bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermal transport in the contact melting of solids
Authors: Griffin O. M.
Published: December 2004

Many industrial processes require that solids be transformed to the molten state, thus accurate correlations of heat transfer and melting rates are important in process design. The heat‐balance integral type of analysis is applied here to melter systems where phase change and convection effects are of equal importance, and the appropriate parameters that govern the thermal transport process are presented. Applications of the results to both Newtonian and non‐Newtonian, power‐law melts are discussed, and extensions to variable property situations are outlined. Although the results herein are directly applicable to contact melting systems, the governing parameters are useful in the correlation of other melting processes as well. Acomparison is made between the theory and some experimental data for a gravity‐feed contact melter. The results are directly applicable in practice to the melting of bulk and granular crystalline polymers on melting grids, tube bundles, and plates.
Cold rolled ABS. Part 2: Rubber morphology and tensile properties of hot stretched and cold rolled ABS
Authors: Grancio M. R. , Bibeau A. A. , Claver G. C.
Published: December 2004

Cold rolling and hot stretching (105°C) both lead to increased failure stress and decreased stress whitening in model ABS composites while hot stretched samples alone retain a tensile yield dip. Further differences between hot stretching and cold rolling are revealed in electron micrographs obtained by the Kato method. In the hot stretched samples the ruber particles appear as elongated “cigar‐like” smooth ellipsoids which reflect the observed macroscopic orientation. SAN occlusions within the ruber particles are deformed to the same degree as the rubber. Ruber particles in cold rolled samples, however, exhibit a jagged, “hairy” surface indicating a high degree of shear distortion; and SAN occlusions within the rubber particles are not deformed in rolling. The rubber particles in cold rolled ABS are flattened and disk‐like rather than ellipsoidal.
Kinetics of the thermal degradation of poly(1,4‐cyclohexylenedimethylene terephthalate)
Authors: Gregory D. R. , Watson M. T.
Published: December 2004

The kinetics for the thermal degradation of poly (1,4‐cyclohexylenedimethylene terephthalate) (PCHDT) were evaluated by means of a melt extruder. The effects of temperature, residence time, and oxygen content of the gas blanketing the polymer during storage on degradation of PCHDT were determined. The rate of thermal degradation was measured in terms of the rate of decrease of inherent viscosity and the rate of increase of carboxyl end group concentration.

Residence time, temperature, and their interaction all contributed significantly to the degradation. For the conditions investigated, the oxygen content of the blanketing gas had no measurable effect on degradation. Analysis of the kinetic data yielded equations based on a random chain scission mechanism. These equations enabled the prediction of inherent viscosity and carboxyl end group concentration as functions of temperature and residence time and the inherent viscosity and carboxyl end group concentration of the original polymer. The activation energies for decrease in inherent viscosity and increase in carboxyl end group concentration of poly (1,4‐cyclohexylenedimethylene terephthalate) were determined as 38.7 kcal/mole, respectively.
The effect of light on some commercially important polymers
Authors: Wiles D. M.
Published: December 2004

Most organic polymers are damaged by exposure to terrestrial sunlight and eventually the useful properties are lost. Once absorbed, radiation in the erythmal region of the solar spectrum has sufficient energy to cause the rupture of polymer chain bonds.

It can be difficult to identify the important chromophores in a polymer system and even more difficult to determine precisely what happens to them following electronic excitation. The number of chemical events leading to the mechanical failure of a plastic can be remarkably small although the variety of them is potentially large.

Polypropylene is discussed as an example of a thermoplastic which invariably contains small amounts of light‐absorbing impurities and which, if unprotected, is highly susceptible to photo‐oxidation. Polyethylene terephthalate is used to illustrate a class of polymers which is susceptible to actinic deterioration owing to chromophores in the repeating unit. The primary photochemical reactions occurring in these two systems are described, with improved methods for UV stabilization in mind.
Vapor sorption and liquid interactions with glassy polyblends of polystyrene and poly(2,6‐dimethyl‐1,4‐phenylene oxide)
Authors: Jacques C. H. M. , Hopfenberg H. B. , Stannett V.
Published: December 2004

Polystyrene, poly(phenylene oxide), and solution‐cast blends of the parent homopolymers were exposed to normal hexane in the liquid and vapor phase. The kinetics of absorption and desorption, the sorption equilibria, and the kinetics of morphological changes were studied as a function of temperature and blend composition.

Absorption kinetics of n‐hexane vapor in all blends were largely controlled by polymer relaxations. The sorption rates from the vapor phase varied monotonically with blend composition and increased over a range of four orders of magnitude with increasing poly(phenylene oxide) content. The equilibrium n‐hexane content similarly increased monotonically with poly(phenylene oxide) content although the increase was only by a factor of two over the entire range of compositions. These results were interpreted in light of and were completely consistent with earlier findings with pure polystyrene homopolymer.

