bluuebunny/crossref_metadata_2025 huggingface dataset:
Elastomeric properties of networks prepared from high‐cis and high‐trans 1,4‐polybutadienes
Authors: Sharaf M. A. , Mark J. E. , Cesca S.
Published: December 2004

Networks were prepared from a sample of 1,4‐polybutacliene having an extremely high cis content (98.5 mol percent) and from other samples having relatively high trans contents (72 to 80 mol percent). The cross‐linking techniques employed were gamma irradiation, ultraviolet irradiation, and peroxide thermolysis. The resulting elastomers were studied in elongation in the unswollen state at several temperatures, to their rupture points, and in swelling equilibrium in a good solvent. Values of the elasticity constant 2C1 obtained from the stress‐strain isotherms at low and moderate elongations gave values of the molecular weight M, between cross‐links in at least approximate agreement with those obtained from the swelling equilibrium data. The other elasticity constant 2C2 generally had relatively large values, suggesting inhomogeneous cross‐linking, but approached zero for small Mc as expected from reduced configurational interpenetration. At high elongations, the reduced stress for the high‐cis polymer showed marked upturns due to strain‐induced crystallization.
The effect of melt compressibility on a high‐speed wire‐coating process
Authors: Chung Tai‐Shung
Published: December 2004

The effects of melt compressibility on a wire‐coating process have been investigated, assuming that the compressible behavior of a polymeric melt obeys the Spencer‐Gilmore equation of state. The compressible model is distinctly different from the incompressible model in two ways: (1) it has substantially lower pressure build‐up within the die, and (2) the location of the maximum velocity is closer to the traveling wire position. As a result, the velocity profile within the die may change from a parabolic shape to a shape somewhat similar to that observed in a drag‐flow case; and the shear stress generated by the fluid on the moving wire is no longer constant. Calculations indicate that the effect of melt compressibility during wire coming may not be neglected if the wire speed Ls greater than 50 cm/s (100 ft/min). In addition, the relationships between processing parameters and product coating thickness for both compressible and incompressible fluids are quite different.
A study on polymer blending microrheology
Authors: Elmendorp J. J.
Published: December 2004

In this paper it is shown that the formation and subsequent breakup of threadlike particles are important disperging mechanisms and largely govern the morphology resulting from a polymer blending process. Experiments on the breakup of Newtonian threads surrounded by a second Newtonian fluid have been carried out and good agreement with Tomotika's theory is achieved. Experiments on the breakup of viscoelastic fluid threads showed the influence of shear thinning and stretch thickening effects of the fluids used. To investigate the influence of non‐Newtonian behavior of molten polymers on capillary instabilities, experiments were carried out on the breakup of molten polymer threads embedded in a second polymer melt. Surprisingly an absence of shear thinning and stretch thickening effects was noticed and good agreement with Tomotika's theory was obtained. Finally, the stability of threads of fluids exhibiting a yield stress was studied. A criterion predicting the stability of such threads was established and verified experimentally. On the basis of this criterion a possible explanation is given for the stability of a certain class of co‐continuous morphologies.
Rheology of curing thermosets: A review
Authors: Roller M. B.
Published: December 2004

Over the past decade great strides have been made in the measurement, modeling and application of the rheology or viscosity history of curing thermosets. This paper will review the work that lead to the formulation of a simple predictive model to simulate the viscosity path of curing epoxies and to the use of the model in the understanding of the epoxy lamination process. Subsequent work by others that has clearly refined, extended, and simplified the method will be discussed.
Two directional coextrusion flow of two molten polymers in flat dies
Authors: Sornberger G. , Vergnes B. , Agassant J. F.
Published: December 2004

A theoretical study has been carried out of the two directional isothermal flow of two molten polymers in a flat die. The viscous behavior of each fluid is described by a power‐law. Using an iterative finite difference method, a numerical program predicts the influence of geometrical and Theological parameters on the variations of the interface position. Theoretical values are in good agreement with experimental results obtained on a fish‐tail die. In the case of a coat hanger‐die, the mean value of the interface position is correct, but the general shape may be quite different.
Pressure‐Induced densification in injection molding
Authors: Greener J.
Published: December 2004

The effect of pressure on the densification of amorphous polymers in the Injection‐molding process is examined. Density distributions in molded polystyrene slabs were measured for several well‐defined molding histories. In all cases the density of the molded part was spatially inhomogeneous, and its distribution in the slab was closely related to the pressure and temperature histories that prevailed in the molding cavity during the process cycle. The density profile in the gapwise direction followed a characteristic “parabolic” pattern with a minimum at the midplane of the slab. A simple phenomenological model, based on the pressure‐induced densification effect, was constructed to explain the observed density profiles, and close agreement with experimental data was found. Annealing of the molded article at a high temperature (<Tg) caused the density to decrease overall and become more uniform across the part. This is generally consistent with volume‐recovery data for the densified material, which were generated independently in a controlled pressure‐densification experiment.
Tensile yield in polyethylene
Authors: Hartmann Bruce , Lee Gilbert F. , Cole Richard F.
Published: December 2004

