bluuebunny/crossref_metadata_2025_split huggingface dataset:
Crosslinking of hydroxyl‐terminated liquid rubber with divalent metal salts of mono(hydroxyethyl) phthalate, anhydrides, and bisepoxide
Authors: Matsuda Hideaki 
Published: December 2004

AbstractCrosslinking of hydroxyl‐terminated liquid rubber with divalent metal salts of mono(hydroxyethyl) phthalate, anhydrides and bisepoxide was investigated by the diols‐anhydridesbisepoxide, reactions. As the anhydride, succinic anhydride and hexahydrophthalic anhydride were used, and bisphenol A diglycidyl ether was the bisepoxide used. The metal carboxylate groups of these metal salts catalyzed the crosslinking reactions and, further, the Mg salt showed higher catalytic activities than the Ca salt. As for the physical properties of the metal‐containing cured rubbers obtained, tensile strength and Shore A hardness increased with increase in the metal salt content. In addition, the rubbers containing Mg showed better physical properties than those containing Ca. Meanwhile, elongation showed a maximum with increase in the metal salt content. Resistance; to water and chemical attack, thermal behavior, and stress relaxation are also discussed.
Processing history in extrusion dies and its influence on the state of the polymer extrudate at the die exit
Authors: Winter Horst Henning , Fischer Ernst 
Published: December 2004

AbstractA method is proposed to describe the processing history in extrusion dies and its influence on the state of the polymer after processing. The approach differs from conventional processing analysis, which uses the shear viscosity function to calculate pressure drop vs flow rate relations. The approach also differs from heuristic analysis which tries to find empirical correlations between rheological observations and processing behavior. The method is applied to the flow in annular extrusion dies. An integral constitutive equation is chosen to calculate the flow and to describe the flow history at the die exit as memorized. In the analysis, the kinematics are locally approximated by isothermal steady shear flow. The velocity and the velocity gradient are used to determine the Finger strain tensor, the path lines, and the residence times of the deforming material elements. Measures of the state of the polymer at the die exit are chosen to be the stress ratio N1/2τ12 and the free recovery. The free recovery calculations presume that the extrudate is chopped into small volumes of homogeneous flow history. The results of the calculations show the polymer very sensitively reacts to small changes of the die geometry. Important applications of this analysis are film blowing and blow molding, where the extensional behavior during the blowing process outside the die depends greatly on the preceding shaping process inside the die.
A study of the structural integrity of graphite composite structure subjected to low velocity impact
Authors: Dobyns A. L. , Porter T. R. 
Published: December 2004

AbstractAn analysis for the transient deflections, bending strains, and interlaminar shear stresses in a simply supported laminated composite plate subject to low velocity impact has been obtained using a series solution of the plate governing equations. Results are presented showing the effect of plate geometry and impact location on damage mode. Computed stresses and strain are compared with impact test data to verify, the analysis.
Similarity in orientation effects on thermal conductivity and flow birefringence for polymers—polydimethylsiloxane
Authors: Chitrangad B. , Picot J. J. C. 
Published: December 2004

AbstractExperimental results on flow birefringence and thermal conductivity measured under shearing strain conditions for liquid polydimethylsiloxane are presented. Both phenomena show similar dependency on strain rate, and this dependency is attributed to net orientation of the macromolecules. An orientation model is presented and is shown to be qualitatively correct.
Rheological and mechanical properties of plasticized poly(vinyl chloride)
Authors: Tse Mun‐Fu 
Published: December 2004

AbstractThe dependence of rheological properties of a plasticized, filled poly(vinyl chloride) compound on three different methods of thermomechanical treatments has been studied. These three different states of the compound are the dry blend mixed at a maximum temperature of 93°C, the two‐roll milled sample prepared at 150°C from the dry blend and the molded sample pressed at 170°C from the previously milled material. At 150°C the viscosity and elasticity of the molded sample are considerably higher than those of the dry blend and the milled sample. At higher temperatures, although their flow curves more or less merge, extrudate swell, extrudate appearance and extrudate tensile properties of the three samples vary. The mechanical and Theological properties of the quenched and annealed molded samples and those of the same compound without filler have also been investigated.
Effect of compaction rate during the cold forming of polymeric powders
Authors: Crawford R. J. 
Published: December 2004

