bluuebunny/crossref_metadata_2025 huggingface dataset:
Polymerization of methyl methacrylate with Ziegler‐Natta catalysts
Authors: Kapur S. L. , Deshpande A. B.
Published: December 2004

The polymerization of methyl methacrylate with Ziegler‐Natta catalyst, anionic catalyst and gamma radiation has been shown possible at temperatures below 0°C. A free radical mechanism is suggested in the case of Ziegler‐Natta catalyst which is known for a coordinate anionic polymerization mechanism. In view of this, the Ziegler‐Natta catalysts based on vanadium compounds were investigated for the polymerization of methyl methacrylate. They were found effective for polymerization of methyl methacrylate at, and around, room temperature. The structure of the polymer was stereoblock. This apparently leads to the conclusion that the mechanism of polymerization of methyl methacrylate was not free radical but coordinate anionic. Similarly, the catalyst system of chromium acetyl acetonate and aluminium triethyl polymerized methyl methacrylate at and around room temperature into an highly stereoblock structure containing high isotacticity.
High‐frequency alpha transition response of some plasticized poly(vinyl chloride) compositions
Authors: Paddison Gary W.
Published: December 2004

A high‐frequency alpha transition of some plasticized poly (vinyl chloride) compositions was measured at 4 MHz employing an ultrasonic pulse technique. The material property used to determine the transition region was the intrinsic loss, which is indicative of changes in both the storage and loss moduli. Four dicarboxylic esters were used as plasticizing agents. These were (1) butyl benzyl phthalate, (2) di‐(2‐ethylhexyl) phthalate, (3) dibenzyl sebacate, and (4) di‐(2‐ethylhexyl) sebacate. Compositions were prepared using 10, 20, and 30 parts by weight of plasticizer per hundred of polymer. A small quantity of thermal stabilizer was added to prevent degradation. Samples were produced by an extrusion process to promote a high degree of fusion and consolidation. Comparison of the data showed the usual decrease in the transition temperature with increasing concentration of the plasticizing agent. However, it was shown that the controlling factor of the transition response was the molecular structure of the plasticizer. Both the structure of the parent dicarboxylic acid and the ester side groups were controlling factors. This relationship was supported when a high‐frequency storage and loss modulus (dilatational) was compared at 25°C to the molecular weight of the side chain. The dimethyl ester was included for both series for comparative purposes. These data showed that the storage modulus increased and the loss modulus decreased with increasing chain length and complexity. However, the factor contributing most was the complexity (steric hindrance) of the plasticizing molecule.
A design approach for thermoplastic flexure components subjected to cyclic loading
Authors: McCammond D. , Nakatsumi F.
Published: December 2004

A recently proposed method for predicting the strains resulting from the application of uniaxial cyclic stresses is developed for application to polymer systems. Experimental results obtained from rectangular cyclic loading tests on prismatic beams and circular plates are compared with theoretical predictions using two sources of basic data, (a) uniaxial isochronous and creep data and (b) deformation data resulting from constant load creep tests conducted on the components. It is concluded that the method would require considerably less computation, to obtain satisfactory accuracy, than the alternative integral superposition methods even for rectangular cyclic loading and would prove much more tractable when applied to other forms of cyclic loading.
A step toward molecular‐level understanding of the toughness of glassy plastics
Authors: Knight A. C.
Published: December 2004

Rigid, glassy plastics differ over a wide range in the amount of energy they can absorb before fracturing under the influence of an applied stress. It is here proposed that molecular structure influences energy absorption more significantly by determining the onset of fracture than by its effect on the energy‐dissipating processes themselves. Emphasis has been placed, therefore, on finding a relationship between molecular structure and the onset of fracture. Since many relationships between molecular structure and bulk mechanical response have already been established, it should be a useful step to relate the onset of fracture to bulk mechanical responses. The hypothesis is developed that the appropriate bulk property is the stress‐deformation function of the material. The observed stress‐deformation function is of such a nature that a highly non‐homogeneous deformation is produced at any point of stress concentration. Typically, this is a narrow region in which the material is highly deformed while the deformation in adjacent material is still slight. Fracture initiation is postulated to occur in such a region of high deformation. Differences among polymers in the shape of the stress‐deformation function are demonstrated experimentally. These differences correlate with tough‐brittle behavior. An explanation is proposed in terms of the probability of fracture initiation.
Polymeric catenanes
Authors: Callahan D. , Frisch H. L. , Klempner D.
Published: December 2004

A crosslinked polybutadiene containing a cyclic depsipeptide (Valinomycin) has been synthesized in which there is some possibility of threading to produce a catenated structure (polymeric catenane). Unthreaded rings were removed by extraction with toluene. An elemental analysis indicated the yield of threaded rings to be greater than the calculated expected yield. The total amount of threaded Valinomycin present was 0.37 percent. The rings showed no effect on the calorimetric glass transition temperature, but did result in an increase in the tensile modulus.
Creep of carbonated plastic beverage bottles
Authors: Thiruvillakkat K. , Mahajan G. K.
Published: December 2004

