bluuebunny/crossref_metadata_2025 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

The 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

We 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

Using 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

An 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

The 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

Physical 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

The 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

A 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

Polymeric 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

Constitutive 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

Preliminary 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

We 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

The 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

A 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

The 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

On‐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

This 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

Plates 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

The 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.
Fiber‐forming properties of polymer mixture melts and properties of fibers on their basis
Authors: Tsebrenko M. V. , Rezanova N. M. , Tsebrenko I. A.
Published: April 2004

The fiber‐forming properties of the following polymer mixture melts have been investigated: polypropylene‐copolyamide (PP/CPA), polyoxymethylene‐copolyamide (POM/CPA), POM‐copolymer of ethylene and vinyl acetate (POM/EVAC), PP/EVAC, EVAC/CPA, and polypropylene‐polyvinylalcohol (PP/PVA). The capability of the polymer mixture melts to fiber‐form was estimated by degree of the polymer melt longitudinal deformation. It has been determined that the fiber‐forming properties of polymer mixture melts can be regulated by changing the chemical nature of the mixture components, structure‐formation processes and by introducing various additives of polymer and non‐polymer nature into binary mixture. The mechanism of action of additives is connected with changing microrheology processes during mixture melt flowing under the influence of the specific interaction between polymer macromolecules and additives at the interphase. The complex threads from PP, POM or EVAC microfibers have been produced and the features of their structure and properties have been investigated. There are the following distinctive properties of the complex threads consisting of microfibers: high strength and initial modulus, high elasticity, exclusive softness, pleasant feel, coupling, capaciousness, and wool‐likeness without special textural procedures, high sorption of moisture, dyes and other substances.
Physical and microstructural effects of heat setting in polyester films
Authors: Greener J. , Tsou A. H. , Blanton T. N.
Published: April 2004

The effects of a controlled heat‐setting treatment on the properties and microstructure of biaxially stretched poly(ethylene terephthalate) (PET) and poly(ethylene‐2,6‐naphthalene dicarboxylate) (PEN) films are described. Substantial changes in crystalline fraction, crystallite size, glass transition temperature and significant enhancement in dimensional stability are observed for both film types upon increase in heat‐set temperature. A distinct melting peak in the vicinity of the heatset temperature, observed in differential scanning calorimetry thermograms for both materials, is shown to be an effective marker of the heat‐setting process underlying the dual nature of the morphology of the heat‐treated films. We also observe that the PET films undergo significant molecular realignment on heat setting, while the orientation of the PEN films is only weakly modified by the heat‐set conditions. A morphological transition is detected for both films at high heat‐set temperature (THS*) near the onset of the primary melting range, marking a qualitative change in the physical response of the biaxially oriented films; Measurable drop in planar orientation and glass transition temperature, and a sharp rise in crystallite size are noted for films heat‐treated above THS*. The morphological models of previous workers (Schultz et al. and Fischer and Fakirov), invoking the idea of fibrillar‐to‐lamellar transformation, are used to explain some of our observations.
Orientation and crystallization in poly(ethylene terephthalate) during drawing at high temperatures and strain rates
Authors: Salem D. R.
Published: April 2004

We review some recent research developments on structure development during drawing of poly(ethylene terephthalate) film, and we report a study of constant‐load drawing of amorphous PET film at temperatures of 120°C and 132°C, including the effects of redrawing high‐temperature drawn film at lower temperature. To permit constant‐load drawing at high temperature without inducing crystallization in the undrawn specimen, a drawing instrument was built that permits very rapid heating of the sample, and its operation is described. The initial stage of drawing at high temperatures is characterized by polymer flow where, owing to high rates of molecular relaxation, neither molecular orientation nor crystallization occurs. Strain‐rate increases sharply in the course of the deformation, reducing the time available for relaxation, and the chains start to orient at a draw ratio that depends on temperature. Orientation rapidly reaches a saturation level, which is lower at the higher draw temperature. Crystallization onset seems to lag only slightly behind orientation onset because the critical orientation for inducing crystallization is very low at these temperatures. It appears that there is time for crystallization to proceed to pseudo‐equilibrium values corresponding to a particular orientation level, which differs from previous results obtained from constant‐force drawing at lower temperatures, and possible reasons for this are discussed. In two‐stage drawing, where film drawn at 132°C was redrawn along the same axis at 100°C, high draw ratios were obtained despite the high strain rates, and the levels of noncrystalline orientation and crystallinity were similar to the levels expected from single stage drawing at 100°C.
Influence of interchange reactions on the crystallization and melting behavior of nylon 6,6 blended with other nylons
Authors: Walia P. S. , Gupta R. K. , Kiang C. T.
Published: April 2004