Films immersed in liquid n‐hexane produced a white, opaque outer shell surrounding an essentially unaffected central core. The kinetics of this whitening process were much more rapid for each of the homopolymers than the kinetics characterizing morphological changes in the blends. These data suggest that film whitening is caused by crazing in the polystyrene‐rich samples and that solvent‐induced crystallization is involved in the whitening of the poly (phenylene oxide) rich material.
Implications of extensional flows in polymer fabrication processes
Authors: Denson C. D.
Published: December 2004

The various types of extensional flows and extensional viscosities are defined and methods of measurement discussed. The role that each of these extensional viscosities plays in various polymer fabrication processes is discussed with examples. Finally, it is shown how engineering analyses of these complex flow fields are conducted using simplified phenomenological equations for the rheological behavior. This approach is recommended for use until such time as tensorially correct, mathematically tractable constitutive equations that are based on molecular theory are available.
Comparison between some empirical equations of state for polymers
Authors: Kamal Musa R. , Levan N. T.
Published: December 2004

Some commonly used empirical equations of state for polymers are considered: the Spencer‐Gilmore equation with two and three adjustable parameters, the Whitaker‐Griskey equation, and the Rehage‐Breuer equation. Also, a new equation is proposed: the Inverse Volume equation. These equations are evaluated with regard to fitting experimental P‐V‐T data and agreement with experimental data on isothermal compressibility and thermal expansion coefficient. The adjustable parameters for each equation are determined with the help of Rosenbrock's optimum‐seeking technique. Analysis of the residuals on specific volume for a variety of materials suggests that the Spencer‐Gilmore equation with three adjustable parameters, the Rehage‐Breuer and the Inverse Volume equations yield the smallest and most random residuals and thus the least systematic error. The same three equations mentioned above yield results in good agreement with experimental isothermal compressibility data. However, among all the equations considered in this study, the Inverse Volume equation yields the best agreement with experimental thermal expansion coefficient data. Furthermore, it is the only equation to correctly predict the rise in thermal expansion coefficient with increasing temperature.
Reflectivity of iridescent coextruded multilayered plastic films
Authors: Radford J. A. , Alfrey T. , Schrenk W. J.
Published: December 2004

Coextruded plastic films containing 231 alternating layers of polystyrene and polymethylmethacrylate have been made with individual layer thickness in the range of .06–0.1μ. Due to the difference in refractive indices these unique films can be made to reflect portions of the visible spectrum, yielding a highly iridescent appearance.

Reflectivity measured on films of known layer thickness distribution correlated with values predicted from optical theory.
An introduction to blood compatible polymer surfaces for use in artificial internal organs
Authors: Olsen Douglas A. , Kletschka Harold D. , Rafferty Edson H.
Published: December 2004

While the body is a hostile environment for all types of polymers, an even more serious problem is that of thrombus formation induced by all foreign surfaces, including polymeric surfaces. This is a still largely unsolved problem which hinders the development of artificial internal organs. The thromboresistant materials presently proposed and used in artificial organs include heparinized surfaces and materials found to be thromboresistant in certain implantation cites. In this article tissue‐polymer interactions are first discussed and then followed by a discussion of blood‐polymer interactions. The mechanism of thrombus formation is presented and some of the possible interactions of blood with surfaces are suggested. Representative nonthrombogenic and thromboresistant materials are discussed.
Heat transfer to flowing thermally softened polymers
Authors: Griskey Richard G. , Choi Min H. , Siskovic Nandor
Published: December 2004

Heat transfer to a flowing thermally softened polymer (polymethylmethacrylate) has been studied. Experimental temperature profiles were determined at various axial lengths. The data are both precise and reproducible. Sizeable viscous dissipation was found to occur. This effect was found to be greater for polymethylmethacrylate than a molten polymer (polyethylene). Cooling as well as heating data were found in this work. The experimentally determined data checked qualitatively with the data computed from a prior analytical solution of the equations of motion and energy.
Development of stress‐crystallized morphology during melt‐spinning of polypropylene fibers
Authors: Fung P. Y.‐F. , Orlando E. , Carr S. H.
Published: December 2004

Melt‐spinning of isotactic polypropylene was performed in an effort to assess how the flow field that exists within a filament affects final as‐spun fiber morphology. It was concluded that the molten filament deforms chiefly by elongational flow, with some small amount of shearing flow bearing localized near the filament periphery. The resulting crystal texture is mostly comprised of lamellae oriented perpendicular (chain direction parallel) to the fiber axis, but a minority population of crystallites whose orientation is orthogonal (chain direction perpendicular) to the primary population is also present in these fibers. Post‐drawing steps initially cause crystallites to rotate toward the axial direction, while the chains within them undergo intralamellar slip and become better oriented parallel to the fiber axis. At larger extensions, lamellar crystallites are pulled into microfibrillar units.
Interpretation of the “melt strength” test
Authors: Wissbrun Kurt F.
Published: December 2004

The “melt strength” test for molten polymers is shown to be a function of several rheological parameters. Interpretation of results in terms of extensional viscosity differences is consequently not straightforward, if possible at all.
Study of the variables affecting pressure drop and temperature rise in blow molding dies
Authors: Kim H. T. , Darby J. P. , Wilson G. F.
Published: December 2004

The extrusion head systems for both pipe and blow molding were analyzed theoretically and relationships derived between pressure drop and temperature rise for various materials at different flow rates and die restrictions.

