bluuebunny/crossref_metadata_2025 huggingface dataset:
The effect of processing variables on the environmental stress crack resistance of blow‐molded polyethylene bottles
Authors: Strebel J. J. , Benson M.
Published: April 2004

The effects of blow‐molding process variables on the environmental stress crack resistance (ESCR) of high‐density polyethylene (HDPE) bottles were studied. Experimental design was employed to test the effect of die temperature, mold temperature, molding time, and drop time. Bottles blown at each condition were tested using the internal pressure ESCR test. Through the use of regression analysis, the effect of each variable was quantified. Increasing die temperature, mold temperature, or molding time decreased ESCR. However, increasing drop time increased ESCR.
Evaluation of collisional damage in polystyrene foam constructions using a dual hammer impact test
Authors: Medding J. A. , Love B. J.
Published: April 2004

Low intensity impacts can reduce the structural integrity of an expanded polystyrene safety helmet by the formation of damage in the foam. This reduces the ability of the foam to protect the user under impact conditions. In these experiments, the introduction of a rubber inter‐layer that acts as a cushioning layer to protect the polystyrene shell during light and intermediate impacts was evaluated. The evaluation was conducted with a dual hammer impact tester, which was constructed for this purpose. Safety helmet cross sections were simulated by two inch square test specimens. The dual hammer impact testing identified a damage threshold energy above which damage was evident. The introduction of the soft rubber inter‐layer between the foam and outer hard shell of these specimens increased the impact loading required to damage the foam by 30%, while the amount of energy transmitted actually increased. Further work is being done on perforated rubber systems that will look at damage and energy transmission in these alternative constructions.
The effect of specimen thickness and stress ratio on the fatigue behavior of polycarbonate
Authors: Pruitt L. , Rondinone D.
Published: April 2004

The cyclic residual stresses ahead of fatigue cracks are known to play an important role in the fatigue fracture response of engineering materials. The size of these residual stresses are directly affected by the stress state of the component. In this paper, we examine the effect of stress state for fully compressive and fully tensile cyclic loading of polycarbonate. The role of stress state is studied using two different specimen thicknesses, one thickness will represent a near‐plane stress condition and the other will represent a near‐plane strain condition. In cyclic compressive loading, it will be shown that the near‐plane stress specimen with its larger zone of residual tension will exhibit enhanced crack saturation lengths. While for cyclic tensile loading, the larger zone of residual compression upon unloading will result in crack retardation for the same unloading stress intensity. A series of systematic experiments on the effects of mean stress on fatigue fracture is reported, and the results of the experiments are rationalized with the aid of scanning electron microscopy of the fracture surfaces. The results of this study have strong implications for both constant amplitude fatigue loading and variable amplitude fatigue loading as well as applicability to other engineering materials.
Generalized warpage parameter
Authors: Kikuchi Hiroyuki , Koyama Kiyohito
Published: April 2004

A warpage index (Δψm) was introduced for studying warpage characteristics of a plastic part injection molded from PA66 compounded with 30 wt% glass fiber. Δψm is defined as Δψm = (Δψm)max – (Δψm)min, where ψm = ψ(θ)max, where ψ(θ) = (ε(θ) – α(θ)ΔT)/| α(θ)ΔT|, where ε is the total strain, α is the linear thermal expansion coefficient, ΔT is temperature difference, and θ is the angle along which ε and α are calculated. Finite element analysis was used for calculating flow field in injection, fiber orientation, material anisotropy and warpage. ψm is calculated in each finite element, and Δψm is calculated in a whole finite element model. Δψm is a measure of the ratio of actual shrinkage to the amount of shrinkage that would occur if an element freely shrank. The characteristics of Δψm were studied. It has been found that warpage is null if Δψm = 0, but that null warpage generally does not indicate Δψm = 0. It is shown that Δψm quantitatively represents the warped and unwarped state. Δψm distinguishes the null warpage state with possible buckling from the null warpage state without possible buckling. It has been shown that material anisotropy is possibly described with Δψm, and that the cause of warpage is self‐restrictive deformation in an injection molded part. It has been deduced that it is generally not possible to eliminate warpage only by controlling material properties. Δψm is obtainable for a plastic part with complex geometry and complex fiber orientation state, and for arbitrary materials. Applications of Δψm are left for future study.
Warpage, anisotropy, and part thickness
Authors: Kikuchi Hiroyuki , Koyama Kiyohito
Published: April 2004

Relations among warpage, material anisotropy, and part thickness were numerically investigated for disks injection molded from PA66 compounded with 33 wt% glass fiber. Finite element analysis was used for calculating flow fields in injection, fiber orientation, material anisotropy, and warpage. Volume averaged anisotropy has been introduced, which is a ratio of the volume averaged linear thermal expansion coefficient in the flow direction to the coefficient in the direction transverse to flow (〈Rα〉 = 〈α11〉/〈α22〉). Good agreement has been obtained between calculation and experiment with respect to 〈Rα〉. A mechanical quantity, (ΔT)b/h2, which is the buckling temperature divided by the square of disk thickness, is also introduced. Differences in mechanical behavior between an injection molded disk and a composite laminate disk have been shown. A linear correlation between the mechanical quantity and the material anisotropy is also found. Parameters that determine the disk warpage are deduced from the correlation. The correlation for the injection molded disk is found to be a subset of the correlation for the composite laminate disk. The correlation between 〈Rα〉 and (ΔT)b/h2 has been extended so that the relation is applicable not only to anisotropic materials but also to isotropic materials.
Synthesis, characterization, and mechanical properties of an injection moldable polyimide based on 1,4‐diaminobutane
Authors: Koning Cor , Teuwen Liliane , Bulters Markus
Published: April 2004