The thermal behavior of blends of nylon 6,6, with an amorphous polyamide, Trogamid‐T, and a semicrystalline polyamide, nylon 6,12, was studied. The blends were prepared both by solution blending and by melt blending, using a Maxwell extruder and a twin screw extruder. The concentration of the blends ranged from 75% to 95% by weight of nylon 6,6. Annealing the blend samples in the molten state in a differential scanning calorimeter (DSC) produced changes in the melting and crystallization behavior. This was attributed to transamidation reactions occurring between the blend components, leading to the formation of in‐situ block copolymers. The length of the blocks decreased with annealing time, as suggested by reduced melting (Tm) and crystallization temperatures (Tc) and heat of fusion values. The changes in thermal behavior were dependent on the blending method, additive concentration, presence or absence of a catalyst, melt annealing time, and the extent of melt mixing. The extent of reaction, measured by the depression in equilibrium melting temperature, was linear with respect to the annealing time. The Trogamid‐T containing blends appeared to be “nearly miscible” while those with nylon 6,12 were initially immiscible. The glass transition temperature (Tg) vs. the composition curve of the nylon 6,6/Trogamid‐T blends showed a positive deviation from linear additivity, with the single Tg decreasing as a function of annealing time in the melt.
Polymer toughness and impact resistance
Authors: Perkins William G.
Published: April 2004

This report is a review of the factors that influence the impact resistance of high polymers, with an emphasis on crystalline polymers. The phenomenology of polymeric fracture is examined, including brittle and ductile failure, and the ductile‐brittle transition temperature (DBTT). An in‐depth discussion of the effects of crystalline morphology follows, with special attention given to the influence of spherulite size, fillers, processing conditions, transitions/relaxations, and multilayer coextrusion. Next, rubber phase addition is considered, including mechanisms, morphology, rubber type and particle size, and test conditions. Finally, common impact test methods are surveyed, including pendulum, falling weight, tensile impact, and tensile elongation tests.
An investigation of shear‐induced mixing in the PSAN/PMMA blend
Authors: Papathanasiou T. D. , Higgins J. S. , Soontaranun W.
Published: April 2004

We investigate experimentally the effect of steady‐state simple shear flow on the miscibility of a 60–40 poly(styrene‐co‐acrylonitrile) with poly(methyl‐methacrylate) (PSAN/PMMA) blend. Thin disks, containing 60% w/w PSAN, are thermoformed from blend pellets made by mixing PSAN and PMMA granules in a co‐rotating, fully‐intermeshing twin‐screw extruder. These disks are sheared at constant shear rate in a cone‐and‐plate mechanical spectrometer at fixed temperatures within the quiescent two‐phase region. At the end of each shearing experiment the sample is quenched and its morphology investigated first visually for optical transparency (cloudiness being an indicator of a phase‐separated blend) and then using transmission electron microscopy (TEM). Results indicate that upon imposition of a shear rate as low as 0.1s−1 the 60–40 blend remains miscible even at temperatures up to 7K within the (quiescent) two‐phase region. These observations are in agreement with theoretical predictions of the phase diagram under shear, based on the concept of a modified Gibbs free energy of mixing. The TEM results concerning the morphology of the phase‐separated blends are also discussed.
Properties of poly(ethylene terephthalate)/poly(ethylene naphthalate) blends
Authors: Rwei Syang‐Peng
Published: April 2004