Because of the complexity of the geometry involved, the die was segmented into several sections axially and momentum and energy equations for these sections were solved with the help of IBM 360. The floating boundary conditions were used in order to take into account the nature of the flow phenomenon involved.

To complement and support this theoretical work, rigid polyvinyl chloride (PVC) bottle compounds were used to obtain extrusion data on a 3½ inch extruder with several different die sizes. A good agreement was found between the predicted versus experimental data. Results showed that temperature rise in the die systems in significant and that neglecting it would result in a gross error in the calculated pressure drop.

Based on this work, a simplified version of the theoretical equation was developed to serve as an engineering tool in estimating pressure drop and stock temperature for a given material where extreme accuracy is not essential. Results of the engineering equation which contains several empirical constants correlate well with the data and support the theoretical effort.
Solvent crazing of polystyrene and polymethylmethacrylate
Authors: Earl B. L. , Loneragan R. J. , Johns J. H. T. , Crook M.
Published: December 2004

The minimum surface strain required to induce crazing in polymethylmethacrylate and polystyrene in the presence of alcohols and n‐heptane has been determined at various temperatures by bending strips of the polymers around formers of varying curvature and immersing them in the liquid reagents. For each polymer/liquid system the long‐term crazing strain was independent of test temperature except within a single 30°C interval in which it decreased as the test temperature was raised. It was found that this temperature region corresponded to the glass‐rubber transition of the given polymer when, after extended periods of immersion it had achieved equilibrium liquid sorption. This suggested that, in the crazing tests, a condition approximating to equilibrium sorption was being established at the craze tip and that crazing occurred on applying small strains in the presence of the liquids because of their plasticising effect.

It was found that not only the plasticizing effect of the liquid environment but also the liquid molecule size influenced the crazing strain; the larger‐molecule liquids caused lower long‐term crazing strains than did the smaller‐molecule liquids.
DTA for control of stability in polyolefin wire and cable compounds
Authors: Howard John B.
Published: December 2004

Differential thermal analysis offers a convenient and rapid way of determining stabilization levels in polyolefin compositions. Since it is normally used at temperatures in the fabrication range, it provides a direct readout of processing stability. At the same time, because the chemistry of the polymer system at these temperatures may be quite different from that at normal use temperatures, judgment must be exercised in attempting to extrapolate high temperature data. New factors can come in at either end of the temperature range which are inoperative at the other extreme.

The experimental procedures used are described, and the special precautions necessary for operation down to the 140–150°C range indicated. Problems arising from sample inhomogeneities are discussed, and the critical importance of stabilizer migration in the solid state pointed out, including invalidation of extrapolation down to normal temperatures of data taken above the melting range.
Glass transition temperature as a guide to selection of polymers suitable for PTC materials
Authors: Meyer J.
Published: December 2004

It has been shown that the only way to predict the size of the PTC effect displayed by a crystalline polymer when filled with conductive particles is through the knowledge of the glass transition point of the polymer. The size of the PTC anomaly is found to decrease sharply with rise in glass transition temperature and for a polymer to be a useful PTC material its glass transition must be below 0°C. It has not been possible to explain this relationship by any of the current theories of the PTC mechanism in filled polymers.
The measurement of melt flow and melt stability
Authors: Longworth Ruskin
Published: December 2004

The melt flow of a plastic as measured by the standard method (ASTM D‐1238) is at a high enough stress so that the flow is non‐Newtonian. If the die in the plastometer is replaced by a nonstandard, tapered die of large orifice, a lower stress can be used and the flows are shown to be comparable to Newtonian viscosities measured in a cone and plate rheometer. Under these conditions the plastometer can be used as a sensitive measure of the melt stability of a plastic.
Stress‐strain behavior of polychloroprene vulcanizates containing polymer‐gel particles
Authors: Kawasaki Nobuhiro
Published: December 2004

The equations of stress‐strain of gel‐filled polymer under large deformation were derived by using a simple model i.e. a sphere in a cubic matrix. The author finds for no adhesion between the phases:equation imageIn case of perfect adhesion between the phases:equation imagewhere σ(α) is the stress of a blend at an elongation ratio of α, σR(α) the stress of a rubber matrix at α, σG(αG) the stress of a gel component at αG, σR(αR) the stress of a rubber matrix at αR, ϕ the volume fraction of gel. The validity ofEq 1was shown for the polychloroprene vulcanizates containing polystyrene‐gel which exhibits no adhesion with the polychloroprene matrix. This result shows the value of the model proposed here. The tensile strength of polychloroprene vulcanizates filled with polychloroprene‐gel at break is discussed by the use ofEqs 2–4.
Simulation of the mold‐filling process
Authors: Wu P.‐C. , Huang C. F. , Gogos C. G.
Published: December 2004

