bluuebunny/crossref_metadata_2025 huggingface dataset:
A critical analysis of the use of sample‐supportive techniques in the measurement of dynamic mechanical relaxation processes
Authors: Neumann R. M. , Senich G. A. , Macknight W. J.
Published: December 2004

It is shown that the technique of dynamic spring analysis (DSA) gives rise to a dynamic mechanical loss dispersion well above the glass transition temperature, Tg, analogous to the Tu process observed in torsional braid analysis. A mechanical model is proposed which explains why any composite sample consisting of an elastic support coupled to a viscous liquid must necessarily produce such a relaxation regardless of whether the liquid is monomeric or polymeric in nature. Loss tangent measurements performed on a series of polystyrenes of varying molecular weight and on glycerol using both DSA and a Rheometrics mechanical spectrometer show that the relaxation observed in DSA is not of molecular origin.
Some qualitative and quantitative features of die swell
Authors: Huilgol R. R.
Published: December 2004

Upper and lower bounds for the die swell ratio are derived for all simple fluids in the presence of surface tension and under the assumptions that the flow remains viscometric up to a finite distance from the exit and that bounds on the shear stress distribution in this length exist. Both circular and plane jets are considered and the bounds so derived depend on the normal stress on the wall in the viscometric region. For Newtonian and power law fluids, this stress can be determined, a priori, from existing theories. However, for viscoelastic liquids, it is an open question at present.
Thermal and swelling properties of polystyrene‐polyolefin blends
Authors: Greco R. , Hopfenberg H. B. , Martusgelli E. , Ragosta G. , Demma G.
Published: December 2004

Model blends of glassy amorphous polystyrene and each of four different crystallizable and rubbery polyolefins of varying side‐chain molecular weight (polyethylene, polypropylene, poly(1‐butene), poly (4‐methyl‐1‐pentene)) have been prepared by melt extrusion of the polymeric components. Density measurements, differential scanning calorimetry (DSC), swelling measurements, and X‐ray diffraction have been performed on the extruded fibers. In all cases, over the entire range of blend composition, the polymeric blends are immiscible and incompatible. The DSC measurements indicated that the polystyrene Tg was not decreased after blending and that the small reductions in the crystallinity and melting point of the respective polyolefins was best explained by thermal and kinetic interference with homo‐crystallization of the respective polyolefins in the blends. The volumetric swelling and gravimetric sorption of n‐hexane in the various blends increased monotonically with polystyrene content. The companion experiments, relating axial swelling with polystyrene content, indicated that this particular mode of distension actually decreased with increasing polystyrene content. The composite results, including DSC, X‐ray, density, volumetric swelling and axial swelling suggest that the polystyrene phase is essentially microfibrillar and oriented in the direction of extrusion.
Studies on structural foam processing II. Bubble dynamics in foam injection molding
Authors: Villamizar C. A. , Han Chang Dae
Published: December 2004

An experimental study was carried out to gain a better understanding of the dynamic behavior of gas bubbles during the structural foam injection molding operation. For the study, a rectangular mold cavity with glass windows on both sides was constructed, which permitted us to record on a movie film the dynamic behavior of gas bubbles in the mold cavity as a molten polymer containing inert gas was injected into it. The mold was designed so that either isothermal or nonisothermal injection molding could be carried out. Materials used were polystyrene, high‐density polyethylene, and polycarbonate. As chemical blowing agents, sodium bicarbonate (which generates carbon dioxide), a proprietary hydrazide and 5‐phenyl tetrazole, both generating nitrogen, were used. Injection pressure, injection melt temperature, and mold temperature were varied to investigate the kinetics of bubble growth (and collapse) during the foam injection molding operation. It was found that the processing variables (e.g., the mold temperature, the injection pressure, the concentration of blowing agent) have a profound influence on the nucleation and growth rates of gas bubbles during mold filling. Some specific observations made from the present study are as follows: an increase in melt temperature, blowing agent concentration, and mold temperature brings about an increase in bubble growth but more non‐uniform cell size and its distribution, whereas an increase in injection pressure (and hence injection speed) brings about a decrease in bubble growth but more uniform cell size and its distribution. Whereas almost all the theoretical studies published in the literature deal with the growth (or collapse) of a stationary single spherical gas bubble under isothermal conditions, in structural foam injection molding the shape of the bubble is not spherical because the fluid is in motion during mold filling. Moreover, a temperature gradient exists in the mold cavity and the cooling subsequent to mold filling influences bubble growth significantly. It is suggested that theoretical study be carried out on bubble growth in an imposed shear field under nonisothermal conditions.
On the limit of linear viscoelastic response in the flow between eccentric rotating disks
Authors: Jongschaap R. J. J. , Knapper K. H. , Lopulissa J. S.
Published: December 2004

