bluuebunny/crossref_metadata_2025 huggingface dataset:
Synthesis and properties of fluoro‐polyetherimides
Authors: Vora Rohitkumar H. , Goh Suat Hong , Chung Tai‐Shung
Published: April 2004

A series of amorphous fluoro‐polyetherimides based on 2,2′‐bis(3,4‐dicarboxyphenyl) hexafluropropane dianhydride (6FDA) and di‐ether‐containing diamines 4,4′‐bis(3‐aminophenoxy)diphenyl sulfone (m‐SED), 4,4′‐bis(4‐aminophenoxy)diphenyl sulfone (p‐SED), 4,4′‐bis(4‐aminophenoxy)diphenyl propane (BPADE) were synthesized. These melt processable polyetherimide polymers fromp‐SED and BPADE showed excellent electrical properties. The dielectric constants, 2.74 and 2.65 at 10 MHz respectively, are lower than commercially available polyetherimide ULTEM® 1000, and polyimide Kapton® H films. In addition, we found that trifluoromethyl groups‐containing polyimides not only show extraordinary electrical properties, but they also exhibit excellent long‐term thermo‐oxidative stability and reduced water absorption relative to non‐fluorinated polyimides. The weight retention of these fluoro‐polyetherimides at 315°C for 300 h in air varies from 93% to 98%. Whereas, their moisture absorption at 100 RH at 50°C was in the range of 0.3% to 1.05%, which is much lower than those of Ultem 1000 and Kapton H. In the case of fluoro‐polyetherimides fromp‐SED andm‐SED (paraandmetaisomers) diamines with ‘ether’ and sulfonyl (‐SO2‐) spacer groups, thed‐spacing andTgvalues decreased from 4.72Å to 4.56Å and 293°C to 244°C respectively. Similarly, the transparency of these polymer films (in the range of 80% to 90%) at 500 nm solar wavelength was higher than Ultem 1000 and Kapton H.
Prediction of the nonlinear poisson function using large volumetric strains estimated from a finite hyperelastic material law
Authors: Kakavas P. A.
Published: April 2004

The aim of this study is to evaluate the transverse strain of hyperelastic solids as a function of its longitudinal using a special constitutive equation for compressible hyperelastic materials. In addition, the nonlinear dependence of the Poisson ratio on longitudinal strain was derived. Experimental data from EPDM elastomers subjected to uniaxial tension were used in order to determine the material parameters, which are incorporated in the constitutive law.
A visual barrel system for study of reciprocating screw injection molding
Authors: Gao Furong , Jin Zhiming , Chen Xi
Published: April 2004

A “visual” barrel system has been developed to promote the understanding of polymer behavior in a reciprocating screw injection molding machine. This system allows the dynamic status of the polymer inside the injection barrel to be conveniently visualized though photography and video recording, and the corresponding material conditions can be measured via a computerized data acquisition system. High density polyethylene (HDPE), a commonly used thermoplastic, is chosen to demonstrate the polymer melting behavior in injection molding. Effects of processing conditions on the melting behavior are analyzed, suggesting that the modeling of the plastication phase should not be treated simply as an extrusion process. The system, therefore, can not only assist in the understanding of the process but also can be used to verify quantitatively the modeling and optimization of an injection molding system.
Rubber modification of low temperature cure cyanate ester matrices and the performance in glass fabric composites
Authors: Hayes Brian S. , Seferis James C. , Parker George A.
Published: April 2004

Low temperature cure cyanate ester resin systems were developed and modified with epoxy‐terminated butadiene acrylonitrile rubber (ETBN) and impregnated into woven glass fabric. Mode I and mode II interlaminar fracture toughness values of the cured laminates were evaluated as a function of rubber concentration. Mode I fracture toughness increased to almost twice that of the unmodified system, while mode II fracture toughness remained essentially unchanged. Composite samples were subjected to aging experiments in water and the absorption/desorption behavior was investigated as was the effect on thermal performance. The presence of rubber was found to reduce the rate of matrix deterioration but also caused a substantial increase in water uptake. It was found that although the addition of rubber to the matrices decreased the unconditioned (dry) Tg all specimens showed the same reduction in Tg, after equilibrium water absorption.
On the growth of a non‐ideal gas bubble in a solvent‐polymer solution
Authors: Favelukis Moshe , Zhang Zhihui , Pai Vivek
Published: April 2004