The transport equations for a power law fluid are used to solve the transient and non‐isothermal problem of filling a disk‐shaped cavity. Using the results obtained it is possible to predict gate pressures, fill times and short shots. Furthermore, the velocity and temperature fields can be obtained throughout the filling process. This information specifies the formation of a frozen surface layer during filling. Rigid PVC was primarily used in the simulations, but some results are also given for linear polyethylene, nylon 6–6, ABS and polystyrene.
Design of extruder dies using thermoplastics melt properties data
Authors: Powell P. C.
Published: December 2004

The procedures developed in this paper enable the die designer to estimate the dimensions of the die at the exit and to define a flow channel within the body of the die appropriate to the required dimensions and output rate of the extruded product. Design procedures are given for predicting die swell (and hence die exit dimensions) from a knowledge of product dimensions, output rate and the basic shear, elasticity, and viscosity data. Within the body of the die the length and included angle of a convergent tapered section should be such that the critical tensile deformation rate is not exceeded. At the die entry the taper angle is related to the tensile and shear viscosities. Analytical expressions based on flow data are given for predicting pressure drops resulting from flow through circular and slot dies of constant cross‐section and through conical and wedge‐shaped dies. A numerical example shows how the theory may be applied to the design of a die for a thin‐walled tube. For the resultant die design, the likely effects are predicted to changes in output rate and melt temperature for the chosen material, of changes in grade of the same type of polymer, and of changes in polymer type.
The concentration and possible source of unstable sites in PVC
Authors: Berens A. R.
Published: December 2004

Copolymers of vinyl chloride with 2‐chloropropene were prepared as models for tertiary‐chlorine branching in PVC. Rates of thermal dehydrochlorination of copolymers containing up to 2 mol percent 2‐chloropropene were found to be a linear function of composition. By comparing the decomposition rates of the copolymers with that of PVC prepared under similar conditions, we estimate the maximum tertiary‐chlorine content of PVC at 0.1 to 0.2 mol percent. This figure is of the same magnitude as estimates of the content of tertiary‐chlorine, random unsaturation, and long‐chain branching obtained in previously published studies of PVC. Possible mechanisms for tertiary‐chlorine branch formation include chain‐transfer to polymer and copolymerization with unsaturated chain‐ends. By applying the conventional copolymerization equation, using the reactivity ratios of the vinyl chloride/2‐chloropropene system, it is shown that the copolymerization mechanism predicts a tertiary‐chlorine branch content close to the estimated value. Both mechanisms also agree qualitatively with reported effects of polymerization temperature and conversion on branching and thermal stability.
Melting of crystallites in polymers with low degree of crystallinity under shear flow conditions I: Poly(vinyl chloride)
Authors: Lyngaae‐Jørgensen J.
Published: December 2004

The aggregates found in dilute solutions of nearly atactic PVC have been shown to consist of 10 to 15 single molecules held together by a crystalline nucleus. Based on the postulate that the last crystallites in a PVC melt have the same structure as found in dilute solution, a relation between the melting temperature in shear (Tdyn), the static melting temperature (Tm) and the shear stress (τ) is found:

where Q is a constant. The model predictions are in accordance with data from a Brabender rheometer and a Rheometrics mechanical spectrometer. Q is found to be a constant for samples with weight average molecular weights in the interval between 70,000 and 160,000 corresponding to polymerization temperatures between 40 and 70°C.
PVC melt rheology III: The effect of order and molecular weight on the shear rate dependence
Authors: Collins Edward A. , Daniels Charles A.
Published: December 2004

The effect of polymerization temperature on the melt flow behavior of PVC of varying molecular weights has been studied over a wide shear rate range. For the same molecular weight, higher melt viscosities are observed for polymers prepared at lower temperatures. The shear rate dependence of the viscosity vs molecular weight plot is shown to be nonlinear over the shear rates examined. The inability to achieve a limiting zero‐shear viscosity is discussed.
Processing‐morphology‐property studies of poly(vinyl chloride)
Authors: Singleton C. , Isner J. , Gezovich D. M. , Tsou P. K. C. , Geil P. H. , Collins E. A.
Published: December 2004

Recent morphological studies of plasticized and unplasticified poly(vinyl chloride) (PVC) are reviewed. Suspension polymerized PVC contains particles in a number of different size ranges 100–200Å, 1000–5000Å, 1μ and larger. The larger size particles are broken down during plasticization but both the 100Å and the 1000Å suspension particles retain their identity. The visibility, and presumably, coalescence of these particles is a function of the processing conditions. In particular, the size of the 100Å particle increases with plasticizer content and is most distinct as characterized both by small angle x‐ray scattering and electron microscopy for milling temperatures in the 160–170°C. range. Consideration is given to the effect of these particles, their structure, and interrelationship on the rheological properties of the resins.
A hysteresis in plasticized poly(vinyl chloride)
Authors: Deanin Rudolph D. , Shah Sharad B. , Kapasi Vikram C. , Pfister David H. , Putriment Paul
Published: December 2004

