bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical prediction of three‐dimensional fiber orientation in Hele‐Shaw flows
Authors: Altan M. Cengiz , Subbiah S. , Güçeri Selçuk I. , Pipes R. Byron
Published: December 2004

A numerical technique is developed to determine the three‐dimensional fiber orientation in complex flows. The fiber orientation state is specified in terms of orientation tensors, which are used in several constitutive models. This method is applied to quasi‐steady state Hele‐Shaw flows in order to predict the flow‐induced fiber orientation during injection molding at zero volume fraction limit. At the inlet, a number of fibers are introduced at a specified rate into the flow and each fiber location is traced during the mold filling. Along these determined paths, the independent components of fourth order orientation tensors are solved, describing the orientation state. The numerical grid generation technique, which is suitable for complex mold shapes, is employed for the flow solution. Orientation ellipsoids are calculated from the second order tensors and are used to present the fiber orientation results. The numerical solutions are obtained for channel and converging flows. Planar, longitudinal, and transverse orientation results are generated from the orthogonal projections of the orientation ellipsoids.
Dynamic behavior of continuous vinyl chloride suspension polymerization reactors: Effects of segregation
Authors: Pinto J. C.
Published: December 2004

Assumed is that there is no mass transfer among the droplets of reacting organic phase in a continuous vinyl chloride (VCM) suspension polymerization reactor. A mathematical model is thus developed to allow the calculation of steady states and the analysis of their dynamic stability. The results obtained are compared with those obtained with the hypothesis of perfect micromixing. It Is shown that both assumptions lead to similar dynamic structures, which confirms the complex behavior of these reactors. There are major differences, however, that can be exploited in future experimental work.
Internal stress, molecular orientation, and distortion in injection moldings: Polypropylene and glass‐fiber filled polypropylene
Authors: Hindle C. S. , White J. R. , Dawson D. , Thomas K.
Published: December 2004

Residual stress measurements and distortion analyses have been conducted on injection molded plaques made from polypropylene (PP) and a short glass‐fiber filled polypropylene (GFPP). The residual stress analyses include measurements both parallel and perpendicular to the direction of flow during mold filling. Residual stresses are very anisotropic in GFPP, but not in PP. The residual stress levels in PP fall on aging at room temperature, whereas in GFPP the proportion of stress relaxation is smaller, and significant stresses remain even after heating to elevated temperatures. A significant contribution to distortion has been linked to the ejection process, and the long‐ and short‐term distortion of moldings is discussed within the framework of the properties of the materials measured here.
A general non‐isothermal model for one‐dimensional multilayer coextrusion flows
Authors: Puissant S. , Vergnes B. , Demay Y. , Agassant J. F.
Published: December 2004

A general computation of multilayer coextrusion flow in a flat die geometry is presented. For any given number of layers of different polymers, characterized by their thermal and rheological behaviors, the model permits computation of velocity and temperature fields along the flow in constant or slightly varying geometries. The influence of different operating parameters (wall regulation temperature, flow rate, initial temperatures) on the interface positions and temperature evolutions is evaluated. Theoretical predictions of interface positions are in agreement with experiments carried out on an industrial multimanifold flat die.
Temperature dependence of the interfacial dielectric loss process in glass bead‐filled polyethylene
Authors: Steeman P. A. M. , Baetsen J. F. H. , Maurer F. H. J.
Published: December 2004

The temperature dependence of the interfacial dielectric loss process in glass bead‐filled high density polyethylene (HDPE) due to an interfacially adsorbed water layer has been studied. The frequency of maximum dielectric loss shifts to lower frequencies with decreasing temperature. This is thought to be due to decreasing mobility of the free charge carriers in the adsorbed water layer, resulting in the reduced conductivity of the layer. The shifting of the loss peaks with temperature can be described with the well‐known Arrhenius relation. The energy of activation, as obtained from this relation, shows a stron dependence on the thickness of the adsorbed layer. For thinner layers a higher activation energy is found, indicating that the charge carriers are increasingly affected by the presence of a layer of bound charges on the glass surface. This thickness dependence of the activation energy offers some possible applications. First, information on the water layer thickness can be extracted from the energy of activation, and second, it becomes possible to study the effect of interfacial modifications such as the application of coupling agents.
Gear pump assisted extrusion
Authors: Pham Hoang T. , Hyun Kun S.
Published: December 2004

Gear pump assisted extrusion is becoming popular in the plastics processing industries. The growth has been tremendous since 1980. In this study, the benefits of gear pump assisted extrusion, especially in single screw applications, is critically reviewed, and a method of predicting the operational conditions of the gear pump assisted extrusion system is discussed. Further, shortening the length to diameter ratio of the extruder in gear pump assisted extrusion was analyzed and found to produce a reduction in energy consumption, provided melting is completed.
The measurement of thermal stress distributions along the flow path in injection‐molded flat plates
Authors: Hastenberg C. H. V. , Wildervanck P. C. , Leenen A. J. H. , Schennink G. G. J.
Published: December 2004

