bluuebunny/crossref_metadata_2025 huggingface dataset:
Kinetic studies on shear degradation of polystyrene during extrusion
Authors: Shur Young J. , Rånby Bengt , Chung Ki‐Hyun , Kim Sang‐Dae
Published: December 2004

Kinetic studies on shear degradation of a polystyrene (M̄n = 115,700 and P̄n = 1113) during extrusion in a model extruder were made at different temperatures (170, 190, 210, and 230°C) and shear stresses (340,406, and 472 g/cm2) for determination of rate constants for degradation, reaction order, and effects of temperature and stress on the rate constants. Mechanical energy and effective activation energy (E*) of bond rupture were related to temperature and applied stress. The following results were obtained. The degradation process is found to be satisfied by a second order reaction over the temperatures and stresses studied with respect to the changes in number average chain length (Pt – P∞), thus –dP/dt = k(Pt – P∞)2, where k is a reaction rate constant and t and ∞ refer to degradation times. The mechanical energy of bond rupture has a maximum and the rate constant a minimum at about 180°C, indicating that the least effective temperature for mechanical degradation is about 180°C. E* decreases with increasing applied stress (τ) as a linear relationship, i.e., E* = EA – ατ. At τ = 0, E* becomes equal to the activation energy for thermal degradation with the value EA = 48.6 kcal/mole which agrees well with literature data. Temperature and stress effects on the rate constant are well expressed for our study by the Arrhenius equation proposed by Zhurkov, et al., i.e., k = A exp[–(Ea – ατ)/RT] where A and α are coefficients.
The influence of morphology on the tensile properties of polyethylenes
Authors: Phillips P. J. , Patel J.
Published: December 2004

The tensile properties of high and low density polyethylene specimens produced under careful crystallization and annealing procedures have been determined. A morphologically controlled brittle‐ductile transition has been observed for high density polyethylene. Although the lamellar thickness appears to determine the transition, a postulate involving molecular fractional on during crystallization as the cause is offered. For ductile materials, dependence of the Young's Modulus on morphology is interpreted using the fiber‐composite analogy of Halpin and Kardos. Yield stress varies as modulus and achieves maximum values consistent with estimates of the critical resolved shear stress of polyethylene crystals.
Mechanical properties of selected injection‐molded thermosets
Authors: Kleinemeier B. , Menges G.
Published: December 2004

Practical ways of processing thermoset materials by injection molding have been developed. These methods have been used particularly in the automotive and electrical industries. The tensile behavior is discussed for specimens which were injection molded from reinforced and filled phenolic unsaturated polyester and epoxy resin. This behavior aids the layout of flow paths. Under static loads the materials show less creep than most thermoplastics. “Post shrinkage” was observed as a shortening of specimens under prolonged heating. Because of brittleness, the materials failed under dynamic load at low strain. The first microcracks directly initiate the final failure. Before the final failure, the materials craze at a certain strain. By means of different testing methods these strain values were determined. For practical applications, these values should be considered in the designing of thermoset parts.
The effects of thermal treatment, residual solvent, and preswelling on the thermal properties and sorption behavior of poly(2,6‐dimethyl, 1,4‐phenylene oxide)‐polystyrene blends
Authors: Apicella A. , Drioli K. , Hopfenberg H. B. , Martuscelli E. , Nicolais L.
Published: December 2004

The effects of thermal treatment, residual solvent, and preswelling on the thermal properties and swelling behavior of solution cast polyblend films of poly(2,6‐dimethyl,1,4‐phenylene oxide) (PPO) and polystyrene (PS) were determined. Repeated cycling in the DSC analysis of the “as cast” films suggested that the original films contained residual casting solvent and that solvent‐induced crystallization occurred in the PPO‐rich compositions. Crystallinity was, apparently, eliminated by the first heating cycle in the differential scanning calorimeter. Sorption kinetics and apparent equilibria, characterizing the penetration of these films by n‐hexane from the vapor phase, indicated that both the sorption rate and apparent equilibria are significantly affected by the prior history of the film samples. The sorption results presented here are quantitatively consistent with earlier studies of the PPO‐PS system. The increased rate and amount of sorption observed in preswollen samples, and the reduced rate and amount of sorption observed in annealed samples are consistent with recent descriptions of sorption behavior in diverse glassy homopolymer systems.
Theory of laminar mixing
Authors: Erwin Lewis
Published: December 2004

An expression is derived for the increase in mixedness due to an arbitrary deformation of a material. For mixtures having initial orientation this expression is a function of the principal values of the strain tensor and the orientation of the fluid. For mixtures without initial orientation, this expression is simply a function of the principal values of the strain tensor. Mixing in pure shear, simple shear, and pure elongation is determined. The rate of mixing for each of these deformations in steady flow is derived. A comparison of these rates of mixing with the energy consumed in the deformation shows that simple shear flow is a very inefficient way to accomplish mixing. For the example cited, five orders of magnitude greater energy is required to accomplish mixing in shear flow as opposed to extensional flows.
The coating of Newtonian liquids onto a roll rotating at low speeds
Authors: Tharmalingam S. , Wilkinson W. L.
Published: December 2004