The dependence on frequency of the limiting value of strain, ψL, for which linear Viscoelastic response occurs in eccentric rotating disks (ERD) flow is studied theoretically and experimentally. The theoretical investigations are based upon the general simple‐fluid theory of Coleman and Noll. It is shown that according to this theory ψL becomes independent of angular velocity, ω, at relatively high frequencies, whereas ψL becomes inversely proportional to ω at sufficiently low frequencies. The results of previous investigations, based upon some special rheological models, are discussed. The behavior predicted by the simple‐fluid theory is confirmed by experiments on polyisobutylene solutions.
Mechanisms of polymer crystallization from flowing solutions
Authors: Acierno D. , La Mantia F. P. , Marrucci G.
Published: December 2004

The recent experimental results on flow‐induced crystallization by Pennings and coworkers show that extremely rigid polyethylene fibers can be obtained in a shear flow. On the other hand, the mechanism by which these flow‐induced crystals are produced is still open to investigation. In this work a few aspects of fibrous crystal growth are theoretically investigated. The molecular dynamics of chains partly attached to the crystal and partly immersed in the solution is considered. The influence of temperature and of geometrical factors is also discussed.
Solubility of vinyl chloride in poly (vinyl chloride) in a water slurry
Authors: Scamehorn John F. , Yang Kang
Published: December 2004

The solubility of vinyl chloride (VCM) vapor in poly (vinyl chloride) (PVC) in a water slurry has been measured between 55 and 65°C. The heat and entropy of sorption were shown to be very close to those of condensation. The solubilities measured in this study were higher than those obtained in other studies on dry PVC and PVC latex. The interaction parameter (x) in the Flory‐Huggins equation has been shown to vary between 0.34 and 0.61 over the composition range studied. The effect of ageing the slurry in the presence of VCM is also discussed.
Recycling of polyurethane and polyisocyanurate foam
Authors: Ulrich Henri , Odinak A. , Tucker B. , Sayigh A. A. R.
Published: December 2004

Heating of isocyanate derived foams with glycol mixtures is a simple and economically attractive recycling process. The process is emission free, not sensitive to varying product mixes and the obtained polyols can be completely reused in the manufacture of rigid polyurethane or polyisocyanurate foam.
Effects of titanate coupling agents on the rheological and mechanical properties of filled polyolefins
Authors: Han C. D. , Sandford C. , Yoo H. J.
Published: December 2004

An experimental study was carried out to investigate the effects of titanate coupling agents on the rheological properties of p articulate‐filled polyolefin melts. Inorganic fillers used were CaCO3, talc, and fiberglass, and polyolefins used were high‐density polyethylene (HOPE) and polypropylene (PP). It was found that the addition of the coupling agent TTS to the PP‐CaCO3 and PP‐fiberglass systems reduced the melt viscosity considerably, whereas the addition of the coupling agent ETDS‐201 to the PP‐talc and HDPE‐talc systems affected the melt viscosity very little. Also carried out was an injection molding study to investigate the effects of different inorganic fillers and the titanate coupling agents used on the mechanical properties of the injection molded specimens. It was found that addition of titanate coupling agents generally resulted in reduced modulus and tensile strength, and increased elongation and impact strength of the filled systems. The PP‐CaCO3‐TTS and HDPE‐talc‐ETDS 201 systems were found to have impact strength improved by approximately 100 percent with the addition of a titanate coupling agent. The PP‐CaCO3‐TTS samples have ultimate tensile elongation approaching that of virgin PP.
Computation of the creep behavior of thermoplastics
Authors: Overath F. , Menges G.
Published: December 2004

The dimensioning of structural parts made of plastics requires the knowledge of the material parameters which depend on the processing and, loading conditions. In this paper, the possibility of describing the stress‐, temperature‐, and time‐dependent deformation behavior of thermoplastics below the linear viscoelastic limit is presented, using simple exponential functions. The formal relationship of the systems of equations have been ascertained based on a large number of experimental results. They enable a mathematical description of the deformation behavior of the material considered with sufficient accuracy for engineering requirements. This is based on parameters for creep experiments with three different stresses, at constant temperature, extending to 102 h. One experimental series extended to 103 h. As shown in examples, based on these experimental results, the computation makes possible a predetermination of the deformations obtained with the time‐factors of 102 to 103. The temperature can vary within the nearly linear region of the semi‐logarithmic shear modulus‐temperature curve. Within the variation of the stress, cyclic changes of the loading can also very simply be taken into account using Boltzmann's superposition principle. Principally, the computation can be carried out using any auxiliary means which contains the exponential function xy. Simple programmable pocket computers allow an automatic calculation.
Geometry of fully wiped twin‐screw equipment
Authors: Booy M. L.
Published: December 2004

The cross section geometry of fully wiped corotating twin screws is derived from simple kinematic principles. A pair of screws can have identical cross sections with each screw running at the same speed, or they can have an unequal number of tips and rotate at different speeds. The more conventional case of equal cross section is reviewed in detail, showing how screw diameter, centerline distance, lead, and number of tips influences design, net volumes, and surface areas. The screw cross section is unique for a given diameter, centerline distance, and number of tips. The construction of the cross section is shown, both for pairs of identical screws, and for screws with a speed ratio. Maps are provided to show applicability of screws with 1, 2, and 3 tips.
Influence of low density polyethylene quality on extrusion coating processability
Authors: Honkanen A. , Bergström C. , Laiho E.
Published: December 2004