Plasticized poly(vinyl chloride) formulations were prepared in solid and foam form, and mechanical hysteresis was measured by low‐speed tension and compression on an Instron tester and by high‐speed rebound on a resiliometer. Hysteresis was greatest in copolymers with vinyl acetate, at low plasticizer concentration, with inefficient plasticizers, at high concentrations of reinforcing fillers, at high expansion to low density, and at high speed of testing. Conversely, resilience was greatest at high plasticizer concentration, with more efficient plasticizers, with non‐reinforcing fillers, and at high density.
Liquid flow through aligned fiber beds
Authors: Williams J. G. , Morris C. E. M. , Ennis B. C.
Published: December 2004

The influence of surface properties on the flow of fluids, including epoxy resin, through aligned glass and other fiber beds has been examined. The observed flow rates were higher than those predicted from the Kozeny‐Carman equation, and were influenced by the surface properties of the fluid used. This is attributed to variations in the distribution of porosities and to the presence of air bubbles trapped during the initial wetting of the bed. The implications of these findings to the preparation of composites are discussed.
Mechanical properties of impregnated asbestos‐cement
Authors: Godard P. , Delvaux P. , Faille M. Della , Mercier J. P.
Published: December 2004

This study is devoted to the mechanical properties of impregnated asbestos‐cements. We studied the influence of the degree of impregnation and of the nature of the resin on the modulus of elasticity and on the strength of the materials. The impregnation of asbestos‐cement by polymeric resins produces composites of outstanding mechanical properties. The relative increase in flexural and tensile strength is much higher for mortar and concrete but the improvement produced by the polymer on asbestos‐cement is especially significant if one takes into consideration the already high absolute strengths of the materials.
Vapor and liquid equilibria in glassy polyblends of polystyrene and poly(2,6‐dimethyl‐1,4‐phenylene oxide) Part I
Authors: Jacques C. H. M. , Hopfenberg H. B.
Published: December 2004

The equilibrium sorption of n‐hexane vapor and n‐hexane liquid in solution cast films of polystyrene, poly(phenylene oxide), and blends of these homopolymers was studied over a significant range of penetrant activity and temperature. These equilibrium sorption measurements were supplemented by density determinations, refractive index measurements, differential scanning calorimetry and differential thermal analysis. A seemingly complicated pattern of results emerged when the equilibrium penetrant content was plotted as a function of blend composition. At relatively low activity and temperature the equilibrium concentration of n‐hexane in these films monotonically increased with poly(phenylene oxide) content in the blend. Conversely, at high activities and in unit activity liquid, the equilibrium penetrant concentration exhibited a distinct minimum when plotted as a function of blend composition. At higher activities, solvent induced crazing accompanied the sorption of penetrant. These results were explained consistently by considering the nature of the sorption isotherm over an activity range sufficient to lower the glass transition temperature, of the equilibrated and swollen blend, below the temperature of the sorption experiment. Most importantly, the interpretation and explanation of these data are based upon phenomena common to all glassy polymer‐organic penetrant systems and no special properties of this blend system were included in the analysis. The results, therefore, reflect the apparent homogeneity of polystyrene‐poly (phenylene oxide) blends and are useful in considering the equilibrium of penetrant sorption in glassy polymers as a general class of materials.
Why do polymer molecules fold?
Authors: Lindenmeyer Paul H.
Published: December 2004

In the process of transforming from liquid to crystal, a polymer molecule must assume conformations which cause it to have a higher free energy than either the liquid or the crystal. This free energy barrier to crystallization is minimized if the molecule folds, thus providing both the driving force for folding as well as the assurance that the crystallization behaves as a classical kinetically‐controlled process. This free energy barrier exists equally well for the melting of extended chain crystals accounting for their observed super‐heating. Finally these ideas can be extrapolated to predict some rather unconventional conclusions with regard to polymer conformation in the melt.
Electron beam processing systems (a state of the art review)
Authors: Hatzakis M.
Published: December 2004

This paper presents a review of electron‐sensitive resists evaluated for electron beam exposure. This includes positive as well as negative resists and their relative merits and drawbacks. The paper also presents general guidelines that can be used in evaluating any electron resist system for performance and usefulness in electron beam microfabrication.
Lithography and radiation chemistry of epoxy containing negative electron resists
Authors: Thompson L. F. , Feit E. D. , Heidenreich R. D.
Published: December 2004

A class of negative electron‐beam resists is described which have excellent lithographic characteristics. The resists are copolymers of glycidyl methacrylate and ethyl acrylate. Their molecular weights, epoxy contents, and polydispersivities can be controlled to give an adjustable range of electron sensitivity and contrast. The copolymers are compared to other epoxy containing, negative electron‐beam resists.

