bluuebunny/crossref_metadata_2025 huggingface dataset:
Relating the heat‐of‐mixing of analog mixtures to the miscibility of hydrogen‐bonding polymers
Authors: French R. N. , Walsh J. M. , Machado J. M.
Published: May 2005

The prediction of polymer/polymer miscibility is addressed using analog calorimetry and molecular modeling. For each polymer, an analog compound representing one or two repeat units was chosen. Heat‐of‐mixing was measured for liquid mixtures of analog compounds and then used in a binary interaction model to predict polymer miscibility. Specifically, we have measured exothermic heats‐of‐mixing for 4‐ethyl phenol, an analog of poly(vinly phenol), with several analogs containing ether, ester, or ketone functional groups. The exothermic heat‐of‐mixing results are consistent with the observed miscibility of poly(vinyl phenol) with polymers containing these functional groups. Using interaction parametes derived from the analog calorimetry in the binary interaction model or using premixes of 4‐ethyl phenol in ethyl benzene, we correctly predict the magnitude and relative order of the fraction of vinyl phenol units in copolymers with styrene required for miscibility with poly(methyl methacrylate), polyacetal, and a polyketone. the miscibility trends for poly(vinyl phenol) blends predicted from analog calorimetry and the binary interaction model are in reasonable agreement with those predicted from the association model of Painter and Coleman, despite the different bases of the two approaches. We have used molecular modeling to complement the analog calorimetry and to assess steric effects on hydrogen‐bonding ability for models of poly(n‐butyl acrylate) and poly(t‐butyl acrylate) with phenol. The modeling results suggest that, in some cases, steric effects and the three‐dimensional structure of the polymer can significantly influence the hydrogen‐bonding ability of polymers relative to their analogs.
J‐Rcurve calculation with the normalization method for toughened polymers
Authors: Zhou Z. , Landes J. D. , Huang D. D.
Published: May 2005

The method of normalization is used to develop theJ‐Rcurve fracture toughness characterization for polymeric materials. This method can developJ‐Rcurves directly from load vs. displacement records without a need for an on‐line crack monitoring system. It was used previously to developJ‐Rcurves for metallic materials and is applied here for the first time to polymer materials. Single edge notched bend specimens of rubber toughened nylon 6/6 and rubber toughened amorphous nylon are used in this study. TheJ‐Rcurves from the method of normalization are compared with the results obtained from the multiple specimen method of ASTM Standard E813. The results show that the method of normalization gives reasonableJ‐Rcurves; both methods show agreement over the earlyJ‐Rcurve region. In addition theJIcvalues are determined for each method and compared. Based on this work it is suggested that the method of normalization could be used as a general test method to developJ‐Rcurves for polymeric materials.
Kinematics and deformation characteristics as a mixing measure in the screw extrusion process
Authors: Kwon T. H. , Joo J. W. , Kim S. J.
Published: May 2005

The present paper proposes “Deformation Characteristics” (DC) as a new deformation measure of screw extrusion processes, based on the Green deformation tensor. In contrast to previous strain measures heuristically proposed by Mohr, et al., Mckelvey, and Pinto and Tadmor, the new DC can naturally incorporate the demixing phenomena and systematically take into account the three‐dimensional circulatory flow with the screw flight effect. Therefore, DC can be regarded as an improved strain measure. “Weighted Average Deformation characteristics” (WADC) is also proposed to indicate the overall deformation characteristics as a quantitative measure to the “goodness of mixing” of the extrusion process. The present paper includes discussion on delicate differences between DC and several other strain measures in case of the two‐dimensional velocity approximation, and on the application of DC into a general three‐dimensional velocity field obtained by a quasi‐three‐dimensional finite element analysis of extrusion processes. In determining WADC in the three‐dimensional application, the residence time distribution function, including the three‐dimensional circulatory flow effect, is used.
The rheological characterization of fluorinated thermoplastics using squeezing flow viscometry
Authors: Deng Yong , Martin George C. , Kohut Gerard P. , Gotro Jeffrey T.
Published: May 2005

A squeezing flow viscometer was developed to characterize the rheological properties of luorinated thermoplastics. The viscosities of CTFE (polychlorotrifluorethylene) and FEP (a copolymer of tetrafluoroethylene and hexafluoropropylene) were determined using the viscometer by assuming that the shear‐rate dependent viscosity can be described by a power‐law, a truncated power‐law, or an Ellis model. The results were in agreement with the viscosities measured with steady shear cone‐and‐plate viscometry and oscillatory cone‐and‐plate rheometry. Although the squeezing flow behavior of the polymers can be well explained by the purely viscous models, the power‐law model is valid only for a limited range of shear‐rates whereas the other two models are useful over a relatively wide range.
Influence of a compatibilizing agent on the phase morphology of a polyethylene‐polyamide 6 blend in a modular intermeshing co‐rotating twin screw extruder
Authors: Lim Soonho , White James L.
Published: May 2005

