bluuebunny/crossref_metadata_2025 huggingface dataset:
Diffusion in polymers
Authors: Hansen Charles M.
Published: December 2004

Concentration dependent diffusion coefficients explain Case II type diffusion. Solutions to the diffusion equation yield straight lines for weight gain vs time when the exponential variation of the diffusion coefficient is included. Boundary layer resistance together with concentration dependent diffusion coefficients explain Super Case II type diffusion. The increase in the rate of weight gain after a prolonged period is predictable. The surface concentration rises slowly to its equilibrium value in this case. Boundary layer resistance appears to be quite common, particularly where the penetrant has low affinity (not a true solvent) for the polymer, such as water in most polymers or hexane in polystyrene. Boundary layer resistance is quite significant for coatings (where film thicknesses are usually measured in microns), accounting for the majority of the resistance in some cases. A method to separate diffusional resistance from the surface resistance is suggested, but studies at different film thicknesses appear mandatory.
Modification to weld lines in extruded thermoplastic pipe using a rotating die system
Authors: Worth R. A.
Published: December 2004

When a polymer melt flows around the cross head or past the fins of a torpedo in a pipe die, a weld line is produced where the separated melt streams rejoin. This weld line may result in an area of weakness in the extruded pipe, although in the case of unfilled materials the effect can be reduced by using a compression section in the die. However, With fiber reinforced polymers it is unlikely that fibers will cross the weld line, and a reduction in strength is inevitable. It is shown theoretically that by rotating the core of the extrusion die the weld line can be modified to form a spiral around the pipe wall, with a large‐surface area for improved strength. Experimental investigations, which employ photographs of thin sections of pipe containing carbon black particles, support these conclusions.
Solid state extrusion of ultra high molecular weight polyethylene. Processing and properties
Authors: Zachariades Anagnostis E. , Watts Michael P. C. , Porter Roger S.
Published: December 2004

The techniques of solid state coextrusion and powder extrusion have been employed for the deformation of ultra high molecular weight polyethylene. Chain folded and chain extended morphologies obtained under different crystallization conditions were coextruded within a nylon 11 casing acting as a processing aid at an extrusion draw ratio (EDR) of 5 at ≤ 120°C and 0.20 GPa. The powder was compacted and extruded at ≤ 128°C and 0.23 GPa up to an EDR of 24. The physical and mechanical properties of the extrudates were evaluated and found to be dependent on intial morphology. An extrudate from the chain‐folded morphology gave a low modulus of 0.71 GPa, the chain‐extended morphology a modulus of 6.7 GPa, and the compacted powder a modulus of 15 GPa.
Structure vs stability in polymer degradation
Authors: Stivala S. S. , Reich Leo
Published: December 2004

All materials are subject to aging, a process of long‐term degradation, but not at the same rate or affected in the same manner. The wide variation in susceptibility (or resistance) of polymers to various degradative agents, e.g., oxidative, thermal, mechanical, chemical, biological, depend on their chemical composition and structure. Accordingly, the chemical, physical, and energy considerations inherent in the pure polymer are discussed in relation to degradative stability.
Design of coat‐hanger sheeting dies based on ratio of residence times in manifold and slot
Authors: Matsubara Yutaka
Published: December 2004

A new coat‐hanger die geometry with a uniform flow rate and optional ratio of residence times in manifold and slot is proposed. Such a die will be effective when thermal degradation in the die occurs, especially at die far end. This geometry is easily determined if the flow behavior index n of polymer is assumed. A suitable ratio greater than unity may be taken considering die‐height and cost, because lower height is attained as the ratio increases above unity. An example of a design calculation is shown.
Oriented monofilaments from blends of poly(ethylene terephthalate) and polypropylene
Authors: Rudin Alfred , Loucks D. A. , Goldwasser J. M.
Published: December 2004

Poly(ethylene terephthalate) and polypropylene are considered, to be incompatible by the usual criteria for polymer blends. Sheath/core filaments of these polymers could not be oriented because of poor adhesion of the base polymers. Melt blends of the two polymers with 30 and 50 weight percent polypropylene produced useful, oriented monofilaments. Tensile and dynamic mechanical properties of these filaments indicate that the structures consist of interlocked microfibrillar domains of the polyester and polyolefim. The glass transition region of poly(ethylene terephthalate) is not affected by admixture with polypropylene. A fine mutual dispersion of the two polymers was possible because the melt viscosities of the ingredients were reasonably well matched under the conditions of mixing. The melt viscosity and elasticity of blends were lower than those of either component as expected if the two polymers are immiscible. Monofilament extrusion and melt flow measurements were made with a one‐half inch single screw extruder.
Impact strength of polymers 2: The effect of cold working and residual stress in polycarbonates
Authors: Thakkar B. S. , Broutman L. J. , Kalpakjian S.
Published: December 2004

