bluuebunny/crossref_metadata_2025 huggingface dataset:
Elastomer biaxial characterization using bubble inflation technique. II: Numerical investigation of some constitutive models
Authors: Rachik M. , Schmidtt F. , Reuge N. , Le Maoult Y. , Abbeé F.
Published: April 2004

An elastomeric material was investigated with a bubble inflation rheometer, and its mechanical behavior was modeled as a rubbeer‐like solid. Classical strain energy functions were considered and the hyper‐elastic were calculated by a direct identification procedure from simple uniaxial and equibiaxial extension test data, and the reults are compared against those obtained by an inverse method from matching the meaured response to a finite element to a finite element analysis solution, which dependent on the unknown material parameters. The optimised employed the Levenberg‐Marquardt algorithm and Abaqus software to compute the cost function and its gradients. The constants so obtained were further used in finite element analysis, and the numerical results were compared with experiments. This study showed that the inverse method, used to estimate the material parameters, is a good alternative to the direct identification, especially since the latter often requires homogeneous strain state, which is very difficult to obtain.
Properties and manufacturing of a new starch plastic
Authors: De Graaf R. A. , Janssen L. P. B. M.
Published: April 2004

Environmental awareness has strongly stimulated the introduction of biodegradable materials based on renewable resources of natural origin. This paper describes the properties and manufacturing of such a bioplastic. In a counter‐rotating twin screw extruder, starch and polystyrene were mixed. To enhance material properties such as tensile strength and impact strength, two routes were followed. First, the starch was altered by grafting polystyrene onto the starch backbone using a counter rotating twin screw extruder. The newly formed material was blended with polystyrene in difierent ratios. Tensile strengths of 10 to 35 MPa were obtained while notched impact strengths varied from 0.5 J m−1to 1.5 J m−1. Soaking the material for a certain time in water end measuring the tensile strength of the wet material revealed that the tensile strength remained more the less the same for blends containing more than 30 wt% PS. Second, polystyrene grafted starch was used as a compatibilizer. A homogenous blend could bobtained (according to scanning electronic microscopy pictures) by adding the compatibilizer to a starch, polystyrene, and water mixture. Again, tensile and impact strengths were measured for different ratios of the polymers used. The tensile strength and the impact strength were of the same magnitude as they were with the blended material. X‐ray diffraction and DSC measurements revealed a highly ordered system. When the fraction of polystyrene was above 60 wt% of the blend, the amylose part of the starch crystallized.
Microstrcture development during the injection molding of PET/LCP blends
Authors: Turcott E. , Nguyen K. T. , Garcia‐Rejon A.
Published: April 2004

A liquid crystal polymer (LCP) was blended polethylene terephthalate (PET) in different concetrations to improve the barrier properties of PET in injection stretch blow molded bottles. The improvement depends on the microstructure developed at various stages of the process.In this work, the emphasis is on the injection molding stage of the preform. The characteristics and number of morphological layers were directly related to the amount and type of LCP in the blend and the loction within the perform. It was found that at 10% LCP, three morphological layers were found across the thickness of the part, while at 30% LCP, five morphological layers could be identified. The LCP structure can be classified into four types: droplets, thick rods, thin fibrils and ribbons. Each morphological layer is made up of one or more types of structures. The evolution of on type structure to another depends on the particular flow regime ongoing at various locations in the mold. This microstructure development, during the flow, was examined in detail.
Structure and performance of impact modified and oriented sPS/SEBS blens
Authors: Yan R. J. , Shinozaki D. M. , Ajji A.
Published: April 2004

Blends of syndiotactic styrene/p‐methyl styrene copolymer (SPMS) and poly (styrene)‐block ‐ploy(ethene‐co‐butylene)‐block‐polystyrene (SEBS) as well as theiruniaxial drwing behavior andd performance were investigated. Mixing was performed using a batch mixer at 280°C. Morphology was evaluted using scanning electron microscopy (SEM).Thermal properties, orientation and tensile properties were determined using differential scanning calorimetry (DSC), the spectrographic birefringence technique, and a tensile testing machine, respectively. The blends of SPMS/SEBS, 90/10 and 80/20 showed a two‐phase structure with an SEBS disperse phase in SPMS matrix. The average sizes of the SEBS paticles and tensile properties of the blends were affected by blending time and compositions. No significant effects on the modulus and strength were observed for the blends containing 10%SEBS or below. The quenched SPMS and SPMS/SEBS (90/10) blends were drawn at 110°C. and their crystallinity and orientation development compared. These were similar for both samples at low draw rations (<3.2), but were much faster for SPMS at higher draw ratios. The orientation process is shown to substantially invrease the strength and modulus in the drawing direction for SPMS and the blends. The toughness (energy under the stress‐strain curve) increased upon addition of SEBS and orientation, with a marked effect of the latter. SEM observation reveals that the dispersed SEBS has been extended to about the same draw ratio as the bulk blend in the drawn blends, indicating effcient stress transfer at the interface.
Reactive blending of poly (dimethylsiloxane) with nylon 6 and poly (styrene):Effect of reactivity on morphology
Authors: Marić M. , Ashurov N. , Macosko C. W.
Published: April 2004