A study of the influence of a compatibilizing agent on phase morphology development in a 75/25 polyethylene/polyamide‐6 blend in a modular co‐rotating twin screw extruder is presented. The development of phase morphology along the axis of the modular screw was observed by cooling the extruder and removing the polymer from the screw channels. Changes in phase morphology due to the addition of a compatibilizer have been investigated using scanning electron microscopy. Sufficient quantities of compatibilizing agent produce significant increases in the rate of mixing and also reduce the scale of the phase morphology. Much larger quantities (5%) than actually required for interface coverage are needed for rapid mixing. This seems to be due to the high viscosity of the matrix.
Does quantum magic impinge on polymer physics?
Authors: Hearle John W. S.
Published: May 2005

Penrose states that quantum effects can occur even in relatively large systems when energy differences remain small. This is just the situation with polymer materials. A quantum description by Penrose of the formation of quasi‐crystals can be rewritten to apply to polymer crystallization. The implications of the need to take account of quantum effects are discussed. Another approach based on the quantization of energy levels in clusters of atoms offers a possible explanation of heat setting in nylon and polyester fibers. Finally some problems of the interpretation of quantum theory are discussed.
Characterization of the interfacial bond in paper‐polypropylene‐paper laminates
Authors: Johnston Stephen A. , Somodi Paul J. , Eby R. K. , Bernstein Bruce S.
Published: May 2005

The interfacial strength of two paper‐polypropylene‐paper laminates used for electrical power transmission cable insulation has been measured using a peel test after a variety of conditionings that simulate the service thermal stress conditions. Immersion in dielectric oil at 23°C causes little decrease in peel strength, but heating in the oil at 90°C causes a rapid initial loss followed by a slow loss of strength. Cyclic and static heating show that cyclic fatigue is not a factor as the initial loss of strength occurs in a time comparable to the first two test cycles and further heating causes much less loss of strength. Tensile and compressive stresses resulting from cable winding have no effect on the loss of bond strength during heating in oil. Vacuum drying of the laminate and oil (as in cable manufacture) before heating results in less decrease in peel strength than heating without prior drying. Optical and electron microscopy show minimal wetting of the paper fibrils by the polypropylene with only a few having been either normal to or at a steep angle to the polypropylene surface. That is, the fibrils appear to be parallel to the interface and only partially immersed in the polypropylene. Micrographs show little, if any, differences between the interfaces on the two sides as well as little paper on the polypropylene after delamination and vice versa. It is suggested that the bonding mechanism is a combination of weak mechanical interlocking and secondary bonds. It is also suggested that swelling of the polypropylene relative to the paper by the dielectric oil at 90°C weakens the interfacial bond.
Thermoplastic polyheterocycles. II: Polyalkylene‐imides
Authors: Preston J. , Tropsha Y.
Published: May 2005

Polyalkylene‐imides (i.e., aliphatic‐aromatic polyimides) were prepared smoothly in N‐methyl pyrollidone from straight chain aliphatic diamines and pyrromellitic dianhydride. Melting points of the polymers ranged from about 300 to 450°C, depending of the length of the alkylene chains. An odd/even effect related to the alkylene chain was noted for melting points and glass transition temperatures (Tg) of the polymers. The Tgs were relatively high, especially when compared to similarly structured polyalkylene‐heterocycles, e.g., polyakylenebenzoxazoles.
Deformation and entanglement in semicrystalline polymers
Authors: Plummer C. J. G. , Cudré‐Mauroux N. , Kausch H.‐H.
Published: May 2005

Transmission electron microscopy and optical studies of thin films of isotactic polystyrene (iPS) and polyoxymethylene (POM) provide evidence for a distinction between crazing mechanisms in semicrystalline polymers above and below Tg. In the latter temperature regime, deformation in iPS and POM crystallized at high supercooling has been discussed in terms of existing models for crazing in amorphous glassy polymers, based on entanglement ideas. Above Tg, where the difference in mechanical behavior of the amorphous and crystalline regions becomes marked, the fibrillar nature of local deformation appears to be a consequence of the inhomogeneity of the undeformed polymer.
Dynamic mechanical analysis and its relationship to impact transitions
Authors: Woo Lecon , Westphal Stanley , Ling Michael T. K.
Published: May 2005

Detailed, instrumented impact tests were carried out between about − 100 and 60°C for flexible poly(vinyl chloride) (PVC), ethylene vinyl acetate (EVA), and polypropylene (PP) films. Secondary impact transitions in addition to the main transitions were detected for all three films, indicating that multiple impact transitions may be far more general in occurrence than commonly expected. Wide frequency (from 0.05 to 100 Hz) dynamic mechanical spectra of the same materials were also generated over similar temperature ranges. A new data treatment method was proposed whereby the material dissipation function was evaluated by summing the responses over broad frequency ranges of the loss modulus and the impulse spectrum. The dissipation function when plotted as a function of temperature was found to accurately (to within 3 to 5°C) predict the location of the main impact transitions for all three polymers. In addition, the existence and location of the secondary impact transitions for both PVC an PP were predicted. Both the functional form and the temperature match between the experiments and predictions strongly support the validity of the proposed method. However, some discrepancy remained in predicting the very low temperature (−65°C) impact transition for EVA.
Blends of a thermotropic LCP and a thermoplastic elastomer. II: Formation and stability of LCP fibers
Authors: Verhoogt H. , Willems C. R. J. , Van Dam J. , De Boer A. Posthuma
Published: May 2005