Internal stresses in injection‐molded parts are the result of thermal, flow, and pressure histories. Internal stresses can be roughly divided into thermal and flow‐induced stresses. In this paper, a modified layer‐removal method is presented to determine thermal stress distributions in injection‐molded flat plates. With this method, the curvature of a rectangular specimen is determined after the removal of a layer from one surface. This curvature is converted into a stress via a mathematical relation, originally derived by Treuting and Read. By determining the local curvatures after successive layer removals, stress distributions along the flow path were obtained within a single specimen. Validation of this modified layer‐removal method is described. A good reproductibility was obtained. The method can be regarded as semi‐quantitative. Flat plates were injection‐molded from three amorphous polymers: polystyrene, polycarbonate, and a polyphenylene ether/high‐impact polystyrene blend. In general, the flat‐plate cross‐section shows a three‐region stress distribution with a tensile stress region both at the surface and in the core of the flat plate and an intermediate region with compressive stresses. The modified layer‐removal method was used to determine influences of mold temperature, annealing treatment, and pressure history on the thermal stress distributions. Increasing mold temperature results in a decreasing overall stress level, while the compressive stress region shifts to the surface. An annealing treatment significantly reduces the overall stress level, without affecting the stress pattern. Stress distributions along the flow path were influenced by the varying pressure histories from the entrance to the end of the mold cavity. The various features of the stress profiles are explained by the influence of the pressure decay rate in the injection‐molding process.
A microdielectric analysis of moisture diffusion in thin epoxy/amine films of varying cure state and mix ratio
Authors: Day David R. , Shepard David D. , Craven Kelly J.
Published: December 2004

Recent work has shown that moisture diffusion coefficients can be measured in thin polymer films through monitoring changes in permittivity with microdielectric sensors. The sensor is constructed in silicon and consists of an interdigitated electrode and two depletion mode field effect transistors. When operated in conjunction with appropriate external circuitry, the sensor measures dielectric constant and loss factor of any material placed on the SiO2 insulator and aluminum electrodes. The dielectric properties are measured locally within the first 10 microns of the film in contact with the sensor. As a thin polymer film on the sensor is exposed to a high relative humidity, the dynamically measured dielectric constant can be used to determine exactly when the moisture arrives at the polymer‐SiO2 interface and the rate at which the concentration increases. The magnitude of the change in permittivity after equilibration has also been related to total amount of moisture uptake. In this investigation, several epoxy/amine films of varying mix ratios and cure state are cured on microdielectric sensors. The films, approximately 100 microns thick, are alternately exposed to wet and dry environments. Diffusion coefficients for both absorption and desorption are determined from the dielectric data as a function of cure state and epoxy/amine mix ratio. In addition, relative changes in amount of moisture uptake after equilibration is monitored.
Analysis of gel formation in imidazole‐catalyzed epoxies
Authors: Heise M. S. , Martin G. C. , Gotro J. T.
Published: December 2004

The network formation processes for imidazole‐cured epoxy resins were examined by relating the reaction chemistry and the physical properties during cure. Network formation models were developed based on kinetic studies and the laws of conditional probability. These models were used to predict the weight‐average molecular weight, the gel point, and the sol fraction as a function of the resin composition and the processing conditions. Rheological and extraction experiments were conducted to confirm the model results and to develop criteria for identifying the gel point.
Free volume theory and nonlinear thermoviscoelasticity
Authors: Losi Giancarlo U. , Knauss Wolfgang G.
Published: December 2004

The rheological behavior of polymers in the neighborhood of the glass transition is investigated in the framework of the free volume theory of nonlinear viscoelastic behavior. Free volume theory as normally applied above the glass transition is modified to account for the effect of the residual volume of vacancies below the glass transition; this modification is accomplished by modeling the changes in the state of the polymer as the sum of viscoelastic changes and a random disturbance deriving from the thermal collisions between molecule segments. The changes in mechanical properties in passing across the glass transition follow from the freezing‐in of relaxation mechanisms and of free volume; the model, which also incorporates a time‐dependent coefficient of thermal expansion under isobaric conditions, does not require additional parameters other than those characterizing the rubbery state. The pressure dependence of the glass transition is found to be in qualitiative agreement with measurements on PVAc, while the ratio of the glassy and rubbery heat capacities is found to coincide with the ratio of the equilibrium bulk compliances in the glassy and rubbery domains.
Analysis of the deformation of polypropylene hot‐tool butt welds
Authors: Gehde M. , Bevan L. , Ehrenstein G. W.
Published: December 2004

Thin microtomed samples from hot‐tool butt welds of polypropylene pipes are subjected to uniaxial tensile stress using a specially built instrumented microtesting machine. The deformation of the interface between the weld and the bulk polymer is measured by an optical method. An analysis of these measurements is carried out using the finite element method, and contours of the effective stress are obtained. There is a steep stress gradient at the junction of the weld flash and the bulk polymer, although the stress concentration factor is relatively low. The stress is essentially constant in the bulk polymer apart from the region near the weld zone. Tests on samples without the weld flash show that the maximum stress occurs within the weld zone. This is consistent with long‐term tests on larger samples, where the fracture is found to initiate within the weld. The method of analysis enables the stress‐strain response of the weld material to be determined.
Polypropylene composites. II: Structure‐property relationships in two‐ and three‐component polypropylene composites
Authors: Chiang Wen‐Yen , Yang Wen‐Der , Pukánszky Béla
Published: December 2004

