the forces were balanced to predict the particle size in polymer blends. The diameter of the dispersed phase was predicted reasonably well for several systems at different operating conditions. It was observed for some systems (PS/PP, PS/EPMA, PS/PA330) that, as the shear rate increased, the diameter of the dispersed phase initially decreased. At a critical shear rate, the diameter reached a minimum value, and beyond it, the diameter increased with shear. This critical value was found to be between 100 to 162.5 s−1 for a PS/PP system. The force balance predicts this minimum drop diameter at a similar critical shear rate. The specific energy input (the amount of energy input into the blend) could not explain the phenomenon of a minimum drop diameter with increase in shear. This minimum is not observed for the high concentration systems, such as the 20% PP dispersed in PS, since the effects of coalescence become significant. In reactive blends, the predicted drop diameter was closer to the experimentally determined diameter, and there was less variation in diameter with changes in shear rate.
Polymer blends for enhanced asphalt binders
Authors: Ait‐Kadi Abdellatif , Brahimi Brahim , Bousmina Mosto 
Published: April 2004

AbstractStraight asphalt binders have been modified by addition of both high‐density polyethylene (HDPE) and a blend of HDPE and ethylene‐propylene‐diene‐monomer (EPDM). The blend composition was fixed to 90/10 HDPE/EPDM to illustrate the possibility of adapting the polymer to be added to the asphalt binder for specific end‐use applications. Linear viscoelastic properties of unmodified and polymer modified asphalts at concentrations ranging from 1 to 5 wt% were studied before and after Thin‐Film Oven Test (TFOT) aging. Temperatures ranging from −15°C to 60°C were considered. Standard tests such as Ring‐and‐Ball softening point, Fraass breaking point and TFOT aging were also performed on the whole set of samples. It was found that addition of rubber‐modified polyethylene (HDPE/EPDM) to the straight asphalt results in materials with enhanced overall properties, and most important, dispersed phase much more stable than the equivalent HDPE modified asphalt, mainly before TFOT aging. Good results were obtained for 1% HDPE/EPDM samples. Optimum design is, however, required for the desired properties to be obtained.
Role of polymer transparency and temperature gradients in the quantitative measurement of process stream temperatures during injection molding via IR pyrometry
Authors: Lai Gwan‐Ywan , Rietveld Jeroen X. 
Published: April 2004

AbstractThe accurate and precise measurement of process stream temperatures during injection molding can be difficult, since the cyclic operation results in spatial and temporal variations of the stream temperature. This paper examines the application of a spectral infrared (IR) pyrometer to monitor the cooling of a polymer melt within the mold cavity during a typical injection molding cycle. An outline for interpreting the radiation signal collected with the IR pyrometer is presented. The discussion includes theoretical aspects as well as experimental results. The theoretical approach accounts for the polymer transparency (attenuation behavior) at the spectral wavelength of the pyrometer and also for the temperature gradient within the polymer, thereby establishing the concept of a critical depth for a given pyrometer/polymer combination. The final analysis reveals good agreement between the predicted and measured results for the transient cooling conditions of the polymer within the mold cavity. Depending on the degrees of polymer transparency used in the theoretical prediction, the deviation between the measured and predicted transient bulk temperatures after mold filling (during the mold cooling stage) varies from ±2°K to ±9°K.
Thermal stability of a novel poly(ether ether Ketone Ketone) (PK99)
Authors: Abate L. , Calanna S. , Pollicino A. , Recca A. 
Published: April 2004

AbstractThe degradation of PK99 was studied by heating the polymer in both isothermal and dynamic conditions under nitrogen flow and in a static air atmosphere. In both environments this polymer's thermal stability exceeded that of PEEK. The dynamic experiments showed that in both nitrogen and air atmospheres the polymer degraded in two stages with formation of the same residue, which was quite stable under nitrogen, while almost completely burned in air. Good agreement was observed with the isothermal experiments. Apparent activation energy values were evaluated. The double linear relationships obtained by the Kissinger equation suggested a complex degradation process.
Modifying the tait equation with cooling‐rate effects to predict the pressure–volume–temperature behaviors of amorphous polymers: Modeling and experiments
Authors: Chang R. Y. , Chen C. H. , Su K. S. 
Published: April 2004

AbstractCooling‐rate effects play an important role in polymer processing because the materials experience rapid cooling when transferring from melt states to solid states. The traditional Tait equation has been used widely in representing the volumetric behaviors of polymers as a function of temperature and pressure, but not of cooling rate. Based on the dependence of glass‐transition temperature on cooling rate (i.e., θ = dTg/d log ∣ q ∣), the volumetric dependence on cooling rate is employed in this work to modify the traditional Tait P–V–T equation to become a time‐dependent P–V–T model. The physical meanings of the traditional Tait equation parameters are interpreted and, thereby, parameters in the new model are derived according to the material constant θ. The controlled cooling‐rate measurements of polymeric volumetric data have been performed in this work to verify the validity of the proposed model. Additionally, the material parameter θ, calculated from the measured data of polystyrene (PS) (Chi‐Mei PG‐33) in this work, equals 2.85 K, which is close to 2.86 K calculated from the Greiner‐Schwarzl work. Furthermore, a comparison of the predicted results with the experimental data both in this work and from literature is discussed under different pressures and various cooling rates. The results have indicated that the proposed non‐equilibrium P–V–T model closely correlates with experimental data.