A partially aliphatic polyimide was synthesized in a two‐step process in N‐methylpyrrolidone (NMP) from 3,3′,4,4′‐benzophenonetetracarboxylic dianhydride (BTDA) and 1,4‐diaminobutane (DAB). Weight average molecular weights ranging from 35,000 to over 160,000 were obtained by adding different amounts of the chain stopper phthalic anhydride, or by using a slight excess of BTDA. Rheological measurements, supported by a size exclusion chromatography (SEC) analysis before and after injection molding, point to branching or even partial crosslinking during molding of poly(BTDA‐DAB) if reactive amine endgroups are present. By reacting these amine endgroups with benzoyl chloride, branching is limited and a more Newtonian flow is observed. Both non‐endcapped and endcapped reactor powders are ∼60% crystalline (Tg = 170 to 175°C, Tm = 290 to 300°C), but according to wide and small angle X‐ray scattering (WAXS and SAXS) studies on test bars, both the more linear polyimides and their branched counterparts are fully amorphous after injection molding. Nevertheless, poly(BTDA‐DAB) shows interesting mechanical properties like a bending modulus of ∼3.9 GPa, a tensile strength of ∼130 MPa, a tensile elongation at break of ∼13%, and a notched Izod impact of ∼4 kJ/m2.
Plasticating single‐screw extrusion of amorphous polymers: Development of a mathematical model and comparison with experiment
Authors: Han Chang Dae , Lee Kee Yoon , Wheeler Norton C.
Published: April 2004

A mathematical model was developed for plasticating single‐screw extrusion of amorphous polymers. We considered a standard metering screw design. By introducing a ‘critical flow temperature’ (Tcf), below which an amorphous polymer may be regarded as a ‘rubber‐like’ solid, we modified the Lee‐Han melting model, which had been developed earlier for the extrusion of crystalline polymers, to model the flow of an amorphous polymer in the screw channel. Tcf is de facto a temperature equivalent to the melting point of a crystalline polymer. The introduction of Tcf was necessary for defining the interface between the solid bed and the melt pool, and between the solid bed and thin melt films surrounding the solid bed. We found from numerical simulations that (1) when the Tcf was assumed to be close to its glass transition temperature (Tg), the viscosity of the polymer became so high that no numerical solutions of the system of equations could be obtained, and (2) when the value of Tcf was assumed to be much higher than Tg, the extrusion pressure did not develop inside the screw channel. Thus, an optimum modeling value of Tcf appears to exist, enabling us to predict pressure profiles along the extruder axis. We found that for both polystyrene and polycarbonate, Tcf lies about 55°C above their respective Tgs. In carrying out the numerical simulation we employed (1) the WLF equation to describe the temperature dependence of the shear modulus of the bulk solid bed at temperatures between Tg and Tcf, (2) the WLF equation to describe the temperature dependence of the viscosity of molten polymer at temperatures between Tcf and Tg + 100°C, (3) the Arrhenius relationship to describe the temperature dependence of the viscosity of molten polymer at temperatures above Tg + 100°C, and (4) the truncated power‐law model to describe the shear‐rate dependence of the viscosity of molten polymer. We have shown that the Tg of an amorphous polymer cannot be regarded as being equal to the Tm of a crystalline polymer, because the viscosities of an amorphous polymer at or near its Tg are too large to flow like a crystalline polymer above its Tm. Also conducted was an experimental study for polystyrene and polycarbonate, using both a standard metering screw and a barrier screw design having a length‐to‐diameter ratio of 24. For the study, nine pressure transducers were mounted on the barrel along the extruder axis, and the pressure signal patterns and axial pressure profiles were measured at various screw speeds, throughputs, and head pressures. In addition to significantly higher rates, we found that the barrier screw design gives rise to much more stable pressure signals, thus minimizing surging, than the metering screw design. The experimentally measured axial pressure profiles were compared with prediction.
An extrusion system for the processing of microcellular polymer sheets: Shaping and cell growth control
Authors: Baldwin Daniel F. , Park Chul B. , Suh Nam P.
Published: April 2004

