bluuebunny/crossref_metadata_2025 huggingface dataset:
Mechanical and morphological behavior in polystyrene based compatible polymer blends
Authors: Chun Byoung Chul , Gibala Ronald
Published: April 2004

Mechanical and morphological behavior of polystyrene (PS) based compatible polymer blend systems were studied using a tensile tester and scanning electron and optical microscopes. Four different binary compatible blend systems were employed and characterized: PS and poly (2,6‐dimethyl 1,4‐phenylene oxide) (PPO), PS and poly(vinylmethylether)(PVME), PS and poly(α‐methyl styrene)(PαMS), and PPO and PαMS. The compositional dependence of the mechanical properties showed a synergistic effect with respect to modulus, but a negative deviation from the rule of mixtures relationship for strain at break. From the scanning electron microscope (SEM) observations, a deformation mode transition from crazing to crazing and shear banding occurs at ˜25 wt% PPO in the PS/PPO blends, as indicated by the patch and river patterns above this composition. In the PS/PVME blends, a similar transition was observed at >10 wt% PVME. The PS/PαMS blends showed brittle fracture regardless of composition. The PPO/PαMS blends showed a brittle fracture for a PαMS content >25 wt%. Optical microscope (OM) observations showed that blending of PS/PPO and PS/PVME resulted in a decrease of craze density and length as the PPO and PVME content was increased. PS/PαMS and PPO/PαMS blends showed few crazes, all of which were localized near the fracture surface. The mechanical and morphological behavior can be explained using models of intermolecular interactions and entanglement density in compatible blends, respectively. Overall the mechanical property and the consequent morphological behavior were similar to the effect of antiplasticization.
Effects of particle size and rubber content on fracture toughness in rubber‐modified epoxies
Authors: Kim D. S. , Cho K. , Kim J. K. , Park C. E.
Published: April 2004

The effects of particle size of core‐shell rubber on the fracture toughness of rubber‐modified epoxies were investigated. Various sizes of core‐shell rubber particles, from 0.16 to 1.2 μm in diameter, were synthesized by seeded emulsion polymerization. Particle size effects were clearly seen for lower crosslinked diglycidyl ether of bisphenol A (DGEBA)/piperidine resin. Fracture toughness increased as the particle size of core‐shell rubber decreased from 1.2 to 0.4 μm. On the other hand, fracture toughness was constant in this range of particle sizes for higher crosslinked DGEBA/diaminodiphenylmethane (DDM) resin. Cavitation in the rubbery core and shear deformation in the matrix are the toughening mechanisms for DGEBA/piperidine resin, whereas cavitation is the only mechanism for DGEBA/DDM resin. Toughening effectiveness decreased with <0.2 μm core‐shell rubber particles since they are difficult to cavitate. The effects of core‐shell rubber content on fracture toughness of rubber‐modified epoxies were also examined. The optimum rubber content for maximum toughness of rubber‐modified epoxies decreased with decreased particle size of core‐shell rubber in shear deformable DGEBA/piperidine resin. But the fracture toughness of rubber‐modified DGEBA/DDM resins increased as the rubber content increased.
Phase behavior, crystallization, and morphology of poly(ether ether ketone)/polyarylate blends
Authors: Krishnaswamy Rajendra K. , Kalika Douglass S.
Published: April 2004

The phase behavior, crystallization, and morphology of blends based on poly (ether ether ketone) [PEEK] and bisphenol‐A polyarylate [PAr] are described. This system is partially miscible in the melt. Upon quenching to an amorphous glass the system displays two glass transitions corresponding to a nearly pure PEEK phase (Tg1) and a PAr‐rich mixed phase (Tg2). The presence of the PAr has a strong retarding influence on the rate of crystallization of PEEK in the blends. Cold crystallization from the amorphous glass occurs in two stages with increasing temperature, corresponding to the mobilization of the PEEK‐rich and PAr‐rich phases, respectively. At lower cold‐crystallization temperatures (below Tg2), the immobile PAr‐rich phase constrains crystallization of the PEEK‐rich phase, as manifested in both a decreased rate of crystallization and decreased bulk crystallinity. Dynamic relaxation studies of the crystallized blends reveal two glass‐rubber relaxations originating from interlamellar amorphous populations in the PEEK‐rich and PAr‐rich phases. In the PAr‐rich phase, there is no evidence of large‐scale PAr exclusion to interfibrillar or interspherulitic regions.
Modeling and simulation of thermally induced stress and warpage in injection molded thermoplastics
Authors: Liu Shih‐Jung
Published: April 2004

Thermally induced stress and the relevant warpage caused by inappropriate mold design and processing conditions are problems that confound the overall success of injection molding. A visco‐elastic phase transformation model, using a standard linear solid for the solidified polymer and a viscous fluid model for the polymer melt, of 2‐D finite element scheme with 8 noded overlay isoparametric elements was used to simulate and predict the residual stress and warpage within injection molded articles as induced during the cooling stage of the injection molding cycle. Computed results are in good agreement with published experimental data. The approach proposed here is to examine and simulate the injection molding solidification process with the intent of understanding and resolving more inclusive and realistic problems.
The observation and origin of micro flow marks in the precision injection molding of polycarbonate
Authors: Yoshii Masaki , Kuramoto Hiroki , Kawana Takeshi , Kato Kazunori
Published: April 2004

