bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

AbstractThis 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

AbstractFatty 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

AbstractThe 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

AbstractThis 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

AbstractPossible 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

AbstractMany 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

AbstractThe 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

AbstractThe 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

AbstractHydrocarbon 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

AbstractCreep 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

AbstractProteins 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

AbstractCommon 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

AbstractStrain 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

AbstractThe 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

AbstractStress 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

AbstractThis 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

AbstractThe 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

AbstractMoisture 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

AbstractThe 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

AbstractSome 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

AbstractAn 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

AbstractAn 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

AbstractThe 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

AbstractTensile 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

AbstractThe 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.