bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effect of structure modification on rheological properties of biodegradable poly(ester‐urethane)
Authors: Helminen Antti , Kylmä Janne , Tuominen Jukka , Seppälä Jukka V. 
Published: April 2004

AbstractBiodegradable lactic acid based poly(ester‐urethanes) (PEU) were polymerized and their structure and rheological properties were characterized. The polymerization process comprised two steps: lactic acid monomer was oligomerized to low molecular weight prepolymer, and this was then linked to high molecular weight PEU with chain extender, 1,6‐hexamethylene diisocyanate. The properties of PEU were modified by varying the amount of chain extender from 1.05:1 to 1.35:1 (NCO/OH ratio). The modification was mostly seen in the molecular weight distribution of the polymers, which was broadened from 2.2 to 3.5 as the amount of chain extender was increased. The telechelicity of the prepolymer was found to play an essential role in successful linking of the prepolymer units. In addition, the rheological properties of poly(ester‐urethane) were determined with capillary and dynamic rheometers. All PEU samples were pseudoplastic and broadening of their molecular weight distribution was accompanied by increased viscosity and complex viscosity at low shear rates and increased shear thinning. The temperature dependency of the measurement was pronounced. Rheological measurements also showed that PEU starts to degrade at 100°C and further rise in temperature increases the rate of degradation significantly.
Nature of contact between polymer and mold in injection molding. Part I: Influence of a non‐perfect thermal contact
Authors: Delaunay D. , Le Bot P. , Fulchiron R. , Luye J. F. , Regnier G. 
Published: April 2004

AbstractIn injection molding, the pressure in the cavity usually reaches the atmospheric pressure before the ejection, therefore the thermal contact between polymer and mold is modified. This paper aims to evaluate the nature of the thermal contact between the polymer and the mold during the holding and cooling phase. An experimental plate mold has been designed to study this phenomenon. Thermal sensors facing each other and pressure sensors have been set in the mold. An inverse method is used to determine the heat flux density crossing the polymer mold interface, and the mold surface temperature. Then, a second inverse algorithm allows to determine the temperature profile at the end of the filling and the time evolution of the thermal contact resistance (TCR). Finally, the polymer temperature distribution in the thickness is determined between the thermal sensors. The results of this study show that the TCR between the polymer and the mold is not negligible and not constant with time. The polymer temperature at the surface can be 20°C higher than the mold surface temperature. Moreover, asymmetric air gaps have been observed when cavity pressure becomes equal to atmospheric pressure, therefore asymmetric temperature profile in the thickness are generated.
Nature of contact between polymer and mold in injection molding. Part II: Influence of mold deflection on pressure history and shrinkage
Authors: Delaunay D. , Le Bot P. , Fulchiron R. , Luye J. F. , Regnier G. 
Published: April 2004

AbstractIn injection molding of thermoplastic parts, high hold pressures are set during the packing phase to generate a post‐filling, which compensates the shrinkage of polymer due to its cooling. The polymer pressure in mold cavity leads to a cavity deformation due to mold and machine compliance. Then, the increase in cavity thickness can modify the post‐filling and consequently the pressure history, the volumetric shrinkage and the part mass. The first goal of this paper is to present a simple method to locally determine mold rigidities: over‐packed slabs are injected and local deflections are determined from measurements of the local residual pressure, the local in‐plane shrinkages and the plate thickness. In the studied plate mold, which can be considered as stiff compared to some industrial molds, a rigidity of more than 1 μm/MPa has been measured close to the center of the plate. The second goal of this paper is to show the influence of mold deflection on dimensional properties. If the cavity thickness is small as for our 1‐mm‐thick plate mold, considering an infinitely rigid mold cannot do realistic predictions of polymer pressure history, volumetric shrinkages and part mass. Nevertheless, in‐plane shrinkage seems to be less affected by mold deflection. It means that the additional polymer mass due to mold deflection is mainly distributed in the part thickness.
Influence of low molecular weight ABS species on properties of PC/ABS systems
Authors: Greco Roberto , Iavarone Michele 
Published: April 2004