In order to obtain explicit information about the influence of different low density polyethylene (LDPE) quality parameters on extrusion coating processability, a test run was made with an autoclave reactor and the products were investigated. All the grades manufactured had melt indices (MI), densities, molecular weight distributions (MWD), and degrees of long chain branching(LCB) typical of commercial extrusion coating grades. The processability characteristics studied were maximum line speed and neck‐in. The influence of MI, density, and extrusion melt temperature were systematically investigated. It was found that the maximum line speed rose with increasing MI, density, and extrusion melt temperature, and that an increasing extrusion melt temperature led to a growing difference between the maximum line speed at a constant coating thickness and the maximum line speed at a constant screw speed. Neck‐in was found to increase with increasing MI, increasing density, and increasing coating thickness. These effects were more pronounced at higher extrusion melt temperatures. When using the extrusion temperature needed to achieve a certain line speed for each grade, the influence of MI on neck‐in was practically non‐existent.
Kinetics of fast (RIM) urethane polymerization
Authors: Richter E. B. , Macosko C. W.
Published: December 2004

The kinetics of the dibutyltin dilaurate catalyzed bulk polymerization of 4,4′‐diphenylmethane diisocyanate (MDI) with poly‐ϵ‐caprolactone were studied by infared spectroscopy and adiabatic temperature rise. The overall reaction order was found to change from 3/2 to 2 with increasing temperature. At temperatures above 80°C, the order with respect to catalyst was found to decrease with concentration from 1 to 1/2. The results were consistent with a Michaelis Menten type kinetic scheme.
A model viscoelastic fluid
Authors: Boger David V. , Nguyen Hang
Published: December 2004

Shear stress and first normal stress difference data are presented for materials which exhibit a constant viscosity and yet at the same time exhibit elasticity levels of the same order as polymer melts. Flow pattern observations in circular die entry flows in conjunction with independent shear and normal stress measurement strongly suggest that these fluids would make excellent model fluids for melt studies. Studies in which the influence of elasticity in the absence of shear thinning and fluid inertia can easily be made. Furthermore it is clearly shown that a realistic solution to the die entry flow problem is not obtained using second order flow theory. In the second order region the secondary cell is observed to be almost identical in size to the cell observed for an inelastic Newtonian fluid in creeping flow. Marked growth in the secondary cell as a function of elasticity is not observed until the shear rates exceed the region of second order behavior. This growth in cell size as a result of elasticity is followed at higher shear rates by a spiraling flow instability like that observed for some polymer melts.
The non‐linear viscoelastic properties of molten polymers and concentrated solutions
Authors: Brereton M. G.
Published: December 2004

For polymer melts and concentrated solutions highly nonlinear effects dominate all aspects of both the transient and steady state mechanical behavior. The first part of this paper will review the salient features of the experimental results and focus attention on those common features which should be understood in a coherent manner. The various constitutive equations, especially the integral representations that have been proposed to describe polymer melts will also be discussed. They fall roughly into three classes: those where the relaxation function depends on the deformation rate, deformation, or stress history. Evidence will be presented which indicates that the stress history rather than the deformation history may be the more relevant variable to account for the non‐linearities. The last part of the paper will briefly review the theories that have been proposed to understand the mechanism for non‐linear behavior at the microscopic level and the influence of molecular weight and concentration.
Tensile, impact and fatigue behavior of an amine‐cured epoxy resin
Authors: Kim S. L. , Skibo M. D. , Manson J. A. , Hertzberg R. W. , Janiszewski J.
Published: December 2004

Although crosslinked networks are commonly used as adhesives and composite matrixes, structure‐property relationships are not as well established as with thermoplastics. For this reason, an extensive study was begun to systematically examine effects of stoichiometry, morphology, and distribution of crosslink density on viscoelastic behavior and ultimate properties. The system selected was based on a bisphenol‐A‐type epoxy cured with methylene dianiline. This paper describes and discusses results obtained for resins in which the amine/epoxy ratio ranged between 0.7 and 2.2. In agreement with reports by others, the tensile strength, modulus, and ultimate elongation were relatively insensitive to stoichiometry but did not show slight maxima or minima when the amine was somewhat in excess. Impact strengths, tensile energies‐to‐break and fracture toughness were, in contrast, quite sensitive, though the patterns of each differed significantly. Both fracture toughness and the stress intensity factor required to drive the crack at a given rate varied directly with the amine/epoxy ratio, as did estimates of the characteristic flaw size. Fatigue striations were observed on the fracture surfaces and corresponded to the incremental advance of the crack in one loading cycle.
On the use of acceleration waves to characterize the dynamic response of non‐linear viscoelastic materials
Authors: Nunziato Jace W.
Published: December 2004