Micro flow marks have been found to occur in injection molding of polycarbonate. Their minimum depth is ˜ 5 nm on the mold smooth surface. Such marks seem to be formed when the molten polymer near the mold wall at the advancing front is cooled to the no‐flow temperature of resin before it comes into contact with the mold wall, preventing the precision transcription of the mold smooth surface. We investigated the molding factors affecting their occurrence by heat transfer analysis. It was found that the size of micro flow marks is related to the melt temperature, mold temperature, no‐flow temperature, thermal diffusivity of the resin, and time pitch formation of flow mark ridges and valleys. The relationships between those factors and the sizes of micro flow marks are clarified quantitatively, and the guidelines for precision transcription in injection molding are formulated.
Prediction of linear viscoelastic response for entangled polyolefin melts from molecular weight distribution
Authors: Wasserman Scott H. , Graessley William W.
Published: April 2004

The linear viscoelastic properties of polymer melts depend strongly and systematically on the molecular weight distribution. A molecular theory relating dynamic modulus and molecular weight distribution for linear polymers, developed and confirmed earlier with data for three other polymer species, is applied here to commercial samples of isotactic polypropylene and high density polyethylene. Experimental master curves are compared with predictions based on only the fundamental rheological parameters of the species and molecular weight distributions as obtained by the methods of size exclusion chromatography. Agreement is fairly good for the two polypropylene samples, about the same as had been found earlier for the other species, but it is highly variable for the ten polyethylene samples. We attribute this variability to differences among high density polyethylenes in the frequency, length, and type of long‐chain branching. However, we could find surprisingly little supporting evidence for this from such supposed signatures of long branches in polyethylene as the flow activation energy Ea. Measured values of Ea agreed well with the literature results for linear polyethylene; none showed the elevation in Ea that would be expected for polyethylene with long branches.
Sorption and migration of organic liquids in poly(ethylene terephthalate)
Authors: Nir M. M. , Ram A. , Miltz J.
Published: April 2004

Sorption kinetics of organic liquids in amorphous poly(ethylene terephthalate) (APET) and biaxially oriented PET (BPET) were determined at 34°C. With heptane and 1,2 propanediol, no sorption or swelling was observed. Estimated diffusion coefficients based on analysis from pseudo‐Fickian sorption data are 3.7 ± 1.0 × 10−9 cm2/sec for toluene sorption in APET, 12.7 ± 4.1 × 10−9 cm2/sec for benzyl alcohol in APET, 0.44 ± 0.4 × 10−9 cm2/sec for toluene in BPET, and 0.33 ± 0.4 × 10−9 cm2/sec for benzyl alcohol in BPET. Weight gain of sorbed APET samples at equilibrium was 11.4 ± 0.1% in toluene and 21.7 ± 0.8% in benzyl alcohol. BPET weight gain at equilibrium was 9.5 ± 0.1% in toluene and 13.5 ± 0.2% in benzyl alcohol. Subsequent migration of sorbed toluene from APET samples into water at 34°C was measured by gas chromatography. Migration from toluene‐sorbed APET films sandwiched between virgin APET layers was two orders of magnitude less than from sorbed films placed directly in water.
Improving poly(ethylene terephthalate)/high‐density polyethylene blends by using graft copolymers
Authors: Boutevin B. , Lusinchi J. M. , Pietrasanta Y. , Robin J. J.
Published: April 2004

The synthesis and the application of graft copolymers prepared from ozonized polyethylene (HDPE) are described. The homopolymer was treated with ozone and then copolymerized with monomers, such as methyl methacrylate, hydroxy ethyl methacrylate, glycidyl methacrylate, maleic anhydride, and ethyl acrylate. The products were used as compatibilizers in HDPE/PET [poly(ethylene terephthate)] blends. The mechanical properties and the influence of graft comonomers are described. The copolymers were characterized by the grafting rate and FTIR spectroscopy.
Three‐dimensional flow modeling of a self‐wiping corotating twin‐screw extruder. Part I: The transporting section
Authors: Goffart D. , Van Der Wal D. J. , Klomp E. M. , Hoogstraten H. W. , Janssen L. P. B. M. , Breysse L. , Trolez Y.
Published: April 2004

A three‐dimensional modeling of the transporting elements in a self‐wiping corotating twin‐screw extruder has been carried out by using the finite element package Sepran (1). This simulation uses the 3D geometry of the channel rolled over the twin‐screw, which consists of the intermeshing and normal areas. The flow profile, the backflow volume, the pressure buildup, the shear and elongation rates, and the adiabatic axial temperature gradient have been calculated by solving the Navier‐Stokes equations and the continuity equation for a Newtonian fluid. These results are given for different extruder parameters such as the throughput of the extruder, the rotation speed of the screws and the helix angle of the screws to better understand the influence of different extruder configurations. This study belongs to a program of research on the self‐wiping corotating twin‐screw extruder that also includes the modeling of the kneading elements (Part II) and, in the future, the study of scale‐up and heat transfer.
Two‐dimensional multilayer coextrusion flow in a flat coat‐hanger die. Part 2: Experiments and theoretical validation
Authors: Puissant S. , Vergnes B. , Agassant J. F. , Demay Y. , Labaig J. J.
Published: April 2004

