bluuebunny/crossref_metadata_2025 huggingface dataset:
Failure mechanisms of 2‐D and 3‐D woven fiber reinforced polymer composites
Authors: Chen H. P. , Jang B. Z.
Published: December 2004

A simple lab‐scale weaving method was used to produce multidirectional fiber preforms to improve the delamination resistance and damage tolerance of composites. Mechanical properties measured in this study included short‐beam shear strength and damage tolerance of 2‐D and 3‐D woven composites. The constituents of fiber and matrix in these composites are Kevlar‐29 (Du Pont) and Epon 828 (Shell Chemical Co.) epoxy. Attention was directed to the differentiation of deformation and failure mechanisms in these composites as a function of material parameters and loading conditions. The sequence of failure mechanisms differ between 2‐D and 3‐D composites. Results indicated that 3‐D woven composites exhibited higher shear strength than 2‐D woven composites. Also, 3‐D composites absorbed more impact energy than 2‐D composites. Failure mechanisms of composites subjected to repeated impacts were observed intermittently by using scanning electron microscopy and light microscopy. The failure of 2‐D composites was due to a combination of shear and tensile mode, but in 3‐D composites the failure was dominated by tensile mode.
Effect of screw design on fiber damage in extrusion compounding and composite properties
Authors: Ramani Karthik , Bank Dave , Kraemer Nick
Published: December 2004

The mechanism of fiber length degradation during twin screw extrusion compounding and methods to reduce it through process and machine design are extremely important in discontinuous fiber reinforced composites. Fiber damage along the screw and the extruder die are determined for three screw designs with different mixing sections. The pellet quality, wet‐out, and fiber dispersion in the extruded strands are compared. The fiber orientation distributions in the screw are determined to identify regions of higher fiber interaction. The fiber damage during subsequent injection molding has also been determined. The tensile, flexural, and impact properties of the tensile bars are compared. It is found that the residence time, fill‐up, and the intesity of mixing during extrusion compounding have a predominant effect on fiber length degradation. The screw designs were seen to have a greater effect on the fiber damage in the 40 wt% glass‐filled polymer than the 30 wt% glass‐filled polymer. However, the mechanical properties of the 30 wt% glass‐filled polymer showed an increasing trend compared to the 40 wt% glass filled polymer. A screw design that provides a balance of the fiber length, wet‐out, and fiber dispersion was noted to give consistent mechanical properties.
Reaction injection pultrusion of thermoplastic and thermoset composites
Authors: Dubé M. G. , Batch G. L. , Vogel J. G. , Macosko C. W.
Published: December 2004

Coventional pultrusion of thermoset composites is under increasing examination for emissions of harmful volatiles from the resin wetout tank. Even though the pultrusion of thermoplastic matrix composites produces no emissions, it is difficult to wet individual fibers due to their high melt viscosities. This paper addresses both the issues of volatiles and wetting with a process called Reaction Injection Pultrusion (RIP). A prototype RIP machine was used to make both thermoplastic polyurethane and thermoset polyisocyanurate matrix composites. The RIP process produces pultruded parts with low void content, good surface finish, and acceptable mechanical properties. The low viscosity constituents used in RIP help improve fiber impregnation, while the small volume of the impregnation bath reduces emissions. Processing parameters such as line speeds, catalyst levels, and die temperaures were varied to establish processing guidelines for sustained production.
Effect of grafting on phase volume fraction, composition, and mechanical behavior: Epoxy/poly (n‐butyl acrylate) simultaneous interpenetrating networks
Authors: Scarito P. R. , Sperling L. H.
Published: December 2004

Grafted simultaneous interpenetrating polymer networks (SINs) were prepared from Epon 828 epoxy resin and n‐butyl acrylate monomer. The amount of grafting monomer (glycidyl methacrylate) was found to effect profound changes in the morphology and mechanical behavior of these materials. While the size of the dispersed rubbery phase increased from approximately 2 microns to 20 microns, the number of domains decreased, with increasing amounts of grafting agent. The total dispersed phase volume decreased with increased grafting. At the highest level of grafting, the two‐phase morphology disappeared, and only one phase was observed. With increased grafting, dynamic mechanical spectroscopy showed a movement of the loss modulus peaks toward each other, confirming an increase in compatibility in the system and showing that the compositions in each phase were becoming more alike. The SIN with the most glycidyl methacrylate (3.0 percent) showed only one peak in the loss modulus curve, supporting the single phase morphology found through microscopy. At the point of compatibility between the two networks, the SIN supermolecular structure may be visualized as becoming one complex network, where the number of grafts between the two polymer chains outnumbers the number of homopolymer crosslinks. The chemical grafts were also shown to significantly alter the free energy of mixing of the two polymers. A grafting level‐composition phase diagram showed that at well defined levels of grafting the free energy of mixing goes from a positive value to a negative value.
Statistical mechanical model of sorption and diffusion of simple penetrants in polymers
Authors: Pace R. J. , Datyner A.
Published: December 2004