The formation of fibers during blending of a thermotropic liquid crystalline polymer (LCP) with a thermoplastic elastomer (TPE) using shear flow, and the stability of the fibers and the blend morphologies at elevated temperatures were studied. The polymers used were Vectra A900 (LCP) and Kraton G1650 (TPE). Fiber formation in (predominantly) shear flow was studied using a single screw extruder of which the die was removed. Fibers were obtained in blends with 5 vol% LCP at shear rates as low as 6.3 s−1. Conventional extrusion through a die was used for preparing materials for the studies of the thermal stability of blends and isolated fibers–isolated LCP‐fibers surrounded by a TPE‐matrix disintegrate when held above the melting point of the LCP. Annealing of the blends at this melting temperature results in changes of the morphology and in a fairly rapid decrease of the modulus of elasticity.
Controller design and performance analysis for a reactive extrusion process
Authors: Pabedinskas A. , Cluett W. R.
Published: May 2005

This paper presents the design and analysis of a process control strategy for a reactive extrusion polypropylene degradation process. The primary control objective is to continuously produce polypropylene with desired properties (viscosity) despite variations in the properties of the feed material. The viscosity of the polypropylene, measured using an In‐line Wedge Rheometer, is controlled by manipulating the feed concentration of the peroxide which acts as the initiator for the degradation reaction. An empirical model of the reactive degradation process is developed which describes the process dynamics and the characteristic process disturbances. Minimum variance (MV), constrained minimum variance (CMV), and pole placement (PP) controllers are first evaluated and compared in simulation. Then, a pole placement controller is implemented on the actual reactive extrusion process, with results being presented for the response of the controlled process to load disturbances due to feed material changes.
Comparative study of warpage, global shrinkage, residual stresses, and mechanical behavior of rotationally molded parts produced from different polymers
Authors: Bawiskar Santosh , White James L.
Published: May 2005

A comparative study of warpage, global shrinkage, and residual quench stresses developed in rotational molding is made for a series of thermoplastics including various polythylenes, polypropylene, polyamide‐6, polycarbonate, and polystyrene. The influence of rate of quench on uniaxial stress strain and impact behavior of rotomolded parts was also studied. Generally, warpage, global shrinkage, and residual stresses increase with increasing quench rate for all the polymers. Further, the levels of warpage and global shrinkage increases with extent of crystallization, i.e., products from glassy polymers exhibit little warpage and those from highly crystalline polymers are highly warped. Increasing rate of quench tends to increase elongation to break and impact strength.
Masked edge effects when measuring diffusion coefficients with the cup method
Authors: Claesson J. , Hagentoft C.‐E. , Wadsö L.
Published: May 2005

When diffusion coefficients are measured with the cup method, the exposed area is often less than the area of the sample. Because of this masking effect the measured diffusion coefficient is overestimated. The present article presents simple formulas based on two‐dimensional analytical solutions to correct for this in cylindrical cup samples. Different cases of anisotropical diffusion are dealt with. The error in the analytical solutions is determined by numerical computer simulations.
Three‐dimensional finite element analysis of polymeric fluid flow in an extrusion die. Part I: Entrance effect
Authors: Wen Shu‐Heng , Liu Ta‐Jo , Tsou Jenq‐Der
Published: May 2005

The Galerkin finite element method has been applied to study the three‐dimensional flow field of power‐law fluids inside an extrusion die. Two inlet designs, i.e., center‐fed and end‐fed, have been considered. The effects of inertial force as represented by the Reynolds number Re, inlet geometry, and the power‐law index n on lateral flow uniformity and vortex formation in the entrance region have been examined. A flow visualization technique has been carried out to experimentally verify the theoretical prediction of the three‐dimensional flow field inside a die. It has been found that increasing Re or decreasing n will deteriorate flow uniformity. Depending on the direction of the inlet jet stream, the inertial force may create a flow peak in the central region of a center‐fed die, or the maximum flow rate will appear close to the end of the die for an end‐fed die. For highly shear‐thinning fluids, lower flow rates are always observed close to the end of the dies. It is concluded that creating a plug flow in the inlet tube of the extrusion die is advantageous for both center‐fed and end‐fed designs.
Continuous crosslinking of ethylene vinyl acetate and ethylene methyl acrylate copolymer blends by on‐line microwave heating
Authors: Cassagnau P. , Michel A.
Published: May 2005

The transesterification reaction catalyzed by dibutyltin oxide has been used to crosslink miscible blends (at about 200°C) of ethylene vinyl acetate (EVA) and ethylene methyl acrylate (EMA) copolymers. Then, microwave heating at 2.45 GHz with the fundamental TE01 mode was used for activation of this crosslinking reaction. The microwave treatment was carried out in a continuous process through a resonant cavity on line with a twin screw extruder equipped with a strip die or a circular die, which imposed the shape of the samples in the waveguide. Therefore, a shape factor due to the geometry of the samples and their orientation with respect to the electromagnetic field was defined. Last, this technique was applied to the microwave crosslinking of an EVA/EMA blend dispersed in a polypropylene matrix and consequently offers a new route to control the morphology of the polymer blends.
Prediction of stationary interfaces in coextrusion flows
Authors: Agassant J. F. , Fortin A. , Demay Y.
Published: May 2005