Micrography of resist profiles generated from a single line scan of the electron beam have been used to illustrate the complex interaction of accelerating voltage of the electron beam and resist contrast on resolution. Optical gratings made from single line scans of the beam have feature sizes less than 300 nm in the resist, etched metals, and dielectrics.
Linear polycarboranesiloxanes
Authors: Roller M. B. , Gillham J. K.
Published: December 2004

Aspects of the present status of structure‐property correlations for linear polycarboranesiloxanes which contain rigid carborane cages and flexible siloxane in‐chain linkages are discussed. Low temperature secondary transitions, glass transitions, crystallization and melting transitions, and high temperature chemical transformations in inert and air atmospheres are emphasized. The linear polymers serve as the basis for new high‐temperature elastomers.
16‐Year creep of polyethylene and PVC
Authors: Findley William Nichols , Tracy Joseph Francis
Published: December 2004

Creep tests at constant values of tensile stress, temperature, and relative humidity for two thermoplastics were conducted for approximately 132,000 hr. The strains, ϵ, for the first 2000 hr of time, t, were described by an equation of the form ϵ = ϵo + ϵ+tn where all other symbols are constants. This equation was found to predict the creep of poly(vinyl chloride) for approximately 132,000 hr with reasonable accuracy. The predicted strains for polyethylene (density 0.924) were somewhat low. Strains during unloading and reloading after 90,000 hr of creep were predicted reasonably well by the Boltzmann superposition principle.
Pressure generation mechanisms in the feed section of screw extruders
Authors: Lovegrove J. G. A. , Williams J. G.
Published: December 2004

The generation of pressure in the feed section of an extruder is analyzed. It is concluded that body forces must be considered since they provide the necessary conditions for pressure initiation. Solutions are given which take into account gravity forces in both vertical and horizontal screws together with centrifugal force. Some numerical results are also given which illustrate the practical importance of these effects.
Characterization of mechanical properties of thermoplastic films by creep measurements
Authors: Huntsberger J. R.
Published: December 2004

Plasticized poly(methyl methacrylate) and methyl methacrylate/acrylate copolymer films were examined by isothermal creep at low loads measured at several temperatures from ∼Tg to Tg + 15°C. Viscosity calculated using η = σ/3\documentclass{article}\pagestyle{empty}\begin{document}$ \dot \varepsilon $\end{document} was plotted vs temperature giving precise values for Tg based on a viscosity criterion of η = 1013 poises. Creep fracture data at various temperatures below Tg were interpreted using the maximum apparent viscosity measured at the minima of strain rate vs strain curves. Plots of ηmax VS stress at several temperatures gave values of ΔTg/Δσ of −1° to 2°C/106 N/m2 in agreement with treatment of ΔTg/Δσ based on free volume. Fracture occurred at low elongations when ηmax was ≥1013 poises, and at higher elongations when ηmax was <1013 poises supporting the concept that fracture is related to the lowering of Tg under stress. Plots of log σ VS log εb (the elongation at fracture) had the same form as that for crosslinked elastomers above Tg reported by T. L. Smith. Plots of log \documentclass{article}\pagestyle{empty}\begin{document}$ \dot \varepsilon $\end{document}b VS log εb also had the same form supporting proposals on the rate sensitivity of fracture.
Behavior of zirconium compounds in polymers—A review
Authors: Blumenthal Warren B.
Published: December 2004

Zirconium compounds dispersed in polymers often bond the polymer molecules together, increasing their stability. This can generally be attributed to the formation of covalent bonds between zirconium atoms and small atoms of high electronegativity of the polymer molecule, to overlapping of pi orbitals of unsaturated moieties of the organic compound with sigma orbitals of the zirconium atoms, to fractional bond formation between zirconium and organic hydrogen, and to combinations of these. Bonding and its effects on physical properties have been achieved by molecular dispersions of zirconium compounds in the polymer, by dispersion of insoluble particles of zirconium compounds, and through residues from zirconium catalysts used in polymer preparation. Coatings and plastic components have been improved in strength and in durability by the dispersions. Compounds of other metals often perform similarly. The totality of relevant properties of zirconium compounds often leads to their preferential use.
Polymer‐glass separation in the spiral mold test
Authors: Kubát Josef , Szalánczi Akos
Published: December 2004

The spiral mold method (moldability test) was used in a study of phase separation occurring in glass‐containing polyethylene and polyamide melts. Pronounced separation effects were recorded for low density polyethylene containing 25 percent glass spheres with diameters ranging approximately from 50 to 100 μm, the glass concentration at the tip of the spiral exceeding 40 percent by weight. For melts containing smaller spheres or fibers the effect was of the order of a few percent. There was a decrease in glass concentration near the center of the spiral.
Maximum pressure developed by solid conveying force in screw extruders
Authors: Chung Chan I.
Published: December 2004

There are two distinct solid conveying theories that can be applied to plasticating screw extruders. One is Darnell and Mol's theory based on a solid‐to‐solid friction model and the other is Chung's theory based on a viscous shearing model. The two theories predict very different solid conveying performances for a same set of conditions. In this paper, the maximum pressures that can be developed inside plasticating screw extruders by the solid conveying force are calculated using each of the two theories. Comparison of the results may shed some light on the applicability of each theory for a particular extrusion operation.
Allyl fluoride copolymers
Authors: Waterman J. A. , Shorr L. M. , Shaham I.
Published: December 2004

