bluuebunny/crossref_metadata_2025 huggingface dataset:
Dispersion viscosity of aluminum trihydroxide of various particle size distributions in an unsaturated polyester resin
Authors: Hsieh H. P.
Published: December 2004

The 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

ABA 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

A 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

Swelling 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

Deformation 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

The 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

The 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

The 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

The 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

Flow 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

Polymeric 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

In‐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

To 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

The 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

Experiments 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

Glassy 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

Mechanical 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

Based 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

As 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

Electron 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

The 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

Improved 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

Heat 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.
The effects of eccentricities on the fracture of off‐axis fiber composites
Authors: Chamis C. C. , Sinclair J. H.
Published: December 2004

Finite element analyses were performed to investigate theoretically the effects of in‐plane and out‐of‐plane eccentricities, bending or twisting, and thickness nonuniformity on the axial stress and strain variations across the width of off‐axis specimens. The results are compared with measured data and are also used to assess the effects of these eccentricities on the fracture stress of off‐axis fiber composites. Guidelines for detecting and minimizing the presence of eccentricities are described.
Carbon fiber structure and stability studies
Authors: Gibbs Hugh H. , Wendt Robert C. , Wilson Frank C.
Published: December 2004

A study has been made of the thermal‐oxidative stability of several commercially available carbon fibers. Significant differences in the weight loss behavior were observed in air aging studies run on the bare fibers at 600°F (589 K). The stability of high temperature laminates, such as those based on NR‐150 polyimide precursor solutions, was found to be directly affected by the stability of the reinforcing carbon fibers. In studies carried out to determine the reasons for carbon fiber instability, residual sodium sulfate was found to be the principle destabilizing factor. A mechanism whereby the sodium sulfate promotes the oxidation of carbon in the presence of air is proposed.
Young's modulus of uniform density thermoplastic foam
Authors: Progelhof R. C. , Throne J. L.
Published: December 2004

A comparison of experimental data for zero strain Young's modulus of uniform density thermoplastic foam for short times has been made with several theoretical and empirical correlations. An analysis of the variance of the data with the predicted values from the many models indicated that the simplistic density squared relationship adequately described the modulus of the foam for basic engineering calculations.
Transverse tensile characteristics of fiber composites with flexible resins: Theory and test results
Authors: Christensen R. M. , Rinde J. A.
Published: December 2004

A theoretical and experimental investigation has been conducted of the transverse tensile properties of flexible‐resin/ glass‐fiber composite lamina. The objective is to increase the elongation at failure of a lamina in a state of transverse tension so that when a lamina is used in a laminate configuration, it does not suffer premature failure (e.g., failure at a lower strain level than that for a lamina in fiber direction tension). We show that the mode of failure in the transverse tensile lamina differs greatly from that in the neat resin. The failure mode in the lamina form is found to be brittle fracture. From this, it follows that the controlling neat resin property is the low elongation modulus rather than the elongation at failure. Significant improvements in the transverse tensile strain at failure were obtained for the flexible‐resin/glass‐fiber systems studied.
Compatible glassy polyblends based upon poly(2,6‐dimethyl‐1,4‐phenylene oxide): Tensile modulus studies
Authors: Kleiner Lothar W. , Karasz Frank E. , MacKnight William J.
Published: December 2004

The mechanical behavior of compatible glassy polyblends based upon poly(2.6‐dimethyl‐ 1,4‐phe nylene oxide) (PPO) was investigated. In particular, the influence of composition, molecular weight, and molecular weight distribution upon the tensile modulus of the blend was assessed. Various possible correlations between the experimentally determined moduli and theory are considered. Included are correlations with density, packing density, composite theory, and lattice fluid theory. The modeling of the properties of mixtures via Simplex lattice design is also presented. Finally, attention is given to the development of compatibility criteria based upon tensile modulus and density measurements.
Studies on poly(vinyl chloride)—copper composites. Part 2: SEM studies of the fracture surfaces
Authors: Bhattacharyya Swapan K. , De Sadhan K. , Basu Sanjay
Published: December 2004

