bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dispersion viscosity of aluminum trihydroxide of various particle size distributions in an unsaturated polyester resin
Authors: Hsieh H. P. 
Published: December 2004

AbstractThe effect of filler particle size distribution on the viscosity of an aluminum trihydroxide/unsaturated polyester resin dispersion was studied. Four basic aluminum trihydroxides with distinctively different particle sizes were combined to generate various particle size distributions systematically. The particle size distribution producing the minimum viscosity was determined by employing a modified extreme vertices experiment design for mixtures to establish a quadratic model which was then optimized. The predicted viscosities in general as well as the particle size distribution corresponding to the minimum viscosity agreed well with the observed data.
Polymerization of α, α‐disubstituted‐β‐propiolactones and lactams. 9. ABA block copolymers of α‐methyl‐α‐butyl‐β‐propiolactone and pivalolactone
Authors: Lenz Robert W. , Dror Michael , Jorgensen Robert , Marchessault Robert H. 
Published: December 2004

AbstractABA block copolymers were prepared by the anionic polymerization of α‐methyl‐α‐butyl‐β‐propiolactone, MBPL (B block), and pivalolactone, PL (A blocks). The MBPL block had a very low decree of crystallinity and a glass temperature of − 13°C, so phase separation with extensive crystallization of the PL blocks gave thermoplastic elastomers when the MBPL block constituted the principal and continuous phase. The observed crystallinity and melting point of 40–45°C in the MBPL homopolymer have not been previously reported. Measurements were obtained by electron microscopy of the initial size distribution of the PL domains as a function of copolymer composition and degree of polymerization, and on the effect of annealing on this parameter. Tensile strengths and elongations at break were both less than those previously observed for equivalent ABA block copolymers of PL and α‐methyl‐α‐propyl‐β‐propiolactone.
Theoretical analysis on the flow of melts in a curved circular tube
Authors: Akita Osamu , Ito Katsuhiko 
Published: December 2004

AbstractA theoretical study is made of molten polymer flow in a curved circular tube. To obtain the velocity profile formed in the tube, a variational approach is used. A variational equation for viscous dissipation has been so determined that its Euler equation satisfies the equation of motion. An approximate velocity profile which satisfies the prescribed boundary conditions is assumed as a function involving unknown coefficients and is substituted into the variational equation to determine the unknown coefficients. Various velocity profiles of polymer melts for different flow behavior indices have been obtained under the assumption that polymer melts obey a power law.
A proposal for a coefficient of hygroelasticity
Authors: Cohn Daniel , Marom Gad 
Published: December 2004

AbstractSwelling and hygroelasticity of polymers are discussed in terms of a coefficient of hygroelasticity defined here by analogy with the coefficient of thermal expansion. The relationship between the proposed coefficient and the mechanical properties of the material and the stresses which develop in it is established. The relationship provides means for predicting the lifetime of the polymer under conditions similar to those used for measuring the coefficient of hygroelasticity. The experimentally examined behaviors of two systems, polyester‐boiling water and epoxy‐methylene chloride at 18°C, are in reasonable agreement with the predictions.
Material response and reversible cracks in viscoelastic polymers
Authors: Wool Richard P. 
Published: December 2004

AbstractDeformation processes in viscoelastic polymers are examined in terms of an energy balance involving work, strain energy, viscous dissipation and damage. The concepts of time dependent damage and reversible cracks are presented. The latter, while giving rise to novel mechanical behavior in viscoelastic materials, are important considerations in temperature dependent recovery phenomena of deformed polymers. Constitutive equations are derived for systems with reversible cracks analogous to Maxwell and Kelvin viscoelasticity models. Retractive forces arising from crack closure occur by conversion of surface energies to strain energy and subsequently to mechanical work. This effect is investigated during contraction of hard‐elastic polypropylene fibers under constant load at different temperatures.
Fracture of fibrous polymers
Authors: Peterlin A. 
Published: December 2004

