bluuebunny/crossref_metadata_2025_split huggingface dataset:
Bonding strength at solid‐melt interface for polystyrene in a sequential two‐staged injection molding process
Authors: Huang D. Y. , Chen R. S. 
Published: April 2004

AbstractThe effects of processing parameters, such as melt temperature, mold temperature and cooling time, on the bonding strength of the interface in a sequential two‐staged injection molding process were investigated both theoretically and experimentally. A theoretical bonding strength model, which accounts for the cooling profile through the thickness of the part and the interpenetration depth of polymer chains across the interface, was proposed. Under various mold and melt temperatures, experiments of sequential two‐staged injection molding processes for polystyrene (PS) were also conducted to verify the validity of the model. Finally, an interrelationship between the average extent of reaching an effective interpenetration depth and the degree of bonding has been constructed. The model proposed in this research would be useful in the CAE analysis for a two‐staged injection molding process in which distortions or even fractures might occur at the interface.
Effect of die gap width on annular extrudates by the annular extrudate swell simulation in steady‐states
Authors: Tanoue Shuichi , Iemoto Yoshiyuki 
Published: April 2004

AbstractWe calculated the steady‐state annular extrudate swell of polymer melts through flow geometries encountered in processes used to control parison thickness. A streamline‐upwinding finite element method with an under‐relaxation for the rate of deformation tensor was used. The Giesekus model was employed as the constitutive equation. An operation that widens the die gap is appropriate for the control of parison thickness corresponding to the change of die gap width. However, a control process that decreases the die gap width is not useful, because the parison thickness does not correspond to the die gap width. Furthermore, thickness swells change strikingly with the Weissenberg number. It is difficult to control the parison outer diameter in the case of a converging die, because the change of the outer diameter swell becomes large with increasing Weissenberg number. In the case of a diverging die, the changing value of the outer diameter swell is smaller than that in the case of a converging die.
The effect of co‐dopants on the processability of intrinsically conducting polymers
Authors: Dahman Sam J. 
Published: April 2004

AbstractUsing a combination of functionalized dopants was found to be a simple method to improve the processability of intrinsically conducting polymers while retaining relatively high levels of conductivity. Two intrinsically conducting polymers, poly(3‐octylthiophene) and polyaniline were co‐doped with various combinations of dopants. In both systems, solubility was improved and coherent films were formed directly from common organic solvents without the need for a post‐processing doping step. Co‐doped intrinsically conducting polymer films exhibited conductivities up to 10−2 S/cm. Additionally, certain polyaniline complexes were capable of being melt processed without loss of conductivity.
Rheological investigations of suspensions of talc, calcium carbonate, and their mixtures in a polystyrene melt
Authors: Kim Kwang Jea , White James L. 
Published: April 2004

AbstractAn experimental study of the rheological properties of talc, calcite, and mixed particle compounds of polystyrene (PS) compounds has been carried out on a range of instruments at 200°C. We investigated the shear viscosity over a very wide range of shear rates in capillary, cone‐plate, and sandwich rheometers. Shear stresses below which there is no flow, i.e. yield stresses, were found. A uniaxial elongational rheometer based on floating samples on a silicone oil bath was used to study the uniaxial extensional flow characteristics. The compounds were found to absorb silicone oil. It was, however, possible to estimate yield values of highly filled compounds in uniaxial extension by investigating the stretching of vertical filaments in a chamber filled with nitrogen.
Application of one‐dimensional mechanical formulations to model the sagging behavior of a polymer sheet
Authors: Stephenson M. J. , Dargush G. F. , Ryan M. E. 
Published: April 2004