Long‐term performance of carbonated plastic beverage bottles depends on a number of critical factors. Testing to predict the effects of these factors is expensive and time‐consuming. Many of these factors are interdependent. The presence of more than one critical factor in a given test makes the analysis of data difficult. The separation and prediction of the contribution of any one factor to long‐term performance is complex even for the single composition studied, a rubber‐modified high acrylonitrile resin. In addition to superior gas barrier properties, the container should exhibit a high degree of creep resistance. Visible manifestations of creep are reflected in gross dimensional changes of the bottle and consequent loss in carbonation. The purpose of this paper is to examine creep deformation of the bottle and its implications on bottle performance. Various factors contributing to the creep are also briefly analyzed. Since the ultimate goal is to predict creep, the merits of relevant short‐term tests in this context are discussed. Finally, the data from short‐term tests are compared with creep data obtained on bottles that were subjected to long‐term tests.
Degradation of chlorinated polyethylene—III: Effect of additives on dehydrochlorination and oxygen absorption
Authors: Abu‐Isa Ismat A.
Published: December 2004

Degradation of chlorinated polymers takes place via two simultaneous reactions; namely, dehydrochlorination and oxygen absorption. The dehydrochlorination and oxygen absorption of five grades of chlorinated polyenthylenes were studied at temperatures varying between 120 and 180°C. The chlorinated polyethylene grades varied in both molecular weight and chlorine content, the latter being in the range of 24.0 to 45.2 percent chlorine. Dehydrochlorination measurements on the pure polymers in both nitrogen and oxygen atmospheres showed that the rate of dehydrochlorination increases with an increase in the degree of chlorination of the polymer. The oxygen absorption rate, however, showed a decrease with higher chlorine content of the polymer.

Dehydrochlorination and oxygen absorption studies were also carried out on chlorinated polyethylene containing dehydrochlorination stabilizers, antioxidants, antimony oxide, and other metal salts and metal oxides. Retardation of both oxygen absorption and dehydrochlorination was observed in the presence of antioxidants. More significant, however, was the observed action of some dehydrochlorination stabilizers as efficient antioxidants in the polymer.
Analysis of a cross head die with the flow analysis network (FAN) method
Authors: Gutfinger C. , Broyer E. , Tadmor Z.
Published: December 2004

The Flow Analysis Network (FAN) method was adapted for solving the isothermal flow problem in a cross head die. Given the polymer rheology and the die geometry, the flow streamlines in the die and the flow rate uniformity at the exit can be calculated for any given head pressure. The optimum geometrical configuration of the die can be computed by repeated simulations. Results of the computations with the present method are shown to be in good agreement with previously published computations.
Oriented short glass‐fiber composites. II. Analysis of parameters controlling the fiber/glycerine orientation process
Authors: Kacir L. , Narkis M. , Ishai O.
Published: December 2004

Nine parameters related to the fiber/glycerine orientation process are analyzed. These parameters can be divided into machine, material and processing variables. The effect of each parameter on the cumulative percent of oriented fibers within specified angle limits (±10 deg) is discussed. Similar effects were found on an accumulative exponential function which is represented by a single empirical constant. Five parameters are shown to have major effects on the alignment which can be achieved in the mats. These parameters include: temperature of the fiber/glycerine dispersion, pressure head on the dispersion and three geometrical variables of the orientation machine.
Structure development during polymer processing: Studies of the melt spinning of polyethylene and polypropylene fibers
Authors: Spruiell Joseph E. , White James L.
Published: December 2004

Experimental studies of structure development in melt spinning of polyethylene and polypropylene fibers are described. Emphasis is given to the influence of applied stresses on the rates of crystallization and on the development of crystalline morphology. The relationship of fiber morphology to mechanical properties, especially “hard elastic fibers” is considered. The relevance of such studies to other polymer processing operations such as film extrusion is discussed.
Non‐isothermal curing of reactive plastics
Authors: Progelhof R. C. , Throne J. L.
Published: December 2004

One dimensional transient heat conduction analysis of reactive, unfilled polyesters and epoxies shows that care must be taken during curing to minimize large temperature excursions due to internal heat generation. Isothermal heat generation rates have been shown to underestimate the non‐isothermal values by more than an order of magnitude.
Dynamic mechanical and thermal properties of fire‐retardant polypropylene
Authors: Chang Eng Pi , Kirsten Rudy , Salovey Ronald
Published: December 2004