Amorphous polymers are assumed to possess a quasicrystalline structure with chain bundles that are locally parallel over distances ∼1 nm. Two possible types of random motion for a spherical penetrant in such a substrate are described, one type determining the jump frequency and activation energy of diffusion, the other type determining the jump length. The former quantities may be calculated from the model, but not the latter. Sorption of simple gases at low penetrant pressures is assumed to occur mostly in pre‐existing holes, both above and below Tg, and the same penetrant diffusion mechanism is assumed to hold in the two regions. The changes in apparent heat of solution and activation energy of diffusion observed at Tg are explained in terms of additional hole formation with increase in temperature above Tg. The theory is shown to be consistent with experimental diffusion data for several glassy and rubbery systems. Evidence is given that hole formation in simple polymers such as polyethylene may occur by chain “kinking”. For polymers possessing articulated side groups, however, it appears that hole formation arises principally from motions within these groups.
Calculator interfacing of a dynamic mechanical analyzer
Authors: Ikeda Richard M. , Starkweather Howard W.
Published: December 2004

The du Pont 980 dynamic mechanical analyzer has been interfaced with a Hewlett‐Packard 9825A calculator. This permits the resonant frequency and loss to be converted automatically into the engineering quantities of modulus, loss modulus, and tan δ presented in both tabular and graphical form as functions of temperature. Productivity is much greater than with previous ways of taking and processing data, and subtle features of the dynamic mechanical spectrum are more easily revealed.
Reprocessing of thermoplastics. II. Polycarbonate
Authors: Abbås Kent B.
Published: December 2004

The effect of recycling on the properties of injection molded polycarbonate was investigated. One unreinforced and two glass‐reinforced grades were studied. Fiber degradation was distinguished from molecular scission by spiral flow measurements and molecular weight analysis. During the first cycles the average fiber length was significantly reduced, but at later stages it approached an equilibrium. The number of scission per original polymer molecule increased linearly with the number of recycles for all systems studied, but the degradation reaction did not follow random scission kinetics. The glass reinforced grades exhibited degradation rates which were at least twice as high as that of an unreinforced polymer. This discrepancy was most probably the result of a more extensive viscous heating in the glass‐reinforced systems. The decrease in molecular weight as well as in fiber length greatly affected the impact strength of the material. The effect of processing temperature on polymer degradation during recycling was evaluated. The fraction of virgin material that has to be added to the regrind to maintain a certain property level was determined. On a 90 percent property level, an icrease in melt temperature by 1°C corresponded to an increase of 1 percent in the required amount of virgin material. Aging tests indicated that there was no significant difference in degradation rate between recycled and virgin material, although the former certainly exhibited lower absolute values of the measured property (impact strength).
Viscosity changes during isothermal and adiabatic urethane network polymerization
Authors: Richter E. B. , Macosko C. W.
Published: December 2004

Viscosity was measured as a function of time for the polymerization of a reaction injection molding (RIM) type urethane system: 4,4′‐diphenyl methane diisocyanate (MDI) with a polyester triol and dibutyl tin dilaurate catalyst. Viscosity was found to be independent of shear rate. Isothermal viscosity rise was related to extent of reaction and to Mw, by branching theory. Isothermal results at several temperatures were able to predict viscosity rise under adiabatic conditions. The gel point test commonly used to evaluate RIM systems is shown to be essentially an adiabatic test.
Rheology of short glass fiber‐reinforced thermoplastics and its application to injection molding. II. The effect of material parameters
Authors: Crowson R. J. , Folkes M. J.
Published: December 2004

The effect of fiber concentration, fiber length, and temperature on the shear viscosity and die swell of several short glass fiber‐filled thermoplastics has been determined. In addition, a study of the injection molding behavior of these materials has been performed. At low shear rates, viscosity increases appreciably with both fiber length and fiber concentration, but at high shear rates the effect is much less pronounced. A qualitative explanation is proposed for these effects in terms of the fiber orientation studies reported in Part I of this paper (1). The die swell is an important parameter in determining the method of mold filling of these materials, and depends strongly on fiber length.
Effects of coupling agents on the rheological properties, processability, and mechanical properties of filled polypropylene
Authors: Han C. D. , Van Den Weghe T. , Shete P. , Haw J. R.
Published: December 2004

An experimental study was carried out to investigate the effects of coupling agents on the rheological properties, processability, and mechanical properties of highly filed polypropylenes (PP). Inorganic fillers used were CaCO3 and glass beads, and coupling agents used were two silane coupling agents, N‐octyl triethoxy silane and γ‐aminopropyl triethoxy silane, and one titanate coupling agent, isopropyl triisostearoyl titanate. It was found that the addition of the coupling agents to the PP‐CaCO3 (50 wt percent) decreased the melt viscosity and increased the melt elasticity (first normal stress difference). However, the addition of the silane coupling agents to the PP‐glass beads (50 wt percent) affected the rheological properties of the melts quite differently. The N‐octyl triethoxy silane had relatively little effect on either the melt viscosity or the melt elasticity, whereas the γ‐aminopropyl triethoxy silane increased the melt viscosity and decreased the melt elasticity. The CaCO3‐ or glass bead‐filled polypropylenes, with and without coupling agents, were injection‐molded and the mechanical properties of the molded specimens were measured by the use of an Instron testing machine. It was found that the effect on the tensile strength and percent elongation of the filled polypropylenes depended upon the specific coupling agent utilized. A melt‐spinning study was also carried out to investigate the effect of coupling agents on the spinnability (defined as the maximum draw‐down ratio) of the PP‐CaCO3 system, and on the mechanical properties of the melt‐spun fibers. It was found that the spinnability of the PP‐CaCO3 was enhanced considerably by the addition of the coupling agents, and that the tensile strength of the melt‐spun fibers was also improved by their addition. Scanning electron micrographs were taken of the fracture surface of injection‐molded specimens and an attempt was made, with the aid of photomicrographs, to explain the mechanical properties of molded specimens observed experimentally.
Influence of viscosity and capillary force on the relationship between crack toughness and crack velocity for an acrylonitrile‐butadiene‐styrene plastic in environmental stress cracking liquids
Authors: Kambour R. P. , Yee A. F.
Published: December 2004