A theoretical treatment is presented for the prediction of the rate at which a liquid is entrained by a roll which is rotating partially submerged in a Newtonian liquid, and also for the prediction of the variation in the thickness of the film around the roll. The method involves the integration of the momentum equation after neglecting inertia forces in the dynamic meniscus region and the matching of the surface curvature with that derived for the static meniscus region near the liquid surface. The resulting equation allows the prediction of the relationship between a dimensionless film thickness parameter, T, and the capillary number, Ca, as a function of the radius of the roll, the withdrawal angle and the position of the roll periphery. The liquid flux on the roll can also be predicted.
Dynamic Poisson's ratio: A novel technique to study interfacial adhesion
Authors: Takemori M. T.
Published: December 2004

A novel technique utilizing the dynamic Poisson's ratio to measure the strength of adhesion in fiber‐filled polymeric composites is described. This technique is based on the observation that glass‐filled composites exhibit a large drop in Poisson's ratio as a function of prestrain at very low prestrains. This drop, which indicates additional volume dilation, is interpreted as due to debonding or void formation at the filler‐matrix interface. This interpretation is consistent with the results obtained by using three very different glass surface treatments, with a description of the debonding process using two simplified models and with mechanical properties data. The dynamic Poisson's ratio technique is insensitive to filler orientation and has high resolution, since very small volume changes are reflected as large drops in Poisson's ratio.
An anomaly in the necking behavior of polyethylene
Authors: Gedde U. W. , Jansson J. F.
Published: December 2004

Tensile creep measurements at constant load on nonoriented polyethylene have shown a marked transition at a certain stress level from a neck formation followed by instantaneous fracture to the formation of a neck which resists fracture for a considerable time. The transition, which shifts towards shorter time and higher nominal stress with increasing molecular weight, has been studied for 16 polyethylenes of different molecular weights, degrees of branching and crystalline structures. The marked. transition has only been observed for high density polyethylene of high molecular weight. Deformation measurements show a more distinct necking for the high density than for the medium density polyethylenes. This is consistent with current molecular deformation theories. A hypothesis for the transition is proposed based on the distinctness of the neck process in the high density polyethylene and the large difference in strength between the spherulitic structure and the fibrillar structure. The dependence of the transition on molecular weight is expected since the number of tic chains incrcrtses with increasing molecular weight.
Role of bond thickness on adhesive failure
Authors: Fourney M. E. , Muki R. , Stone S. F. , Westmann R. A.
Published: December 2004

An analytical, numerical and experimental program is described which establishes the basic fracture mechanics properties of an adhesive joint. A finite element analysis of a homogeneous finite tapered double cantilever beam is first presented and the results compared with elasticity and strength of materials solutions. Using analytical results developed in another paper, a finite bond line thickness correction factor is introduced to determine the crack tip stress intensity factor as a function of crack length. An experimental program is described wherein the crack tip stress intensity factor for the cantilever beam adhesive joint is measured by the compliance method and the results compared with those obtained by analytical and numerical methods. Finally, the critical value of the adhesive crack tip stress intensity factor is determined using the analytical and experimental techniques presented.
Further developments of a damage theory for filled polymers
Authors: Rubinstein R. , Fitzgerald J. E.
Published: December 2004

This paper investigates matrix debonding from filler particles as a mechanism for weakening of a filled polymer. We analyze several simplified models of debonding. Our main concern is its effect on the overall elastic instants; for each debonding model, we calculate the change ΔW in overall strain energy density due to debonding. The resulting formulas for ΔW are all special cases of one general expression. Accordingly, we propose that this expression describes a broad class of debonding models, including some for which a detailed stress and strain analysis is not possible.
Evaluation of resin‐glass fiber interface under environmental stress
Authors: Haarsma John
Published: December 2004

A test method has been developed to evaluate resin‐glass composite materials for their resistance to environmental, thermal and hydrolytic stresses, humidity, radiation, and immersion in aggressive fluids. The advantages this method offers are ease of specimen preparation, small specimen size, and maximum exposure of resin, glass and interface to the test environment.
Selection and sensitivity of pellet dimensions and operating parameters to maximize production rate
Authors: Johnson Glen E. , Townsend Miles A.
Published: December 2004

The manufacture of pellets from extruded plastic strands is modeled as a constrained nonlinear programming problem. The objective is to maximize the production rate by choice of pellet dimensions and pelletizing machine operating parameters. A general solution strategy leading to identification of a globally maximum production rate for any numerical case is given. It is shown that increases in the maximum production rate can be obtained by selective relaxation of the constraints. A numerical example is presented and discussed.
Effects of extrusion on the structure and properties of high‐impact polystyrene
Authors: Kalfoglou Nikos K. , Chaffey Charles E.
Published: December 2004