Reactive compatibilization was used to control and stabilize 20–30wt% poly(dimethylsioxane) (PDMS) dispersions in nylon 6 (PA) and poly(styrene) (PS), respectively. The effect of the type of reation (amine (NH2)/anhydride (An), NH2/ epoxy(E) and carboxylic acid (COOH)/E) on the morphology was studied with electron microscopy. PS and PDMS have mutual solvents thus it was possible to use gel permeation chromatography (GPC) to determine the concentration of block copolymer in PS/PDMS blends. Reactive blending of PA6 with difunctional PDMS‐(AN)2 did not decrease the PDMS particle size compared to the non‐reactive blend (∼10μm). Particle size decreaeased significantly to about 0.5 μm when PA6 was blended with a PDMS containing about 4 random An groups along the chain. For the PS/PDMS blends, GPC revealed that the NH2/An reaction formed about 3% block copolymer and produced stable PDMS particles ∼ 0.4 μm. No reaction was detected for the PS‐NH2/PDMS‐E blend and the morphology was coarse and unstable. Also, PS‐NH2/PDMS‐An reactivity was lower compared to other systems such as PS/ poly (isoprene) and PS/poly(methaacrylte) using the same reaction. This was attributed to the relatively thinner PS/PDMS interface dueto the high PS/PDMs immiscibility.
Reactive modification of polyethylene terephthalate with polyepoxides
Authors: Xanthos M. , Young M‐W. , Karayanndis G. P. , Bikiaris D. N.
Published: April 2004

In attempts to produce modified poldified polyethlene terephthalate (PET) ressins with improved rheology for applications requiring high viscosity and elasticity (e.g., lowdensity extrusion foaming, extrusion blow molding), a novel dimidodiepoxide of low molecular weight was evaluated aschain extender/branching ageent. Its reactivity was compared with that of an ethylene/glycidy1 methacrylate copolymer. The diepoxide showed higher reactivity than the copolymer and could be used at muchlower concentrations. The complex chain extension/degradation reactions occurring in the melt were followed in a batch mixer by torque changes, and by analyzing the prouducts for residual carboxy1 and hydroxy1 content, intrinsic viscosity, insoluble content and melt viscoelastic properties. The perliminary results of this work indicated an overall decrease in carboxy1 content, increase in hydroxy1 content, increase in intrinsic viscosity ans melt viscosity and storage modulus values depending on mixing time and the type and concentration of the additive. It is shown that under certain conditions. reaction of PET with less than 1 wt% diimidodiepoxide may produce materials with rheological characteristics similar to thouse of PET grades that are extrusion foamable by gas injection to low densities.
Transient elongational properties of an in situ generated polymer/polymer composite
Authors: Boyaud M. F. , Cassaugnau P. , Michel A. , Bousmina M. , Aït‐kadi A.
Published: April 2004

The elaboration of a n in‐situ composite consisting of ethylene vinyl acetate copolymer (EVA) and polybutylenetherephtalate (P m was investigated. An inter‐chain chemical reaction during processing operations was used to generate a grafted PBT‐g‐EVA copolymer at the interface of the two polymers. Composites with either nodular or fibrillar morphologies were obtained. Fibrillar morphology was achieved by stretching the extruded blend at the exit of the die. Elongational properties of such composites were investigated by using the fiber wind‐up technique. The influence of the aspect ratio of PBT solid inclusions on the elongational viscosity was discussed for a series of EVA/PBT composites. Clearly, the strain hardening softening properties were found to be strongly affected by the aspect ratio. Increasing the aspect ratio of PBT solid particles made the strain hardening weaker and even gave strain‐softening. This behavior is emphasized by the presence of the grafted PBT‐g‐EVA copolymer. The results suggest that strain‐hardening or softening of such composites is correlated to the homogeneity of the flow at EVA‐PBT interface: the elongational flow is disrupted in the interphase region so that the deformation around the particle is not homogeneous.
Rheological study of the miscibility of LLDPE/LDPE blends and the influence of Tmix
Authors: Hussein Ibnelwaleed A. , Williams Michael C.
Published: April 2004

The miscibility of LLDPE and LDPE blends and the influence of mixing temperature (Tmix) are discussed. Adequate amounts of antioxidants were added during melt blending. Dynamic and steady shear measurments were carried out at 190°C in a Rheometrics Mechanical Spectrometer 800.The dependence of rheological properties on blend composition indicated that blends of LLDEPE (butene) and LDPE mixed at 190°C and 220°C are only partially miscible; immiscibilty is likely to occur around the 50/50 composition and in the LDPE‐rich blends. Blends at 190°C are likely miscible in the LLDPE‐rich range. Tncreaasing Tmix did improve the miscibility of LLDPE/LDPE blends at 190°C or influence the dynamic sher properties (η′ or G′) of the “pure” resins of blends. Suggested that the molecular order [see Hussein and Williams, J. Non‐Newt. Fluid Mech., 86 105 (1999); Hussein and Williams, Macromol. Rapid Commun., 19, 323 (1998)] and mismatch of the molecular conformations of different polyethylene structures provide an explanation for the immiscibility of polyethylenes. Agreement was observed between themeasured dynamic properities and theortical predictions of Palierne and Bousmina‐Karner emulsion models.
Effective properties of cellular materials
Authors: Schjødt‐thomsen J. , Pyrz R.
Published: April 2004

