bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

AbstractA 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

AbstractTemperature 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

AbstractThe 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

AbstractThe 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

AbstractWeld 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

AbstractThe 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

AbstractSolid 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

AbstractDimensionless 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

AbstractRelevant 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

AbstractThe 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

AbstractThe 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

AbstractAn 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

AbstractMeasurement 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

AbstractA 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

AbstractThe 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

AbstractA 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

AbstractApplication 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

AbstractCraze 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

AbstractThe 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

AbstractEfforts 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

AbstractIn 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.