A computation method for the development of the interface in coextrusion flows is proposed. It is based on the transformation of the nonmixing condition at the interface into a transport equation of the rheological constants in the whole domain. The coextrusion flow of a Newtonian fluid and of a Carreau fluid is tested. It is pointed out that the interface location is strongly dependent on the flow rate and on the flow rate ratio.
Melt crystallization kinetics of syndiotactic polystryrene
Authors: Wesson R. D.
Published: May 2005

The crystallization kinetics of syndiotactic polystyrene (SPS) were studied using nonisothermal DSC analysis. Crystallization rates and half‐times were determined from the glass transition temperature (∼ 100°C) up to the melt temperature (∼ 270°C) for various molecular weight SPS polymers. The results suggest that the crystallization rate of SPS is molecular weight dependent. These results are also compared with previously determined crystallization kinetics of high density polyethylene. The maximum crystallization rate of high density polyethylene is approximately ten times greater than that of SPS.
Processing effects on poly(ethylene terephthalate) from bottle scraps
Authors: Giannotta Giorgio , Po' Riccardo , Cardi Nicoletta , Tampellini Elena , Occhiello Ernesto , Garbassi Fabio , Nicolais Luigi
Published: May 2005

Processing of virgin and recycled poly(ethylene terephthalate) (PET) in a twin screw extruder evidences the degradative effect caused by thermal decomposition of poly(vinyl chloride) (PVC) and other impurities, e.g. adhesives, at the processing temperature. Lower melt viscosity and molecular weight, along with higher carboxylic end group concentration, were observed for recycled PET, the extent depending on PET purity. In an attempt to investigate the correlation between the kinetics of degradation phenomena and the level of thermomechanical stress, a novel dynamic method of evaluating thermal stability in processing conditions was developed. Such a method allows the achievement of long equivalent residence times while using lab‐scale extruders. As a result of these experiments, PVC‐rich recycled PET was shown to reach very low melt viscosity after less than 10 min in processing conditions, while virgin PET retained high viscosity even after 30 min.
Flow field analysis of a cavity transfer mixer
Authors: Wang Chicheng , Manas‐Zloczower Ica
Published: May 2005

The cavity transfer mixer (CTM) was primarily designed as a distributive mixing device to be used as an add‐on unit to existing extruders. In determining the CTM overall mixing efficiency as well as its potential use for various applications, the flow patterns/characteristics within this mixer must be well understood. In this work, a fluid dynamics analysis package, FIDAP, based on the finite element method was employed to simulate the flow patterns in a CTM with 6 rows and 4 cavities per row. A 3D, isothermal flow analysis was carried out and the fluid of choice was a flexible polyvinylchloride whose rheological behavior is described by a power‐law model fluid. The flow field was characterized in terms of velocity profiles, pressure distributions, shear rates/shear stresses generated and a parameter λ quantifying the elongational flow components. The results of the flow simulations were compared with experimental data. The CTM potential use for dispersive mixing was discussed.
Parameter estimation for analysis of vapor diffusion in polymers
Authors: Hsu W. P. , Lo P. Y. , Kwei T. K. , Myerson A. S.
Published: May 2005

This paper presents a general method for estimation of diffusion coefficient and other relevant parameters for the analysis of vapor diffusion in polymers. Sorption curves generated by the constants estimated using the parameter estimation method presented here are in closer agreement with experimental curves than curves generated by other conventional methods.
Coupling agent and glass fibers in polyester mortar
Authors: Mebarkia S. , Vipulanandan C.
Published: May 2005

This study investigates the influence of aggregates, glass fibers and a coupling agent on the compressive and flexural (three‐point and four‐point bending) behavior of a polyester mortar. Particle size of fine aggregates (quartz and limestone) varied from 0.1 to 5 mm (0.004 to 0.2 inch) and the glass fiber content was varied up to 6% by weight of mortar. A silane was introduced into the polyester mortar by pretreating the aggregates and the glass fibers. The mechanical properties of mortar were studied at room temperature. The test results indicate that the selection of aggregate type, size and distribution is very important. Silane treated aggregate systems showed more than 66% increase in compressive strength and 35% increase in flexural strength when compared to the untreated systems. Addition of glass fibers enhances the strength and toughness of the polyester mortar, and silane treatment of glass fibers helps to further enhance these properties. Flexural (three‐point bending)‐to‐compressive strength ratio varied from 0.28 to 0.35 for unreinforced system and from 0.26 to 0.54 for the reinforced system. The mortar with only 14% polyester and 86% aggregates (by weight) and a coupling agent had a compressive strength of 103 MPa (15,000 psi) which is 94% of the polyester polymer strength. A stress‐strain relationship is proposed to represent the complete stress‐strain response under compression and flexural loading. Also, a method is proposed to quantify the failure patterns.
Curing of acrylated epoxy resin based on bisphenol‐S
Authors: Liaw Der‐Jang , Shen Wen‐Chang
Published: May 2005