In a previous paper (1), a two‐dimensional computation model for multilayer flows in coat‐hanger dies was proposed. It was based on lubrication approximation theory and enabled us to obtain the pressure field, the streamlines, and the interface positions in the whole die. The present paper is aimed to present experimental results obtained on an industrial line for a three‐layer configuration and to compare the results to the theoretical computation. The order of magnitude of pressure drops, flow rates, and interface positions were correctly predicted by the model. Some remaining discrepancies may be explained by the isothermal assumption and the lack of encapsulation mechanism in the computation.
Chemorheological analysis of unsaturated polyester‐styrene copolymerization
Authors: Muzumdar Shailesh V. , James Lee L.
Published: April 2004

An important feature of free radical crosslinking copolymerization of unsaturated polyester resin (UP) ‐ styrene is the formation of a heterogeneous structure through intra‐molecular reactions and phase separation. Such structure formation affects not only the cure behavior, but also the rheological changes. The chemorheology and the effect of shear on the structure formation, as well as the rheological changes, were investigated using rheometry, electron spin resonance spectroscopy, and dynamic light scattering goniometry. Based on experimental results, a conceptual model and a simple mathematical formulation are proposed to explain the shear effect on resin viscosity changes. Predictions obtained from the mathematical model are compared with experimental results.
Effect of compression process on void behavior in structural resin transfer molding
Authors: Ikegawa Naoto , Hamada Hiroyuki , Maekawa Zenichiro
Published: April 2004

To realize low void content molded parts, we propose structural resin transfer molding (SRTM) with the compression process. Resin was injected with a gap height between the upper and lower halves of matched metal dies. Mold filling was performed by a squeezing motion of the upper mold die. The usefulness of the compression process was examined by comparison to a conventional SRTM method. Void distribution and bending properties in both processes were compared. The SRTM method with compression was better at driving out voids. The effects of the gap height between the upper and the lower halves of the molds and of the gap closure rate during mold closing after injection on the void distribution were examined. The gap height did not affect the void distribution. When the gap closure rate was high, the voids were expelled towards the end of cavity, whereas voids remained on the top surface of the molded parts using a small gap closure rate. The difference in void behavior due to the gap closure rate was determined by a balance of the permeability between the flow and the transverse directions.
The effect of processing variables on the formation and removal of bubbles in rotationally molded products
Authors: Spence A. G. , Crawford R. J.
Published: April 2004

The rotational molding processing method for plastics is steadily expanding its product range and market areas. However, a drawback of the process has always been the surface pin‐holes and internal bubbles that occur in the products because of the inherent nature of the process. In an attempt to alleviate this problem, a program of research has been carried out to investigate the factors that affect the formation of the bubbles and, more importantly, that influence their removal. This paper describes the results of the first stage of this work and covers variables such as the viscosity of the polymer melt, the nature of the pigmentation, the particle size, shape and distribution in the powder feedstock, the mold release agent, the metal used for the mold, the temperature distribution in the mold, etc. It is shown that the mechanisms of bubble formation and removal can be explained and having done this, steps can be taken to ensure that once formed, the bubbles will decrease in size rapidly. This provides significant advantages in terms of reduced cycle time and improved product quality.
Optical properties of extruded polyethylene thin films related to anisotropy and inhomogeneous microstructure
Authors: Bernabeu E. , Boix J. M.
Published: April 2004

In this paper a method has been developed to extend the use of the well‐known expression of Clausius‐Mosotti for inhomogeneous materials, considering their anisotropy through a series expansion based on the structural factor of nonsphericity. This is related to experimental results available from the ordinary and extraordinary refractive indices of a set of samples of low‐density polyethylene films, where such phenomena are observed. Here results are obtained which are valid for the microscopic optical response, as it is shown by the linear fitting of these general expressions, with excellent correlation coefficients. Furthermore, if we apply the Bergman‐Milton limits, we can theoretically confirm the existence of two neutral lines experimentally obtained.
The relation between thickness and warpage in a disk injection molded from fiber reinforced PA66
Authors: Kikuchi Hiroyuki , Koyama Kiyohito
Published: April 2004

The relation between warpage and part thickness was investigated for a disk injection molded from PA66 compounded with 33 wt% glass fiber. A thin disk (1.5 mm thick) showed significant warpage, of magnitude 6.5 mm, while a thick disk (5.0 mm thick) did not warp. Finite element analyses were conducted, and the experimental results were numerically reproduced with 21% accuracy. It has been found that the thickness dependence of the disk warpage originates from the thickness dependence of the buckling temperature of the disk, and that quantitative disk warpage depends on the temperature of warpage measurement. Thickness change affects the amount of warpage but does not change essential warpage characteristics of the disk, characteristics such as inherent warpage deformation geometry and qualitative fiber orientation.
The effect of heat treatment on the microfibrillar network of poly(p‐phenylene benzobisthiazole)
Authors: Cohen Yachin , Gartstein Efim , Arndt Karl‐Friedrich , Ruland Wilhelm
Published: April 2004