Allyl fluoride can be copolymerized with vinyl chloride, vinyl acetate, ethyl acrylate, or SO2 using free radical types of initiation. The copolymerization of allyl fluorida with vinyl chloride is comparable to the free radical initiated copolymerization of propylene with vinyl chloride. The allyl fluoride‐vinyl acetate couple tends to form completely random copolymers, the reactivity ratios of the monomers being close to unity.
The thermal conductivity of nickel and copper dispersed in poly(vinyl chloride)
Authors: Kusy Robert P. , Corneliussen Roger D.
Published: December 2004

The thermal conductivity of segregated distributions of poly (vinyl chloride)/nickel (PVC/Ni) and poly(vinyl chloride)/copper (PVC/Cu) was measured for volume fractions ranging from 0 to 0.15. The thermal conductivities increased from 0.15 Btu/hr ft °F for unmodified PVC to 2.79 Btu/hr ft °F for PVC/15 percent Cu. While the thermal conductivity increased smoothly with volume loading, the electrical resistivity decreased discontinuously over fifteen orders of magnitude. Using the parallel slab model as a basis, a semi‐empirical model was deduced which described the thermal conductivity as a function of volume loading. With this work, a survey of the thermal, electrical, and mechanical properties of segregated PVC composites is complete.
Mecahnics of composites
Authors: Nicolais L.
Published: December 2004

The fundamental analysis of the mechanical response of composite media involves investigations on two levels of abstructions: the micro and the macro scale. These areas of study are known as micromechanics and lamination theory. This format is employed to treat a series of problems concerning (1) stiffness, creep, or viscoelastic properties; (2) strength and expansion properties for oriented continuous and short fibers; (3) randomly oriented fibers; (4) injection‐molded materials; and (5) particulate reinforcements.
Engineering potential of composite materials
Authors: Crivelli‐Visconti Ignazio
Published: December 2004

This note illustrates how the development rate for the use of composites as engineering materials has recently increased. Reasons for the expected even larger number of applications of composites in industry is explored. The engineering potential of composites is outlined in terms of properties and design aspects and mainly by pointing out how the proper use of a composite requires a clear knowledge of its application as well as the appropriate design technology. Examples of applications in different fields are reported with the aim of showing the high versatility of composites for a variety of engineering applications. The final part is devoted to cost aspects, which are considered in connection with the effects of composite use upon the total structure. The purpose is to show that a large number of interesting applications are already cost effective.
Ultra‐high‐modulus fibers from solution spinning
Authors: Ciferri A.
Published: December 2004

Ultra‐high‐modulus fibers such as Du Pont PRD‐49 (initial modulus up to ∼1000 g/den) and Monsanto X‐500 (initial modulus up to ∼600 g/den) are spun from solutions. Both polymers are characterized by a high intrinsic rigidity of individual molecular chains and considerable orientation along the fiber axis. The thermodynamics of solution for rigid and semirigid macromolecules is critically reviewed in order to illustrate conditions under which spontaneous formation of highly oriented fibers is expected. In the case of semirigid polymers, the free energy of (random) mixing pure solvent and parallellized polymer may, according to Flory, become positive for some critical value of a “flexibility parameter.” Formation of an ordered phase for semirigid polymers is not, however, observed by lowering temperature or increasing polymer concentration. In the case of rod‐like polymers, still according to Flory, at some critical value of polymer concentration (which decreases with the axial ratio of the macromolecule) the isotropic solution of rods undergoes phase separation with formation of a partly ordered solution. This theoretical prediction is satisfactorily verified by data. While Du Pont fibers are spun from this anisotropic solution, Monsanto's X‐500 only yields an isotropic solution at room temperature up to the limit of polymer concentration at which crystallization occurs. This inability of X‐500 to form anisotropic solutions at the expected critical concentration is attributed to a partial degree of flexibility. Mechanical properties and orientation of fibers spun from the anisotropic solution appear to be superior to those obtained by spinning from isotropic solution, according to Du Pont's results. When a polymer has a partial degree of flexibility, alteration of physico‐chemical variables such as solvent type, solvent composition, temperature, and polymer concentration may still be used in order to increase its rigidity. Theoretical arguments and data supporting this contention are discussed. Moreover, alteration of these variables may also be used to alter the crystallization temperature, allowing formation of the anisotropic solution to occur at a high enough polymer concentration. This expectation was verified in the case of X‐500. Finally, the all important role of mechanical orientation of solutions is emphasized. According to Hermans, under high enough shear stress, the difference between the isotropic and the anisotropic solution vanishes. In line with these consideration, drawing techniques are particularly useful in order to achieve almost‐perfect orientation and theoretical moduli.
Polymer modulus and morphology: The tensile properties of polyethylene
Authors: Porter Roger S. , Southern John H. , Weeks Norman
Published: December 2004

The general properties of a novel process for producing high modulus polyolefins are discussed. The technique is an extrusion drawing involving a crystal‐crystal transformation. The principal tests have been made on polyethylene and the guidelines have been established for extending the technique to other polyolefins. The characterization of such materials is extensively discussed, particularly in the light of the concept of continuous crystals.
Ultra‐high‐modulus linear polyethylene through controlled molecular weight and drawing
Authors: Capaccio G. , Ward I. M.
Published: December 2004