The influence of cold working on the toughness improvement in glassy amorphous polycarbonates was studied. Cold working processes, namely rolling and. Steckel rolling were used to produce thickness reductions up to 40 percent in flat‐strip specimens. The notched Izod impact strength and tensile properties were measured as a function of strip thickness reduction. It was shown that the toughness enhancement in polycarbonates cold worked to low thickness reductions was due to the residual stress state present as opposed to molecular orientation which becomes significant at higher degrees of cold work. Residual stress measurements were made by using the layer removal technique. Residual tensile stresses as high as 2100 psi were present in 1/4‐in. cold‐rolled polycarbonate at the surface. The maximum stress in the center of the specimen was 1100 psi in compression. The residual stresses at the surface decreased with increasing thickness reduction. The residual stress state for Steckel rolled. 1/2‐in. polycarbonate was also measured and found to be more complex than for the thinner samples, The results demonstrated that surface tensile stresses and interior compressive stresses can produce large values of impact strength if the notch is to be machined after cold working. Thus, the values of impact strength measured from the notch Izod specimen are sensitive to the residual stress state in the polymer. This behavior is in contrast to earlier studies on thermally quenched material in which the material was quenched after notching. The thermal quenching produced surface compressive stresses which were also present at the notch tip. The presence of compressive residual stresses at the center of the notch suppressed the formation of a craze leading to toughness enhancement in cold worked polycarbonate strips. It is shown that by control of residual stresses in polycarbonate, strips at least 1/2 in. in thickness can be made to exhibit ductile failure in the notched Izod impact test.
Nodal positioning analysis (NPA)—A numerical method for determining flow behavior of thermoplastic materials
Authors: Echenagucia J. , Fricke A. L. , Hassler J. C.
Published: December 2004

A finite difference method is presented for the solution of two dimensional flow problems in polymer processing. The method is applicable to narrow gaps of any shape and variable thickness. NPA was developed for analyzing the filling stage of the injection molding cycle, but it could be used in extrusion, blown film, and other polymer processing operations. In NPA the position of the flow front is calculated at the end of each time increment, and an axial node is placed at the newest location of the flow front. Each axial node is then divided into a determined number of radial nodes. The velocity and temperature profiles are obtained from the simultaneous solution of the momentum and energy equations. The use of finite differences transforms the continuity, momentum, and energy equations into a system of linear equations which can be solved by any direct or iterative technique. The procedure is repeated until axial nodes have been placed throughout the whole flow channel or until the flow front stops due to polymer solidification. The main advantage of this technique, when compared to the use of a fixed finite difference grid, is that computation time is saved by considering only nodes filled with the fluid. Empty nodes are not considered and corrections for partially filled nodes are not needed. No complications due to the parabolic‐shape of the flow front profile are introduced because the axial nodes are placed at average front locations determined by the average velocity at the particular time interval under consideration.
On the rheology of packed polymer powders
Authors: Umeya Kaoru , Hara Ryuichi
Published: December 2004

The rheology of polystyrene powder beds was examined by two kinds of experiments. From stress relaxation measurements during powder compaction, it was found that relaxation at the shorter times could be attributed to sliding between particles. This is followed by a relaxation attributed to the deformation of the polystyrene particles themselves. From dynamic mechanical measurements, an increase was found in the value of vibrational absorption coefficient (Q−1 value) at a temperature below that of the main relaxation dispersion of bulk polystyrene, attributed to the slipping around tight particle junctions. These phenomena appear characteristic of powder‐like materials.
Reactive polymer processing
Authors: Biesenberger J. A. , Gogos C. G.
Published: December 2004

This paper addresses some of the general engineering problems in reactive polymer processing: thermal effects on reactor stability and polymer properties due to rapid exothermic polymerization, the formulation of reaction viscosity relationships required in simulations, and the generation of flow and mixing via technology available from both ends of the viscosity spectrum, which is spanned in its entirety when going from monomer to molded polymer. Methods of analysis are discussed and general design concepts are suggested, which can be applied to the construction of innovative future processing equipment.
Impingement mixing in reaction injection molding
Authors: Lee Ly James , Ottino Julio M. , Ranz William E. , Macosko Christopher W.
Published: December 2004

Impingement mixing is the unique feature of the reaction injection molding (RIM) process but mixheads are largely designed by trial and error. To visualize the impingement process we have taken high speed photographs. To characterize mixing quality we have followed adiabatic temperature rise of mixtures, varying Reynolds number, mixhead geometry and the reaction rate. These results are examined in terms of a simplified model which includes both fluid mechanical and polymerization aspects of the problem.
Polymer devolatilization: Theory of equipment
Authors: Biesenberger Joseph A.
Published: December 2004

The role of surface renewal and feedback phenomena in devolatilization equipment is clearly illustrated via staged models. A continuous model for the vented, single‐screw devolatilizer is developed, including barrel evaporation and bulk surface renewal as well as backmixing, which represents de‐volatilization data more accurately than previous models. Numerous sample computations are included. The models are used to demonstrate the sensitivity of devolatilization equipment to certain design parameters.
Mathematical analysis of transport properties of polymer films for food packaging. II. Generalized water vapor models
Authors: Peppas Nikolaos A. , Khanna Rohit
Published: December 2004