The dependence of crack propagation energy R of an acrylonitrile‐butadiene‐styrene (ABS) resin on crack velocity was characterized in air and in several organic liquids. In the liquids an abrupt transition in R from a level like that in air down to a level characteristic of the liquid occurred with decreasing crack velocity. The velocity at the transition varied strongly with liquid viscosity. A simple model of each craze at the crack tip as a set of pipes through which liquid flows, driven by capillary force and retarded by viscous drag, serves to predict the transition velocity.
Nylon‐6 containing metal halides II: Tensile properties
Authors: Siegmann A. , Baraam Z.
Published: December 2004

Following the reported pronounced effects of metal halides incorporated into nylon‐6 on its glass transition temperature, melting temperature, melt viscosity, crystallization rate and final crystallinity, the tensile mechanical properties and crystallinity of nylon‐6 as affected by the absorption of metal halides were studied. At low salt content, some of the mechanical properties are substantially altered and at higher salt concentrations the ductile polymer becomes brittle. There is no marked difference between the salts studied (CuCl2, CuBr2, FeCl3) regarding their effects on the polymer mechanical properties. In the concentration range studied, absorbed Cu salts do not significantly change the polymer's degree of crystallinity, whereas absorbed FeCl3 results in a pronounced reduction, indicating its effect also on the crystalline phase.
A comparison of impact tests for assessment of fiberglass reinforced plastic toughness
Authors: Owen Gwilym E.
Published: December 2004

All measures of impact resistance have shortcomings. The ASTM tests, Izod, Charpy, and drop‐dart, measure impact at a single velocity. Furthermore, the Izod and Charpy tests impose an unrealistic unidimensional stress on the test specimen. Indirect gauges of impact toughness, such as the area under the tensile stress‐strain curve (tensile work), flexural modulus, or resin cracking in mandrel bend tests, are normally conducted at unrealistically low straining rates. Variable‐rate impact testers have been developed to overcome these shortcomings. In this paper, results obtained from a variable‐rate tester are compared with those from other methods for assessing composite toughness. Data are reported for flexible and brittle low profile press molding resins, tested as SMC (sheet molding compound) moldings by Izod, drop‐dart and variable‐rate impact. Indirect measures of impact resistance, mandrel bend and flexural modulus, are also discussed. The effects of resin flexibility and the composite glass content are demonstrated. The glass content affects the ultimate failure strength of the composite but not the failure of the resin matrix. The resin flexibility affects the initial stages of failure.
Polymer blends and alloys—a review of selected considerations
Authors: Barlow J. W. , Paul D. R.
Published: December 2004

A brief overview of the important issues governing the behavior of polymer blends is presented. Thermodynamic issues which determine the phase behavior of blends are reviewed and qualitatively related to physical interactions between blend components. The influence of melt processing conditions on the resulting properties and behavior of both miscible and immiscible blends is reviewed. The physical properties of blends are reviewed and illustrated by examples from recent work on miscible blends of polycarbonate with a copolyester and on the immiscible blends of polystyrene with high density polyethylene.
Hydrolysis of poly(butylene terephthalate)
Authors: Kelleher P. G. , Wentz R. P. , Falcone D. R.
Published: December 2004

The hydrolytic stability of poly(butylene terephthalate) (PBT) resins and compounds was studied. Rates of reaction were determined by measuring changes in melt flow rate. Hydrolysis was slightly accelerated by contact of PBT with glass containers and reduced by incorporation of some flame retardant additives. Melt flow rates were related to tensile elongation ofunfilled PBT and tensile strength ofthe glass fiber reinforced polymer and used as failure criteria. Reaction rates were used to predict failure times at various conditions.
Processing properties of high‐ and low‐density polyethylenes and their blends
Authors: Maxwell Bryce , Dormier E. J. , Smith F. P. , Tong P. P.
Published: December 2004