AbstractThe deformation of a heated plastic sheet clamped on two opposite sides subject to sagging under its own weight was examined experimentally and then modeled using two separate one‐dimensional approaches based upon cable (membrane) and beam formulations. The cable formulation neglects both bending and shear deformation, but includes a generalized Maxwell viscoelastic constitutive model to capture the time‐dependent nature of sheet sag. The resulting equations are integrated using a Runge‐Kutta technique and solved via a shooting method. The beam formulation is based upon the Timoshenko theory and thus includes shear deformation along with the flexural contributions. A finite element method is developed from application of the principle of virtual work for the beam written in curvilinear coordinates in order to include the effects of finite deformation. A generalized Maxwell model is again employed to account for the time‐dependent material response. In both formulations, the method of reduced variables is used to describe the variation of material response with temperature. The effect of temperature and thermal relaxation is included. The particular case of a styrenic material is discussed in detail.
Pseudo super‐miscibility: Blends of semi‐crystalline nylon pairs exhibiting a single Tg and a single Tm
Authors: Khanna Y. P. , Murthy N. S. , Kuhn W. P. , Day E. D. 
Published: April 2004

AbstractPhysical blends of nylon 6 (or nylon 66) homopolymer with random copolymers of nylon 6/nylon 66 or of nylon 6/nylon 12 were melt extruded into films and characterized by Differential Scanning Calorimetry (DSC) and X‐ray Diffraction (XRD) techniques. The films containing up to 50–65% of the copolymer exhibited only a single melting temperature (Tm) corresponding to that of the pure homopolymer without any trace of the otherwise crystallizable, lower melting copolymer component. These observations are quite unusual since the binary blends of the homopolymers of nylon 6, nylon 66, and nylon 12 exhibit their characteristic 2 Tm's. That result was significant in that at least 20% nylon 6 units (Tm = 222°C) can be incorporated into nylon 66 (Tm = 262°C) without any depression either in the Tm or in the crystallinity of nylon 66 while retaining its Tm = 262°C as the only melting phase. Also, it has now become possible to develop blend compositions based on ≥ 4 polyamide moieties that exhibit a single Tg, high crystallinity, and a sigle Tm corresponding to the higest melting component. We believe that the observed phenomenon, pseudo super‐miscibility, is kinetically driven (i.e., only the higher melting homopolymer crystallizes), rather than thermodynamically or crystallographically, since the structural units originate from polymers that are inherently not isomorphic. In view of the unexpected observation, at least in the field of nylons and its technological significance, we anticipate renewed interest in this area and more definitive understanding to emerge from future studies.
Investigation of wave‐like flow marks in injection molding: Flow visualization and micro‐geometry
Authors: Tredoux Louis , Satoh Isao , Kurosaki Yashuo 
Published: April 2004

AbstractThe wave‐like flow mark phenomenon is one of the surface defects that can occur during the injection stage of the injection molding process. The generating mechanism of this phenomenon is not yet well understood. In this paper the flow mark generation mechanims is investigated by (i) directly observing the behavior of the polymer in the flow front and contact line areas under molding conditions when flow marks are generated, and (ii) studying the micro‐geometry of the flow marks after molding. Specific attention was given to (i) the point of origin of flow marks (relative to the moving contact line, as well as the history along the flow path), and (ii) the effect of thermal boundary conditions on the micro‐geometry of flow marks. These findings and their significance in relation to the flow mark generation mechanism are discussed. It is proposed that the flow marks are caused by nonuniform thermal contraction in the solidifying layer immediately behind the contact line.
Preparation and characterization of hollow microcapsules for use as ultrasound contrast agents
Authors: Narayan Padma , Wheatley Margaret A. 
Published: April 2004

AbstractA laboratory‐scale method of producing micron‐sized hollow microscapsules from a biodegradable polymer such as 50/50 poly(D, L‐lactide‐co‐glycolide) (PLGA), for use as a diagnostic ultrasound contrast agent, was developed. The technique involved microencapsulation of a volatile solid core material, and subsequent sublimation of the core to leave a hollow microsphere. A core material, such as ammonium carbonate, was ground to a suitable size distribution and encapsulated by a modified solvent evaporation or coacervation technique. This study investigated process parameters to produce diagnostically viable microscapsules by these two en‐capsulation methods, such as polymer molecular weight (from 10,000 to 50,000), initial polymer concentration, agitation method, and stabilizer type. Polymer solution viscosity, polydispersity, and agitation rates significantly controlled the mean size of the microcapsules. Stabilizers were essential in solvent evaporation, but corrupted the morphology of spheres made by coacervation. Zeta potential values of microsphere dispersions revealed differences in surface characteristics between both encapsulation methods. Incubation of microcapsules with serum improved their dispersion in aqueous media. Preliminary in vivo ultrasound studies with the New Zealand white rabbit model, using color Doppler, showed that the microcapsules gave significant contrast in the right kidney.
Formation mechanism of porous structure in polytetrafluoroethylene (PTFE) porous membrane through mechanical operations
Authors: Kitamura Taketo , Kurumada Ken‐Ichi , Tanigaki Masataka , Ohshima Masahiro , Kanazawa Shin‐Ichi 
Published: April 2004