A study of the effect of a series of fire retardants and antimony oxide upon the dynamic mechanical and thermal properties of polypropylene suggests three categories. (1) “Inert Fillers”—These raise the elastis modulus and the heat distortion temperature of polypropylene without shifting its glass transition temperature. The melting point of polypropylene is only depressed by 1–3°C, the heat of fusion and the percentage of crystallinity of polypropylene in these composites is ∼10 percent lower at additive concentrations of ∼30 percent. Very poor interaction exists between the additive and the thermo‐plastic which apparently exist in two separate phases. (2) “Chain Stiffener”—These raise the elastic modulus (∼25 percent) and the glass transition (∼11°C) for polypropylene; the melting point of polypropylene in the composite is lowered by ∼6°C indicative of good interaction between the additive and polypropylene. (3) “Plasticizer”—These lower the room temperature elastic modulus (∼20 percent) and the glass transition temperature (∼11°C) of polypropylene; the melting point of polypropylene in the composite is depressed by ∼10°C indicating good interaction. The efficacy of the “plasticizer” and “chain stiffener” are attributed partially to melting of polypropylene at the processing temperature.
Structural thermoplastic foam—A low energy processed material
Authors: Throne James L. , Griskey Richard G.
Published: December 2004

Shortages of both energy and materials make it imperative that low cost substances, processed with low energy requirements, be developed as soon as possible. One promising type of materials are the structural thermoplastic foams since they further enhance the favorable strength to weight ratio of plastics while reducing overall material needs. In addition, foam processing also capitalizes on the generally lower energy consumption and manpower‐hour requirements for plastics. Finally, the possibility of forming larger and more complex shapes opens up new application areas. The largest deterrent to the use of structural foams is the lack of appropriate basic engineering and scientific knowledge. This paper not only summarizes and extends such understanding, but also shows how appropriate design procedures can be developed.
Low velocity surface fracture patterns and energies in poly(methyl methacrylate)
Authors: Osborne P. W.
Published: December 2004

Steady‐state fracture techniques were used to investigate the surface fracture patterns and surface fracture energies of poly(methyl methacrylate) at low velocities (10 cm/sec to 10−5 cm/sec). Several anomalies were discovered: (1) Small surface cracks, running parallel to the crack front, which were initiated by imperfections; (2) a “zero velocity” transition from the normal surface fracture patterns to a “laminar” pattern; and (3) a subsequent transition from the laminar pattern to a “turbulent” pattern. The velocities at which these anomalous fracture patterns occurred were of the order of 10−4 to 10−6 cm/sec. The corresponding surface fracture energies were as low as 105 erg/cm2.
The injection molding of thermosets
Authors: Fleischmann J. J.
Published: December 2004

Current industry trends toward increasing automation, as well as increased flexibility in material selection have focused a strong spot light on thermoset injection molding. The growth of thermoset injection molding is reviewed comparatively with the technical history and growth of thermoplastic injection. The progress we see to date and the promise for the future in material characteristics and properties, mold design features, equipment features, changing concepts and new thoughts are discussed.
The modeling of molecular motions in crystalline polymers
Authors: Boyd Richard H.
Published: December 2004

Regions in which the mechanical and dielectric properties of polymers change rapidly with temperature (transitions or relaxations) are supposed to be due to the onset of certain types of molecular motions. A precise description of these various molecular motions would be invaluable in the areas, of structure vs property relationships and the tailoring of polymers to end‐uses. However, our knowledge concerning these motions is quite limited and qualitative at best. The biggest stumbling block has been an inability to test the consequences of proposed mechanisms in terms of experimentally observed quantities. The problem in many cases has not been a lack of adequate theory but rather an insufficiency of knowledge, appropriate for input into the theory, concerning the energetics of chain motions. However, in the past few years there has been considerable progress in studying chain energetics by means of conformational energy calculations (molecular mechanics). In the present paper, this work on crystalline polymers will be reviewed and some recent calculations which illustrate the present state of the art are discussed.
Predictions of limiting mechanical performance for anisotropic crystalline polymers
Authors: McCullough R. L. , Wu C. T. , Seferis J. C. , Lindenmeyer P. H.
Published: December 2004

A four‐stage synthesis of molecular, micromechanical, and macromechanical models is used to predict the dependence of the longitudinal and transverse Young's moduli and the axial and transverse shear moduli of anisotropic polyethylene on percent crystallinity and the state of molecular orientation. Variational methods are employed to establish the upper and lower limits for anisotropic elastic response. The difference between lower and upper bound limits is interpreted as the potential for improving mechanical performance. A modified form of the Tsai‐Halpin equation is used to examine parametric ranging (via a contiguity factor, ξ) between the lower and Tupper bound limits. In this application, the contiguity factor is interpreted as a characteristic of the internal stress‐strain distribution which is dependent upon the size, shape, packing geometry, and elastic properties of the crystalline and amorphous regions. The potential for achieving high modulus polymeric materials is illustrated by treating percent crystallinity, molecular orientation, and contiguity as materials design variables subject to control by processing conditions. Optimum property trade‐offs, necessary for balancing the over all mechanical behavior of anisotropic materials, are illustrated through the control of orientation and contiguity, The theoretical predictions for the moduli of anisotropic polyethylene are in good agreement with values reported for material processed by traditional procedures as well as ultra‐oriented polyethylene.
Theoretical analysis of residence time distribution functions and strain distribution functions in plasticating screw extruders
Authors: Lidor G. , Tadmor Z.
Published: December 2004