Blends of two characterized linear polyethylenes with a branched polyethylene have been prepared by melt extrusion. It has been found that the linear polyethylenes can be shear modified in a reversible manner similar to branched polymers and that this shear modification and its reversal by re‐heating does not change the molecular weight distribution, thereby indicating that the shear modification is a physical rather than chemical change in structure. Because both the high‐ and low‐density polyethylene components of the blends are capable of undergoing reversible shear modification, it is possible to produce blends with either greater or less melt elasticity than the individual components by adjusting the conditions of blending. This demonstrates that the correlation of the properties of blends with the properties of their components should not be attempted without consideration of the effect of the blending process on the properties of the individual components.
Capillary and slit flow behavior of concentrated solutions of a rod‐like polymer
Authors: Kao C. H. , Baird D. G.
Published: December 2004

This paper is concerned with the flow behavior of isotropic solutions of the rod‐like polymer, poly(p‐phenyleneterephthalamide) (PPT), in 100 percent sulfuric acid. Studies include entry flow visualization in a slit die and solution fracture, and die swell in capillaries and a slit die. It was observed that solutions of PPT exhibit nearly negligible die swell, a slip‐stick type of fracture that disappears at high shear rates, and radial entry flow patterns similar to Newtonian fluids. Fracture was associated with the plateau in the shear stress vs shear rate curve. Because values of the wall shear stress (τw.) obtained from capillary measurements were in good agreement with those obtained from a cone‐and‐plate rheometer and values of the loss modulus (G″) obtained from small‐strain dynamic oscillatory measurements, it is believed that the rheological properties lead to the flow instability. These results are in agreement with the predictions of a recent theory by Doi and Edwards for concentrated solutions of rod‐like molecules. Data are also presented for a flexible chain polyamide, nylon 6,6, in 100 percent H2SO4 for the purpose of comparing the flow characteristics of rigid and flexible chain polymers.
Effect of composition and processing on rheological properties of multicomponent polymer melts
Authors: Ahuja S. , Chang H. , Schreiber R.
Published: December 2004

Polyamide and polyether maleic anhydride were blended with carbon black at various compositions and processing conditions. The compositions were varied from 0/92/8 percent, 23/69/8 percent, 46/46/8 percent, 69/23/8 percent to 92/0/8 percent of polyamide/polyether maleic anhydride/carbon black. The polymer blends were processed by a Banbury roll mill and an extruder under various conditions and were spray dried. The effects of composition and processing conditions on steady state and dynamic viscoelastilc properties were determined. These effects were compared with the thermal and morphological properties of the blends.
Positional small‐angle X‐ray scattering
Authors: Legrand D. G. , Tryson G. R. , Olszewski W. V. , Forth M.
Published: December 2004

Positional small‐angle X‐ray scattering has been implemented and developed as a new nondestructive technique to study the formation and growth of flaws in polymers. The technique consists of measuring the intensity of scattering at a constant scattering angle while the sample is moved through the incident x‐ray beam. Examples of applications of the technique from several different materials are presented.
Use of dielectric relaxation spectroscopy to monitor deformation of polycarbonate
Authors: Venkataswamy K. , Ard K. , Beatty C. L.
Published: December 2004

A study has been carried out to determine the effect of deformation on the dielectric properties perpendicular to the deformation direction of amorphous polycarbonate. The dielectric tan δ shows a decreasing trend during mechanical creep and increases during recovery. The reverse trend was observed for the dielectric constant, ϵ′. The experiments at different stress levels indicated that the changes in tan δ closely follow mechanical creep and recovery. Under stress, the β‐relaxation appears to shift to a higher temperature as a function of frequency.
Equilibrium solubility and permeability of sulfur dioxide in epoxy resin of aliphatic diglycidyl ether
Authors: Ranade G. R. , Nadgir V. M. , Plank C. A. , Laukhuf W. L. S.
Published: December 2004

Equilibrium sorption isotherms were obtained for the sulfur dioxide‐epoxy resin of aliphatic diglycidyl ether system over a temperature range of 1° to 45°C. The sorption isotherms indicated the presence of Langmuir sorption due to specific interaction. This is uncommon for rubbery polymers, though similar behavior was also observed previously. Zimm‐Lundberg's clustering analysis indicated a slight tendency for clustering of the penetrant molecules at low temperatures and higher activities. The number of Langmuir sites for sorption was found to be independent of temperature. The mobilities of the molecules sorbed in Henry's law mode and the Langmuir mode were found to be approximately equal. Predictions of the permeability values for this system are presented and compared with other data from the literature. The temperature dependence of different sorption parameters is presented and discussed in detail.
Isothermal and nonisothermal crystallization of polyethylene
Authors: Kamal Musa R. , Chu Edward
Published: December 2004

Differential scanning calorimetry is employed to study the crystallization kinetics of two commercial injection‐molding high‐density polyethylene resins. Also, polarized light microscopy has been used to elucidate the morphological structures formed at various crystallization conditions. Corrections and operating procedures are recommended in order to correct for temperature lag in scanning, transient response during isothermal crystallization and for thermal gradients within the polymer sample. As a result of these studies, a modified Avrami equation has been proposed in order to obtain a more extensive and reliable characterization of isothermal crystallization kinetics. Moreover, a procedure is recommended and employed to predict nonisothermal crystallization behavior on the basis of isothermal crystallization kinetics.
Newtonian sintering simulator of two spherical particles
Authors: Rosenzweig N. , Narkis M.
Published: December 2004