AbstractPolymeric porous membranes were prepared from polytetrafluoroethylene (PTFE) fine powder by a series of mechanical operations, such as extrusion, rolling, and stretching. The structure of the prepared porous membrane was well characterized by a spatial periodicity of nodes (domain of agglomerated PTFE particles) and fibril domains. The fibrils were highly oriented in the direction of the stretching operation, providing pores in the polymeric membrane as slit‐like voids between adjoining fibrils. The unit size of the periodic structure varied depending on the number averaged molecular weight of PTFE and the stretching conditions, the temperature of stretching, and the stretching rate and stretching ratio. A fibril consisted of several thread‐like structures that were easily formed between PTFE particles due to the rolling operation in parallel with their direction. The dependence of the steady tensile stress in the stretching operation on the PTFE molecular weight was much weaker than that presumed for noncrystalline polymeric systems. The activation energy of 11.3 kJ/mol for the growth of fibrils was only several times as large as the thermal energy at the ambient temperature. These results imply that the thread‐like structures can easily be pulled out of PTFE particles. This view is in accordance with the previously proposed microstructure in PTFE particles.
Constitutive relations for compressible glassy polymers
Authors: Drozdov Aleksey D. 
Published: April 2004

AbstractConstitutive equations are derived for the isothermal viscoelastic response of glassy polymers at small strains. The model employs the concept of temporary polymeric networks for shear relaxation and the diffusion mechanism for volume recovery of compressible materials. Adjustable parameters are found by fitting experimental data for poly(methyl methacrylate) and polycarbonate in uniaxial tensile tests. It is demonstrated that the stress‐strain relations correctly predict nonmonotonic changes in the specific volume observed in creep tests.
Polystyrene‐graft‐acrylic acid as compatibilizer of polystyrene/nylon 6,6 blends
Authors: Subramanian Srinivas , Lee Sunggyu 
Published: April 2004

AbstractPreliminary investigations to study the feasibility of using polystyrene grafted with acrylic acid to blend polystyrene (PS) and nylon 6,6 (N66) have been done. The graft copolymer (PS‐g‐AA) was synthesized by reacting polystyrene with acrylic acid in the presence of a free radical initiator using the solid phase graft copolymerization technique. Binary blends of N66/PS and N66/PS‐g‐AA were synthesized by melt mixing. The formation of a (PS‐g‐AA)‐co‐N66 copolymer during the blend preparation has been desired. The blend morphologies were observed by scanning electron microscopy (SEM). Significant reductions in the domain sizes of the dispersed minor phase were observed when PS‐g‐AA instead of PS was incorporated into the blend. The tensile properties of the blends were investigated. The belnds containing PS‐g‐AA were found to be stiffer (higher modulus) and stronger (higher tensile strength) as compared to the blends containing PS. These results are due to the better miscibility and adhesion between nylon 6,6 and the graft copolymer. The results of the rheological measurement of these blends further supports the above result and also indicates an increase in the molecular weight distribution (MWD) of the blend when polystyrene was replaced by the graft copolymer. This increase in the MWD of the compatibilized blend can be attributed to above assumed copolymer formation between the graft copolymer and nylon 6,6 due to the reaction between the carbonyl group of the acrylic acid and the amide and the terminal amine groups of nylon 6,6.
In line study of droplet deformation in polymer blends in channel flow
Authors: Migler K. B. , Hobbie E. K. , Qiao F. 
Published: April 2004

