bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of nuclear radiation on the thermal conductivity of polyethylene
Authors: Tomlinson J. N. , Kline D. E. , Sauer J. A.
Published: December 2004

Thermal conductivity curves for the 0°C to 170°C temperature region are presented for six irradiated low density polyethylene samples (radiation doses from 0 to 3100 megarads) and one irradiated high density sample (120 megarad dose). In agreement with data in the literature for unirradiated polyethylene, the thermal conductivity values for lightly irradiated polyethylene are found to decrease with increasing temperature in the elevated temperature region where the crystallites begin to melt. Beyond the crystalline melting point, test results for lightly irradiated and crosslinked samples indicate that the thermal conductivity is almost independent of temperature. Although radiation doses of less than 250 megarads produce only small changes in the thermal conductivity, higher radiation doses result in a significant lowering of the conductivity in the room temperature region and an increase of the conductivity at temperatures above the melting point. The decrease in conductivity at low temperatures is considered to be a result of disordering of the crystallites by the radiation, and the increase above the melting point is attributed primarily to radiation induced crosslinking.
The influence of resin strength and defects on the interlaminar shear strength of filament‐wound composites
Authors: Petker I.
Published: December 2004

The interlaminar shear strength of reinforced plastic composites has long been recognized as a critical property in the structural performance of composites. However, its role in structural performance and the many factors that influence it have not been clearly elucidated. Although much attention has been given to the importance of resin‐glass adhesion, little is known regarding the contribution of resin strength and composite quality. In this article it is shown that interlaminar shear strength is a direct function of both resin strength and composite void content. The curves of resin tensile strength vs interlaminar shear strength indicate a limiting value for interlaminar shear above which increases in resin tensile strength do not increase defects.
Resins and reinforced plastic laminates for continuous use at 650°F
Authors: Freeman James H. , Frost Lawrence W. , Bower George M. , Traynor Edward J.
Published: December 2004

This article reports the preparation of a number of high molecular weight aromatic amide and imide polymers. An order of relative thermal stability of a series of alternative linkages between benzene rings in aromatic polymers is established on the basis of weight loss of thin films in air. It is found to agree with the stability order established by others by study of model compounds. It is further confirmed by the aging performance of laminates employing such resins. Electrical properties of the polymers were measured as a function of temperature. Change in the dissipation factor with temperature was used to determine Tg, which in turn was correlated to the minimum temperature required to produce laminates. Examples of the performance of these organic polymers in long time exposure tests at elevated temperature are given. Flexural properties of laminates aged and tested at temperatures of 600–650°F are reported.
Effect of stearate processing aids upon polypropylene stability
Authors: Russell C. A.
Published: December 2004

Fatty acid salts are often added to polymers as processing aids. Although calcium stearate promoted highly reduced mixing torque requirements in polypropylene compositions, this was due largely to lowering of the polymer molecular weight. However, the amount of shear withstood without severe degradation was less. The effects of calcium stearate upon polypropylene stabilization systems were investigated by oxygen absorption studies Up to 50% stabilization was lost, particularly with metals such as copper, with 0.1% calcium stearate even in compositions protected by inhibitors. The stearate evidently reacts with transition metals or their oxides, particularly if acidic materials are present, to give metallic stearates which are extremely effective polyofin oxidation catalysts. Considering these results, the use of stearate processing aids should be avoided if property retention and stability are important in the fabricated article.
The effect of filler particle‐size distribution in epoxy casting formulations
Authors: Kuhlmann H. W. , Wolter F. W. , Mueller E. R.
Published: December 2004

The selection of particle size distribution is based on a theoretical concept of the “close packing” of particles. The usefulness of this concept was investigated using silica as the filler in a single epoxy‐hardener system. The viscosity and settling characteristics for several particle‐size distributions and concentrations of silica fillers were studied. These studies show that significant decreases in the viscosities of casting formulations can be obtained using a two‐component filler system which permits the use of higher filler loadigs. The increase in the ratio of coarse filler to fine filler reduced the flexural strength of the castings and increased the rate of settling in the formulations. The effect of parameters other than particle size is demonstrated by the use of non‐silica fillers.
The application of infrared spectrophotometry to the reactivity and cure state determination of epoxy resins
Authors: Feltzin J. , Longnecker D. M. , Petker Irvin
Published: December 2004

This article describes a simple and accurate method for measuring the reactivity and final cure state of epoxy resins. In the method, the reaction of a thin film of epoxy resin between two Nace plates is followed during a complete curing cycle. The method makes it possible to study effect of temperature and catalyst on cure rate, as well as comparing the equivalence of various materials. The techniques discussed in the article may be useful in the application of thermosetting resins other than epoxies.
Why do plastics stress‐crack?
Authors: Howard John B.
Published: December 2004