This paper considers the effective properties of cellular materials. The present approach and some earlier proposed methods are compared and discussed. The main effort is placed upon the continuum mechanics approaches' ability to predict effective elastic properties. It is shown that two methods are distinctly better, namely a slight modification of the Mori‐Tanaka approach and a new approach by Dvorak and Srinivas, which is shown to predict the Young's modulus and shear modulus of the Divinycell H‐grade PVC foam almost exactly.
Recycled and restabilized hdpe bottle crates: Retention of critical properties after heat aging
Authors: Kartalis C. N. , Papaspyrides C. D. , Pfaendner R. , Hoffmann K. , Herbst H.
Published: April 2004

Oven aging was applied for about 8800 hours (more than one year) to evaluate the long‐term thermal stability of post‐used HDPE material recycled from bottle crates. For recycling, the remelting‐restabilization technique was applied. To study the effect of restabilization, crystallinity and melt flow rate were monitored during heat aging. Furthermore, tensile strength and tensile impact strength were followed together with the time until embrittlement. These data were enriched with microphotographs of the specimens' surfaces. Finally, repigmentation was used to evaluate the role of new pigments on the final performance of the recycled material. The results illustrate that restabilization is mandatory for improving the long‐term thermal stability of the post‐used crate material, enabling its reuse in the original application.
Visual analysis of cavity filling and packing process in injection molding of thermoset phenolic resin by the gate‐magnetization method
Authors: Ohta Takashi , Yokoi Hidetoshi
Published: April 2004

The Gate‐Magnetization method developed by Yokoi and coworkers for thermoplastics was used to investigate the flow behavior of glass‐fiber reinforced phenolic resin compound inside a mold cavity. Plug flow builds up in the cavity with a decrease of the local viscosity along the cavity wall due to the heat transfer from the wall and shear heating. Simultaneously, a high viscosity layer builds up from the crosslinking reaction along the cavity wall. The thickness of the high viscosity layer increased as the injection rate decreased. An unstable flow boundary formed between the reacted high viscosity layer along the wall and the low viscosity layer just under the layer.
An investigation of heat transfer effects in isothermal crystallization studies of low‐density polyethylene
Authors: Grady B. P. , Genetti W. B. , Lamirand R. J. , Shah M.
Published: April 2004

Isothermal crystallization kinetics of low‐density polyethylene (LDPE) were measured from 96°C‐103°C using a power‐compensating differential scanning calorimetry (DSC). Crystallization kinetics were measured using different sample thicknesses and on samples compounded with nickel, a filler with high thermal conductivity. For the unfilled material, sample thickness and temperature had a significant effect on the rate of crystallization as measured by the Avrami rate constant K, but had no effect on the nucleation mechanism and dimensionality of growth, as measured by the Avrami constant n. The crystallization growth rate as expressed by K1/n scaled approximately with the thickness of the sample. For the filled material, K was much higher and independent of nickel content, suggesting a limiting growth rate for polyethylene at a given temperature in this equipment. The dependence of crystallization rale on sample thickness indicates that barriers to heat transfer can be important. This work shows that for most crystallization rates, thermal conductivity, rather than interfacial resistance between sample and pan, limits heat transfer. Even though thermal conductivity typically dominates heat‐transfer resistance, sample‐pan thermal contact is still important, and some guidelines are given to determine whether good contact is being made.
Modeling of structural reaction injection molding process. I. Mathematical model
Authors: Malkin Alexander Ya. , Kuznetsov Victor V. , Kleba Ingo , Michaeli Walter
Published: April 2004

A mathematical model of the infusion process in producing reinforced articles is proposed. The model is based on the analysis of flow of a Newtonian liquid inside a rectangular multilayer channel. According to the model, a liquid enters the central (feeding) layer, moves through this layer, and simultaneously impregnates peripheral layers. So, the flow is two‐dimensional. Flow inside the porous layers is treated in terms of the Darcy equation with different permeability coefficients in two directions. Principal solutions for the flow front development and pressure evolution were obtained and analyzed. Then the initial model, developed for a Newtonian liquid, is generalized for the so‐called “rheokinetic” liquid, which changes its rheological properties in time as a result of temperature variation and/or any possible chemical process, in particular, the reaction of curing of a binder. It was proven that in this case the solution is automodel. This means that the solutions obtained for a Newtonian liquid in the dimensionless form are valid for an arbitrary rheokinetic liquid.
Numerical simulation of moving free surface problems in polymer processing using volume‐of‐fluid method
Authors: Kim Ju Min , Ahn Kyung Hyun , Lee Seong Jae , Lee Seung Jong
Published: April 2004