The residence time distribution (RTD) function in a single screw plasticating extruder was theoretically calculated. The calculation is based on the solids conveying, melting, and melt conveying models in extruders. The screw channel is divided into small axial increments and the path of each exiting fluid particle is followed from hopper to die. In addition to the residence times the total shear deformation or strain imposed on the fluid particles was also calculated. This together with the RTD function has led to the definition and calculation of the strain distribution function (SDF). This function is proposed for quantitative characterization of the mixing performance of screw extruders as well as other laminar mixers. Some simple idealized batch and continuous laminar mixers are analyzed in terms of the SDF. Finally, the effect of extruder operating conditions and screw design on the RTD and SDF were investigated by computer simulations.
An approach to thermodynamics of polymer flow based on internal state variables
Authors: Astarita G. , Sarti G. S.
Published: December 2004

Two kinds of thermodynamic theories, which seem to be applicable to polymer deformation and flow, have been developed in the recent literature. One of these approaches utilizes entropy far from equilibrium as a primitive undefined concept. The alternate kind of theory involves the idea of a quasi‐static process as a primitive concept. In this work, an approach based on internal state variables (specifically, the micro structure of the polymeric material) is used to argue that both primitive concepts are in some sense legitimate on physical grounds. In particular, the legitimacy of the quasi‐static process concept is related to the smoothness of the function delivering the rate of change of the microstructure.
Flow‐induced crystallization of linear polyethylene above its normal melting point
Authors: Tan Victor , Gogos Costas G.
Published: December 2004

The phenomenon of flow‐induced crystallization was investigated using a linear polyethylene above its normal melting point flowing continuously in a Biconical Rheometer. It was found that the resin crystallized in the superheated state at rates which increased with increasing shear rate and decreasing temperature. A method of analysis of the temperature dependence of the various stages of flow induced crystallization is proposed. It deals with and attempts to explain the experimental fact that a higher viscosity enhances the rate of flow‐induced crystallization in contrast to the effect of viscosity on the rate of quiescent crystallization. Some of the flow‐induced crystallization samples were transparent and exhibited a high DSC thermogram “tail”.
Cold compaction molding and sintering of polystyrene
Authors: Jayaraman G. S. , Wallace J. F. , Geil P. H. , Baer E.
Published: December 2004

It is the objective of this paper to demonstrate the applicability of cold compaction molding followed by a sintering treatment to the processing of polystyrene powders. The influence of pressure, compaction speed, and peak pressure dwell time on the green (as compacted) density and the green tensile strength, as well as the effect of sintering on the tensile strength and dimensional change, were evaluated. The resulting data indicate that room temperature compaction alone is insufficient to provide adequate tensile strength for the compacts. Sintering the green compacts at temperatures of 150 to 173°C markedly improves the tensile strength while simultaneously causing a thickness change in the compacts. This thickness change results from gas evolution, pore shrinkage, and viscoelastic recovery of the residual stresses induced by pressure. For compacts of 0.225 in. thickness, an optimum sintering treatment of 173°C for 30 mins is recommended to provide a tensile strength of 4,000 psi and a thickness change of less than + 7 percent. Coining (repressing) the green compacts does not appreciably affect the sintered strength. However, a finer particle size improves the sintered properties. A review of the literature on the flow behavior of polystyrene suggests that a non‐Newtonian viscous flow mechanism is followed by a Newtonian one as sintering progresses.
Transition behavior of poly(vinylidene fluoride)/poly(ethyl methacrylate) blends
Authors: Imken R. L. , Paul D. R. , Barlow J. W.
Published: December 2004

Previous work has shown evidence that PMMA and PEMA are miscible with PVF2. The present paper examines in detail the behavior of PEMA/PVF2 blends by thermal analysis and dynamic mechanical testing. All transitions and relaxations are affected by blond composition but in a complex manner owing to the crystallization of PVF2 from blends rich in this component. Inadequacies of the simple two‐phase picture of semi‐crystalline polymers is believed responsible for some of the transitional behavior observed here. The melting point depression observed for PVF2 was found to be consistent with an exothermic heat of mixing for this pair comparable in value to that found for PPMA/PVF2/All evidence here are consistent with the previous conclusion of miscibility for these systems.
Prediction of the onset of extrudate distortion in polyethylenes from rheological data
Authors: Smith F. P. , Darby R.
Published: December 2004

An extensive set of rheological data, including steady shear, normal stress, and oscillatory response functions, have been obtained for several polyethylene melts, and a modified form of the Spriggs nonlinear co‐rotational model has been used to represent the data. The resulting model was used to predict the transient stress response of the melts in a simplified model of the extrusion process, with a resulting criterion for the onset of melt distortion in terms of readily evaluated rheological parameters. The predicted occurrence of melt distortion based on this criterion agreed well with observations for the polymers in this study as well as for a variety of other polymers reported in the literature.
The preparation of ultra‐high modulus polypropylene films and fibres
Authors: Cansfield D. L. M. , Capaccio G. , Ward I. M.
Published: December 2004