AbstractThe fibrous material obtained by drawing or extrusion exhibits a more than linear increase in the axial elastic modulus with draw ratio, a much slower increase in tensile strength and a decrease in strain to break. The reason for such a behavior is found in the existence of structural defects of fibrous material, which is composed of very long and narrow microfibrillar elements. At their ends the axial connection by taut‐tie molecules is almost completely interrupted. Hence the transfer of tensile stress through such a defect is only possible by lateral shift of the load to adjacent microfibrils. The incompleteness of this transfer, the excess straining of the material in the defect area, and the relatively easy axial displacement of the ends of microfibrils favor the local formation of microcracks which grow and coalesce with close‐by microcracks until a critical size crack is formed and the strained sample fails. The process is favored by a high elastic modulus of microfibrils which is practically identical with that of the drawn or extruded sample. Hence the fibrous polymer fails at lower strain the higher its axial elastic modulus, i.e., the higher the draw ratio.
Microscopic flow and failure processes in polymer glasses
Authors: Morgan Roger J. , O'Neal James 
Published: December 2004

AbstractThe microscopic flow and failure processes, the structural parameters controlling these processes, and how such processes are modified by the service environment are presented for three classes of polymer glasses: polycarbonate, polyimides, and epoxies. The microscopic flow characteristics of polycarbonate are controlled by (a) the ease of shear band deformation which depends on free‐volume and previous thermal history and (b) surface crazes whose characteristics depend on exposure to organic compounds, thermal history, and to surface crystallization and fabrication stresses. Polyimides deform and fail in the bulk by crazing with extensive fibrillation. The growth and development of shear bands from microvoids in polyimides are discussed. Epoxies predominantly deform and fail by crazing with regions of high crosslink density remaining intact during the flow processes. Craze cavitation and growth are enhanced in epoxies by the presence of absorbed moisture.
Effect of temperature on the compressive stress‐strain properties of polystyrene
Authors: Beatty Charles L. , Weaver Judith L. 
Published: December 2004

AbstractThe compressive stress‐strain behavior of a commercial polystyrene has been studied and the effect of deformation temperature on modulus, yield stress, percent yield strain and yield energy was determined. Yield energy is the only one of these parameters that is linear with temperature in the ductile region. A change in the mode of failure from ductile to brittle occurs between 5–30°C at a strain rate of O.1/in./in./min. At all temperatures studied, the yield or fracture stress varied linearly with the rate of deformation for strain rates ranging from 0.1 to 1.0 in./in./min. The yield data as a function of temperature were analyzed via a rate expression modified to incorporate the Coulomb‐Navier yield criterion, Activation energy was found to be a function of deformation temperature with a change in slope occurring near the β transition. Activation volume increased linearly with deformation temperature, for the range studied. Agreement of dynamic mechanical and yield activation energies imply that the type of motion and the height of the energy barrier are similar for both. However, an increase in activation volume for stressed vs unstressed conditions suggests that a greater number of chain segments move as a result of stress biasing. Also the increase of both activation volume and activation energy with temperature implies that the correlated length of chain movement increases as temperature is increased. Similar to activation energy, yield stress exhibits a change in temperature dependence near the β transition. Data on other glassy polymers suggest that the highest temperature sub‐Tg, transition is related to the change in the temperature dependence of yield stress.
SPE International Award Address–1978 Barrier properties and migration problems of plastics
Authors: Stannett Vivian T. 
Published: December 2004

AbstractThe present state of knowledge of the manner in which small molecules dissolve and diffuse in plastic materials is briefly described. The advantages and disadvantages of these phenomena are outlined. Two aspects, one positive and one negative, are reviewed in more detail. The use of plastic materials as barriers to gas and vapor transport particularly in packaging applications is described and illustrated by examples. Typical permeability values for water vapor, oxygen and carbon dioxide in various polymer films are given. Values for hydrogen and helium are included to illustrate the possible use of plastic films for gas separations. On the negative side, the migration of residual monomers and other, possibly toxic, substances out of plastic materials can be a serious problem. Some of the basic considerations and practical solutions to the migration problem are discussed in more detail.
Rheological behavior of molten epoxide prepolymers
Authors: Aleman J. V. 
Published: December 2004