Two‐ and three‐component polypropylene (PP) blends and composites were prepared to study their structure/property relationships. Butadiene‐styrene (BDS) copolymers of low compatibility formed large particles of poor adhesion in PP resulting in inferior mechanical properties. Better miscibility of ethylene‐propylene‐diene (EPDM) elastomer results in more finely dispersed particles and the experimental results indicate a transition to an interpenetrating network (IPN)– like structure with increasing elastomer content. Effective impact modification can be achieved only with EPDM elastomers of sufficient miscibility. Mutual wettability and adhesion of the components determine the structure and properties in PP/elastomer/filler systems. Modification of PP by acrylic acid grafting promotes PP/filler adhesion which, in turn, results in the separate dispersion of the components. In an unmodified PP matrix, a significant amount of the filler is encapsulated by the elastomer. At low filler content, better low temperature impact strength is achieved in the case of separately dispersed components, while encapsulation is more advantageous at high filling grades.
Rheology of phase separated blends of two thermotropic liquid crystalline copolyesters
Authors: Lin Y. G. , Winter H. H.
Published: December 2004

The melt rheology of phase separated blends of two thermotropic liquid crystalline polymers (LCPs) have been studied. The two components are a random copolyesters consisting of 73 mol% 4‐hydrobenzoic acid (HBA) and 27 mol% 6‐hydroxy‐2‐napthoic acid (Vectra A900 of Hoechst Celanese Corp.) and a poly(ethylene terephalate‐co‐4‐oxybenzoate) containing 60 mol% HBA units (PET/60HBA of Eastman Kodak Corp.). Most striking is the effect of adding 10% PET/60HBA to Vectra A900: The viscosity at 290°C drops by a factor of 4 and the terminal zone of the relaxation time spectrum is shifted to much shorter times. This is an interesting effect that could be used for LCP processing even if its origin is not yet understood. Differential scanning calorimetry measurements support the hypothesis that the blend is phase separated and that no transestification reaction occurs during the experiments.
Toughening behavior of elastomer‐modified polycarbonates based on thej‐integral
Authors: Lee Chang‐Bing , Chang Feng‐Chih
Published: December 2004

TheJ‐integral method to determine the fracture toughness of tough and ductile polymeric materials previously developed has been applied to the elastomer‐modified polycarbonates. This investigation compares three different methods to obtainJc: the conventional crack growth length, the stress whitening zone, and the newly developed hysteresis method.Jcvalues obtained from these three comparative methods are fairly close. The hysteresis method has the advantage over the other two methods of obtainingJcwithout requiring the measurement of the crack growth length or the stress whitening zone, therefore avoiding the controversy in defining crack blunting. Results also indicate that the effect of elastomer quantity in polycarbonate onJcis insignificant as long as the crack is in a stable condition. Higher elastomer contents in polycarbonate result in higherdJ/dΔa,dJ/dΔl, and tearing modulus (Tm). This indicates that the elastomer toughening mechanism is due to the increase of the energy required for crack growth extension. The hysteresis loss energy is directly related to the size of the crack tip plastic zone, and the presence of more elastomer indeed increases the crack tip plastic zone, thus making the polycarbonate tougher. Besides, the presence of elastomer tends to increase the crack initiation displacement and shift the failure modes from an unstable fracture.Jcand the criterion for crack initiation based on rate change of hysteresis energy are discussed in detail.
Photoinitiated crosslinking of low density polyethylene. IV: Continuous extrusion application
Authors: Qing Yan , Rånby Bengt
Published: December 2004

A new continuous method is developed to crosslink polyethylene, based on a photoinitiated radical reaction. An experimental production line for low density polyethylene (LDPE) extrudate is constructed with a Brabender® extruder and an “Irradiation Unit” on line. Some new initiators of benzophenone derivatives are prepared to overcome the volatility of benzophenone and increase its compatibility with the polymer matrix. Extraction and gel swelling experiments are performed to characterize the crosslinking of the product and the results are quite satisfactory: under the conditions used, crosslinking can be optimized to about 65% gel content within 5 to 15 s irradiation time, corresponding to a production rate of about 1.5 to 0.5 m/min, respectively. The dynamic mechanical properties of the crosslinked polymer are measured through the melting region and the effects of crosslinking are demonstrated. Without affecting the rate of crosslinking, the stability against thermal oxidation of the crosslinked products is greatly improved by adding stabilizers to the compounds before crosslinking.
Blends of modified polycarbonate and high density polyethylene
Authors: Mekhilef N. , Kadi A. Ait , Ajji A.
Published: December 2004