AbstractDifferential scanning calorimetry (DSC), scanning electron microscopy (SEM) rheological, mechanical and impact tests were performed on alloys consisting of polycarbonate (PC) and diverse acrylonitrile‐butadiene‐styrene copolymers (ABS), from which different amounts of low molecular (M) weight (W) species had been previously extracted in a Soxhlet apparatus by methanol. The influence on properties of the alloy composition and of the low MW species amount was investigated. The glass transition temperature (Tg) was found to be a useful probe for monitoring the migration trends of low MW ABS species towards the PC domains for the different alloys. In a morphological analysis it was found that the higher the ABS extraction extent the less the penetration of the etching agent into the surfaces of smoothed specimens. The blend rheological behavior showed that the capability of improving the PC processability, characteristic of commercial ABS's, was strongly lowered by the ABS extracted ones. The alloy modulus was higher when the ABS extraction extent was larger. The yield stress of alloys showed higher values than that of the PC one, particularly at low ABS content. The alloy composition, for which the impact resilience was at its maximum value, strongly depended on the extraction extent. All the above findings seem to suggest an increased adhesion between PC and ABS domains with enhanced extraction amounts of low MW species from the ABS component.
Modeling of the mechanical response and evolution of optical anisotropy in deformed polyaniline
Authors: Makradi A. , Ahzi S. , Gregory R. V. 
Published: April 2004

AbstractThe mechanical response under large deformation at room temperature of amorphous polyaniline (PANI) is simulated using an elastic‐viscoplastic model for large strain of glassy polymers. The evolution of optical anisotropy under deformation is also simulated by coupling the mechanical anisotropy due to molecular alignment to the optical properties. Several homogeneous deformation tests such as tension, compression and shear are considered. For the evolution of the mechanical anisotropy and the associated optical anisotropy, we compare the results from three network models. Our predicted results are compared to experimental observations and good agreement is found.
Coupled thermo‐mechanical analysis for plastic thermoforming
Authors: Song Yuhua , Zhang K. F. , Wang Z. R. , Diao F. X. , Yan Y. N. , Zhang R. J. 
Published: April 2004

AbstractAn FEM software ARVIP‐3D was developed to simulate the process of 3‐D plastic thermoforming. The coupled thermo‐mechanical analysis, thermal stress and warpage analysis for plastic thermoforming was carried out by means of this software. Rigid visco‐plastic formula was adopted to simulate the deforming process. During this process, the method of comparing velocity, time and area was adopted as the contact algorithm at different nodes and triangular elements. Sticking contact was assumed when the nodes become in contact with tool surface. The Arrhenius equation and the Williams equation were employed to ascertain the temperature dependence of material properties. In order to analyze the temperature field of plastic thermoforming, the Galerkin FEM code and the dynamic heat conduction boundary condition were adopted; latent heat and deformation heat were treated as dynamic internal heat sources. Based on the above, the model of coupled thermomechanical analysis was established. Assuming that the thermal deformation occurs under elastic conditions, the thermal stress and the warpage following the cooling stage were estimated. Experiments of plastic thermoforming were made for high‐density polyethylene (HDPE). An infrared thermometer was used to record the temperature field and a spiral micrometer was used to measure the thickness of the part. Results of numerical calculation for thickness distribution, temperature field and warpage were in good agreement with experimental results.
Multilayer method as a tool for depth dependent polymer film photodegradation studies
Authors: Nepotchatykh O. V. , Power J. F. 
Published: April 2004

AbstractA new polymer film destructive depth profiling protocol is presented for the analysis of photo‐ and thermally degraded thin films on the depth scale of less than 100 microns. The method, demonstrated here on thin films of poly(vinyl chloride) (PVC), provides a means of preparation of thin laminates of high optical quality comprised of many (>20) thin layers of individual thickness less than 15 microns. The constituent layers are fused together under appropriate pressure, temperature and time treatment to yield a film assembly of high optical quality that behaves like a uniform single layer during photodegradation exposure, but which may still be separated after treatment. Compared to previous techniques, this new method is relatively simple and non‐labor intensive. Film adhesive properties are controlled to within ± 5% Concentration depth profiles of polymer photolysis products were reconstructed by analyzing each of the separated layers using UV‐visible spectrophotometry. The continuity of these film assemblies with respect to mechanical properties, adhesive properties and the depth distribution of key photolysis reagents and products was confirmed using photothermal and reference microscopy techniques. Optical absorption depth profiles examined in UV‐ photodegraded poly(vinyl chloride) (PVC) films exhibited the classic dependencies expected in the presence of nitrogen and oxygen atmospheres.
Measurement of cohesive zone parameters in tough polyethylene
Authors: Pandya K. C. , Williams J. G. 
Published: April 2004