We consider the analysis of data obtained in one‐dimensional acceleration wave experiments on a non‐linear viscoelastic material and discuss how such data can be used to characterize the dynamic response of the material. To begin, we review briefly the general theory of one‐dimensional motions in viscoelastic materials and the methods employed to generate and observe acceleration waves in a material sample. We then discuss two methods of data analysis, a wave front analysis and a wave profile analysis, and indicate the type of information each analysis provides with regard to the dynamic properties of the material. Finally, using a known model for poly(methyl methacrylate) in a finite‐difference, Lagrangian wave‐propagation code, we calculate acceleration wave profiles at several locations in the sample and, treating these profiles as “experimental” data, we then illustrate how data from three or more acceleration wave experiments can be used to formulate a specific viscoelastic constitutive model for the material.
The effect of temperature on compressive fatigue of polystyrene
Authors: Weaver Judith L. , Beatty Charles L.
Published: December 2004

Compressive fatigue experiments have been designed to compare this long term mechanical life property with shorter term stress‐strain behavior. Fatigue lifetime curves can be represented by three distinct regions. The fatigue failure curves shift to shorter lifetimes and lower stresses as temperature is increased. The results are discussed in terms of the Zhurkov model of static fatigue failure. Using a Coulomb‐Navier yield criterion modified rate expression, it is clear that activation energy and activation volume are functions of temperature. A change in temperature dependence of activation energy and endurance limiting stress occurs near the β transition suggesting that this molecular process is related to the fatigue process. The nearly identical dependence of fatigue and stress‐strain activation energies and activation volumes with temperature suggest that both deformation processes may be controlled by a similar mechanism, i.e., localized plastic deformation. Utilizing these concepts, a simple model of fatigue allows correlation of the endurance limiting stress and the number of stress cycles at the endurance limiting stress with measures of resistance to plastic flow as determined from stress‐strain data for this polystyrene. These data are used to project the longest and shortest mechanical fatigue lifetimes for these deformation conditions.
Scission and crosslinking during oxidation of peroxide cured EPDM
Authors: Landi V. R. , Easterbrook E. K.
Published: December 2004

The chemorheology of polymers prepared by peroxide curing terpolymers of ethylene propylene and diene monomer (EPDM) was studied at 375°F in air. Measurements were conducted on terpolymers containing dicyclopentadiene (DCPD), ethylidene norbornene (ENB) or 1,4‐hexadiene (HD) and also on copolymers. Effects of the level of dicyclopentadiene were investigated. A linear relationship is found between crosslinks formed during oxidation and chain scissions. At low termonomer level and in copolymers, this relationship is linear only during the early stages of oxidation. Results are consistent with a kinetic model in which crosslinking sites and scissioning sites on the polymer compete for free radicals which propagate the oxidative chain reaction. Termonomer units apparently act primarily as crosslinking sites with the tendency to crosslink being substantially greater in DCPD than ENB and HD. The number of crosslinks per scission derived from stress relaxation correlates well with elongation to failure retained after air aging 3 days at 350°F. Adjustment of termonomer level can lead to a ratio of crosslinking to scission which strikes a balance between softening of copolymer and embrittlement of some terpolymers at elevated temperature.
Distinguishing amorphous polymer blends from copolymers by wide angle X‐ray diffraction
Authors: Riga Alan T.
Published: December 2004

Amorphous homopolymer blends were differentiated from the corresponding random copolymers with wide angle X‐ray diffraction (WAXRD) using the diffraction angle and the band width at one‐half peak maximum. The diffraction angle was also used to determine the composition of copolymers and of mixtures of homopolymers. A procedure has been developed to predict the WAXRD patterns of polyblends and/or random copolymers based on those of the corresponding homopolymers.
Multistage latex particle size analysis by disc centrifuge photosedimentometry
Authors: Seidewand Robert J. , Erickson James R.
Published: December 2004

Characterization of a heterogeneous latex polymer synthesis requires quantifying the association of successive stage compositions with the previous stage latex seed particles. A new method for performing this analysis is presented for uniform sized latex particles by use of a Joyce Loebl disc centrifuge photosedimentometer. An iterative procedure is employed to solve a problem of unknown particle density when a successive polymerization produces new latex particles. The procedure is applicable regardless of the monomer compositions of the various stages and eliminates problems encountered with electron microscopy of soft deformable latex particles.
Polymer blends containing poly(vinylidene fluoride). Part IV: Thermodynamic interpretations
Authors: Paul D. R. , Barlow J. W. , Bernstein R. E. , Wahrmund D. C.
Published: December 2004