In this work, blends of polycarbonate and a high density polyethylene were investigated through their morphology, mechanical properties, and the effect of compatibilizers: a copolymer styrene‐butadiene‐styrene and an ionomer. Blending was performed in the melt state at 220°C, and the concentration of the compatibilizers was varied from 1% to 5% by weight. In the case of the copolymer modified blend, the results showed no change in the mechanical properties compared to the neat blend, whereas the morphology showed that the copolymer might interact with only one phase. For the ionomer, the addition of 1% increased the Young's modulus and the tensile strength of the blend. For the morphology, a large change in the size of the dispersed phase (polyethylene) is observed. This was attributed to the compatibility of the ethylene group of the ionomer with the minor phase, and the reaction between the carbonate group of polycarbonate (PC) and the acid group of the ionomer. An investigation on the binary blends of PC and the ionomer showed the occurrence of a chemical reaction that might be of a transesterification type. Differential scanning calorimetry and Fourier transform infrared techniques were used to characterize these blends.
Influence of thickness and processing history on fatigue fracture of nylon 66. Part I: Crack propagation measurements
Authors: Wyzgoski Michael G. , Novak Glen E.
Published: December 2004

The influence of sample thickness on fatigue crack propagation rates in injection molded nylon 66 was determined by preparing 12.7 mm thick plaques along with more conventional 3.0 mm thick samples. Initial results suggested a large effect of thickness as the crack propagation rates were accelerated in the thicker samples and the stress dependence was also increased. Since the calculated thickness for a plane stress to plane strain transition in nylon 66 is 9.0 mm, it was thought that these results were related to the stress state at the crack tip. However, a more thorough study of the thicker plaques has now demonstrated that neither the magnitude nor the stress dependence of the fatigue crack growth rates is necessarily changed under plane strain conditions as similar results can be obtained for thick and thin plaques. It is suggested that the earlier results were confounded by a previously unrecognized processing history effect which does accelerate fatigue fracture. The latter effect is shown by thermal analysis and optical microscopy to be related to a rearrangement of the polymer network during melt processing.
Constitutive modeling and simulation of energy absorbing polyurethane foam under impact loading
Authors: Sherwood James A. , Frost Colin C.
Published: December 2004

The compressive‐stress strain response of polyurethane foam under uniaxial compressive impact loading has been studied. The development of a uniaxial constitutive model from strain rate controlled compression tests is detailed. Density and temperature functions have been added to the integral power model proposed by Schwaber, Meincke, and Nagy. The model assumes that the effects of density, temperature, strain and strain rate on stress are separable functions. The model correlated well with actual static compression tests and was used successfully to predict the impact response of energy absorbing polyurethane foam under uniaxial compressive loading.
Elastic moduli of semicrystalline polyethylenes compared with theoretical micromechanical models for composites
Authors: Janzen Jay
Published: December 2004

A large collection of data on Young's modulus and density of unfilled polyethylenes at ambient conditions has been compared with various competing theoretical mixing rules developed for composite micromechanics. The objective was to see if such theories usefully predict the dependence of stiffness on crystalline content in an archetypal isotropic semicrystalline thermoplastic polymer above its glass trnsition temperature. It was found that the self‐consistent scheme derived by Hill and Budiansky from continuum micromechanics appears to have valid application to this system. The scheme naturally and coherently incorporates information on bulk and shear moduli and Poisson's ratios, while giving a good account of the main trend in the Young's modulus data. Conversely, other theoretical models frequently invoked in the polymer literature were explicitly found to be unsuitable for representing principal features of modulus‐density relationships dectated by the data.
Indentation behavior of polymer coatings on glass
Authors: Ritter J. E. , Sioui D. R. , Lardner T. J.
Published: December 2004

For relatively soft polymer coatings on soda‐lime glass substrates the indentation load increases substantially when the indenter penetrates into the glass substrate since the glass can now directly support some of the indenter load. A model for the indentation load‐depth behavior is developed by accounting for the indentation load shared by the coating and substrate. This model accounts for the additional load supported by the coating due to the pile‐up of coating material underneath the indenter. The model predicts the indentation behavior as a function of coating and substrate hardnesses and coating thickness. Comparison of the model to experimental data for a wide range of polymer coatings (two epoxies, epoxy acrylate, and urethane acrylate) on soda‐lime glass substrates shows good agreement.
Effectiveness of polymer coatings on reducing indention damage in glass
Authors: Ritter J. E. , Gu W. , Lardner T. J.
Published: December 2004

Polymer coatings are widely used to protect glass from indentation damage. A model for the strength degradation that occurs when a sharp indenter penetrates through the coating is developed by accounting for the indentation load shared by the coating and substrate. This model accounts for the additional load supported by the coating due to the pile‐up of coating material underneath the indenter. The model predicts the strength degradation as a function of indentation load, coating and substrate hardnesses, and coating thickness. Comparison of the model to experimental data for a wide range of polymer coatings (two epoxies, epoxy acrylate, and urethane acrylate) on soda‐lime glass substrates shows good agreement.
Effect of melt history on the crystallization kinetics of poly(phenylene sulfide)
Authors: Mehl Nathan A. , Rebenfeld Ludwig
Published: December 2004