Uniaxial tension tests to the yield point were performed on polyethylene as a function of temperature from 21 to 117°C at a strain rate of 2 min−1. At 21, 45, and 69°C, measurements were also made at strain rates from 0.02 to 8 min−1. Yield energy was found to be a linear function of temperature extrapolating to zero at the melting point (140°C). The ratio of thermal to mechanical energy to produce yielding is about three times smaller than for glassy amorphous polymers. The ratio of yield stress to (initial) Young's modulus is 0.021 at room temperature and increases to 0.059 at 117°C. Also this ratio was found to decrease with log strain rate. For instance, at 21°C for a strain rate of 0.02 min−1 the value was 0.023, while at 8 min−1 this value decreased to 0.020.
Correlation of blown film optical properties with resin properties
Authors: Pucci M. S. , Shroff R. N.
Published: December 2004

The optical properties of conventional, free‐radical polymerized low density polyethylene (LDPE) blown films are due essentially to surface irregularities that develop during fabrication. Past studies have shown that the extent to which these irregularities occur (and therefore optical properties) correlates well with the melt elasticity of the resin. Specifically, it has been shown that resins with higher melt elasticity result in films with poorer optical properties. However, it was recently reported that the optical properties of film blown from a Sci of three generically similar LDPE resins were found to correlate with the crystallization kinetics of the resins. Specifically, it was reported that the resins that exhibited faster crystallization rates produced films with better optical properties. This present work shows, however, that this apparent correlation is only coincidental. It has been shown that resins exhibiting faster crystallization rates do not necessarily result in films with better optical properties. On the other hand, it has been shown that resins with higher melt elasticity consistently result in films with poorer optical properties.
Phase structure of polyetherpolyol‐4,4′‐diphenylmethane diisocyanate‐based reaction injection molded (RIM) polyurethanes
Authors: Nishimura H. , Kojima H. , Yarita T. , Noshiro M.
Published: December 2004

A series of polyetherpolyol−4,4/‐diphenylmethane diisocyanate based polyurethanes were prepared by reaction injection molding (RIM). The degree of phase separation and morphology, which govern the mechanical properties, was investigated by X‐ray scattering, dynamic mechanical spectroscopy, and electron microscopy. The phase reversion occurred at just a 70 weight percent concentration of the based reagent. The degree of phase separation increased with the molecular weight of polypropyleneglycol and decreased with the ethyleneoxide capping content. Morphology was influenced by injection rates.
Crystallization of poly(etheretherketone) (PEEK) in carbon fiber composites
Authors: Lee Youngchul , Porter Roger S.
Published: December 2004

The tendency of carbon fiber to nucleate the zation of poly(etherettterlcetone) (PEEK) has been evaluated by DSC and other techniques. As the carbon fiber content was increased, the supercooling necessary for PEEK crystallization decreased. The repeated melting (at 396°C) of the same PEEK sample results in a decrease of the number of nuclei for crystallization. At equivalent thermal histories, PEEK with carbon fiber was found to have a higher nucleation density than PEEK itself. The surface of carbon fibers and nuclei in the PEEK matrix compete for crystallization growth. As the holding time in melt was increased, the number of matrix spherulites formed on cooling decreased, hence a more pronounced transcrystalline region was developed. Correspondingly, the composites preheated in the melt for 100 min showed about two times the transverse tensile strength and strain‐to‐failure of those preheated for only 30 min. Corresponding fracture surface produced in tension showed that the former samples had a greater matrix adhesion to the carbon fiber than the latter.

A strong interfacial bond is thus developed by crystallization on carbon fiber surface. Destroying nuclei in the PEEK matrix by long preheating enhances crystallization on the carbon fiber.
Measurements of cycle time in injection molding of filled thermoplastics
Authors: Boldizar Antal , Kubát Josef
Published: December 2004

This study presents the results of measurements of the sealing and cooling periods of the injection molding cycle of filled thermoplastics, both periods constituting a major part of the cycle. The compounds used were based on HDPE, PP, and PS. The fillers were calcium carbonate, carbon black, and magnesium oxide. The latter two materials were chosen for their high thermal conductivity. The sealing time was determined by a gravimetric method, while the measurement of the cooling time was based on the assessment of the recovery of the ejector marks for samples ejected after varying times of cooling. Increasing filler content produced significant and reproducible reductions of the cycle time. Such effects were especially pronounced with the high thermal conductivity fillers. The cooling process was also treated theoretically, starting from the heat conduction equation and producing a fully satisfactory description of the experimental data. Furthermore, the value of the thermal diffusivity, exemplified by the HDPE/MgO compounds, was in good agreement with the values obtained from current composite expressions.
General consequences of the packing phase in injection molding
Authors: Greener J.
Published: December 2004

