bluuebunny/crossref_metadata_2025 huggingface dataset:
Glass transitions of organic compounds. III. Cellulose substrate technique and aliphatic alcohols
Authors: Koleske J. V. , Faucher J. A.
Published: December 2004

The cellulose blotter/torsion pendulum technique used for the determination of relaxations that occur in low molecular weight compounds, oligomeric materials, and amorphous polymers is discussed. The glass transition temperature of a number of aliphatic alcohols and hydrocarbons have been determined and correlated with a method proposed by Gorskii in 1934. The glass transition temperature and molecular weight of these compounds follow the relationshipTg=BMarather thanTg=Tg(∞) ‐K/M. Although differences exist between the primary, secondary, and tertiary alcohols, they appear to follow a similar general pattern. In contrast, the hydrocarbons investigated have markedly different behavior.
Volume fraction determination of Kevlar 49/epoxy composites
Authors: Allred Ronald E. , Hall Nancy H.
Published: December 2004

A knowledge of filament, matrix, and void content is generally required in order to characterize and study composite materials. It is difficult to obtain such data for Kevlar 49/epoxy composites due to chemical attack of the Kevlar filaments when techniques developed for other composite systems are used. This paper presents a chemical dissolution technique for Kevlar 49/epoxy composites by which less than one percent loss of the filament weight occurs. The procedure involves swelling the epoxide matrix in hot dimethylsulfoxide and then rapidly dissolving the degraded epoxide in a nitric aciddimethylsulfoxide solution. This technique allows the determination of filament, matrix, and void volume fractions of Kevlar 49/epoxy composites with a single procedure and has been successfully applied to fabric and filament‐wound composites and to a variety of epoxides. Results obtained with this dissolution technique show excellent agreement with those from optical and weight‐difference methods.
The effect of hot drawing on the properties of short fiber reinforced extruded sheets
Authors: Nicolais L. , Nicodemo L. , Masi P. , Dibenedetto A. T.
Published: December 2004

The hot drawing of extruded composite sheets can be used to control the orientation of both matrix and reinforcing fibers. A study was made of the effect of draw ratio on the properties of an extruded polystyrene sheet containing 0 to 1 percent of short glass fibers. An increase in draw ratio resulted in an increase in fiber orientation. A model of a rigid fiber rotating in an elongational flow field was used to describe the effect of draw ratio on the final orientation distribution. An increase in draw ratio also caused an increase in the amount of fiber breakage. A shear‐lag analysis was used to estimate the extent of damage as a function of draw ratio. It was also found that the mechanical properties were dependent upon both the draw ratio and fiber concentration.
Measurement of the elastic properties of polymer melts
Authors: Maxwell Bryce , Nguyen My
Published: December 2004

A method and apparatus for measuring the elastic and other properties of polymers in the melt state is presented. The recoverable strain magnitude and the rate of strain recovery have been measured as a function of: applied shear rate, applied shear magnitude, temperature and molecular weight. The elastic properties indicate that there is an abrupt change or “transition” in the response of polystyrene melts at temperatures well above the glass transition. This abrupt change is found to be molecular weight dependent. The results are interpreted qualitatively in terms of molecular structure and practical processing operations. The possible relationship of this “transition” to Tu, is briefly discussed.
An improved concept in solubility parameter theory applied in amorphous polymers. I. Poly(ethyl methacrylate)
Authors: Karim K. A. , Bonner D. C.
Published: December 2004

Gas‐liquid chromatography has been used to estimate thermodynamic parameters of a variety of aromatic and aliphatic solvents at infinite dilution in poly(ethyl methacrylate). Heats of solution, Flory‐Huggins interaction parameters, and specific interaction parameters were calculated from specific retention volumes. Comparative interpretation of these thermodynamic quantities has led to the establishment of a solvent selectivity scale for poly(ethyl methacrylate). Limitations of the threedimensional solubility parameter theory on the systems tested here are demonstrated. A significantly improved concept is developed and tested.
Transitions, relaxations, and thermodynamics in the glassy state
Authors: Simha Robert
Published: December 2004

The PVT properties of polymer glasses are discussed from two points of view. First, as a low frequency tool in the study of sub‐glass relaxations. Dilatometric results illustrate the sensitivity of the thermal expansivity and its temperature coefficient to dynamic processes occuring in the glass. The second point of view considers the quasi‐thermodynamics of the non‐equilibrium system, under conditions where the rates of relaxational processes are small in comparison with experimental rates, and time dependent processes are practically absent. The starting point is a theory of the equilibrium melt which describes the characteristic liquid disorder in terms of a temperature and pressure dependent hole or loosely, free volume fraction. This function is obtained by the minimization of a configurational free energy. Upon reaching the glass transition, this dependence is reduced, and further so in a sub‐glass relaxation region. However, it is not eliminated until temperatures of the order of 50 to 70 K are reached. While this picture is qualitatively universal, significant quantitative differences are observed with different chemical structures and different thermal and pressure histories. A comparison of thermal expansivities of high and low Tg systems indicates that in the former the free volume retained upon reaching Tg is comparatively large and the departure from equilibrium or degree of freeze‐in comparatively small. Similarly, it appears that the glassy densification generated by cooling the melt under pressure is more extensive in high Tg glasses. Such results imply structural differences. These should be investigated by comparative studies of (a) time dependent processes in terms of the free volume functions, (b) sorption and transport, and (c) the temperature dependent dynamics of density fluctuations.
Synthesis of permselective membranes by radiation induced grafting of hydrophilic monomers into poly(tetrafluoroethylene) films
Authors: Chapiro A. , Jendrychowska‐Bonamour A.‐M.
Published: December 2004