Differential scanning calorimetry (DSC) was used to study the effects of melt history on the isothermal crystallization kinetics of poly(phenylene sulfide) (PPS). Crystallization of the polymer was shown to be permanently altered by both the time and the temperature spent in the melt. Suggested explanations are nonequilibrium melting, chain scission, chain extension, and crosslinking. Molecular weight was also shown to affect the rates of these processes, PPS of lower molecular weight being more susceptible to the observed changes.
The separate roles of phase structure and interfacial adhesion in toughening a brittle polymer
Authors: Liu N. C. , Baker W. E.
Published: December 2004

The effects of rubber particle size and rubber/matrix adhesion on the impact properties of a brittle polymer have been separated using polystyrene (PS)/acrylonitrile‐butadiene rubber (NBR) as a model system in which interfacial chemical reaction could be controlled. It has been proven that the interfacial adhesion between the rubber phase and the PS matrix not only greatly aids in reducing the rubber particle size but also plays a further role in improving the impact properties of the matrix polymer. The impact energies of PS/NBR blends with interfacial chemical bonding are four to ten times as high as those without interfacial bonding for the same average rubber particle size. However, at temperatures below the glass transition temperature of the rubber, there is no difference in impact energies with or without interfacial chemical bonding. It has been found that the optimum rubber particle size for toughening PS is influenced by interfacial adhesion. Smaller optimum rubber particle size is observed for blends with greater amounts of interfacial chemical bonding.
Use of T1ρH as a probe for polymer blend phase structure
Authors: Natansohn A.
Published: December 2004

T1ρH′ the proton spin‐lattice relaxation time in the rotating frame, can be used as a probe for polymer blend miscibility in the same way the glass transition temperature (Tg) is used. T1ρH has some advantages over Tg. It is indicative of the separate phases at a level of a few nanometers, below what Tg can distinguish. Also, T1ρH is the only parameter related to the local proton density in a sample. This paper shows a few examples of T1ρH investigations, including thermally reversible blends, phase separated composites, and mixtures of polymers with small molecules.
Rheological properties of corona modified cellulose/polyethylene composites
Authors: Dong S. , Sapieha S. , Schreiber H. P.
Published: December 2004

The rheological behavior of wood fiber/polyethylene composites made of corona treated constituents was investigated. Corona treatment of one or both of the constituents resulted in decreased melt viscosities relative to compounds containing untreated materials. The reduction of melt viscosity may originate from low molecular weight moieties formed on the surfaces of both polyethylene and cellulose during corona treatment. These may act as lubricants at interfaces. Also it was found that the corona treatment of fibers leads to higher packing volumes; this may result from a reduction in fiber length when treated fibers are processed under high shear conditions. As a result these fibers perturb the normal flow pattern in the melt to a lesser degree than the longer fibers of untreated cellulose.
Extrudate swell of high density polyethylene. Part I: Aspects of molecular structure and rheological characterization methods
Authors: Koopmans R. J.
Published: December 2004

Two high density polyethylene (HDPE) resins–samples 801 and 802–both nominally the same material, as they are taken from successive batches of the same commercial grade, are characterized for their molecular structure and rheological properties. Gel permeation chromatography (GPC) and low angle laser light scattering (LALLS) results must be interpreted in combination with rheological data to show the presence of somewhat more high molecular weight material in 802 that in 801. Small amplitude oscillatory shear, steady shear, and capillary shear measurements performed in different laboratories show consistently higher shear viscosity values at low shear rates for sample 802. Extensional viscosity measurements show similar results. The interpretation of rheological data in terms of molecular structure could be complicated by the possible presence of long chain branching (LCB). The zero shear viscosity and discrete relaxation spectrum is estimated for both samples. The small rheological difference between 801 and 802 forms the basic information for understanding their time dependent extrudate swell behavior, as will be described in Part II.
Extrudate swell of high density polyethylene. Part II: Time dependency and effects of cooling and sagging
Authors: Koopmans R. J.
Published: December 2004

For two high density polyethylene resins, the isothermal time dependency of extrudate swell has been measured. Very minor differences in the large molecular weight part of the molecular weight distribution, hardly detectable with gel permeation chromatography and low angle laser light scattering techniques, dramatically influence the time dependency of extrudate swell as well as the maximum swell attainable. The presence of larger molecules in sample 802 than in 801 is reflected in a lower short time (after seconds) and a larger long time (after minutes) or maximum extrudate swell value. Extruding the polymers through a capillary die L:D = 30:2 mm into air at ambient temperature allows only the short time swelling behavior to be observed, because cooling and sagging of the strand.
Morphology development in polymer blends
Authors: Sundararaj Uttandaraman , Macosko C. W. , Rolando R. J. , Chan H. T.
Published: December 2004