A new processing system for the extrusion of microcellular polymer sheets is presented. Specifically, the detailed design of a shaping and cell growth control system is discussed in the context of an overall extrusion system design with particular emphasis on the system level functional requirements of cell nucleation, cell growth, and shaping. The principle of the basic extrusion system design is to shape a nucleated polymer/gas solution flow under pressure and accurate temperature control. In this way, the initial cell growth is controlled so as to prevent degradation of the nucleated cell density during shaping. Two foaming die designs for satisfying the initial shaping and cell growth requirements are presented. Critical experiments are then presented which verified the concept of shaping a nucleated polymer/gas solution. Moreover, these experiments demonstrated the feasibility of the overall microcellular polymer sheet extrusion system design.
A microcellular processing study of poly(ethylene terephthalate) in the amorphous and semicrystalline states. Part II: Cell growth and process design
Authors: Baldwin Daniel F. , Park Chul B. , Suh Nam P.
Published: April 2004

Microcellular semicrystalline polymers such as poly(ethylene terephthalate) show great promise for engineering applications because of their unique properties, particularly at higher densities. Recent studies have shown that some high density microcellular polymers have longer fatigue lives and/or equivalent strengths relative to the neat polymer. Relatively few microcellular processing studies of semicrystalline polymers have been presented. In general, semicrystalline polymers are relatively difficult to microcellular process compared to amorphous polymers. In this paper, the microcellular processing of poly(ethylene terephthalate) in the amorphous and semicrystalline states is studied in order to quantify the processing differences. Particular emphasis is given to the cell growth stage of microcellular processing comparing the processing characteristics of semicrystalline and amorphous PET. Based on the results of this study, a number of critical process parameters are identified. Another goal of this analysis is to derive robust microcellular process design strategies for the amorphous and semicrystalline materials. Process design strategies are given for both semicrystalline and amorphous PET.
Online pattern‐based part quality monitoring of the injection molding process
Authors: Woll Suzanne L. B. , Cooper Douglas J. , Souder Blair V.
Published: April 2004

The quality of injection molded parts is currently monitored in the plant using techniques that focus on the statistical analysis of discrete data and, in particular, peak values. This paper presents an alternative online technique for part quality monitoring that focuses on the analysis of complete data patterns. Specifically, this paper discusses the application of artificial neural networks (ANNs) as part quality monitoring tools. The method of approach is to train a back propagation network (BPN) to associate part quality with the corresponding data pattern produced during injection. In Part I of this work, the data pattern consists of a series of discrete values and the part quality measure is defined as part weight. In Part II, the data pattern is the measurement profile observed from a pressure sensor placed in the mold cavity and the part quality measure is defined as part length. Results show that ANNs are successful in predicting part quality based on data patterns when an entire sensor profile is analyzed. Furthermore, demonstrations show that the approach is superior in predicting part quality when compared to statistical techniques now widely practiced by the injection molding process industry.
The development of flow instabilities during the injection molding of multicomponent resins
Authors: Hobbs S. Y.
Published: April 2004

In this study, several blends of BPA polycarbonate and acrylonitrile/butadiene/styrene (ABS) resins having different gloss levels and microscopic surface roughness values were injection molded over a range of injection rates. Changes in surface appearance were monitored by visual observation, optical microscopy, and electron microscopy. The onset of unstable flow was marked by the development of regularly spaced surface patches on the molded parts. The surface irregularities were found to be strikingly similar to those produced by dragging crosslinked rubbers across hard surfaces. It was observed that blends having higher surface roughness values had lower coefficients of friction and exhibited unstable flow at lower stresses than compositions with smoother surfaces. The data were used to quantify the rheological parameters and surface characteristics defining an acceptable molding envelope for these materials.
Melt blends of αSAN with a phenoxy
Authors: Kim Byung Kyu , Choi Chi Hoon
Published: April 2004

Melt blends of poly(α‐methyl styrene‐co‐acrylonitrile) (αSAN) with a phenoxy were prepared using a Brabender Plasticorder. Morphological, thermal, rheological, and mechanical properties of the blends were studied. DSC (differential scanning calorimetry) measurements showed two Tg (glass transition temperature) of the blends. Tg of αSAN decreased by 5 to 7°C, whereas that of phenoxy increased slightly. Melt viscosity measured using an RDS (Rheometrics dynamic spectrometer) showed a small negative and relatively large positive deviation in αSAN‐ and phenoxy‐rich blends, respectively. Transverse views of SEM (scanning electron microscopy) micrographs of the fractured surfaces again showed two phases, regardless of composition. Traces of full‐out upon fracture were seen in αSAN‐rich but not in phenoxy‐rich blends, indicating stronger interfacial adhesion in phenoxy‐rich blends. Longitudinal views of the SEM micrographs showed highly elongated structure of disperse phases (30 to 70% of phenoxy), especially when phenoxy forms dispersed phase, resulting in finer and well developed phenoxy fibrils. Tensile modulus and strengths showed a negative deviation in αSAN and positive deviation (strength) or additivity (modulus) in phenoxy‐rich blends.
Prediction of optimal preform thickness distribution in blow molding
Authors: Lee D. K. , Soh S. K.
Published: April 2004