AbstractDuring many plastics processing methods, both conventional and novel, plastic powders or granules are subjected to pressure. The pressure transmissibility through the powder has an important effect on the success and efficiency of the process, and so it is desirable to be able to predict the pressure at any point from a knowledge of the applied pressure and the geometry of the system. To examine this pressure transmissibility effect, poly(vinylidene chloride) powder has been compacted in a metal die under different rates using either load or displacement control. It has been found that rate effects are particularly important for loading rates greater than 8 MPa/s and displacement rates greater than 7.5 mm/s. The ratio of transmitted pressure (P2) to applied pressure (P1) has been measured for a range of compact geometries, and it has been found that the ratio is approximately constant during the latter stages of the compaction process. Various laws for predicting the transmitted pressure have been studied, but it has been found that the simplest equation that agrees with the data is of the form
The hydrostatic extrusion and die‐drawing of glass‐fiber‐reinforced polyoxymethylene
Authors: Hope P. S. , Richardson A. , Ward I. M. 
Published: December 2004

AbstractThe solid‐phase forming of glass‐fiber‐reinforced poly‐oxymethylene has been investigated using the techniques of hydrostatic extrusion and die‐drawing. Although considerable orientation of the glass fibers and the polymer matrix occurs in both processes, there are very appreciable differences between the stiffnesses of the glass‐filled products in the two cases. For hydrostatic extrusion, the moduli of the glass‐filled products are significantly higher than those of the unfilled products. In die‐drawing, however, the absence of hydrostatic pressure allows debonding of the fibers from the matrix to occur, accompanied by extensive void formation. The fibers are, consequently, no longer effective as a reinforcing phase, the moduli of the glass‐filled products being no higher than those of the unfilled products.
A proposed model for accelerated‐stress life‐test data exhibiting two failure modes
Authors: Derringer George C. 
Published: December 2004

AbstractAccelerated‐stress life‐testing involves testing of a material or system at a series of stresses higher than that which is normally seen in service. An estimate of the service life is then obtained by extrapolating the failure time vs stress relationship to use stress. A common problem with this methodology is that a change in failure mechanism may occur if stresses become too high. When this occurs, the data above and below the failure mode transition point are generally treated separately. This paper discusses a model that allows for a change in failure mechanism and characterizes the transition by a probability density function over stress. Advantages of the model are: it allows representation of all test data by a single equation; it allows probability statements to be made about the probability of failure of either failure mode; it allows optimal experiments to be designed; and it allows data in the area of the failure mode transition to contribute to the precision of the estimated service life.
Experimental studies of phase separation in reaction injection‐molded (RIM) polyurethanes
Authors: Camargo R. E. , Macosko C. W. , Tirrell M. V. , Wellinghoff S. T. 
Published: December 2004

AbstractA series of polyether polyol (polyoxypropylene capped with polyoxyethylene), 4‐4′ diphenylmethane diisocyanate, and 1,4 butane diol urethanes were prepared by reaction injection molding with different levels of catalyst (dibutyl tin dilaurate). The degree of phase separation, morphology, and molecular weight were compared by dynamic mechanical spectroscopy, wide‐angle x‐ray scattering, optical microscopy, and gel permeation chromatography. Slowly reacted (uncatalyzed) samples displayed better phase separation, crystallinity, low molecular weight, and poor mechanical properties. Fast‐polymerized (highly catalyzed) samples showed a high degree of phase intermixing, low crystallinity, high molecular weight, and good mechanical performance. Differences between these two behaviors are discussed with the aid of a simplified phase diagram. Slowly reacted samples phase‐separate through nucleation and growth of large spherulites, while quickly reacted samples form a much finer, interconnected microstructure. Infrared studies of phase separation for slow systems are presented and used to discuss phase separation in fast polymerizations.
Rigid polyurethane foams: A model of the foaming process
Authors: Rojas A. J. , Marciano J. H. , Williams R. J. 
Published: December 2004