Deterioration or spoilage of dehydrated food products stored in flexible packaging materials depends on the partial pressure of water vapor in the environment of the stored food. Mathematical analysis of the diffusion of water vapor through semipermeable polymer films using Nernst‐Planck equations is combined with non‐liner water sorption isotherms on food to establish criteria and optimum conditions for storage stability of dehydrated food. Langmuir, Brunauer‐Emmet‐Teller (BET), Halsey, Oswin and Freundlich isotherms are used for various ranges of water activity. It is shown that a single parameter, the permeability‐sorption constant, based on the physical properties of the polymer and the sorptive properties of the food, accounts for both diffusion and adostption and can be used to accurately determine maximum storage times and can be used to accurately determine maximum storage times and to optimize the selection of packaging films. The theory is extended to thermodynamically compatible solute‐polymer systems, where the polymer film is swollen appreciably by the diffusing species.
Relative influence of the mobility and the solubility parameters of fluids on the mechanical behavior of high impact polystyrene
Authors: Hoa S. V.
Published: December 2004

Among different fluid parameters having some effect on the environmental stress cracking of plastics, the surface tension and the solubility parameter are generally accepted as dominant ones. However, experimental evidence to date indicates that one single parameter can not be used as an index for predicting failure in all cases and a distinction of the conditions of their importance has not been made. This paper presents the results obtained from the creep and fatigue response of high impact polystyrene in different environments, especially those environments that do not show any effect on the unstressed polymer. The results indicate that at high stresses, the mobility of the fluid in penetrating into the polymer craze networks is more important and that at smaller stresses, the solubility parameter is more important.
Reaction injection molding (RIM) elastomers having superior high temperature performance
Authors: Rice D. M. , Dominguez R. J. G.
Published: December 2004

Reaction injection molding (RIM) elastomers are being seriously considered by major automotive companies as a substitute for metal in exterior body panels. One major consideration in this application is dimensional stability at a 325°F paint bake cycle. Reported here are formulations which via novel processing result in finished parts with excellent dimensional stability at 325°F. In addition, other properties such as impact resistance and flex modulus ratio improve parallel with high temperature performance. Mechanical properties as a function of processing and molding parameters are presented. Other studies are presented and a tentative explanation of the superior performance of these RIM elastomers is made.
Dynamic mechanical properties of high nitrile resins
Authors: Yanik R. W. , McMaster A. D.
Published: December 2004

Dynamic mechanical measurements have become increasingly more common as an interpretative tool for identifying structure‐property relationships in polymers, especially in multi‐phase systems. There are many literature references citing the application of this analytical technique to the study of rubber reinforced polymers such as high impact polystyrene and aerylonitrile‐butadiene‐ styrene. This paper illustrates further extensions of the technique to study the effects of composition and processing parameters on the mechanical relaxation behavior of rubber reinforced high nitrile resins. Storage and loss curves vs temperature are compared for three related polymer systems: (1) a high nitrile glassy copolymer, (2) mechanical blends of the glassy copolymer with rubber, and (3) a copolymer grafted onto a rubber backbone. Particular attention is given to the size and shape of the tan δ loss peak for blended and grafted resins having different rubber levels. The importance of dispersing the rubber particles during processing is also shown. Dynamic mechanical studies have shown a pronounced decrease in the size of the rubber loss peak for oriented rubber modified high nitrile resins. This is further evidence that dynamic mechanical results are sensitive to variations in processing conditions as well as resin composition.
Polymer compatibility: Ternary blends of poly(vinylidene chloride‐co‐vinyl chloride), poly(vinyl chloride) and poly(acrylonitrile‐co‐butadiene)
Authors: Wang Yung‐Yun , Chen Show‐An
Published: December 2004

Mixtures of two compatible polymers, poly(vinyl chloride) and poly(acrylonitrile‐co‐butadiene) containing 40 percent acrylonitrile, can be compatible with poly(vinylidene chloride‐co‐vinyl chloride), which is incompatible and partially compatible respectively with these two polymers. The crystalline melting temperature and relative heat of fusion of poly(vinylidene chloride‐co‐vinyl chloride) in blends are higher than those in the pure component. This is attributed to greater ordering of the polymer chains in the crystalline phases of the blends. Replacing the rubber by poly(acrylonitrile‐cobutadiene) containing 30 percent acrylonitrile, shows that these three polymers, in which each pair is incompatible or at most partially compatible, also form compatible ternary blends. The crystalline melting temperature is higher and relative heat of fusion lower than those in the pure component. This is attributed to dissolving of parts of the polymer chains originally located in the crystalline phases in the amorphous phases of the blends.
Properties and processing characteristics of open‐celled foams produced by leaching NaCl from high density polyethylene
Authors: Bigg D. M.
Published: December 2004