We have developed a numerical algorithm based on 2D/3D finite element method for solving non‐Newtonian fluid flow with the moving free surface encountered in polymer processing. The power law model is considered as a rheological constitutive equation. The standard Galerkin finite element formulation/penalty formulation are applied to discrctize the governing equations, the volume‐of‐fluid (VOF) scheme is used to track the moving free surface, and the donor‐acceptor model introduced by Hirt and Nichols is modified and implemented on FEM. We applied the numerical scheme to simulate fountain flow and viscous buckling problems. For fountain flow, the numerical prediction of this study is in good agreement with the experimental results of other investigators. For viscous buckling, both 2D and 3D numerical simulations show that the shear thinning effect retards buckling. As this algorithm is very effective in treating moving free surface problems and requires less memory than previous algorithms, it may help solve challenging problems in polymer processing such as transient visroelastic flow simulations with moving free surfaces.
A theoretical and experimental heat of mixing study for polymer‐polymer mixtures
Authors: Taimoori M. , Modarress H. , Saboury A. A. , Moosavi‐movahedi A. A.
Published: April 2004

Heat of mixing is introduced as a guide for phase stability predictions of polymer mixtures, and an appropriate equation is presented for it. The form of this equation is a combined function of temperature and mixture composition. The capability of the presented equation has been treated qualitatively and it has been shown that all types of exothermic, endothermic, and s‐shaped or sigmoidal heat of mixing curves can be produced. Utilizing the low molecular weight analogue calorimetry method, heat of mixing was measured at two temperatures, 27°C and 37°C for three polymer mixtures—poly(styrene)/poly(vinylchloride) (PS/PVC), poly(styrene)/ poly(methylmethacrylate) (PS/PMMA), and poly(styrene)/poly(vinylacetate) (PS/ PVAc) at an entire composition range. It has been shown that excellent agreement between the results of the calculations and the experimental heat of mixing data was achieved. Using the results of analogue calorimetric measurements for phase stability studies of polymer mixtures, it was found that often, acceptable predictions can be made by this method, but they are not always completely true.
Creep and stress relaxation in methacrylate polymers: Two mechanisms of relaxation behavior across the glass transition region
Authors: Higgenbotham‐bertolucci P. R. , Gao H. , Harmon J. P.
Published: April 2004

This study explores the long‐term behavior of poly(methyl methacrylate), poly(ethyl methacrylate), and poly(2, 2, 2‐trifluoroethyl methacrylate) by creep and stress relaxation (SR) experiments. Dielectric analysis (DEA) and dynamic mechanical analysis (DMA) are used to measure and compare the structural relaxations associated with side group motion and with the glass transition, Tg, region. An analysis of shift factor data for creep and SR experiments reveals two modes of molecular motion in the glass‐rubber relaxation region, but the modes are less discernible than those reported previously for a series of styrene polymers. The high temperature side exhibits WLF behavior while the low temperature side exhibits Arrhenius behavior. The extent of definition of the two modes of deformation is related to the effect of cooperative α dynamics on the β relaxation process. Some discussion is presented concerning the magnitude of the activation energy for both processes and the sharpness of the transition betwen the two modes.
Pre‐melting temperature effect on the isothermal melt crystallization and multiple melting behavior of syndiotactic polystyrene
Authors: Chiu Fang‐chyou , Shen Kuan‐yeu , Tsai Stanley H. Y. , Chen Chien‐ming
Published: April 2004

This work examined how pre‐melting temperature (Tmax) affects the isothermal melt crystallization kinetics, the resulting melting behavior and crystal structure of syndiotactic polystyrene (sPS) by using differential scanning calorimetry (DSC), polarized light microscopy (PLM) and the wide angle X‐ray diffraction (WAXD) technique. Experimental results indicated that raising Tmax decreased the nucleation rate and the crystal growth rate of sPS. The Avrami equation was also used to analyze the overall crystallization kinetics. The Avrami exponent n and rate constant K were determined for different Tmax specimens at various crystallization temperatures (Tc's). Our results indicated that the nucleation type of sPS is Tmax and Tc dependent as well. Evaluation of the activation energy for the isothermal crystallization processes revealed that it increases from 375 kJmol−1 to 485 kjmol −1 with an increase of Tmax. From the melting behavior study, we believe that the Tmax and Tc‐dependent multiple melting peaks are associated with different polymorphs as well as recrystallized crystals formed during heating scans. Moreover, the percentage content of α form in the crystals formed under different crystallization conditions was estimated through WAXD experiments.
Fusion bonding of polyamide 12
Authors: Zanetto J.‐E. , Plummer C. J. G. , Bourban P.‐E. , Månson J.‐A. E.
Published: April 2004

The strength of fusion bonds between polyamide 12 plaques has been investigated as a function of processing conditions, using the double cantilever beam geometry to measure the mode I critical strain energy release rate, Gc. Bonding was carried out using an instrumented press, which allowed systematic variation of the bonding time, the holding pressure, the interface temperature and the initial difference in temperature between the plaques. Gc was generally found to increase with hold time and interface temperature. However, for a given hold time, hold pressure and estimated interface temperature, the highest Gc were obtained under nonisothermal conditions, that is, when the initial temperatures of the plaques were different. Based on fractographic analysis and observations of the effect of the hold pressure, it is concluded that enhanced wetting is an important factor in the improved efficiency of non‐isothermal bonding.
Copolymerization of ethylene and 1‐decene by metallocenes: Direct comparison of Me2C(Cp)(Flu)ZrMe2 with Et(Cp)(Flu)ZrMe2
Authors: Kim Il , Kim Ki Tae , Lee Min Hyung , Do Youngkyu , Chung Hoeil
Published: April 2004

