bluuebunny/crossref_metadata_2025_split huggingface dataset:
A model of advancing flow front in RIM
Authors: Anturkar Nitin R. 
Published: May 2005

AbstractA 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

AbstractCommonly 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

AbstractThe 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

AbstractThis 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

AbstractA 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

AbstractThe 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

AbstractThis 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

AbstractThe 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

AbstractLiquid 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

AbstractTwo 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

AbstractThe 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

AbstractIt 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

AbstractThe 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

AbstractThe 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

AbstractA 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

AbstractThe 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

AbstractVarious 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

AbstractThe 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

AbstractThe 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

AbstractNylon 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.
Permeable boundary condition for numerical simulation in resin transfer molding
Authors: Wu Ching‐Jenn , Hourng Lih‐Wu 
Published: May 2005

AbstractIn the present study of resin transfer molding, an effective gap located between the side wall and the fiber mats is proposed. The concept of the effective gap leads to a permeable boundary condition on the interface between the fiber mats and the side wall. The porosity is no longer assumed to be a constant in the whole domain. Results show that the effective gap concept can explain the phenomena of edge effects reasonably. In our model, the filling process is simulated by the body‐fitted finite element method and the limitation of the time increment for the quasi‐steady state process is discussed in detail.
Aromatic polyetherimides as promising fusible film binders
Authors: Svetlichnyi V. M. , Zhukova T. I. , Kudriavtsev V. V. , Yudin V. E. , Gubanova G. N. , Leksovskii A. M. 
Published: May 2005

AbstractPolyetherimides (PEI) based on dianhydrides of 3,3′, 4,4′‐dipheniloxytetracarboxylic acid and 1,3‐bis‐(3,4‐di‐carboxyphenoxy)benzene that contain fragments of such thermoplastic polymers as poly(ether sulfone) or poly(phenylene oxide) have been synthesized. Thermoplastic properties of synthesized PEI were characterized by flow temperature Tf and melt viscosity ηm. The properties obtained are outstanding for the production of PEI as fusible film binders, and composites can be produced without toxic solvents. Carbon fiber reinforced plastics (CFRP) based on PEI films were analyzed using an Acoustic Emission (AE) technique.