AbstractA model of the manufacture of rigid polyurethane foams by free rising is presented. The extent of cream and rise periods as well as the amount of blowing agent necessary to give the desired foam density are theoretically predicted. The rate of blowing agent evaporation is calculated from an experimental boiling temperature vs. composition curve. Experimental runs were carried out with a formulation consisting of a polymeric isocyanate, a polyether polyol based on sorbitol, a silicone‐polyol block‐copolymer as surfactant, dibutyltin dilaurate as catalyst, and trichlorofluoromethane as blowing agent. Mixing was performed in situ in the mold using a commercial foaming machine. Experimental results gave a satisfactory agreement with model predictions. A diagram containing all the relevant information may be theoretically built and used for the selection of adequate operating parameters for a given formulation.
Measurement of dielectric tan δ during deformation of a polyurethane elastomer
Authors: Venkataswamy K. , Ard K. , Beatty C. L. 
Published: December 2004

AbstractDielectric measurements were carried out during deformation of a polyurethane elastomer. Dielectric tan δ was used to monitor deformation during and after stress relaxation experiments. The polyurethane elastomer exhibited multiple dielectric relaxation behavior: an α peak associated with the glass transition and a β peak attributed to the local motions of the groups in the main chain or pendant to it. At high stress levels, both α and β peaks are shifted to higher temperatures, resulting in higher activation energies. These results can be interpreted in terms of increasing chain orientation and the resultant changes in the local environments of chain segments during deformation.
Moisture absorption by tetraglycidyl 4,4′ ‐diaminodiphenyl methane/4,4′‐diaminodiphenl sulfone epoxies containing brominated epoxy copolymers
Authors: Goobich J. , Marom G. 
Published: December 2004

AbstractThe effect on moisture absorption of introducing bromine into epoxy resins is investigated. The research is carried out with a tetraglycidyl 4,4′‐diaminodiphenyl methane/4,4′‐diaminodiphenyl sulfone system, and compared with a reference system of diglycidyl ether of bisphenol A/diaminodiphenyl methane epoxy, both systems containing brominated reactive epoxy additives. The results indicate that the presence of bromine reduces drastically the rate and the maximum level of moisture absorption. The presence of bromine is shown to have only a small effect on the high‐temperature properties and on the glass‐transition temperatures of the dry resins. Moreover, due to their lower moisture absorption capacity, the glass‐transition temperatures of the wet brominated resins are higher than the counterparts of the original bromine‐free epoxies.
Computer simulation of injection molding
Authors: Kamal Musa R. , Laflrur P. G. 
Published: December 2004

AbstractThe injection‐molding process consists of three consecutive stages: filling, packing, and cooling. In order to obtain some insight into the phenomena involved in the process, and particularly in order to evaluate the moldability of certain resins and to predict the microstructure and properties of products molded therefrom, a number of workers have employed a variety of techniques based on mathematical simulation of the process. Mathematical simulation involves writing the relevant continuity, momentum, and energy equations governing the system, with appropriate boundary and initial conditions representing the prevailing conditions in the cavity and delivery channels. In order to obtain meaningful solutions to the above equations, detailed information is required regarding the thermodynamic, thermal, and rheological properties of the resin. Moreover, the prediction of the microstructure and ultimate properties of the molded article requires a knowledge of the morphological, crystallization, and orientation phenomena that take place under the influence of the thermo‐mechanical history experienced by the resin. The complexity of the equations involved results in the utilization of a number of simplifying assumptions and the resort to computer simulation and numerical solutions of these equations. A variety of numerical schemes based on finite difference and finite element methods has been employed by various researchers.
Fracture toughness (KQ) testing with a mini‐compact tension (CT) specimen
Authors: Lee C. Y‐C. , Jones W. B. 
Published: December 2004