Blends composed of poly(ethylene terephthalate) (PET) as the majority component and poly(ethylene naphthalate)(PEN) as the minority component were melt‐mixed in a single screw extruder at various PET/PEN compound ratios. Tensile and flexural test results reveal a good PET/PEN composition dependence, indicating that the compatibility of the blends is effective in a macrodomain. In thermal tests, single transitions for Tg, Tm and Tc (crystallization temperature), respectively, are observed from DSC as well as single Tg from DMA except for 50/50 blends. These results suggests that the compatibility is sufficient down to the submicron level. Moreover, isothermal DSC tests along with Avrami analysis indicate that PET's crystallization is significantly retarded when blended with PEN. Results in this study demonstrate that PEN is a highly promising additive to improve PET's spinnability at high speeds.
Polypyrrole conductive polymer characteristics as an optical display device
Authors: Al‐Attar H. A. , Al‐Kabbi A. S. , Faris F. A.
Published: April 2004

The redox dynamic of electrochemically prepared thin films of polypyrrole is studied. A semi‐empirical formula to explain the redox behavior is formulated and it seems applicable to the reduction dynamic. The redox dynamic is dominated by a diffusion process, depending on the relation between the film thickness and the rise time (t1/2) of the reduction process. The diffusion coefficient, D, was measured to be 2 × 10−9 cm2/sec for perchloride (ClO4−) anion dopant and 1.1 × 10−9 cm2/sec for para‐toluenesulfonate (PTS−) anion dopant. The polypyrrole films exhibited a color change during the oxidation and reduction processes. The electrooptical properties of these films are studied.
Convective and radiant (IR) curing of bulk and waterborne epoxy coatings as thin layers. Part II: Infrared curing
Authors: Blanc D. , Laurent P. , Andrieu J. , Gerard J. F.
Published: April 2004

In the first part of this paper, a method for studying the curing of 100‐μm‐thick epoxy‐based layers on steel substrates was described. In this second part, we extend our study to radiative (infrared) heating conditions. A simple waterborne epoxy reactive system based on a diglycidylether of bisphenol‐A prepolymer and a polyether triamine was used. The chemical kinetics during infrared heating were studied with the reaction kinetics recorded during convective heating. A second order autocatalytic model described the data. The curing mode had no significant influence on the heating kinetics but the heating rate had a significant influence on the curing kinetics. Higher heating rates can be achieved by infrared heating conditions compared with convective heating. The gelation phenomenon was changed for infrared conditions. Microdielectrometry can be used to record in situ the extent of reaction of the epoxy reactive system for thin layers during radiant heating.
Simple shear plastic deformation behavior of polycarbonate plate due to the equal channel angular extrusion process. I: Finite element methods modeling
Authors: Sue Hung‐Jue , Dilan Hector , Li Chris K.‐Y.
Published: April 2004

Simple shear plastic deformation behavior of polycarbonate (PC) plates due to the novel equal channel angular extrusion (ECAE) process is modeled using a commercial finite element methods (FEM) package. The true stress and true strain contour plots as well as the strain rate variation across the PC plate during the ECAE process are analyzed. The FEM results correlate well with the experimental findings. The present study indicates that the novel ECAE process is effective in producing a high degree of simple shear plastic deformation across the extruded polycarbonate plate. The high degree of plastic deformation due to ECAE induces a high level of nearly uniform molecular orientation across the extruded PC plate. As a result, significantly improved physical and mechanical properties in PC are expected. The simple shear plastic deformation behavior of PC plate, as a function of extrusion rate and temperature, is investigated. The significance of the ECAE process for fabricating polymer parts is also discussed.
Critical assessment of methods for evaluatingJICfor a medical grade ultra high molecular weight polyethylene
Authors: Pascaud R. S. , Evans W. T. , McCullagh P. J. J. , Fitzpatrick D.
Published: April 2004

Various methods for the evaluation of the critical J‐integralJICbased on the standard ASTM E813–89 are analyzed by conducting investigations on a ductile medical grade ultra high molecular weight polyethylene (UHMW‐PE) at room temperature. Differences inJICreaching almost 50% were recorded between the methods investigated. The controversy surrounding the construction of the crack blunting line is discussed in terms of the stretch zone width together with the size requirements of ASTM E813–89. The findings of this investigation suggest that an R‐curve construction based on mid‐thickness crack growth and ultimate tensile strength (UTS) combined with a blunting line of slope m = 2 and modified exclusion lines provides consistent and conservativeJICvalues. Using this technique, a near plane strain value, smaller than previously published data, of 66.5 kJ/m2was obtained at 23°C.
Measurement of internal stresses in coatings using time resolved fluorescence
Authors: Shiga Tohru , Narita Takeshi , Tachi Kazuyuki , Okada Akane , Takahashi Hideroh , Kurauchi Toshio
Published: April 2004