Possible applicability of Griffith's theory to stress‐cracking in microcrystalline organic polymers is considered. Although the time‐dependent nature of the phenomenon and the plastico‐elastico‐viscous character of the medium make such application debatable, it is found that this approach in combination with the contributions of others notably Rebinder and his associates, can provide rationalization for many of the empirical facts. The observed “case‐hardening” action of surfactants on specimens under stress suggests that the mobility of polymer chain segments in surface layers may in fact be restricted under these conditions as theorized, facilitating local concentration of stresses to a level exceeding the strength of the material.
Weathering of polyolefins under stress
Authors: Newland G. C. , Tamblyn J. W.
Published: December 2004

Many plastic articles when exposed outdoors deteriorate first at points of highest stress. Consequently, weathering of polyolefins under stress speeds the deterioration and hence the evaluation of ultraviolet stabilizers used to retard it. Cracking of the stressed polyolefin specimens denotes failure and is a direct measure of the minimum useful outdoor lifetime of the materials, whereas in other methods the change in some property, such as elongation, is used to predict the useful lifetime. In this work, the results of nine years of natural and artificial weathering illustrate the usefulness of the stresscracking method for evaluating polyethylene and polypropylene compositions. The evaluation of compositions by this method was found to correlate with that made by measuring the loss of elongation during outdoor weathering.
Recent aspects of the uncatalyzed thermal oxidation of isotactic polypropylene
Authors: Stivala S. S. , Reich Leo
Published: December 2004

The authors previously reported work on the kinetics and mechanism of the uncatalyzed thermal oxidation of isotactic polypropylene. The data, obtained form infrared absorption spectra of the carbonyl region, was utilized in developing the theoretical expressions presented. This paper summarizes this work and presents further evidence which substantiates the derived expressions. The additional evidence is obtained from infrared absorption spectra involving the apparent hydroperoxy region and from measurements on the rate of formation of volatile products. Some recent pertinent literature is also discussed.
Rate dependent response of modified polystyrene to multiaxial loading
Authors: Walker D. A. , Roberts L. R.
Published: December 2004

The balance of engineering properties of rubber‐modified polystyrene make it attractive for many applications, but it is difficult for the design engineer to relate laboratory data to service requirements because of differences in strain rates, temperatures, etc. Data are presented which show how the toughness and stiffness of an appliance‐grade, impact polystyrene vary with impact velocity (or loading rate), temperature, fabrication method, and pigment level. The ability to survive multi‐axial impact loads is strongly dependent on loading rate; a maximum in energy‐absorbing ability was observed in the range 500–2000 in./in./min, where the failure mechanism changed from ductile to brittle.
Mechanisms contributing to the autoxidation of hydrocarbon polymers
Authors: Hawkins W. Lincoln
Published: December 2004

Hydrocarbon polymers and many polymers which contain hydrocarbon segments are oxidized by a free‐radical, chain mechanism. In most commercial polymers, radicals which initiate this chain reaction originate from such reactive products as hydroperoxides rather than from cleavage of CH or CC bonds. These intermediates are formed in many polymers by preoxidation reactions occurring during synthesis and formulation. The dependence of autocatalysis on the homolytic decomposition of hydroperoxides is evidenced by inhibition reactions in which peroxide deactivators are used rather than chain terminating stabilizers.

Hydroperoxides are decomposed by certain types of stabilizers into nonradical products, and the oxidation of polymers which oxidize through these intermediates does not become autocatalytic. Sulfur compounds and high concentrations of carbon black inhibit oxidation of hydrocarbon polymers primarily by this mechanism. Other types of peroxides, e.g., diperoxides and cyclic peroxides, which may be formed during autoxidation of certain hydrocarbon polymers, are much more stable to decomposition by sulfur compounds.
Creep experiments and examples for viscoelastic material under combined stress with abrupt changes in state of stress
Authors: Onaran K. , Findley W. N.
Published: December 2004

Creep experiments under combined tension and torsion loading are reported for tubular specimens of polyvinyl chloride copolymer. Experiments include a sequence of several combinations of tension and torsion on each specimen with abrupt changes between combinations, including reversal of sense of torsion, recovery and reloading after recovery.

Results show a strong path and time dependence for the strain and for the direction of the strain‐rate vector at constant state of stress following a change in state of biaxial stress.

The character of the results is described reasonably well by the Boltzmann superposition principle of linear viscoelasticity using a constitutive equation of the form:
equation image
Examples are given of the use of this equation for common states of stress.