A summary of the transitional behavior of blends containing poly(vinylidene fluoride), PVF2, and various oxygen‐containing polymers is presented. These data are used to establish the presence of a single miscible amorphous phase. The depression of the PVF2 melting point in those blends judged to be miscible is analyzed using standard thermodynamic arguments to determine the heats of mixing between the amorphous diluents and the PVF2. These heats of mixing are exothermic indicating the presence of strong interactions between the binary pairs. A comparison between the observed interaction strengths and the dipole moments of the various diluents suggests that the exothermic heats of mixing are the result of strong dipole‐dipole interactions. Nearly all the miscible blends with PVF2 show Lower Critical Solution Temperature (LCST) behavior. The direct correlation between the temperature location of this phase instability and the observed interaction strength suggests that the instability is more the result of enthalpic considerations than entropic ones.
Effects of environment on the mechanical properties of plastics under high pressure
Authors: Trent John S. , Moet Abdelsamie Y. , Miles Mervyn J. , Baer Eric
Published: December 2004

Polystyrene (PS), high‐impact polystyrene (HIPS), and polyethylene (PE) have been investigated studying the pressure dependence of stress‐elongation behavior in tension over the range from atmospheric pressure to four kilobars at room temperature. The effect of strain rate was also observed for PS specimens. Tensile deformation of PS and HIPS has shown that the pressure‐transmitting fluid (silicon oil) acts as a stress crazing and cracking agent. Non‐sealed specimens of PS showed a brittle‐to‐ductile transition at 2.95 kbar while specimens sealed from the environment showed the same transition at only 0.35 kbar. Scales HIPS and PE specimens exhibited ductile behavior at all pressures. The extent of plastic deformation for PE was affected when specimens where exposed to the silicon oil environment. Surprisingly, HIPS exposed to the oil exhibited two transitions as the applied hydrostatic pressure was raised: a ductile‐to‐brittle followed by a brittle‐to‐ductile transition. Analysis of the stress‐elongation curves for sealed PS and HIPS specimens indicated that the pressure dependency of craze‐initiation stress differs from that of shear band initiation stress. The brittle‐to‐ductile transition occurred when the initiation stresses of both processes became equal. The principal stress for craze initiation showed almost no pressure dependency, suggesting that crazes initiate when the principal stress level of the tensile specimen reaches a critical value irrespective of the applied hydrostatic pressure.
Thermochemical characterization of some thermally stable thermoplastic and thermoset polymers
Authors: Kourtides Demetrius A. , Gilwee William J. , Parker John A.
Published: December 2004

The thermochemical and flammability properties of some thermally stable polymers considered for use in aircraft interiors are described. The properties studied include: (a) thermomechanical properties such as glass transition and melt temperature; (b) dynamic thermogravimetric analysis in anaerobic environment; (c) flammability properties such as oxygen index, flame spread and smoke evolution; and (d) selected physical properties. The thermoplastic polymers evaluated included polyphenylene sulfide, polyaryl sulfone, 9,9‐bis(4‐hydroxyphenyl)‐fluorene polycarbonate‐poly(dimethylsiloxane) and polyether sulfone. The thermoset polymers evaluated included epoxy, bismaleimide, a modified phenolic and polyaromatic melamine resin. These resins were primarily used in the fabrication of glass reinforced prepregs for the construction of experimental panels. Test results and relative rankings of some of the flammability parameters are presented and the relationship of the molecular structure, char yield, and flammability properties of these polymers are discussed.
Mineral fillers in low density‐polyethylene films
Authors: Arina Markku , Honkanen Arto , Tammela Viljo
Published: December 2004

The use of fillers is an established method of modifying the properties of plastics. The recent increase in prices of plastic raw materials and the new developments in compounding technology have heightened the interest of the plastic industry in compounds of fillers and polyethylene. This article discusses briefly the literature dealing with the effect of fillers on the properties of polyethylene, and research carried out on the effects of different mineral fillers, talcs, micas, clays, wollastonite and dolomite on the many properties of low density polyethylene films. The fine grade talcs have proved to be better than the other fillers with respect to most film properties. The platy talcs decreased the oxygen permeability by as much as 80 percent and the water vapor transmission rate by as much as 70 percent. With talcs, clays and dolomite the yield strength increased but with all fillers the tensile strength at break weakened with increasing filler content. A low elongation at break and a low tearing, resistance indicate the brittleness of the films especially at high filler contents (over 30 wt percent). The coefficients of friction decreased considerably with all fillers and a significant improvement in printability was achieved. However, none of the fillers had more than a very minor effect on the heat sealability of low density polyethylene.
Radical formation and deformation in poly‐p‐(2‐hydroxyethoxy) benzoic acid fibers
Authors: Nagamura T. , Devries K. L.
Published: December 2004

Radical generation during tensile deformation of poly‐p‐(2‐hydroxyethoxy) benzoic acid (PEOB) fibers was studied by electron spin resonance techniques under various stretching conditions. Primary phenoxy radicals were detected at room temperature, indicating main‐chain rupture during mechanical loading. The kinetics of phenoxy radical formation were observed at constant strain, constant load, constant strain‐rate, and in constant load rate experiments. The effect of strain rate on the radical formation was found to be larger in this sample than was observed in Nylon 6. These results coupled with other experimental observations have yielded information on a basic structural model and improved insight into the basic molecular mechanism responsible for deformation and fracture.
Creep failure and fracture of polyethylene in uniaxial extension
Authors: Crissman J. M. , Zapas L. J.
Published: December 2004