The acrylated diglycidyl ether of bisphenol‐S was prepared by reacting diglycidyl ether of bisphenol‐S (DGEBS) with acrylic acid using dimethyl benzylamine as a catalyst. The acrylated epoxy resin thus obtained was characterized by IR, 13C‐NMR, and DSC. The curing reaction of the acrylated epoxy resin with dicumyl peroxide was investigated by differential scanning calorimetry at three different heating rates. The overall curing kinetics were found to be approximately second order, independent of the scan rate. The TGA was used to investigate the thermal decomposition of acrylated epoxy resin and to determine the kinetic parameters such as activation energy, preexponential factor, and reaction order. Such information can be used for quick estimation of polymer lifetimes.
Thermal and mechanical properties of injection molded blends of a liquid crystalline polymer and poly(butylene terephthalate)
Authors: Engberg K. , Ekblad M. , Werner P.‐E. , Gedde U. W.
Published: May 2005

The microstructure and the thermal and mechanical properties of injection molded samples of different blends of Vectra (LCP) and poly(butylene terephthalate) (PBT) have been studied. Differential scanning calorimetry and hot‐stage polarized light microscopy showed that the crystallization of PBT was unaffected by the presence of LCP. X‐ray diffraction showed that the PBT component was always unoriented in the injection molded samples. Blends with less than 28 vol% LCP exhibited the same stiffness and the same coefficient of linear thermal expansion as PBT. Blends containing more than 38 vol% LCP contained an oriented LCP phase and had a stiffness in accordance with the upper‐bound composite equation. The coefficients of linear thermal expansion for these blends were close to that of pure LCP.
A numerical model for single screw extrusion with poly(vinyl chloride) (PVC) resins
Authors: Thibault F. , Tanguy P. A. , Blouin D.
Published: May 2005

A computer model has been developed to simulate the behavior of molten polymer in the melt conveying zone of extruders. This model, based on a hybrid finite difference/finite element resolution of the equations of change governing momentum and heat transfer, allows the prediction of the pressure profile while accounting for wall end effects as well as the solid bed velocity. Simulation results are compared with analytical and finite difference method results found in the literature. A fairly good agreement is obtained in the case of low density polyethylene. Numerical tests are also carried out with rigid poly(vinyl chloride) compound used for window profile extrusion. The good agreement found between the predictions and experimental measurements obtained on an industrial extruder confirms the performance of the proposed model.
A model of advancing flow front in RIM
Authors: Anturkar Nitin R.
Published: May 2005

A two‐dimensional model is developed for mold filling in Reaction Injection Molding using a Petrov‐Galerkin finite‐element method with free surface parameterization. Dependence of viscosity on the conversion and temperature is represented by the Castro‐Macosko function. The model predicts the velocity, pressure, temperature, and conversion distributions with time during the filling stage of a rectangular mold. No a priori assumptions are made regarding the shape of the advancing flow front, or regarding any variables in the flow front region. The accuracy is further improved by using the Petrov‐Galerkin formulation, rather than the Galerkin formulation. The results are presented for well‐characterized polyurethane systems, for which reliable experimental data is available. The predictions of the model for the pressure rise are in excellent agreement with the experimental data (1) even close to the gel point. These refined predictions are expected to assist in estimating fiber orientation and bubble growth in the final RIM parts, in which the flow front region plays the most important role. Characterization of polyurethane/polyurea and polyurea materials is underway, and will be subsequently incorporated in the model.
Single screw extrusion of viscoplastic fluids subject to different slip coefficients at screw and barrel surfaces
Authors: Lawal Adeniyi , Kalyon Dilhan M.
Published: May 2005

Commonly encountered viscoplastic fluids including concentrated suspensions of polymeric and ceramic composites, foams, gels, concrete, food products, and energetic compounds exhibit wall slip during their flow and processing. For some viscoplastics fluids, especially highly filled suspensions, wall slip may dominate the flow and deformation and hence the processing behavior of the suspension. The wall slip velocity is generally a function of the wall shear stress and temperature. Various factors including the materials of construction i.e., chemical nature and the roughness of the wall surface affect the wall slip behavior of viscoplastic fluids. In this study an analytical model of the extrusion of viscoplastic fluids under isothermal and fully‐developed conditions in shallow channels is developed. The model accommodates the use of different slip coefficients at barrel and screw surfaces. It thus permits the investigation of effects of introducing different materials of construction for the barrel and screw surfaces and development of design expressions.
Tension of carbonization for carbon fiber
Authors: Tsai Jin‐Shy
Published: May 2005

The mechanical properties of carbon fiber, especially tensile modulus, are closely related to the orientation of crystals. Hence, the stretching of carbon fiber during carbonization is of importance. In this study, the tension arm between the carbonization furnaces was used to stretch carbon fiber. The relationships among the stretching tensions of the first stage carbonization (< 800°C) and the second stage carbonization (> 1200°C), the aromatization index for oxidized polyacrylonitrile fiber, and the properties of carbon fiber are discussed.
Interrelationship of strength and flow characteristics of polystyrene
Authors: Crowder Mark L. , Ogale Amod A. , Moore Eugene R. , Dalke Brian D.
Published: May 2005

