bluuebunny/crossref_metadata_2025 huggingface dataset:
Morphology of polymer blends in the melting section of co‐rotating twin screw extruders
Authors: Potente H. , Bastian M. , Bergemann K. , Senge M. , Scheel G. , Winkelmann Th.
Published: April 2004

The properties of polymer blends are largely determined by the morphological structure of the polymer combinations that are involved. In terms of extruder design, this means it is necessary to have models available for estimating the development of the morphology over the length of the screws. Since significant morphological changes are observed in the melting section, in particular, is it necessary to analyze not only the plasticizing process for binary material combinations but also the initial formation and further development of the morphology in this section of the extruder. In the framework of this study, experimental investigations were conducted into polypropylene/polyamide 6 (PP/PA6) blends with small components (by weight) of the disperse PA phase. Apart from varying the process conditions of screw speed and throughput, the viscosity ratio was also varied through the use of two different PP grades. The degree of melting and the development of the morphology over the length of the screws were determined for the individual tests. The study of blend morphology in the melting section reveals key findings that must be taken into account for modeling the initial formation and further development of the morphology. It is very clear that, on the second component, which melts at higher temperatures, a kind of melt film removal occurs at the surface of the granules as they melt. The drops of second component in the melting section, which are directly adjacent to components that have not yet fully melted in some cases, have already assumed dimensions (in the μm range) similar to those that are seen at the end of the extrusion process. This means that, in the melting section of the twin‐screw extruder, no volumes become detached from or are worn off the already‐molten granule surfaces. An evaluation of scanning electron micrographs also shows that, in the melting section of co‐rotating twin‐screw extruders, virtually all the degradation mechanisms that can essentially be distinguished, such as quasi‐steady drop breakup, folding, end pinching and decomposition through capillary instabilities, take place in parallel.
Superposed hydrodynamic disturbances from feeders in a starved flow modular intermeshing co‐rotating twin screw extruder
Authors: Kim Eung Kyu , White James L.
Published: April 2004

A process dynamic model of surging in a modular self‐wiping co‐rotating twin screw extruder caused by superposed disturbances from feeders is developed. The changes of output flow rate with time (surging) are predicted for various time dependent input modes such as step function and sinusoidal function inputs into the hopper and other ports part way along the length of the machine.
Effects of rheological properties and processing parameters on ABS thermoforming
Authors: Lee Je Kyun , Scott Chris E. , Virkler Terry L.
Published: April 2004

Understanding effects of material and processing parameters on the thermoforming process is critical to the optimization of processing conditions and the development of better materials for high quality products. In this study we investigated the influence of both rheological properties and processing parameters on the part thickness distribution of a vacuum snap‐back forming process. Rheological properties included uniaxial and biaxial elongational viscosity and strain hardening and/or softening while processing parameters included friction coefficient, heat transfer coefficient, and sheet and mold temperatures. The Wagner two parameter nonlinear viscoelastic constitutive model was used to describe rheological behavior and was fit to shear and elongational experimental data. The linear viscoelastic properties along with the Wagner model were utilized for numerical simulation of the thermoforming operation. Simulations of pre‐stretched vacuum thermoforming with a relatively complex mold for a commercial refrigerator liner were conducted. The effects of nonlinear rheological behavior were determined by arbitrarily changing model parameters. This allows determination of which rheological features (i.e., elongational mode, viscosity, and strain hardening and/or softening) are most critical to the vacuum snap‐back thermoforming operation. We found that rheological and friction properties showed a predominant role over other processing parameters for uniform thickness distribution.
Viscoelastic properties of reactive and non‐reactive blends of ethylene‐methyl acrylate copolymers with styrene‐maleic anhydride copolymer
Authors: Bayram G. , Yilmazer U. , Xanthos M.
Published: April 2004

The effects of compatibilizing reactions on the viscoelastic properties and morphology of ethylene‐methyl acrylate copolymers were studied. Potentially reactive blends of styrene‐maleic anhydride copolymer (SMAH) and a terpolymer of ethylene/methyl acrylate/glycidyl methacrylate (E‐MA‐GMA) were compared with a non‐reactive blend of SMAH and an ethylene/methyl acrylate (E‐MA) copolymer with similar rheological properties. Melt mixing was carried out in a batch mixer and in a co‐rotating twin screw extruder. The morphology of the reactive blends showed smaller domain sizes than the non‐reactive blends, and the viscoelastic properties of the blends were very different. The storage and loss moduli and the complex viscosity of the reactive blends were greater than those of non‐reactive blends. The reactive blends had a higher zero shear viscosity, plateau modulus and mean relaxation time than their non‐reactive counterparts, indicating a higher degree of melt elasticity. The melt elasticity was maximum at 25% functionalized ethylene‐methyl acrylate concentration.
Rheological analysis of polyvinyl butyral near the glass transition temperature
Authors: Juang Yi‐Je , Lee L. James , Koelling Kurt W.
Published: April 2004