Better agreement with the data is obtained from a similar but non‐linear equation employing hyperbolic sine functions of stress.
Brief review of biochemical degradation of polymers
Authors: Kulkarni R. K.
Published: December 2004

Proteins and synthetic polypeptides undergo specific catalytic cleavage by enzymes. It is the object of this article to review the specific hydrolytic, redox, and electron transfer reactions involving enzymes and their mechanisms. The stability of the synthetic high polymers in the biochemical environments is much higher than that of proteins in general, but the increasing use of these materials in the field of surgical implants and internal prostheses has necessitated the systematic long range study of the systems in these surroundings. The enzymatic attack on the synthetic polymers has not been the subject of general study until now, but the intimate knowledge of the specificity and mode of attack of the enzymes, in case of the proteins, would pave the way towards experimental designs to elucidate the comparative stability of various synthetic plastics in these environments. The study of the correlation of the mechanical strength and the chemical structures of these polymers tested as implants in living animals is reviewed, and the suitability of several synthetic polymers for this application is discussed.
The calculation of screw characteristics for the extrusion of non‐Newtonian melts
Authors: Kroesser F. W. , Middleman S.
Published: December 2004

Common methods of calculating screw characteristics are reviewed, and predictions of performance based on these techniques are compared with those based upon the exact solution for simultaneous pressure and drag flow in a plane infinite slit. The error made in superimposing pressure and drag flow, as if each were independent of the other, is indicated. Some brief remarks are also made with regard to the effect of transverse (cross‐channel) flow on the output of the extruder.
Internal stresses developed in an epoxy resin potting compound during long‐term storage
Authors: Steele Doris V.
Published: December 2004

Strain gage techniques have been developed to monitor the internal stresses in epoxy resin castings. The data obtained are a measure of the stresses developed on a transducer held in the center of a mass of polymerizing epoxy resin or those caused by thermal cycling of the potted unit at intervals of storage time. Results show that the stresses developed on the transducer during the first 70 hours of room temperature polymerization reached 900 psi in axial compression. Further polymerization during storage increased the stress to 2300 psi after 12 months. During thermal cycling approximately 10,000 psi compressive stress was developed at −54°C. These stresses were relieved at 71°C but reappeared at the lower temperatures upon subsequent cooling.
Effect of type and amount of comonomer on the properties of four copolymers of ethylene
Authors: Alexander R. L. , Anspon H. D. , Brown F. E. , Clampitt B. H. , Hughes R. H.
Published: December 2004

The plastics industry is now coming to realize that copolymers are unique thermoplastics which have broad areas of application. It is believed that ethylene‐methyl acrylate copolymers of 2 melt index may be extrusion coated to paper by a cap‐coat process or by use of a chill roll with an adhesive coating. Copolymers of ethylene and vinyl monomers can be made into film by the same methods used for polyethylene. Methyl acrylate and methyl methacrylate copolymers may be processed on a wide range of molding equipment. Table VII in the article gives a list of applications for each polymer, along with expected physical properties.
Strength of polybenzimidazole and phenolic laminate‐to‐metal joints
Authors: Strauss Eric L.
Published: December 2004

Stress concentration effects and strengths of bonded and bolted butt joints were investigated for a glass fabric polybenzimidazole lalminate at room temperatuer and 700°F for a gloass fabric phenolic laminate at room temperature and 500°F. Specimen configurations included: (1) standard tensile specimen, (2) stress concentration specimen, (3) bolted double shear butt joint, (4) bolted single shear butt joint, (5) bonded double shear butt joint and (6) bonded single shear butt joint.

Both polybenzimidazole and phenolic laminates exhibited high room temperature tensile strengths and little degradation of that strength occured as a result of elevated temperature exposure. However, low joint effencies (22 to 32%) were obtained for bolted butt joint specimens. Although bonded joints exhibited higher efficiencies, they suffered from a thermal expansion mismatch between the plastic laminate and the Inconel butt plates.
The mechanism of thermal degradation of certain polyether‐polyurethans
Authors: Ingham J. D. , Rapp N. S.
Published: December 2004

This paper is an account of some studies of the mechanism of degradation of an uncrosslinked polyurethan prepared from poly(propylene oxide) (PPO) and 2,4‐tolylene diisocyanate (TDI) at temperatures up to 320°C in a vacuum or inert atmosphere. Fractionation of polymers before and after degradation provides information about the mechanism of degradation since the molecular weight distributions obtained are dependent on the mode and sites of bond scission. A recent publication describes the column elution method of fractionation developed for undergraded and slightly degraded PPG‐TDI. PPO‐TDI gives essentially most probable molecular weight distributions at an initial intrinsic viscosity [η] of ∼ 0.68 dl/g and also after degradation to [η] ∼ 0.24 dl/g. This invariancy of the distribution strongly suggests a randon scission process. Other types of degradation, e.g., free‐radical unzipping initiated at the chain ends, could also give invariant most probable distributions. However, such depolymerizations would be accompanied by much larger extents of volatilization than were observed for these polymers (<5% volatilization).
Monitoring the curing process of reinforced plastics structures
Authors: Kinna Marlin A. , Warfield Robert W.
Published: December 2004