Sintering of amorphous polymer particles above their glasstransition temperature is a slow coalescence process in which surface tension is the main driving force, tending to decrease the total surface area, resisted by the polymer viscosity. The shape, and therefore the boundaries of the coalescing particles, change with time. A numerical finite‐element method (FEM) was used to solve the momentum and continuity equations for a coalescing spherical‐particles pair. The solution obtained describes a limited sintering time interval with reasonable agreement. Future modifications of the solution technique are suggested in order to extend its validity to longer sintering periods.
Shear stress at polymer/metal interface during melting in extrusion
Authors: McClelland D. E. , Chung C. I.
Published: December 2004

Prediction of the screw horsepower requirement involves, among many others, the calculation of the shear stress (τs) between the solid polymer and the barrel surface during melting. Prediction of the solid bed down‐channel velocity also requires the calculation of τs. However, the pseudoplastic nature and strong temperature dependence of melt viscosity make the mathematics of calculating τs extremely difficult.

As a first step of developing a reasonable mathematical model for calculating τs, experimental measurements of τs were made over a wide range of metal temperature and sliding speed for five commercial polymers using molded, block samples. Although dependences of τs on metal temperature and sliding speed were found to have similar functionality to those of the dependences of melt viscosity on melt temperature and shear rate, this study showed that τs could not be expressed as a sole function of the melt rheological properties. Our subsequent study, to be reported in a follow up paper, will show that τs must be expressed as a function of the thermodynamic properties and melt density of the polymer as well as the melt rheological properties and the melting conditions.
The rate of crystallization of poly(ethylene terephthalate) by differential scanning calorimetry
Authors: Lin C. C.
Published: December 2004

The value of tmax in differential scanning calorimetry is correlated with the crystallization kinetics of poly(ethylene terephthalate) (PET). The Avrami exponent, n, obtained varies as a result of a change in slope of the curve at the point tn, a secondary crystallization transition. The plot of tn vs. tmax shows a linear relationship. The rate of crystallization depends upon both molecular weight and crystallization temperature. Under a nucleation controlling step, the plot of log tmax vs. \documentclass{article}\pagestyle{empty}\begin{document}$ t_{\max } vs.\frac{1}{{T^2 \Delta T}} $\end{document}gives a linear relationship. Theoretical concepts of the treatment are discussed.
Flow instabilities of epoxide prepolymers
Authors: Aleman J. V.
Published: December 2004

Flow of molten epoxide prepolymer (Tg = 303 K, M̄n 889, M̄u/M̄n = 1.46) shows stress jumps. A hydrodynamic explanation is forwarded, and a check of the theoretical jump is carried out, with shear viscosites and shear moduli measured at 361 K. The increase in pressure produces a decrease in volume, which increases the rigidity of the polymer, which is then reduced by relaxation of the compressed chain segments.
A low‐energy solvent separation method
Authors: Gutowski T. G. , Suh N. P. , Cangialose C. , Berube G. M.
Published: December 2004

This paper presents a new low‐energy method to separate solvents from polymers. The method is based upon the lower critical solution temperature (LCST), a phenomenon exhibited by all nonpolar polymer‐solvent systems. Three key issues concerning this new separation method are discussed for the specific system of high cis polybutadiene in a commercial grade n‐hexane. The first issue, energy cost, is greatly reduced from present commercial separation processes by avoiding the liquid‐vapor phase transition for more than half of the solvent. The predicted energy cost for the new method (not including inefficiencies) is about 15 percent of the present energy cost (including inefficiencies). The second issue, recycling of the dilute phase with terminator, is shown not to be a serious problem, and a solution is suggested based upon available methods. The third issue discussed, and perhaps the most difficult, is the physical separation of the two phases. This is solved by inducing spinodal decomposition, which leads to rapid gravity separation. Several alternative separation scenarios based upon this idea are presented at the end of the article.
Studies on whitening phenomena induced by some non‐solvents on highly oriented glassy polymers
Authors: Sung N. H. , Gahan R. E. , Haven R. E.
Published: December 2004