AbstractWe present in situ measurements of a dilute polymer blend in channel flow using an optical flow cell placed at the exit of a twin screw extruder. At weak shear stress, we find mildly deformed ellipsoidal droplets whereas at moderate sher rtes we find coexistence between large aspect ratio strings and ellipsoidal droplets. In the regime of low to moderate stress, depth resolved optical microscopy reveals that the deformation is a function of local shear stress. At large shear stress, the droplet breakup is suppressed; mildly deformed droplets at high capillary number are observed, in contrast to the Taylor model. Optical light scattering provides complementary morphological information that is averaged over the channel depth and confirms the optical microscopy. We discuss these results in terms of Taylor theory and normal forces.
Rheology of metallocene‐catalyzed monomodal and bimodal polyethylenes
Authors: Muñoz‐Escalona A. , Lafuente P. , Vega J. F. , Santamaría A. 
Published: April 2004

AbstractThe effect of molecular architecture on the dynamic viscoelastic properties of new metallocene high density polyethylenes has been analyzed. Bimodal molecular weight distribution metallocene polyethylenes show features different from conventional polydisperse and bimodal polyethylenes. Higher values of Newtonian viscosity (ηo) at the same values of weight average molecular weight (Mw) and stronger frequency dependence of dynamic viscosity (η′) than in conventional HDPE‐s have been observed; this leads to lower values of the characteristic frequency for the onset of non‐Newtonian behavior (ωo) and higher values of the power law index (α). These features are probably due to the presence of very small amounts of long chain branching (LCB). The implications of these results in polymer processing are analyzed comparing extrusion rheometer data, which leads to the conclusion that extrusion difficulties in metallocene catalyzed polyethylenes can be overcome with bimodal molecular weight distributions.
Postfilling analysis of viscoelastic polymers with internal structure parameter
Authors: Huang Xiahong , Zhou Chixing 
Published: April 2004

AbstractA new constitutive model with internal structure parameter is presented in this study for simulating orientation and deformation of polymer chain in the postfilling stages of injection molding process. Implementation of such a model is based on a hybrid finite‐element/finite‐difference numerical solution of the generalized Hele‐Shaw flow. The simulation of a compressible viscoelastic fluid under nonisothermal conditions has not yet been discussed in most previous works. In addition to the distribution of pressure, temperature, density, and velocity, theoretical predictions also include shear and normal stresses, which can be used for subsequent calculation of residual stresses. An amorphous material, namely a commercial‐grade polystyrene (PS), was used in the present work. Good agreement is obtained between the simulation and experimental pressure trace from this study.
The stress optical behavior of PET fibers and films
Authors: Ward I. M. , Bleackley M. , Taylor D. J. R. , Cail J. I. , Stepto R. F. T. 
Published: April 2004

AbstractThe use of stress‐optical measurements to characterize oriented PET fibers is reviewed. The implications of a molecular network for the development of orientation in spun fibers, cold drawn and hot drawn fibers are also considered. Early research made use of the Kuhn and Grün theory of photoelasticity, and their model has been shown by many workers to be a useful starting point for understanding the development of molecular orientation in PET provided that it is suitably modified for high chain extension at high draw ratios. The principal thrust of recent research at Leeds has been to explore the applications of more precise molecular modelling using the Monte Carlo rotational isomeric state model developed by Stepto and Taylor, and applying it to the development of optical birefringence with strain, as well as the shrinkage stress. It has been shown that the Kuhn and Grün theory, where the actual network is replaced by a model network of freely jointed random links, cannot provide a consistent description of the shrinkage stress and the optical birefringence.
On‐line measurement of orientation development in the high‐speed melt spinning process
Authors: Kikutani Takeshi , Nakao Kazuhito , Takarada Wataru , Ito Hiroshi 
Published: April 2004