Materials exhibiting exceptional mechanical properties can be fabricated from rigid polymers. In a spinning process, an oriented solution is solidified by the action of a nonsolvent, which induces crystallization of an oriented rigid polymer. Drying and heat treatment result in the final material having the desired properties. The effect of heat treatment on the morphology of poly(p‐phenylene benzobisthiazole) (PBZT) films was studied by measurements of small‐angle X‐ray scattering (SAXS) and wide‐angle X‐ray diffraction (WAXD). Films were formed by coagulation in water. The wet films were dried with supercritical CO2 to maintain an open network structure. Coagulation in water resulted in formation of microfibrils having diameter of ∼9 nm. Heat‐treatment at 600°C caused significant coalescence of microfibrils. The crystallite size was increased by heat treatment from a value that is smaller than the microfibrillar diameter indicating defects in chain packing, to a value comparable to the microfibrillar diameter.
Analysis of the thermal expansion behavior of oriented polyoxymethylene sheets
Authors: Zahran R. R. , Shenouda S. S. , El‐Tawil Y. A. , El‐Kayar A.
Published: April 2004

The applicability of the molecular composite model is extended to include the analysis of the thermal expansion behavior of oriented (anisotropic) polyoxymethylene. The model accounts for changes in the morphological and structural aspects of polyoxymethylene during solid state‐induced orientation. The results are reported and analyzed in terms of three‐dimensional surfaces. Apart from the effect of temperature, it has been found that the crystalline phase orientation distribution, λ, is the most crucial parameter affecting the thermal expansion behavior of anisotropic polyoxymethylene followed by the volume fraction crystallinity. The size and the geometry of the crystalline phase have negligible effects on the thermal expansion behavior of oriented polyoxymethylene. Above the glass‐transition temperature, a minimum in the transverse thermal expansion coefficient is exhibited in the vicinity of λ = 2 for volume fraction crystallinities ≤0.75. It is sufficient to align 75% of the crystallites with their c‐axis at ±10° to the draw direction, to attain the ultimate degree of anisotropy in the thermal expansion behavior of oriented polyoxymethylene sheets.
Mechanics of steady flow in coextrusion fiber spinning
Authors: Ji Ching‐China , Yang Jyh‐Chau , Lee Woei‐Shyong
Published: April 2004

The steady flow of isothermal bicomponent coextrusion fiber spinning has been investigated. A model has been chosen in which a Newtonian fluid and a Phan‐Thien/Tanner (PTT) fluid were considered to be the core and the skin layer, respectively. This model was adopted to study the effect on spinline velocity of an interaction between two fluids with quite different extensional rheology. The effects of the hoop stress, gravity, inertia, and surface and interfacial tensions were disregarded. Only viscous and viscoelastic forces were considered. A uniaxial extension was also assumed as the radius variation in the axial direction is small. The Newtonian fluid has been considered prone to fluctuate during melt processing while the viscoelastic skin layer has a stabilizing effect. The velocity profile was affected by the choice of two characteristic parameters: extensional and shear‐thinning parameters, as well as the viscoelastic skin flow rate ratio. Both shear‐thinning and extensional parameters play important roles in melt flow. The results show that as the draw ratio increases, the system is dominated by the extensional parameters, whereas slow drawing is dominated by shearing, in spite of the thin viscoelastic skin.
Homogeneous alkylation of poly(m‐phenylene isophthalamide)
Authors: Suzuki Kimihiro , Ikeda Isao , Yamamoto Ikuya , Okubo Mitsugu
Published: April 2004

Homogeneous alkylation of poly(m‐phenylene isophthalamide) (PMIA) was carried out in N‐methyl‐2‐pyrrolidone. Alkyl halides such as benzyl bromide and allyl bromide were reacted with sodium‐metallated PMIA. When the Taft equation was applied to this substitution reaction, the linear relationship was apparently obtained between log k/k0 and σ*. The molecular weight of alkylated PMIA decreased by sodium‐metallation and alkylation reactions. The weight loss of PMIA derivatives on heating increased with an increasing degree of substitution of the benzyl group, but it was improved by the reaction of the unsaturated alkyl group with 1,2‐ethanedithiol.
Orientation of triblock copolymers in planar extension
Authors: Lee Helen H. , Register Richard A. , Hajduk Damian A. , Gruner Sol M.
Published: April 2004

Three commercial styrenic triblock copolymers were subjected to planar extension in a lubricated channel die, as a model for the orientation that may occur during processing operations. Materials that contain cylinders of polystyrene show a pronounced orientation of the cylinder axis in the flow direction, as revealed by small‐angle X‐ray scattering in the three orthogonal directions. This anisotropy produces small‐strain tensile moduli that differ by a factor of 10 or more in the two in‐plane directions. A material that contains lamellae of polystyrene shows pronounced orientation of the lamellae in the plane of the sample; in particular, lamellar normals are strongly forbidden from pointing along the flow direction. For similar strains, planar extension is much more effective in orienting these materials than simple shear.
Accurate determination of a deformation measure in the screw extrusion process
Authors: Kim S. J. , Kwon T. H.
Published: April 2004

It is important to evaluate the deformation process accurately in analyzing mixing in extrusion. This paper discusses numerical methods to determine a representative deformation measure over the entire cross‐section of the extruder channel accurately and efficiently. Two different numerical methods are introduced to determine a deformation measure over the entire cross‐section of the extruder channel efficiently: (i) the first method based on the mapping sequence of the deformation gradient tensor; and (ii) the second method which does not require the evaluation of velocity gradient fields. These two methods are applied to the extrusion process of a single‐screw extruder and are compared with respect to their numerical accuracy. It is found that trajectories of fluid particles are difficult to obtain especially near the screw flight and barrel surface, which causes numerical inaccuracies with respect to obtaining a deformation measure. In this paper an inverse mapping method is employed to overcome such a numerical problem. For computational efficiency and accuracy, the second method was found to be more powerful compared with the first one, especially when there are singular points as in an extruder channel.
Melt miscibility in blends of polypropylene, polystyrene‐block‐poly(ethylene‐stat‐butylene)‐block‐polystyrene, and processing oil from melting point depression
Authors: Ohlsson Bertil , Törnell Bertil
Published: April 2004