A finite element optimization method is presented that determines the optimal thickness profile of a preform for a blow‐molded part having the required wall thickness distribution. The optimization method is based on a method of feasible directions and the design variables are thicknesses of finite elements. The step size is determined by using a Brent 1‐dimensional minimization method. Two methods for determining feasible directions are compared. A finite element model is formulated based on the thin membrane approximation, which relates the preform wall thickness distribution to the wall thickness distribution in the blow‐molded part. Triangular or conical frustra elements are used to describe deformed shapes of the preform for 2‐dimensional axisymmetric deformations. An incompressible nonlinear elastic constitutive model describes the material response. The accuracy of the finite element model used is evaluated by comparing the model predictions to published experimental data and computer simulations.
Basic studies of blow molding of talc‐thermoplastic compounds
Authors: Suh Chang Ho , White James L.
Published: April 2004

An experimental study of the blow molding of talc‐polyethylene and talc‐polypropylene compounds is presented. These compounds are found not to exhibit zero shear viscosity but rather yield stresses, below which there is no flow. The annular swell of the compositions is greatly reduced compared to the neat thermoplastics, but extrusion sag is minimized. Blow molded bottles of talc‐thermoplastic compounds were found to have much greater thickness uniformity than blow molded neat polyolefins. The talc particles were determined, by X‐ray diffraction, to be oriented with the flake surfaces parallel to the mold surface or equivalently to the bottle surface.
Reactive processing of thermoset/thermoplastic blends: A potential for injection molding
Authors: Fujiwara Hiroaki , Kim Bong Sup , Inoue Takashi
Published: April 2004

Poly(2,6‐dimethyl‐1,4‐phenylene ether) (PPE) is an engineering plastic with high heat distortion temperature. Melt processing of neat PPE is usually accompanied with thermal degradation. The degradation problem is solved by blending with polystyrene to reduce the processing temperature. We propose an alternative using triallylisocyanurate (TAIC). TAIC is a low viscosity liquid that can be cured by peroxide, e.g. α,α′‐bis(t‐butylperoxy‐m‐isopropyl)benzene (PBP), to provide a thermoset. The PPE/TAIC mixture was shown to have the upper critical solution temperature (UCST) type phase behavior. At the single‐phase regime above UCST and below the cure temperature (∼180°C for PBP), the mixture had a low viscosity, less viscous than a conventional thermoplastic such as PC and PP. That is, a nice window for injection molding was available, e.g., at 100°C to 160°C for a 50/50 blend. After injecting into a hot mold set at cure temperature, the blend cured in a short time (∼80% conversion in 5 min). Then the molded and partly cured material kept its shape and dimensions during post‐cure in a hot chamber at higher temperature (e.g. 250°C). Using transmission electron microscopy and dynamic mechanical analyses, it was shown that the cured blend had a bicontinuous two‐phase structure with periodic spacings of ∼30 nm, suggesting a structure formation via a spinodal decomposition driven by the increase in molecular weight of TAIC during cure. The cured material showed excellent flexural strength and high chemical resistance.
Interphase and compatibilization of polymer blends
Authors: Ajji Abdellah , Utracki L. A.
Published: April 2004

Polymer blends are mixtures of at least two polymers and/or copolymers comprising more than 2 wt% of each macromolecular component. Most blends are immiscible, and need to be compatibilized. The compatibilization must not only ensure improvement in performance, but it must be reproducible, insensitive to forming stresses and repeated processing. This review on compatibilization of polymer blends is prepared in three parts: (i) description of the interface/interphase; (ii) compatibilization by addition of a copolymer (with a special emphasis on the use of block copolymers); and (iii) reactive compatibilization.
Microstructural characterization of polymer blends
Authors: Vesely D.
Published: April 2004

Microscopy techniques for direct visualization of phases in polymer blends are reviewed. Light microscopy is suitable for immiscible blends and contrast techniques include polarized light, phase contrast, differential interference contrast, and fluorescence. Each technique has an application for a particular polymer system. Scanning electron microscopy is used for study of surface morphology and contrast can be enhanced by electron beam damage or by chemical etching. Cutting often provides sufficient contrast, but surface preparation by fracture or by solvent extraction must be used with caution. Surface carbon replica is a good alternative that provides better resolution and contrast. A new technique of selective swelling will be discussed. Transmission electron microscopy has very good resolution and can thus be used for the study of very fine dispersion in miscible blends. Contrast can be enhanced electronically or by staining of pre‐irradiated samples. It will be shown that the latter, together with mass loss measurements, can provide some new and unique information on the polymer blend system. Crystallographic studies are limited by the beam damage. It is nevertheless possible with some specialized techniques (STEM and microdiffraction) to obtain several dark field images and diffraction patterns from one area of highly beam sensitive polymers.
Polymer blends with a crystallizable diblock copolymer: Thermal properties and phase behavior
Authors: Kammer H. W. , Kummerloewe C.
Published: April 2004

We report on the thermal behavior of polymer blends comprising a block copolymer and random copolymers of styrene and acrylonitrile (SAN). The block copolymer constituents are ε‐caprolactone (CL) and a carbonate. Melting as well as crystallization behavior of the blocks are strongly influenced by addition of amorphous SAN, which is miscible only with PCL block. Blends under discussion can undergo different phase changes as macro‐ and microphase separation and crystallization. Hence, morphology formation is controlled by different transitions and even a cooperative interplay between them. Phase behavior of the blends is discussed and correlated with results of morphological studies.
Prediction of dispersed phase drop diameter in polymer blends: The effect of elasticity
Authors: Ghodgaonkar Parag G. , Sundararaj Uttandaraman
Published: April 2004