A large variety of permselective membranes were prepared by radiation grafting techniques. Grafting of styrene into poly‐(tetrafluoroethylene) films followed by sulfonation led to strong anionic membranes showing good performance in reverse osmosis. Carboxylic membranes were prepared by grafting acrylic and methacrylic acids. Cationic membranes were obtained via grafting 4‐vinylpyridine. These membranes were tested in various fractionation processes including reverse osmosis. N‐vinylpyrrolidone grafts exhibited high selectivity for separating water from organic solvents by pervaporation. Bifunctional membranes containing both carboxylic and pyridine groups were obtained by two successive grafting steps either in bulk giving rise to “homogeneous” membranes with unusual swelling properties, or into localized areas generating mosaic membranes which exhibit negative osmosis and increased rates of ion‐pair diffusion.
Performance of extrusion crossheads in multi‐layer cable covering
Authors: Nadiri F. , Fenner R. T.
Published: December 2004

Experiments are reported concerning the performance of an extrusion crosshead used in the three‐layer covering of high voltage electrical cables. Both extrusion pressure requirements and circumferential distributions of polymer layer thicknesses in the finished cable were measured and compared with the results of a previously published finite element method of melt flow analysis within the crosshead. While agreement on pressure is good, it is necessary to allow for the effects of both gravity and slight misalignments of crosshead components if the thickness distributions are to be correlated satisfactorily. The latter effect emphasizes the need for a high degree of accuracy in crosshead design and manufacture.
The degradation of an aromatic polyamideimide in an NO2 atmosphere
Authors: Kambe Hirotaro , Yokota Rikio
Published: December 2004

Films of an aromatic polyamideimide showed a significant degradation in an NO2 atmosphere at 100 mm Hg at 50°C. The degradation was followed by the dynamic tensile measurements. In the curves of temperature dependence of dynamic loss modulus of degraded films, a separate mechanical absorption α′ peak appeared below the glass transition α peak. In the course of degradation, the α′ peak grew and shifted to lower temperature. On thermal treatment of degraded films, the α′ peak shifted to higher temperature and finally merged into the α peak. The formation of reacted surface layers by the diffusion of NO2 was confirmed by scraping off and by solvent extraction. Infrared spectroscopy showed that most amide linkages were destroyed by NO2. The gel permeation chromatography of extracted products showed that the low molecular products were occluded in degraded layers. The influence of these components caused the α′ absorption in dynamic loss curves.
Cushioning energy dissipation in foam polymers
Authors: Peleg Kalman
Published: December 2004

Derivation of dynamic hysteresis loops (force deflection curves) of shock absorbing bushing materials by means of double integration of accelerometer signals is described. The significance of energy dissipation capability of expanded polymers with associated peak deceleration and maximal strain is discussed along with damping characteristics. A “Cushion Efficiency Factor” is introduced, in terms of the ratio of peak acceleration transmitted by a cushion to the energy dissipated per unit cushion area. Three types of expanded polymers commonly used as cushioning materials are evaluated accordingly. Expanded polyethylene (2,2 lb/cu ft), expanded polyurethane (2.1 lb/cu ft) and polystyrene filled polyurethane (1.7 lb/cu ft), all conditioned at 73°F and 50 percent RH. For each of these, two effective drop height tests were conducted, with heights of 12 in. and 42 in. Depending on the polymer type, peak product accelerations were between 33–38 g's in the 12 in. drops and 65–118 g's in the 42 in. drops, with corresponding maximal cushion strains of 0.15–0.20 and 0.39–0.47, respectively. Energy dissipating capabilities of polymers tested during first half cycle following drops were 148–179 lb in. and 477–708 lb in., respectively, depending on polymer type. This approach may facilitate optimal selection of cushioning materials for shock protection in packaging, as well as enable development of improved polymers for cushioning applications.
The interpretation of dynamic mechanical behavior in ultra high modulus polymers
Authors: Gibson A. G. , Davies G. R. , Ward I. M.
Published: December 2004

Recent studies of the dynamic mechanical behavior of ultra high modulus polyethylene? are discussed in the context of our present understanding of the structure of these materials. In particular, the Takayanagi model is shown to achieve a new status in the light of direct measurements of crystal continuity from wide angle X‐ray diffraction data. It is further shown that the Takayanagi model in one formulation is compatible with the Cox model for a short fiber reinforced composite. The fiber composite model offers a simple physical understanding of the fall in modulus due to the α‐relaxation in terms of shear lag. This reduces the effectiveness of the continuous crystal fraction postulated in the Takayanagi model. The γ‐relaxation is considered to be associated primarily with an amorphous relaxation, consistent with the conclusions of previous workers for materials of lower draw ratio.
Crystalline and amorphous orientations in injection molded polyethylene
Authors: Moy Francis H. , Kamal Musa R.
Published: December 2004