The miscibility of isotactic polypropylene (PP) in blends with (a) polystyrene‐block‐poly(ethylene‐stat‐butylene)‐block‐polystyrene (SEBS) and processing oil, (b) poly(ethylene‐co‐propylene) (EPM), and (c) EPM and processing oil, has been studied using the method of melting‐point depression. Near equilibrium melting temperatures were determined by applying the Hoffman‐Weeks method to PP melting temperatures determined by DSC on samples crystallized isothermally for 20 h at 80, 100, 120 and 140°C. A large melting point depression was observed for PP in blends with SEBS and processing oil, suggesting that PP was soluble in the molten blends. On melting, the turbidity of the PP/SEBS/Oil blends increased, suggesting that the equilibrium melt contains two liquid phases. For PP in blends with EPM or EPM and processing oil, a melting‐point depression was not observed. The results indicate why PP/SEBS/Oil blends, within a wide composition range, formed bicontinuous interpenetrating network structures on cooling from the melt, whereas all of the blends with EPM formed solid blends with one continuous phase and one dispersed phase.
Polymer and oligomer melts: Thermodynamics, correlations, and lattice‐hole theory
Authors: Simha Robert
Published: April 2004

We discuss the position of lattice hole theories in the original Simha—Somcynsky formulation and modifications by Nies, Stroeks and Xie, as applied to a series of mixed systems, of the intermolecular as well as teh intramolecular type. The former encompass molecular mixtures of low and high molar mass constituents, and also composites. The latter include statistical copolymers as well as oligomers with their distinctive terminal and internal constituent groups. An important ingredient of these theories is the temperature and volume dependent hole fraction, obtained by the minimization of the configurational free energy. It has the character of a free volume quantity and is shown to bear a close relation to the free volume fraction extracted from positron probe spectroscopy. Its importance is implicit in the above applications. It is explicit in problems of phase relations and in correlations between surface tension and bulk properties of polymer and oligomer melts. Its significance for transport processes in the melt was pointed out by Utracki, and subsequently for viscoelastic processes in melt and glass, by several authors.
Droplet deformation in immiscible polymer blends during transient uniaxial elongational flow
Authors: Delaby I. , Ernst B. , Froelich D. , Muller R.
Published: April 2004

The deformation of dispersed droplets in immiscible polymer blends was studied in elongational flow by means of an original method based on quenching specimens elongated in the melt. Results for nearly Newtonian phases at high capillarity numbers were found to be in good agreement with the predictions of the small deformation Newtonian theory, up to relatively high drop deformations. The linear theory could be generalized to viscoelastic phases, using Palierne's theory of viscoelastic emulsions. The description of some experimental data could be improved in this way, but discrepancies due to nonlinear effects remained. Numerical simulations were carried out for different capillarity numbers in the Newtonian case and were in good agreement with experimental data. Preliminary results were also obtained for viscoelastic constitutive equations.
Influence of normal stress difference on polymer drop deformation
Authors: Levitt Leon , Macosko Christopher W. , Pearson Scott D.
Published: April 2004

Polypropylene drops of varying viscosity and elasticity were sheared in a polystyrene matrix. Two transparent, counter‐rotating parallel disks provided simple shear flow. By adjusting the speed of one disk the drop center was fixed in the laboratory frame and deformation followed via high magnification video camera. It was found that with high matrix elasticity drops of the minor phase stretched perpendicular (x3) to the flow direction (x1). This is the first report of widening of drops in shear flow. An analytical relation was established between the second normal stress differences of the phases and degree of widening. The formation of sheets and the phenomena of widening results in a larger than affine area generation.
Viscosity ratio effects in the compounding of low viscosity, immiscible fluids into polymeric matrices
Authors: Scott Chris E. , Joung Sandra K.
Published: April 2004

Many low viscosity, immiscible fluids are difficult to incorporate into polymer matrices because of thermodynamic immiscibility and a large mismatch of melt viscosities. In this investigation, a model system was used to determine the mechanisms and kinetics of mixing in such formulations. The model systems consisted of a series of different molecular weight polyethylenes in polystyrene. The viscosity ratio, η(polyethylene)/η(polystyrene), at 180°C and 100 s−1 was varied from 0.7 to 0.003. Phase inversion was observed during the compounding of these formulations. The phase inversion was associated with a transition from low to high mixing torque during compounding. This change was primarily due to an increase in the blend viscosity caused by the morphological transformation. The melting behavior during compounding depended on the melt viscosity of the polyethylene. A critical viscosity ratio of ≈ 0.1 exists below which softening of the polystyrene, and thus mixing of the two components, was greatly retarded. Even at very low concentrations, low viscosity polyethylene can have a significant effect on the processing behavior. Effects of mixer set temperature, degree of fill, and polyethylene particle size were explored. The roles of thermal conduction and mechanical energy input were evaluated in the melting regime of the process.
Polymer blend mixing and dispersion in the kneading section of a twin‐screw extruder
Authors: Huneault M. A. , Champagne M. F. , Luciani A.
Published: April 2004