The feasibility of monitoring curing processes in large reinforced plastics structures by electrical volume resistivity techniques has been studied. It has been found, by embedding electrodes and thermocouples within a heavy‐walled structure during fabricaton and by monitoring the change is resistance during the curing process, that information indicative of the rate and extent of curing can be obtained. The resin system used in this study was Epon 826/MNA/BDMA.
Effects of moisture on glycidyl reactions with carboxylic acid anhydrides
Authors: Kaplan S. L. , McAllister L. E. , Stewart A. T.
Published: December 2004

Moisture present in epoxy anhyride composites may hydrolyze the anhydride and cause major changes in the mechanical and chemical properties of the final composite. Heat distortion data and infrared spectroscopy are used to analyze the changes caused by the presence of the moisture. As the concentraton of water is increased, there is a decrease in the heat distortion or gass transition temperature. The decrease is due to a change in the crosslinking network and is caused by the reduction of the functonality of the epoxy group for acid as compared to the anhydride. Where rigid specifications must be met it is essential that the moisture level in the fillers, resins, etc. be kept constant.
Evaluation of methods for the determinaton of resin advancement in asbestos‐phenolic prepregs
Authors: Shuman W. P. , Wronski J.
Published: December 2004

The determination of the state of resin advancement in asbestos‐phenolic prepregs is important to the processor of this material. Many tests have been proposed for measuring this condition. In this article the follwing tests were made on the prepreg and resin extracted from the prepreg to measure advancement: viscosity, Chang Index,‐infrared absorption dielectric constant, dissipation, dielectric constant, and dissipation factor, volume resistivity, and tear strength. Infrared absorption, dielectric constant, and dissipation factor correlated best and were the most sensitive indicators of resin advancement.
The significance of slip of polymer melt flow
Authors: Westover R. F.
Published: December 2004

Some recent observations of catastrophic yielding or bimodal flow behavior in linear polyethylene melts have indicated certain inadequacies in the commonly accepted flow theories and practices. Examples of some “non‐ideal” behavior are presented along with some evidence that slip at or near the polymer‐die interface, rather than a flow phenomenon, is the mechanism associated with the discontinuity in the flow curve. The discontinuity shear stress is observed to be independent of hydrostatic pressure. The significance of this bimodal flow behavior is related to polymer processing problems.
A method of rapid determination of thermal expansion and apparent second‐order transition temperature of polymer films
Authors: Rothstein Edwin C. , Spechler Daniel
Published: December 2004

An Instron tensile tester has been modified to measure the thermal expansion of polymer films. The method greatly simplifies the experimental procedure necessary for the standard ASTM dilatometric thermal expansion measurement, particularly for thin films. Thermal expansion measurements were made for films of polyester, polycarbonates, vinyls, cellulosies, and polyolefins from room temperature up to 300°F. Second‐order transition temperatures were determined by plotting thermal elongation vs temperature; the transition temperature is indicated by a change in slope. Both expansion coeffcients and transition temperatures as determined by this method give excellent agreement with values reported in the literature.
Photometric method for measuring crazing in transparent plastic materials
Authors: Leghissa Sabino , Salvatore Osvaldo
Published: December 2004

An optical method has been developed to provide quantitative results useful for characterizing the crazing of transparent plastics. The procedure consists of the detection of discontinuities in a beam of light that scans the specimen in a direction perpendicular to the line of crazing. The light is transmitted to a photomultiplier that is connected with an amplifying system and a recorder that provides a diagram of the light energy modulated by the lines of crazing. The specimen is scanner both before and after subjecting it to a treatment that causes crazing, and the crazing index is considered to be the difference between the area below the two curves.
Static coefficients of friction for polyethylenes
Authors: Friehe C. A.
Published: December 2004

The static coefficients of friction of solid polyolefins against metal surfaces has been determined as functions of pressure, temperature, and metal surface finish. The polymers studied were a low debsity (branched) polyethylene, a high density copolymer, and a high density (linear) polyethylene homocopolymer, and a high density (linear) polyethylene homopolymer. Four metal surfaces were used, with surface roughnesses ranging from 1 1/2 to 18 microinches. The pressure and temperature ranges were 0 to 355 psig and 72 to 225°F, respectively. Data were obtained for the polymers in two forms: granules and flat smooth dise, except for the high density homopolymer which was tested in the disc from only. In general, the results indicated that, for all granules, the coefficient was essentially independent of pressure, but decreased with increasing temperature until the melting point was reached; it varied with metal surface roughness which was greatest for the low density polymer. For the smooth surfaced disc samples, the coefficient also decreased with increasing pressure with high values at low pressure indicating strong adhesion between the polymer and metal surfaces.
Stress rupture of polypropylene
Authors: Forsman J. P. , North H. C. , Hakala T. H.
Published: December 2004