The properties and processing characteristics of open‐celled foams produced by leaching small NaCl particles from high density polyethylene has been investigated. In a random dispersion of salt particles in the polymer matrix a minimum volume loading of 40 percent was required to produce an open‐celled foam. The time required to remove this quantity of salt with 50°C water was 100 min. The maximum porosity of the foam is limited to the maximum packing fraction of the salt. For randomly dispersed isotropic particles the maximum packing fraction is approximately 0.64. Because the composite rapidly loses melt strength as the filler content nears the maximum packing fraction, the practical upper limit of extruded foam porosity is approximately 0.60.
The melting behavior of a low density polyethylene powder in a screw extruder
Authors: Cox A. P. D. , Williams J. G. , Isherwood D. P.
Published: December 2004

An experimental investigation into the performance in general and the melting behavior in particular of a single screw extruder running with a low density polyethylene power has been carried out and the results compared with those for a granular feedstock of low density polyethylene having similar melt properties. It was found that the tendency was for the output rate, pressure generated and specific power consumption to be lower for the powders, and that the removal of barrel heating near the feed hopper increased these parameters. Two melting mechanisms were observed in powder extrusion; one being the classic “Maddock” type, and the other such that the solid bed and melt pool were in reversed positions relative to the Maddock case. There was a trend for this latter mechanism to operate with low screw speeds, shallow channels and full heating. Melt initiation occurred nearer the feed end and melting was completed much more quickly with powders. An explanation of the mechanisms is proposed which is based on the observation of early melt initiation, and the industrial practices of feed zone cooling and increasing feed pressure generation to improve the performance of extruders running with powders are seen to be consistent with this proposition.
Study of the curing of a polyurethane using the Weissenberg Rheogoniometer
Authors: Hartley Mark D. , Williams H. Leverne
Published: December 2004

Gel Permeation chromatography (GPC) yielded high values for branching frequency. Low polymers persisting long into the reaction and impurities resulted in almost constant number average molecular weights and steeply rising polydispersity. The percent insolubles was low and passed through a maximum attributed to a 1,2,3‐propantriol/isocyanate reaction product which was insoluble and became solubilized by the addition of polybutadiene. The dynamic viscosities of the products rose with conversion. When studied over various shear rates, the curves could be extrapolated to zero shear values. The relationship between zero shear viscosity and molecular weight yielded a slope of 3.5 for linear samples and a lightly branched sample prepared using 1,6‐hexamethylene diisocyanate. The lightly branched samples made using 2,4‐toluene diisocyanate yielded slopes less than 3.5. The highly branched samples yielded slopes well above 3.5. The moduli increased rapidly with reaction time and then levelled off. In the absence of 1,2,3‐propantriol, the loss modulus surpassed the storage modulus. When 1,2,3‐propantriol was added, the moduli increased more rapidly, levelled off at higher values, and the storage modulus exceeded the loss modulus. Studies of the swelling of the final product showed that these measurements yielded abnormally high values for the molecular weight between crosslinks; evidence of poor network formation.
Rheology of polyphosphazene melts and solutions—some surprises
Authors: Ho Perry K. , Williams Michael C.
Published: December 2004

Rheological tests are reported for two types of polyorganophosphazenes, one being a fluorinated alkoxy terpolymer (PNFT) and the other an aryloxy copolymer (PAP). Non‐Newtonian viscosity η(\documentclass{article}\pagestyle{empty}\begin{document}$ {\rm \dot \gamma } $\end{document}) and complex viscosity components η′(ω) and η″(ω) were measured as functions of shear rate\documentclass{article}\pagestyle{empty}\begin{document}$ {\rm \dot \gamma } $\end{document}and oscillatory frequency ω, using a Weissenberg rheogoniometer, and a limited amount of normal stress data was also obtained. Solutions of both polymers in tetrahydrofuran were tested, over a concentration range 0‐22 percent for PNFT and 0‐35 percent for PAP. Melts of PNFT were examined for temperatures 50‐178°C, and melts of PAP at 210°C even though they were not truly fluid at this temperature. Solution and melt data are shown to obey conventional superposition principles to give master curves. For solutions, superposition is achieved by using the Bueche relaxation time as a concentration reducing factor with no adjustable parameters, and the Spriggs model also proves useful in predicting normal stress and shear stress results. For PNFT melts, master curves are fitted by the new WS2H2model which incorporates detailed molecular weight distribution (MWD) information and extracts the entanglement lengthMefrom the data. Temperature shift factorsaTshow Arrhenius behavior and the corresponding activation energiesEreare reported. Results for PNFT melts were complicated by lack of agreement between two samples of nominally the same composition; η′(ω) shapes and levels andErevalues differed widely. This is interpreted in terms of detailed MWD information and the possibility of mesomorphic phase transitions occurring in these nominally amorphous materials.
Torsion impregnated cloth analysis (TICA): A forced torsion technique to study resins supported by inert substrate
Authors: Lee C. Y‐C. , Goldfarb I. J.
Published: December 2004