The post‐filling phase in injection molding was analyzed via simple heat‐transfer and P‐v‐T models. An expression for the evolution of (volume‐averaged) pressure in a molding cavity during the cooling phase of the process was derived from the empirical Tait model combined with the transient heat‐conduction equation. This expression was used to establish general optimization criteria for the packing phase in injection molding, based on simple heuristics, and to assess the effects of various process and material parameters on the packing response of the system. The effects of gate geometry, part geometry, mold temperature, and melt temperature on the packing characteristics of a simple part are examined, and the general implications to the dimensional integrity of the part are discussed.
The recent developments of thermotropic liquid crystalline polymers
Authors: Chung Tai‐Shung
Published: December 2004

The historical development of both main‐chain (M.C.) and side‐chain (S.C.) liquid crystalline polymers (LCPs) is presented. Synthetic routes and characterization techniques for LCPs are introduced. Various approaches to reduce the melting points of M.C. LCPs and to increase the mesogenic order of S.C. LCPs are reviewed and evaluated. The criteria to form a liquid crystalline phase are then discussed. Comparisons among thermotropic, lyotropic, and low‐molecular‐weight liquid crystals are also made. It is concluded that the preparation of LCPs has been well developed by the industry, but that the understanding of the formation of LC domains has not been completely understood. The theoretical explanations for some unexpected results are still not available. These anomalies are detailed in this work. Future research activity en LCPs for plastics engineers is also mentioned in this article.
The biaxial deformation and yield behavior of bisphenol‐a polycarbonate: Effect of anisotropy
Authors: Carapellucci L. M. , Yee A. F.
Published: December 2004

The biaxial tension stress‐strain‐yield behavior of glassy bisphenol A‐polycarbonate has been investigated at constant octahedral shear stress rate and at 25°C and −40°C. The specimens possess a small amount of anisotropy. Hill′s criterion for yielding of anisotropic materials is modified to take into account the sensitivity of the yield locus to the hydrostatic stress component. This modified yield criterion fits the 25°C data quite well. However, the data at −40°C cannot be fitted using reasonable parameters.
Analysis of steady state of free radical solution polymerization in a continuous stirred tank reactor
Authors: Choi K. Y.
Published: December 2004

The steady state structure of non‐isothermal free radical solution polymerization in a continuous stirred tank reactor is analyzed. With mean residence time as a bifurcation parameter, five regions of steady states are identified. The effect of reactor operating conditions on the structure and the stability of steady state is discussed.
Evaluating screw performance: Extrusion process stability and the degree of mixing from melt rheology data and from measurement on an instrumented extruder
Authors: Plochocki A. P. , Dey S. K. , Wilczynski K.
Published: December 2004

A comprehensive study of polyethylene extrusion was carried out with an instrumented extruder on several screws differing in geometry and paralleled with capillary rheometry of the extrudate leading to melt viscosity and elasticity functions. Assuming Oldroyd's constitutive equation for molten polyethylene and the extrudate melt temperature oscillation (ΔTm) as a measure of the process stability and an indication of melt mixing quality, it was found that the product of the dimensionless numbers (Deborah, De and Brinkman, Br) correlates well (r = 0.93) with ΔTm. Since the Br and De groups follow from the rheological characteristics of the melt and the extrusion process parameters, a relationship of type: ΔTm = a + b (De) (Br) appears useful in designing an extrusion process (for a polymer of known rheology) with respect to its stability, and indirectly, its mixing efficiency.
Simulation of welding flows in a slit. Part I: Kinematics
Authors: Wei K. H. , Malone M. F. , Winter H. H.
Published: December 2004

The kinematics of ideal welding flows generated by a thin‐plate divider, a cylinder, or a slab in a slit channel are studied by using a finite element analysis. The analysis includes simulations of Newtonian and Carreau fluids. There are two flow configurations. First, a single plate‐divider or an obstacle was positioned symmetrically in a slit channel with no‐slip at the walls. In the second, an infinite number of plate‐dividers or obstacles were positioned in parallel, and the boundary walls were infinitely far away. It was found that extensional flow dominates the region near the stagnation points of obstacles and plate‐dividers, and that the fluid elements near the weld interfaces have a strain history of both high stretching and shearing. The thickness of the elongated region is reduced as the thickness of the plate‐divider increases. Shear‐thinning tends to increase the rate of extension. However, its influence on the flow field tends to lessen as the width of the flow channel or the obstacle size increases. A no‐slip condition at walls causes slightly stronger elongational flow in the weld interface than does the symmetric condition of perfect slip at walls.
Using the optical microscope to characterize molecular ordering in polymers
Authors: Viney C.
Published: December 2004

This review aims to encompass various situations where optical microscopy—particularly observation and measurement of birefringence—can be used to deduce the nature of intermolecular correlations in polymers. The necessary background dealing with light propagation in anisotropic media is summarized in practical terms. The review is especially concerned with illustrating how unjustified assumptions and ambiguous terminology can cause erroneous interpretation of results. Many references cited are themselves reviews or even textbooks; they afford detailed access to the wide and diffuse literature that full coverage of this subject demands, but would constitute an unwieldly bibliography if listed as individual publications.
Effect of cryo‐ground rubber on melt flow and mechanical properties of polypropylene
Authors: Phadke A. A. , De S. K.
Published: December 2004