This paper discusses the prediction of the dispersed phase drop diameter in polymer blends considering the viscoelastic properties of polymers. The prediction is based on a simple force proportionality. Polymers are viscoelastic, and thus the elasticity of the matrix and the elasticity of the dispersed phase affect the drop size. The forces that deform a polymer droplet in a polymer matrix are the shear forces, ηmγ, and the matrix first normal stress, T11,m. This deformation is resisted by the interfacial forces, 2 Γ/D and the drop's first normal stress, T11,d. As a first approximation, the forces were balanced to predict the particle size in polymer blends. The diameter of the dispersed phase was predicted reasonably well for several systems at different operating conditions. It was observed for some systems (PS/PP, PS/EPMA, PS/PA330) that, as the shear rate increased, the diameter of the dispersed phase initially decreased. At a critical shear rate, the diameter reached a minimum value, and beyond it, the diameter increased with shear. This critical value was found to be between 100 to 162.5 s−1 for a PS/PP system. The force balance predicts this minimum drop diameter at a similar critical shear rate. The specific energy input (the amount of energy input into the blend) could not explain the phenomenon of a minimum drop diameter with increase in shear. This minimum is not observed for the high concentration systems, such as the 20% PP dispersed in PS, since the effects of coalescence become significant. In reactive blends, the predicted drop diameter was closer to the experimentally determined diameter, and there was less variation in diameter with changes in shear rate.
Polymer blends for enhanced asphalt binders
Authors: Ait‐Kadi Abdellatif , Brahimi Brahim , Bousmina Mosto
Published: April 2004

Straight asphalt binders have been modified by addition of both high‐density polyethylene (HDPE) and a blend of HDPE and ethylene‐propylene‐diene‐monomer (EPDM). The blend composition was fixed to 90/10 HDPE/EPDM to illustrate the possibility of adapting the polymer to be added to the asphalt binder for specific end‐use applications. Linear viscoelastic properties of unmodified and polymer modified asphalts at concentrations ranging from 1 to 5 wt% were studied before and after Thin‐Film Oven Test (TFOT) aging. Temperatures ranging from −15°C to 60°C were considered. Standard tests such as Ring‐and‐Ball softening point, Fraass breaking point and TFOT aging were also performed on the whole set of samples. It was found that addition of rubber‐modified polyethylene (HDPE/EPDM) to the straight asphalt results in materials with enhanced overall properties, and most important, dispersed phase much more stable than the equivalent HDPE modified asphalt, mainly before TFOT aging. Good results were obtained for 1% HDPE/EPDM samples. Optimum design is, however, required for the desired properties to be obtained.
Role of polymer transparency and temperature gradients in the quantitative measurement of process stream temperatures during injection molding via IR pyrometry
Authors: Lai Gwan‐Ywan , Rietveld Jeroen X.
Published: April 2004

The accurate and precise measurement of process stream temperatures during injection molding can be difficult, since the cyclic operation results in spatial and temporal variations of the stream temperature. This paper examines the application of a spectral infrared (IR) pyrometer to monitor the cooling of a polymer melt within the mold cavity during a typical injection molding cycle. An outline for interpreting the radiation signal collected with the IR pyrometer is presented. The discussion includes theoretical aspects as well as experimental results. The theoretical approach accounts for the polymer transparency (attenuation behavior) at the spectral wavelength of the pyrometer and also for the temperature gradient within the polymer, thereby establishing the concept of a critical depth for a given pyrometer/polymer combination. The final analysis reveals good agreement between the predicted and measured results for the transient cooling conditions of the polymer within the mold cavity. Depending on the degrees of polymer transparency used in the theoretical prediction, the deviation between the measured and predicted transient bulk temperatures after mold filling (during the mold cooling stage) varies from ±2°K to ±9°K.
Thermal stability of a novel poly(ether ether Ketone Ketone) (PK99)
Authors: Abate L. , Calanna S. , Pollicino A. , Recca A.
Published: April 2004

The degradation of PK99 was studied by heating the polymer in both isothermal and dynamic conditions under nitrogen flow and in a static air atmosphere. In both environments this polymer's thermal stability exceeded that of PEEK. The dynamic experiments showed that in both nitrogen and air atmospheres the polymer degraded in two stages with formation of the same residue, which was quite stable under nitrogen, while almost completely burned in air. Good agreement was observed with the isothermal experiments. Apparent activation energy values were evaluated. The double linear relationships obtained by the Kissinger equation suggested a complex degradation process.
Modifying the tait equation with cooling‐rate effects to predict the pressure–volume–temperature behaviors of amorphous polymers: Modeling and experiments
Authors: Chang R. Y. , Chen C. H. , Su K. S.
Published: April 2004