The major morphological changes during polymer blending occur during the initial softening stage. This work explains the evolution of phase morphology of polymer blends from pellets to submicron particles in a co‐rotating twin‐screw extruder. The extruder was opened and blend samples were taken along its length. The major phase component was extracted by means of a selective solvent so that the dispersed phase morphology could be viewed directly by using scanning electron microscopy. The two systems studied were 80:20 polystyrene/amorphous polyamide and 80:20 polystyrene/polypropylene. In both systems, the initial morphology consisted of sheets of dispersed phase. Holes form in the sheets, and these holes grow as a result of interfacial tension forces until they coalesce with each other, forming thin ligaments. These fluid ligaments are unstable and break up via mixer shear forces. Very large changes in dispersed phase size are observed during the softening stage. The particle size changes less after the polymers are completely melted. The extruder results are compared to results from a batch mixer. The same dispersed phase sheeting mechanism is seen in the initial morphology in the batch mixer and the breakup of the dispersed phase domains parallels the breakup seen in the extruder.
Development of polymer blend morphology during compounding in a twin‐screw extruder. Part III: Experimental procedure and preliminary results
Authors: Bordereau V. , Carrega M. , Shi Z. H. , Utracki L. A. , Sammut P.
Published: December 2004

Currently, selection of screw configurations as well as the operating conditions for compounding polymer blends with desired morphology in a co‐rotating twinscrew extruder is an art based on experience. In this paper a quenching section of a twin‐screw extruder is described. The section may replace any segment of the extruder barrel. It allows, on the one hand, a regular operation of the machine, and on the other, a rapid quenching and removal of blend specimens for morphology analysis from any place along the extruder barrel and at any time of the blending. The experimental observation of development during compounding of polymer blends enables verification and improvement of the theoretical model, aimed at predicting and controlling the size and polydispersity of the minor phase. Development of the predictive model for blend morphology will provide a valuable guide to the polymer processing industry. The preliminary data were collected using polystyrene/high density polyethylene (PS/HDPE) blends at low concentration of the dispersed phase, 5 wt% of either PS or HDPE. It was observed that the viscosity ratio, blend composition, screw configuration, temperature, throughput, and screw speed significantly influence the blend morphology.
Cyclic deformation and relaxation characteristics in polypropylene
Authors: Ariyama Takashi
Published: December 2004

Cyclic deformation and stress relaxation after cyclic preloading in polypropylene were investigated by using an electrohydraulic, servocontrolled testing machine. The cyclic deformation tests were performed under various sets of strain rate, number of cycles, and strain amplitude in the as‐received sample and a quenched sample. The stress relaxation tests were made after a cyclic preloading in both samples. The distinctive shape of the hysteresis loop, termed a propeller‐like shape, is characteristic of the as‐received polypropylene with large spherulites, in marked contrast to the behavior of metals. The curves at strain amplitudes from ± 1.5% to ± 5% indicate a propeller‐like shape; these loops change into the steady state response as the number of cycles (N) is increased up to N = 30 to 50. The drop of stress in relaxation tests for the quenched samples is smaller than that for the as‐received samples at the same strain levels. This stress drop behavior reflects the difference of spherulite structure. The stress relaxation behavior depends on the morphology, the predetermined strain amplitude, and the process of the tests.
Nondestructive quantitative determination of starch content in polyethylene by solid state NMR and FTIR
Authors: Tikuisis T. , Axelson D. E. , Sharma A.
Published: December 2004

Fourier transform infrared spectroscopy (FTIR) and carbon‐13 solid state nuclear magnetic resonance spectroscopy (NMR) were used quantitatively (and non‐destructively) to determine the starch content in a series of starch filled polyethylene samples (nominal addition levels range from 3 to 6 wt%). Data acquisition times (including sample preparation and instrument analysis) were typically a few minutes for both techniques. Current methodologies for starch analysis in polyethylene are based upon wet chemical techniques (gravimetric or enzyme analysis). The proposed methods offer several advantages over these traditional methods: they are less labor intensive, do not require chemical reagents, are relatively insensitive to changes in the sample matrix, and are fast.
Self‐Reinforced composites of two thermotropic liquid crystalline polymers
Authors: Akhtar S. , Isayev A. I.
Published: December 2004

Blends of two thermotropic liquid crystalline polymers (LCP) based on 6‐oxy‐2‐naphthoyl and p‐oxybenzoyl moieties and p‐oxybenzoyl, terephthaloyl and hydroquinone moieties have been studied. The blends were prepared by melt mixing using a twin screw extruder. Thermal, rheological, mechanical, and morphological studies were carried out. Based on the dynamic mechanical thermal analysis and the morphological observations, the blends are found to be immiscible. The viscosity ratios of pure LCP melts exceed values of 10 over a wide range of shear rates, with the viscosity of the blends lying between those of the pure components. The prepared blends are shown to be self‐reinforced composites in which one LCP enhances the molecular orientation of the other. Studies of the injection molded bars by scanning electron microscopy indicate a complicated hierarchical morphology with microfibrils of submicron level in diameter, bundled, and intertwined into fibrils of a substantially larger diameter. Due to self reinforcement, impact and tensile properties of the blends show significant synergism when compared to those of the pure LCP components. The properties obtained are remarkably higher than those known for any high performance engineering thermoplastics.
Analysis of unsaturated polyester‐polyurethane interpenetrating polymer networks II: Phase separation behavior
Authors: Lee Sun Suk , Kim Sung Chul
Published: December 2004