This study investigated the interrelationship between strength and flow characteristics of general‐purpose polystyrene (GPPS) used in injection molding applications. The ease of flow was chosen as a measure of processability and was evaluated using the melt flow rate and capillary rheometer techniques. Of the different strength tests that were examined, flexural and notched tensile strength tests were most effective in differentiating between commercial grades of high and low molecular weight GPPS. While characterizing strength of injection molded specimens, the degree of molecular orientation was taken into consideration. For unplasticized resins, increasing the weight average molecular weight by about 100,000 enhanced the flexural strength by 10%, but also increased the viscosity at low shear rates (10 to 100 s−1). The increase in molecular weight had virtually no effect on viscosity at the highest shear rates (up to 10,000 s−1). Plasticized resins displayed a 6% loss in flexural strength as well as a significant reduction in viscosity (throughout the shear rate range) as compared with the unplasticized resins. As expected, the improvement in strength achieved by increasing molecular weight leads to a simultaneous increase in the viscosity, i.e., a deterioration of processability. In addition, our study indicates that for samples without preferential molecular orientation, narrowing the molecular weight distribution significantly improves the balance of strength and melt flow rate properties.
Modeling the dielectric behavior of epoxy resin blends during curing
Authors: Maistros George M. , Bucknall Clive B.
Published: May 2005

A model is developed to describe the evolution of dielectric behavior during the cure of epoxy resins and of blends containing soluble polymeric additives. Data on cure kinetics are used to predict: (a) changes in viscosity and hence in ion mobility; (b) gelation times; (c) vitrification times; and (d) dipolar relaxation times, for both resin and blends. These predictions are then used in conjunction with the Maxwell‐Wagner‐Sillars (MWS) theory to calculate dielectric permittivity ϵ′ and loss ϵ″ as functions of cure time and test frequency in both resin and blends. The predictions are compared with experimental data on dielectric behavior obtained during cure of both neat epoxy resin and of blends containing 15 wt% CTBN (carboxyl‐terminated poly(butadiene‐co‐acrylonitrile)).
The heterogeneous nucleation of microcellular foams assisted by the survival of microvoids in polymers containing low glass transition particles. Part I: Mathematical modeling and numerical simulation
Authors: Ramesh N. S. , Rasmussen Don H. , Campbell Gregory A.
Published: May 2005

The existing models based on classical nucleation theory are not able to explain satisfactorily the nucleation phenomenon of microcellular foams in thermoplastics. Here, we extend the analysis of Kweeder (24), who developed a new model that considers the presence of microvoids, resulting from the thermal processing history of the polymer, as potential nucleation sites. The nucleation model “concentrates” on the stresses and thus void formations in the rubber particles. Since these are pre‐existing microvoids, bubble nucleation depends on the survival of these voids to grow rather than the formation of a new phase as modeled by classical nucleation theory. The population of viable microvoids with a sufficiently large radius to survive and overcome surface and elastic forces has been modeled to yield the cell density. A log‐normal distribution, which relates to the rubber particle size, has been used to model the distribution of microvoids in the polymer composite material. The model depends on various process parameters such as saturation pressure, foaming temperature, concentration of nucleating agents, solubility of the blowing agent in the polymer, and the modulus. High impact polystyrene (HIPS) was added to polystyrene to obtain polymers with different concentrations of rubber gel particles, the nucleating agent, and used here for this study.
Long‐term properties of hot‐water polyolefin pipes—a review
Authors: Gedde U. W. , Viebke J. , Leijström H. , Ifwarson M.
Published: May 2005

This is a review on the long‐term behavior of polyolefin pipes used in hot‐water environments. Included in the review is work done on pipes of crosslinked polyethylene, isotactic poly(butene‐1), isotactic polypropylene and medium‐density polyethylene, and in particular the extensive work performed at Studsvik, Sweden. A collective view of the changes in antioxidant concentration profiles and molecular/physical structure accompanying hot‐water exposure is presented. Failure at high stress levels is preceded by gross deformation (Stage I failure), whereas at lower stresses fracture is brittle either without any signs of thermal oxidation (Stage II) or induced by a strong and spatially concentrated thermal oxidation (Stage III). It is shown that the Stage III lifetime can be divided into three phases, denoted Regimes A, B, and C. They involve internal precipitation of antioxidant from a supersaturated solution (Regime A), diffusion‐controlled migration of antioxidant to the surrounding media (Regime B), and degradation of the polymer by thermal oxidation (Regime C). For hitherto reported cases the Regime B life constitutes 80% to 90% of the entire life. A presentation is also made of current lifetime extrapolation methods.
Physical aging of nylon 66
Authors: Spinu I. , McKenna G. B.
Published: May 2005

The physical aging behavior of nylon 66 as a function of aging temperature, magnitude of applied stress, and aging time has been investigated. Creep tests were performed for samples quenched from a stabilization temperature of 160°C to aging temperatures between 41°C and 65°C, for aging times ranging from 0.5 to 64 h, and at stresses levels from 4 MPa to 24 MPa. Volume recovery was investigated for samples quenched from 160°C to aging temperatures of 41°C and 65°C. The creep compliance curves at different aging times were able to be superimposed. The double logarithmic shift rate was calculated and its dependence on aging temperature and applied stress was determined. Also, it was found that the volume recovery rate depends on the aging temperature. The time‐temperature and stress‐temperature superpositions were not possible for our data.
Micro scale flow behavior and void formation mechanism during impregnation through a unidirectional stitched fiberglass mat
Authors: Patel N. , Rohatgi V. , Lee L. James
Published: May 2005