AbstractFlow properties of four molten epoxide prepolymers of number average molecular weight 900(I), 1,500(II), 2,100(III) and 4,000(IV), were measured at temperatures ranging from 361 to 463K, and shear rates from 500 to 10,000 s−1. Apparent shear viscosities showed that all prepolymers used have Newtonian behavior up to shear rates of 2,000 s−1. Shear thinning occurs at higher shear rates. Flow activation energies at constant shear rates in the range of 500 to 7,000 s−1 vary for prepolymer III from 5 to 24 kcal/mol, and for prepolymer IV from 9 to 25 kcal/mol. Flow indices in the same shear rate range vary for prepolymer III from 1.0 to 0.7 and for prepolymer IV from 1.0 to 0.3.
A survey of film processing illustrated with poly(ethylene terephthalate)
Authors: Heffelfinger C. J. 
Published: December 2004

AbstractPolymeric films are used to enclose other materials (as for packaging), to carry information (as for magnetic tapes), and as an engineering material (as for capacitor dielectrics). There is an appropriate combination of the bulk and the surface properties engineered to fit each particular use. This duality is illustrated by the “processing for properties” of poly(ethylene terephthalate) films. An overview is presented of stretching, stabilization and relaxation methods of manufacture. These processing techniques, in conjunction with changes in the polymer composition, provide the property levels that are commercially significant.
Anisotropy and dimensional stability of polyimide films
Authors: Blumentritt Bruce F. 
Published: December 2004

AbstractIn‐plane mechanical properties, coefficients of thermal and hygroscopic expansion, and dimensional changes due to stress relaxation were measured as a function of direction in one, three, and five‐mil polyimide films. Although these films were made by a casting process, they exhibited significant anisotropy in the properties tested. This anisotropy was apparently due to preferential orientation of the polymer which occurred during the manufacturing process.
Polymer blends containing poly(vinylidene fluoride). Part III: Polymers containing ester, ketone, or ether groups
Authors: Bernstein R. E. , Wahrmund D. C. , Barlow J. W. , Paul D. R. 
Published: December 2004

AbstractTo further investigate the nature of the specific interaction leading to the miscibility of poly(vinylidene fluoride), PVF2, with certain oxygen containing polymers, blends of PVF2 with poly(ε‐caprolactone), PCL, with poly(vinyl methyl ether), PVME, and with poly(vinyl methyl ketone), PVMK, were prepared. PVMK/PVF2 blends were found to be miscible while blends of PVME/PVF2 and PCL/PVF2 were found not to be miscible. These results show that the specific interaction with PVF2 involves mainly the carbonyl group rather than the entire ester group. The relative effectiveness of having this group in the chain or pendant to it is not yet resolved.
Application of small system thermodynamics to polymer molecules. III. Molecular fractionation and tertiary nucleation
Authors: Lindenmeyer P. H. , Beumer H. , Hosemann R. 
Published: December 2004

AbstractThe statistical mechanical methods developed in Parts I and II in this series permit the postulation of a thermodynamic criterion for the molecular fractionation which occurs during crystallization. Using this criterion we define a “local equilibrium” melting temperature as that temperature at which a polymer molecule (considered as a small thermodynamic system) has the same free energy when crystallized into the lowest possible free energy conformation on a given crystal surface (or surfaces) as it does in a completely molten state but still in contact with the same surfaces. This temperature will be a function not only of molecular length but also of the nature of the crystal surfaces to which it is exposed. Lowest “local equilibrium” melting temperatures occur on large flat crystal surfaces (secondary nucleation sites), higher temperatures result from the intersection of two crystal surfaces (tertiary nucleation sites). A number of such potential tertiary nucleation sites have been investigated and the resulting temperatures satisfactorily cover the range over which molecular fractionation has been observed.
Mechanics of crack growth in epoxide resins
Authors: Gledhill R. A. , Kinloch A. J. 
Published: December 2004