In many polymer manufacturing operations, the material is processed near the glass transition temperature (Tg). Examples are thermoforming, blow molding, film blowing, hot embossing, forging, plastic welding, and de‐airing in safety glass lamination. In these processes, solid‐like behaviors such as strain hardening and yielding play important roles. These material properties cause the material to flow (or deform) in a way that substantially differs from a polymer melt. In order to understand the flow behavior near the Tg, polyvinyl butyral (PVB), a rubbery polymer used in safety glass lamination, was studied in this work. The flow properties of the polymer above the Tg were characterized by using both shear and elongational rheometers, and a tensile tester. The measured flow properties were described by a viscoelastic constitutive model.
Orthotropic elastic constants for polyimide film
Authors: Cho Seo Hyun , Kim Gene , McCarthy Thomas J. , Farris Richard J.
Published: April 2004

The orthotropic constants of polyimide film have been characterized using the theory of elasticity of an anisotropic material. Experimental techniques coupled with the mechanics of orthotropic materials are used to determine all 9 independent orthotropic elastic constants (3 tensile moduli, 3 shear moduli, and 3 Poisson's ratios) and 3 coefficients of thermal expansion. Vibrational holographic interferom‐etry is used to determine the orthotropic axes of symmetry. For this polyimide film, the two principal axes coincided with the machine and transverse directions. It is also used to evaluate the 2 in‐plane Poisson's ratios by measuring residual stresses in 2‐D and 1‐D square membranes. Using other instruments such as a high pressure gas dilatometry apparatus, a tensile tester, a pressure‐volume‐temperature apparatus, a thermornechanical analyzer, and a torsion pendulum, the 7 other orthotropic constants and the 3 coefficients of thermal expansion are determined.
Crystallization kinetics of poly(trimethylene terephthalate)
Authors: Chuah Hoe H.
Published: April 2004

The bulk isothermal crystallization kinetics of poly(trimethylene terephthalate) (PTT) was studied using a differential scanning calorimeter. Avrami's theory was used to analyze the data. Based on crystallinity growth rate, Avrami rate constant, K, and crystallization half‐time, PTT's crystallization rate is between those of poly(butylene terephthalate) (PBT) and poly(ethylene terephthalate) (PET) when compared at the same degree of undercooling. PBT has the highest crystallization rate with K in the order of 10−2 to 10−1 min−n. It is about an order of magnitude faster than PTT at 10−3 to 10−2 min−n, which in turn is an order of magnitude faster than PET with K of 10−4 to 10−2 min−n. Contrary to previous reports (PTT was not included in the study) that aromatic polyesters with odd numbers of methylene units were more difficult to crystallize than the even‐numbered polyesters, PTT did not fit in the prediction and did not follow the odd‐even effect.
The effect of talc on the crystal orientation in polypropylene/ethylene‐propylene rubber/talc polymer blends in injection molding
Authors: Obata Yutaka , Sumitomo Takashi , Ijitsu Toshikazu , Matsuda Masatoshi , Nomura Takao
Published: April 2004

The effect of tale on the b‐axis orientation of the polypropylene crystals in polypropylene (PP)/ethylene‐propylene rubber (EPR)/talc blends of injection moulding was examined using the X‐ray diffraction method. The b‐axes of the PP crystals were most strongly oriented in the thickness direction for the injection molded PP/EPR/talc blends. The b‐axis orientation in the thickness direction of injection moldings was promoted by increasing the concentration of talc, by reducing the particle size, or by purifying the tale. The dependence of the specimens' rigidity on talc content, particle size, and purity was also investigated. The rigidity depended on the degree of b‐axis orientation. The result of our investigated suggest that increasing the orientation of the PP crystals that are near talc particles may improve the rigidity.
Quantitative measurement of adhesion between polypropylene blends and paints by tensile mechanical testing
Authors: Tang Houxiang , Foran Brendan , Martin David C.
Published: April 2004

A tensile mechanical test suiable to measure the adhesion between brittle coatings and ductile substrates was applied to measure the adhesion of painted layers on polypropylene blends. The test involves the tensile deformation of the painted assembly, resulting in the periodic cracking of the brittle coating on the ductile substrate. The interfacial shear strength was determined by measuring the strength of the coating, the thickness of the coating, and the average width of paint fragment after the crack density reaches saturation. Apparent interfacial shear strength was obtained for different paints on the same kind of blend, which gave consistent results over the experimental strain rate range from 10−4 to 10−3 sec−1. Interfacial delamination was studied by optical microscopy (OM) and transmission electron microscopy (TEM). The delamination was observed to mainly occur near the adhesion promoter and substrate interface.
Crystallization of poly(ethylene terephthalate) and poly (butylene terephthalate) modified by diamides
Authors: Bouma Krista , Gaymans Reinoud J.
Published: April 2004