The influence of cryo‐ground rubber (CGR) on melt flow and mechanical properties of polypropylene has been investigated. Cryo‐ground rubber was incorporated in the polypropylene matrix (a) in powder form and (b) as masterbatch with natural rubber. Natural rubber was found essential as a dispersing agent. The loading of cryo‐ground rubber has no significant effect on viscosity at high shear rates (>61 s−1) but at lower shear rates (>61 s−1), viscosity functions change shape with increasing cryo‐ground rubber content. The dynamic mechanical properties revealed that polypropylene is thermodynamically incompatible with natural rubber and cryo‐ground rubber. Cryo‐ground rubber in the powder form shows poor adhesion to polypropylene matrix and, therefore, decreases the impact strength at higher loading. Addition of masterbatch of cryo‐ground rubber and natural rubber improves the impact strength of polypropylene.
The role of the latent image in a new dual image, aqueous developable, thermally stable photoresist
Authors: Feely Wayne E. , Imhof Joann C. , Stein Cynthia M.
Published: December 2004

A new dual image, aqueous developable photoresist can be processed to yield either positive or negative images that are crosslinked and thermally stable to temperatures >300°C. Positive images have similar resolution and processing parameters to conventional positive novolak resists. Negative resists from this system have a number of new and interesting properties that surpass the capabilities of their positive counterparts. In addition to producing highly resolved submicron images, thick coatings of resist can be used to form images with high aspect ratios. By adjusting the exposure of the resist, images with inward sloping wall profiles can be realized. As a result of the images being crosslinked and Insoluble in the resist coating solution, images can be recoated and new images formed over the top of existing patterns to form structures. A hypothetical mechanism that suggests that resist defects caused by dust on the mask or photoresist surface can be reduced In negative mode processing is also presented.
Poly(alkenylsilane sulfone)s as positive electron beam resists for two‐layer systems
Authors: Gozdz Antoni S. , Craighead Harold G. , Bowdkn Murrak J.
Published: December 2004

Alternating copolymers of sulfur dioxide and vinyltrimethylsilane (VTMS) and terpolymers with allyltrimethylsilane (ATMS) and 1‐butene have been synthesized by low‐temperature, free radical‐initiated polymerization. The co‐polymers with VTMS were soluble but hydrolytically unstable. Whereas the copolymer from ATMS was insoluble, terpolymers containing less than 75 mol‐percent ATMS (relative to butene) were soluble in a variety of organic solvents. Moreover, they were stable against hydrolysis and had good film forming properties. Their electron beam sensitivity was 1.5 °C/cm2 at 20 keV. and their contrast was ∼2. The terpolymers have been used as a top imaging layer in a two‐layer resist system to transfer half‐micron features into a 1.2μm‐thick Novolac planarizing layer by oxygen reactive ion etching (O2, RIE).
Differential scanning calorimetry investigation of curing of bisphenolfurfural resins
Authors: Patel Pradip S. , Shah Praful P. , Patel Shanti R.
Published: December 2004

Bisphenolic resins have been prepared by alkali catalyzed condensation of bisphenol‐F, bisphenol‐A, and bisphenol‐C, respectively, with furfural. The resin samples have been characterized by elemental analysis, dilute solution viscosity measurement, and measurement of number‐average molecular weight. Curing reactions of these bisphenolic resins with hexamine have been investigated by differential scanning calorimetry. The overall apparent activation energies for the curing have been found to be 24 ± 2, 34.2 ± 1.9, and 36.8 ± 2.3 kcal/mole for bisphenol‐F‐furfural, bisphenol‐A‐furfural, and bisphenol‐C‐furfural resin, respectively. The curing reactions have been found to follow an overall first‐order kinetics.
Simulation of reacting flow during filling in reaction injection molding (RIM)
Authors: Lekakou C. N. , Richardson S. M.
Published: December 2004

This paper deals with computer simulation of the filling stage of the Reaction Injection Molding (RIM) process for cavities of rectangular, cylindrical, and disc shapes. The computer model is in two parts: the main flow and the flow by the moving front. In the main flow part, the transient equations of axial momentum, energy and species conservation and also the continuity equation are solved numerically by finite‐difference methods using a moving, changing mesh. In the flow front part, which is quite novel, the transient (parabolic) vorticity, energy and species conservation equations and the elliptic streamfunction equation are again solved by finite‐difference methods. An important feature of both parts is that convection along and across the flow is included in all the transient equations. Results are presented for all three cavity shapes and those for rectangular cavities are compared with the experimental results of previous investigators.
Pressure losses in the packing stage of injection molding
Authors: Darlington M. W. , Scott A. J. , Smith A. C.
Published: December 2004

The pressure loss between the mold and the nozzle in the injection molding of bar and box moldings has been monitored. The pressure drop observed during filling of the mold is reduced during the packing stage but remains finite. This has been attributed in the literature to solidification of polymer across the cavity transducer and to melt relaxation phenomena. Experiments have been carried out with hot molds to prolong the packing stage at the expense of the ‘cooling’ stage. Under these circumstances the pressure drop is reduced but not eliminated. The observed pressure drop may be related to the viscosity of the melt and its dependence on pressure and temperature although strain‐induced crystallization and the pressure dependence of the melting point can confer effects similar to the cooling stage.
The effect of rolling orientation on the brittle‐ductile transition in polycarbonate fracture
Authors: Oh Hie‐Young , Kim Byung H.
Published: December 2004