Tensile stress rupture is an important engineering property of plastics required in desiging parts subject to continuous or intermittent stress over long periods of time, especially in corrosive environments. This paper presents tensile stress rupture results on polypropylene and some of their applications in a program conducted over the past several years. Among the structural and compositonal paramaters studied in this work are the effects of molecular weight, molecular weight distribution, isotactic content, polyblends, and fillers on the shape and slope of the stress rupture‐time curve. Data are presented showing the interrelationships between these variables, and the agreement with current stress rupture theories is discussed.
Fundamentals of melt rheology, heat generation, and heat transfer as applied to polymer processing
Authors: Carley James F.
Published: December 2004

The flow of polymer melts is normally laminar, but pseudoplastic in character. That is, flow rate increases in proportion to a power higher then 1, usually between 1.5 and 4, of the applied pressure difference. Viscosities are extremely high—more then a mollion times that of water—so considerable heat is generated in the flowing melt by viscous dissipation of flow energy. This mode of heat generation is put to good practial use in the screw extruder, a device that converts plastic pellets into hot melt for shaping into pipe, sheets, coatings and molded products. Equations are given for computing flow rates and viscous dissipation rates. Heating (except by viscous working) and cooling of polymers are slow processes because all these materials are poor heat conducts nad their extreme viscosities make convection impracticable. The princliples of heat transfer are reviewed, and the solutions are given for some transient‐conduction problems frequenlty encountered in processing. Equations are given for judging the operation of extruders.
Fundamentals of plasticating extrusion. III. Development of a mathematical model
Authors: Klein Imirich , Marshall D. I.
Published: December 2004

This article describes a general mathematical model summarized in the form of a computer program for the plasticating extruder. The model combines features of the metering‐zone model previously published, the melting‐zone model described in paper No. I of this series, and a feed‐zone model based on an extension of known theories. It is based on theoretical models for each zone unified and improved by non‐linear estimation to accurately describe the extrusion experiments.

The mathematical model predicts temperature, pressure, and melt channel width profiles of the plastic being processed in the plasticating extruder as a function of design and operating variables of the machine. It enables for the first time the design of the whole machine based on temperature and pressure profiles, including new combinations of cylindrical and tapered roots.
Non‐Newtonian tangential flow in cylindrical annuli. IV
Authors: Tadmor Zehev
Published: December 2004

Tangential flow of a “power law” model fluid between two concentric cylinders is analyzed. A constant angular pressure gradient is imposed and one of the cylinders is rotating at a constant angular velocity. This type of flow is of interest in screw extrusion theory. The error in the superposition, i.e., linear addition of tangential pressure and drag flows, for a “power law” model fluid, is quantitatively calculated and plotted in the form of a correction factor. Tangential pressure flow is compared to a pressure flow between parallel plates and additional correction factor to account for the curvature is derived and plotted. The applicability of the “power law” model for flow of polymer melts in extruders is also discussed.
Fractional crystallization of polypropylene
Authors: Kamath Pandurang M. , Wild Leslie
Published: December 2004

The development of a fractional crystallization technique for characterization of polypropylenes with respect to stereoregularity is described. It is a simple technique which is attractive for routine analysis and under suitable conditions yields quantitative data with good reproducibility. Separation by fractional crystallization from hot xylene solution is shown to take place according to polymer crystallizability and is relatively independent of molecular weight. It thus represents an alternative and in some ways superior approach to the more commonly used fractional extraction method. Preliminary work indicates that the fractional crystallization method may prove of value in establishing correlations between the stereoregular nature of polypropylenes and their physical properties.
AI polymer laminates for high temperature stability
Authors: Bolton B. A.
Published: December 2004

Amoco AI amide imide polymer is an all aromatic polymer which is currently being used as a high temperature wire enamel. It also looks promising as a high temperature laminating material. It is available in a stable solid form and is readily formulated in its laminating solvents. B‐Staged coated glass cloth with excellent shelf stability is easily prepared. AI laminates retain their initial flexural strength after four weeks at 500°F. They retain 50% of their initial flexural strength after one week at 572°F. Other modifications of this type of polymer are being investigated as laminating materials.
Stabilization of polypropylene
Authors: Gordon D. A. , Rothstein E. C.
Published: December 2004

Antioxidants and UV absorbers are vital to the commercialization of polypropylene because of their influence on this polymer's light stability, heat or oxidative stability, processing stability, and gas fading due to nitrogen oxides. The effects of these stabilizers are measured in terms of polypropylene's initial color, color retention, and retention of physical properties when the polymer is exposed to direct weathering and to elevated temperatures. The relative washfastness or resistance to extraction by aqueous systems under various laundering conditions is another important, measurable property of UV absorbers and antioxidants in polypropylene. Such measurements are usually made using stabilized polypropylene molded plaques and monofilaments containing UV absorbers, antioxidants and, often, combinations of the two.
Properties of a propylene‐ethylene block copolymer
Authors: Tusch R. L.
Published: December 2004