It is shown that under conditions of uniaxial creep the fracture of high density polyethylene can be categorized as one of three types, depending upon the magnitude of the applied load, molecular architecture, and environment. When subjected to relatively large loads, the specimens neck and then fracture almost immediately. At the other extreme of very small initial loadings, the specimens fracture in a brittle fashion through crack formation and growth. In the intermediate range of loadings the specimens neck and, depending upon the molecular weight and molecular weight distribution, may then elongate substantially before fracture. It is shown that the uniaxial creep behavior for the region where drawing occurs, when plotted in terms of isochrones, represents a type of phase diagram, one boundary of which describes the fracture enelope. In addition, experiments employing different constant rate of loading histories are described and an additivity of damage criterion used to predict the time to failure under constant load conditions, and visa versa.
An instability leading to failure of polyethylene in uniaxial creep
Authors: Zapas L. J. , Crissman J. M.
Published: December 2004

Based on a continuum model, a point of instability is predicted for the uniaxial creep of high density polyethylene. From dead load experiments it has been found that the instability occurs for linear polyethylene at around 10–12 percent strain, depending upon molecular weight and molecular weight distribution. It is shown that in the range of applied stresses for which the specimens neck during uniaxial creep, the time required to reach the critical point is related by a constant factor to the time at which the neck appears. A synopsis of theoretical considerations, as well as experimental work in support of this idea, is given.
A comparison of the thermal and mechanical degradation of glassy polystyrene by Fourier transform infrared spectroscopy
Authors: D'Esposito L. , Koenig J. L.
Published: December 2004

The thermal and mechanical degradation of glassy polystyrene has been studied by Fourier Transform Infrared, FT‐IR, spectroscopy. Using difference spectroscopy we have found that the products formed from these two modes of degradation were significantly different. This result is in contrast with other workers who found similar products for the thermal and mechanical degradation of polystyrene by mass spectroscopy. Our result suggests a reassessment of the thermal activation mechanism for mechanically‐induced bond scission. We have also found that the distribution of oxidation products appears to depend upon the environment in which the polymer is mechanically degraded. Finally, we have demonstrated the utility of FT‐IR spectroscopy for studying the mechanical degradation of polymers.
The adhesion to hydrophilic surfaces of plasticized poly(vinyl chloride) containing novolac ‐ hexamethylenetetramine
Authors: Robertson Richard E.
Published: December 2004

The addition of relatively small amounts of novolachexamethylenetetramine phenolic to poly(vinyl chloride) plastisols has been used to increase the adhesion of the fused plastisol to hydrophilic surfaces like those of glass and steel. The principal mechanism by which this occurs has been studied and found to be, first, the dissolution of the novolachexamethylenetetramine complex in the plasticizer; second, the interaction of the nearby phenolic groups with the hydrophilic surface; and, third, the chain extension and crosslinking of the phenolic to form perhaps a very open cell foam structure through the plasticized vinyl that is attached to the substrate. Additional adhesion may arise from the adsorption of particles of the undissolved novolac complex on the surface and from viscoelastic effects from the cured vinyl composition. The problem with the decreased adhesion of thin plastisol coatings was also studied. It was found to be unrelated to the thickness per se. Rather, it seems to arise from the loss of hexamethylenetetramine at the air interface. Though hexamethylenetetramine is lost also from thicker coatings, the concentration near the adherend interface is less affected.
Studies on poly(vinyl chloride)‐copper composites. Part 1: State of segregation of filler particles, electrical and mechanical properties in presence of plasticizer and stabilizer
Authors: Bhattacharyya Swapan K. , De Sadhan K. , Basu Sanjay
Published: December 2004

The presence of additives influences the state of segregation of filler particles in the polymer matrix which in turn controls the electrical and mechanical properties of poly(vinyl chloride)‐copper composites. The liquid plasticizer seems to form a coating on the filler surface which introduces quasirandomness in the segregated network. In accordance with the mathematical model proposed earlier, the strength properties were found to be proportional to dm−½ where dm is the mean free path between the filler particles. Calculations of dm were based on two different models, one for segregated network (unplasticized and low plasticized composites) and the other for quasi‐random distribution of filler particles (plasticized composites). Extruded samples in general show more randomness in the filler distribution than the compression molded samples.
Anomalous dynamic mechanical behavior of poly(vinyl chloride)
Authors: Calleja R. Diaz
Published: December 2004

In this paper, we present a study of the dynamic mechanicall behavior of a quenched poly(vinyl chloride). A new relaxation between the glass transition and the β transition is reported. We have related this new relaxation to an absence of physical aging.
The selection and use of free radical initiators
Authors: Sheppard Chester S. , Kamath Vasanth R.
Published: December 2004