Cooling‐rate effects play an important role in polymer processing because the materials experience rapid cooling when transferring from melt states to solid states. The traditional Tait equation has been used widely in representing the volumetric behaviors of polymers as a function of temperature and pressure, but not of cooling rate. Based on the dependence of glass‐transition temperature on cooling rate (i.e., θ = dTg/d log ∣ q ∣), the volumetric dependence on cooling rate is employed in this work to modify the traditional Tait P–V–T equation to become a time‐dependent P–V–T model. The physical meanings of the traditional Tait equation parameters are interpreted and, thereby, parameters in the new model are derived according to the material constant θ. The controlled cooling‐rate measurements of polymeric volumetric data have been performed in this work to verify the validity of the proposed model. Additionally, the material parameter θ, calculated from the measured data of polystyrene (PS) (Chi‐Mei PG‐33) in this work, equals 2.85 K, which is close to 2.86 K calculated from the Greiner‐Schwarzl work. Furthermore, a comparison of the predicted results with the experimental data both in this work and from literature is discussed under different pressures and various cooling rates. The results have indicated that the proposed non‐equilibrium P–V–T model closely correlates with experimental data.
Fracture behavior of glass bead‐filled poly(oxymethylene) injection moldings
Authors: Hashemi S. , Din K. J. , Low P.
Published: April 2004

The mechanical properties of glass bead filled poly(oxymethylene) were investigated as a function of glass bead content and glass bead diameter using injection molded test pieces. Fracture toughness measurements were made using single edge‐notched tension and single edge‐notched bend specimens. The effect of notch orientation with respect to the mold fill direction on fracture toughness was studied using single gate and double gate moldings. Tensile strength and flexural modulus were measured using standard test pieces.

It was found that; (i) fracture toughness of the filled and unfilled polymer was relatively independent of notch orientation, (ii) the presence of weldlines in the molded test pieces did not affect the fracture toughness of unfilled polymer or its composites, (iii) fracture toughness of filled polymer was always considerably lower than that of the unfilled polymer; fracture toughness decreased sharply with increasing bead concentration, (iv) fracture toughness was not a sensitive function of glass bead diameter; it decreased slightly as bead diameter increased, (v) strain energy release rate as measured under impact decreased with increasing bead concentration, (vi) tensile strength decreased linearly with increasing glass bead concentration and was inversely proportional to the square root of the bead diameter, (vii) weldlines did not affect the tensile strength of the polymer or its composities, (viii) flexural modulus increased linearly with increasing glass bead concentration according to the Einstein equation.
Prediction of process‐induced warpage in injection molded thermoplastics
Authors: Akay M. , Ozden S. , Tansey Tony
Published: April 2004

The main cause of warpage in injection moldings is the imbalance of the thermal residual stresses that are caused by a non‐uniform temperature distribution through the thickness of the moldings resulting from variation in cross sections, part geometries, and temperature difference between the mold surfaces. As the hot plastic melt is injected into the relatively cooler mold, a temperature gradient develops between the core of the molding and its surfaces, determining the magnitude of the residual stresses and warpage deflection. The relationship between the temperature difference of the two halves of the mold and warpage for a flat plate was measured and predicted by use of a finite element software package. The development of warpage in a 3D component (L‐shaped bracket) was also measured, and the results were compared with computer predictions.
The effect of interfacial instabilities on the strength of the interface in two‐layer plastic structures
Authors: Ranjbaran Mohammad M. , Khomami Bamin
Published: April 2004

We have experimentally investigated the coupling between interfacial instabilities and mechanical interlocking in polymeric films consisting of the incompatible polymer pair of polypropylene/high‐density polyethylene and the compatible polymer pair of linear low‐density polyethylene/high‐density polyethylene. Our experimental results show that mechanical interlocking between the two phases can be achieved by controlling the extent of interfacial instabilities by properly selecting the initial disturbance frequency and amplitude as well as the layer depth ratio. Additionally, it has been shown that strength enhancement of the interface due to mechanical interlocking is directly proportional to the extent of wave bending in the processing apparatus. In fact, it has been demonstrated that in our test geometry maximum strength enhancement can be achieved at dimensionless wavenumbers near unity that correspond to disturbances with the largest growth rates. Overall, it has been shown that mechanical interlocking induced by a controlled amount of interfacial instabilities (i.e., based on knowledge of the stability of the interface and growth/decay rate of interfacial waves) can significantly increase the interfacial strength of two layer polymeric structures consisting of incompatible and compatible polymer pairs. Moreover, this effect is more pronounced in incompatible polymer pairs that possess negligible interfacial strength in absence of mechanical interlocking.
The characterization of the halatopolymers: A review
Authors: Ibidapo T. Adesanya
Published: April 2004