Liquid composite molding (LCM) processes such as resin transfer molding (RTM) and structural reaction injection molding (SRIM) have been perceived as high potential processes for the near‐net‐shape manufacturing of composite parts. This paper addresses two major issues in LCM technology: fiber wetting and void formation during mold filling. Flow visualization experiments were carried out to develop a better understanding of the flow induced voids. The formation and elimination of voids were studied using several liquids and a unidirectional stitched fiberglass mat. Void formation was correlated to capillary number and liquid‐fiber‐air contact angle.
Analysis of volumetric changes of unsaturated polyester resins during curing
Authors: Hill Ronald R. , Muzumdar Shailesh V. , Lee L. James
Published: May 2005

Two models were proposed to predict the volume changes that occur during the cure of unsaturated polyester resin/styrene systems. These models are able to account for both thermal expansions/contractions and polymerization shrinkage during processing. One model, which is based on coversion, was developed by combining experimental results from differential scanning calorimetry and dilatometry. The second model is based on radical concentration, and was developed using results from electron spin resonance spectroscopy and dilatometry. Predictions obtained from both models were compared with experimental results and reasonable agreement was obtained.
Characterization of poly(3‐octylthiophene). I: Molecular characterization in dilute solution
Authors: Heffner Glenn W. , Pearson Dale S. , Gettinger C. L.
Published: May 2005

The poly(3‐alkylthiophenes) are a class of electrically conducting polymers which are of particular scientific and commercial interest due to their solubility and meltability. A series of poly(3‐octylthiophene) (P3OT) fractions having molecular weights in the range Mw=30,000 to 400,000 were generated by preparative gel permeation chromatography (GPC). Although the polymer remained weakly aggregated when dissolved in pure THF, the addition of an organic salt (1 wt.% tetrabutylammonium p‐toluenesulfonate) resulted in complete molecular dissolution. We were thus able to completely and consistently describe the polymer's single‐chain properties using three dilute solution characterization methods: viscometry, GPC, and integrated light scattering. The molecular weight dependence of the intrinsic viscosity and the radius‐of‐gyration were established, and were characteristic of solutions near the theta condition, indicating poor solvent quality. Calculation of the persistence length from our data revealed that the polymer backbone is only 2 to 3 times more rigid than common flexible polymers, despite its conjugated ring structure.
Injection molding of polypropylene discs. I: Effect of holding pressure on orientation distribution
Authors: Sjönell Ylva , Terselius BjöRn , Jansson Jan‐Fredrik
Published: May 2005

It is well known that the injection molding process has a major impact on the properties of injection‐molded polymers. In this study, the effect of the holding pressure on the orientation in injection‐molded discs of polypropylene has been examined. The orientation has been determined by IR‐dichroism and the orientation factors calculated according to Herman's orientation function, the average factor as well as the crystalline and the amorphous. The distribution of the orientation in the length as well as in the depth direction has also been exmined in order to understand how the flow has propagated in the cavity during both the filling and the packing phases. The results show that the holding pressure clearly affected the orientation, but that it was an unevenly distributed effect over the disc.
An overview of the basic aspects of polymer adhesion. Part II: Application to surface treatments
Authors: Fourche Georges
Published: May 2005

The main surface treatments of materials (metals and plastics in particular) to be joined are presented. It is observed that these treatments modify the roughness, morphology, and chemical composition of the surface. As a result of these operations, the substrate surface energy is generally increased. A correlation is often noted between the increased surface energy and the assembly adhesive qualities.
Copolymerization of t‐butoxycarbonyloxystyrene and sulfur dioxide
Authors: Bohrer Michael P. , Mixon David A.
Published: May 2005

The reaction kinetics of radical chain copolymerization of t‐butoxycarbonyl‐oxystyrene (TBS) and sulfur dioxide have been studied using a reaction/sampling apparatus that permits accurate determination of the reaction mixture concentrations during polymerization. The results are compared with the styrene‐sulfur dioxide copolymerization kinetics. The influence of temperature and reactant concentrations on the polymerization rate and copolymer composition are reported. With increasing reaction temperature, the amount of SO2 incorporated and the molecular weight fo the copolymer are found to decrease. For a constant TBS concentration in the reaction solutio, raising the SO2 concentration causes an increase of SO2 incorporation in the copolymer, up to a maximum SO2 content corresponding to a TBS:SO2 mole ratio of 2:1. However, for a constant SO2 concentration, the amount of TBS incorporated in the copolymer increases with decreasing TBS concentration in the reaction solution. The polymerization rate and copolymer molecular weight increase proportionally with monomer concentration as expected for a normal radical chain polymerization mechanism. Comparison of these findings with various kinetic models for styrene‐SO2 copolymerization indicates good agreement with models proposed by Barb (1‐3) and Walling (4); however, the data do not agree with the predictions of Matsuda et al. (5) The understanding of the kinetics and reaction mechanism provided in this study will aid in the manufacture of this lithographically important copolymer.
Phtocrosslinking of polyethylene for production of thin wall insulated wire
Authors: Qu Baojun , Shi Wenfang , Liang Renyou , Jin Sizhan , Xu Yunhua , Wang Zhenhua , Rånby Bengt
Published: May 2005