Whitening phenomena, characterized by optically opaque regions when a highly oriented glassy polymer is immersed in some liquids, were investigated as a function of temperature, extent of molecular orientation, different solvent and molecular weight, using oriented polymethyl methacrylate (PMMA) obtained by hot‐stretching and cold drawn polycarbonate (PC). Whitened PMMA is highly porous resembling foamed plastics and shows the same Tg as in unwhitened PMMA, while whitened PC is denser with much smaller pores and exhibits melting behavior characteristic of solvent‐induced crystallinity. Whitening progresses with a sharp boundary between whitened and unwhitened layers, which advanced at a constant velocity. This feature is similar to Case II transport. However, whitening differs from Case II sorption in that it only occurs in highly oriented polymers in contact with liquids of negligible sorption. Activation enthalpy of 44.1 and 39.7 kcal/mol has been found in a certain temperature range for PMMA/N‐methyl formamide (N‐MF) and PC/di‐isopropyl amine (DIPA) respectively. At a given temperature, a higher extent of orientation leads to faster whitening process. Entropy correlation theory, in which the decrease in the configurational entropy (ΔSc) due to orientation is assumed to approximate an inerease in the activation entropy, was employed to correlate the dependency of the whitening rate on orientation. For hotstretched PMMA, where ΔSc is proportionl to \documentclass{article}\pagestyle{empty}\begin{document}$ (\alpha ^2 + 2/\alpha - 3) $\end{document} since affine deformation applies, a good correlation is observed. For cold drawn PC, correlation was poor, probably because ΔSc cannot be expressed to be proportational to \documentclass{article}\pagestyle{empty}\begin{document}$ (\alpha ^2 + 2/\alpha - 3) $\end{document}. In PMMA, when the molecular weight is in the same order as the average molecular weight between entanglements, the orientation and the whitening rate are both lower than higher molecular weight speciments. This may be due to a smaller number of chain entanglements and consequent chain slippage. In PMMA, whitening induced liquids seem to have a solubility parameter somewhat greater (2.5 ∼ 5.0) than that of PMMA. For PC, no consistent tendency is found.
Toughened nylon resins
Authors: Hobbs S. Y. , Bopp R. C. , Watkins V. H.
Published: December 2004

The impact failure of blends of nylon 6,6 and low density polyethylene grafted with maleic anhydride (PEgMA) is discussed in terms of fracture morphology, composition, and particle adhesion and dispersion. Basic criteria for effective impact modification of these materials are developed. A numerical model for estimating the extent of shear banding resulting from shear stress field overlap between neighboring impact modifier particles is presented.
Investigation of the solvent‐evaporation effect on spin coating of thin films
Authors: Chen B. T.
Published: December 2004

A simple empirical relationship exists between the thickness and the solvent‐evaporation rate of spin‐coated thin films. The thickness of a film formed from an organic solvent solution can be approximated by the relationship\documentclass{article}\pagestyle{empty}\begin{document}$ D = K_0 \mu ^{0.36} \omega ^{ - 0.50} (E\lambda /C_p)^{0.60} $\end{document}, where μ is the viscosity of the coating solution, ω is the rotation speed, E is the solvent‐evaporation rate, λ is the latent heat of evaporation, Cp is the heat capacity of the solvent, and K0 is a constant for volatile organic solvents. A similar relationship for aqueous polymer solutions is\documentclass{article}\pagestyle{empty}\begin{document}$ D = K_0 \mu ^{0.36} \omega ^{ - 0.50} (1.0 - RH)^{0.60} $\end{document}, where RH is the relative humidity of air around the spin coater and Ka is a constant for aqueous solutions. These relationships are helpful in understanding the mechanism of thin‐film formation in spin coating.
Fluorescence study of polymer chain interpenetration and of the rate of phase separation in incompatible polymer blends
Authors: Morawetz H.
Published: December 2004

The application of fluorescence techniques has been demonstrated for the study of four polymer problems: (a) If two different polymers are labeled with donor and acceptor fluorophores, respectively, which exhibit nonradiative energy transfer, the emission spectrum of their blends will depend on whether the two polymeric species are miscible or segregated into separate phases. Thus, the emission spectrum may be used as a measure of polymer compatibility. (b) Since rapid freeze‐drying preserves the extent of chain interpenetration which existed in solution, the energy transfer between labeled polymers may be used to study the extent of such interpenetration on solution concentration. (c) Phase separation when heating blends of poly(methyl methacrylate) and poly(benzyl methacrylate) may be followed by the change in the emission spectrum of the latter. (d) The interdiffusion of separated poly(ethyl methacrylate) molecules labeled with donor and acceptor fluorophores may be monitored by the increase in the nonradiative energy transfer.
Diffusion of ethyl acetate vapor in strained low density polyethylene
Authors: Phillips J. C. , Peterlin A.
Published: December 2004

At a fixed vapor pressure p of the penetrant and constant temperature of the experiment, the sorption S = c/p or concentration c of the ethylacetate vapor in the uniaxially strained low density polyethylene (LDPE) increases most rapidly at low strains. If, however, on the basis of strain relaxation one separates the total strain ϵ into an elastic ϵe, and a plastic ϵpl, deformation, one obtains an almost linear increase of the concentration c or sorption S of the sorbate with elastic strain ϵe. The separation of ϵ = ϵe + ϵpl depends very much on the time th the sample is kept elongated and the vapor pressure p of the sorbate. The elastic component decreases and the complementary plastic fraction increases with th and p. An almost stationary state is reached after th of about 1/2 h. The calculation of the diffusion coefficient Ds1 from the first sorption immediately after the stretching is affected by this slow adjustment in the interval 0 ≤ th ≤ ½h and shows a pseudo maximum at a strain of ϵ∼ = 10 percent. The first desorption experiment and all the later sorptions and desorptions yield the same DD = DS < DS1 that is the correctly calculated diffusion coefficient D. The coefficient D decreases with the strain ϵ or ϵe in contrast with the expected increase of Da of the amorphous component. Such an increase of Da is expected as a consequence of the fractional free volume (FFV) increase caused by the elongation. According to the FFV concept, a decrease of the measured apparent diffusion coefficient D = ψDa requires that with increasing ϵ, the tortuosity factor ψ decreases faster than the increase in Da.
Effect of a diamine additive on the structure‐property relationships of rim polyurethane elastomers
Authors: Blackwell John , Quay Jeffrey R. , Turner Robert B.
Published: December 2004