Copolymerizations of ethylene with 1‐decene have been carried out by using two syndiospecific metallocenes synthesized by modifying the bridge: highly syndiospecific isopropylidene(1‐η5‐cyclopentadienyl)(1‐η5‐fluorenyl)‐dimethylzirconium (Me2C(Cp)(Flu)ZrMe2, 1) and less syndiospecific (1‐fluorenyl‐2‐cyclopentadienylethane)‐dimethylzirconium (Et(Cp)(Flu)ZrMe2, 2), in the presence of [Ph3C][B(C6F5)4] as a cocatalyst. The ethano bridged 2 compound of smaller dihedral angle showed much higher activity than 1 compound. The catalytic activities of the two compounds were enhanced about twice when a suitable amount of 1‐decene comonomer is present in the feed. The compound 1 showed better comonomer reactivity than 2. The properties (Tm, density, and crystallinity) of copolymers seem not to be affected by the type of bridge of the metallocenes, and mainly depend on 1‐decene content in the copolymer.
On helical flows of polymer fluids
Authors: Jeong Jae‐Hyeuk , Leonov Arkady I.
Published: April 2004

Isothermal and non‐isothermal steady helical flows are theoretically investigated under the assumption that the flow is fully developed in both the thermal and hydrodynamic senses. It is well known that the basic gross characteristics of steady isothermal helical flows of non‐Newtonian liquids can be found relatively easily if the flow curve (or non‐Newtonian viscosity) in simple shearing is known. Nevertheless, evaluation of more detailed viscoelastic properties in this type of flow is also sometimes desirable. These properties are shown to be exactly determined in both the isothermal and non‐isothermal cases as soon as a nonlinear viscoelatic constitutive equation is specified. Shear thinning due to fluid rotation and strong temperature dependence of Newtonian viscosity highly increase dissipative heat. This can produce significant non‐isothermal effects in intense helical flows, even when the wall temperature is kept uniform and constant. It is shown that the energy consumption in isothermal and non‐isothermal helical flows is always higher than in respective annular flows with the same flow rate. Comparisons between our calculations and available experimental data are also discussed.
Thermally stimulated depolarization currents in poly (ethyleneterephthalate‐ran‐p‐hydroxybenzoates)
Authors: D'Souza Nandika Anne
Published: April 2004

Thermally stimulated polarization (TSPC) and depolarization currents (TSDC) are measured on polyethylene terephthalate (PET) copolymerized with p‐hydroxy benzoic acid (PHB). These systems are important since they comprise components of many commercial polymer liquid crystals (PLCs). There has been some speculation about the origins of the multiple transition peaks in TSDC of PLCs and secondary peaks have frequently been designated as resulting from Maxwell‐Wagner interphase polarization. The applicability of this designation for main chain PLCs has been investigated. TSDC as a function of field strength and window polarization has been conducted and the transitions have been identified as glass transition peaks as opposed to space charge relaxations. A comparison of the TSDC current versus the polarization current (TSPC) reveals that TSPC is not generated for transitions associated with the PHB component.
Preparation of fibers with nanoscaled morphologies: Electrospinning of polymer blends
Authors: Bognitzki Mikhail , Frese Thomas , Steinhart Martin , Greiner Andreas , Wendorff Joachim H. , Schaper Andreas , Hellwig Michael
Published: April 2004

The aim was to prepare fibers with diameters below the micrometer range characterized by specific bulk morphologies and surface topologies. Such materials are of interest for various applications including reinforcement, sensors or filtration as well as the formation of functional tubes by the use of fiber templates. We were able to manufacture highly structured submicrometer fibers by electrospinning from ternary solutions using polylactide (PLA) and polyvinylpyrrolidone (PVP) as polymer model components. Co‐continuous phase morphologies resulted from phase separation processes taking place during fiber formation. In a subsequent step, specific surface topologies or fine pores were generated by selective removal of one of the components.
Evolution of structure in the softening/melting regime of miscible polymer mixing
Authors: Burch Heidi E. , Scott Chris E.
Published: April 2004

Structure development in the softening/melting processing regime is investigated using the model miscible blend poly(styrene‐co‐acrylonitrile) (SAN)/poly(methyl methacrylate) (PMMA). Feed materials of four different particle sizes are compounded to study their effects upon structure development. Fourier‐transform infrared spectroscopy is used to help determine the normalized sample variance, a quantitative measure of mixing. The normalized sample variance is determined both as a function of sample size and as a function of feed particle size in an effort to assess the characteristic size scale(s) present in the blend at short mixing times. Results of these experiments indicate that the distribution of size scales in the softening regime is at least bimodal. Optical examination of pigmented mixtures reveals that this multimodality is due to the operation of the Scott/Macosko sheeting mechanism of morphology development, which was previously shown to be active in immiscible blends. This is contrary to the currently accepted laminar mixing model, which postulates the formation of a striated mixture while ignoring the softening/melting regime.
Glass‐polymer melt hybrids. I: Viscoelastic properties of novel affordable organic‐inorganic polymer hybrids
Authors: Adalja Sunil B. , Otaigbe Joshua U. , Thalacker Jason
Published: April 2004