The techniques of density, birefringence, and wide X‐ray diffraction were employed to characterize the microstructure of injection molded polyethylene parts. Generally, maximum crystallinity (density) occurs at the center of the molding, while the minimum crystallinity occurs near the surface. Higher densities are observed near the gate. Raising the injection temperature tends to cause a marginal increase in the crystallinity throughout the molding. Birefringence measurements suggest that the maximum orientation occurs near the surface and that the relative orientation distribution is independent of the injection temperature. X‐ray diffraction indicates that the crystallographic a‐axis tends to orient in the flow direction while the b and c axes vary symmetrically about that direction. Increasing the injection temperature creates c‐axis orientation near the surface, while towards the core region a‐axis orientation is observed. Generally, near the surface it is the amorphous phase that makes the major contribution to the total orientation as measured by birefringence. Increasing the injection temperature tends to decrease the amorphous phase orientation near the surface. The crystalline phase contribution to the total orientation increases as distance from the surface increases, regardless of injection temperature.
Recent advances in the photodecomposition mechanisms of diazo‐oxides
Authors: Pacansky J.
Published: December 2004

In 1902, Wolff proposed a mechanism to explain the formation of carboxylic acids from diazo‐oxides; Süs in 1944 invoked this same mechanism for the formation of indene carboxylic acid from diazo‐oxides. Since these materials are currently used in the well known class of AZ photoresists, the Süs mechanism has been referred to many times to explain the positive working nature of the photoresists. In spite of the widespread use and industrial importance of the AZ resists, the validity of the Süs mechanism had not been unequivocally demonstrated to any degree of satisfaction. For these reasons, photochemical studies were initiated to establish the following: (1) Obtain direct spectroscopic evidence for ketene intermediates in the Wolff rearrangement of diazooxides. (2) Determine the reactivity of the ketene towards water and hydroxyl containing organic compounds. (3) Determine the reactivity of the ketene in the AZ resists. Fundamental photochemical decomposition mechanisms have been established for the AZ‐type photoresists; these and recent theoretical results on the Wolff rearrangement are used to convey the technological implications of the studies.
Electron sensitive negative resists of vinylaromatic polymers
Authors: Jagt J. C. , Sevriens A. P. G.
Published: December 2004

Electron resist properties of three vinylaromatic polymers, polystyrene, polyvinylcarbazole and poly(3‐bromo‐N‐vinylcarbazole) have been examined. Polystyrene and polyvinylcarbazole are high contrast resists of high dry etch resistance, but for adequate sensitivity (D ⩽ ca. 10 μC/cm2 at 25 kV) high molecular weights are needed (Mw ⩾ 106). Poly(3‐brotno‐N‐vinylearbazole) has a much higher sensitivity (D = ca. 2 μC/cm2) than the unsubstituted polymer. The sensitivity of polystyrene and polyvinylcarbazole is increased appreciably by addition of organic bisazides as crosslinking agents, e.g. a sensitivity increase of almost an order of magnitude was found upon addition of 3% 4, 4′‐diazidostilbene to polystyrene, high contrast being maintained.
Device processing using the trilevel technique
Authors: Moran J. M. , Maydan D.
Published: December 2004

Three front runners for the next generation of devices for fine line lithography are photo, electron, and X‐ray lithography. Each of these techniques has both advantages and disadvantages when considered for direct wafer processing. This paper discusses the problems encountered using each of these techniques and how a trilevel technique can be applied to make each of these techniques more viable.
Impact strength of polymers. 3: The effect of annealing on cold worked polycarbonates
Authors: Thakkar B. S. , Broutman L. J.
Published: December 2004

Cold working (rolling) of polycarbonates introduces residual stresses and molecular orientation both of which can improve, the notched Izod impact value. Annealing relieves both residual stresses and orientation. Annealing for various time periods established the critical level of residual stress necessary for the ductile failure mode of polycarbonate in the Izod impact test. The relaxation of both residual stress and molecular orientation was measured as a function of annealing temperature, for annealing times of 2 hs, and the relative changes have thus been determined. It is shown that residual stresses cannot be entirely removed without significantly influencing orientation for 2 h annealing times.
Thermal and mechanical properties of linear segmented polyurethanes with butadiene soft segments
Authors: Brunette C. M. , Hsu S. L. , Rossman M. , MacKnight W. J. , Schneider N. S.
Published: December 2004