This paper describes a new nondestructive technique for detecting internal stresses in coatings using time resolved fluorescence. The measurement principle is based upon an experimental result that the decay time of fluorescence from poly(3‐octylthiophene), P3OT, dispersed in uniaxially‐stretched polymer films decreases with increasing tensile stress acting on the films. Internal stresses in the clear coat and in the base coat of a multilayer structure, which was composed of electrodeposited coat, surface coat, base coat, and clear coat, were estimated from the decay time of fluorescence from P3OT in both coats. The order of internal stresses in the clear coat and base coat of the multilayer system was 1 MPa. When the coatings were piled up, the internal stress decreased as the distance from a metal substrate was increased. It was found that moisture and temperature influenced internal stresses in the clear coat rather than in the base coat. Internal stress in the clear coat, which was one layer coated on a metal substrate, was measured by the traditional bimetallic method or by the time resolved fluorescence technique. Comparing both methods, it was concluded that the time resolved fluorescence technique gave reliable values for internal stresses in coatings.
Physical aging in polymers and polymer composites: An analysis and method for time‐aging time superposition
Authors: Bradshaw R. D. , Brinson L. C.
Published: April 2004

The ability to include the effects of physical aging is critical to the design of engineering structures involving advanced polymers and polymer composites. Physical aging, a phenomenon caused by material evolution towards thermodynamic equilibrium, is typically described by reducing short‐term momentary compliance curves, via time‐aging time superposition, into a predictive reference curve and shift factor function. This paper presents an analytic method based on error minimization for this data reduction task, and introduces the concept of a total reference curve as an alternative to choosing a single momentary curve for the reference. Four different predictive approaches are considered to determine the efficacy of the total reference concept, and whether vertical shifting is beneficial. For most of the materials studied, the total reference using horizontal shifting alone is the recommended method; in the few remaining cases, the total reference procedure with both horizontal and vertical shifting resulted in the best outcome.
Effect of processing history on the morphology and properties of polypropylene/thermotropic liquid crystalline polymer blends
Authors: Machiels A. G. C. , Denys K. F. J. , Van Dam J. , De Boer A. Posthuma
Published: April 2004

Preparation, morphology, and mechanical properties were studied of blends of a thermotropic liquid crystalline polymer (TLCP) with two different grades of polypropylene, one with and one without overlap in processing temperatures, using two different blending methods. The highly viscous grade (PP‐1) was of sufficient thermal stability to be blended with the TLCP (Vectra A950) in a single‐screw extruder with an Egan mixing section on the screw. The low viscous grade (PP‐2) could not be processed at the same temperature as the TLCP because of degradation. Its blends were, therefore, prepared by a special coextrusion technique, i.e. feeding the two components from two separate extruders to a Ross static mixer. In both methods drawing of the extrudate is necessary to obtain satisfactory mechanical properties. The PP‐1/TLCP blends had to be extruded twice in order to obtain proper mixing. The morphology of these blends ranges from a pronounced skin‐core morphology at low extrudate draw ratio (DR = 3) to a high‐aspect ratio fiber/matrix morphology at high draw ratio (DR = 15). The morphology of the PP‐2/TLCP blends was always a high‐aspect ratio fiber/matrix morphology even at low draw ratios. The TLCP fibers were generated in this coextrusion process under conditions where the viscosity of the dispersed phase was higher than the viscosity of the matrix. Breakup experiments demonstrate that fibers of a thickness of approximately 1 μm disintegrate into droplets within a few seconds at temperatures above the melting point of the TLCP. This is probably the cause of the skin‐core morphology obtained with single‐screw extrusion. Tensile modulus and strength of all blends increase with extrudate draw ratio. The deformation of the TLCP phase in the drawn blends is less than affine, probably because of slip between the phases. The moduli of the PP‐1/TLCP blends as a function of the draw ratio can be described well by a modified Halpin‐Tsai equation taking into account both changes in aspect ratio and molecular orientation of the TLCP fibers. The level of reinforcement in the PP‐2/TLCP blends is lower than expected, probably because of the low temperature of drawing. This demonstrates a limitation of the coextrusion process: blending at temperatures that are too low reduces mechanical properties.
Tensile properties and stress relaxation of polypropylene at elevated temperatures
Authors: Ariyama Takashi , Mori Yasunari , Kaneko Kenji
Published: April 2004