The effect of orientation on the brittle‐ductile transition in rolled polycarbonate was examined. It has been believed that the brittle‐ductile transition is governed by the residual stress at low reduction and the orientation at high reduction. But, our experimental results revealed that the brittle‐ductile transition is caused by neither the residual stress nor orientation. It is proposed that the brittle‐ductile transition may be ascribed to the morphological change which is produced during plastic deformation on rolling.
A kinetic approach to multifunctional polymerization with cyclization
Authors: Kumar Anil , Misra Sanjay
Published: December 2004

A kinetic model for the step growth polymerization of multifunctional monomers RAf valid up to the gel point has been presented which accounts for the intramolecular reactions. From the Jacobson‐Stockmeyer equation, the average rats constant for this step has been derived and is found to be chain length dependent. A computation scheme has been evolved by which the molecular weight distribution of the linear, branched as well as cyclized polymer can be determined up to the gel point. It is found that even though the molecular weight distribution of cyclic oligomers is little affected for the range of the values of the intramolecular rate constant (kc) studied, the average chain length μn and the polydispersity index p of the polymer formed are extremely sensitive to kc near the gel point. Numerical computations confirm that as the gel point is approached, larger polymer chains are formed which have a higher tendency to react intramolecularly. However, even at high conversions the number of the cyclic rings per polymer chain remains small, which is consistent with experimentally observed results.
A study on polymer blending microrheology: Part IV. The influence of coalescence on blend morphology origination
Authors: Elmendorp J. J. , Van Der Vegt A. K.
Published: December 2004

The influence of shear induced coalescence on the origination of morphologies in polymer blending processes is investigated both theoretically and experimentally. In the theoretical part a route is proposed to estimate the fraction of collisions between disperse phase domains in simple shear flow that result in an actual coalescence. It was shown that under polymer blending conditions this “coalescence probability” is only substantial if the polymer/polymer interfaces exhibit a high degree of mobility. In the experimental part, the phenomenon of gravity induced droplet/planar interface coalescence is utilized to show the high degree of mobility of molten polymer interfaces. Seoul experiments on the relation between domain size and disperse phase concentration in polymer blends prepared on a single screw extruder were carried out. For extremely low concentration (<½ %) the domain size could be predicted satisfactorily by means of Taylor's classical criterion for Newtonian liquids, while at higher concentration coalescence increased the average domain size manifold.
Bryce maxwell: Scientist, innovator, teacher
Authors: Boyer Raymond F.
Published: December 2004

We first discuss two scientific publications by Maxwell: a pioneering paper on the nature and kinetics of crazing on atactic polystyrene; and his development of a new mechanical spectrometer with a frequency range from 6 × 10−4 to 1.6 × 102 Hz, and storage and loss modulus obtained with it on atactic poly(methyl methacrylate). An informal association with Maxwell and his group starting in 1970 has permitted us to appreciate him as an inventor and an innovator with a broad impact on the polymer field; and also to follow him in his role of teacher/professor.
A new approach to capillary viscometry of thermoset transfer molding compounds
Authors: Blyler L. L. , Bair H. E. , Hubbauer P. , Matsuoka S. , Pearson D. S. , Poelzing G. W. , Progelhof R. C. , Thierfelder W. G.
Published: December 2004

A new capillary rheometer incorporated in an instrumented transfer molding press has been developed. This rheometer is effective for determining the viscosity characteristics of thermoset molding compounds under both isothermal and typical molding conditions. In examples of the rheometer's utility, the power law indices of two commercial epoxy molding compounds have been determined to be approximately 0.7. Additionally it has been shown that preconditioning typical epoxy compounds at 47 percent relative humidity causes a viscosity decrease of about 40 percent owing to plasticization of the epoxy resin.
Characterization of mixtures of linear polyethylenes of ultrahigh and moderate molecular weights
Authors: Ueda H. , Karasz F. E. , Farris R. J.
Published: December 2004

The crystallinity, density, dynamic mechanical properties, (25 to 250°C, 11 Hz), and tensile properties at 25°C have been studied for two mixtures of ultrahigh‐molecular‐weight linear polyethylene (Mw = 2.0 × 106), abbreviated UHMWLPE, and moderate‐molecular‐weight linear polyethylene (Mw = 5.7 × 104), abbreviated LPE. These mixtures, which covered the entire composition range, had been prepared with differing solvent‐thermal histories. An enhancement of both crystallinity and density and an obvious synergism in tensile properties were observed for quenched films made from the mixture in which both components had been co‐dissolved. The data indicate that UHMWLPE and LPE can cocrystallize under given circumstances.
Chloroform transport in stress‐whitened polypropylene
Authors: Chau C. C. , Fear D. L.
Published: December 2004