This paper examines the mechanisms by which a polymer is dispersed in a co‐rotating twin‐screw extruder. An experimental investigation of the morphological evolution has been carried out on a 45‐mm co‐rotating twin‐screw extruder. Polyethylene/polystyrene (PE/PS) blends in the low concentration range (i.e., 5–15 wt% of PE) were used as a model system. The following general trends were observed. First, the minor phase right after melting is predominantly in a fibrillar form. Secondly, droplet and fiber diameter at this early stage of compounding are already in the micron or sub‐micron range. Even though a wide variety of mixing section configurations were used, the fibers created in the early compounding stages were relatively stable throughout extrusion. Morphological evolution after melting must therefore be discussed in terms of variation in the fiber fraction (i.e., fiber to droplet transition) rather than in a change in particle diameter. A control volume model for the flow in kneading blocks is used to interpret the morphological results and to predict the deformation and breakup of dispersed phase fibers under shear and in absence of coalescence. Theoretical results indicate that fiber breakup under shear is not likely in the kneading block under the normal processing conditions, which is confirmed by morphological observations made at the mixing section exit. The influence of several geometrical parameters on mixing and pumping in kneading blocks is also discussed with the use of flow model results.
A new rheometer measuring infrared dichroism in molten polymers subjected to transient and steady shear flow
Authors: Skytt M.‐L. , Färnert G. , Jansson J.‐F. , Gedde U. W.
Published: April 2004

A rotational parallel plate rheometer that enables simultaneous measurement of the transient or steady‐state rheological properties and infrared dichroism was designed and constructed to study orientation in molten polymers. Measurements can be carried out at shear rates between 0.05 and 300 s−1 and at temperatures between 20 and 300°C. Both shear stress and axial normal force together with dichroism are continuously measured during shear flow. Infrared dichroism data for polypropylene showed excellent agreement with data obtained with a FTIR‐instrument. The Hermans orientation function for molten poly(dimethyl siloxane) at steady state showed a strong shear‐rate dependence in the region 0.1−20 s−1. Rheological data for molten poly(dimethyl siloxane) agrees with data obtained from a conventional rheometer.
New developments in the melt rheology of nylons. I: Effect of moisture and molecular weight
Authors: Khanna Y. P. , Han P. K. , Day E. D.
Published: April 2004

Peculiar observations on the melt rheology of ultra‐dry nylon resins, nylon 6 in particular, are reported. One aspect of this study deals with a sharp increase in zero shear melt viscosity (e.g. 2 to 5 times) as the nylon 6 resin moisture is taken from 0.10 down to 0.00%; the effect being reversible. Changes of such magnitude are unexpected considering that there are no detectable variations of the chemical/compositional/molecular weight type in the starting resin, when subjected to the imposed drying conditions. Another aspect of this study deals with a deviation of nylons (6, 6,6, and 12) from the Bueche (1952) relationship, well accepted for polymers to date. Under moderate drying conditions (e.g. 50°C/17 h/110 millitorr), the molecular weight exponent is found to be 3.8, which is within the range of 3.4 to 3.8 reported for nylon 6. However, under more severe drying conditions (e.g. 110°C/17 h/110 millitorr), the molecular weight exponents for nylon 6, nylon 66, and nylon 12 are 4.8, 5.4, and 4.6, respectively. We are proposing that a sharp increase in melt viscosity of ultra‐dry nylon 6 is partly due to an increase in the molecular weight of the melt (extrudate) which then, has a more pronounced impact on melt viscosity in view of the 4.8 exponent. Such unique results, in contrast to polyethylene (free radical polymer) and poly(ethylene terephthalate) (condensation polymer) are tentatively attributed to H‐bonding in nylon melts. Yet another aspect of this study deals with the rheology of supercooled molten polymers that can offer advantages for analytical characterization.
Evidence for inversion of phase continuity during morphology development in polymer blending
Authors: Sundararaj Uttandaraman , Macosko C. W. , Shih Chi‐Kai
Published: April 2004

When polymer blends are prepared from a mixture of pellets, the melting order of the components is important in determining the mechanism of morphology development. Here, we show that an inversion of phase continuity occurs during processing when a minor phase component has a softening or melting transition temperature which is lower than the softening temperature of the major phase component. Three 80:20 concentration systems were studied: polyarylate/rubber, polyamide 6,6/polystyrene, and polystyrene/ethylene propylene rubber. Initially, the minor phase was the continuous phase and coated the major phase in all three systems. As the major phase melted, a switching of phase continuity occurred, and in the final blend state, the major phase was the continuous phase. An increase in power input was required during the switching of the dispersed and matrix phases. The compounding process was studied through continuous video monitoring, torque‐temperature analysis, and microscopy of quenched samples. A continuity inversion mechanism is proposed. It is found that the initial morphology of the blend consists of sheets of the major phase inside the minor phase. These sheets break up into irregularly shaped particles, which then coalesce around the minor phase. The effects of compatibilization (using reactive polymers or adding a premade diblock) on the rheology and morphology of the blend are also investigated. Interfacial reaction is seen to delay and intensify the inversion of phase continuity, whereas addition of premade diblock does not have any significant effect. The torque increases due to interaction of the major phase domains and due to reactive stabilization of the interface against coalescence, and the contributions of each to the torque can be decoupled.
Three‐dimensional finite element analysis of polymer rotational extrusion
Authors: Tzoganakis Costas , Karagiannis Aristotelis
Published: April 2004