Torsion Impregnated Cloth Analysis (TICA) uses fiber glass cloth as support for polymeric resins and measures the clothresin composite's in‐phase and out‐of‐phase dynamic mechanical responses with a Rheometrics mechanical spectrometer. The TICA thermoscan results of a thermoplastic were compared with that of the neat material. A similar comparison was made between the isothermal curing results of a thermosetting resin and the corresponding parallel plate and TBA measurements. The peaks associated with the vitrification were verified to correspond to those in the glass transition region. Conventional thermoscans of partially cured specimens with known Tg were shown under certain conditions to give erroneous results about the glass transition temperatures. A reduced parameter (T‐Tg) was introduced to describe the response of a specimen undergoing additional cure while being subjected to a thermoscan. Examples using this parameter to understand seemingly complex experimental results are given.
Dynamic properties of crosslinked epoxy resin at large cyclic and static deformation
Authors: Isayev A. I. , Katz D. , Smooha Y.
Published: December 2004

Measurement of dynamic properties of crosslinked epoxy resin have been performed under torsional cyclic deformation with different amplitudes and frequencies and with extensional creep under different loads. It is found in both cases that the dynamic modulus decreases above a certain critical value of deformation. Truncation of the glassy state region and shifting of the transition zone to lower temperatures and higher frequencies have been observed as effects of large amplitude deformation. The maximum reduction in the modulus value and the minimum in the critical amplitude both occur in the region of Tg Shear fatigue of the material has been observed in the glassy state with a frequency‐ and temperature‐dependent fatigue life. It is found that the loss modulus under extensional creep depends upon the values of the deformation and stress whereas the storage modulus depends solely upon the deformation. The ratio of energy expended during static and cyclic deformations is shown to depend only upon the extensional deformation.
Plasma polymerization of hexamethyldisiloxane in the gas phase. II. Formulation of various selected parameters affecting rate of polymerization and their optimization
Authors: Akovali G.
Published: December 2004

Formulation of three selected operational parameters (flow rate of monomer, radio frequency power applied, and reactor tube pressure) affecting rate of polymerization of HMDS by plasma at 13.56 MHz is made by use of rotatable central composite (RCC) statistical design. The flow rate is found to be the most important parameter in determining deposition rate, followed by power and pressure; optimum values of these three to yield maximum deposition rate are also evaluated.
Time‐dependent rheological properties and transient structural states of entangled polymeric liquids—A kinetic network model
Authors: Liu T. Y. , Soong D. S. , Williams M. C.
Published: December 2004

A kinetic network model has been developed to describe the nonlinear rheological behavior of entangled polymer solutions and melts in either steady‐state or transient flows. This model is based on the concept of flow‐induced structure variation, controlled by the simultaneous existence of entanglement loss and regeneration. When steady‐state is attained, both processes occur at the same rate and the structural state (entanglement density) of the fluid remains constant with time. Under transient flow conditions, the fluid structure becomes time‐dependent as a result of unequal rates of the two competing processes affecting entanglement density. The viscoelastic response of the fluid is, in turn, influenced by the varying structural state. This is incorporated into the model through the use of structure‐dependent coefficients in the contravariant Maxwell constitutive equation for entanglement stress. Model predictions are generated for a number of transient flow programs, including the stress growth and relaxation, interrupted flow, sudden change in shear rate, and nonlinear creep experiments. Comparison with literature data supports not only the qualitative success but also the quantitative ability of this model.
The determination of residual stresses in plastic pipe and their role in fracture
Authors: Williams J. G. , Hodgkinson J. M. , Gray A.
Published: December 2004

A method for the determination of residual stresses in plastic pipe by layer removal and subsequent slitting is described. Results are analyzed from deflections measured on a high density polyethylene pipe. The use of these data in the calculation of KI around a semi‐elliptical flaw at the pipe wall is then discussed.
Computer simulation of steady polymer melt spinning
Authors: Gagon Del Kenneth , Denn Morton M.
Published: December 2004

An interactive computer simulation program has been developed for steady polymer melt spinning. The program includes inertial and air drag effects, and fluid viscoelasticity is described by the Phan‐Thien and Tanner constitutive equation. Simulation results are compared with experiments by George on poly(ethylene terephthalate) (PET) at spinning speeds of 1000 and 3000 m/min, and the effect of elasticity under other spinning conditions is explored with computer experiments.
Effect of tensile strain, time, and temperature on gas transport in biaxially oriented polystyrene
Authors: Levita Giovanni , Smith Thor L.
Published: December 2004

The permeability and diffusion coefficients (P and D) for gases in a biaxially oriented polystyrene film have been found to increase when a specimen is stretched in simple tension and to decrease with time when the strain is held constant. These effects are attributed, respectively, to an increase in free volume with strain and to the continuous volume recovery (densification) at constant strain. The strain dependence, at small strains, of P and D for Ar, Kr, N2, CO2, and Xe at 1 atm pressure and 50°C indicates that the size distribution of free‐volume elements is not distorted when a specimen is stretched. At a constant strain of 1.8 percent at 50°C, P and D for xenon decrease about 13.8 and 11.8 percent, respectively, per decade of time—two to threefold faster than for carbon dioxide. These results and those obtained with argon, whose molecular diameter is significantly smaller than that for xenon, suggest that the larger free‐volume elements decrease in size faster than the smaller ones as volume recovery progresses.
Effect of physical aging on stress relaxation of poly(methyl methacrylate)
Authors: Cizmecioglu M. , Fedors R. F. , Hong S. D. , Moacanin J.
Published: December 2004