AbstractA testing method using the Rheometrics Mechanical Spectrometer as the loading instrument to measure the fracture toughness KQ, which is related to a specific sample geometry and dimensions (half‐inch compact tension) is reported. The small sample size requirement makes it attractive to do fracture toughness testing on newly synthesized material for preliminary material study and comparison purposes. Commercially available epoxy resins were used to check the procedure at different temperatures (−150° to 250°C). An empirical crack length averaging method was used that appears to give constant KQ values independent of the a/W ratio values. The fracture surfaces were studied using scanning electron microscopy.
Effects of shearing conditions on crystalline orientation and relaxation in polyethylene
Authors: Hsiue E. S. , Robertson R. E. , Yeh G. S. Y. 
Published: December 2004

AbstractThe effects of shearing conditions (i.e., shear temperature and shear rate) on the degree of orientation of polyethylene (Marlex 6006) and to what extent the induced orientation could be relaxed were examined in this study. Two types of samples were prepared: namely, SIC (shear‐induced crystallization) and non‐SIC samples. The SIC samples show induction times and possess a high degree of c‐axis orientation along the shear direction. The induced orientation of SIC samples can be relaxed to a small extent but does not reach a steady value. Non‐SIC samples do not show induction times and they show low degrees of c‐axis orientation. The induced orientation of non‐SIC samples can be relaxed to a steady state value with an activation energy of 90 kJ/mole. Our results also indicate that, when the shear temperature is at and above 145°C, polyethylene can be sheared up to 200X without introducing any significant molecular orientation even at very high shear rates.
Modeling of transport of small molecules in polymer blends: Application of effective medium theory
Authors: Sax J. , Ottino J. M. 
Published: December 2004

AbstractThis article concerns itself with the prediction of effective diffusion coefficients of small permeants in binary polymer blends of varying degrees of miscibility and microstructural order. Several models have been critically evaluated with the help of previously published experimental data and in terms of consistency of morphological information provided by small permeants serving as morphological probes. Completely random, two‐phase media have been modeled in terms of Effective Medium Theory with the coordination number (z) describing the average morphology. A comprehensive analysis of experimental data has shown a correlation between z and various physical situations. Near the percolation threshold, z attains a maximum value while, above it, z tends to decrease with increasing content of the conductive component. Accurate predictions of effective diffusivity can be made for volume fractions between 0.3 and 0.8 by letting z = 6. Evidence for phase inversion was studied in terms of models with ordered microstructure and transport data.
Influence of external environments on fatigue crack growth in epoxy resin
Authors: Mizutani K. , Iwatsu T. 
Published: December 2004

AbstractA fatigue crack propagation in an epoxy resin in the presence of organic solvents or water was studied from the viewpoint of fracture mechanics. The fatigue crack growth rate (da/dN) of the resin under various stress‐intensity‐factor ranges (ΔKl) was measured using a tapered double‐cantilever beam specimen. In air environment, plots of da/dN against ΔKl were found to be represented by the Paris equation: da/dN = C(ΔKl)n, where C and n are empirical constants. In this case, the constant n was about 6.5. The fatigue crack growth rate in the presence of organic solvents decreased to 1/10 ∼ 1/4 of that in air environment at the same ΔKl. It was considered that a penetration of the solvent molecules into the resin enlarged a region of plastic deformation near the crack tip. Therefore, more fracture energy was needed for the growth of the fatigue crack. Also, observations of the fatigue fracture surfaces suggested that a large plastic deformation occurred at the crack tip in the presence of solvents.
Residual stress craze and crack formation in poly(methyl methacrylate)
Authors: Bevan L. , Nugent H. 
Published: December 2004

AbstractSamples of poly(methyl methacrylate) with a central circular hole are compressed, and crazes form on or after unloading, provided that the strain attains or exceeds a threshold value ϵt. Crazes induced in air are transformed rapidly to cracks, but environmental crazes are more stable. These residual stress crazes form at the diameter of the hole on a plane perpendicular to the applied stress direction. In contrast, during loading, crazes form on the vertical plane containing the hole axis. Unloading crazes are relatively insensitive to changes in strain rate, whereas loading erazes have a pronounced rate dependence. Environmental residual stress crazing exhibits an apparent rate sensitivity at constant time, but the critical applied strain ϵt is essentially constant, irrespective of rate, if the sample is in contact with the environment for a sufficiently long time to ensure that the minimum ϵt is obtained. Residual stress crazes appear to initiate at the equator of the hole, and the maximum tensile residual strain, indicated by a strain gauge, occurs in this position.
Structure‐properties relationships in biaxially oriented polypropylene films
Authors: De Vries Albert J. 
Published: December 2004