A commercial heat‐resistant polystyrene (M̄n = 7 × 104, M̄w = 3 × 105), containing 9 percent cis‐1, 4‐polybutadiene, was extruded either repeatedly (2 to 8 times) at 220°C, or else only once at a higher temperature (up to 290°C). Neither treatment significantly altered the melt rheology at 220°C (pseudoplastic, with n = 0.39), or the tensile modulus (1.5 GPa) and yield stress (20 MPa), or the material's rubber content, determined by both infrared spectrophotonietry and Wijs iodometry. Other properties, only slightly affected by recycling at 220°C, were changed after one extrusion at 290°C: elongation at tensile failure was reduced by 57 percent; in impact testing the strength was 29 percent less, and the mode of fracture (revealed by scanning electron microscopy of the surfaces) became brittle instead of ductile; the rubber particles seen in the transmission electron microscope had agglomerated and lost sphericity; and the ratio of weight‐to‐number‐average molecular weight of the polystyrene component, calculated from gel permeation chromatograms, increased by 93 percent. Mechanical spectra (Rheovibron), from −120 to + 120°C at 110 Hz, changed gradually with increasingly harsh treatment of the material, a peak emerging at ∼50°C due to a beta relaxation of the polystyrene. Thus, good properties were retained after normal processing, but were lost after shearing at too high a temperature, probably because of destruction of entanglements and of the bonds between polystyrene and rubber.
Impact behavior of nylon‐66 compositions: Ductile‐brittle transitions
Authors: Flexman Edmund A.
Published: December 2004

The ductile‐brittle transitions of nylon‐66 compositions were studied by Izod and falling weight tests. Samples included unmodified and impact modified compositions. Brittle breaks did not occur in the toughest resin with changes in rate of loading, notch radius, thickness, or distance and orientation to the gate. A fracture mechanism is proposed.
Investigation of the Tu(>Tg) relaxation in homopolymers and block copolymers of styrene by torsional braid analysis
Authors: Gillham J. K.
Published: December 2004

Investigation of the Tu (>Tg) relaxation in amorphous polymers of styrene by the technique of torsional braid analysis is reviewed. For the most part the relaxation behaves like the glass transition (Tg) in its dependence on molecular weight, on average molecular weight in binary polystyrene blends, and on composition in a polystyrene homogeneously plasticized throughout the range of composition. Diblock and triblock copolymers also display a T > Tg relaxation above the Tg, of the polystyrene phase. Two results in particular suggest that the Tu relaxation is molecularly based. (1) The Tu temperature is determined by the number average molecular weight for binary blends of polystyrene when both components have molecular weights below Mc. (the critical molecular weight for chain entanglements). (2) Homopolymers, and diblock and triblock copolymers of styrene, have a T > Tg relaxation at approximately the same temperature when the molecular weight of the styrene block is equal to that of the homopolymer.
Effect of cure cycle on mechanical properties of thick section fiber‐reinforced poly/thermoset moldings
Authors: Mallick P. K. , Raghupathi N.
Published: December 2004

One of the major factors of concern in compression molding of fiber‐reinforced thermosets is the mold cycle time which directly affects the processing cost. An ideal system would be the one which cures in a relatively short time resulting in excellent mechanical and physical properties. However, in practice, a compromise has to be made between the mold cycle time and ultimate property requirements. The effects of cure cycle time, temperature, preheating and post‐cooling on mechanical properties of continuous as well as chopped glass fiber reinforced polyester and vinyl ester systems involving 1/4 to 1 in thick sections have been studied. Mold cycle time is strongly influenced by the part thickness and mold temperature. Internal heat generation due to curing reaction causes high thermal gradients across the thickness. Preheating offers advantages of reducing both the mold cycle time and the thermal gradient. The flexural and interlaminar shear strengths are strongly dependent or, the mold cycle time. Maximum strengths are obtained when the mold is opened at the instant when there is no thermal gradient across the thickness.
Critical parameters for thermoset curing in heated molds
Authors: Adabbo Humberto E. , Rojas Alfredo J. , Williams Roberto J. J.
Published: December 2004

The change in temperature and conversion during the curing of a thermosetting resin in a slab‐shaped heated mold is analyzed theoretically. Results show that there is a critical value of β = AL2/k, for which the maximum center exotherm takes place (A = Arrhenius pre‐exponential factor, L = slab thickness, k = thermal conductivity). Beyond this value, increasing β decreases the center exotherm. The temperature rise at the slab center may be substantially greater than under adiabatic conditions. Wall temperature has a great effect on the process behavior, implying the need of an adequate control system. A description of the temperature profiles and conversion rates is provided and some criteria for the process design are stated.
On the linear viscoelastic limit of polymers—exemplified on poly(methyl methacrylate)
Authors: Brüller O. S. , Schmidt H. H.
Published: December 2004

The linear viscoelastic limit of poly(methyl methacrylate) (PMMA) is established on the basis of the Reiner‐Weissenberg criterion of strength. The obtained limit is not simply a “strainlimit” or a “stress‐limit” but a function of both strain and stress, an energetical limit. In stress‐strain representation the limit is independent of time and temperature, which means that the linear or non‐linear behavior of the material depends only on the actual values of strain and stress. Some experimental data obtained on PMMA confirm the theory.
Cavity temperature—an important parameter in the injection molding process
Authors: Čatić Igor J.
Published: December 2004