Scanning electron microscopy (SEM) studies of fracture surfaces of poly(vinyl chloride)—copper composites at various metal loadings and different processing conditions reveal characteristic features. In general, metallic fillers introduce brittleness, while plasticizers increase the ductility of the composites. Results of the fracture studies have been correlated with the properties of the composites reported earlier.
A simple procedure of accounting for physical aging in the prediction of the modulus of glassy plastic materials
Authors: Booij H. C. , Minkhorst J. H. K.
Published: December 2004

The basic relationships are presented for predicting the creep and stress relaxation as a function of physical aging, loading time, and temperature of amorphous polymers processed under such conditions that their thermal treatment amounts to a quench from the melt to the glassy state. A nomogram construction, based on these relations, is proposed and developed for a particular polymer, namely an extrusion type acrylonitrile‐butadiene‐styrene (ABS), RONFALIN EST. The applicability of the procedure is restricted to the isothermal viscoelastic behavior at low stresses and strains of unplasticised amorphous plastic materials quenched from the melt to the glassy state.
Predicting the creep rupture life of polyethylene pipe
Authors: Barton S. J. , Cherry B. W.
Published: December 2004

A number of techniques have been developed in the past for the prediction of the dependence of the creep rupture life of polyethylene pipe on applied stress and temperature. It is now proposed that, using a modified form of the activated rate procss equation in which the activation volume varies predictably with temperature, a generalized equation may be derived which describes the “brittle” creep rupture curve over a range of temperatures, and also allows the use of a Larson‐Miller type equation. Since the known “ductile” creep rupture curve at 20°C can be extrapolated from measurements carried out over a short period at room temperature in the laboratory, the intersection point between the extrapolated “ductile” curve and the calculated “brittle” curve can easily be calculated. If the proposed method is applied to creep rupture data obtained from Hoechst AG (GM5010, HDPE pipe) as an example, a transition at about 11 years is predicted.
Time‐temperature cure behavior of epoxy based structural adhesives
Authors: Doyle Michael J. , Lewis Armand F. , Li Hin‐Mo
Published: December 2004

Time/temperature cure profile diagrams of a nylon‐epoxy adhesive and a rubber‐modified epoxy based structural adhesive have been established from isothermal‐cure time torsional braid analysis measurements. The characteristic zones of liquid, gel‐rubber and glassy state behavior are noted on the diagrams. With the nylon‐epoxy adhesive, the time/temperature cure profile is ill‐defined since all the TBA data had to be obtained (due to the particular curing agent involved) at isothermal conditions above the glass temperature of the finally cured adhesive. In comparison, the rubber‐modified epoxy system showed distinct zones reflecting the various rheological states traversed during the thermosetting process. The dynamic mechanical. (Rheovibron), morphology, and adhesive joint strength properties are examined as a function of cure cycle.
Dynamic thermomechanical investigation of polymeric systems supported on inert substrates
Authors: Cowie J. M. G.
Published: December 2004

The use of inert supports for the study of mechanically weak polymer systems is becoming more widespread, particularly since Gillham established its acceptability in the torsional braid technique. A description and review of work using glass braid, glass filter mat and cellulose mat supports is presented. This consists of coverage of the dynamic mechanical response of a series of mono and di‐alkyl esters of polyitaconic acid ranging in ester chain length from C1 to C18. The major features, e.g., glass and sub‐glass transitions, are identified and evidence of a double glass transition was found, when the ester chain length exceeds C6. The relaxations of ring systems in the glass phase are also examined. Controversy over the precise value of Tg for amorphous polyethylene has continued for some time and our attempt to resolve the problem has centered on a study of hydrogenated polybutadienes. The data obtained support the proposition that the polyethylene Tg is about 195K and that its γ‐relaxation, suggested by some workers to be the Tg, arises from crankshaft motion involving methylene sequences of 6 to 10 units. Other topics discussed include the damping characteristics of low molecular weight polymers such as poly(dimethylsiloxane), polystyrene, and poly(propylene oxide) with special reference to the existence of Tn transitions.
Influence of molecular weight on crystallization rate of oriented, glassy nylon 6
Authors: Engler Philip , Carr Stephen H.
Published: December 2004