A series of segmented polyurethanes based on a hydroxyl terminated polybutadiene soft segment (HTPBD) have been prepared with varying hard segment content between 20 and 60 weight percent. These materials are linear and amorphous and have no potential for hydrogen bonding between the “hard” and “soft” segments. The existence of two‐phase morphology was deduced from dynamic mechanical behavior and thermal analysis. Both techniques showed a soft segment glass transition temperature, Tgs, at −56°C and hard segment transitions between 20 and 100°C, depending on the urethane content. The low value of Tg, only 8° higher than the Tg of free HTPBD and independent of hard segment concentration indicated nearly complete phase segregation. Depending on the nature of the continuous and dispersed phases, the urethanes behaved as elastomers below 40 weight percent hard segment or as glasslike materials at higher hard segment contents. The effect of thermal history on transitions of the HTPBDurethanes was also investigated and the results suggest that the absence of hydrogen bonding to the soft segment must account for the extraordinary insensitivity to thermal history in dynamic mechanical, thermal and stress‐strain behavior. Comparisons are made to the more common polyurethanes containing polyether and polyester soft segments.
Electrothermal study of carbon loaded ethylene‐vinylacetate copolymer
Authors: Sircar A. K. , Wells J. L.
Published: December 2004

Temperature dependence of resistance of carbon black loaded ethylene‐vinylacetate (EVA) copolymer was studied from −100 to 250°C in a modified differential scanning calorimeter (DSC) apparatus. Both room temperature resistivity and positive temperature coefficient of resistance (PTC) effects can be correlated with carbon black parameters (structure, surface area, porosity). Room temperature resistivity and the degree of increase of resistivity, (ratio of maximum to minimum) progressively decrease with carbon black structure if occlusion of polymer by carbon black is considered in calculating the volume fraction. An integrated surface areastructure‐porosity equivalence of the carbon black is derived by introducing factors proportional to the volume and porosity of the black used. Any black parameter that increases conductivity (loading, surface area, structure, porosity) decreases the PTC effect. A cable compounder can therefore minimize the undesirable impact of PTC by suitable choice of black‐parameters. The necessary considerations for other uses, where PTC effect is used for microswitches, heaters, etc., will be just the opposite. The modified DSC method provides a quick scanning tool for determining the suitability of semicrystalline polymer recipes, either for cable or for any other material using the PTC effect.
Electrical properties of carbon black filled crosslinked polyethylene
Authors: Narkis M. , Ram A. , Stein Z.
Published: December 2004

The electrical resistivity of peroxide and radiation crosslinked polyethylene/carbon black compounds was studied as a function of black concentration and, temperature in heating/cooling cycles. Different carbon blacks in compounds with polyethylene responded differently, regarding electrical resistivity, to the effect of crosslinking. In one case (fine black) the resistivity and PTC (positive temperature coefficient) effect did not significantly change, whereas in another case (coarse black) the effect of crosslinking‐was to significantly increase the resistivity and reduce the PTC effect. The main advantages of crosslinking were to give compounds having good electrical reproducibility and to practically eliminate the NTC (negative temperature coefficient) effect in compounds containing fine, coarse, or mixtures of carbon blacks. Crosslinked compounds containing mixtures of carbon blacks have shown good conductivity, electrical reproducibility, and switching properties.
The relationship between mechanical properties and structure in rolled polypropylene
Authors: Dhingra V. J. , Spruiell J. E. , Clark E. S.
Published: December 2004

The relationship between mechanical properties and fine structure has been studied in polypropylene rolled both unidirectionally and biaxially (cross rolled). In unidirectionally rolled samples, a complex dependence with cold work is observed with a substantial change being observed at about 50 percent cold work. At 70 percent cold work, the yield strength and tensile strength increase substantially in the roll direction as compared with the starting billet but decrease only slightly in the transverse direction. Above 50 percent cold work, Young's modulus increases rapidly in the roll direction with a smaller increase in the transverse direction. The elongation to freak decreases in the roll direction but increases in the transverse direction. A striking feature is the large increase in ductility due to a small amount of cold work (ca., 10‐20 percent). Analogous property changes are observed for cross rolled samples although no significant variation with direction in the sheet was found. The complex property changes are accompanied by complex changes in the molecular orientation as observed by wide angle X‐ray pole figures and by changes in the morphology as observed with small angle x‐ray scattering. These changes are interpreted in terms of a model incorporating tilting both of lamellae and of chain stems within the lamellae at early stages of rolling followed by breakup of lamellae and molecular rearrangement at later stages.
Weld line structures and properties in injection molded polypropylene
Authors: Malguarnera S. C. , Manisali A. I. , Riggs D. C.
Published: December 2004

Weld regions are formed wherever polymer flow fronts meet. The present study examines the effects of melt temperature, mold temperature, mold cooling conditions, injection speed and annealing on the tensile properties and morphological structure of weld regions in four commercially available polypropylene resins. One of the resins contained nucleation particles. Scanning electron micrographs of the weld region revealed a wide range of morphologies from very strong welds which formed part of a stable neck to brittle failures at low elongation caused by the presence of large nucleation particles in the weld region. The melt temperature, mold temperature, and annealing had the greatest effect on the weld region's tensile properties.
Sintering rheology of amorphous polymers
Authors: Rosenzweig N. , Narkis M.
Published: December 2004