A model for the growth of an ideal and a non‐ideal spherical gas bubble in a quiescent viscous liquid is presented. The growth of the bubble is assumed to be controlled by both mass transfer and viscous forces. Using the integral method, the differential momentum and binary mass balances were transformed into ordinary differential equations, which were numerically solved. Some analytical solutions for simple cases are also presented. The relevance of this work to the process of polymer melt devolatilization is discussed.
Morphology of injection molded modified poly(phenylene oxide)/polyamide‐6 blends
Authors: Son Younggon , Ahn Kyung Hyun , Char Kookheon
Published: April 2004

The morphology of injection molded poly(phenylene oxide)/polyamide‐6 blends was investigated. A distinct skin layer, subskin layer, and core region were found across the part thickness, and the morphology of the skin layer was clearly observed. The shape and size of the dispersed phase depended on the position across the part thickness and the viscosity ratio of the component polymers. For low viscosity ratios, small and large particles coexisted in the subskin layer, implying that both coalescence and breakup of the dispersed phase occurred in that layer. For high viscosity ratios, an intermediate zone, in which little deformation of the dispersed phase occurred, was found between the skin layer and the subskin layer. These findings are expected to help foster understanding of the mechanism of morphology evolution during the filling and cooling stages of the injection molding process.
Failure mechanisms in stereolithography injection molding tooling
Authors: Palmer A. E. , Colton J. S.
Published: April 2004

Stereolithography tooling is a form of rapid tooling that has been used to injection mold limited runs of prototype parts. However, the process is not well understood and tooling life for fine mold features is difficult to predict. Injection molding processing conditions and feature geometry affect the number of parts that can be made before a mold fails. To study the effects of feature geometry, general purpose polystyrene parts were injection molded in molds made of DSM Somos 7110 stereolithography resin. The ACES build style was used, and no polishing was performed on the mold. The experimental results were compared with theoretical models developed for the two failure mechanisms for raised features in a stereolithography mold—failures during injection due to the flow pressure of the injected polymer; and failures during ejection, whereby the part pulled out a feature of the mold. Injection failures occurred in taller mold features due to the force of flow and the feature's geometry. Ejection failures occurred in the shorter features when the stress from the ejection force (distributed over the bond area) exceeded the yield strength of the mold material. Models were developed to predict the number of parts that a mold could make before mold features break off and were validated through experimental results.
Mechanical and viscoelastic properties of semi‐interpenetrating polymer networks of poly(vinyl chloride)/thermosetting resin blends
Authors: Pittman Charles U. , Xu Xiaoming , Wang Lichang , Toghiani Hossein
Published: April 2004

Semi‐interpenetrating polymer networks (SIPNs) of PVC/thermoset were prepared by premixing porous, 150 μm diameter particles of PVC and a small quantity (from 5 to 15% by weight) of a single thermosetting liquid preresin from one of five types (e.g. methylene bis‐phenyl diisocyanate (MDI), oligomeric MDI isocyanates (PAPI), toluene diisocyanate (TDI) prepolymer, epoxy, and vinyl ester resins, respectively). Two roll milling of these mixtures was followed by hot‐press curing. Mechanical testing indicated that most of these blends exhibited increased tensile, impact, and flexural strengths. The strength increments were greater when going from 0 to 5% thermoset content than when going from 5 to 10% or 10 to 15% thermoset. In many cases, increasing thermoset content from 10 to 15% gave slightly decreased or unchanged tensile, impact, and flexural strengths. This behavior is in accord with a “thermoset dilution effect” in PVC. Most of these SIPN blends exhibited a tan δ peak temperature lower than that for pure PVC in the glass transition region. The tan δ peak temperatures were progressively lowered as the amounts of thermoset increased. Also, a single distinct peak existed in the E″ curves for most of the blends. Only the PVC/epoxy (90/10) blend showed two peak maxima in E″ vs. temperature curves. All blends exhibited peak E″ values at a lower temperature than those of PVC which had been exposed to the same processing temperatures. These observations seem to rule out the presence of large domains of PVC, which are phase‐separated from PVC/thermoset SIPN, and pure thermoset domains. A substantial amount of the added thermoset appears to exist in SIPN type phases in these five blend types.
Cure kinetics and properties of epoxy/dicyanate blends
Authors: Kim Dae Su , Shin Ju Ho
Published: April 2004