AbstractExperiments have been conducted employing tapereddouble‐cantilever‐beam joints with different epoxide adhesives. Depending on the adhesive employed, crack propagation occurred either (a) in a continuous stable manner with crack propagation velocities in the range 10−4 to 5 m/s and values of the adhesive fracture energy, GIc, being almost independent of the crack velocity, or (b) intermittently in an unstable manner when the initial crack velocity was never less than about 20 m/s and, in some instances, rose to about 450 m/s; values of GIc (initiation) increased rapidly with increasing velocity. It is proposed that the amount of localized plastic deformation arising from shear yielding that occurs at the crack tip prior to crack propagation is controlling. Secondly, the longterm strength of stressed, structural adhesive joints has been investigated. The fracture of these joints over eight decades of time is uniquely described by a critical plastic zone size developed at the crack tip at failure.
Influence of crosslinking on the tensile strength and fractography of poly(methyl methacrylate)
Authors: Lee H. B. , Turner D. T. 
Published: December 2004

AbstractGlassy crosslinked networks were prepared by copolymerization of methyl methacrylate with up to 4.7 mole‐percent ethylene dimethacrylate. These networks were degraded by exposure to γ‐rays and the solubilized fraction estimated by benzene extraction using the analysis of A. R. Schultz. The efficiency of the Crosslinking agent was found to be 0.5 and this value was used to calculate the molecular weight between crosslinks. The molecular weight of the primary molecules in the network, M, was estimatfrom the radiation dose using the known fact that one fracture requires an energy deposition of 59 ev. Crosslinking was found to have little influence on the tensile strength of networks of primary molecular weight > 105. In contrast. crosslinking raised, the strength of polymers of M < 105 to, a value approaching that of a high molecular weight linear polymer (ca. 70MN/m2). Crosslinking was found to have only a small influence on the gross morphology of fracture surfaces.
High speed electron spin resonance techniques applied to polymer fracture
Authors: Britt A. D. , Moniz W. B. , Chingas G. C. 
Published: December 2004

AbstractMechanical fracture of nylon 6 produces free radicals as a direct result of bond‐breaking; these initial free radicals rapidly decay into secondary free radicals at room temperature. Aromatic nitro‐compounds react with the initial, but not the secondary, free radicals. The rate of reaction is sufficiently fast to compete with the usual initial radical decay process, even at room temperature. Considerations involved in applying high speed (microsecond) electron spin resonance techniques are discussed.
A slender‐body theory for interfacial failure in unidirectional fiber‐reinforced composites
Authors: Goddard J. D. 
Published: December 2004

AbstractBased on asymtotic techniques which have been recently developed for the mechanics of linear continuous media containing slender inclusions, a theory is presented for the nonlinear problem of interfacial failure in a fiber‐reinforced composite. Based on the lowest order slender‐body theory, and a correspondingly simple model of interfacial slip or plastic yielding, a constitutive equation is, derived for unidirectional, dilute‐fiber composites. This equation provides a tensile stress‐strain relation which exhibits microscopic, ductile yield arising from the microscopic failure process. Approximate formulae are proposed to account for fiber interactions among closely‐spaced parallel fibers and for interfacial slip with sliding friction. It is shown that all the results can be represented in terms of a “reduced‐variable” plot, which suggests that experirniental data for various fiber aspect ratios and concentrations might he reducible to a single curve, depending only on tine mode of interfacial failure.
Failure sensitivity of high density polyethylene in compression
Authors: Clements Linda L. 
Published: December 2004

AbstractAs part of an investigation of the compressive mechanical behavior of high density polyethylene between room temperature and the crystalline melting temperature, the strain‐to‐failure as a function of temperature and strain rate was studied. The two resins studied in applied‐strain‐rate tests were found prone to fail, as judged by decreased strain‐to‐failure, at temperatures from 70 to 88°C. The strain‐to‐failure decreased as the temperature was increased or as the strain rate was decreased. This behavior is opposite to that observed in tension at lower temperatures. At temperatures just below melting, the strain‐to‐failure apparently began to increase again. By analogy to the results of tearing experiments on polyethylene and other thermoplastics, the findings are explained in terms of the influence of the α relaxation in polyethylene. Differences in the behavior of the two polyethylene resins were also examined.
Origin, extent, and effect of molecular stress concentration in fibrillar structures
Authors: Kausch H. H. 
Published: December 2004