The paper stresses the importance of cavity temperature in the injection molding process of thermoplastics. From the study of the temperature field in the mold, it follows that there is no such thing as a uniform mold temperature. The heat balance equation for the injection mold is discussed in detail. It shows that the sum of the heat exchanges during the cycle equals zero. There is an extensive explanation of the heat transfer from the melt to the mold, the heat exchange with the environment, and between the heat exchange medium and the mold. New criteria are given for the cavity material selections. The cavity temperature is a complex function of static and dynamic parameters and should be kept constant in the equal parts of the cycle. This demands a new way of regulating the temperature.
Determination of the structure of the noncrystalline regions in isotropic and oriented poly(ethylene terephthalate)
Authors: Zachmann H. G.
Published: December 2004

The mechanical properties of polymers are influenced strongly by the structure of the noncrystalline regions. The different methods for characterization of these regions are reported and the results obtained on polyethylene terephthalate, are discussed. The orientation function of the noncrystalline chains can be determined by measurements of the X‐ray scattering and the birefringence. The fraction of taut noncrystalline chains is obtained from NMR measurements combined with a determination of the degree of crystallinity. For a further evaluation of the results it is also necessary to use calculations of the NMR‐ line‐width and the birefringence of chains with fixeu ends. With help of such calculations the end‐to‐end distance of the taut and mobile non‐crystalline chains can be determined, It is also possible to distinguish between tie molecules and loops. With increasing orientation, the amount of taut noncrystalline chains increases. The taut chains are tie molecule rather than taut loops. The end‐to‐end distances increase with increasing crystallization temperature.
Non‐isothermal phenomena in polymer engineering and science: A review. Part I: Non‐isothermal polymerization
Authors: Stolin A. M. , Merzhanov A. G. , Malkin A. Ya.
Published: December 2004

This paper reviews non‐isothermal polymerization processes in which the chemical reaction occurs with thermal selfacceleration. A macrokinetic approach to the description of these processes, with consideration of their specific characteristics, allows the study of the thermal operating behavior of periodic and continuous reactors utilized in polymer engineering. Development of non‐isothermal methods for the determination of chemical kinetics in polymerization processes is discussed.
Simulation of extrusion coating by tape drawing
Authors: Shaw M. T. , Miller J. C.
Published: December 2004

Neck‐in and maximum stress were studied in a tape‐drawing experiment using a 3.5 MI low density polyethylene at 300°C. The conditions of the experiment were designed to reproduce closely those found in extrusion coating lines. The maximum stress was found to increase roughly with the 1.6 power of the drawdown ratio and the 1.0 power of the extrusion speed over a stress range of 4 × 103 to 5 × 105 Pa produced by drawdown ratios ranging from 2 to 22 and extrusion speeds of 2.3 to 6.1 cm s−1. The neck‐in decreased weakly with drawdown ratio at low extrusion speed and with extrusion speed at constant drawdown ratio. After carefully characterizing the test resin in shear and extension, the similarities between predicted pure‐shear (planar extension) transients and the tape experiments were studied. It was found that the trends, but not the magnitude of the experimental maximum stress were quite similar to the calculated longitudinal stress in pure shear. The behavior of the transverse to longitudinal stress ratio in pure shear was similar in behavior to the neck‐in results, but considerable improvement was achieved by adding in a decayed stress from a simple‐shear transient to simulate the conditions produced by the extrusion die. The philosophy of purposefully studying similarities between transient, pure or simple deformations and steady, complex processes is discussed.
An investigation of spin coating of electron resists
Authors: Lai Juey H.
Published: December 2004

This paper reports the results of spin coating studies of an electron resist using several different solvents. Two problems which were frequently observed during the spin coating studies were the appearance of orange peel coatings and the formation of cloudy films. The appearance of orange peel is attributed to the rapid drying of low‐boiling solvents. The formation of a cloudy film is believed to be caused by the hygroscopic nature of the solvents used. The resist film thickness can be approximated by the relationship l = KC2.1/ω0.5, where l is film thickness, C is volume fraction of polymer resist, K is a constant and ω is the rotation speed. The results are compared with the theoretical modelings of Washo (1) and Meyerhofer (2).
Effect of hydrostatic pressure on the deformation behavior of polyethylene and polycarbonate in tension and in compression
Authors: Spitzig W. A. , Richmond O.
Published: December 2004