The cure behavior and properties of epoxy/dicyanate blends containing a stoichiometric amount of an amine curing agent for epoxilde groups were investigated as a function of blend composition. Differential scanning calorimetry (DSC) was used to investigate the dynamic and isothermal cure behavior of the blends. The cure rate of the blend increased with increasing dicyanate content. A second order autocatalytic reaction mechanism described the cure kinetics of the blends. The kinetic parameters were determined by fitting the dynamic DSC data to the model kinetic equation. The k10 and E1 values were mainly affected by the change of dicyanate content. The glass transition temperature of the blend decreased with increasing dicyanate content. The thermal decomposition characteristics of the blends were investigated by thermogravimetric analysis (TGA). Dynamic mechanical analysis (DMA) and thermal mechanical analysis (TMA) were used to investigate the mechanical properties of the blends. With increasing dicyanate content, the cure rate increased but the thermal and mechanical properties of the cured blends were not improved.
Temperature dependence of work of fracture parameters in polybutylene terephthalate (PBT)
Authors: Hashemi S.
Published: April 2004

Essential work of Fracture (EWF) analysis was used to study the effect of temperature on fracture toughness of PBT film. Using Double Edge Notched Tension (DENT) specimens, it was found that between +25°C and +80°C, the specific essential work of fracture,we, of PBT film is independent of temperature, having an average value of 33.40 kJ/m2. Thewevalue was reduced to 27.51 kJ/m2as temperature was raised to 100°C. It is demonstrated that both specific essential (we) and non‐essential work of fracture (βwp) terms can be partitioned into two components, one linked to yielding (we,yand βywp,y) and the other to necking/tearing (we,n tand βntwp,nt), of the ligament region. The essential terms,we,yandwe,nt, were lowest at 100°C, having values of 9.14 kJ/m2and 18.57 kJ/m2, respectively, compared to 14.83 kJ/m2and 19.17 kJ/m2obtained at 25°C. As for non‐essential work tems, it was found that βywp,ydecreased with increasing temperature, whereas change in βntwp,ntand βwpvalues was dependent on the temperature range being considered.
Efficient mixing of polymer blends of extreme viscosity ratio: Elimination of phase inversion via solid‐state shear pulverization
Authors: Furgiuele Naomi , Lebovitz Andrew H. , Khait Klementina , Torkelson John M.
Published: April 2004

A novel, continuous process, solid‐state shear pulverization (S3P), efficiently mixes blends with different component viscosities. Melt mixing immiscible polymers or like polymers of different molecular weight often requires long processing times. With a batch, intensive melt mixer, a polyethylene (PE)/polystyrene (PS) blend with a viscosity ratio (low to high) of 0.019 required up to 35 min to undergo phase inversion. Phase inversion is associated with a morphological change in which the majority component, the high‐viscosity material in these blends, transforms from the dispersed to the matrix phase, and may be quantified by a change from low to high mixing torque. In contrast, such blends subjected to short‐residence‐time (∼3 min) S3P yielded a morphology with a PS matrix and a PE dispersed phase with phase diameters ≤ 1 μm. Thus, S3P directly produces matrix and dispersed phases like those obtained after phase inversion during a melt‐mixing process. This assertion is supported by the similarity in the near‐plateaus in torque obtained in the melt mixer at short times with the pulverized blend and at long times with the non‐pulverized blend. The utility of S3P to overcome problems associated with melt mixing like polymers of extreme viscosity ratio is also shown.
Rheological behavior of a polymerically stabilized latex for use in water‐borne coatings
Authors: Shay Jennifer S. , English Robert J. , Khan Saad A.
Published: April 2004

A unique urethane linkage that permits chemical grafting of poly(ethylene oxide) (PEO) linear chains to the surfaces of polystyrene (PS) latex particles has been developed. Chemically grafting the functionalized hydrophilic PEO macromers to the PS particle surface allows the latex to be polymerically stabilized in a water‐based medium. Advantages of the urethane linkage include the high yield of the macromer synthesis and the hydrolytic stability of the final latex. Rheological experiments are used to examine both processing behavior and interparticle interactions for latex systems with different amounts of grafted PEO. Dynamic rheological experiments reveal that, at high macromer concentrations, the grafted PEO layer is effective in shielding the attractive interactions of the core PS particles that lead to flocculation. However, at low macromer concentrations, strong interactions are seen even at low particle weight fractions, indicating the presence of a flocculated system. Steady shear rheological evaluations show that the latex systems possessed suitable flow behavior for coating applications, even at relatively high particle weight fractions. Experimental steady shear data is utilized in conjunction with the Krieger‐Dougherty equation to determine the size of the PEO stabilizing layer. The stabilizing layer thickness decreases as particle concentration increases, indicating a compressible system. Finally, the relationship between the strength of interparticle interactions and PEO graft density is gauged from the dependence of the power‐law exponent of the elastic modulus on particle concentration.
Modeling of molecular weights in industrial autoclave reactors for high pressure polymerization of ethylene and ethylene‐vinyl acetate
Authors: Sarmoria C. , Brandolin A. , López‐Rodríguez A. , Whiteley K. S. , Fernández B. Del Amo
Published: April 2004