The phase separation behavior of unsaturated polyester (UPE)‐polyurethane (PU) interpenetrating polymer networks (IPNs) was investigated by light scattering measurements during simultaneous polymerization. The scattered light intensity change with time showed the formation of the dispersed domains, and the average domain correlation length could be calculated from the angle of maximum scattering intensify. It was noted that the dominant phase separation process was spinodal decomposition due to fast reaction. The morphology observed by the transmission electron micrographs for various process conditions showed similar results as obtained from the light scattering experiment.
Electronic structure of polyaromatic nitrogen compounds: Surface analytical and electro‐optical investigations
Authors: Kessel R. , Stöckert D. , Schultze J. W.
Published: December 2004

The polymers of the aromatic nitrogen compounds N‐methyl‐pyrrole (P‐N‐Me‐PPY), carbazole (PCarb), and aniline (PANI) have been investigated with electro‐optical and surface analytical methods. The in‐situ reflection spectra indicate the formation of polarons or bipolarons during electrochemical oxidation, depending on polymer type. The absorption bands can be attributed to changes in the electronic structure with regard to the applied potential. Photocurrent spectra of P‐N‐Me‐PPY and PCarb show a p‐type semiconducting behaviour for the polymers in the reduced state. The transition to the oxidized state with quasi‐metallic properties is indicated by a significant shift in the Fermi level energy and can be followed with XPS and UPS measurements.
Blends of a thermotropic liquid crystalline polymer and a thermoplastic elastomer. I: Mechanical properties and morphology
Authors: Verhoogt H. , Langelaan H. C. , Van Dam J. , de Boer A. Posthuma
Published: December 2004

Blends of a thermotropic liquid crystalline polymer (LCP), Vectra A900, and a thermoplastic elastomer, Kraton G1650, were made on a single screw extruder. During extrusion, fibers of the LCP are formed under influence of shearing and elongating forces. The stiffness and tensile strength of the elastomer are greatly improved by the addition of the LCP. The modulus of elasticity of blends containing up to 20% LCP can be described well with the Halpin‐Tsai equation. Differential scanning calorimetry and dynamic mechanical thermal analysis (DMTA) measurements show that the polymers are immiscible, but the DMTA results show a shift of the glass transition temperature of the elastomeric block of the Kraton polymer. This shift may be attributed to a layer of elastomer adsorbed on the LCP particles.
Melt elasticity of incompatible blends of poly(butylene terephthalate)(PBT) and polyamide 6 (PA6)
Authors: Wakita Naoki
Published: December 2004

The extrudate swell and the dynamic rheological properties of poly(butylene terephthalate) (PBT) and polyamide 6 (PA6) binary blends were investigated at 240°C. The extrudate swell of the blend varies with the viscosity ratio and composition of constituents, and it is several times larger than that of homopolymers when the viscosity ratio of constituents is around unity. The dynamic oscillatory data could be interpreted by Oldroyd's emulsion model proposed by Graebling, et al. These results suggest that the extrudate swell is caused by the shape recovery of the dispersed particles. A semi‐empirical method to estimate the terminal relaxation time with experimental data was introduced, and a clear correlation between the extrudate swell and the terminal relaxation time was obtained.
Processing and properties of polyimide melt blends containing a thermotropic liquid crystalline polymer
Authors: Blizard K. G. , Haghighat R. R.
Published: December 2004

Several polymer blend compositions of LaRC‐TPI 1500 and New TPI 450 (Mitsui Toatsu) with Xydar SRT 900 LCP (Amoco Performance Products) were extrusion processed. In addition to binary blends containing one TPI with an LCP, ternary blends consisting of an alloy containing both TPIs as the matrix were also processed. By varying the ratio of the polyimides in the matrix, the blends' thermal behavior could be tailored. This paper addresses both processing issues and film properties of these blends. Rheological and thermal studies were conducted on both blends made in a torque rheometer and on biaxially oriented film produced with a counter‐rotating annular die. These biaxial blend films were further characterized by measuring tensile and electrical properties. For 70/30 New TPI/Xydar equal biaxial films of 50 μm thickness, a modulus of 3.8 GPa and a stress at break of 100 MPa were measured. For near uniaxial blend films (±3°) a modulus of 14.5 GPa and a strength of 220 MPa in the machine direction (MD) were measured. The transverse direction (TD) properties were still higher than the neat New TPI. The electrical properties of these blends were outstanding. The dissipation factor was typically less than 0.01 for most blend compositions. Similarly, the dielectric constant was typically less than 3 up to temperatures as high as 300°C.
Rheological behavior and processability of neoprene and acrylic rubbers
Authors: Kumar Nalini R. , Gupta B. R. , Bhowmick Anil K.
Published: December 2004