There are over 50 different organic peroxides and azo compounds (in over 100 different formulations) produced commercially as free radical initiators (curing agents) for the polymer and resin industries. Thus, the user has many initiators to choose from and has usually relied on the resin and/or initiator producer to select his initiator system. This paper will discuss these initiators in general showing the different types‐ of initiator classes; how and why the activity of each class of initiator is varied by structure changes; how different initiators and/or promoter levels affect the curing process; and present guidelines that an end user might use to choose the right initiator for his resin system.
Fracture toughness testing of dental biomaterials
Authors: Koblitz F. F. , Luna V. R. , Glenn J. F. , Devries K. L. , Draughn R. A.
Published: December 2004

The adaptation of a cylindrical geometry fracture toughness test specimen to testing of polymeric dental biomaterials is demonstrated. The specimen configuration facilitates the fabrication of small specimens and simplifies the experimental study of environmental effects on properties of dental biomaterials. The test method is used to measure critical stress intensity factor, KIC for poly (methyl methacrylate) (PMMA), particulate composite restorative materials, and dental polymers. Values obtained are in agreement with data reported for other specimen configurations.
Extrudate swell from slit and capillary dies: An experimental and theoretical study
Authors: Huang David C. , White James L.
Published: December 2004

A comparative experimental study of extrudate swell from long slit and capillary dies is reported for rheologically characterized polystyrene and polypropylene melts. Generally extrudate swell from a slit is greater than that from a capillary die. At low die wall shear rates it goes to a value of about 1.2 as opposed to about 1.1 found for capillary dies. The onset and character of extrudate distortion have been studied. The experimental results are compared with theories of swell based on unconstrained recovery from Poiseuille flow in these geometries. A detailed analysis of such theories of extrudate swell based on the original work of Tanner has been carried out. The analysis is placed in a more general form which should be valid for a range of die cross‐sections.
Fluid transport in thin film polymer processors
Authors: McKelvey James M. , Sharps G. Vincent
Published: December 2004

An analysis of fluid transport in a polymer processor consisting of a hollow vertical cylinder with rotating blades is presented. The action of the rotating blades causes a thin film to be deposited on the inner surface of the processor and a bow wave to form in front of the blade. Fluid transport through the processor depends upon flow within the bow wave. Three types of flows are identified as contributing to the fluid transport: flow under the influence of a pressure gradient, flow due to gravitational force, and drag flow due to the action of the rotating blades. Equations describing these flows are derived as well as an equation for the bow wave profile. Experimental data in good agreement with the theoretical development are presented.
Thermoset and coatings technology: The challenge of interdisciplinary chemistry
Authors: Roller M. B.
Published: December 2004

Modem thermoset and coatings technologies provide the challenge of combining in situ polymer synthesis and processing with the task of characterizing an insoluble, intractable product. During the last dozen years several tools have been developed in J. K. Gillham's Princeton Laboratory which provide insight into this complex interrelationship. Although not necessarily conceived exclusively for thermoset characterization, these tools have been found to be uniquely suited to the task. To be discussed are the application of the torsional braid analyzer, a programmable pyrolyzer and thermal analysis to the study of coatings and thermosets in general. Also included is a discussion of a time‐temperature phase diagram for the thermoset analysis and the study of the formation of spiral and helical cracks in reinforced thermosets.
Linear decomposition of thermomechanical relaxations in polymers
Authors: Hazony Yehonathan
Published: December 2004

The methodology of linear decomposition of thermomechanical relaxation phenomena in polymers is outlined. Experimental data obtained from Torsional Braid Analysis (TBA) experiments for tactic poly(methyl methacrylate) are analyzed and the physical significance of the results is discussed.
Equation of state of cis‐1,4‐polybutadiene melt
Authors: Jain R. K. , Simha Robert
Published: December 2004

Recent equation of state data are analyzed in terms of the hole theory of polymer melts. The good agreement between experimental and theoretical volume‐temperature curves at atmospheric pressure, observed previously for a number of amorphous and crystallizable polymers, is again confirmed. Similarly, satisfactory theoretical results for the isotherms ensue, with deviations however becoming noticeable at elevated pressures and low temperatures. The linearity of the isochores observed experimentally is confirmed by the theory, however with somewhat different slopes. Departures of maximally 10 percent from the thermal pressure coefficients derived from the experimental PVT data are noted. Significant differences between theory and experiment apper only in the third derivatives of the partition function, as has also been observed with other pollymers. The characteristic scaling parameters of volume, temperature and pressure show the expected similarity with hevea rubber. Earlier correlations for scaling entropy and segmental volume with scaling temperature are found to be valid within the scatter of these relations. Finally, the applicability of the empirical Tait equation in the form applied to the equation of state in other polymer melts is confirmed. Although the resulting thermal pressure coefficient exhibits an explicit even if smal dependence on temperature, in disagreement with experiment or theory, the Tait equation remains a useful relation for the representation of PVT information.
Laser degradation of polymer coatings on reflective heat sinks
Authors: Cozzens Robert F. , Fox Robert B. , Echols William H.
Published: December 2004