We have incorporated mass balances of monomer, radical and polymer species to a previously developed mixing model for high pressure autoclave polymerization reactors. The customary quasi steady state approximation is not used, and the method of moments is used to simplify the mass balance calculations. The resulting moment model is able to calculate conversions, average molecular weights, long chain branching and melt flow indexes at any point in the reactor. It may also calculate concentration and temperature profiles along the reactor. Results for two base cases are presented in detail. Model predictions were compared with experimental data obtained at the industrial reactor; excellent agreement was obtained. The moment balance equations are presented in a modular way so that they may be easily adapted to be used with any other mixing model for this type of reactor.
Thermal cycling of plastics—relaxation and set in polycarbonate and polypropylene
Authors: Fesko Donald G.
Published: April 2004

The residual stress state or the amount of permanent set as a result of thermal cycling a plastic specimen white it is restrained can be estimated by a simple model using the thermal expansion coefficient, modulus vs. temperature data, stress relaxation data and knowing the time spent at elevated temperature. This offers the opportunity to model the end result of thermal cycling of plastic components by finite element analysis (FEA) without resorting to a viscoelastic FEA. The method combines the developed thermal strain with the relaxation taking place at the elevated temperature for the elapsed time and assumes the set is frozen in on cooling. Experimental data for polycarbonate and polypropylene show the method to be a good approximation. Data also show that it works for multiple cycles by simply treating the accumulated time at elevated temperature.
Polystyrene microcellular plastic generation by quick‐heating process at high temperature
Authors: Sumarno  , Sunada Tomoko , Sato Yoshiyuki , Takishima Shigeki , Masuoka Hirokatsu
Published: April 2004

Generation of microcellular plastic in the polystyrene‐nitrogen system was studied in a batch process. In this study, a quick‐heating method was applied to study the effects of saturation temperature, decompression rate and heating time on the microcellular structure for sheet samples with a thickness of 1.3 mm. The saturation pressure in each process was kept constant at 25 MPa. At saturation temperatures above 393 K, we found that, although the solubility of nitrogen increased with increasing saturation temperature, cell density decreased, and the average cell diameter and volume expansion ratio increased. The samples that were saturated at 433 K shattered after microcellular processing. The change in decompression rate affected the supersaturation degree of the dissolved gas in the polymer, and affected the cell structure. Variation of heating time for difference saturation/heating temperature could be used to obtain the optimum relation between cell density, average cell diameter, and volume expansion ratio.
Copolymerization of carbon dioxide and propylene oxide using various zinc glutarate derivatives as catalysts
Authors: Ree M. , Bae J. Y. , Jung J. H. , Shin T. J. , Hwang Y.‐T. , Chang T.
Published: April 2004

Various zinc dicarboxylate catalysts were synthesized by the reaction of zinc oxide with eleven different glutaric acid derivatives, and their coordination characteristics were investigated by infrared spectroscopy. The electronic nature and steric hinderance of substituents influenced the coordination of the carboxylate and the zinc metal ion. The coordination characteristics were classified into three categories: (i) compounds exhibiting bridging bidentate coordinating bonding modes, such as syn‐anti and syn‐syn bridging; (ii) compounds with only unidentate coordination; and (iii) compounds with mixed coordinations of unidentate and bridging bidentate. All the zinc carboxylate catalysts produced poly(propylene carbonate)s (PPCs) by the copolymerization of carbon dioxide and propylene oxide. The first category of catalysts produced relatively higher yields than the other categories. Zinc glutarate without any substituent, which is a catalyst in the first category, produced PPC with the highest yield and the highest molecular weight. The catalytic activity of zinc glutarate was suppressed by incorporation of substituents. The suppression of the catalytic activity might be due to the variation in the Lewis acidity of the zinc site as well as changes in the morphological structure caused by the substituents. Methylaluminoxane was also evaluated as a catalyst for the copolymerization, but it produced copolymers containing a large amount of ether linkages.
Deformational behavior of polyolefins at high temperature and strain rate: Experimental analysis and constitutive laws
Authors: Briatico‐Vangosa Francesco , Rink Marta , D'Oria Francesco , Verzelli Alberto
Published: April 2004