A photocrosslinking precess for polyethylene and its industrial irradiation apparatus has recently been developed and used successfully in the manufactre of thin wall crosslinked polyethylene‐insulated wires. Polyethylene (PE) resin with the desired amounts of additives, such as photoinitiator, multifunctional crosslinker, and antioxidant is mixe homogeneously. The amixture of PE is granulated, and then extruded on a conductor wire. The coated PE layer in the melt is subsequently irradiated in a specially designed UV irradiation apparatus for 5 to 10 s. The studies show that the photocrosslinked PE‐insulation high voltage television wires produced by this new technique possess excellent electrical and mchanical properties and much lower operating cost compared with wires produced by the electron beam crosslinking technique.
Analysis of titanium dioxide agglomerate dispersion in linear low density polyethylene and resulting properties of compounds
Authors: Lee Young‐Jin , Manas‐Zloczower Ica , Feke Donald L.
Published: May 2005

The dispersion of titanium dioxide agglomerates within linear low density polyethylene (LLDPE) melts has been investigated by using a cone‐and‐plate device installed within a temperature controlled oven. Observation of fragment evolution indicates that erosion is the predominant mechanism of dispersion. The erosion rate of titanium dioxide agglomerates in LLDPE was consistenty with the results obtained in previous dispersion studies of titanium dioxide in polydimethyl siloxane (PDMS). The effect of agglomerate dispersion on the optical, tensile, and dynamic mechanical properties of compounds incorporating titanium dioxide was also investigated. Changes in compound properties were correlated with observed morphology changes of agglomerates in order to clarify the effect of dispersion.
Effect of blocking agents on the shock absorbing properties of the films of polyurethane adhesives
Authors: Roy Surajit , Kumar Anil
Published: May 2005

Various 4,4‐diphenylmethane diisocyanate (MDI0) based polyurethane adhesives have been developed using polyethylene glycols (PEG) of different moleclar weights. The formulations were modified using different blocking agents to inhibit the isocyanate‐moisture reaction. Composites of poly(methyl methacrylate) sheets were developed in which these adhesives gave transparent films and their shattering characteristics were tested in a bullet firing machine developed here. The damaged area was measured and used to characterize the adhesive strength. The molecular weight of the soft segment (diol) and the nature of the blocking agent both were found to affect drastically the urethane film properties.
On the structure/properties relationships in photoinitiators of polymerization
Authors: Fouassier J. P.
Published: May 2005

The choice of photoinitiators is partly governed by the requirement of a high curing speed. Many reactive monomers and efficient photoinitiators have been synthesized and are commercially available. However, improved photoinitiator systems, exhibiting increasingly faster curing speeds and/or increased photosensitivity, are increasingly required. The intrinsic reactivity in the exicited states determines te interest of a given photoinitiator with reference to its efficiency. However, other factors e.g. high molecular absorption coefficients and a broad spectral absorption range, synergistic effects, yellowing, extractability, and th effect on the long‐term stability, must be considered as important. An attractive field of research and development is found in the role played by decisive parameters affecting the reactivity of a given structure, such as chemical substitution in well‐chosen positions, the character of water solubility, acid release ability, and copolymerization potential. Laser spectroscopy proved a most convenient tool for the real time investigation of the excited state dynamics and the processes involved.
In situ, quantitative characterization of gelation and fusion mechanism in poly(vinyl chloride) plastisols by small angle light scattering (SALS)
Authors: Kwak Seung‐Yeop
Published: May 2005

The present paper explores an effective means of characterizing structural changes of poly(vinyl chloride) (PVC) particles during gelation and fusion of PVC plastisols with small angle light scattering (SALS). The SALS method was shown to provide an in situ observation of swelling of PVC particles as well as quantitative information of average size of swollen particles while they are in progress of gelation and fusion. In addition, the SALS method enabled one to evaluate the relative solvent power of plasticizers from the manner of increase in the correlation distances.
Semianalytical solution of isothermal nylon‐6 polymerization in batch reactors
Authors: Haswani Rajeev , Gupta Santosh K. , Kumar Anil
Published: May 2005

Nylon 6 polymerization in batch reactors has been assumed to consist of important reactions of ring opening, step growth and polyaddition steps and a set of ordinary differential equations (initial value problem) for the concentrations and moments of the various reacting species has been derived. We have proposed a series solution for these variables in terms of conversion of ε‐caprolactam. A technique similar to the finite element method for boundary value problems is used to divide the conversion domain into subdomains. The size of these is determined by a convergence criterion and the results determined at the end of conversion domain through sequential computations. This technique of solution involves the evaluation of constant coefficients of the series only and gives comparable results with those of Runge Kutta or Gear's algorithm (which involves evaluation of functions) in fewer steps. The scheme can easily be implemented on a personal computer and is considerably faster and more efficient.