Although polypropylene has a unique combination of properties, its impact strength at low temperatures is sometimes insufficient. This need has been met by polypropylene/polyisobutylene blends. Today, polypropylene type copolymers (block copolymers) are available with low temperature toughness and property and processing advantages over the above blends. Ordinarily, copolymers from addition polymerization are random. In a block copolymer, the monomeric units of propylene are segregated from those of the second monomer. A block copolymer, propylene, low pressure polyethylene, ABS and polypropylene‐polyisobutylene blends are compared as to general and mechanical properties, stress relaxation, stress rupture performance, low temperature performance (impact strength), high temperature performance (flexural stiffness) and processability. Not every material was used in each test. Block copolymers find applications in automotive and appliance industries, industrial parts and packages for cosmetics and food.
Thermal conductivity of high polymers—the influence of molecular weight
Authors: Hansen David , Kantayya R. C. , Ho C. C.
Published: December 2004

Some earlier observations on the influence of molecular weight, plasticizer, and irradiation on the thermal conductivity of polymers is reviewed. Also some new data on polystyrene and some new calculations based on the theory of Hansen and Ho are presented. These data show almost a two fold increase in the thermal conductivity of polystyrene as the molecular weight goes from 900 to 100,000. Data on the moleculer weight effect on thermal conductivity appear to be consistent with the theoretical calculations.
Long‐term hydrostatic strength characteristics of thermoplastics pipe
Authors: Reinhart Frank W.
Published: December 2004

A method for developing long‐term hydrostatic design stresses, defined as the estimated tensile stress in the wall of the pipe in the circumferential orientation due to internal hydrostatic pressure that can be applied continuously with a high degree of certainty that failure of the pipe will not occur, for thermoplastic pipe materials is described. The background information used to develop this method, data to confirm its validity, and several of its more important peculiarities are presented and discussed. The method treats hydrostatic stress–failure time test results by the method of least squares with time as the dependent variable. The long‐trem performance of thermoplastic pipe materials is evaluated by stresses calculated for periods of 100,000 hours (11.43 years) and 50 years.
Kinetics of the thermal degradation of linear polyethylene
Authors: Arnett Raymond L. , Stacy Carl J.
Published: December 2004

For a system of equivalent bonds undergoing random bond scission it is reasonable to assume that the rate of bond breaking (hence the rate of creation of new molecules) reported in the literature and data presented here demonstrate that the number of molecules created is not proportional to the time of thermal treatment hence they seem to belie this reasonable hypothesis. Other authors have adduced the presence of some non‐equivalent bonds in order to account for the observed cruvature and still retain the hypothesis. Implicit in these arguments is the assumption of a steady‐state concentration of reactive fragments. Our analysis explores the consequences of abandoning the steady‐state assumption and shows that a quantitative explanation of the observed degradation behavior may be had by this means wihile still retaining the hypothesis of a constant probability of a bond being broken per unit time.
Residence time dependence of molecular weight distributions in continuous polymerizations
Authors: Biesenberger J. A. , Tadmo Z.
Published: December 2004

Residence time distribution (RTD) is a spectral property of contiuous chemical reactors. Batch reactors may be viewed as having “monodisperse” residence time distributions. This article discusses molecular weight distributions (MWDs) of polymeic materials formed in continuous and in semicontinuos process and how they are affected by reaction time distributions. All synthetic high polymers, even those Prepared in batch reaction, possess a MWD which may sometimes, for a given monomer, be altered chemically by a proper choice of catalyst and diluent. An interesting concept suggested by the present work is the prospect of “tailoring” the MWD for a given monomer‐catalyst‐diluent system physically by selecting appropriate reactor conditions. Hence, althought this work involves analysis the results may provide a guide to synthesis.
Velocity profiles of the exit region of molten polyethylene extrudates
Authors: Gogos C. G. , Maxell Bryce
Published: December 2004

The objective of the work described herein is the experimental investigation of the velocity field of polymer melts flowing through a capillary in the regons of flow prior to and after the capillary exit. The fluids studied are branched polyethylene melts in steady laminar isothermal flow. The technique employed for the determination of the Eulerian velocity profiles is one that utilizes phototomicrogroaphy of the reflected light from tracer particles dispersed in the flowing medium.

Axial acceleration of the fluid elements just before the capillary exit was observed. It was found that this accelearation is more pronounced in melts of low bulk viscosity. This observation region, non‐viscometric.

The translation of the velocity profiles of the fluids studied, from one resembling a parabola to that of “plug” flow, involves inflection points with minima in the velocity vector v(r, z). These minima appear near the surface of the extrudates and can not be accounted for by an existing theory.