The activation energy for sintering of poly(methyl methacrylate) particle pairs is shown to be similar to their activation energy for Newtonian flow. Sintering progress with time is in good agreement with the Frenkel's coalescence theory. Typical sintering shear rates are shown to be very low and potential energy change (two particles) is small in comparison with the surface energy change. These results lead to the conclusion that the coalescence sintering mechanism of amorphous polymers above their glass transition temperature is essentially a Newtonian viscous flow mechanism where surface tension is the major driving force. A periodical phenomenon associated with sintering progress with time is reported and a supporting mechanism is proposed.
High modulus semi‐crystalline polymers by solid state rolling
Authors: Bigg D. M. , Smith E. G. , Epstein M. M. , Fiorentino R. J.
Published: December 2004

Solid state rolling of semi‐crystalline polymers is shown to be an effective method of producing high strength, high modulus tape at acceptable production rates. High density polyethylene tape was produced having a tensile strength exceeding 300 MPa and a tensile modulus of 8.7 GPa at production rates exceeding 8 m/min. A significant factor in producing highly oriented tape by the rolling process is roll temperature. Increasing the roll temperature from 25°C to 125°C not only increases the maximum extent of orientation achievable, but increases the mechanical properties at a given degree of thickness reduction. Internal frictional heat development limited the maximum thickness reduction ratio of polypropylene to 6.6:1. This reduction was reached by rolling at 150°C. The resultant tape had a tensile modulus of 5.1 GPa and a tensile strength of 300 MPa.
Estimation of injection pressure during mold filling
Authors: Titomanlio G.
Published: December 2004

Dimensionless diagrams for estimating the bulk temperature of the flow front and injection pressure in the limit of small viscous generation are obtained. Also, a criterion for neglecting viscous generation is identified, The diagrams, based on the Lord and Williams model, refer to rectangular geometry and amorphous materials. A satisfactory comparison is obtained with literature data taken on polystyrene. A reasonable estimate of polyethylene injection pressure was obtained by roughly accounting for latent heat of crystallization through modified thermal diffusivity.
Thermodynamic aspects in extrusion of wall‐slipping materials
Authors: Mennig G. , Subramanian N.
Published: December 2004

Relevant calculations are made based on the application of the first law of thermodynamics to a steady polymer flow through a plasticating extruder. The results obtained for various processing conditions for poly(vinyl chloride), which exhibits a slip at the wall during flow at lower temperatures, are compared with polyethylene showing no such slip. For a wall‐slipping material, it is observed that, with increasing throughputs the addition of enthalpy per unit mechanical energy increases (1), the net‐specific thermal energy input increases (2), and the specific mechanical energy required shows a decreasing trend (3). Contrary behavior is found in the case of non‐slipping materials.
Optical properties of thermally crystallized poly(ethylene terephthalate)
Authors: Jabarin Saleh A.
Published: December 2004

The optical properties of thermally crystallized polyethylene terephthalate (PET) were investigated using the methods of small‐angle light scattering, density, and haze measurements. The results indicate that the haze in crystallized PET results from scattering due to crystalline aggregates called spherulites. The formation of spherulites can lead to high levels of haze even at very low levels of crystallinity. A detailed analysis of polarized light‐scattering patterns was employed in order to define the various structural parameters responsible for haze. The relationships between haze, crystallinity, spherulite size, and volume fraction of spherulites were developed for PET.
Anisotropic hygroelastic behavior of poly(methyl methacrylate) under case II diffusion
Authors: Cohn Daniel , Marom Gad
Published: December 2004

The hygroelastic behavior of polymers, in which the diffusion mechanism is characterized by a sharp advancing boundary between the swollen shell and the core, was studied. A highly anisotropic swelling response was observed. The an‐isotropy of the swelling strains was caused by the mechanical constraints exerted by the stiff core on the penetrated shell. The swollen systems were viewed as analogous to a composite material comprising a stiff fiber embedded hi a soft matrix. The size and relative dimensions of the core were found to be the crucial factor determining the antsotropic response en‐countered. The experimental system employed was of poly(methyl methacrylate).
The effect of surface embrittlement on the mechanical behavior of rubber‐modified polymers
Authors: So Paul , Broutman Lawrence J.
Published: December 2004

An experimental study was conducted to better understand the mechanism of surface embrittlement in rubber‐modified thermoplastics. Brittle polymer films were laminated onto acryionitnie‐Duraaiene‐styrene terpolymer and high‐impact polystyrene to simulate either embrittlement due to environmental degradation or brittle paint systems. The effect of varying coating thickness and molecular weight was studied in tensile and impact testing. Results of this study suggest that the multiple crazing mechanism normally associated with the energy‐absorbing capability of rubber‐toughened polymers is severely restricted due to the formation of multiple surface cracks resulting from coating failure. This is particularly true when the coating thickness reaches a critical value at which a single surface crack is able to propagate across the coating/substrate interface in an unstable manner.
An electrical method of measuring crack length during crack propagation tests of polymers
Authors: Serrano A. M. , Welsgh G. E. , Gibala R.
Published: December 2004