Poly(ethylene terephthalate) (PET) and poly (butylene terephthalate) have been modified by diamide units (0.1–1 mol%) in an extrusion process and the crystallization behavior studied. The diamides used were: for PET, T2T‐dimethyl (N, N′‐bis(p‐carbomethoxybenzoyl)ethanediamine) and for PBT, T4T‐dimethyl (N, N′‐bis(p‐carbomethoxybenzoyl)butanediamine). The above materials were compared to talc (0.5 wt%), this being a standard heterogeneous nucleator, and to diamide modified copolymers obtained by a reactor process. Two PET materials were used: a slowly crystallizing recycled grade obtained from soft drink bottles and a rapidly crystallizing injection molding grade. The crystallization was studied by differential scanning calometry (DSC) and under injection molding conditions using wedge shaped specimens; the thermal properties were studied by dynamic mechanical analysis. T2T‐dimethyl is effective in increasing the crystallization of PET in both of the extrusion compounds as well as in the reactor materials. It was also found that the crystallization temperature of poly(butylene terephthalate) could be slightly increased by the addition of nucleators.
Transport modeling and thermophysical properties of cellular poly(urethane‐isocyanurate)
Authors: Peng Shuo , Fuchs Alan
Published: April 2004

Transport behavior, thermophysical properties and kinetics of cellular poly(urethane‐isocynurate) were investigated. The heat and momentum transport of the flowing and reacting polymers systems was modeled using a computational fluid dynamics (CFD) approach. Two models were developed and compared with the experimental results in order to provide insight into the optimum processing. The models allowed prediction of the temperature profiles under a variety of operating conditions. The model prediction of momentum and heat transport agreed with the experimental results well. the thermophysical properties of the polymer system were obtained from experimental data and were used in the transport model. These properties included heat capacity and thermal conductivity. Reaction kinetics were investigated using differential scanning calorimetry (DSC). The rate constant, activation energy and heat of reaction and the rate constant were obtained from the experimental data.
Stress‐initiated void formation during cure of a three‐dimensionally constrained thermoset resin
Authors: Eom Yongsung , Boogh Louis , Michaud Véronique , Sunderland Paul , Månson Jan‐Anders
Published: April 2004

During cure of epoxy resins, polymerization induces an increase in mechanical properties, which is accompanied by a volumetric shrinkage. When the resin is cured in a constrained mold to which it adheres, tensile stresses will hence develop, which may exceed the stremgth of the resin at a given curing stage. Voids will then form. The origin and governing parameters of void formation are studied using an epoxy resin cured in a three‐dimensionally constrained glass mold following isothermal cure cycles. Two types of voids are shown to appear during cure, one early in the process and a second around the gelation point. A viscoelastic analysis of the material stress state over the whole range of cure is performed. Both the viscoelastic modulus obtained from a time‐cure‐temperature superposition and the volumetric shrinkage, which was continuously measured by density change, are taken into account. A value for the critical internal stress at void initiation is thus proposed. This criterion can be used to provide guidelines for tailoring the material properties toward an increase of the critical stress for void initiation. Also, since during theprocessing of composite materials, cases may arise where the resin cures within the interstices left between consolidated fibres that do not move, this critical stress failure criterion can be of use in the eastablishment of a process window providing guidelines for the production of void free composites.
Elastomer biaxial characterization using bubble inflation technique. I: Experimental investigations
Authors: Reuge N. , Schmidt F. M. , Le Maoult Y. , Rachik M. , Abbé F.
Published: April 2004

The biaxial rheological behavior of materials such as elastomers or polymers can be obtained using a bubble‐inflation‐technique. A circular membrane is clamped at the rim and expanded under gas pressure. The inflation of the circular membrane is recorded using a CCD video camera and the blowing pressure by a pressure sensor. Then, from elongation and curvature radius measurement at the pole of the bubble, one can deduce equibixial stress‐strain data. This study describes the optimization of a bubble‐inflation rheometer. The most sensitive point of the technique is the estimation of the elongation at the bubble pole, deduced from video camera measurements. A direct measurement of the bubble thickness was performed using a magnetic probe in order to validate rheometer results. Such a validation has evidently never been carried out before. Results of quasi‐static equibiaxial characterisation of elastomers are presented and analyzed.
Effect of poly(acrylic acid)‐g‐PCL microstructure on the mechanical properties of starch/PCL blend compatibilized with poly(acrylic acid)‐g‐PCL
Authors: Kim Chang‐Hyeon , Cho Kuk Young , Park Jung‐Ki
Published: April 2004

Poly(acrylic acid)‐g‐polycaprolactone (PAA‐g‐PCL) graft copolymer was synthesized and starch/PCL blends compatibilized with PAA‐g‐PCL were prepared. The mechanical properties of the starch/PCL blends compatibilized with various PAA‐g‐PCLs that have different graft degrees and graft lengths were investigated. As the graft degree of the PAA‐g‐PCLs that have the same graft length increased, the modulus and the strength of the blends decreased. However, the elongation at break and the tensile toughness of the blends showed a maximum at a certain graft degree (10.8 mol%) owing to the better compatibilizing effect compared to the low (3.9 mol%) and the high (23.4 mol%) graft degree of PAA‐g‐PCL. It was also found that the modulus and the strength of the blends increased with the increase of graft length of the PAA‐g‐PCLs that have the same graft degree (∼11 mol%). However, the blend compatibilized with the short graft length (M.W. of PCL graft: 530) exhibited the highest value of the elongation at break and the tensile toughness. This result is attributed to the self‐crystallization of PAA‐g‐PCL in the blend that has longer PCL grafts.
Weldline morphology of injection molded modified poly(phenylene‐oxide)/polyamide‐6 blends
Authors: Son Younggon , Ahn Kyung Hyun , Char Kookheon
Published: April 2004