A three‐dimensional finite element approach has been employed to model steady, creeping, isothermal helical flows and to study the effect of an imposed rotational field in a wire coating process and a tube extrusion process. It has been shown that the rotational field can affect process characteristics with an underlying viscous character, such as the velocity profile, pressure drop, viscous extrudate swelling, material pathlines, and deformation field. Significant pressure drop reduction may be achieved with implications on the process productivity, pressure drop reduction being most prevalent at low power‐law indices because of the increased nonlinearity in the shear‐thinning viscosity function. Extrudate swelling has been shown to be affected by the rotational field owing to the shear‐thinning nature of polymeric materials. Finally, it has been shown that significant material deformation may result from the imposition of the rotational field.
Three‐dimensional flow simulation of a film‐casting process
Authors: Sakaki Kazutaka , Katsumoto Ryuichi , Kajiwara Toshihisa , Funatsu Kazumori
Published: April 2004

Three‐dimensional flow simulation of a film‐casting process was performed using a finite element method assuming an isothermal and steady Newtonian flow. The simulation was carried out under industrial operation conditions. The neck‐in and the edge bead phenomena could be simulated. The effects of draw ratio, air gap length, and die width on these phenomena are discussed. The neck‐in and the edge bead phenomena were affected by the draw ratio and air gap length and not by the die width. The neck‐in value, which was defined as the difference between the die width and film width at the chill roll, increased with the draw ratio and air gap length.
Ultrasonic wave attenuation during water sorption in poly(2‐hydroxyethyl methacrylate) hydrogels
Authors: Maffezzoli A. , Luprano V. A. , Montagna G. , Esposito F. , Nicolais L.
Published: April 2004

A scanning laser acoustic microscope (SLAM) was used to measure the acoustic attenuation during water sorption in a film of crosslinked poly(2‐hydroxyethyl methacrylate) [poly(HEMA)] hydrogel. The contribution of reflection, scattering, and absorption of acoustic waves to the measured attenuation is evaluated. The analysis of a model accounting only for the possible reflection of the acoustic waves at the swollen/unswollen boundaries indicates that the time dependence of the attenuation during water sorption cannot be explained simply by accounting for the presence of two additional interfaces. A predominant contribution of acoustic wave absorption during the glass transition, occurring at the two swollen/unswollen interfaces, is assumed. Also, microvoids cannot be excluded as contributors to craze growth in the glassy matrix at the penetrant/polymer interface.
Equilibrium and dynamic swelling of polyacrylates
Authors: Bell Cristi L. , Peppas Nikolaos A.
Published: April 2004

Polyacrylates were prepared by solution polymerization of partially neutralized acrylic acid at 37°C. The swelling behavior of the polyacrylates was examined using equilibrium and dynamic swelling studies. Equilibrium swelling studies in deionized water were used to determine the molecular weight between crosslinks using the Flory‐Rehner theory. The amount of crosslinking agent incorporated into the network was a function of the nominal crosslinking ratio. Dynamic swelling studies in saline solutions were used to investigate the initial swelling rate for the polyacrylates. Swelling studies of the polyacrylates in saline solutions under load were used to elucidate the degree of swelling under load, the compliance, and sample elasticity.
Residual thermal stresses in injection molded products
Authors: Zoetelief W. F. , Douven L. F. A. , Housz A. J. Ingen
Published: April 2004

Nonisothermal flow of a polymer melt in a cold mold cavity introduces stresses that are partly frozen‐in during solidification. Flow‐induced stresses cause anisotropy of mechanical, thermal, and optical properties, while the residual thermal stresses induce warpage and stress‐cracking. In this study, the influence of the holding stage on the residual thermal stress distribution is investigated. Calculations with a linear viscoelastic constitutive law are compared with experimental results obtained with the layer removal method for specimens of polystyrene (PS) and acrylonitrile butadiene‐styrene (ABS). In contrast to slabs cooled at ambient pressures, which show the well‐known tensile stresses in the core and compressive stresses at the surfaces, during the holding stage in injection molding, when extra molten polymer is added to the mold to compensate for the shrinkage, tensile stresses may develop at the surface, induced by the pressure during solidification.
Simulation of slit dies in operation including the interaction between melt pressure and die deflection
Authors: Sander R. , Pittman J. F. T.
Published: April 2004

A simulation of slit dies in operation is described. Two‐dimensional finite element analyses are used for the pressure field in the die (based on Hele‐Shaw flow assumptions), and for the deflection of the die body resulting from this internal pressure (using Mindlin thick plate theory). These analyses are coupled in an iterative scheme, which converges to give results for the dynamic operating performance of the die. Predictions of deflections and pressure drops agree closely with experimental data. Post‐processing of primary pressure results yields the stream function, melt residence time, total melt strain, and wall shear stresses. The calculation routines are enclosed within a graphical user interface in the MS‐Windows operating environment, running on PCs, and providing a powerful and convenient computational aid for the designer and process operator.
Effect of pressure history on shrinkage and residual stresses—injection molding with constrained shrinkage
Authors: Jansen K. M. B. , Titomanlio G.
Published: April 2004