The transport property of chloroform in undeformed and stress‐whitened polypropylenes was studied. The rate of penetration of liquid chloroform in whitened samples prepared by uniaxial stretching was slower than that of the undeformed material. In the whitened region, the process appeared to be Fickian diffusion, while in the undeformed material, it was a combination of Fickian and Case‐II. The diffusivity (at 50°C) in the whitened region increased about 8 times as the strain rate of stretching decreased from 0.67 to 0.033/min. The temperature dependence of diffusivity (ε = 0.67/min) showed an activation energy of 10.16 Kcal/mole. The whitening effect was greatly reduced as chloroform was absorbed; the final residual whitening after desorption increased with the rate of stretching as determined by transmission densitometry. For the undeformed polypropylene, Case‐II type of matrix relaxation contributed significantly to the total flux. The transport process was relaxation controlled at the surface: it gradually changed to Fickian diffusion behavior toward the middle plane. The flux contribution of relaxation across the thickness increased with the sorption time, and that of diffusion decreased. These observations seem to indicate that cold drawing impeded the deformation by swelling stress from occurring at the penetration front.
Prediction of gas barrier properties of high polymers
Authors: Salame Morris
Published: December 2004

This paper studies the correlation of polymer structure and morphology and gas permeability. A scale of numerical values based on polymer cohesive energy density and fractional free volume has been devised to predict permeability and also to estimate diffusion and solubility properties.
Crystallization kinetics of polyetheretherketone (peek) matrices
Authors: Velisaris Chris N. , Seferis James C.
Published: December 2004

Differential scanning calorimetry (DSC) and the density gradient technique (DGT) were used to determine, both isothermally and dynamically, the crystallization kinetics of polyetheretherketone (PEEK). The data were analyzed by a model utilizing, for the first time, two crystal nucleation and growth processes which were observed experimentally in a typical Avrami plot of the isothermal data. Thus, by modeling the data as two separate Avrami type crystallization processes occurring in parallel, both isothermal and dynamic data could be predicted with the same model constants. The first process provided an Avrami exponent of 2.5 and an onset temperature of 320°C. The second process displayed an Avrami exponent of 1.5 and an onset temperature of 342°C. The validity of this dual mechanism crystallization model was proven in practice by predicting with best fit model constants, a wide range of crystallinities of both neat and carbon fiber‐reinforced PEEK samples that had been made at different cooling rates from the melt.
Fracture surface characteristics of unfilled thermosets
Authors: Robertson Richard E. , Mindroiu Viorica E.
Published: December 2004

Many of the features that cause the great complexity of the fracture surfaces of thermosets are suggested to have a simple explanation. These features include the “basic longitudinal texture,” “steps,” “welts,” “arrays of skewed cracks,” and the “stacked lamellar texture.” The explanation for their occurrence is based on the hypothesis of an instability of the propagating crack front that produces a “fingering” ahead of the crack.
Intermolecular interaction in polymer alloys as studied by crack healing
Authors: Kausch H. H. , Petrovska D. , Landel R. F. , Monnerie L.
Published: December 2004

The “method of crack healing” permits measuring the mechanical effects resulting from an interdiffusion of chain molecules across an interface. Having shown that in highly cross‐linked ruptured styrene‐acrylonitrile (SAN) a two‐stage healing mechanism is active, a similar phenomenon was expected in blends of polystyrene (PS) with a more flexible component such as poly(vinyl methyl ether) (PVME), or with a more rigid component such as poly(−2,6 dimethyl 1,4 phenylene oxide) (PPO). However, in both cases crack healing at a temperature 10 K above the respective glass transition temperature (Tg) was linear with the healing time to the power of 1/4 and slower than with pure PS. This unexpected observation is explained by analysis of the thermal and viscoelastic behavior of these blends and by the different contribution to the stress intensity factor resulting from the entanglements formed by the interdiffusing molecules.
Skin‐Core morphology and failure of injection‐molded specimens of impact‐modified polypropylene blends
Authors: Karger‐Kocsis J. , Csikai I.
Published: December 2004

The structure‐property relationship as well as the failure phenomena of injection molded polypropylene (PP) blends modified with ethylene/propylene/diene terpolymer (EPDM) and thermoplastic polyolefinic rubber (TPO) were investigated. Single and double‐gated tensile bars were injection molded by different Injection speeds. Microscopic studies on the failure behavior of knit lines were carried out using microtomed sections taken from the doublegated specimens. It was found that during injection molding, a skin‐core morphology is formed in both the continuous PP matrix as well as in the modified PP blends containing rubber particles of various deformation. The characteristics of the latter are in agreement with those described by the Tadmor flow model. The skin consists of a thin pure PP layer, whereas the subsurface layer contains more or less elongated rubbery particles due to the elongational flow at the wall. The deformation of the rubbery particles decreases, but their concentration increases with increasing distance from the skin towards the core. The deformed particles are oriented tengentionally to the flow front profile. Failure during tensile and tensile impact loading is initiated in the shear zone along the skin‐core boundary. This zone has a transcrystalline character and favors the formation of crazing. Final fracture of the bars depends, however, on how crazing and shear yielding simultaneously interact. Their interaction is a function of the average particle size of the dispersed phase. Above an average particle size of 0.6 μm, crazing is prevented by shear bands. For injection molding of PP/rubber blends a moderate injection speed is recommended, if the melt viscosities of the components are closely matched. In this way a pronounced dispersion gradient of the rubber particles across the plaque thickness is avoided. However, for the blends modified with rubber of high viscosity ratio and greater melt elasticity, use of higher injection speed is advantageous. Here, the higher shear stress field decreases the average particle size taken into the direction perpen dicular to the lead, since the cross section of the stronger deformed particle decreases.
Dynamic mechanical properties and morphology of polypropylene block copolymers and polypropylene/elastomer blends
Authors: Karger‐Kocsis J. , Kiss L.
Published: December 2004