Measurement of fatigue crack propagation rate (da/dn) in polymers is normally done optically with a travelling microscope. Electrical methods have not been very successful due to lack of sensitivity and to inaccuracies caused by factors such as plastic deformation and temperature variation. Use of electrically conductive surface grids eliminates these problems. An electrically conductive grid pattern is vapor‐deposited onto the surface of a compact tension specimen. The electrically conductive grid pattern is vapor‐deposited onto the surface of a compact tension specimen. The electrically conductive grid lines run across the expected path of the crack. With crack advancement, the grid lines are successively torn apart. Proper interpretation of the discontinuous steps that result when electrical current is plotted against time directly generates da/dn data.
Variation of dynamic mechanical properties of polycarbonate as a result of deformation
Authors: Kolman H. J. , Ard K. , Beatty C. L.
Published: December 2004

A combination of different experimental apprati has allowed dynamic mechanical spectroscopic measurements to be made as function of variable, constant offset stress, as well as during creep of bisphenol‐A‐polycarbonate. The deformation system was calibrated with aluminum and by comparison of low‐stress dynamic mechanical spectra with literature data of polycarbonate. Dynamic mechanical spectra acquired at high offset stress result in an apparent shift in sub‐Tg relaxation processes to higher temperatures at differing rates, resulting in separation of the various relaxation processes. This observed phenomenon is analogous to similar effects that are observed viathe application of pressure. The creep process can be clearly monitored by changes in dynamic mechanical properties, with these changes being dependent upon the stress and temperature utilized.
Diffusion and localized swelling resistances in glassy polymers
Authors: Gostoli C. , Sarti G. C.
Published: December 2004

The sorption of swelling penetrants in glassy polymers is modeled as a diffusion problem with moving boundary. The velocity of the swelling front is related to the stress exerted by the penetrant on the glassy matrix at the moving boundary. The solvent stress is considered as the sum of the osmotic tension and of the differential swelling stress. The latter increases as the residual thickness of the glassy core is reduced, giving rise to an acceleration of the front velocity (Super Case II). It is shown that the stress relaxation properties in the swollen region must be taken into account in order to obtain a thickness‐dependent Super Case II effect, which disappears in thick samples, according to experimental evidence. All the observed sorption behaviors, including Fickian diffusion, Case II, and Super Case II sorption, are properly accommodated in the theory.
Composition and processing effects on the properties of one‐component polyurethanes
Authors: Iobst S. A. , Cox H. W.
Published: December 2004

A polyurethane consisting of a poly(propylene oxide) soft segment and a diphenylmethane diisocyanate—hydroquinone di‐(b̃‐hydroxyethyl) ether (HQEE) hard block has been characterized over the composition range of 30 to 60 percent hard block. The flexural modulus varied from 60 to 900 MPa over this composition range. The elongation was approximately 250 percent at the lower hard block contents but fell below 100 percent at 60 percent hard block. Differential scanning calorirnetric measurements showed that the crystallinity associated with the hard phase increased with increasing hard block content but decreased with increasing cure temperature. The heat sag was found to decrease with increasing hardblock and increase with increasing cure temperature. A material with properties comparable to current fascia materials had a significantly better heat sag resistance than a current RIM (reaction injection molding) polyurethane. The combination of the solid chain extender, HQEE, and a solid catalyst, zinc stearate, lowing it to be processed as a one‐component resin having a pot life of greater than 8 h at 20°C al‐injection molding machines. The one‐component nature of the resin has made it possible to use a continuous in‐line mexer and to reduce the amount of scrap by using cold runner molds. In addition, any scrap that is generated can be used as regrind in the system.
Effect of shear rate on solution polymerization of acrylonitrile
Authors: Kumar A. , Kumar A. , Gupta S. K.
Published: December 2004

Application of shear is found to increase the rate of solution polymerization of acrylonitrile in N,N‐dimethyl formamide (DMF) initiated by benzoyl peroxide by as much as 400 percent of the value in absence of shear. The solvent DMF acts as an inert and maintains a homogeneous reaction mass during the entire course of polymerization. To study the effect of shear systematically, a special dilatometer has been constructed such that a constant shear rate, \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop \gamma \limits^. $\end{document} could be applied to the reaction mass. The rule of solution polymerization has been measured under the variation of \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop \gamma \limits^. $\end{document} and monomer concentration in the system. The measurements of induction time on the addition of a strong inhibitor, hydroquinone, reveal that the increase in the rate of polymerization with shear rate can be largely attributed to the change in the initiator efficiency. As a further confirmation of the above hypothesis, the decomposition of benzoyl peroxide in nitrobenzene at 80°C was measured and was found to increase significantly on application of shear. This confirms the importance of mass‐transfer resistance in removal of CO2, and the increase in the rate of polymerization of acrylonitrile occurs because the decomposition of benzoyloxy radicals is favored in the forward direction. Since the polymerization of acrylonitrile is preferentially initiated by phenyl radicals, the rate of polymerization is found to increase.
Solvent‐Crazing criteria
Authors: Wright D. C. , Gotham K. V.
Published: December 2004