The stress‐strain response of crystalline high density polyethylene and of amorphous polycarbonate has been determined in tension and in compression at superimposed pressures up to 1104 MPa(160 ksi). Strain softening occurred in the polycarbonate at low pressures but was inhibited by pressure. Tensile necking occurred in both materials, but was promoted by pressure in polyethylene and inhibited in polycarbonate. The initial modulus,E, and the flow stress, σ, at a given offset strain varied linearly with the mean pressure,P, with essentially the same pressure coefficient, α. Thus,E= (1+αP)E0and σ = (1+αP)σ0, whereE0and σ0are values at zero mean pressure. In polyethylene, the coefficient, σ0, was the same in tension and compression, indicating that the strength differential between tension and compression was a simple manifestation of pressure‐dependent yielding. In polycarbonate the coefficient, σ0, was different in tension and in compression, implying an effect due to the third stress invariant or to anisotropy. The results suggest a constitutive model for polymers in which the flow stress is linearly dependent on mean pressure, but in which inelastic volume change is negligible. The results also suggest that the pressure dependence of flow stress in polymers is the same as that of the initial modulus.
Superposition of the notched strength of composite laminates
Authors: Pipes R. Byron , Gillespie John W. , Wetherhold Robert C.
Published: December 2004

An improved macroscopic model for predicting the strength of a composite laminate containing a circular notch is developed. Two constants are introduced which uniquely determine the notch sensitivity of a given material. A superposition method for the notched strength of composite laminates is developed which allows data for arbitrary materials and laminate configurations to be superimposed upon a single master curve. The influence of material orthotropy upon notched strength is discussed. A relative notch sensitivity parameter is introduced which allows quantification of the notch sensitivity of a given composite material system, stacking sequence, or laminate configuration.
Theoretical prediction of the pressure gradients in coextrusion of non‐newtonian fluids
Authors: Han C. D. , Chin H. B.
Published: December 2004

In previous publications we have reported our experimental observations that, when the less viscous component flows outside the more viscous component in sheath‐core coextrusion through a cylindrical die, or in sandwich three layer film coextrusion through a slit die, the pressure gradients in a two‐phase system can be lower than those in the two components flowing individually. The experimental observations suggest that the energy requirement for extrusion can be decreased, and the throughput increased, when one judiciously chooses proper combinations of materials and/or optimal processing conditions. In this paper, we present a theoretical analysis, which shows that the seemingly anomalous behavior of the experimentally observed pressure gradient reduction is indeed possible, depending on the rheological properties of the individual components involved in coextrusion.
High‐strength polyethylene
Authors: Wu W. , Black W. B.
Published: December 2004

Polyethylene (PE) continuous filaments having high tensile strength as well as high Young's modulus have been obtained from several linear polyethylene materials by stretching a partially oriented spun yarn to a draw ratio of ≃30. The high draw ratio was readily attained for linear PE fiber extruded at a temperature of at least 250°C and quenched in air while under some intermediate tension. The number average molecular weight of the polymer was found to have the predominant effect on the ultimate tensile strength of the drawn fiber. Yarn with a tensile strength of 19 gpd (167 kg/mm2) and a Young's modulus of 854 gpd (7380 kg/mm2) was produced. Yarn with a Young's modulus of 1145 gpd (9890 kg/mm2) was made by sacrificing some tensile strength.
Residence time distribution of polymer melt in the T‐die
Authors: Matsubara Yutaka
Published: December 2004

Theoretical or rheological calculations for crosshead die geometry were thought not worthwhile until recently, and restrictor, or choker, bars were often excessively relied upon for film uniformity. Thus, the residence time distribution of a polymer melt was infrequently calculated especially in the T‐die, because it was assumed to be very wide in T‐dies. This report provides a general equation expressing the residence time distribution of polymer melts in T‐dies, and indicates how to take an optimum combination of the flow‐path dimensions in order to obtain both a high flow uniformity and a comparatively narrow residence time distribution across the die width. Such a T‐die designed by the above considerations will produce a shorter heat history and improved physical properties of the sheet or film produced.
Residual stresses and aging in injection molded polypropylene
Authors: Coxon L. D. , White J. R.
Published: December 2004

The residual stresses in injection molded bars of polypropylene have been examined using a stress relaxation method and by the layer removal technique. A positive value for the internal stress parameter was obtained with newly molded specimens and was found to be retained by specimens stored at liquid nitrogen temperature. The stress relaxation parameter reduced to zero both for specimens aged at room temperature and also for those aged at −40°C. Nevertheless the relaxation behavior of specimens aged at all three temperatures was quite distinct. The layer removal technique showed that the stresses near to the surface were compressive and those in the interior tensile, in apparent contradiction to the interpretation of Kubat and Rigdahl for the meaning of a positive internal stress parameter. A marked reduction in stress levels on aging at room temperature was confirmed, however. The relevance of the relaxation spectrum of polypropylene to these observations is discussed.
Sorption and diffusion of ionic dyes in anionic cellophane membranes
Authors: Hori T. , Ott R. J. , Rys P.
Published: December 2004

Experimental steady‐state permeability studies have been made with non‐ionic, anionic and cationic dyes using carboxy cellulose membranes as anionic substrates. The experimental results show that with increasing bulk ionic strength the diffusion velocities of anionic and cationic compounds increase and decrease, respectively. The diffusion behavior of non‐ionic compounds is independent of the ionic strength. Empirical relationships have been deduced which fit the permeation data of the anionic compounds. A new concept is introduced which postulates that the diffusion behavior of colons within an anionic membrane is dependent on the basicity of the fixed ionic groups. In substrates with matrix‐bound anionic groups of high basicity, such as carboxy cellulose, the permeability behavior is described in terms of a new diffusion mechanism referred to as the “fluctuating” charge mechanism. This concept can provide a semi‐quantitative understanding of the different electrostatic obstruction effects which matrix‐bound carboxylate and sulfonate groups have on the permeability of colons. The measured permeability of the counter ions is in qualitative agreement with the proposed diffusion model.
Oxidation of polypropylene powder
Authors: Frank H. P.
Published: December 2004