Rheological behavior of neoprene and acrylic rubbers and their carbon blackfilled compounds has been studied using a Monsanto Processability Tester. These systems show pseudoplastic flow behavior. Die swell increases with increase in shear rate up to a limit beyond which it decreases. It also decreases with increase in filler loading and temperature. The maximum recoverable deformation has been calculated by assuming that the viscous response of the rubbers obeys the power law model and elastic behavior is described by Hooke's law and has been correlated with die swell. A linear generalized relationship has been obtained between the die swell and the recoverable deformation. The principal normal stress difference has been found to increase nonlinearly with shear stress. Activation energy of melt flow process increases with increase in shear rate up to a limit, after which it decreases for acrylic rubber and 10 phr filled neoprene rubber.
Basic ideas of microwave processing of polymers
Authors: Chen M. , Siochi E. J. , Ward T. C. , McGrath J. E.
Published: December 2004

The objective of this effort has been to investigate the relationship between polymer structure and microwave absorptivity. Dielectric loss factor, ε″, loss tangent, tan δ, and oscillator strength, (εS −‐ ε∞), were used to evaluate potential material processability under applied microwave radiation. Numerous polymeric materials varying in chemical and physical structures were irradiated in a low power (≤ 100W) electric field at 2.45 GHz. Electromagnetic radiation was applied as either traveling or resonant wave modes in cylindrical and rectangular waveguides. In general, heatability was found to be a direct function of the dielectric loss dispersion dependence on temperature and frequency. The dielectric loss factor obtained at low frequency measurements was found to be directly proportional to the heatability of polymers. A WLF plot was used to predict the shift of dielectric loss maxima into or out of the microwave frequency range.
A slightly compressible transient finite element model of the packing phase in injection molding
Authors: Tanguy P. A. , Grygiel J. M.
Published: December 2004

A 2‐D finite element model of the packing phase using an Augmented Lagrangian approach is described. The model is tested for various geometrical configurations. The influence of the cavity thickness, length, and shape on the packing time and flow patterns is investigated, showing a good agreement with published data.
Construction of fast‐response heating elements for injection molding applications
Authors: Jansen K. M. B. , Flaman A. A. M.
Published: December 2004

A new type of heating element was developed capable of changing the mold surface temperature by about 70 K in 0.2 s, thus enabling reduction of frozen‐in orientation and stresses in injection molded products without undue increase in cycle time. The heater, which consists of two insulation layers with a resistance layer in between, is discussed in this paper. The thickness of this insulation layer proves to be the most important design parameter. Too thick an insulation layer increases the cooling time too much, whereas with a thin layer the surface temperatures will stay too low. Temperature measurements at the heater surface and in the mold wall are reported and demonstrate the extreme fast response characteristics.
Instrumented impact evaluation of a toughened carbon fiber epoxy composite
Authors: Woo E. M. , Chen J. S.
Published: December 2004

Instrumented impact testing and analysis were performed on an interlaminartoughened carbon fiber epoxy composite (Toray 3900‐2/T800H) and a conventional (untoughened) epoxy composite (Fiberite 934/T300). Severity of impact was varied by using a wide range of impact energy. The effect of difference in the tup of the impact instrument was discussed. The residual compressive strengths after compact (CAI's) were measured by using a universal mechanical tester. The impact damage and delamination resistance of the toughened and conventional composites were quantitatively compared. At the same impact energy, the extent of damage was much less severe and the CAI was higher for the toughened composite. Relationships between the CAI's, the state of impact damage, and impact energy were investigated. Impact damage mechanisms for these two composites were not exactly the same. The impact damage of the conventional composite exhibited much greater extents of delamination. By contrast, interlaminar delamination in the toughened composite was found to be significantly suppressed, and the impact damage was more dominated by controlled matrix cracking/fiber damage, instead of catastrophic delamination. As a result, the CAI's of the toughened composite exhibited a monotonous decrease with increase in the impact energy and in the linear dimension of extents of damage.
Microwave processing of two‐phase systems: Composites and plymer blends
Authors: Chen M. , Hellgeth J. W. , Ward T. C. , McGrath J. E.
Published: December 2004

The objective of the current paper was to extend the relationships between complex polymer structures and microwave absorptivity that were formulated in the first three papers of this series (1–3). The microwave processing of composite and polymeric blends via a cylindrical resonance wave cavity and a rectangular standing wave applicator is described. These polymeric materials were irradiated in a low power (< 100W) electric field at 2.45 GHz. Graphite‐epoxy laminates were processed in both standing and traveling wave applicators. Rapid heating and curing were achieved in both cases. An observation of significance was that, with proper tuning of the traveling wave device (the precursor of a protable repair tool), it proved to be highly effective in processing. Additionally, a compatible blend of poly(methyl methacrylate) and poly(vinylidene fluoride) was heated in and applicator and the rates of temperature rise were demonstrated to depend upon morphology.