Craze initiation in amorphous thermoplastics can be regarded as a transition from the safe to the unsafe state and, as such, can constitute a rational engineering design limit. A critical appraisal is made of three different criteria for initiation, which are of current interest. From this, it is concluded that the approach presented in this article, which is based upon the concept of inelastic strain, is to be preferred to the two other criteria, which are based upon an asymptotic total strain or constant inelastic strain energy criterion. The inelastic strain criterion is not only capable of modeling high stress/strain crazing in air but also satisfies the case of low stress/strain crazing in solvents. Furthermore, it offers an accurate method of extrapolating data to long times and, thus, satisfies a fundamental requirement for a parameter that can be used in engineering design.
Physical properties of high‐pressure ethylene vinylacetate copolymers and their saponified derivatives
Authors: Koopmans R. J. , Linden R. Van Der , Vansant E. F.
Published: December 2004

The physical properties of high‐pressure ethylene vinylacetate (EVA) copolymers having an average melt index of 8.5 g/10 min and a mol% of VA less than 20 are studied. A comparison is made with the properties of their saponified derivatives, the ethylene vinylalcohol (EVAl) co‐ and ethylene vinylalcohol vinylacetate (EVAlVA) terpolymers. A melt‐index effect is noted. Density, thermal, and mechanical properties of EVA copolymers are determined by the degree of crystallinity, which depends on the mol% VA and on the degree of alkyl shortchain branches. EVAlVA terpolymer properties depend on the residual mol% VA. EVAl copolymers proved to have some properties similar to low‐density polyethylene. The hydrogen‐bonding effect via hydroxyl groups was negligible for this level of vinylalcohol incorporation.
Zero migration of monomers in glassy polymers: A possible artifact of thermal depolymerization
Authors: Osborne J. L. , Sarti G. C. , Koros W. J. , Hopfenberg H. B.
Published: December 2004

Efforts to remove traces of monomers contained in polymers by stripping with steam have resulted in reports that a small concentration of monomer is inextractable, or “locked‐in,” the polymer. Any concomitant depolymerization to monomer and diffusive elution of the formed monomer would, in the steady state, result in a constant concentration of monomer within the confines of the polymer. If only the polymer phase were sampled and depolymerization were ignored, this result could be interpreted as an apparent “zero migration” level of monomer. A model that describes the coupled processes of depolymerization and diffusion is presented; predictions and estimates of an apparent “zero‐migration” concentration are offered for various polymer/monomer systems considering a variety of kinetic schemes. The effects of temperature, geometry, and sample size on the transient and apparent steady‐state, residual‐weight fraction of monomer in the polymer are considered. Also, the weight fraction of monomer, neglecting diffusive elution, is estimated for comparison with the steady‐state weight fractions calculated for the case in which diffusive elution significantly lowers the residual steady‐state monomer level. The results predicted by the model presented are compared with experimental data reported in the literature. Transient approaches to the steady state are included in the model analysis. The steady‐state monomer concentrations predicted for polystyrene and poly(acrylonitrile) at 100°C vary from 0.0001 ppm to 100 ppm as the diameter of the respective polymeric spheres varies between 0.5 μ and 500 μ. The predicted steady‐state concentrations for vinyl chloride monomer in poly(vinyl chloride) are, under comparable conditions, seven orders of magnitude lower, reflecting the extraordinarily small tendency of polyvinyl chloride to degrade to monomer.
Failure of rubber‐modified plastic liners
Authors: Mai Y. W.
Published: December 2004

In order to analyze the failure phenomenon of plastic liners in freezers and refrigerators the mechanical properties of the freon blown polyurethane (PU) foam insulator material and the acrylonitrile‐butadiene‐styrene (ABS) plastic liner are determined. The properties considered essential for this problem are the elastic modulus, the tensile strength and the fracture toughness over the temperature range −40 to 20°C. By laminating a layer of the polyurethane foam to the ABS liner and depending on the test temperature brittle to semi‐brittle fractures are promoted and the maximum load fracture toughness of the liner material is reduced. The reduction is more severe for notched bend than for single‐edge notched tension specimens. Based on these mechanical properties plausible reasons for liner fractures are discussed.
Engineering and molding properties of poly(vinyl chloride), acrylonitrile‐butadiene‐styrene and polyester blends
Authors: Khanna S. K. , Congdon W. I.
Published: December 2004

Polymer blends with varying amounts of poly(vinyl chloride) (PVC), acrylonitrile‐butadiene‐styrene (ABS) and polyester have been developed to produce parts with highly flexible, good impact strength, and flame retardant hinge properties. In the present work, the rheological and dynamic mechanical properties are balanced by changing the blend formulations. It is shown that blends morphology and rheology have greater impact on the dimensional stability and delamination at the surface of the molded hinge parts.
Rheological properties of blown film low‐density polyethylene resins
Authors: Montes Sergio A.
Published: December 2004