A novel class of organic‐inorganic polymer hybrids was developed by melt‐blending up to 50 (v/v) % [about 83 (w/w) %] tin‐based polyphosphate glass (Pglass) and low‐density polyethylene (LDPE) in conventional plastics processing equipment. The liquid‐ and solid‐state rheology of the polymer hybrids was studied under oscillatory shear flow and deformation to understand the behavior of these materials and to accelerate efforts to melt process the Pglass with organic polymers. All the materials were found to be linearly viscoelastic in the range of temperature and frequencies examined and their viscoelastic functions increased with increasing Pglass concentration. The Pglass significantly enhanced the shear‐thinning characteristics of the Pglass‐LDPE hybrid, indicating the presence of nonlinear chemical and physical interactions between the hybrid components. Morphological examination of the materials by scanning electron microscopy revealed interesting evolution of microstructure of the Pglass phase from droplets (or round beads) to elongated and interpenetrating network structures as the glass concentration was increased in the Pglass‐LDPE hybrids. Melt viscosities of the materials were well described by a simple power‐law equation and a Maxwellian (Hookean) model with three relaxation times. Time‐temperature superpositioning (TTS) of the complex viscosity versus frequency data was excellent at 170°C < T < 220°C and the temperature dependencies of the shift factors conformed excellently well to predictions from an Arrhenius‐type relation, enabling calculation of the flow‐activation energies (25–285 kj/mol) for the materials. The beneficial function of the Pglass in the hybrid system was significantly enhanced by pre‐treating the glass with coupling agents prior to incorporating them into the Pglass‐LDPE hybrids.
The effect of feeding mode on dispersive mixing efficiency in single‐screw extrusion
Authors: Elemans P. H. M. , van Wunnik J. M.
Published: April 2004

In the case of dry color compounds, where polymer pellets are coated with a pigment powder, the latter tends to form agglomerates during extrusion, owing to the hydrostatic pressure that prevails in the screw channels. In single‐screw extruders, this pressure is due to the Coulombic fricional transport in the solids conveying zone. The formation of agglomerates can be prevented to a considerable extent by operating the extruder in an underfed mode. This result has emerged from a study of the problems encountered when dispersing pigments in poly(butylene terephthalate) (PBT), but can also be applied in the case of numerous compounds where a fine dispersion of solids in polymers is required.
Blends of two thermotropic liquid crystalline polymers: The influence of reactions during injection molding on the phase structure and the mechanical behavior
Authors: Vallejo F. J. , Eguiazábal J. I. , Nazábal J.
Published: April 2004

Blends of two different thermotropic liquid crystalline polymers, poly(p‐hydroxy benzoic acid‐co‐2, 6‐hydroxy naphthoic acid), VA, and poly(p‐hydroxybenzoic acid‐co‐terephthalic acid‐co‐aminophenol), VB, were obtained by direct injection molding throughout the full composition range. The blends were almost fully immiscible apart from a low degree of reaction. This, as well as the nature of the blends, probably influenced their mechanical properties. Enhanced properties were obtained both in the modulus of elasticity and in the tensile strength, at all the compositions studied, with absolute maxima at VB contents between 50% and 75%. These synergisms were mainly due to a greater orientation of the components in the blends than in the pure components.
Effect of molecular weight and branch structure on the crystallization and rheological properties of poly(butylene adipate)
Authors: Chae Han Gi , Kim Byoung Chul , Im Seung Soon , Han Yang Kyoo
Published: April 2004

High molecular weight linear and branched poly(butylene adipate)s (PBAs) were prepared, and crystallization behavior and rheological properties were investigated. PBAs showed multiple melting behavior. Increasing molecular weight retarded the crystallization rate and increased the induction time for crystallization. Introducing branches to the polymer led to similar results. The Avrami exponent (n) for the linear and branched PBAs were 3.79–4.39 and 2.09–3.64, respectively. The Mark‐Houwink exponent of the PBAs was 0.554. Unlike general‐purpose polyesters, high molecular weight PBAs did not exhibit a Newtonian flow region. High molecular weight PBAs exhibited gel‐like rheological properties, producing high elasticity. The slopes of a log‐log plot of storage modulus (G′) vs. loss modulus (G″) ranged from 1.75 to 1.17, and the slope decreased with increasing molecular weight. For comparable molecular weights, the branched PBAs had higher viscosity and G′ than the linear polymers.
The dependence of rapid crack propagation in polyethylene pipes on the plane stress fracture energy of the resin
Authors: Brown Norman , Lu Xici
Published: April 2004

The critical temperature [CT] for rapid crack propagation [RCP] was measured in 11 polyethylene [PE] 200 mm diameter gas pipes each with different resins. The plane stress fracture energy [PSFE] in thin Charpy impact specimens of the resin was found to correlate with the CT. The higher the PSFE, the lower the CT. This result was related to the observation that the PSFE decreases as the temperature decreases. It was found that the impact energy of specimens from compression molded pipe that was remelted at 180°C gave a better correlation with the CT than specimens that were machined from the inner wall of the pipe. Consequently, it is now possible to predict the CT of a pipe by measuring the PSFE of the resin without making the pipe.
Effect of entanglement on brittle‐ductile transition in polyethylene
Authors: Kitao Koichi
Published: April 2004