Differential scanning calorimetry and wide angle X‐ray diffractometry were used to investigate the effects of molecular weight and molecular weight distribution on the crystallization kinetics of oriented, glassy nylon 6. The samples had number average molecular weights ranging from 10,000 to 42,000 and polydispersity indices ranging from 2.0 to 3.1. Noncrystalline films were prepared by quenching molten films between plattens chilled with liquid nitrogen. These films were drawn 4X and 5‐1/3X, and the resultant uniaxial orientation was observed to enhance markedly the room temperature crystallization kinetics. Although macroscopic deformation can be assumed to be affine at the molecular level, it is hypothesized that wholechain molecular relaxation occurs at rates inversely proportional to the square of molecular weight, thereby creating a distribution of extension ratios which reflect the actual molecular weight distribution. Thus, the crystallization rate and the degree of crystallinity depend on the fraction of high molecular weight molecules present in the sample. Given two samples with the same molecular weight, the one with the broader distribution crystallizes more rapidly. Similarly, samples having the larger molecular weight crystallize to a greater extent when two samples have the same molecular weight distribution.
Influence of molecular weight on the creep behavior of undiluted polyisobutylenes
Authors: La Mantia F. P. , Acierno D.
Published: December 2004

The elongational behavior in constant force experiments has been considered for three samples of commercial polyisobutylene. The results compare favorably with the predictions of two existing non‐linear theories as long as the samples deform homogeneously. Some qualitative observations have been made with reference to the “failure point”, i.e., the point where a non‐homogeneous deformation begins.
Effect of bonding temperature on the joint strength of polyolefln/butyl rubber and polyolefin/ethylene‐vinylacetate copolymer
Authors: Sung Nak‐Ho
Published: December 2004

The effect of bonding temperature on the peel strength of adhesive joints, polyolefin/butyl rubber and polyolefin/ethylene‐vinylacetate copolymer, has been investigated. The peel strength, measured at room temperature, undergoes a sharp transition from its low values to higher values as the bonding temperature is changed from below to above, the melting point of the substrate. This increase in peel strength is accompanied by changes in failure mode from the apparent interfacial failure to cohesive failure through the adhesives. Investigation of the interface using Fourier Transform Infrared Internal Reflection spectroscopy and interference microscopy indicates that the sharp increase in the peel strength at the melting temperature of substrate is associated with the presence of an interdiffused layer at the interface.
Viscosities and normal stress coefficients of high impact polystyrene‐mineral oil mixtures
Authors: Kruse R. L. , Southern J. H.
Published: December 2004

Measured melt viscosities and primary normal stress coefficients are presented for a well‐characterized, rubbermodified polystyrene as a function of shear rate and mineral oil diluent concentration. The logarithmic blending relationship accurately predicts the observed data. Melt relaxation times and shear compliance data are also calculated. The compliance numbers are consistent with molecular models based on a simple dumbbell (appropriately modified for rubber and mineral oil addition).
Chemiluminescence of incompatible polymer mixtures
Authors: Naito K. , Kwei T. K.
Published: December 2004

Chemiluminescence of an incompatible mixture of polystyrene and cis‐1, 4‐polybutadiene was studied. The luminescence characteristics of the component polymers are preserved in the incompatible blend and the intensity for the blend can be represented as the surface‐area‐average of the individual intensities.
A simplified method for analyzing mold filling dynamics. Part II: Extensions and comparisons with experiment
Authors: Stevenson James F. , Chuck Winston
Published: December 2004

A dimensional analysis based on four parameters has been developed previously to predict injection pressure; clamp force, and bulk temperature for the injection molding of amorphous materials in center‐gated disk‐shaped cavities. In this paper geometric and semicrystalline‐materials approximations are introduced and tested for extending the previous analysis to include multigated thin cavities and semicrystalline materials. The combination of these approximations and the previous analysis, known hereafter as the Radial Flow Method (RFM), greatly simplifies the analysis of mold filling. The geometric approximation, which is based on a simple model for the axial stress distribution in the cavity, is shown to give reasonable predictions when compared with experimental data and a numerical two‐directional flow simulation for the filling of an off‐center‐gated rectangular cavity with acrylonitrilebutadiene‐styrene copolymer (ABS). The semicrystallinematerials approximation, in which heat capacity and viscosity changes during crystallization are neglected, is shown to give good agreement with experimental data for the filling of a center‐gated disk‐shaped cavity with polypropylene. As an illustration, the Radial Flow Method is used to analyze the molding of a large, thin‐wall automobile interior trim panel. The inlet melt temperature, mold‐wall temperature, part thickness, injection rate, viscosity and gate locations are varied in a series of calculations to determine the relative effectiveness of these variables in lowering the injection pressure and Clamp force. The results obtained with the Radial Flow Method are in good agreement with those obtained by a finiteelement simulation of two‐directional flow.
Effects of dispersion on flow and mechanical properties of polymer blends
Authors: Kapuscinski M. , Schreiber H. P.
Published: December 2004