AbstractElectron spin resonance and infrared spectroscopy investigations of the deformation of oriented polymers have given insight into the loading and rupture of chain segments. Whereas there is agreement on the phenomenology of chain scission, fiber deformation, and stress relaxation, quite controversial interpretations have been given of the observed phenomena. Particularly disputed have been the extent of interfibrillar slip, the effect of chain scission on macroscopic stress‐strain behavior, and the cause of microcrack formation. Dealing with polyamide‐6 fibers it is shown that the microfibrils do not unload through slippage and that the lateral rigidity of the crystal blocks within the sandwich‐structured microfibrils must be large enough so as to permit the build‐up of large stress concentrations. The extent of molecular stress concentration is calculated. The qualitative agreement between the slopes of stress‐strain and free radical‐strain curves is analyzed. Unless this agreement is coincidental, it can be sought in an amplification effect accompanying the rapid release of stored elastic energy. The ensuing local temperature rise will facilitate the extension of kinked chains tinder annihilation of kinks. This is practically equivalent to unloading those chains without breaking them. The formation of submicrocracks is not related to the breakage of chains. The direct influence of submicrocracks as potential stress concentrators is weak and ineffective with regard to accelerating chain scission.
The load‐bearing capability of short‐fiber thermoplastics composites—A new practical system of evaluation
Authors: Stephenson R. C. , Turner S. , Whale M. 
Published: December 2004

AbstractThe load‐bearing capabilities of short‐fiber reinforced thermoplastics composites can be evaluated, in principle, by the methods known to be satisfactory for unreinforced thermoplastics, but in practice the cost of a comprehensive evaluation of a composite would be prohibitive because of the anisotropy of the properties and its variation from point to point. For the same reasons the properties measured on a specimen cut from a molding may have little relevance to its overall performance. This paper describes recent experiments that could lead to a radical change in testing strategy. Instead of the classical method in which standard specimens cut from moldings are assumed to provide the various stiffness coefficients needed for anisotropic stress analysis, simple moldings such as discs or plaques are tested directly. The sacrifice of precision in the measurements and the loss of rigor in the definition of the measured quantities is more than compensated for by a gain in the general utility of the data and the substantial reduction in the cost of evaluations. The mechanical properties of shortfiber thermoplastics composites are particularly sensitive to mold geometry and the new methods of testing enable the effects to be assessed readily, whereas the information generated by the classical method is virtually indecipherable in that context. Examples are given in the paper.
The effect of mandrel rotation on power consumption in polypropylene extrusion
Authors: Worth R. A. 
Published: December 2004

AbstractImproved properties of thermoplastic pipes may be achieved by rotating the core of the extrusion die, to produce orientation in the tangential direction. It has been suggested that a further advantage of mandrel rotation is an increased output rate for a given power input. The flow of a “power law” fluid through a rotating die is analyzed, and the power consumption and throughput are investigated. Experimental results for polypropylene melt are presented, which illustrate the effect of rotation on the die characteristics. It is found that the output is increased, but the savings are minimal in view of the power which must be introduced via the rotating mandrel.
Softening temperature of glassy polymers as affected by residual stresses
Authors: Siegmann A. , Narkis M. , Rosenzweig N. 
Published: December 2004

AbstractHeat deflection temperature and Vicat softening point of polystyrene and polymethylmethacrylate with various thermal histories were measured. Surface residual stresses were characterized by liquid crazing. Residual stress profiles across the sample thickness were also measured. It is suggested that the softening behavior of glassy polymers is affected by the state of the residual stresses in addition to the traditionally accepted free volume approach.