AbstractThe initiation, growth and final failure of the craze ahead of a crack tip generally controls the onset of crack growth in polyethylene, particularly in slow crack growth. In this research, circumferentially deep notched tensile specimens are used to analyze the evolution and failure of crazes in polyethylene under plane strain conditions. An experimental method is used wherein the traction‐separation behavior of the craze structure is measured directly in‐situ. Results yield a cohesive zone type analysis in which a two parameter traction curve, containing within it all information pertaining to local decohesion, fully describes the separation of the interface. Experimentally measured rate dependent trends in the work of separation (I) provide good discrimination between different grades of tough polyethylene at both high and quasi‐static test speeds, and highlight the exceptional long term behavior of one particular grade. The method also allows for the quantification of the long term behavior of each grade by more traditional stress‐time analysis.
Transesterification reactions in triphenyl phosphite additivated‐poly(ethylene terephthalate)/poly(ethylene naphthalate) blends
Authors: Dias Marcos L. , Silva Alexandre P. F. 
Published: April 2004

AbstractThe occurrence of transesterification reactions in poly(ethylene terephthalate) (PET)/poly(ethylene naphthalate) (PEN) blends prepared in presence of triphenyl phosphite (TPP) was investigated. When PEN was processed with TPP, which is a known chain extender for PET, chain extension reactions also took place. Torqueprocessing time curves obtained during preparation of 75/25 PET/PEN blends containing TPP, showed a build‐up profile followed by a fast decrease that was interpreted as chain extension between blend components and degradation due to phosphite residues formation, respectively. Although transesterification inhibition was expected, this type of reaction was not suppressed by TPP.
Healing of stress‐whitening in polyethylene and polypropylene at or below room temperature
Authors: Pae K. D. , Chu H.‐C. , Lee J. K. , Kim J.‐H. 
Published: April 2004

AbstractStress‐whitening occurs in many crystalline polymers when they are subjected to cold‐drawing at atmospheric pressure and at room temperature. The exact structure and morphology of stress‐whitening are still in contention, although it is widely believed that stress‐whitening is a combination of crazes and voids. The healing of stress‐whitening at room temperture may be divided into two stages: transient, which is a short time‐dependent and post‐transient. The post‐transient healing phenomenon involves a long time‐dependent or time‐independent healing. Stresswhitening in the post‐transient stage reaches a steady or permanent state. Healing of stress‐whitening in the post‐transient stage would occur when acted upon by an external agency, such as stress and temperature, or a combination thereof. A methodology has been developed to heal the permanent stress‐whitening at or below room temperature in HDPE and PP. The study involved the following procudure: tensile samples of HDPE and PP were cold‐drawn in an Inston testing machine at atmospheric pressure and room temperature to develop stress‐whitening; the stress‐whitened samples were subsequently, after days of rest, pulled in hydrostatic pressure environment at room temperature; the stress‐whitened section was partially or completely healed depending on the magnitude of the applied stress (or strain) and the intensity of hydrostatic pressure.
Morphological modeling of polymer solidification
Authors: Huang Tao , Kamal M. R. 
Published: April 2004

AbstractA physical model of semicrystalline polymer solidification is proposed, along with an outline of general theoretical aspects of morphological modeling. Computational modeling, based on the proposed envelop evolution equation associated with a primary nucleation model and the elastic energy equation of the lamellae director field, predicts the nucleation‐growth processes, domain patterns and internal lamellae organization of spherulitic structures in semicrystalline polymer solidification. Results of computer simulation are reported and compared with experimental observations.
Strain rate dependence of the work of fracture response of an amorphous poly(ethylene‐naphthalate) (PEN) film
Authors: Karger‐Kocsis J. , Czigány T. 
Published: April 2004