The weldline morphology of modified‐poly(phenylene‐oxide)/polyamide‐6 blends has been investigated. A distinct contacting layer consisting of fine spherical particles was observed from the V‐notch at the surface to the center of the molded part for the low viscosity ratio blend. In contrast, such small particles were not found and a slight deformation was observed near the part's surface for the high viscosity ratio blend. The weldline morphology was found to be dominated by the deformation, the breakup, and the relaxation of the dispersed modified‐poly(phenyleneoxide) phase. The effect of injection conditions on the weldline morphology has also been investigated. The morphology of the meldline was quite complicated. Distorted multi‐layered structures were observed. It was found that those structures arise from the subsequent flow after merging of the two flow fronts. Weldlines and meldlines have been studied separately, and their formation mechanisms were found to be basically similar.
Biaxial stress relaxation of high impact polystyrene (HIPS) above the glass transition temperature
Authors: Hummel Scott R. , Hossain Kishwar , Hayes Gregory T.
Published: April 2004

A procedure was developed and experiments were performed to measure the biaxial stress relaxation of High Impact Polystyrene (HIPS) sheets above the glass transition temperature. Tests were performed at various temperatures and strain magnitudes. The data were normalized to unity at time zero to isolate the time dependence of the stress from the strain dependence. The results show that the time dependent biaxial stress relaxation properties were independent of the magnitude of the stress or strain for small strains. The stress relaxation curves were fitted to a Prony series and i1 was found that time‐temperature superposition could be applied to interpolate the normalized relaxation. Uniaxial stress relaxation tests were also performed and the results were compared to that of the biaxial testing program.
Izod impact strength of a product molded of poly(vinyl chloride)/impact modifier containing voids (void MOD)
Authors: Takaki Akira , Narisawa Ikuo , Kuriyama Takashi
Published: April 2004

The Izod impact strength of a PVC (polyvinylchloride)/MOD (impact modifier) molded product was investigated by suitably reducing the amount of crosslinking agent in the rubber of MOD or by making rubber particles void when they were in the form of a latex. As a result, (1) when the amount of crosslinking agent in rubber was suitably reduced, the Izod impact strength of the PVC/MOD molded product was improved in both ordinary MOD and void MOD. However, with the extremely small amount of crosslinking agent, low Izod impact strength was exhibited. With the same amount of crosslinking agent, the void MOD showed higher Izod impact strength than the ordinary MOD. (2) SEM (scanning electron microscope) and TEM (transmission electron microscope) observations on the broken surface revealed that shear yield and crazing occurred in a whitened portion, and crazing was observed only near the surface of the broken section in a non‐whitened portion. It was also found that when the crosslinking degree of rubber was reduce, cavitations were liable to be formed in rubber under stress and expanded under rubber stress in the void MOD mor‐; than in the ordinary MOD. (3) As a result of a tensile test on the molded product, it was found that the void MOD caused lower yield stress than the ordinary MOD, thereby increasing in stress concentration. (4) P'rom these results, an estimation was earned out of the mechanism of improvement in the Izod impact strength of the MOD or void MOD using rubber with an appropriately lowered crosslinking degree.
Rheokinetics and the influence of shear rate on the Trommsdorff (gel) effect during free radical polymerization
Authors: Cioffi M. , Hoffmann A. C. , Janssen L. P. B. M
Published: April 2004

Some rheokinetic studies of free radical polymerization have been published In the past. They generally make modeling of the time dependent increase of viscosity possible at low degrees of conversion, where Newtonian behavior holds and the rheokinetic equations can be linearized. In this paper we try to extend the rheokinetic approach to the region of high degrees of conversion, where the reacting solution is non‐Newtonian and the shear rate at which the polymerization is performed becomes a fundamental parameter. Moreover, nonlinear phenomena such as the Trommsdorff effect and phase separations are likely to occur‐ The principal result of this study is that the Trommsdorff effect is reduced and sometimes eliminated when the polymerization is performed at high shear rate. Instabilities of the time dependent increase of viscosity occurred when the conversion was higher than 85%. They were attributed to phase separation of the macromolecules under shear flow.
Mentallocane plastomer modification of polypropylenes
Authors: C. Yu Thomas
Published: April 2004

Plastomers are ethylene alpha‐olefin coplymers made from the single site metallocdene catalyst using a variety of polymerization processes. The key features are uniform intermolecular and intermolecular comonomer distribution, low extractables, comonomer dependent. meleting point, and low ashcontent. The uniform comonomer behavior. The dual characterplastomer evolved into a new class of impact modifiers for polypropylenes replacing the conventional ethylene‐propylene cooplymer (EPR)to produce both thermoplastic olefins (TPOs) and thermoplastic elastomers(TPEs). Ahybrid TPE based on grafting of a functional butyl rubber to plastomer was explored. Low temperature impact and clarity can be achieved by matching the reflective index of a plastomer with a random polypropylene copolymer (RCP).
Disprsion in high viscosity ratio polyolefin blends
Authors: Huneault Michel A. , Mighri Frej , Ko Glen H. , Watanabe Fuminao
Published: April 2004