Halatopolymers belong to a group of ion‐containing materials that display both salt‐ and polymer‐like properties. Their mode of synthesis and other characteristics have been widely reported. This work considers the various reports as defined by both polymeric structure and by the metal ions involved in formation. Also provided are data on other characteristics by which this group of materials can be identified. Synthesis of simple nonpolymeric backbone structures can give highly crystalline salts, which become more amorphous after thermal treatment. While the polymeric backbone‐structured halatopolymers are soluble, the nonpolymeric backbone counterparts are generally insoluble. The halatopolymers exhibit relatively high thermal stabilities.
Influence of melt stability on the crystallization of bis(4‐aminophenoxy)benzene‐oxydiphthalic anhydride based polyimides
Authors: Srinivas Srivatsan , Graham Marvin , Brink M. Heather , Gardner Slade , Davis Richey M. , McGrath James E. , Wilkes Garth L.
Published: April 2004

Novel high performance semicrystalline polyimides, based on controlled molecular weight phthalic anhydride (PA) endcapped 1,4‐bis(4‐aminophenoxy)benzene (TPEQ diamine) and oxydiphthalic dianhydride (ODPA), were synthesized. They exhibited excellent thermal stability in nitrogen and air atmospheres as determined by thermogravimetric analysis (TGA). The glass transition temperatures (Tg) for these polymers ranged from 225°C for the 10,000 Mn (10K) polymer, to 238°C for the 30,000 (30K) Mn material. The observed melting temperatures for all the polymers were ∼420°C. The crystallization behavior of these polymers showed a strong molecular weight dependence, as illustrated by the observation that the 10K and 12.5K polymers crystallized with relative ease, whereas the 15K, 20K, and 30K polymers showed little or no ability to undergo thermal recrystallization. The thermal stability of these polymers above Tm was investigated by studying the effect of time and temperature in the melt on the cold crystallization and melting of these polymers. Increased time and temperature in the melt resulted in lower crystallinity because of melt state degradation, such as crosslinking and branching, as evidenced by an increase in melt viscosity, which was more prominent for the higher molecular weight polymers.
Effect of constitutive models on the numerical simulation of viscoelastic flow at an entry region
Authors: Loh K. W. L. , Tay A. A. O. , Teoh S. H.
Published: April 2004

The poor solutions of numerical simulations at a contraction has often been attributed to the numerical scheme used. However, the solution of a numerical simulation is also highly dependent on the constitutive equation. A study of various constitutive equations on the simulation of the 4:1 contraction flow is made in this paper, and their effects on the results analyzed. The constitutive models considered include the Upper Convected Maxwell model, the Oldroyd‐B model, the White‐Metzner model, the Phan‐Thien‐Tanner model and the Giesekus‐Leonov model. It was found that although the Phan‐Thien‐Tanner model gave the best results, the solution at higher shear rates were still not satisfactory.
Study of shear modification of LDPE by an NMR relaxation technique
Authors: Van Prooyen M. , Peemoeller H. , Rudin A.
Published: April 2004

A low‐density polyethylene was shear modified by repeated extrusions. These operations resulted in no detectable changes in the polymer molecular weight distribution. The apparent melt viscosity and elasticity decreased after extrusion, as is commonly observed in shear modification. These rheological effects were fully reversible by annealing the melt. Transverse proton relaxation measurements showed the existence of four identifiable different regions in the polymer melt. The range of relaxation times encompassed two orders of magnitude. These reflect the existence of regions with different degrees of conformational order. Shear modification results in the breakup of a minor proportion of the most constrained regions, which have the shortest relaxation times. The apparent “entanglements” that are inferred from rheological measurements probably reflect the coexistence of segments of more than one macromolecule in chain‐folded domains, as indicated by molecular dynamics calculations. These results are evidence that the equilibrium state of LDPE is not a chain‐entangled, highest entropic condition, but rather a lowest free energy state in which chain folding is favored. They are consistent with other longstanding observations, such as the failure of experiments to produce amorphous polyethylene and the apparent lack of mixing of HDPE and LDPE on a molecular level.
In‐mold shrinkage and stress prediction in injection molding
Authors: Titomanlio G. , Jansen K. M. B.
Published: April 2004

In‐mold shrinkage may occur for product parts that solidify under low holding pressure and are not restricted by ribs or flanges. It not only affects the final product dimensions but in addition may have a large effect on the residual stress distribution. A simple elastic model is used to study the effect of in‐mold shrinkage on final product dimensions and residual stress distributions. Friction between polymer surface and mold wall as well as deformation of the mold cavity are taken into account. The model uses local values for temperature, pressure, and crystallization, which belong to the standard output of most simulation codes.
Computer simulation of weld lines in injection molded poly(methyl methacrylate)
Authors: Dairanieh I. S. , Haufe A. , Wolf H. J. , Mennig G.
Published: April 2004

Computer simulation packages have had success in predicting filling behavior in extremely complicated geometries. However, few packages offer the possibility of predicting the location and strength of weld lines. This work examines the sensitivity of Moldflow's weld‐line prediction algorithm to variations in material properties and processing conditions. Qualitatively, the algorithm correctly predicted the effects of changes in viscosity, density, and PVT relationship on weld‐line strength of a poly(methyl methacrylate). The algorithm is also successful in predicting the influence of variations in the injection time on weld line strength. However, the algorithm predictions for changes in the mold and die temperatures were at odds with the experiment. An attempt was made to correlate Moldflow's computed viscosities with the experimentally measured reduction in the strength in the weld‐line area. It was shown that a one‐to‐one relationship existed between these two quantities. Whereas the potential of using the viscosity to predict weld‐line strength has been demonstrated, further refinement of this new concept is needed and its validity for other systems has to be established.
Morphology, thermal, and mechanical properties of polyacetal/ionomer blends
Authors: Horrion J. , Cartasegna S. , Agarwal P. K.
Published: April 2004