Following the discovery that linear polyethylene can be drawn to very high draw ratios to produce oriented fibres and films with ultra‐high initial moduli, a similar study has been undertaken for polypropylene. In particular, the modulus/draw ratio relationship has been obtained for a range of polymers of different molecular weight and molecular weight distribution. The effects of thermal history and draw temperature were studied, and it was shown that under optimum conditions material with an initial modulus at room temperature of 1.9 × 1010 Nm−2 (205 gdtex, 3 × 106 psi) can be obtained. This value is at least 50 percent greater than those previously recorded for drawn fibres and about one half of the theoretical modulus.
A review of techniques for processing ultra‐high modulus polymers
Authors: Bigg D. M.
Published: December 2004

Linear crystalline polymers can be processed to high degrees of orientation sufficient to produce dramatic increases in tensile strength and modulus. Three processes have been identified for inducing such orientation: cold drawing, hydrostatic extrusion, and solution spinning. All three processes utilize a high elongational velocity gradient in a critical temperature range to produce a high strength crystalline morphology. Although the molecular superstructure may differ in each case, the mechanical properties are similar, An increase in strength is achieved either through the creation of new tie molecules between crystal lamellae or through the creation of an extended chain crystal substructure. Temperature and molecular weight are the prime variables in determining which morphology will develop. The optimum processing temperature for many of the specific techniques is the crystalline dispersion temperature. At this temperature, the crystal structure is particularly adaptable to forming a new crystal morphology. Ul‐tradrawn polymers are more Hookean in behavior than isotropic polymers and have properties similar to steel and glass. Polyoxymethylene has been processed most closely to its theoretical strength. Polyethylene, which is the most difficult to process, has achieved the highest modulus of any common polyolefin polymer, about 7 × 1010 Pa.
Residual stresses in polymers and their effect on mechanical behavior
Authors: So Paul , Broutman Lawrence J.
Published: December 2004

Plates of bisphenol‐A polycarbonate and poly(methyl methacrylate) have been quenched in ice water from temperatures slightly above their glass transition temperatures. Residual stresses are thus created, Measurement of these residual stresses has been accomplished by the “layer removal” method and the stress distributions through the thickness are presented. Compressive stresses, approximately 3000 psi, exist at the surface while tensile stresses‐of at least 1000 psi exist in the interior. It is shown that these residual stresses can influence the notched Izod impact strengths for polycarbonates. The mechanism is thought to be suppression of craze initiation in advance of the notch due to the presence of residual compressive stresses for specimens notched prior to quenching. In the case of poly(methyl methacrylate), it is shown that compressive residual stresses at the surface can cause plastic yielding to occur in bending experiments resulting in permanent deformation and greater energy absorption.
Inhibitor selection for vinyl monomers by differential scanning calorimetry
Authors: Riga Alan T.
Published: December 2004

Inhibitors to prevent vinyl polymerization were selected rapidly and effectively by differential scanning calorimetry. The autopolymerization temperature (APT) and the relative polymerization rate constants were used to define the type and amount of inhibitor necessary to prevent polymerization of acrylic esters and acrylamides. The APT was also used to determine the amount of inhibitor in a vinyl monomer. The rate of polymerization and storage stability of vinyl monomers were determined by these methods.
The effect of corona and ozone treatment on the adhesion of ink to the surface of polyethylene
Authors: Stradal M. , Goring D. A. I.
Published: December 2004

Low density polyethylene sheet was subjected to treatment by corona discharge in oxygen, nitrogen, helium and argon; in addition some sheets were treated with ozone gas. The bond strength between two similarly treated sheets was then measured using a commercial flexographic ink as an adhesive. The results showed that although surface oxidation improved both the ink adhesion and the wetting properties of polyethylene it is not a necessary prerequisite for good bonding. When the sheet was subjected to electrical discharge in nitrogen, argon or helium, considerable enhancement of ink adhesion was obtained without any detectable change in the surface chemistry of the polymer. The results indicate that ink adhesion after treatment in various gases follows closely the trends established previously in corona‐induced autohesion of polyethylene. This suggests that the mechanism of bonding is similar in the two cases.
Techniques for compounding glass fiber‐reinforced thermoplastics
Authors: Stade K.
Published: December 2004

The processing characteristics of various glass fiberreinforced thermoplastics (FRTP) and the basic approaches for their production are discussed. Experimental work on twostage production‐scale continuous kneaders was conducted to define the most important process variables in compounding FRTP materials. Results demonstrate how processing conditions and screw design influence the temperature profile in the kneader and the glass‐fiber length in finished products. Feed steek appearance (i.e., pellet shape and size), melt viscosity, and volume percentage of fibers are basic material variables. High quality products can be achieved through a careful, layout of the continuous kneader in order to minimize thermal degradation of the base polymer and to effect adequate dispersion of the glass fibers in the matrix.
Molecular order and orientation in aromatic polyamide fibers by internal reflection spectroscopy and wide angle X‐ray diffraction
Authors: Druschke F. , Siesler H. W. , Spilgies G. , Tengler H.
Published: December 2004