The dispersion of polyethylene and polyropylene in a polypropylene matrix using a co‐rotating twin screw extruder has been investigated. Poymer pairs were selected to study the effect of viscosity ratio, defined as the viscosity of the minor component over that of the matrix, in the range 0.1 to 900. The dispersion quality was defined by determining the number of “gels,”i.e., large undispersed particles, present in thin films and by conventional microscopy techniques. The gel numbers were found to increase steadily with the viscoty ratio. It was also observed that particle size distributions in the high viscosity ratio blends was very broad, with particles as large as a hundred microns coexisting with much finer ones in the sub‐micron range. For a given polymer blend, the re‐processing was found to have and important effect on gel reduction. The effect of rotation speed, flow rate minor phase feeding position was aso investigated and is discussed in the paper.
Shrinkage behavior and optimization of injection molded parts studied by the taguchi method
Authors: Chang Tao C. , Faison Ernest
Published: April 2004

Shrinkage behavior of a plastic plays a critical role in determining the final dimensions of an injection‐molded part. It is well known that process conditions affect many properties of plastic parts, including shrinkage. This study applies the Taguchi method to systematically investigate the effects of process conditions on the shrinkage (along‐ and across‐the‐flow directions) of three plastics: high‐density polyethylene (HDPE), general‐purpose polystyrene (GPS), and acrylonitrile‐butadiene‐styrene (ABS). The results show that HDPE, a semicrystalline plastic, shrinks more than GPS and ABS, two amorphous materials. The extent of anisotropic shrinkage in the along‐the‐flow and across‐the‐flow directions for HDPE is different from GPS and ABS. More shrinkage occurs in the across‐the‐flow direction of HDPE than in its along‐the‐flow direction. The reverse is true for GPS and ABS. Mold and melt temperatures, along with holding pressure and holding time, are the most significant influences on the shrinkage behaviors of three materials, although the importance of each is different for each plastic. The optimal conditions for reducing shrinkage identified by the Taguchi method are experimentally verified and validated by t‐statistic tests. The prediction matches very well with the experimental value for the along‐the‐flow shrinkage of GPS.
Industrial high pressure ethylene polymerization initiated by peroxide mixtures: A reduced mathematical model for parameter adjustment
Authors: Asteasuain M. , Pereda S. , Lacunza M. H. , Ugrin P. E. , Brandolin A.
Published: April 2004

We present a method for the adjustment of parameters in the mathematical modeling of industrial tubular reactors for high pressure polymerization of ethylene. We propose a reduced mathematical model for these reactors that aids in the task of model parameter update commonly done periodically in industrial plants. This reduced model was built from a detailed model for multiple peroxide and oxygen initiator systems we had developed before. Some of the assumptions in that rigorous model were reviewed in order to minimize computational effort. Good and faster predictions were obtained by assuming different constant jacket temperatures and pressures at each zone. Pressure pulse equations had to be included in the model. A simplification of the adjustment procedure is also proposed here. It consists in using only the reactions considered crucial for the description of this polymerization. The peroxide initiator and solvent mixtures were treated as fictitious unique initiator and solvent respectively. A procedure was established for the quick estimation of the kinetic parameters that represent initiator and solvent mixtures of different compositions. This resulted in a model that can be adjusted rapidly to predict the behavior of a specific industrial reactor. The reduced model was validated using experimental runs initiated by oxygen either alone or together with peroxide mixtures.
Association between plasticized starch and polyesters: Processing and performances of injected biodegradable systems
Authors: Avérous Luc , Fringant Christophe
Published: April 2004

Different formulations of wheat thermoplastic starch (TPS) have been processed with various plasticizer/starch ratios and moisture contents. The biodegradable polyesters tested are polycaprolactone (PCL), polyester amide (PEA), polybutylene succinate adipate (PBSA) and polybutylene adipate co terephtalate (PBAT). TPS and polyesters are melt blended in different proportions by extrusion and then injected to obtain dumbbell specimens. Various properties are evaluated such as the mechanical properties (tensile and impact tests), and the hydrophilic character with contact angle measurements. Additionally, uniaxial shrinkage is evaluated. Results show that the addition of polyester to TPS increases the dimensional post‐injection stability. Blend modulus values are close to the results of the classical rule of mixture. Elongation at break, resilience values and SEM observations seem to give some indications about the compatibility between both polymeric systems. PBAT and PEA present better results than PCL and PBSA. Contact angle measurement show that we have a drastic increase of the hydrophobic character from 10% of polyester in the blend. The different combinations of TPS and polyesters give a wide range of mechanical behavior for compostable materials, to be developed in specific applications.
Foaming of low‐density polyethylene in a dynamic decompression and cooling process
Authors: Song Kwangjin , Apfel Robert E.
Published: April 2004