A study was made on the stress relaxation behavior at 25°C of poly(methyl methacrylate) in uniaxial tension as a function of physical aging at both room temperature and 60°C. Test specimens were compression molded at 165°C, then quenched to room temperature and allowed to age for up to 30 days prior to testing. Stress relaxation curves measured after different aging times could be superposed to a single master curve for each aging temperature. Superposition was achieved by applying vertical and horizontal shifts. Hence, the shape of the response curves was not changed by aging. This is in accordance with observations made by Struik for tensile creep curves. Volume changes as a function of physical aging were also determined. Simple exponential relationships were observed between volume and both horizontal and vertical shifts. The horizontal shift implies a shift in the effective time scale caused by a change in free volume. The vertical shifts could be correlated with changes in Young's modulus caused by a change in density. For the range of aging studied, the response time scale varied over nearly two decades of log‐time. For the same conditions modules varied by 30 percent.
The inhomogeneous structure of glass
Authors: Lindenmeyer P. H.
Published: December 2004

Application of the fundamental variational principle of nonequilibrium thermodynamics has permitted recognition that all polymer solidification including glass formation occurs by a dissipative process which results in an inhomogeneous dissipative structure rather than an equilibrium structure. Although an equilibrium structure must he homogeneous and time independent, the definition of both homogeneity and time independence depends upon the scale and precision of the measurement of time and distance. Thus, whether one considers a glass to be a homogeneous equilibrium structure or an inhomogeneous nonequilibrium structure, depends upon the scale and precision of measurement. However, progress in understanding the molecular arrangement in glass can only come by considering a glass as an inhomogeneous dissipative structure.
Mass transfer and depolymerization of styrene in polystyrene
Authors: Blanks R. F. , Meyer J. A. , Grulke E. A.
Published: December 2004

This work shows how laboratory experiments may provide parameters which are useful in modeling a commercial process of polystyrene devolatilization. Such processes often occur at temperatures where depolymerization of polystyrene to monomer may be significant. Polystyrene devolatilizers function by forming thin films of the polymer, with styrene loss by flashing and diffusion and styrene generation by depolymerization. The modeling parameters of importance are: depolymerization rate constant, monomer diffusivity, and thermodynamic equilibrium polymer‐vapor partition coefficient. Typical levels of styrene in polystyrene in the last stage of devolatilization are 100 to 1000 ppm. Pressures and temperatures in the devolatilizer are often less than 10 torr and greater than 200°C. For styrene‐polystyrene the desired parameters have not been reported, nor apparently measured, at the concentration, pressure and temperature levels of interest.
Adhesive and composite evaluation of acetylene‐terminated phenylquinoxaline resins
Authors: Hergenrother Paul M.
Published: December 2004

A series of acetylene‐terminated phenylquinoxaline (ATPQ) oligomers of various molecular weights were prepared and subsequently chain extended by the thermally induced reaction of the ethynyl groups. The processability and thermal properties of these oligomers and their cured resins were compared with that of a relatively high molecular weight linear polyphenylquinoxaline (PPQ) with the same chemical backbone. The ATPQ oligomers exhibited significantly better processability than the linear PPQ but, the PPQ displayed substantially better thermooxidative stability. Adhesive (Ti/Ti) and composite (graphite filament reinforcement) work was performed to evaluate the potential of these materials for structural applications. The PPQ exhibited better retention of adhesive and laminate properties than the ATPQ resins at 260°C after aging for 500 h at 260°C in circulating air.
Mechanical and thermal properties of aromatic copolyesters containing rigid binaphthyl units
Authors: Manusz J. , Lenz R. W. , Macknight W. J.
Published: December 2004

Mechanical and thermal properties of terephthalic acid copolyesters of 4,4′‐binaphthol‐1,N monomer, and 2,2‐bis(4‐hydroxyphenyl)propane, A monomer (Bisphenol A), have been examined by differential scanning calorimetry (DSC) and dynamic mechanical methods. The copolyesters had different amounts and sequence distributions of diphenolic units. When the content of N units in the copolyesters was increased from 27 to 55 percent a significant increase of the dynamic Young's modulus, from 2485 to 4540 MPa at 110 Hz and room temperature, and an enhancement of the stress at yield, from 53.5 to 66.5 MPa, were observed. In the glass transition region of the copolyesters a smaller decrease in the value of E′ was noted compared with the homopolymers. For the copolyesters containing 55 percent of N units, the E′ decrease was only about 1.6 decades at 110 Hz within a range of temperatures of over 74 Kelvins. The DSC measurements of the copolyesters under consideration showed that the Tg depended only to a slight extent on their composition and structure and all Tg values were within the range of 494 ± 2 Kelvins, corresponding to that for poly [2,2‐bis(4‐ hydroxyphenyl)propane terephthalate], the homopolymer of the A bisphenol monomer.
Pressure development in the melting zone of a single‐screw extruder
Authors: Lindt J. T.
Published: December 2004