AbstractThe essential work of fracture (EWF) response of an amorphous film of high molecular weight poly(ethylene‐2, 6‐naphthalate) (PEN) was determined on tensileloaded deeply double‐edge notched (DDEN‐T) specimens at various deformation rates (v=1, 10 and 100 mm/min) at ambient temperature. The DDEN‐T specimens showed full ligament yielding (marked by a load drop in the force‐displacement curves) based on which the yielding was separated from the subsequent necking. The yielding related specific essential work of fracture (We,y) changed parallel with the yield strength (σy), whereas the critical crack tip opening displacement (ϵy, 0) remained practically constant in the v range studied. As a consequence, We,y(v) could well be estimated by the product of σy(v).ϵy,0. Necking occurred by cold drawing superimposed by some strain‐induced crystallization at the highest deformation rate. The necking‐related EWF terms strongly depended on the deformation (strain) rate. Based on previous results on amorphous PENs of various molecular weight (MW), it was argued that increasing deformation rate corresponds to decreasing MW and vice versa. This was reasoned by assuming that only a part of the entangled molecular chain participates in the load distribution under high strain rate conditions.
Time‐resolved light scattering and FTIR spectroscopic studies on blends of polypropylene grafted with maleic anhydride and zinc salt of sulfonated EPDM lonomer
Authors: Ha Chang‐Sik , Cho Young‐Wook , Cho Won‐Jei , Kim Youngkyoo , Inoue Takashi 
Published: April 2004

AbstractTime‐resolved light scattering and Fourier‐transform infrared (FTIR) spectroscopic studies were performed on blends of polypropylene‐g‐maleic anhydride (PPg‐MAH) and sulfonated EPDM ionomer neutralized with zinc cation (ZnSEPDM). The temperature exhibiting maximum crystalline growth rate (TG,max) decreased as ZnSEPDM contents were increased. The results of wide‐angle X‐ray diffraction also confirmed that the degree of crystallinity of PP‐g‐MAH decreased when the content of the ionomer was increased. A shift in the glass transition temperatures of both EPDM and PP phases in the blends was observed, confirming the enhanced miscibility between PP and EPDM. It was concluded from the FTIR spectroscopic studies that the enhanced miscibility is caused by a specific interaction between PP‐g‐MAH and ZnSEPDM.
Theoretical analysis of the devolatilizing performance of an intermeshing co‐rotating twin‐screw extruder with a type of square‐channel flighted element
Authors: Wang Ning He 
Published: April 2004

AbstractThe local film interfaces in the long vent section of an intermeshing, co‐rotating twin‐screw extruder (ICoTSE) with square‐channel flights (SFs) and the exposure time to the vapor phase were analyzed. A theoretical overall film‐interface geometry factor (OFIGFcal) was calculated from a new devolatilization (DV) model proposed previously by the authors, and the predictions were compared to the experimental results (OFIGFexp) for polystyrene/ethylbenzene (PS/EB). The OFIGF represents a measure of the devolatilization performance of the long vent section. The ratio of the experimental to the predicted apparent film interface areas was 5.5, which demonstrates the enhancing effect of the roughness and bubble‐forming behavior of the film interfaces on DV. The predicted concentrations of EB in the PS melt at the exit of the long vent section agreed well with experimental results.
Effect of supercritical carbon dioxide on morphology development during polymer blending
Authors: Elkovitch Mark D. , Tomasko David L. 
Published: April 2004

AbstractSupercritical carbon dioxide (scCO2) was added during compounding of polystyrene and poly(methyl methacrylate) (PMMA) and the resulting morphology development was observed. The compounding took place in a twin screw extruder and a high‐pressure batch mixer. Viscosity reduction of PMMA and polystyrene were measured using a slit die rheometer attached to the twin screw extruder. Carbon dioxide was added at 0.5, 1.0, 2.0 and 3.0 wt% based on polymer melt flow rates. A viscosity reduction of up to 80% was seen with PMMA and up to 70% with polystyrene. A sharp decrease in the size of the minor (dispersed) phase was observed near the injection point of CO2 in the twin screw extruder for blends with a viscosity ratio, ηPMMA/ηpolystyrene, of 7.3, at a shear rate of 100 s−1. However, further compounding led to coalescence of the dispersed phase. Adding scCO2 did not change the path of morphology development; however, the final domain size was smaller. In both batch and continuous blending, de‐mixing occurred upon CO2 venting. The reduction in size of the PMMA phase was lost after CO2 venting. The resulting morphology was similar to that without the addition of CO2. Adding small amounts of fillers (e.g. carbon black, calcium carbonate, or nano‐clay particles) tended to prevent the de‐mixing of the polymer blend system when the CO2 was released. For blends with a viscosity ratio of 1.3, at a shear rate of 100 s−1, the addition of scCO2 only slightly reduced the domain size of the minor phase.
Melt tearing and ovality in wire coating
Authors: Hade Aaron J. , Giacomin A. Jeffrey 
Published: April 2004