The results of wide angle X‐ray diffraction and, ATR polarization measurements are reported in order to characterize the anisotropy in poly(m‐phenyleneisophthalamide) and poly(p‐phenyleneterephthalamide) (Fiber B) fibers. Additional information on the state of order of the investigated fibers is derived from ATR spectroscopic accessibility measurements by deuterium exchange.
Interfacial (polymer‐substrate) failure of ultraviolet radiation curable coatings
Authors: McGinniss Vincent D. , Kah Ann
Published: December 2004

The development of ultraviolet radiation technology to cure or photopolymerize acrylic unsaturated monomers, oligomers, and polymers into tight network structures introduces several adhesion problems that can be related to or associated with interfacial polymer‐substrate failure. This paper discusses network formation, polymer‐interfacial growth association and failure as a function of the following variables: light intensity (effect on sol/gel conversion), photoinitiator (structurereactivity as a function of conversion), polymer shrinkage, and substrate wetting. The results of this study show that all of the above variables interact in a composite fashion to influence the final properties of the ultraviolet cured coatings.
Effect of center block structure on the physical and rheological properties of ABA block copolymers. Part II. Rheological properties
Authors: Futamura Shingo , Meinecke Eberhard A.
Published: December 2004

The effect of the chemical structure of the center block on the rheological properties of ABA block copolymers with polystyrene end blocks has been investigated. The chemical structure of the center blocks investigated in the present paper are polybutadiene, polyisoprene, ethylene/butene copolymer, ethylene/propylene copolymer and polydimethyl‐siloxane. The chemical structure of the center block was found to have a pronounced effect on the rheological properties of the ABA block copolymer melts. The long range relaxation times of these block copolymer melts increases with increasing incompatibility between the styrene block and the center block. However, the rheological properties of the block copolymers are not influenced significantly by the glass transition or the entanglement molecular weight of the center block.
Transitions in polymer melts
Authors: Nielsen Lawrence E.
Published: December 2004

It is shown that the liquid‐liquid transition Tll in polymer melts need not be a true polymer transition but can be an artifact of the torsional braid analysis technique. The shift in Tll with molecular weight then is due to the variation of viscosity with molecular weight.
Predicting the service life of polysulfone in steam or hot water
Authors: Dearing Rogers K.
Published: December 2004

A quantitative definition of stress‐environmental, interactions on polymers must be made in order to designstructural parts. This definition for design urposes is best obtained by measuring creep of the plastic under constant stress and in the environment in which it is to perform. In order to measure creep in steam or hot water, a relatively simple test apparatus was devised so that clamped circular test specimens acting as a diaphragm were stressed by controlled steam pressure. Creep was measured by deflection of the diaphragm. A case history was developed with polysulfone: the allowable stress limits at various temperatures were determined; and a method developed for predicting the long time service life of the material from short time data using the Goldfein equation of state. Creep measurements over a year in steam were in excellent agreement with predicted values.
Craze and creep resistance of high‐impact polystyrene in alcohols
Authors: McCammond D. , Hoa V. S.
Published: December 2004

In the present state of development of the polymer industry, all of the lower cost, widely used, plastics exhibit some susceptibility to environmental stress crazing. Past developments have improved some polymers' resistance to this phenomenon (e.g., the addition of rubber to polystyrene) and this paper considers one such improved polymer, high‐impact polystyrene, and examines its craze and creep resistance in the alcohols. This family of fluids does not affect the unstressed polymer but has a marked effect when the polymer is stressed. The results of creep tests at different stresses indicate the existence of a delay time after which the creep rate accelerates rapidly. The requirement of a definitive time under stpess before this acceleration occurs is supported by the results of cyclic stress tests. Plots of delay time against stress for the different alcohols show two distinct regions: (i) at high stresses, where the delay time increases from methanol to butanol and the mechanism would appear to be one of molecular volume controlling the mobility of the fluid to “penetrate” the polymer, and (ii) at low stresses, where the delay time decreases from methanol to butanol and the criterion would appear to be that of ability to “plasticize” the polymer as evidenced by the solubility parameters.
An improved method for determining polymer melting temperatures
Authors: Predecki Paul , Karr P. H.
Published: December 2004

A method for determining polymer melting temperatures,Tm, based on a simple modification of thermo‐optical analysis is described. The method makes use of a small, highly conducting substrate and a preselectedTm, procedure which results in rapid heating rates (∼1500°C/min) without temperature overshoot or superheating. Accuracies to within ±0.15°C are readily obtained. Application of the method to isothermally crystallized polyoxymethylene (Delrin 100 and 500) shows thatTm, increases with both time and temperature of crystallization as well as with increasing molecular weight. The potential of the method for characterizing polymer thermal history and molecular weight is discussed.
Flow visualization of fiber suspensions
Authors: Lee Wei‐Kuo , George Henry H.
Published: December 2004