Blends of linear polyethylene and ethylene‐propylenediene elastomer, representing the entire composition range, were prepared under various conditions of shear intensity. It was found that both viscoelastic flow parameters and mechanical properties at large deformation respond strongly to variations in shear history of material preparation. Mechanical degradation of the polymers not being detected, it is postulated that property variations are due to morphological effects related to domain sizes of the two components and to the ease of molecular diffusion across domain boundaries. Thus, mechanical properties develop over finite times of mixing, consistent with the attainment of steady states in domain sizes. Maximum sensitivity of mechanical properties to mixing variables is found for 50/50 blends of the polymers, which have maximum interdomain contact areas. It appears feasible to develop desired balances of flow and mechanical properties in such polyblends through the close control of component dispersion processes.
Chemorheology of crosslinked epoxy resins subjected to large strains
Authors: Buchman A. , Katz D.
Published: December 2004

The previously reported work on chemorheological changes occurring in two epoxy resins when aged under large strains at temperatures above their Tg was extended. Ageing times up to 100 h were applied and the phenomenon of orientation occurring in these samples was investigated, mainly by measurements of their birefringence index. It was found that the orientation of the air‐aged samples, when studied at room temperature, depended on the ageing conditions (strain, temperature, time) and was not uniform throughout the bulk of the samples, being higher in two narrow external layers and lower in the core layer. After reheating oriented samples in air without strains for different lengths of time at temperatures above Tg, disappearance of the orientation in the external layers was observed. This is probably due to oxidation and degradation occurring in the network and scission of part of the network links, mainly those strained due to orientation. The decrease of orientation, especially in the inner layers of the polymer samples, was much slower when the reheating of the oriented‐ and unstrained samples took place in an inert atmosphere, this showing again the great influence of oxygen when it participates in ageing and heating processes of epoxy resins.
Rheo‐optical studies on the deformation mechanism of semicrystalline polymers. VIII. Dynamic x‐ray diffraction of a high‐density polyethylene film having row‐structure of C‐axis orientation
Authors: Suehiro Shoji , Yamada Takeshi , Kyu Thein , Fujita Ken‐Ichi , Hashimoto Takeji , Kawai Hiromichi
Published: December 2004

Dynamic x‐ray diffraction is employed to scrutinize the structural origin of the α mechanical dispersion of a highdensity polyethylene having preferentially oriented rownucleated cylindritic texture around the machine direction (MD). Results indicate that the α1 dispersion is associated with two kinds of orientation processes of crystallites: (1) the orientation process involving the rotation of crystallites around the crystal b‐axis (lamellar axis) dominates in the MD specimen; (2) the other process accompanying the rotation of crystallites or lamellar segments around their crystal a‐axis dominates in the TD (transverse direction) specimen. The complex apparent crystal lattice compliances show no frequency dependence in the real component and no appreciable value in the imaginary component, indicating that the α1 process is definitely associated with the intercrystalline process, but not relavent to the intracrystal process. However, at elevated temperatures, the complex lattice compliances exhibit a remarkable frequency dependence, suggesting that the α2 dispersion concomitant to intracrystalline nature takes place in this time scale. The α2 dispersion was found to be more pronounced upon stretching along the lamellar axis (TD) than normal to it (MD).
The effect of moisture on the mechanical behavior of a nylon‐epoxy adhesive
Authors: Agarwal Pawan K.
Published: December 2004