Effects of the properties of polymers and blowing liquids on the macrostructure and microstructure of foamed products in a dynamic decompression and cooling (DDC) process have been investigated. When the homogeneous solutions, prepared by the heating and mixing of the mixtures of low‐density polyethylenes (LDPE) and chlorinated hydrocarbons under nitrogen (N2), go through a rapid pressure quench above the boiling point of the liquids, bubbles nucleate out through liquid/gas phase separation and grow through diffusion and expansion of the gaseous phases. Foam cell stabilization is improved by polymers exhibiting higher extensional hardening and blowing liquids possessing higher latent heat of evaporation. Resultant LDPE foams have mixed cell structures: in the skin parts, more cells are closed, but more cells are open in the core parts. In the polymer matrix, micromorphologies of granules, fibers, and fiber networks, with oriented lamellae, are observed. The formation of these complex structures is described in terms of phase and deformation behaviors of the solutions.
Geometric mean vs. Arithmetic mean in extrusion residence time studies
Authors: Unlu Emine , Faller James F.
Published: April 2004

Geometric mean residence time was compared with the arithmetic mean residence time for a residence time distribution study conducted on a twin‐screw extruder using a salt tracer and electrical conductivity measurements. Electrical conductivity of the cornmeal melt was measured at the die exit. All RTD curves obtained during the study were skewed to the right with very long tails that resulted in inflated arithmetic mean residence times. In order to alleviate the problem of long tails, different approaches were considered. Among these approaches, logarithmic transformation of the time scale to calculate the geometric mean residence time was shown to best represent the residence time distribution in terms of mean residence time and spread of the RTD. The log transformation of the time scale alleviates the problem of inappropriate shifting of the mean residence time due to long tails. The difference between the upper limits and lower limits for the log transformed data was found to be more appropriate to define the spreads of the distributions as the untransformed data resulted in quite variable spreads.
Cure kinetics and physical properties of dicyanate/polyetherimide semi‐IPNs
Authors: Kim Dae‐su , Choi Khee‐hwan
Published: April 2004

The curing behavior and physical properties of dicyanate/polyetherimide (PEI) semi‐interpenetrating polymer network (IPN) systems were investigated. Differential scanning calorimetry (DSC) was used to study the curing behavior of the dicyanate/PEI semi‐IPN systems. The curing rate of the semi‐IPN system decreased as the PEI content increased. An autocatalytic reaction mechanism can describe well the curing kinetics of the semi‐IPN systems. The reaction kinetic parameters were determined by fitting DSC conversion data to the kinetic equation. The glass transition temperature of the semi‐IPNs decreased with increasing PEI content. Two glass transitions due to phase‐separated morphology were observed for the semi‐IPN containing over 15 phr (parts per hundred parts of dicyanate resin) PEI. The thermal stability and dynamic mechanical properties of the semi‐IPNs were measured by thermal analysis.
A two‐zone melting model for polymer blends in a batch mixer
Authors: Li Huxi , Hu Guo‐hua
Published: April 2004

The rate of the morphology development of immiscible polymer blends is closely related to the rates of melting of the polymer constituents. A two‐zone model was developed to describe the rate of melting of the polymer pellets of mixtures of two semicrystalline polymers in an internal batch mixer. The mixing chamber was divided into two zones: high temperature and high shear zone, and low temperature and low shear zone. Melting was assumed to occur mainly in the first zone. Moreover, pellets were assumed to be spherical, and melting proceeded from the outersurface to the core in a gradual manner. For a given pellet, the rate of melting depended, among other things, upon the number of passes through the high shear and high temperature zone and the time it experiences therein. The validity of the model was confirmed experimentally in terms of the number and weight fraction of solid pellets as a function of mixing time.
Surface structure and adhesive properties of biaxially oriented polypropylene film grafted with poly(acrylic amide) using corona discharge
Authors: Lei Jingxin , He Guangjian , Li Qiman , Lin Xiaohong
Published: April 2004

Corona discharge was explored as a means of forming chemically active sites on the surface of biaxially oriented polypropylene (BOPP) film. The active species formed in air was used to induce graft copolymerization of acrylic amide (AAM) in aqueous solution. The surface structure, hydrophilicity and adhesion of the grafted BOPP film were characterized by the extent of grafting, electron spectroscopy for chemical analysis (ESCA), scanning electron microscopy (SEM), peel strength and contact angle measurements. Surface graft‐copolymerization of AAM onto BOPP film by corona discharge in air can be carried out with high efficiency. With increasing copolymerization time, the degree of grafting of AAM onto BOPP increases. The degree of grafting achieved a relatively high value of 2.13 wt% for the conditions of 1 min corona discharge and a copolymerization reaction time of 2.5 hr in 20% AAM aqueous solution at 70°C. After corona discharge grafting, the contact angle of water on the BOPP film decreased and the peel strength increased compared with those for ungrafted BOPP film. The hydrophilicity and adhesion of BOPP were improved by surface graft copolymerization with AAM induced by corona discharge.
Nonisothermal crystallization kinetics of peo in ethylene terephthalate‐ethylene oxide segmented copolymers
Authors: Kong Xiaohua , Yang Xiaoniu , Zhou Enle , Ma Dezhu
Published: April 2004