A visualization study of the flow of fiber‐filled resin through cylindrically convergent channels has been conducted. Epoxy resins filled with glass fibers were tested to simulate the flows experienced during the processing of fiber reinforced thermoplastics. Specific phenomena which have been investigated include the kinematics, orientation of the suspended fibers, formation of possible unwanted stagnant eddies at the entrance of the channel, and the fiber length degradation. It was found that the extensional flow in the convergent channel plays an important role in orienting the fibers.
Impact and yield properties of polycarbonate as a function of strain rate, molecular weight, thermal history, and temperature
Authors: Ryan James T.
Published: December 2004

A study has been made on the impact and yield properties of polycarbonates from two manufacturers as a function of strain rate, melt flow rate, notch radius, thermal history, and test temperature. The yield stress increases with the strain rate and annealing time in exactly the way predicted by a recently proposed theory on nonlinear viscoelasticity of glassy polymers. The critical molecular weight for the transition from a ductile to a brittle break increased at higher rate of strain and also with the longer annealing times.
Two‐phase mixture—viscoelasticity and general equivalent mechanical model
Authors: Marinov Pencho
Published: December 2004

Quasistatic viscoelastic behavior of a two‐phase mixture is discussed on the basis of simple mechanical models. The mixture consists of a viscoelastic matrix with Kelvin‐Voigt properties and elastic inclusions. The Gibbs' equation of a two‐phase mixture is derived. Finally a linear constitutive theory of a two‐phase mixture is obtained that takes into account the interaction between the phases.
Theory of mixing sections in single screw extruders
Authors: Erwin Lewis
Published: December 2004

A discussion of the effect of deformation on mixing leads to reorientation of fluid interfaces as a proposed mechanism for special “mixing sections” in single screw extruders. Based on the kinematics of mixing it is shown how a mixing section can greatly decrease the amount of work necessary to accomplish extensive mixing through orienting the fluid more favorably for mixing by subsequent shear. Mathematical development quantitatively describes favored configurations of mixing sections. An upper bound for the mixing performance of a simple model of an extruder with special sections is shown to be similar to turbulent mixing. Based on this theory the key actions of the special sections are identified.
A simplified method for analyzing mold filling dynamics Part I: Theory
Authors: Stevenson James F.
Published: December 2004

A graphical method based on dimensional analysis is presented for estimating the injection pressure and clamp force required for injection molding amorphous polymers to form disk‐shaped parts with a constant wall thickness. A procedure is suggested for estimating clamp force when the projected area of the mold cavity is smaller than the surface area of one side of the molded part. The results reported here are based on a numerical simulation of a power‐law fluid filling a cold mold at a constant injection rate. The dimensionless bulk temperature and the ratios of the nonisothermal injection pressure (clamp force) to the isothermal injection pressure (clamp force) are given as functions of the dimensionless cooling time τ, the Brinkman number Br which characterizes viscous heating, the power‐law exponent n, and a dimensionless temperature β which includes the inlet melt and mold wall temperatures and the temperature coefficient for viscosity.
The effect of molecular weight and weight distribution upon polymer melt rheology
Authors: Pearson G. H. , Garfield L. J.
Published: December 2004

A major objective in polymer rheology is to predict a fluid's response to a general deformation from molecular information. A method has been developed which allows one to predict the viscoelastic properties of polymer melts from a limited amount of rheological and molecular data for the polymer. The input parameters are: (a) zero‐shear viscosity; (b) molecular weight distribution; (c) temperature and density; and (d) constants relating Graessley's relaxation time to the Rouse relaxation time. The technique then “simulates” a discrete relaxation spectrum using G′ and G″ data from the Rouse theory and finally requires that a continuum model of polymer viscoelasticity be fit to shear viscosity data predicted by Graessley's theory. Examples of the utility of the procedure are given to illustrate the role of molecular weight and weight distribution in determining rheological behavior.
Concentration dependence of zero‐shear viscosity for polymer solutions: A test of the lyons‐tobolsky equation
Authors: Rink M. , Pavan A. , Roccasalvo S.
Published: December 2004

The empirical equation proposed by Lyons and Tobolsky (1) to describe the concentration dependence of zero‐shear viscosity in polymer solutions was tested on a variety of data taken from the literature, covering different polymer‐solvent systems, molecular weight, temperature, and the whole concentration range. This equation was fitted to each set of experimental viscosity‐concentration data by a least squares method. The validity of this equation is verified. The dependence of the optimal values obtained for the three parameters intrinsic viscosity, [η], Huggins constant, k, and new empirical constant, b, on molecular weight, temperature, and solvent is also discussed.
A model for the transient flow of thermoplastics in annular hot runners
Authors: Lord H. A.
Published: December 2004

Annular hot runner systems, in which the inner surface is heated and the outer surface cooled, are being used increasingly in the injection molding of thermoplastics. In this paper a computer model which has been developed to calculate transient pressure, temperature, and velocity fields is described. Using the properties of acrylonitrile‐butadiene‐styrene for illustration, some detailed temperature and velocity profiles computed with the model are presented for atypical hot runner section. The effects of a number of design and operating variables on the pressure drop are also presented.
The effect of additives on the crystallization of poly (butylene terephthalate)
Authors: Pi Chang Eng , Kirsten Rudolf O. , Slagowski Eugene L.
Published: December 2004