The mechanical properties of a commercial nylon‐epoxy resin have been studied using a sensitive creep apparatus which employs a frictionless levitation magnetic bearing. Isothermal creep measurements over a temperature range of 30‐170°C and covering a time scale of five decades were made on the wet and dry state of the material. Following the usual time‐temperature reduction scheme, master curves for each state were constructed from the experimental data. The effect of moisture was found to be more than that of a simple plasticizer. The steepness of the reduced curves in the transition region was determined and the distribution function of retardation times of the two states of the sample were calculated. The problem of predicting the physical state of the bulk adhesive at higher temperatures was found to be complicated, possibly due to the presence of nylon crystallites.
The role of inter‐ and intra‐links in the transformation of folded chain lamellae into microfibrils
Authors: Tarin P. M. , Thomas E. L.
Published: December 2004

In this study we investigate the effect of crystallization rate on the extensibility (draw ratio) of spherulitic polyethylene film uniaxially deformed at room temperature. Draw ratios for deformed films increased with increasing crystallization temperature. Transmission electron microscopy of the microfibrillar structures revealed and interconnected network of fibrils. The degree of connectivity between microfibrils was found to decrease with increasing‐crystallization temperature. A model of the deformation process is developed in which inter‐ and intra‐link (extended chain fibers formed during crystallization) distribute the applied stress, initiate the micronecking process and influence the amount of chain unfolding during drawing.
A dielectric study of the crystal and amorphous fractions in oriented polyethylenes
Authors: Boyd Richard H. , Yemni Tarik
Published: December 2004

Polyethylenes have relaxation processes separately assignable to the crystal and amorphous components. The possibility thus presents itself for studying the interaction between the two phases by investigating the anisotropy of the separate relaxation processes induced by overall orientation of the material. Such a study was carried out here by the dielectric method on samples rendered dielectrically active by the introduction of a few carbonyl groups by oxidation. In addition to the usual advantage of ease of frequency variation, the dielectric method in this case has a very great advantage in interpretation resulting from the similarity of dielectric constants of the two phases. In specimens oriented by solid‐state extrusion, it was found that the crystalline relaxation process (α) develops the expected anisotropy resulting from dipoles normal to C‐axis alignment in the extrusion direction. In branched polyethylene (BPE) no accompanying anisotropy of the amorphous β and γ processes was observed. Since the extrusion was carried out well above the glass temperature of the amorphous component, this indicates that constraints from the crystal phase are not sufficient to prevent dissipation of amorphous orientation by segmental motion. However in linear polyethylene (LPE) (where there is no well‐developed β process) some anisotropy of the γ process was observed. It is proposed that a higher degree of constraint of the amorphous component by the crystals in LPE results in suppression of the glass‐rubber (β) relaxation and permits amorphous orientation to accompany crystal orientation.
Some relationships between injection molding conditions and the characteristics of vitrified molded parts
Authors: White James L. , Dietz Wolfgang
Published: December 2004

The various mold filling phenomena influencing the characteristics of fabricated parts are surveyed. The phenomena leading to jetting in injection mold filling are considered. These are associated with the magnitude of swell by the melt as it exits the gate into the mold. Special attention is given to the influence of non‐isothermal runner flow. A theory of extrudate swell of polymer melts with temperature profiles is developed using Tanner's unconstrained recovery theory. In the. absence of jetting, mold filling by a simple advancing front takes place. The hydrodynamics of the advancing front and the stress fields in the flowing melt are determined. Analysis and modeling are presented based on the use of hydrodynamic lubrication theory involving a solid layer along the mold wall and a hot isothermal melt core. This theory is compared with experimental measurements of pressure losses in mold filling. The development of birefringence in injection molding processes is analyzed. Birefringence distributions are due to frozen‐in flow birefringence. A new experimental study is presented and its results compared with theoretical predictions. The problem of thermal stresses in injection molded parts is considered.
The dynamic properties of elastomers above the limit of linear viscoelastic response
Authors: Lidor Gershon , Maxwell Bryce
Published: December 2004

A method of measuring the dynamic viscoelastic properties of polymers at large strain magnitudes, well above the limit of linear viscoelastic response, has been developed. A straight line relationship has been found between the dynamic stress and the dynamic strain above the limit of linear viscoelastic response. This straight line relationship can be described by a dynamic in‐phase modulus that is a function of the maximum strain applied and the frequency of the applied dynamic strain. This rheological characterization method is demonstrated for a series of synthetic elastomers with various carbon black loadings.