A simple elastic model for residual stresses and shrinkage of a thin solidifying product is proposed. The model results in expressions ready to be used. It accounts for shrinkage anisotropy between in‐plane and thickness directions, caused by different constraints in deformation. The model uses local values for temperature, pressure, crystallization, and (if present) extent of reaction, which belong to the standard output of most simulation codes. It is therefore assumed to be valid also for complex shaped products.
Crystallization behavior and mechanical properties of poly(aryl ether ether ketone)/poly(ether imide) blends
Authors: Frigione Mariaenrica , Naddeo Carlo , Acierno Domenico
Published: April 2004

Crystallinity and mechanical properties of blends with different amounts of semicrystalline poly(aryl/ ether ether ketone) (PEEK) and amorphous poly(ether imide) (PEI) polymers have been studied. The blends, prepared by melt mixing, have been investigated by differential scanning calorimeter (DSC) to analyze the miscibility between the components and the final crystalline content. Moreover, for the 20/80 PEEK/PEI blend, crystallization in dynamic and isothermal conditions has been carefully investigated in order to find proper conditions for maximum development of crystallinity. Mechanical tests (static and dynamic) have been performed to evaluate the properties of the as‐molded and crystallized blends and to compare them with those of crystalline PEEK and amorphous PEI neat resins. Finally, a few SEM observations have been performed to compare the fractured surface of the blend with those of the pure constituents.
Studies of optical haze and surface morphology of blown polyethylene films using atomic force microscopy
Authors: Smith P. F. , Chun I. , Liu G. , Dimitrievich D. , Rasburn J. , Vancso G. J.
Published: April 2004

Atomic force microscopy (AFM) has been used to examine the inner and outer surfaces of commercial blown polyethylene films. When this technique has been used, direct‐space images of surface lamellae have been obtained, and the surface roughness determined. The haziness of the films has been measured, both in the as‐produced state and when coated with suitable oil. Thus, both surface and bulk contributions to the apparent turbidity have been estimated. The aim of this study has been to correlate in turn the haziness, roughness, and surface morphology. Results obtained showed that the haze is related primarily to the surface roughness and can be reduced by lowering the frost line. AFM images unveiled lamellar features that were oriented predominantly in the transverse direction. The observed wide‐angle X‐ray diffraction (WAXD) intensities were consistent with an a‐axis type of orientation.
Conductivities and thermal studies of polymeric electrolytes based on poly(epichlorohydrin)/sodium salts
Authors: De Almeida Alessandra P. , Silva Glaura Goulart , De Paoli Marco‐A.
Published: April 2004

The halogenated polyether named Hydrin‐T® is a terpolymer constituted of epichlorohydrin‐ethylene oxide‐allyl glycidyl ether. It was studied as a polymeric electrolyte in polymer/NaX systems (X = Br−, I−, SCN−, ClO4− and B(C6H5)4−). In this work we present an investigation of the ionic conductivity (measured by impedance spectroscopy) and thermal properties (measured by differential scanning calorimetry–DSC, modulated DSC and thermogravimetry) of the polymeric electrolyte as a function of the composition in the range of 5 to 40 m/m(%) of the sodium salt. The solubility of sodium salts in the elastomer terpolymer matrix is comparable to the solubility in the best known matrix of linear semicrystalline PEO. The conductivities of the terpolymer/NaI electrolytes are higher than those of membranes prepared with other salts studied (10−5 S/cm for the former versus 10−7 to 10−6 S/cm for the latter). This system also is the most homogeneous up to 40 m/m (%) and showed the smallest increase of Tg values as a function of salt concentration [between ‐53°C for the pure polymer and ‐35°C for the 40 m/m (%) of NaI]. Modulated DSC confirmed the homogeneity of the terpolymer/NaI system showing Tg transition in a range of only 5°C. A decrease of variation of heat capacity during glass transition with the increase of salt concentration was observed.
Synthesis and characterization of photocrosslinkable poly(organophosphazene)‐bearing cinnamyloxide side groups
Authors: Choung Yun Sic , Lee Ki Ho , Lee Dong Choo
Published: April 2004

Two different poly(organophosphazene)s‐bearing single‐substituents (two cinnamyloxide side groups per repeating unit) and phenoxide‐co‐substituents (one phenoxide and one cinnamyloxide group per repeating unit) were prepared to study their photochemical reaction behavior. Structural formulas confirmed by the NMRs (1H, 31P) and IR were [NP(OCH2CH = CH  C6H5)2]n  (I) and [NP(OCH2CH = CH  C6H5)0.8 (O  C6H5)1.2]n  (II). Molecular characterization yielded \documentclass{article}\pagestyle{empty}\begin{document}$ \overline {M_w {\rm s}} $\end{document} of the order of 103 kg/mol for both the polymers. The onset temperature of decomposition found by TGA was about 250°C. DSC measurements gave Tgs as 1°C for I and 3°C for II. Their photolytic crosslinking behaviors were monitored by UV spectroscopy. The single‐substituents polymer I showed a faster rate of photo reaction than the polymer II. The potential use for practical photosensitive application is considered to be greater for the polymer I.