The brittle ductile transition temperature (BDTT) of polyethylene with different degrees of entanglement density produced by crosslinking was evaluated using the Charpy impact test. BDTT was defined as the temperature at which the Charpy impact value Et changed abruptly from low to higher values. The increase in entanglement density brought about only a slight fall in BDTT, although that led to an increase in Et at ambient temperature corresponding to the occurrence of a dimple type fracture. A transition model between brittle fracture, patchwork type fracture (craze‐like) and yielding deformation, depending on the degree of crosslinking, was proposed to explain those experimental results.
An investigation on craze growth at a crack tip in polymers
Authors: Yang Ting‐Qing , An Qunli , Luo Wenbo
Published: April 2004

A craze zone model with damage at the crack tip in polymers under creep is presented. By taking into account a power law material, time‐dependence of both craze advance and thickening at the tips of a center crack is investigated. Numerical results show that both length and thickness of the craze zone increase with time while the mean stress decreases. It is also shown that the calculated craze zone profile is coincident with previous experiments, and the size of the craze zone with a damage model is larger than that without considering damage at crack tip zone.
Thermophysical property modifications in functional polymers via lanthanide trichloride hydrates
Authors: Belfiore Laurence A. , Ruzmaikina Izolda Y. , Das Pronab K.
Published: April 2004

Fourteen water‐soluble trivalent metal chlorides from lanthanum to lutetium in the 1st‐row of the f‐block form complexes with poly(vinylamine) and increase the glass transition temperature from 57°C to well above 100°C at very low molar concentrations of the lanthanide. The large ionic radii of these hard‐acid cations allow several hard‐base amino sidegroups in the polymer to occupy sites in the first shell coordination sphere via ion‐dipole (i.e., electrostatic) interactions, which leads to microclustering of the ligands about a single metal center. The enhancement in the glass transition temperature is explained in terms of multi‐functional coordination crosslinklng. f‐Block salts induce larger increases in Tg, relative to transition metal‐complexes from the d‐block, however CoCl2(H2O)6 performs comparably to some of the more efficient lanthanides. Blends of poly(vinylamine) and trimethoxysilyl‐propylpoly(ethylene imine)hydrochloride form complexes with europium(III) and exhibit synergistic single Tg response. Since lanthanides form very stable complexes with chelating (i.e., bidentate) oxygen ligands, it is possible to increase the elastic modulus of commercially important copolymers of ethylene and methacrylic acid via Eu3+ complexation with the carboxylate anion. This claim is verified by infrared spectroscopy. Temperature and pH‐sensitive applications for drug delivery and removal of contaminants from wastewater streams should increase the utility of these lanthanide complexes.
Melt‐spun hollow fibers: Modeling and experiments
Authors: De Rovère Anne , Shambaugh Robert L.
Published: April 2004

Polypropylene hollow fibers were prepared via melt spinning at speeds of 1000–2500 m/min. The outside diameters of the fibers were measured on‐line with high‐speed photography. The fiber formation process was modeled with momentum, energy, and two continuity equations (one for the polymer, and one for the lumen fluid). The equations were solved numerically, and the results were compared to the on‐line diameter data. Both Newtonian and viscoelastic constitutive equations were considered.
Styrene grafting onto a polyolefin in an internal mixer and a twin‐screw extruder: Experiment and kinetic model
Authors: Cha Jaehyug , White James L.
Published: April 2004

There has been relatively little effort to quantitatively understand graft copolymerizaution in either batch mixers or twin‐screw extruders. Most efforts have concentrated on grafting maleic anhydride, which does not homopolymerize. In this paper we consider grafting with styrene, which may homopolymerize as well as graft. The influence of residence time on degree of grafting in an internal mixer and a twin‐screw extruder were studied by measuring reaction yields with respect to reaction time in a mixer and along the screw axis in a twin‐screw extruder. The degree of grafting increased with initial monomer and peroxide concentration. Grafting reactions with three different peroxides were also investigated. The degree of styrene grafting in an internal mixer is slightly higher than that in a twin‐screw extruder. The rate of reaction along the screw axis in terms of residence time seems higher than for the batch mixer. The melt viscosity dropped dramatically with addition of peroxide. A kinetic scheme is proposed and the experimental results are critically compared with it.
Blends of bitumen with polymers having a styrene component
Authors: Fawcett A. H. , McNally T.
Published: April 2004

The properties of a 100 penetration grade bitumen are modified considerably, and in a number of ways by the addition of 10 to 40 parts per hundred (pph) of a homopolystyrene and graft, block and random copolymers of styrene with butadiene and acrylonitrile. At low temperatures some blends have a similar stiffness to or even lower stiffness than the bitumen, but generally the blends are more than one order of magnitude stiffer, even when a rubber is added. The contrasting behavior is displayed by a polystyrene and a high impact polystyrene, ∼3% to 4% of grafted rubber on the latter being sufficient to cause the enhancement, even at the 10 pph level, by two different random styrene‐butadiene copolymers, and also by blends consisting of different amounts of SBS block copolymer. Some polymers apparently trigger a Hartley inversion of the micellar structure of the asphaltene micelles. High low temperature stiffness correlates roughly with a lower Tg' as measured by the peak maximum in the E″ plots of the dynamic mechanical thermal analysis (DMTA) and by the steps in the differential scanning calorimetry (DSC) curves at temperatures below O°C. Tan δ maxima and DSC traces detected the glass transition in the continuous phase and in the dispersed phases, but none of these amorphous polymers formed a crystalline phase, though the DSC traces of the polystyrene and the SBS blends suggested that the polymer‐rich phases underwent an aging/ordering process on cooling. Our SBS blends differ in phase inversion behavior and the pattern of loss processes from others that had a smaller asphaltene component.
The design of conformal cooling channels in injection molding tooling
Authors: Xu Xiaorong , Sachs Emanuel , Allen Samuel
Published: April 2004