The relation between the dynamic mechanical properties and the morphology of polypropylene (PP) block copolymers and polypropylene/elastomer blends was studied by dynamic mechanical analysis (DMA), light‐ and electron microscopy. The latter techniques contributed to an improvement in assignments of relaxation transitions in the DMA spectra. It was established that PP block copolymers had multiphase structure since the ethylene/propylene rubber phase (EPR) formed in the copolymerization contained polyethylene (PE) domains. An identical morphology was found in the case of PP/polyolefin thermoplastic rubber (TPO) blends. Impact modification of PP by styrene/butadiene block copolymers led to a multiphase structure, too, due to the polystyrene (PS) domains aggregated in the soft rubbery polybutadiene phase. In the semicrystalline polyolefinic and in the amorphous styrene/butadienebased thermoplastic rubbers, PE crystallites and PS do mains acted as nodes of the physical network structure, respectively. PP/EPDM/TPO ternary blends developed for replacing high‐density PE showed very high dispersion of the modifiers as compared to that of PP block copolymers. This fine dispersion of the impact modifier is a basic regulating factor of impact energy dissipation in the form of shear yielding and crazing.
Studies of dissolution phenomena in microlithography
Authors: Krasicky P. D. , Groele R. J. , Jubinsky J. A. , Rodriguez F. , Namaste Y. M. N. , Obendorf S. K.
Published: December 2004

During the dissolution process, polymer in the glassy state is, transported into a dilute solution. In some cases, a transition layer can be measured using laser interferometry. This layer is seen as a difference in reflected light intensity between the bare substrate and the maximum during dissolution. When poly(methyl methacrylate) dissolves in methyl ethyl ketone, the layer is not detectable below a polymer number‐average molecular weight of about 30,000. The layer becomes more pronounced as molecular weight of polymer increases.
Characterization and control of interfaces in emulsified incompatible polymer blends
Authors: Fayt R. , Jerome R. , Teyssié P. H.
Published: December 2004

Information on the interfacial region in incompatible polymer mixtures can be gathered using various techniques including electron microscopy, thermal transition analysis, and more sophisticated methods such as nonradiative energy transfer (NRET). Selected examples are reported here to illustrate the exciting potentialities offered by diblock copolymer emulsifiers in controlling interfacial adhesion and devising high performance polymer blends.
Shrinkage analysis of forged ultra‐high molecular weight polyethylene parts
Authors: Gauvin R. , Nguyen Q. X. , Chalifoux J.‐P.
Published: December 2004

Some engineering thermoplastics cannot be easily processed by injection molding because of their high viscosity. This is the case for Ultra‐High Molecular Weight Polyethylene (UHMWPE). Parts are either compression molded or machined from extruded shapes. Over the years, forging has been increasingly used to produce more or less complicated parts. Forging is a process in which a preform is subjected to bulk deformation in constraining dies, by applying heat and pressure, but with the polymer remaining in the solid (semi‐crystalline) phase. To fabricate acceptable mechanical components such as gears and sprockets, a close control of the operating conditions and a good prediction of shrinkage are necessary, For a better understanding, a study has been conducted on forged UHMWPE disks and gears. Parameters such as material and mold temperatures, dwell time, speed of forging and dwell pressure were investigated. Results show that material and mold temperatures are the most important parameters. For gears, optimization of processing conditions led to a shrinkage of ∼0.2 percent, measured on pitch diameter. The effect of post‐annealing at various temperatures is also reported.
Polymer melt elongation—methods, results, and recent developments
Authors: Meissner Joachim
Published: December 2004