Structural and mechanical data have been compared for reaction injection molding (RIM) polyurethanes prepared from uretonimine‐modified diphenylmethane 4,4′‐diisocyanate (MDI), ethylene glycol (EG), and a polyol (a polyether; Mn ≃ 5000), in order to investigate the effect of addition of a small amount of a polyetherdiamine (PEDA; Mn ≃ 400) to the reaction mixture, A series of specimens containing 18 parts and 30 parts EG, with and without the diamine additive, were examined both as‐prepared and after thermal annealing. The specimens were compared in terms of their x‐ray crystallinity, elongation, flexural modulus, impact strength, and heat‐sag behavior. All of the specimens showed evidence for crystalline hard segments, which are more abundant in the series containing 30 parts EG. The crystallinity is lowest in the as‐prepared specimens without the PEDA additive, and is increased by annealing for 1 hour at 120°C. The as‐prepared specimen with additive has a hard segment crystallinity similar to that of the annealed specimen without additive. These results correlate with the mechanical property data, which improve as a result of annealing and/or the use of a PEDA additive. It is argued that the use of the polyetherdiamine enhances the phase separation and facilitates hard segment crystallization, leading to better heat‐sag behavior. It is significant that the unannealed/with PEDA and annealed/without PEDA specimens have similar properties. Use of PEDA additive improves the green strength and impact strength of molded parts.
Characterization of polymer conformation and morphology through small‐angle neutron scattering—A literature review
Authors: Sperling L. H.
Published: December 2004

Small‐angle neutron scattering, SANS, stands forth as one of the most important of the new tools for evaluating polymer chain conformation and morphology. This paper reviews the SANS literature through 1982, with a few early 1983 references added. The theory of SANS is outlined and compared to light scattering. SANS values of polymer molecular weights and radii of gyration obtained in the bulk state were found to be in agreement with values obtained from dilute solutions by light scattering. In each case, deuterated fractions of polymer were inserted into the hydrogeneous matrix, or vice versa, to provide contrast. Several new research areas are then discussed, including unidirectional stretching of elastomers, stress‐relaxation, polymer‐polymer miscibility, crystallization from the melt compared with crystallization from dilute solutions, nonclassical aggregation during bulk polymerization of thermoset systems, morphology of polymer blends, block copolymers and ionomers, the core‐shell structure of latexes and polymer blocks, and grafts as surfactants in emulsions and latexes. Much new and sometimes unexpected information is being provided by the SANS research now in progress.
Fluorescence techniques in the study of polymer colloids
Authors: Winnik Mitchell A.
Published: December 2004

Applications of fluorescence techniques to the study of polymer colloids are reviewed, with emphasis on excimer and exciplex forming probes and fluorescence energy transfer processes. In these experiments non‐aqueous dispersions covalently labelled with naphthalene or anthracene were examined by a variety of techniques in order to elucidate aspects of core morphology with a resolution of about 10Å. The current “concentric sphere” or “core‐shell” model of colloid structure was found to be inconsistent with the results of the luminescence experiments. A new “microphase” model is proposed which overcomes these difficulties. In this model, the core structure is seen to be made up of phase‐separated microdomains of core and stabilizer chains.
A note on the numerical treatment of the thermally developing flow in screw extruders
Authors: Elbirli B. , Lindt J. T.
Published: December 2004

This paper proposes a new solution for the problem of thermally developing flow in a single‐screw extruder with power law fluids. It is shown that a transformation to a Lagrangean frame enables one to extend the solution to extrusion situations where appreciable “pressure back flow” exists. The utility of the model is demonstrated using a polystyrene melt as a model fluid.
The flow of thermoplastic melts: Experimental and predicted
Authors: Cox Howard W. , Mentzer Charles C. , Custer Russell C.
Published: December 2004

The flow of polypropylene, nylon 6,6, and 33‐percent glass‐fiber‐filled nylon 6,6 into a tensile bar mold was investigated. Pressures needed to fill the cavity and runner system were measured as a function of fill time and melt temperature. The experimental results were compared to pressures predicted using the Moldflow flow‐analysis programs. Correlation between experimental and predicted pressures was good provided that accurate input data to the computer programs were used. The choice of runner diameter in the approximation of the irregular shaped runner of this tensile bar mold was found to be important, since the runner length was approximately 40 percent of the total flow length. Material properties of particular importance were thermal conductivity, viscosity, and no‐flow temperature (the temperature at which the resin will no longer flow). Viscosity/shear rate/temperature data are needed for the computer programs and two methods of obtaining the data were examined: an Instron capillary rheometer and a capillary nozzle on an injection‐molding machine. Good agreement between the two methods was found for polypropylene over a shear rate range of 100 to 10,000 s−1. Only the injection‐molding capillary nozzle could be used for the nylon‐ and glass‐filled nylon due to the thermal degradation that occurred in the Instron rheometer.
Residence time distribution in a twin screw extruder
Authors: Kao S. V. , Allison G. R.
Published: December 2004

The residence time distribution (RTD) in a fully intermeshing, corotating twin screw extruder was determined with a stimulus‐response technique. In addition to varying three process parameters (i.e. throughput, screw rotational speed, and barrel temperature), two screw configurations were also studied: one containing four kneading block mixing sections, and the other consisting only of regular screw bushings. Although screw configuration was an important variable, it was found that for both configurations the throughput had the largest effect on RTD. The screw rotational speed was second in importance, and the barrel temperature change produced no effect.