AbstractOn‐line measurement of birefringence was performed in the high‐speed melt spinning process of poly(ethylene terephthalate) using an apparatus that incorporates a rotating polarizer for the measurement of the optical retardation of running filament. Particular attention was paid to the detailed measurements in the vicinity of neck‐like deformation. Through the measurement at the take‐up velocity of 5 km/min, development of birefringence under the strain rate up to about 1 ms−1 was investigated. To analyze the relation between applied stress and birefringence, tension and temperature profiles of the spin‐line were calculated based on the experimentally obtained diameter profiles. Even though the strain rate is extremely high, a linear relationship between birefringence and a parameter calculated by dividing stress by temperature was confirmed to hold up to birefringence and stress/temperature values of about 0.017 and 10 kPa/K, respectively.
Effect of structure on the deformation and failure of oriented polymer films
Authors: Samuels Robert J. 
Published: April 2004

AbstractThis study compares the effect of anisotropic structure on the room temperature (23°C) deformation and failure behavior of two distinctly different polymers. One a single phase nematic polymer, PMDA‐ODA polyimide [PI] with a glass transition, Tg, near 400°C; the other a previously studied anisotropic two phase molecular polymer composite, isotactic polypropylene [IPP] with a glass transition near 14°C. Although isotactic polypropylene has a two phase crystal‐noncrystalline structure its deformation behavior is controlled by the noncrystalline phase. A series of oriented PMDA‐ODA polyimide [PI] films are fabricated and their orientation characterized. The present study investigates whether the deformation and failure behavior of these anisotropic single phase nematic PMDA‐ODA polyimide films (tested at a very low strain rate at room temperature) is similar to that previously observed for isotactic polypropylene at its low strain rate failure envelope limit.
Constitutive viscoplastic behavior of amorphous PET during plane‐strain tensile stretching
Authors: Vigny M. , Aubert A. , Hiver J. M. , Aboulfaraj M. , G'Sell C. 
Published: April 2004

AbstractPlates of polyethylene terephtalate (PET) were prepared by an injection‐compression process such that the initial microstructure was almost completely amorphous. Specimens machined from these plates were subjected to plane‐strain stretching experiments by means of an original video‐controlled testing system (VidéoTractionTM) that gives access directly to the intrinsic stress‐strain behavior at constant strain rate above the glass transition temperature. True strain was controlled from the current distortion of an array of ink dots printed initially onto the samples. Drawing was performed at 5 × 10−3, 1 × 10−3 and 5 × 10−4 s−1. The stretching behavior has revealed a marked strain hardening, which increases drastically at large strain. Furthermore, the influence of temperature on the strain rate sensitivity coefficient was determined in the glass transition by means of a special technique based on mechanical spectroscopy. The true stress‐true strain constitutive behavior of PET thus characterized was analyzed in terms of a theoretical model using viscoplasticity and finite chain entropic hyperelasticity. Parameters of this model, especially those describing the ultimate stretching response, are correlated to the strain‐induced crystallization of the PET samples upon stretching, which was assessed by DSC measurements.
The effects of roll drawing on the structure and properties of oriented poly(ethylene terephthalate)
Authors: Matthews R. G. , Ajji A. , Dumoulin M. M. , Prud'Homme R. E. 
Published: April 2004

AbstractThe effect of processing conditions on the structure and properties of roll drawn poly(ethylene terephthalate) (PET) was examined. It was found that, when roll drawing amorphous PET at temperatures just above the glass transition, only very low draw ratios were obtained. This is probably because there were no crystallites to lock in the applied extension. Roll drawing at high temperatures, above 130°C, where there was significant thermal crystallization, produced film of high strength. At temperatures between 130°C and 190°C, the properties were almost independent of processing temperature. Mechanical tests performed on roll drawn samples, processed in this temperature range, showed that the initial modulus and the yield stress increased linearly with draw ratio. The yield strain decreased with draw ratio up to λ = 4.0, and then became almost constant. The processing temperature that produced samples with the greatest strength was 170°C. This was because the highest draw ratios were obtained at this temperature while maintaining constant width deformation. At low draw ratios, the crystallinity increased with the processing, whereas at higher draw ratios, it was independent of temperature. This constant level of crystalline fraction may have produced the constant failure strain that was observed at high draw ratios. The orientation functions were similarly unaffected by the processing temperature, although birefringence measurements did suggest that lower processing temperatures may have produced higher levels of orientation. The orientation of the trans conformers was independent of the temperature, but the overall content was increased at higher processing temperatures.