An analysis is given of the pressure generation mechanism in the tapered channel of a single‐screw extruder. It is shown that when increasing the throughput the pressure build‐up capacity of the melting zone tends to decrease. As a result, severe pressure drops may occur in the tapered sections. A relationship between the pressure profile and the melting mechanism (solid bed/melt pool configuration) is described in terms of the cross‐channel melt circulation.
Residence time distribution in a real single screw extruder
Authors: Kembłowski Z. , Sȩk J.
Published: December 2004

The residence time distribution in an industrial single screw extruder was investigated experimentally in the case of melt and plasticating extrusion. The investigations performed proved that the extrusion parameters influence strongly the residence time distribution in the extruder. It was found that the resistance to flow through the die‐head of the extruder is very important from this point of view, as well as other parameters like rotational speed of the screw and the screw channel depth. Variation of these parameters can change the residence time distribution over a broad range between the extreme idealized cases of plug flow and flow with perfect mixing. In order to obtain quantitative dependences three moduli were used and a correlation equation was obtained. This equation enables an estimation of residence time distribution on the basis of experimental characteristics of the extruder and the actual extrusion parameters.
Addition polyimide adhesives containing various end groups
Authors: Clair Anne K. St. , Clair Terry L. St.
Published: December 2004

Addition polyimide oligomers have been synthesized from 3,3′,4,4′‐benzophenone tetracarboxylic acid dianhydride and 3,3′‐methylenedianiline using a variety of latent crosslinking groups as end‐caps. The nominal 1300 molecular weight imide prepolymers were isolated and characterized for solubility in amide, chlorinated and ether solvents, melt‐flow and cure properties, glass transition temperature, and thermal stability on heating in an air atmosphere. Adhesive strengths of the polyimides were obtained both at ambient and elevated temperatures before and after aging at 232°C. Properties of the novel addition polyimides were compared to a known nadic end‐capped adhesive, LARC‐13.
Residual stresses in polymers I: The effect of thermal history
Authors: Siegmann A. , Buchman A. , Kenig S.
Published: December 2004

The distribution of residual stresses in quenched modified poly(phenylene oxide) (PPO) specimens was investigated. Quenching was carried out from temperature level above Tg to various temperatures below Tg. As expected, compressive stresses were measured at the surface layers while tensile stresses were in the inner layers. The ratio between the tensile and compressive stresses varied, depending on the thermal history. The level of residual surface stresses was found to depend on both the total temperature difference during cooling and the initial specimen temperature. At constant initial temperature the surface stresses are proportional to the total temperature difference, whereas, at constant final temperature the surface stresses are inversely proportional to the total temperature difference. An empirical correlation describing the surface stresses as a function of thermal history has been suggested. The differences between present theories and experimental data are discussed. emphasizing the apparent discrepancy regarding the influence of initial temperature above Tg on the level of residual stresses.
Miscibility phenomena in polyester/chlorinated polymer blends
Authors: Prud'homme Robert E.
Published: December 2004

Poly(caprolactone) (PCL)/poly(vinyl chloride) (PVC) blends are known to be miscible in the solid state. Recents measurements however indicate that a large number of polyesters are also miscible with PVC if the ratio CH2/CO of the polyester is between 4 and 10. At low CH2/CO ratios, polyesters are too rigid to interact specifically with PVC. At high CH2/CO ratios, the number of interacting groups becomes too small to give miscibility. Similarly, a large number of chlorinated polymers are shown to be miscible with PCL if their chlorine content is high enough. Surprisingly, polyesters are not in general miscible with chlorinated polymers if the mixture does not contain either PCL or PVC. The results presented in this paper suggest that a dipole‐dipole interaction, between the carbonyl groups and the C‐Cl groups, is responsible for the miscibility phenomena observed in polyester/chlorinated polymer blends.
Melt rheology of polymer blends
Authors: Utracki L. A. , Kanial M. R.
Published: December 2004

The rheological behavior of polymer blends is compared with that reported for emulsions, block polymers and homologous polymer blends. It has been shown that the properties of polymer alloys frequently differ from those of these “model” systems—the principal difference being the lowering of at least one rheological function below the value predicted In the log‐additivity rule. Primarily, the most recent (post 1977) results are reviewed. The data obtained by the authors on the flow of poly(ethylene terephthalate)/Polyamide‐6,6 are discussed in detail.
Model of steady‐state melt spinning at intermediate take‐up speeds
Authors: George Henry H.
Published: December 2004