A fluid mechanical model based on the fluid flow in a partially‐filled rectangular channel was used to explain the experimentally observed dependence of RTD on the process parameters. Reaction engineering approaches were adopted to compare the RTD results of two screw configurations with two idealized flows.
Mathematical modeling of squashing flows of heated polymer particles
Authors: Kuo Youti
Published: December 2004

A combination of shear and extension is encountered in the squashing flows of heated polymer particles. Extensional rate affects the non‐Newtonian viscosity in determining the flow field in the squashing of cylindrical particles, but both the extensional and shear rates are equally important for disc‐like particles.

A viscous‐type constitutive equation is used for simplicity. The solution of the momentum equations satisfying no‐slip boundary conditions leads to a particle flattening equation that can predict flattening ratios of nonisothermal particles in terms of rheological parameters and dimensionless groups of process variables. Application of this analysis to roll fusing of toner particles in copiers is described in a companion article in this issue.
Rheological and heat‐transfer considerations for the processing of reactive systems
Authors: Ryan M. E.
Published: December 2004

Thermosetting materials have found widespread use over a broad spectrum of engineering applications due to their intrinsic mechanical strength, thermal and dimensional stability, and other unique properties. Consideration is given to those aspects of reaction kinetics, rheology, fluid mechanics, and heat transfer which are of relevance for the mathematical modeling of reactive polymer processing. Particular emphasis is given to the characterization of reaction kinetics under non‐isothermal conditions, the effect of fillers or reinforcing agents on the heat transfer and kinetic behavior, and the complex nature of the interactions brought about by the reactivity of these systems. In addition, the current status of the mathematical simulation of reactive polymer processing is briefly reviewed.
Numerical simulation of entry and exit flows in slit dies
Authors: Mitsoulis E. , Vlachopoulos J. , Mirza F. A.
Published: December 2004

A general‐purpose finite element program has been used to simulate the flow of Newtonian, power‐law, and viscoelastic fluids in the entry and exit regions of a slit die. It was found that shear‐thinning increases the entrance correction while it decreases the exit correction. Shear‐thinning reduces the size of the small corner vortex that forms in the entry flow of a Newtonian fluid. The swelling ratio had a value of 1.196 for Newtonian fluids and decreased as the value of the power‐law index decreased. Viscoelastic calculations were performed using the Criminale‐Ericksen‐Filbey (CEF) constitutive equation. Convergence of the iterative scheme was unattainable for Deborah numbers above 1.0. The results showed a decrease of the entrance correction and an increase of the exit correction with elasticity. Extrudate swell first decreased slightly and further increased with the Deborah number.
Processing of composites with titanate coupling agents—a review
Authors: Monte Salvatore J. , Sugerman Gerald
Published: December 2004

It is proposed that titanium‐derived coupling agents react with free protons at the inorganic interface to form organic monomolecular layers on the inorganic surface, which causes inorganic/organic phase compatibilization resulting in new composite property, catalysis, adhesion, and rheology performance standards. Processing techniques and rheology effects using titanates are discussed. The injection pressures of CaCO3, carbon black filled polystyrene, and glass‐fiber, talc‐filled poly(phenylene sulfide) are shown to be reduced 50 percent by use of cumyl phenyl type titanate. Adhesion effects are discussed in many composites such as epoxy/aluminum, acrylic/slate, carbon fiber/polyester, etc., followed by data showing significant property improvements in 1/16 inch milled glass fiber and Wollastonite RRIM urethane, printed circuit boards and amide and anhydride cured aramid fiber‐reinforced epoxy.
Nonlinear viscoelastic response in two dimensions—numerical modeling and experimental verification
Authors: Keren B. , Partom Y. , Rosenberg Z.
Published: December 2004

Recently we developed a nonlinear viscoelastic constitutive model which called the Phases Model (PHM) [10]. The main advantages of the PHM over existing nonlinear viscoelastic models are that it lends itself to simple, straightforward calibration of the material functions, and that it is naturally suitable to step‐by‐step computer simulation. In this paper we apply the PHM to two dimensional (2‐D) situations. To this end, we've developed a 2‐D finite difference code in cylindrical geometry which is based on the PHM. We demonstrate the validity of our modeling by applying the code to a 2‐D set‐up developed for this purpose. The 2‐D specimen is in the form of a disc of the test material compressed between two rigid metal anvils by a velocity‐controlled Instron machine. We monitor the response of the viscoelastic disc in terms of the overall axial force history, and the axial stress component at the disc center. We get good agreement between theory and experiment.