AbstractA series of biaxially oriented polypropylene films has been extensively investigated with respect to structural characterization and with regard to various end‐use properties. The relationships between properties and structural characteristics such as crystallinity content and molecular orientation in crystalline and non‐crystalline phases were compared with similar relationships in uniaxially oriented polypropylene films. Notable differences between uni‐ and biaxially oriented films, in particular with regard to non‐linear mechanical behavior (tenacity, impact strength, tear strength) could be explained, at least partly, in terms of structural characteristics (molecular orientation and mobility) related to the non‐crystalline phase.
The length of a transfer unit (LTU) for polymer devolatilization processes in screw extruders
Authors: Collins G. P. , Denson C. D. , Astarita G. 
Published: December 2004

AbstractIn this paper we introduce the concept of the length of a transfer unit (LTU) for polymer devolatilization and show that the LTU is an appropriate measure of the effectiveness of the process unit in which the devolatilization operation is conducted. The utility of the concept is demonstrated for the case when the process unit is a twin screw extruder for which values of the LTU were determined from experimentally measured values of devolatilization rates. Values of the LTU were found to depend solely on the fluid mechanics in the extruder as expected and were in good agreement with the predictions of a theoretical expression developed for the system that was studied. Finally, we discuss the implications of the LTU concept in relation to the engineering design and analysis of polymer devolatilization processes.
Plane strain fracture toughness of polyethylene pipe materials
Authors: Mandell J. F. , Roberts D. R. , McGarry F. J. 
Published: December 2004

AbstractThe plane strain fracture toughness of medium density polyethylene pipe materials has been investigated over a range of test temperatures and rates. Conditions are defined under which valid fracture toughness values can be obtained; at higher temperatures the material is notch‐insensitive. Fracture surface morphology is described, and features are compared with predictions from the Dugdale model. The toughness derives from a band of fibrillar, drawn morphology associated with crack initiation or slow growth. The plane strain fracture toughness correlates with percent crystallinity according to the same relationship whether the crystallinity is varied by thermal treatment, comonomer content, or molecular weight.
Dynamic mechanical and thermomechanical properties of silicone‐polycarbonate block copolymers
Authors: Maung W. , Chua K. M. , Ng T. H. , Williams H. Leverne 
Published: December 2004

AbstractRepresentative random, alternating block copolymers of polydimethylsiloxane (PDMS) and bisphenol‐A‐polycarbonate (BPAPC) were studied by thermomechanical and dynamic mechanical techniques. Data on glass transition temperatures (Tg), heat‐deflection temperatures (Td), Vicat softening temperatures (Ts), coefficients of linear expansion (α), stress‐strain, and stress relaxation for four PDMS‐BPAPC block co‐polymers are presented. The effect of casting films from mixed n‐hexane‐methylene chloride solution on the thermomechanical and dynamic mechanical properties was also studied.
Relationship between polymerization conditions and rheological properties for styrene‐acrylonitrile copolymers
Authors: García‐rejón A. , Rangel‐nafaile C. , Ríos L. , Cid F. 
Published: December 2004

AbstractStyrene‐acrylonitrile (SAN) copolymers are widely used in industrial applications in the fields of appliances, automotive, housewares, medicine, and packaging. They possess most of the features of polystyrene, with improved resistance to chemical attack, stress eracking, and heat deflection, and with greater strength and toughness. Their properties depend on several factors, the most important being the composition of the feed (monomer ratio), the type and quantity of the initiator, and the solvent to monomer ratio in the feed. This work presents the results of a continuing program that studies the effect of the above‐mentioned polymerization variables on the viscoleastic properties, and the way in which these variables can be adjusted in order to obtain a SAN copolymer with specific properties.