A model of melt spinning has been developed for speeds above which the effects of gravity, inertia, and aerodynamic drag become significant. The model has as an upper bound the speed at which stress crystallization begins to occur on the spin line. For poly(ethylene terephthalate), these velocities are approximately 750 and 3500 meters/minute. The calculated temperature and velocity profiles are shown to agree with measured values. The stress at the freeze point is calculated and found to correlate well with the spun yarn birefringence which, in turn, is shown to predict uniquely the spun yarn physical properties on a “simple” spin line. The stress‐optical coefficient derived from the calculated stress at the freeze point and measured birefringence agrees well with the literature.
Large deformation behavior of some thermoplastics
Authors: Mittal R. K. , Singh I. P.
Published: December 2004

In this experimental study the deformation behavior of two thermoplastics under uniaxial and biaxial loadings has been investigated. The experiments were conducted on thin walled tubular specimens of nylon‐6, a semicrystalline polymer, and polymethyimethacrylate (PMMA),:an amorphous polymer. These specimens were subjected to tension, torsion and combined tension‐torsion loadings until very large deformations were produced or specimen failure took place. The results are presented in the form of generalized stress‐generalized strain curves which are applicable to all types of loadings, provided the generalized stress is monotonically increasing. In addition, the results show that the generalized stress‐generalized strain relationship for nylon‐6 is parabolic in nature, whereas that for PMM A can be represented by a bilinear curve. This characterization of the response of the thermoplastics under a biaxial stress field can be used to obtain a more realistic stress interaction between fiber and matrix in composite materials, since until now all theoretical studies on this aspect have assumed an elastic or elastic‐perfectly plastic behavior of the matrix.
Melt rheology of high impact polystyrenes at high shear stresses
Authors: Santamaría Antón , Guzmán Gonzalo M.
Published: December 2004

A study of the theological properties of commercial polystyrenes, (PS), and high impact polystyrenes (HIPS), is made in the range of shear stresses of practical interest in industrial polymer processing.

A general viscosity‐shear rate‐temperature relationship is defined for these products, with a power law exponent of n = 0.3 and an activation energy of 27 Kcal/mol.

The fluid elasticity is studied in terms of steady state shear compliance. An expression relating shear compliance, viscosity and molecular weight distribution is obtained for HIPS. As in other two‐phase systems, a decrease in elasticity with viscosity is observed.
Rheology of polymer blends: Simultaneous slippage and entrance pressure loss in the ethylene‐propylene‐diene (EPDM)/viton system
Authors: Kanu R. C. , Shaw M. T.
Published: December 2004

Because the exact nature of the mechanism governing the marked viscosity reduction in the highly incompatible EPDM/“Viton” fluoroelastomer system is not fully understood, a study was undertaken to shed more light on the phenomenon. Interracial. Slippage in the blend has been suggested as the mechanism by which a substantial reduction in the melt viscosities of either component takes place upon addition of a small amount of the other, In the present investigation, a Mooney slip analysis demonstrated wall slippage in the EPDM/Viton system over the shear stress range of 40 kPa to 160 kPa. The capillary surface was examined for evidence of coating by the minor component of the blend (Viton), and 9‐fold enrichment was found by elemental analysis. However, on no occasion was pure Viton found. In other experiments, the dynamic linear viscoelastic properties and the transient squeezing flow response of the blend were found to be no different from those of the neat elastomer. In addition, the slip velocity in a capillary (and consequently, the viscosity‐lowering effect) was reduced by a factor of 2 to 3 in capillaries with a 90° included entrance angle. It is postulated that the reduction in the flow resistance for the blend is unique to the sharp‐entry capillary geometry and results from removal of Viton from the melt in the recirculating flow at the entrance. This material then feeds along the capillary wall, disrupting the already tenuous adhesion of the elastomer to the metal surface.
Analytical melting model for extrusion: Melting rate of fully compacted solid polymers
Authors: Mount E. M. , Watson J. G. , Chung C. I.
Published: December 2004

The melting mechanism inside screw extruders is presently analyzed using numerical, iterative methods that are too complex to be used widely by practicing engineers. Our theoretical and experimental investigations of the melting mechanism have produced simple, analytical equations for predicting the melting rate of fully compacted solid polymers without iterative calculations. The accuracy of these equations was found to be satisfactory. Consideration of the temperature and shear dependencies of the melt viscosity was found to be essential for the accurate prediction of the melting rate.
Estimation of the effective permeability of thin surface layers created by exposure of polyethylene to fluorine
Authors: Koros W. J. , Stannett V. T. , Hopfenberg H. B.
Published: December 2004

The significantly improved barrier properties of polyethylene, that, result from surface treatment with small amounts of fluorine are explained in terms of the reduced permeability of a thin layer produced by such treatments. Several approaches for correlating the permeabilities of the treated and untreated polymer layers to various penetrants are discussed. An analysis is also presented that permits estimation of the treatment depth corresponding to a given loss rate is related explicitly to the relative permeabilities of the penetrant in the treated and untreated polymer regions.