The nonisothermal crystallization behavior of Ethylene Terephthalate‐Ethylene Oxide (ET‐EO) segmented copolymers has been studied with the use of differential scanning calorimetry (DSC). The kinetics of PEO in ET‐EO segmented copolymer under nonisothermal crystallization conditions has been analyzed with the Ozawa equation. The results show that there is no agreement with Ozawa's theoretical predictions in the whole crystallization process owing to the constraint of ET segments imposed on the EO segments. A distinct two‐crystallization process has been investigated by using the Avrami equation modified by Jeziorny to deal with the nonisothermal crystallization data. The value of the Avrami exponent n is independent of the length of soft segments. However, the crystallization rate is sensitive to the length of soft segments. The longer the soft segments, the faster the crystallization will be.
Cure kinetics modeling of epoxy resins using a non‐parametric numerical procedure
Authors: Skordos A. A. , Partridge I. K.
Published: April 2004

The paper presents the development of a novel non‐parametric procedure for modeling of the chemical cure kinetics of a commercial resin‐transfer‐molding epoxy resin, RTM6. The procedure is entirely numerical and involves interpolation between experimentally determined values of cure reaction rates. The base data are obtained by Differential Scanning Calorimetry (DSC). The newly developed procedure is set against a background overview of other cure kinetics modeling approaches. It is shown that the numerical procedure can achieve a satisfactory level of accuracy in describing the progress of cure in this resin system. The important advantage, compared with other techniques, is that no information on the chemical naturr of the process is required.
Ultrasonic monitoring of the seal quality in flexible food packages
Authors: Ozguler Ayhan , Morris Scott A. , O'brien William D.
Published: April 2004

Ultrasonic Backscattered Amplitude Integral (BAI) values are used to detect critical and major defects such as nonbonding, wrinkles and bubbles distributed within the seal area of flexible food packages. The BAI‐mode imaging by itself is not capable of detecting such nonbonding, wrinkles and bubbles distributed within the seal area. For this study, model delects in the seal region of all‐plastic and foil‐containing films were created by varying the sealing‐bar temperature. Seal regions were scanned by a 17.3‐MHz ultrasonic transducer, and the waveform for each scan point was processed by the BAI‐mode method. The mean and the coefficient of variation of the BAI values (BAICV) were calculated. It is shown that a combination of mean BAI vaiae and BAICV value can detect defects distributed in seals in flexible food packages. This technique has the potential of providing a real‐time, on‐line control by sensing whether a proper seal has been achieved.
3‐D non‐isothermal flow field analysis and mixing performance evaluation of kneading blocks in a co‐rotating twin srew extruder
Authors: Ishikawa Takeshi , Kihara Shin‐ichi , Funatsu Kazumori
Published: April 2004

We have developed a three‐dimensional non‐Newtonian and non‐isothermal flow analysis of the twin screw extruder (TSE) using the finite element method. This code can simulate the fully filled parts of several kinds of screw elements, such as full flight screws, kneading blocks, rotors and their combinations. A marker particle tracking analysis has also been developed to evaluate the mixing performance of the screw elements.

In this paper, simulations for the kneading blocks in a co‐rotating TSE were carried out. The screw configurations are combinations of 2‐lobe kneading blocks with several stagger angles and disk widths. The effects of screw configurations on pressure and temperature distributions are examined. We also evaluate the dispersive and distributive mixing via stress magnitude and area stretch obtained by marker particle tracking analysis. Additionally, we discuss the desirable stagger, disk width and their combinations that promote the mixing performance.
Mixing efficiency in a pin mixing section for single‐screw extruders
Authors: Yao W. G. , Tanifuji S. , Takahashi K. , Koyama K.
Published: April 2004

Non‐Newtonian, non‐isothermal, 3D finite‐element simulation of mixing performance in a pin mixing section with different axial gaps in the pins has been carried out according to their realistic configurations. The quantitative evaluation of mixing ability was based on the theory of kinematics of fluid mixing. To learn and to compare the local mixing performance in a standard screw and a pin mixing section, the local mixing efficiency distribution proposed by Ottino was calculated. Also, the RTDs of these mixers were calculated in an attemt to measure mixing. The integration of the two, namely, the integrating local mixing efficiency along a number of particle pathlines from entrance to exit, together with statistical treatment, which was referred as integral mixing efficiency, then gives a quantitative judgment of the total mixing ability of a continuous mixer. The calculated results showed a nonlinear dependence of the mixing ability of a pin mixing section on the axial gap of the pins. Finally, the calculation results were compared with the experimental ones obtained in our previous study.
Crystal‐crystal transformations in isotactic polybutene‐1 oriented filaments and in thick molded rods
Authors: Choi Cheol‐Ho , White James L.
Published: April 2004

This paper reports two related studies of the Form II → Form I crystal‐crystal transformation in isotactic polybutene‐1. First, it was found that in melt spun filaments, the rate of transformation is higher in filaments possessing higher levels of crystalline orientation. Second, we consider the occurrence of this phase transformation in thick quenched cylindrical rods. It was found that the phase transformation occurs more rapidly in the core than at the surface of the part. It is hypothesized that the mechanism of the higher transformation rate in the core is due to the development of residual quench stresses associated with densification at solidification. These stress levels have been calculated and our results compared with earlier studies.
Nonisothermal crystallization behavior of poly(aryl ether ether ketone)
Authors: Seo Yongsok , Kim Sehyun
Published: April 2004