Three blown‐film‐grade low‐density‐polyethylene (LDPE) resins were studied using different rheological techniques. Eccentric rotating disks (ERD), cone‐plate viscometry, capillary rheometry, annular die extrusion, and non‐isothermal stretching of a filament were used. The viscoelasticity of the melts was found to play a dominant role in the observed behavior. Extrudate appearance in annular flow, melt strength, and extensibility are affected by melt elasticity. A correlation was found between the maximum draw ratio of a filament stretched under non‐isothermal conditions and minimum film thickness.
A rheo‐optical study on the reformation of structure in racemic poly(γ‐benzyl glutamate) liquid crystals
Authors: Asada Tadahiro , Onogi Shigeharu , Yanase Hiromi
Published: December 2004

Transmitted light intensities were measured by means of the polarized light technique for the nematic liquid crystal phase of racemic poly(γ‐benzyl glutamate) (PBG) in m‐cresol at 25°C after cessation of steady flow at shear rates ranging from 0.2 to 110 s−1. Weight‐average molecular weights of PBG used were 1.5, 2.1, and 2.6 × 105, while the concentrations varied between 20, 30, and 40 wt percent. Transmitted light intensities with crossed and parallel polarizers, Ix and I|, show wavy changes with time after cessation of steady flow, indicating the retardation decreases with time. An attempt was made to explain experimental results on the basis of a simple model, in which not only relaxation of molecular orientation but also effects of the wall and disclination were taken into account.
The determination of the thermodynamic interaction parameter χ in polymer blends
Authors: Riedl Bernard , Prud'homme Robert E.
Published: December 2004

The miscibility of polymer blends is related to the polymer‐polymer interaction parameter χ23, Several methods can be used to evaluate this parameter and five of the most important ones are reviewed: two equilibrium methods (melting‐point depression and vapor sorption), a transport method (inverse‐phase gas chromatography) and two scattering methods (neutron scattering and small‐angle x‐ray scattering). Examples are cited where χ23 values for a given blend were determined by several of these methods. This comparison leads to the conclusion that a reasonable agreement is often reached despite conceptual differences between the methods involved.
A review of miscibility enhancement via ion‐dipole interactions
Authors: Eisenberg A. , Hara M.
Published: December 2004

It is shown that ion‐dipole interactions induce considerable miscibility enhancement in blends of styrene ionomers with poly(alkylene oxides). Dynamic mechanical studies, in conjunction with transparency and brittleness of the samples, are used to evaluate miscibility. The effect is clearly thermodynamics in that phase separation can be induced in miscible samples by raising the temperature, with miscibility reestablished ons cooling. The miscibility enhancement in these systems is compared with that resulting from hydrogen bonding. In addition to the styrene/alkylene oxide system, ion‐dipole interactions are found to be effective in enhancing the miscibility of many ionic polymer/polar polymer pairs. The ionomers used in this study were styrene lithium methacrylate and ethyl acrylate lithium acrylate copolymers, while polyethers, polysulfides, polyesters, polyimines, and substituted polyethylenses served as polar polymers.
Polycarbonate blends with polystyrene and polypropylene
Authors: Rudin Alfred , Brathwaite N. E.
Published: December 2004

Blends of polycarbonate/polystyrene (PC/PS), polycarbonate/polypropylene (PC/PP) and ternary blends of the three components (PC/PS/PP) were studied. Extrudate swell of the molten blends increased with increasing concentrations of the minor components and leveled off at characteristic blend compositions. These compositions corresponded to the limits of compatibility as judged by the onset of brittleness in tensile tests. Both PS and PP appear to have some limited practical compatibility with PC. The change in extrudate swell behavior with concentration may be a rapid and convenient test for the effective concentration limits of partially miscible polymers.
Chemiluminescence apparatus and method for studying thermal oxidative stability of polymers
Authors: Zlatkevich L.
Published: December 2004

A chemiluminescence multi‐sample apparatus and method are described for determining polymer stability by measuring the intensity of the light emitted during thermal oxidation. Depending on the nature of a material analyzed the experiments are performed either under O2 atmosphere at a constant temperature or under N2 atmosphere at a constant heating rate. In the former case applicable to polypropylene (PP) and acrylonitrile‐butadiene‐styrene copolymers (ABS), parameters such as induction time and oxidation rate can be evaluated. In the latter case applicable to nylon and polyethylene terephthalate (PET), the extent of oxidation in a certain temperature region can be evaluated by measuring the area under the intensity of light—temperature curve. Along with providing a great deal of knowledge on thermal oxidative stability, the chemiluminescence approach gives the additional information concerning polymer quality. The appearance of the low‐temperature pulses on the chemiluminescence curve observed before the onset of autocatalytic oxidation is associated with the history and processing of the sample and with the natural aging of the polymer.
Deformation recovery behavior of a solid polymer after tensile yielding
Authors: Rizzo Giovanni , Spadaro Giuseppe
Published: December 2004

The deformation recovery at room temperature of a polycarbonate after large tensile deformation and subsequent stress relaxation is measured as a function of time. The effect of the main parameters which affect the amount of recovered deformation is analyzed. This suggests a plot of the recovery versus time curves by means of proper coordinates which allow shifting of all curves towards a single master curve, thus indicating that most of the phenomena involved in the recovery process are taken into account.