Large deformation behavior of two polyolefins has been investigated under high temperatures and high strain rate conditions. During uniaxial tensile tests at constant true strain rate, volume, stress, and deformation ratio were measured. At the temperatures considered, the mechanical behavior tends to be elastic (rate‐independent) as strain rate increases. Thus elastic models can be used to describe the deformational behavior of these resins under such conditions. Models proposed by Ogden, by Coleman as modified by Radi, and by Sweeney‐Ward have been considered to fit experimental data and their adequacy has been discussed. Sweeney‐Ward's model has been found to provide the best fit of the examined polymer's behavior at high temperatures and high strain rates.
Elongational behavior of polyethylene melts—effect of deformation
Authors: Micic P. , Bhattacharya S. N.
Published: April 2004

Transient elongational viscosity of linear low density polyethylene (LLDPE) and two low density polyethylenes (LDPE1 and LDPE2) was measured at one temperature and different deformation rates in constant strain rate elongational rheometer. The elongational viscosity measurements revealed stronger strain hardening characteristics for LDPEs than that observed for LLDPE. The different response to stretching of these polymers is thought to relate to the presence of long chain branches in LDPEs, which affect the elongation viscosity profoundly. The onset of strain hardening for all long chain branched LDPEs as well as for linear LLDPE occurs at the same value of the critical strain, which is independent of temperature or deformation rate. An attempt has been made to explain this phenomenon in terms of the changes that occur in the macromolecular network upon stretching.
Draft angle and surface roughness effects on stereolithography molds
Authors: Cedorge Thomas , Colton Jonathan
Published: April 2004

Stereolithography (SL) is a rapid prototyping process, which allows one to build complex shapes quickly. Current research investigates the possibilities of using this process to make injection molds. This would allow designers to manufacture and test molds easily and rapidly. One of the main issues with this technique is the effects of its surface on the part. Molds built by SL have high roughness. This gives rise to a high friction force between the part and the mold, and increases the ejection force needed to eject the part from the mold. High ejection forces often lead to damage or breakage of the part and the mold. Research was undertaken on the effects of draft angle and roughness on ejection forces. It was found that increasing the draft angle does not necessary assist the ejection of the part. As the draft angle increases, the roughness and hence the friction force between the part and the mold also increase. There is a trade‐off between draft angle and roughness. A model based on Glanvill's equation was developed to predict ejection force and was consistent with experimental results.
Peroxide‐catalyzed swell grafting of maleic anhydride onto polypropylene
Authors: Ko Tze‐Man , Ning Ping
Published: April 2004

A new grafting method was developed to incorporate maleic anhydride directly onto solid‐state polypropylene powders. Maleic anhydride grafts altered the nonpolar characteristics of polypropylene so that much better mixing was achieved in blends and composites of polypropylene with many other polymers and fillers. Maleic anhydride was grafted onto polypropylene by the peroxide‐catalyzed swell grafting method, with a maximum extent of grafting of 4.60%. Fourier transform infrared spectroscopy, differential scanning calorimetry, thermogravimetric analysis, scanning electron microscopy, tensile testing, and impact testing were used to characterize the isotactic polypropylene (iPP), maleic anhydride grafted polypropylene (MAH‐g‐iPP), and (isotactic polypropylene)/(calcium carbonate) composites (iPP/CaCO3). The crystallinity and heat of fusion of the MAH‐g‐iPP decreased as the extent of grafting increased. The mechanical properties of the CaCO3 filled polypropylene were improved by adding MAH‐g‐iPP as a compatibilizing agent. The dispersion of the fillers in the polymer matrix and the adhesion between the CaCO3 particles and the polymer matrix were improved by adding the compatibilizer.
Synthesis of poly(2,5‐di‐n‐butoxy‐p‐phenylene vinylene) and its application in light‐emitting diodes
Authors: Wang Guojie , Huang Jingsong , Li Min , Chen Xinfang , Liu Shiyong
Published: April 2004

Poly(2,5‐di‐n‐butoxy‐p‐phenylene vinylene) (DBPPV) was synthesized in a mixed solvent of xylene and tertbutyl alcohol via a dehydrochlorination route, using potassium tert‐butoxide as the initiator. The polymer was soluble in organic solvents such as xylene, chloroform and THF. The polymer was characterized by elemental analysis, FTIR, 1H NMR and UV‐Visible spectroscopy. Single‐layer and a double‐layer light‐emitting diodes (LEDs) were fabricated using the polymer as the active layer. The peaks of the photoluminescence (pl) and electroluminescence (el) spectra of the LEDs were at 580 nm and 577 nm, respectively. The turn‐on voltage and the maximum luminescence of the single‐layer LED were 6.4V, and 100 cd/m2, while that of the double‐layer LED were 4.3V, and 630 cd/m2, respectively.
Mechanical and thermal anisotropy for uniaxially and biaxially drawn PET
Authors: Ellis John W. , Picot J. J. C.
Published: April 2004