A study has been made of the crystallization behavior of poly(aryl ether ether ketone), PEEK, under nonisothermal conditions. A differential scanning calorimeter (DSC) was used to monitor the energetics of the crystallization process from the melt. For nonisothermal studies, the melt was crystallized by cooling at rates from 1°C/min to 10°C/min. A kinetic analysis based on the recently proposed model for nonisothermal crystallization kinetics to remedy the drawback of the Ozawa equation was applied. The Avrami exponent for the nonisothermal crystallization process was strikingly different from that of the isothermal process, which indicates different crystallization behaviors. The results agree with the morphological observation reported in the literature. This study shows that correct interpretation of the Avrami exponent provides valuable information about the crystal structure and its morphology.
Heterogeneization of polymerization catalysts on natural substances
Authors: Eberhardt A. M. , Ferreira M. L. , Damiani D. E.
Published: April 2004

The use of biomass as support for zirconocene catalysts in ethylene polymerization was studied. Cellulose, starch and chitosan were conveniently characterized. Many factors affecting the activity of the catalysts were examined. Parameters such as surface area were found to have no significant influence on the activity of the catalysts. The activity of the catalysts sharply increased with the degree of deacetylation in the chitosan supports. Using this support the highest activity in ethylene polymerization was obtained. The polymers obtained with the zirconocene supported on chitosan or cellulose pretreated with methylaluminoxane exhibited a higher molecular weight than those obtained with a homogeneous system. Polymer particles obtained with these supported metallocene catalysts showed a good replication of the original support particles.
Creep analysis of polymeric pipes under internal pressure
Authors: Guan Z. W. , Boot J. C.
Published: April 2004

Medium density polyethylene pipes have been used in the water and gas industries for over a decade. One of the major problems with these pipes is creep under their service pressures. Life prediction is usually based on the secondary creep path until the onset of tertiary creep. Constitutive models such as visco‐hyperelasticity and elasto‐viscoplasticity can be used to make such prediction. Owing to complexity, the latter is usually used in numerical modeling, Medium density polyethylene is an extremely ductile material with a low modulus of elasticity. The corresponding elongation prior to rupture under a tensile creep test can reach a few hundred percent. The appropriate creep law must be established before any life prediction can be made. In this paper, based on a creep law obtained from a series of material creep tests under different stress levels, a visco‐hyperelastic model was developed to simulate Medium density polyethylene pipes under internal creep pressures. Reasonably good correlation has been obtained between the experimental results and the theoretical analysis.
Study on the flow field of the air jet from dual slot die in the melt blowing process
Authors: Chen Ting , Huang Xiubao
Published: April 2004

The possibility of describing the jet from the dual slot die in the melt blowing process with a vortex pair was studied according to the nature of the vortex. A model of the synthesis of two jets was developed. The reliability of the model was confirmed by experimental data cited from literature. The prediction of the fiber diameter using this model coincided with that using the fitted equation with the data advanced by Harpham and Shambaugh. The effects of the equipment parameters, such as the angle between the air flow and the axis of the spinneret, the width of the die head and the width of the slot were also discussed.
Prediction of long‐term service performance of polymeric materials from short‐term tests: Creep and prediction of the stress shift factor of a longitudinal polymer liquid crystal
Authors: Akinay Ali E. , Brostow Witold , Maksimov Robert
Published: April 2004

The material studied is a longitudinal polymer liquid crystal (PLC). The creep behavior of the PLC is examined in the region of nonlinear viscoelasticity. The creep compliance D curves at nine different stress σ levels, from 10 to 50 J.cm−3 at a constant temperature are determined and shifted along the log time axis for σref = 10 J · cm−3 to produce the D versus t/aσ master curve. A fairly general formula for stress shift factor aσ based on free volume vf and the chain relaxation capability (CRC) derived by one of the authors is applied. The formula predicts values that agree with the experimental ones within the limits of the experimental accuracy. Thus, experiments at several stress levels can serve for prediction of long‐term behavior from short‐term tests. The same value of the Doolittle constant B is obtained separately from temperature shift and stress shift experiments for the PLC.
Gas absorption with filled polymer systems
Authors: Chen Lee , Sheth Himanshu , Kim Roland
Published: April 2004

This paper deals with the gas absorption behavior of polymer systems. The emphasis is on the difference between filled and unfilled polymers to explain heterogeneous nucleation in filled polymers. A Foaming Process Simulator has been built to study the gas absorption. It consists of a test chamber that holds the polymer samples. The chamber can be pressurized with gas up to 5000 psi and heated up to 450°F. The gas pressure is monitored by a high‐accuracy pressure transducer and recorded by a data acquisition system. The amount of gas absorbed by a polymer is determined from the pressure change in the test chamber. A rotor applies shear to the polymer melt to investigate the shear effects. Two polymer systems were tested: HDPE with/without talc, and PVC with/without calcium carbonate. The fillers were well dispersed as verified with scanning electron microscope. The tests were done at the melt temperatures from 120°C to 177°C and a saturation pressure of about 18.9 MPa. It was found that the filled polymers absorb more gas compared to the unfilled ones. It is suggested that there is a certain amount of gas accumulated in the filler‐polymer interface. This accumulated gas helps to create cells during the foaming process.