This study is directed towards the development of modifiers for and the understanding of their role in improving the impact properties of an engineering polymer, polyacetal (POM). It is demonstrated that modifiers that induce ion‐dipole interactions can lead to substantial enhancements in the room temperature impact performance of POM without sacrificing its unique balance of mechanical, thermal, and chemical resistance properties. The mechanical and physical properties of blends of a commercial copolymer type polyacetal (POM) with terpolymers of ethylene, methylacrylate and acrylic acid (EAAT) and its zinc ionomer form (EAAT‐Zn), are reported. Substantial differences both in the mechanical and impact performance were found in these two modified POM systems. DSC and optical microscopy studies of such blends demonstrates only minor differences in the microcrystalline structure of the two blend systems. A nearly three fold reduction in the spherulite size of POM was found from addition of as little 5% of either modifier, thus ruling out this mechanism for the observed increased toughness of the blends. Dynamic mechanical measurements and cryofractured surface microscopy observations indicate that enhancements in the physical properties of POM modified with zinc ionomers of EAAT are due to enhanced interfacial adhesion and to the (inherent) mechanical rigidity (due to ionic interactions), of the modifier. In these blends the tensile and impact strength are found to be a function of the degree of neutralization of the terpolymer acid content. In particular, an optimum balance of impact and tensile properties is obtained with partial neutralization (in the range of 25 to 50% of the terpolymer acid content) and at modifier addition levels in POM in the range of 5 to 10%. The EAAT modifier for POM was found to be ineffective even up to 20% addition as compared to EAAT‐Zn modifier. Ion‐dipole interactions are thus shown to be more influential than the hydrogen bonding that occurs in EAAT‐POM blends. The study suggests a new approach to modify polar engineering polymers via such interactions.
Structure and crack growth in gas pipes of medium‐density and high‐density polyethylene
Authors: Tränkner T. , Hedenqvist M. , Gedde U. W.
Published: April 2004

The microstructure and resistance to slow crack growth of two commercial polyethylene pipe materials were studied. Differential scanning calorimetry, small‐angle X‐ray scattering, and transmission electron microscopy were used to reveal the crystallite thickness and width distributions and the size of the lamellar stacks. The resistance to slow crack growth was assessed by uniaxial constant loading of notched specimens and by hydrostatic pressure testing of notched and unnotched pipes. The high‐density material contained roof‐lamellae, suggestive of a segregation of low molar mass species. Notched uniaxial testing revealed large differences in slow crack growth‐resistance between the two PEs despite the fact that the average tie‐chain concentration was similar. Hence, low‐molar mass segregation, which was found to be higher for the high‐density material, definitely decreases the resistance to slow crack growth. Notched uniaxial testing was a sensitive method for ranking these PEs according to their resistance to slow crack growth, and 15 times faster than that achieved in conventional unnotched pressure testing. Failure time extrapolations from higher temperatures to 20°C were made, using a multiple linear regression method (SEM‐Q1), the Arrhenius equation, and universal shift‐functions to investigate their applicability. The extrapolations resulted in longer life times compared with experimental data, regardless of the method used. The SEM‐Q1 method (lower‐confidence‐limit data) gave the best fit to the 20°C experimental data followed by the Arrhenius equation.
Sorption of low molar mass silicones in silicone elastomers
Authors: Gedde U. W. , Hellebuych A. , Hedenqvist M.
Published: April 2004

Elastomers based on polydimethylsiloxane (PDMS) are used as insulating material in outdoor electrical power applications. It is believed that migration of small molecule PDMS species plays an important role in the recovery of hydrophobicity of oxidized or polluted PDMS elastomer surfaces. This paper reports data on diffusivity and solubility of low molar mass PDMS liquids in PDMS rubbers (8000 < Mc < 16,000 g/mol) obtained by sorption measurements. It was found that the diffusivity (D) of linear PDMS liquids was approximately independent of the concentration of penetrant and that in the molar mass range 400 < Mc < 18,000 g/mol it decreased with molar mass (Mc) of the diffusing liquid according to D α Mc−0.8. Theory and previous data for other oligomers and elastomers predict that D is proportional to M−1. Linear PDMS liquids of lower molar mass exhibited a stronger molar mass dependence. The diffusivity of a given PDMS liquid increased with increasing elastomer crosslink density. The activation energy of the diffusivity was constant at 15.5 ± 2 kJ/mol for linear PDMS liquids of Mc larger than 1000 g/mol−1 with only a negligible influence of network density and filler content. The activation energy of the lowest molar mass penetrant was considerably lower, 6 to 7 kJ/mol. The solubility increased markedly with decreasing molar mass of the penetrant and with decreasing elastomer crosslink density.