Recent work is presented on the plastic deformation of linear polyethylenes. This work demonstrates the importance of molecular weight and initial morphology in determining the drawing behavior, and shows that by appropriate choice of these two factors a substantial increase in draw ratio and hence stiffness can be achieved over conventionally‐oriented polyethylenes. Under optimum conditions a modulus of approximately 700 Kbar was obtained at a draw ratio of ∼30. These very high modulus materials displayed an extensibility to break of at least 3 percent and a strength of about 4 Kbar. In some cases they also exhibited very high melting points (∼139°C) and exceptionally good thermal stability.
Long term thromboresistance of heparinized surfaces
Authors: Ehrlich Julian
Published: December 2004

It has long been known that interaction of blood with artificial surfaces results in thrombogenic effects. With the increased use of prosthetic cardiovascular appliances, it is becoming more evident that surfaces which are thromboresistant are of utmost importance. A review is presented of the recent research on binding of heparin by ionic, covalent and thermal means, to different polymer surfaces, with the results of in vitro and in vivo tests. Additionally, a survey of theories on the role of heparin surfaces in thromboresistance is given.
Polyphosphazenes: Synthesis—properties—applications
Authors: Singler Robert E. , Schneider Nathaniel S. , Hagnauer Gary L.
Published: December 2004

Various aspects of polyphosphazene chemistry are reviewed. Stable poly (organophosphazenes) can be prepared from an inorganic precursor, poly(dichlorophosphazene), by careful control of polymerization and substitution reaction conditions. The bulk structure and properties of polyphosphazenes are discussed, and attention is given to those polymers which have promise as useful engineering materials. The successful preparation of stable poly(organophosphazenes) appears to have resulted in a new class of polymers for both specialty and large scale commercial development.
Polyurethane—polystyrene interpenetrating polymer networks
Authors: Kim S. C. , Klempner D. , Frisch K. C. , Frisch H. L. , Ghiradella H.
Published: December 2004

Two component interpenetrating polymer networks (IPN) of the SIN type (simultaneous interpenetrating networks), composed of a polystyrene network (crosslinked with divinyl benzene) and a polyester‐polyurethane network (crosslinked with trimethylolpropane), were made. Electron microscopy and glass‐transition measurements showed that phase separation had resulted with some interpenetration, presumably occurring at the boundaries. At a composition of about 75 percent polyurethane, a phase inversion occurred, the continuous phase being polystyrene at polyurethane compositions of less than 75 percent. The stress‐strain properties and hardness measurements agreed with these results. Enhanced tensile strength was observed in the IPN's in a concentration range where modulus reinforcement was not evident. A small enhancement in tear strength and thermal stability was also noted.
Molecular orientation effects on thermal conductivity of polydimethylsiloxane under shearing strain
Authors: Picot J. J. C. , Debeauvais F.
Published: December 2004

Experimental results for thermal conductivity and flow birefringence on liquid poly (dimethyl siloxane), PDMS, under a shearing strain are discussed. An increase in thermal conductivity with increasing shear rate is attributed to an increased degree of orientation in a direction at 45° to the flow direction for simple shear. A mathematical model is set up. It is based on the assumption that the macromolecules do not change their time‐average shape and otherwise behave as rigid, thin cylinders which can be influenced by convection and external fields and are endowed with rotational Brownian motion. The model predicts that thermal conductivity will reach a maximum value at moderate rates of strain and begin to decrease eventually reaching a minimum value (the transverse thermal conductivity of the basic element) at very high rates of strain when the molecules are completely aligned in the flow direction. Liquids studied were a 12,500 centipoise PDMS in the pure state and in solution in methyl ethyl ketone, MEK, as well as a 65,000 centipoise solution in MEK.
Certain aspects of film blowing of low‐density polyethylene
Authors: Menges G. , Predöhl W. O.
Published: December 2004

This article considers two topics: (1) Cooling of the film bubble and (2) Production of shrinkable film. Heat is transported by conduction, convection, and radiation, but only convection and radiation are relevant for the cooling results. Heat radiation can be calculated with known surface area, temperatures, and emission coefficient. Here we learn that the emission coefficient depends on the film thickness. Heat transfer by radiation amounts to about 15 percent of the total heat transfer. Heat transfer by convection normally can be calculated by known methods assuming ideal flow conditions. Because the flow conditions of the cooling air differ considerably from ideal conditions, known heat‐transfer laws give incorrect results. Therefore, a new formula was set‐up by determining the heat transfer conditions in real experiments.

Each blown film is shrinkable, but in most cases the influence of the die on the shrinkage is disregarded. The die causes an important anisotropy in the elastic behavior of the film. Further on, shrinkage is influenced by the degree of bubble deformation, the temperature profile, and the deformation velocity between die exit and freeze line. This is discussed qualitatively. A calculations is not yet possible because of the unknown relaxation behavior of the melt. The shrinkage of an LDPE blown film depends on time and temperature. Time and temperature are exchangeable variables.