Solid Freeform Fabrication technologies have demonstrated the potential to produce tooling with cooling channels, which are conformal to the molding cavity. 3D Printed tools with conformal cooling channels have demonstrated simultaneous improvements in production rate and part quality as compared with conventional production tools. Conformal cooling lines of high performance and high complexity can be created, thus presenting a challenge to the tooling designer. A systematic, modular approach to the design of conformal cooling channels is presented. Cooling is local to the surface of the tool, so the tool is divided into geometric regions and a channel system is designed for each region. Each channel system is itself modeled as composed of cooling elements, typically the region spanned by two channels. Six criteria are applied, including: a transient heat transfer condition, which dictates a maximum distance from mold surface to cooling channel; considerations of pressure and temperature drop along the flow channel; and considerations of the strength of the mold. These criteria are treated as constraints, and successful designs are sought that define windows bounded by these constraints. The methodology is demonstrated through application to a complex core and cavity for injection molding.
Comparison of structure development in quiescent crystallization, die extrusion and melt spinning of isotactic polypropylene and its compounds containing fillers and nucleating agents
Authors: Yu Yishan , White James L.
Published: April 2004

The influences of fillers and nucleating agents on crystalline structure and stress induced crystallization of isotactic polypropylene were studied under a range of cooling and processing conditions, including die extrusion and melt spinning. Continuous cooling transformation curves were determined for polypropylene and various polypropylene filler compounds. The influence of spinline stress on crystallization was studied. The experiments reveal that under quiescent conditions, the kinetics and crystalline forms produced by the crystallization of polypropylene are dominated by nucleating fillers and impurities. The crystalline orientation‐spinline stress relationship, on the other hand, was found to be the same for polypropylene and its compounds. At high uniaxial stresses, kinetics and orientation development are dominated by homogeneous orientation crystallization.
Molecular characterization and rheological properties of modified poly(ethylene terephthalate) obtained by reactive extrusion
Authors: Nguyen Quoc Tuan , Japon Sonia , Luciani André , Leterrier Yves , Månson Jan‐Anders E.
Published: April 2004

The use of a tetrafunctional epoxy‐based additive to modify the molecular structure of poly(ethylene terephthalate) (PET) was investigated with the aim of producing PET foams by an extrusion process. The molecular structure analysis and shear and elongation rheological characterization showed that branched PET is obtained for 0.2, 0.3 and 0.4 wt% of a tetrafunctional epoxy additive. Gel permeation chromatography (GPC) analysis led to the conclusion that a randomly branched structure is obtained, the structure being independent of the modifier concentration. The evolution of shear and extensional behavior as a function of molecular weight (Mw), degree of branching, and molecular weight distribution (MWD) were studied, and it is shown that an increase in the degree of branching and Mw and the broadening of the MWD induce an increase in Newtonian viscosity, relaxation time, flow activation energy and transient extensional viscosity, while the shear thinning onset and the Hencky strain at the fiber break decrease markedly.
Visualization and microscopic modeling of phase inversion during compounding
Authors: Ratnagiri R. , Scott C. E.
Published: April 2004

A detailed description of the sequence of deformation steps leading to phase inversion during compounding in a low‐viscosity‐ratio co‐polyester/polyethylene blend is presented. Visualization using a glass window and sampling of the blend at different mixing times enabled identification of the intermediate morphologies of the major component en route to phase inversion. Based on these observations, a theoretical model is developed to predict the time to phase inversion. The model incorporates a simplified flow‐field approximation and the calculation of strain imparted to the major component domains. A strain‐based criterion for phase inversion is then proposed, which, in conjunction with the model, yields an explicit expression for the time to phase inversion during compounding, tP.I.. The model predictions are seen to be in good agreement with the increase of tP.I., on scaleup between two mixing bowls. The correct functional dependence of tP.I. on the nominal maximum‐shear‐rate is predicted. Using combination of pure drag and planar extensional flow, the model predictions are shown to be consistent with the observed dependence of tP.I. on the volume fraction of the minor component and the blend viscosity ratio.
Nonlinear viscoelastic and viscoplastic response of glassy polymers
Authors: Spathis G. , Kontou E.
Published: April 2004

The main features of inelastic mechanical behavior of glassy state were studied theoretically and experimentally in terms of tensile stress‐strain and tensile creep experiments. A theoretical treatment introduced in earlier work, which takes into account the viscoelastic path at small strains and the viscoplastic one at higher stresses, proved to be capable of describing the main aspects of mechanical response of glassy polymers, i.e. nonlinear viscoelasticity during creep procedure, and yield stress, yield strain, strain softening and rate effect in a constant crosshead speed test.