The effect of glass fibers and some fire retardant additives on the kinetics and mechanism of crystallization of poly(butylene terephthalate) (PBT) has been investigated. Shorter half times of crystallization and higher optimum crystallization temperatures of the filled samples are attributed to the nucleating ability of the additives. Based on the percent crystallinity determined, the efficiency of the different quenching media studied can be arranged in the order: ice water > 25°C water ⩾ dry ice/ethanol > liquid nitrogen. The inefficient quenching of dry ice/ethanol arid liquid nitrogen media is attributed to their poor heat transfer. The Tg of these quenched samples is, however, independent of the percent crystallinity.
Application of small system thermodynamics to polymer molecules. I. The entropy barrier between liquid and crystalline state
Authors: Lindenmeyer P. H. , Beumer H. , Hosemann R.
Published: December 2004

The methods of small systems thermodynamics have been applied to the calculation of the entropy barrier to the growth of polymer crystals. The height of this barrier at the equilibrium melting point of polyethylene molecules of typical lengths (X = 4,000 to 10,000 segments) is estimated to be of the order of 4 to 5 Kcal per molecule. This barrier increases linearly with ln X if the crystal is very large but retains the approximate values mentioned for crystals with the lamella thicknesses usually found. This entropy change causes the free energy to go through a maximum as in a nucleation phenomena but no new surface formation is involved. The existence of such a barrier explains why crystallization (or melting) never occurs at the equilibrium melting temperature.
Elastic modulus and strength of fibrous material
Authors: Peterlin A.
Published: December 2004

As a rule, the large increase of elastic modulus with increasing draw ratio obtainable in highly‐drawn or extruded semicrystalline polymers is not reflected in a similarly large increase of strength. This is closely connected with the wellknown fact that with increasing plastic deformation one obtains fibrous material with decreasing strain to break. The axial elastic modulus is mainly caused by the taut tie molecules which bridge the amorphous layers between consecutive crystal blocks and thus provide an efficient axial force transmission through the sample. The defects at the ends of microfibrils interrupt this transmission because they contain few if any taut tie molecules connecting the end of microfibril with adjacent fibrillar elements. As a consequence of the small number of such ends, they only marginally reduce the elastic modulus. But as the mechanically weakest areas of the fibrous material, they drastically depress the strength. They fail as soon as the strain concentration upon them reaches their strain to break. The growth and coalescence of resulting microcracks finally lead to bulk fracture as the growing crack reaches critical dimensions.
Stress‐strain isotherms for polymer networks at very high elongations
Authors: Mark James E.
Published: December 2004

Some polymer networks show an anomalous increase in the modulus or reduced stress at very high elongations. This behavior has now been investigated definitively by determining stress‐strain isotherms for both crystallizable and noncrystallizable networks, prepared using several curing techniques (carried out so as to yield a wide range in degree of cross‐linking). The networks were studied unfilled at a number of temperatures, and at several degrees of swelling. The results clearly implicate strain‐induced crystallization as the origin of the upturn in the modulus, and thus demonstrate that the wide spread interpretation of this upturn in terms of limited chain extensibility is incorrect.
Determination of fiberglass lengths: Sample preparation and automatic image analysis
Authors: Sawyer L. C.
Published: December 2004

The optimization of end product properties of fiberglass reinforced engineering thermoplastics must be based upon knowledge of the constituents, including the fiber length distribution. This paper presents the techniques developed for the recovery, dispersal and length distribution analysis of glass fibers recovered from filled engineering resins. An automatic image analyzing computer system is used for the determination. The tedious manual method of measurement from optical photomicrographs is replaced by a rapid, quantitative and reproducible analysis.
Strain‐induced crystallization, Part IV: Induction time analysis
Authors: Yeh G. S. Y. , Hong K. Z. , Krueger D. L.
Published: December 2004

The empirical equation, 1/ti = AeEi/RT, which expresses the exponential dependence of the reciprocal of crystallization induction time, ti, has been analyzed and shown to be equivalent to the nucleation rate equations derived earlier in Part III (1). Consequently we have used the ti measurements obtained earlier by Krueger and Yeh to calculate not only the nucleation rate enhancements but also the melting point elevations, the relative crystal thickness changes and molecular coil extension ratios of shear‐crystallization polyethylene. It is shown that polyethylene when crystallized between 129 and 131°C at shear rates between 1.56 and 9.70 sec−1 can have melting point increases of 4.2 to 7.2°C and crystal thickness decreases of 20 to 25 percent, when compared to those crystallized at 130°C in the quiescent state. The predicted “coil” extension in the melt just prior to shear‐induced crystallization ranges between 21 and 36 percent. The results of these analyses as well as those on nucleation rates of polyethylene oxide are discussed in detail.