It was also found that the density of the viscoelastic fluids studied is a function of the axial position, in the region of flow investigated. The density decreases before the exit and, before it reaches an equilibuiu value at an axial position downstream equal to one or two diameters, increases beyond that value upon exit. This phenomenon is attributed to an “overshoot” in the process fo elastic recoil of the high polymer melts fron a strained structure to a random one.
Fatigue mechanisms of thermoplastics
Authors: Riddell M. N. , Koo G. P. , O'Toole J. L.
Published: December 2004

Failure in fatigue by the mechanism of crack initiation and propagation originationg at flaws and stress concentrations has been fairly well established. It explains the fatigue phenomena in highly elastic materials, namely metals and certain thermosetting plastics such as reinforced polyester and epoxy resins. We have found, however, that a different mechanism dominates the fatigue behavior of thermoplastics. Specifically, the mechanism involves the generationa of heat within the material due to viscous damping or hysteresis. This paper presents fatigue, damping data and temperature measurements during cyclic stress to support this conclusion on three themoplastic resins of widely different mechanical properties, polyetrafluouoethylene (PTFE), Nylon 6, and polymethyl‐methacrylate (PMMA). In addition to the usual S‐N fatigue curves, we wil show how surface temperature changes with fatigue life and how this change is affected by stress, Frequency, crystallinity, specimen geometry and other parameters. Alos, the loss compliance of the materials will be presented as afunction of temperature to show the relationship of fatigue to damping properties.
Deformation of free holes of arbitrary shape in a viscoelastic plate
Authors: Wachs M. H.
Published: December 2004

Two independent methods for predicting the deformation of free openings of arbitrary shape in a viscoelastic plate are illustrated.

The first method is experimental and is based on the interference of two systems of lines representing the initial and final positions of the material. To demonstrate the moire method, the creep compliance function for polymethylmethacrylate is determined as preliminary information. This function is used as input data in the ensuing theoretical analysis to insure realistic viscoelastic behavior.

The second method involves techniques to approximate viscoelastic displacements from known elasticity solutions and known material properties.

The methods are applied to two examples: (1) The square hole—to determine the motion of an opening of complicated shape; and (2) an ellipse loaded at 45°—to indicate qualitative agreement with an existing prediction of the motion of cracks in a viscous plate.
Comparative swelling behavior of various thermoplastic polymers
Authors: Metzger A. P. , Matlack J. D.
Published: December 2004

The elasticity of polymer melts is of major concern in the processing of plastics. It is usually reflected by dimensional changes. Since the swelling of polymer extrudates depends on the capillary dimensions and the volumetric flow rate, the blow‐up must be examined over a range of conditions. Of course, the swelling is also dependent on polymer structure. Consequently, variations in materials and operating conditions necessiate changes in tooling. This paper describes the swelling behavior of several different polymer types and illustrates that viscosity measurements can not be used to predict elasticity.
Dynamic mechanical properties of polymer melts: The effect of molecular weight distribution on the temperature dependence of viscoelastic properties
Authors: Chartoff Richard P. , Maxwell Bryce
Published: December 2004

An experimental investigation of the dynamic mechanical response of molten polymers was performed using the Maxwell Orthogonal Reheometer. One purpose of the study was to evaluate the effect of molecular weight distribution on the temperature dependence of viscoelastic properties. Data were obtained over a range of temperatures for both monodisperse and polydisperse materials which indicate that viscoelasticity is highly temperature dependent only for monodisperse polymers. On a molecular basis the reduction in temperature sensitivity for polydisperse materials logically can be attributed to the influence of the low molecular weight species present in a distribution on the relaxation spectrum. Since the relaxation spectrum largely determines all viscoelastic functions, the observations made from th dynamic data shown in this paper can be generalized to all viscoelastic experiments.
Dependence of mechanical properties on molecular motion in polymers
Authors: Boyer R. F.
Published: December 2004

Considerable progress has been made in the past 20 years in the synthesis, characterization and fabrication of plastics. Previous SPE Award winners, such as Mark, Natta, and Marvel dealt largely with synthesis; Flory with characterization; Alfrey and Du Bois with fabrication. One of the still unsolved problems lies in the realm of relating mechanical properties, such as impact strenght and creep to molecular structure.

The design enginner who wishes to use a plastic part is concerned primarily with how some property such as impact strenght varies with temperature, speed of test, test method, etc. The polymer scientist must know why. Through knowing why, he may be able to design better plastics.