AbstractWe investigate how to avoid tearing, egg‐shaped cross sections or foldover of the polymer melt cone in tube coating of wire. We use an isothermal Newtonian model for the melt cone. We calculate the melt stress and the draw ratio balance, the parameter used in industry to avoid process problems. The stress calculations help us explain ovality and tearing. To help practitioners apply the results we provide examples.
Nonisothermal two‐dimensional film casting of a viscous polymer
Authors: Smith Spencer , Stolle Dieter 
Published: April 2004

AbstractA model is presented for simulating two‐dimensional, nonisothermal film casting of a viscous polymer. The model accommodates the effects of inertia and gravity, and allows the thickness of the film to vary across the width, but it excludes film sag and die swell. Based on the simulation results, three factors are shown to contribute to reducing neck‐in and promoting a uniform thickness: the self‐weight of the material, for low viscosity polymers; nonuniform thickness and/or velocity profiles at the die; and cooling of the film, especially when localized cooling jets are employed.
Overall numerical simulation of extrusion blow molding process
Authors: Tanifuji Shin‐Ichiro , Kikuchi Tsuyoshi , Takimoto Jun‐Ichi , Koyama Kiyohito 
Published: April 2004

AbstractThis paper focuses on the overall numerical simulation of the parison formation and inflation process of extrusion blow molding. The competing effects due to swell and drawdown in the parison formation process were analyzed by a Lagrangian Eulerian (LE) finite element method (FEM) using an automatic remeshing technique. The parison extruded through an annular die was modeled as an axisymmetric unsteady nonisothermal flow with free surfaces and its viscoelastic properties were described by a K‐BKZ integral constitutive equation. An unsteady die‐swell simulation was performed to predict the time course of the extrudate parison shape under the influence of gravity and the parison controller. In addition, an unsteady large deformation analysis of the parison inflation process was also carried out using a three‐dimensional membrane FEM for viscoelastic material. The inflation sequence for the parison molded into a complex‐shaped mold cavity was analyzed. The numerical results were verified using experimental data from each of the sub‐processes. The greatest advantage of the overall simulation is that the variation in the parison dimension caused by the swell and drawdown effect can be incorporated into the inflation analysis, and consequently, the accuracy of the numerical prediction can be enhanced. The overall simulation technique provides a rational means to assist the mold design and the determination of the optimal process conditions.
Novel variations in the microstructure of auxetic ultra‐high molecular weight polyethylene. Part 2: Mechanical properties
Authors: Alderson K. L. , Webber R. S. , Evans K. E. 
Published: April 2004

AbstractA highly fibrillar auxetic form of ultra‐high molecular weight polyethylene (UHMWPE) has been fabricated by using a powder processing route comprising two stages—sintering and extrusion. The resulting material has a low density (720 kg/m3) and low flexural strength and modulus (up to 6 MPa and 62 MPa, respectively) but much larger negative Poisson's ratio when compared with auxetic UHMWPE fabricated using an additional preliminary compaction stage followed by sintering and extrusion. The effects of die geometry on the mechanical properties of this material are examined. The indentation resistance and ultrasonic attenuation of the novel, highly fibrillar auxetic material were measured, and it was found that the indentation resistance was enhanced only at very low loads (i.e. 5 N and 10 N) when compared with conventionally processed UHMWPE. After this, the lack of structural integrity of the material outweighed the benefits of its being auxetic. However, the ultrasonic attenuation was found to be extremely good, and much enhanced over conventionally processed UHMWPE, with the attenuation coefficient being at least 47 dB/cm, compared with 8 dB/cm.