Four polypropylene powders were prepared under different drying conditions. They were tested with respect to their oxidation induction period (120°C) which ranges between 75 and 347 min. The effect of these differences on processing stability was investigated. Also studied was the oxidation behavior of powder in a fluidized bed (air) in the temperature range 80–140°C.
Cold compaction molding and sintering of ultra high molecular weight polyethylene
Authors: Truss R. W. , Han K. S. , Wallace J. F. , Geil P. H.
Published: December 2004

Cold Compaction Molding and Sintering of Ultra High Molecular Weight Polyethylene (UHMWPE) has been examined as a function of particle size, sintering time and temperature, and cooling rate. Properties nearly equivalent to those obtained by compression molding can be obtained from samples with a fibrous particle morphology, sintered just above the melting point, with further improvement possible by control of particle size and addition of fine particles of normal molecular weight linear polyethylene. UHMWPE with a nodular particle morphology sintered poorly.
Infrared studies of deformation in semicrystalline polymers
Authors: Wool R. P.
Published: December 2004

Infrared (IR) spectroscopy was used to study molecular deformation processes in polymers as a function of stress, strain, time and temperature. Stress‐induced frequency shifts were found to depend on temperature and morphology. Deformation of viscoelastic polypropylene was examined in terms of time dependent molecular stress distributions, orientation changes, conformational variations, and chain fracture. A tie chain length distribution model was used to quantitatively interpret the IR data. Molecular deformation processes of creep and stress relaxation were found to be opposite in nature, Observed long lifetimes of highly stressed chains suggest a reappraisal of existing fracture theories.
Mixing for reaction injection molding II. Impingement mixing of fiber suspensions
Authors: Tucker Charles L. , Suh Nam P.
Published: December 2004

The performance of confined impinging jet mixers on suspensions of milled glass fibers in Newtonian liquids is investigated experimentally. Also studied are the performance of these devices in conjunction with an impingement aftermixer and a rotating mechanical mixing aid. In contrast to the behavior of unfilled liquids, fiber suspensions exhibit significant large‐scale mixing defects. Over the range of fiber lengths and loadings tested, large‐scale mixing quality is found to be dependent on an effective Reynolds number based on the shear viscosity of the suspension at a strain rate characteristic of the length of fibers. Both mixing aids are shown to provide improved mixing quality and could be useful in situations where length of fibers. Both mixing aids are shown to provide improved mixing Quality. and could be useful in Situations where an impingement mixer alone is not adequate.
Some considerations of heat‐transfer problems in thermoforming
Authors: Brinken F. , Potente H.
Published: December 2004

Details are given below of how the heat‐up process for radiation methods may be expressed mathematically. In order to fulfill practical requirements, a process must ensure calculation of necessary heating time using process‐specific characteristic curves with a minimum of mathematical effort. To this end the amount of heat actually absorbed by the surface of the O product must be known when sheets are heated by radiation. This can easily be determined through measurement of sheet surface temperature. It will be shown that if certain preconditions are satisfied, then variations in the distance of the IR‐heaters have no effect on the temperature profile of the sheet. With poly(methyl methacrylate) (PMMA) the nature of coloration does not play a significant role. Investigations into the cooling process centered on a number of cooling methods and tool materials. The dynamic behavior of tempered and untempered thermoforming tools showed similarities to work already carried out in the injection molding sector. Consideration was given to possible ways of using the “Thermolog” analog computer, developed at IKV, to calculate the necessary cooling times in the production of thermoformed parts. Input values and basic data on temperature‐time curves, necessary for the compilation of cooling curves using the analog simulator, were derived from appropriate tests on a thermoforming machine.
Viscoelastic properties of linear polymers in the fluid state and their transition to the high‐elastic state
Authors: Vinogradov G. V. , Yanovsky Yu. G. , Titkova L. V. , Barancheeva V. V. , Sergeenkov S. I. , Borisenkova E. K.
Published: December 2004