This paper attempts to survey some of the world‐wide progress made in this area in the past 10 years. The ultimate goal is to understand these mechanical properties in terms of internal molecular motions which occur in solid polymers. Internal motion can be detected by electrical, electromagnetic and dynamic mechanical measurements. When these three methods are applied on a given polymer over a range of temperatures, insights can be gained as to the variation of impact strength and other properties with temperature and frequency for that same polymer. These three fundamental methods, which require very small samples (less than 50 grams), can provide insight into the practical behavior of plastic materials over the wide range of temperatures and frequencies encountered in the real world.
Morphology of quenched polypropylene
Authors: Gezovich D. M. , Geil P. H.
Published: December 2004

The morphology of the quenched form of polypropylene was investigated. Thin films of the quenched form consist of small ball‐like structures which we suggest are defective hexagonal crystals. In thicker films they aggregate to form spherulites with no observable fine structure. Quenching of thin films of molten polypropylene to a temperature below 0°C results in the formation of numerous, isolated monoclinic spherulites with a better defined morphology than the smectic spherulites obtained by quenching above 0°C. This result suggests that the films (quenched below 0°C) were quenched to the glass and subsequently crystallized to the monoclinic form upon heating to room temperature.
Properties of block versus random copolymers
Authors: Kenney J. F.
Published: December 2004

Physical and mechanical properties of block copolymers are compared and correlated with the corresponding random copolymers. The important properties of melting point, transition temperatures, tensile strength, modulus, and elastic properties depend upon the structural arrangement of the molecular units comprising the polymer strecture. All available data suggest overwhelmingly that properties of block copolymers are superior to those of random copolymers. A block copolymer can have properties characteristic of each of the homopolymers from which it is derived as well as a set of properties due to the polymer strcture as a whole. Block copolymers have an advantage over random copolymers in that a crystalline polymer can be modified without significant reduction of its melting point, modulus, tensile strength, and elastic properties, and by suitable selection of a second component it affords a means of “building in” a particular property.
Spiral and helical fractures
Authors: Gillham J. K. , Reitz P. N.
Published: December 2004

Spiral and helical fractures can be formed around high‐modulus filaments and yarns which are embedded in brittle, amorphous, crosslinked resins. The phenomena are of particular interest because the stress field imposes a highly regular geometry upon the propagating fractures, and because the formation of the large surface area of the spiral fractures provides an efficient mechanism for dissipating strain energy. Development of the approach of the production of discrete geometrical voids with large surface area at predicatable sites may well provide resistance to impact in inherently brittle materials.
Morphology and properties control on rubber‐epoxy alloy systems
Authors: Hsich Henry S.‐Y.
Published: December 2004

Morphology and properties of polymer alloys can be controlled by thermody‐namlcally reversible (structure freeze‐in) or irreversible (structure lock‐in) processes by simultaneously manipulating miscibility, mechanisms of phase separation, glass transition temperature (structural relaxation), and cure kinetics of polymer systems. Using phase diagrams consisting of binodal and spinodal curves, the morphology of epoxy/CTBN (carboxyl‐terminated butadiene acryloni‐trile copolymer) systems can be controlled by the mechanism of nucleation and growth or by spinodal decomposition via simultaneously manipulating the kinetic processes of phase separation and curing reactions. We have found that the particle size of the rubber reinforcement in epoxies is affected by the mechanisms of phase separation. Phase separation by nucleation and growth gives larger rubber particles than the corresponding phase separation by spinodal decomposition. This contrast in the morphology development is the consequence of controlling phase separation through chemorheological behavior. Medication of the phase separation kinetics in epoxy/CTBN systems was extremely effective at altering both morphology and properties of these alloys. This technique offers a means to shift the glass transition temperature of the rubber‐rich phase drastically without reducing the glass transition temperature of the epoxy‐rich phase significantly. Such control over morphology is the key to ultimately controlling material properties. This morphology manipulation allows us to tailor the mechanical properties of alloy systems.
Mechanical fracture behavior of polyacetal and thermoplastic polyurethane elastomer toughened polyacetal
Authors: Chang Feng‐chih , Yang Mi‐Yun
Published: December 2004

Polyacetal (POM) toughening with thermoplastic polyurethane (TPU) elastomer was investigated in terms of Theological, mechanical, and morphological properties. Polyacetal can be effectively toughened by the blending with TPU elastomer and the improvement on toughness is found most significant with TPU content from 20 to 30 percent. POM does fracture in ductile mode under extremely low deformation rate and the ductile‐brittle transition rate is at 0.5 mm/min. The transition rate is increased with the increase of elastomer content. The precrack hysteresis energy is important in dictating the failure mode. The experimental results show the hysteresis energy (under constant load) increases with the increase of elastomer content and the decrease of deformation rate. Greater hysteresis energy results in larger precrack plastic zone size and thus tends to shift the fracture mode from brittle to ductile as the critical size of the plastic zone is reached. The adoption of the slow rate fracture method has the advantages of ranking toughness of very brittle polymeric materials vs. the conventional Izod or Charpy impact method by varying temperatures. FTIR shows significant interaction between POM and TPU which is probably responsible for the TPU elastomer being such an efficient toughening agent for POM. Delamination in the buffer zone between the plane‐strain and the plane‐stress is discovered and the possible mechanism is discussed.