For film blowing of polyethylene it has been shown previously that melt elongation is very powerful for polymer characterization. With two types of rheometers, simple (also called “uniaxial”) elongational tests as well as creep tests can be performed homogeneously. In simple elongation, the melts of branched polyethylene show a remarkable strain hardening. With respect to their advantages and disadvantages, these rheometers complement each other. For multiaxial elongations the various modes of deformation can be performed by means of the rotary clamp technique. With the strain rate components ordered such that \documentclass{article}\pagestyle{empty}\begin{document}$ \dot \varepsilon $\end{document}11 ⩾ \documentclass{article}\pagestyle{empty}\begin{document}$ \dot \varepsilon $\end{document}22 ≥ \documentclass{article}\pagestyle{empty}\begin{document}$ \dot \varepsilon $\end{document}33, the ratio m = \documentclass{article}\pagestyle{empty}\begin{document}$ \dot \varepsilon $\end{document}22/\documentclass{article}\pagestyle{empty}\begin{document}$ \dot \varepsilon $\end{document}11 characterizes the test mode. The Stephenson definition of the elongational viscosities makes use of the linear viscoelastic material equation and proves to be very efficient because the linear shear viscosity (t) (“stressing” viscosity) can act as the reference for the nonlinear behavior in elongation. Results are given for polyisobutylene measured not only in simple, equibiaxial, and planar elongations, but also in new test modes with a change of m during the deformation. This allows one to investigate the consequences of a deformation‐induced anisotropy of the rheological behavior.
Measurement of the viscosity of guar gum solutions to 50,000 s−1 using a parallel plate rheometer
Authors: Kramer Jeffrey , Uhl Jonathan T. , Prud'Homme Robert K.
Published: December 2004

It is frequently necessary to measure the viscosity of polymer solutions at high shear rates to obtain data under the conditions encountered in industrial processes. Such measurements are most often made on a capillary viscometer. This paper presents a method of determining solution viscosities at shear rates up to 50,000 s−1 in a rotational rheometer using a parallel plate geometry. The two keys to performing these measurements are very small gaps between the parallel plates (on the order of 50 microns) to eliminate inertial secondary flows, and the ability to increase and decrease the shear rate quickly to minimize viscous heating. A technique for setting and measuring small gaps is presented. Possible sources of error including inertia, axial compliance, and viscous heating are analyzed. A comparison Is made between the viscosity of a 0.7 percent hydroxypropyl guar (HPG) solution measured on the parallel plate rheometer and the viscosity measured in a capillary viscometer. Viscosities of HPG solutions having concentrations of 0.25, 0.50, 1.00, and 1.45 percent are presented over the shear rate range 100 to 50,000 s−1.
Properties of polycarbonate/acrylonitrile‐butadiene‐styrene blends
Authors: Chiang Wen‐Yen , Hwung Dao‐Shinn
Published: December 2004

To help make a good polymer blend by melt blending, the properties of polycarbonate (PC)/acrylonitrile‐butadiene‐styrene (ABS) systems with various compositions have been investigated. As ABS is blended into PC to form a binary system, Brabender torque is reduced, a phenomenon that results in Improved processability of PC. With increasing ABS content, the mechanical properties of the blends such as tensile strength, modulus, hardness, and shrinkage decrease. However, with the variation of composition, Izod impact strength shows a maximum, while elongation at break exhibits a minimum. These phenomena are discussed with dynamic viscoelasticities and scanning electron microscopic morphological results. The value of ΔTg(TgβPC − TgβABS) is at its smallest when the ratio of PC to ABS is 90:10, However, the value rises with an increase in ABS because the butadiene content of the ABS hinders compatibility in the binary system. At the 90:10 composition, the damping height is optimal. In addition, the dispersed phase of the ABS is most ideal, absorbing the impact force and showing high impact strength. Composition ratios other than 90:10 present high damping as well as undesirable phase separation because of poor adhesion between two phases. As a result, the mechanical properties are reduced.
Mechanical and flow properties of high‐density polyethylene/low‐density polyethylene blends
Authors: Garcia‐Rejon Andres , Alvarez C.
Published: December 2004

The recycling of plastic waste is of particular interest in large urban areas where municipal waste represents a large ecological problem. To achieve their objective (consumer products from plastic waste), formulators of a recycling program have to understand the implications of working with mixtures of different resins. Furthermore, in a multiphase system, the thermomechanical history experienced by the resins during processing represents an important link between operating conditions, resin properties, and final product performance. High‐density polyethylene/low‐density polyethylene (HDPE/LDPE) blends (10, 20, 35, 50, 65, 80, and 90 percent by weight HDPE) were melt blended in an internal mixer. A complete rheological characterization was performed on each blend. The resulting blends were extruded under different processing conditions. The extruded sheets were further characterized to determine their mechanical properties, The experimental results show important differences in the mechanical properties (transverse and longitudinal) of the sheets obtained from the blends. These differences are explained on the basis of the processing conditions (thermomechanical history) and the rheological properties of the molten blends.
Laminar morphology in polymer blends: Structure and properties
Authors: Subramanian P. M. , Mehra V.
Published: December 2004

Polymer‐polymer blends offer a route for enhancement of various properties. When immiscible polymers are blended together (in the presence of a compatibilizer), the blend properties are dependent on the morphology of the phases. Uniform, fine dispersions generally result in “average” properties. Discussed here are blends of polyamides or polyesters with polyolefins, particularly polyethylene, where small amounts (3–20 percent) of the former polymers dispersed as essentially parallel, thin, large laminae produce substantial reduction (3–100 times) of permeability properties in blow‐molded/extruded articles. Physical properties of such blends, their permeability properties, and morphologies are discussed.