Samples of isotactic polypropylene(PP) were subjected to stress‐relaxation experiments after simple tensile tests at four strain rates and at different levels of temperature. The relaxation moduli were determined in the range of temperature between 20 and 80°C with a relaxation period of 1200s duration. The activation energy value of the shift factor was determined using the time‐temperature superposition principle. The calculated stress‐strain curves and stress‐relaxation curves were obtained from constitutive equations based on an overstress theory in which the temperature dependence of viscosity and the activation energy were considered. The temperature dependence of viscosity was amenable to an Arrhenius type equation. The quasi‐equilibrium stress depends on both the current strain and the temperature. The calculated results were obtained by the proposed constitutive equation and compared with the data. The proposed constitutive equations based on the overstress model explain well the viscoelastic‐plastic behavior of PP samples.
Crystallization in blends of poly(ethylene terephthalate) and poly(butylene terephthalate)
Authors: Yu Yishan , Choi Kyung‐Ju
Published: April 2004

Blends composed of poly(ethylene terephthalate) (PET) and poly(butylene terephthalate) (PBT) were melt‐mixed in a Brabender cam mixer at different mixing speeds. The glass transition (Tg) and the crystallization behavior of the blends from glassy state were studied using DSC. It was found that although the blends had the same composition and exhibited the similar Tg, their properties of crystallization could be different; some exhibited a single crystallization peak and some exhibited multiple crystallization peaks depending upon experimental conditions. Results indicated that the behavior of crystallization from glassy state were influenced by entanglement and transesterification of chains. The crystallization time values were obtained over a wide range of crystallization temperature. From curve fitting, the crystallization time values and the temperature, at which the crystallization rate reaches the maximum, were found.
Electrical conductivity of poly(vinyl chloride) plastisol–short carbon fiber composite
Authors: Guoquan Wang , Peng Zeng
Published: April 2004

In this work, short carbon fibers were blended with poly(vinyl chloride) (PVC) plastisol forming a conductive network of the fibers in the composite. The effects of concentration and initial length of the carbon fibers on the conductivity of the network were studied. For an initial fiber length of 3 mm (L/D = 428), the volume resistivity of the network decreased rapidly from 4.3 × 105 to 5.1 × 100 Ω‐m for a change in the fiber concentration of 0.5 to 1.0 phr. The samples prepared by the plastisol method also showed excellent antistatic properties at very low fiber concentration (e.g. 1.0 phr), better than the samples that were prepared by mill mixing. Observation of the morphology showed that the short carbon fibers maintained their initial length in the PVC plastisol‐carbon fiber composite, without obvious breakage. This is why a conductive network in the plastisol‐carbon fiber composite can be formed at very low fiber concentrations.
Viscosity measurement of polycarbonate by using a penetration viscometer
Authors: Yang Fuqian
Published: April 2004

Using a penetration viscometer, the viscosity of polycarbonate was measured in a temperature range of 419 to 443 K and under punching stresses between 0.25 to 20 MPa. The flow behavior under these conditions is Newtonian and the activation enthalpy is 413 kJ/mole.
Ambient temperature compaction of polycarbonate powder
Authors: Vick Linda W. , Kander Ronald G.
Published: April 2004

Solid‐state processing of polymer powders through compaction and sintering has potential advantages over conventional polymer processing methods; however, pressureless sintering of compacted polymer powders has often been unsuccessful. Room temperature compaction of polycarbonate (PC) powder was studied in an effort to better understand the fundamental mechanisms that control polymer compaction and sintering. It was found that differences in the degree of physical aging affect the compaction behavior of PC powder. The results presented in this paper show that the degree of physical aging of thermoplastic polymer powders, which can be influenced by commonly used powder handling operations such as drying and long term storage, can ultimately affect the ability of the powder to be successfully compacted at room temperature.