The experimental results of the Viscoelastic properties of linear polymers of narrow molecular weight distribution (MWD) and of their mixtures have been analyzed and generalized. Based on the study of the properties of polymers of narrow MWD, we propose a classification of high molecular weight compounds. It specifies a distinct boundary between oligomers and polymers, assuming that the most important feature of polymers is the manifestation of large high‐elastic recoverable deformations of entropy character. For polymers to be characterized, not the absolute molecular weight is essential, but the molecular weight referred to the boundary values. The corresponding state for polymers is attained at temperatures 100°C away from the glass temperature. The transition from the fluid to the high‐elastic state with increasing deformation rate (or frequency for cyclic deformation) has been studied. Transition to the high‐elastic state takes place over a narrow stress range (0.1‐1.0 dynes/cm2), independent of molecular weight, whereas the critical deformation rates (frequencies), like viscosity, depend greatly on molecular weight. An increase in the amount of deformation shifts, to u certain extent, this transition to lower Kites of deformation (frequencies). In the region of deformation rates (frequencies) corresponding to the high‐elastic state, the effect of large deformations during shear manifests itself largely in the tear‐off of polymers Iron, the confining surfaces and in specimen rupture. Polydispersity has a strong effect on the properties of polymeric systems. As the rate of deformation is increased, the transition proceeds successively from the higher molecular weight components. This relaxational transition is tantamount to a change of the structure for polymeric systems. It is responsible for non‐linear, particularly, non‐Newtonian behavior of such systems. The transition to the high‐elastic state and all the related phenomena are observed also in concentrated solutions of high molecular weight polymers. The long‐term durability of un‐cured rubbers in the high‐elastic state is described by the same relationships.
A trilogy on surfaces. I. The temperature‐surface tension coexistence curve
Authors: Legrand D. G.
Published: December 2004

Experimental data and theoretical considerations on the shape of the temperature‐surface tension coexistence curve are presented for binary mixtures. It is found that the interfacial tension is proportional to the difference between the surface tensions raised to the nth power where n is of the order of 4.0.
A trilogy on surfaces. II. On Gibb's adsorption equation and Antonow's law
Authors: Legrand D. G.
Published: December 2004

The Gibb's adsorption equations for a multicomponent multiphase system are used to discuss the relationship between the surface tensions and interfacial tension. It is shown for binary systems that when the terms involving the surface excesses vanish, Antonow's rule is obtained.
The change in mechanical behavior of linear polymers during photochemical aging
Authors: Pabiot José , Verdu Jacques
Published: December 2004

Films of low‐density polyethylene, polypropylene, and rigid poly(vinyl chloride) were exposed for 1700 h to artificial aging in a Weather‐O‐Meter. Photochemical aging was characterized by tensile measurements. We noted that only ultimate properties are affected, whereas properties defined in the low strain range remain unchanged. The kinetics of strain and stress at break depend as much on the polymer's initial rheological characteristics as on the rate of the chemical degradation. The results show that aging results in localized chain breaking leading to defects at the supermolecular level. The average decrease of molecular weight does not seem to influence the mechanical behavior.
Studies on structural foam processing. III. Bubble dynamics in foam extrusion through a converging die
Authors: Yoo Hee Ju , Han Chang Dae
Published: December 2004

An experimental and theoretical study was carried out to achieve a better understanding of bubble dynamics in foam extrusion through a converging die. For the experimental study, a number of converging channels were constructed of aluminum, with glass windows on both sides. Bubble dynamics in the flow channel were recorded on movie film as a gas‐charged molten polymer was extruded. The dies had various converging angles (30, 45, 60, 90, and 150 degrees), and the polymer was polystyrene. As blowing agent, sodium bicarbonate (generating CO2) was used. It was found that the gas bubbles moving along the centerline of the channel grow initially at the upstream end of the die, and then start to collapse as the gas‐charged molten polymer approaches the exit plane of the die. In order to help interpret the experimental results, a theoretical analysis was made of bubble dynamics in a converging channel, in which a thread‐like bubble was assumed to flow along the centerline of the converging channel and the Coleman‐Noll second‐order fluid model was assumed to describe the rheological behavior of the polymer melt. Some mathematically convenient simplifying assumptions not‐withstanding, the theoretical analysis corroborates the experimental observations. The practical significance of the present investigation is discussed in connection with controlling the cell structure in extruded foam products.
Rheological aspects of thermoplastic foam extrusion
Authors: Kraynik A. M.
Published: December 2004

Several rheological aspects of thermoplastic foam extrusion are described by a phenomenological model of the flow in an extrusion die. The macroscopic effects of the phase change, from a homogeneous polymer melt that contains a blowing agent, to a foam, are described in terms of two dimensionless parameters. α is defined as the ratio of the pressure gradient in the melt phase to the average pressure gradient in the foam phase. Θ represents the ratio of the pressure drop in the melt phase to the pressure drop in the foam phase. The position at which the phase change initiates, the exit contribution to the Bagley ends pressure correction, and the true wall shear stress in the melt phase are related to α and Θ. The quality of the foam produced is discussed in terms of the extrusion conditions and their effect on the foaming position in the die. It is demonstrated that the ends pressure correction cannot be neglected on the basis of a long die alone. Asymptotic conditions for which the phase change has negligible effect on the melt flow rate are predicted. α is calculated from the data of Han and Villamizar, who measured the pressure distribution in the die and observed the phase change directly. The prediction of α from theory is complicated by the lack of suitable constitutive relations for the foam phase. Since Θ only requires knowledge of the pressure at which the phase change initiates, it is relatively easy to evaluate.
Structural and mechanical properties of polybutadiene‐containing polyurethanes
Authors: Brunette C. M. , Hsu S. L. , Macknight W. J. , Schneider N. S.
Published: December 2004