Sheets of two molding grades of polyethylene terephthalate (PET) with weight average molecular weight of 57,000 and 52,000 were drawn uniaxially or biaxially to ratios of up to 3 in a compression mold at 200°C. Tensile modulus measurements were done for axial and transverse strain. Thermal conductivity measurements were done with a transient‐state surface probe for thermal conductivity in the normal‐to‐the surface direction (Kn), as well as the axial (Ka) and transverse (Kt) directions in the plane of the sheet. Values are presented as normalized by the tensile modulus (Mo) or the normal conductivity (Kno), respectively, of undrawn isotropic specimens. For the uniaxial experiments, both M/Mo and Ka/Kno were linearly related to draw ratio. A regression analysis on results for both grades of PET for Ka/Kno in terms of M/Mo gave Y = 0.804*X + 0.286; std. err. of Y est. equal to 0.17. Kn/Kno decreased slightly. This non‐intrusive conductivity measurement provides a convenient means for monitoring the development of increased modulus in hot‐forging processes. Results on biaxially oriented specimens showed lesser modulus increases with draw ratio, consistent with orientation distribution in a plane, rather than in a single direction. Thermal conductivity (Ka/Kno as well as Kt/Kno), however, increased to a greater degree than for the case of uniaxial draw for the higher molecular weight material, suggesting the possibility of tilting of crystalline aggregates in the deformation process.
Nondestructive testing of polyaramide cables by longitudinal wave propagation: Study of the dynamic modulus
Authors: Ferreira M. , Lam T. M. , Koncar V. , Delvael Y.
Published: April 2004

It has been observed that cables at different states of fatigue had their own speed of longitudinal propagation of acoustic waves (1). This speed can be measured with piezoelectric captors and is proportional to the square root of the sonic modulus. Our experiments, which have been carried out on Technora cables of diameter 2 mm, show that the modulus obtained from the wave speed has the same behavior in fatigue as the modulus obtained from tensile tests. Furthermore, our experiments also show that the residual strength in the cable is proportional to the modulus. A nondestructive control of cables can hence be made from these sonic modulus measurements.
Thermal, mechanical, and diffusional properties of nylon 6/ABS polymer blends: Compatibilizer effect
Authors: Jang Seung Phil , Kim Dukjoon
Published: April 2004

The thermal, mechanical, and water absorption properties of blends of nylon 6 (PA6) and acrylonitrile‐butadiene‐styrene copolymer (ABS) with and without the compatibilizer maleic anhydride (MAH) were studied. Polymers were melt‐blended using a twin screw extruder, and injection molded into sheets. Tensile and impact properties, hardness, heat deflection resistance, and dimensional stability were enhanced by the incorporation of MAH. Synergistic effects were observed for tensile elongation and flexural properties. The melting temperature and the thermal stability were not significantly affected by the incorporation of MAH. The mechanical property enhancement by the introduction of compatibilizer was explained by the formation of a micro‐domain structure in the blends. The equilibrium water uptake increased with increasing concentration of PA6, and the diffusion coefficient was determined from the water transport kinetics at different temperatures. Activation energy was extracted from the temperature dependence of the diffusion coefficient. No compatibilizer effect was observed in the swelling behavior.
Flow behavior of LCP melts and its influence on morphology and mechanical properties of injection molded parts
Authors: Nguyen T. N. , Geiger K. , Walther Th.
Published: April 2004

The flow behavior of two commercial liquid crystalline polymers (LCP), Vectra B 950 and Vectra L 950 (Ticona GmbH), was investigated using a capillary rheometer with a new double slit die. The influence of pre‐shearing of the melt on its viscosity and the apparent geometry dependence of its flow behavior were analyzed. The dependence of flowability on the part was determined with a modular spiral mold in which the thickness of the channel was varied. The influence of processing parameters and part geometry on the mechanical properties and morphology of molded parts was also studied.
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

Biodegradable 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

In 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

In 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

Differential 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

The 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

An 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

A 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

The 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

The 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

Stress‐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

A 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

The 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

Time‐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

The 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.