The 10.6 μm laser‐induced degradation and volatilization of thin non‐char forming organic polymer coatings on aluminum heat sinks has been investigated. Volatilization rates were determined from coating absorptivities measured as a function of irradiation time at 110 W/cm2. First order volatilization rate constants (kJ−1) were: poly(ethylene‐co‐ethyl acrylate) 0.30, polystyrene 0.85, poly(ethyl methacrylate) 1.6, poly(methyl methacrylate) 2.1, and nitrocellulose 3.1. Residual coating thicknesses at infinite irradiation time are reported. Degradation results from exposure to the thermal environment provided by the heat sink as well as by the direct absorption of laser radiation. Relative polymer thermal stabilities measured at this laser irradiance level and by conventional heating methods are in agreement.
Simultaneous interpetrating network based on castor oil elastomers and polystyrene. III. Morphology and glass transition behavior
Authors: Devia N. , Manson J. A. , Sperling L. H. , Conde A.
Published: December 2004

Electron microscopy and dynamic mechanical spectroscopy (DMS) techniques were used to study the morphology and glass transition behavior of simultaneous interpenetrating networks (SIN's), based on three different castor oil derived elastomers, and polystyrene (PS) plastic erosslinked with 1 percent divinyl benzene. The castor oil elastomers consisted of either the sebacic acid polyester, 2,4‐tolylene diisocyanate polyurethane, or the mixed poly(ester‐urethane). Emphasis was placed on two compositions having 10 and 40 percent elastomer contents by weight of each type, the remainder being PS. In all cases, a two‐phase morphology emerged. With the 10 percent elastomer composition, the use of vigorous stirring during the early stages of reaction resulted in materials having the crosslinked polystyrene as the continuous phase and elastomer domains (ranging from 100 to 8000 nm in size) as the discontinuous phase. The elastomer domains contained a polystyrene cellular structure, with the polystyrene cell sizes ranging from 50 to 300 nm size. Several examples showed morphologies resembling high impact polystyrene. Materials having a 40 percent elastomer content always showed a continuous phase of castor oil elastomer, with the PS displaying a bimodal size cellular structure. Domain sizes ranged from 10 to 860 nm. The DMS studies showed two well‐defined glass transitions near their respective homopolymer glass transitions, but shifted inwards to greater or lesser extents indicating some molecular mixing between the two polymers. The glass transition of the pure elastomer phase occurred at −66°C for the castor oil polyester elastomer, −4°C for the castor oil polyurethane elastomer and −50°C for the castor oil poly(ester‐urethane) elastomer. Phase separation in these materials is postulated to occur by two mechanisms: (1) multiple precipitation of polystyrene chains at progressive levels of polymerization and (2) microsyneresis processes. The thermodynamics of mixing and phase separation in polymerizing SIN's is examined in some detail.
Heat transfer in blow molding operations
Authors: Edwards M. F. , Suvanaphen P. K. , Wilkinson W. L.
Published: December 2004

A one‐dimensional model of unsteady state heat conduction has been applied to the cooling and solidification of a polymer in a blow molding process. The approach includes a temperature‐dependent specific heat term to account for latent heat effects during the phase change. The model is used to predict temperature profiles in a thick‐walled component of high‐density polyethylene. These profiles lead to a clearer understanding of the heat transfer process. It is further shown that these temperature distributions can be used to study the influence of the major process variables upon the cooling of the molded component.
Aluminum/carbon fiber hybrid composites
Authors: Hancox N. L. , Wells H.
Published: December 2004

An effective, economic way of using carbon fiber is to combine it with a resin and another material, either a fiber or a metal, to produce a hybrid structure. Some of the properties of a hybrid beam made by attaching carbon composite to either side of an aluminum channel section are described here. The structure has considerable potential in the orthotics field; the aluminum core assists in the forming of, for instance, orthoses (calipers), modifies the failure characteristics of the carbon fiber composite, and eases the problem of jointing and adjustment of finished articles. Difficulties can arise when combining carbon composites and metals because of differences in thermal expansion behavior. To alleviate these effects a urethane modified epoxide resin matrix, which has very good adhesive properties, was employed. The work covers measurements of strength and modulus, evaluation of the aluminum/aluminum bond strength, and the flexural fatigue performance.
Coupling of optical and mechanical properties in crystalline polymers
Authors: Seferis James C. , Samuels Robert J.
Published: December 2004

The modules and birefringence of oriented polymers are known to couple through the structural and intrinsic properties of the polymer. Recent developments in both optical and mechanical theories have allowed this coupling to be expanded so that it includes predictions of modulus and refractive indices of uniaxially‐oriented polymer films at various angles to the draw direction. The validity of these theories has been tested in this study by predicting the angular dependence of the optical and mechanical properties of seven uniaxiallyoriented films of isotactic polypropylene. The present study also provides intrinsic material properties associated with the crystalline and noncrystalline components of the polymer, and consequently allows the identification of the structural parameters that control the properties of ultra‐high oriented isotactic polypropylene.