A series of segmented polyurethanes based on hydroxylterminated polybutadienes (HTPBD) and their hydrogenated derivatives (HYPBD) has been synthesized. Thermal, mechanical, and spectroscopic studies were carried out over a wide temperature range to elucidate the structure‐property relationships existing in these polymers. Both thermal and dynamic mechanical response showed a soft segment Tg at −74°C for the unsaturated polyurethanes and at −69°C for the hydrogenated samples. In addition, two hard segment transitions are observed by differential scanning calorimetry (DSC) at 40 and 75°C and a softening region by thermal mechanical analysis (TMA) at 190°C. The low Tg, very close to that of the free HTPBD and HYPBD and independent of hard segment content, indicated that these polymers were well phase separated. Results of infrared analysis revealed that at room temperature, 90‐95 percent of the urethane N‐H groups formed hydrogen bonds. Since hydrogen bonding resides only within the hard segment domain in these butadiene‐containing polyurethanes the extent of H‐bonding served as additional evidence for nearly complete phase segregation. From dynamic mechanical studies, the plateau modulus above the soft segment Tg and stress‐strain behavior depended upon the concentration of hard segments. A slight increase in the modulus, a moderate increase in stress (σb), and decrease in elongation accompanied a higher hard segment content. The thermal and mechanical response of these polyurethanes appears to be consistent with behavior observed for other phase segregated systems. Variations in behavior resulting from hydrogenation of the precursor prepolymer are discussed.
Internal stress levels in xerographic papers
Authors: Agbezuge Lawrence K.
Published: December 2004

The stress relaxation method for determining internal stress levels in polymers has been used to estimate internal stress levels in certain fine papers typical of those used in xerographic processing. The effects of stress relief, obtained by wetting and redrying a sheet without restraint, strain rate, initial stress and sheet anisotropy on the results were examined.
Analysis of the tensile stress‐strain behavior of elastomers at constant strain rates. I. Criteria for separability of the time and strain effects
Authors: Hong S. D. , Fedors R. F. , Schwarzl F. , Moacanin J. , Landel R. F.
Published: December 2004

Considering the case where the relaxation time spectrum is preserved at finite deformations, a theoretical analysis of the tensile stress‐strain relation of elastomers at constant strain rates has been carried out. The finite strain effect is taken into account by replacing the Cauchy strain by a general strain function, ƒ(ϵ), in the Boltzmann superposition integral. The analysis shows that there are two cases where the time and strain effects are separable when: (1) the segment of the stress relaxation modulus which coincides with the experimental time of stretching can be represented by a single power law; and (2) the general strain function, ƒ(ϵ), is linearly proportional to the Cauchy strain. Separability of the time and strain effects, therefore, can be achieved by adjusting the stretching time (or strain) and temperature, if the relaxation time spectrum remains unchanged by the deformation. The tensile stress‐strain relations derived from the theoretical analysis were applied to analyze data on a crosslinked styrene butadiene rubber obtained in the temperature range −40 to 60°C. Γ(ϵ), which describes the strain dependence of tensile stress, Bϵ, the ratio of isochronal stresses at different strains, and ai, slope of a segment of the relaxation modulus Ei(t) on log t plot, were obtained directly from the experiment. Values of Γ(ϵ), Bϵ and ai obtained at −40°C are quite different from those obtained at −30°C or higher. Results obtained from our analysis are generally in agreement with those obtained by an empirical method for analyzing the experimental data.
Haloaldehyde polymers. XXIII: Thermal and mechanical properties of chloral polymers
Authors: Kubisa P. , Corley L. S. , Kondo T. , Jacovic M. , Vogl O.
Published: December 2004

Samples of chloral homopolymers and copolymers with aromatic isocyanates of high chloral content were prepared by cryotachensic polymerization as films of 0.1 to 5 mm thickness. Thermal, mechanical, and electrical properties of these polymers were measured. Polychloral is unlike most other linear polymers as it does not show any melting or glass transition below 220°C, at which temperature the polymer starts to degrade by depolymerization to monomer. The polymer is of moderate crystallinity and shows properties characteristic of engineering plastics.
Processing of polyolefin blends
Authors: Ho Wu‐Jing , Salovey R.
Published: December 2004

The morphology of binary and ternary polyolefin blends of polypropylene (PP), ethylene‐propylene‐diene terpolymer (EPDM) and polyethylene (PE) following processing by injection and compression molding has been examined by optical and scanning electron microscopy. Internal surfaces were generated by low temperature fracture and etching with cyclohexane. In binary blends, droplets of EPDM are elongated in the flow direction within 400μm of the mold surface in injection molding, yielding a skin region which is distinct from an isotropic core containing spherical EPDM inclusions. Spherical droplets of EPDM or PE in binary blends with PP increase in size with increasing compression molding time. In ternary blends, spherical inclusions containing both EPDM and PE are dispersed in PP. With increasing compression molding time, EPDM separates from PE and concentrates at the outer edges of the PE inclusion, effectively isolating PE from the PP matrix.