bluuebunny/crossref_metadata_2025_split huggingface dataset:
The use of oven heat sag to determine heat resistance in polypropylenes
Authors: Kempthorn James T. 
Published: May 2005

AbstractHeat deflection is often the only test used to determine a materials ability to withstand exposure to elevated temperatures under load. This test has its limitations, simply because not all materials operate under loads of 1820 kPa (264 psi) or 455 kPa (66 psi). Consequently, heat deflection cannot always give a true indication of a materials high temperature capabilities. The automotive industry has used the heat sag test to measure the deformation of elastomeric materials during the paint curing process. The heat sag test measures the sag of a molded bar. One end of the bar is clamped while the other end is free to sag or deflect. Samples are tested over a range of temperatures to determine the failure deflection point. This study examines the correlation of the heat sag to heat deflection and dynamic mechanical analysis (DMA) on polypropylene resins and compounds and polystyrene.
Percolation behavior in morphology and modulus of polymer blends
Authors: Hsu William Y. , Wu Souheng 
Published: May 2005

AbstractThe tensile property of a plastic/rubber blend depends critically on the morphology and connectivity of the two phases. At low plastic volume fractions, the plastic phase forms isolated domains in the matrix of rubber phase, and the tensile property of the blend is largely controlled by the continuous rubber phase. As the plastic volume fraction increases, the plastic phase gradually connects into a pervasive network that eventually dominates the tensile and shear properties of the blend. The transition of the blend from a rubber‐dominated to a plasticdominated behavior is a manifestation of percolation transition. The plastic volume concentration at which the transition takes place is the percolation threshold. Its dependence on morphology is discussed by contrasting the behaviors of anisotropic injection‐molded specimens vs. isotropic compression‐molded specimens of the two‐phase blends of an amorphous thermoplastic polyester, PETG, and an ethylene‐propylene‐diene rubber, EPDM. It is found that the tensile modulus just above the percolation threshold obeys a power law as a function of the plastic volume concentration in excess of the percolation threshold. By analyzing the longitudinal tensile modulus of injection‐molded PETG/EPDM specimens just above the threshold, it is shown that the scalar elastic percolation theory of de Gennes is at work here. For compression‐molded PETG/EPDM specimens, it is found that the isotropic tensile modulus over the entire composition range obeys the symmetric effective medium theory.
Comparison of “all trans” enzymatically prepared unsaturated polyesters with chemically synthesized and industrial polyesters
Authors: Geresh S. , Gilboa Y. , Abrahami S. , Bershadsky A. 
Published: May 2005

AbstractThe synthesis of unsaturated polyesters (UP) by high‐temperature polycondensation is accompanied by isomerization of the double bond from the cis to the trans configuration. The presence of the trans double bonds facilitates crosslinking and may have an important influence on rheological and mechanical properties of the UP and the cured end product. All‐trans polyesters are not available on the market. A study of “all‐trans” low‐temperature polycondensation based on chemical and enzymatic lipase catalysis was recently reported. This paper presents the characteristics of lipase‐synthesized UP vs. general‐purpose UP, as obtained by X‐ray, differential scanning calorimetry (DSC), and other methods. In contrast to the commercial amorphous UP, crystallinity was found in the “alltrans” enzymatically and chemically synthesized UP. The crystallinity of the enzymatically and chemically synthesized UP. The crystallinity of the enzymatically synthesized UP was confirmed by higher values of elasticity. DSC analyses complemented the results obtained by other methodologies.
On the tensile testing of high modulus polymers and the compliance correction
Authors: Turek Douglas E. 
Published: May 2005

AbstractThe application of a method to determine and correct for the influence of non‐specimen extension in tensile testing is reviewed and demonstrated using two different thermotropic liquid crystalline polymers. In the tensile testing of high modulus polymer extrudate, where the amount of specimen extension is inferred from the crosshead travel, the error associated with system compliance can be significant and parameters such as modulus and elongation will be in error. The need to apply the correction depends on the magnitude of the product of the sample modulus and cross‐sectional area, divided by the test gage length, relative to the system compliance value. Its application is not necessarily restricted to high modulus materials, and can be extended to samples of larger cross‐sectional area and lower modulus. Guidance to assist in the choice of a suitable gage length to avoid compliance correction and a method to quantify the error contribution is presented.
Gapwise density distributions in injection‐molded poly(methylmethacrylate)
Authors: Wimberger‐Friedl R. , de Bruin J. G. 
Published: May 2005

AbstractResidual density distributions are determined in injection‐molded poly(methyl‐methacrylate) (PMMA) with the aid of a quantitative Schlieren optical technique. The gapwise distributions typically show a maximum beneath the surface. The height of the maximum as well as the level in the core vary with distance from the gate of the mold. The density distributions and the influence of the molding parameters are explained by the pressure course measured in the cavity and the process of vitrification of the sample during molding. The magnitudes of the variations of the gapwise distributions agree with the average density variations measured in a density gradient column. Residual stresses do not contribute significantly to the determined distributions. The density maximum is found closer to the surface than the maximum in birefringence that is induced by the shear flow during filling. The magnitude of the density variations is less than predicted by the pseudocompressibility, as determined in samples vitrified under constant pressure.
Coefficients of dynamic friction for low density polyethylene
Authors: Spalding Mark A. , Kirkpatrick Donald E. , Hyun Kun S. 
Published: May 2005

AbstractThe coefficient of dynamic friction is often the controlling factor for solids conveying, pressure generation, and thermal decomposition of a resin in the feed section of a single‐screw plasticating extruder. The coefficients of friction are, however, very poorly understood, and the interpretation of the measurements are complicated by the dissipation of frictional energy at the sliding interface. A new instrument was recently built to help understand dynamic friction, and a numerical technique was developed to estimate the interface temperature. The coefficients of dynamic friction for a low‐density polyethylene resin are presented in this paper as a function of the surface temperature, pressure, and velocity.
Mechanical properties‐structure relationship in blends of polyamide 6 with γ‐irradiated LDPE
Authors: Valenza A. , Gallo L. , Spadaro G. , Calderaro E. , Acierno D. 
Published: May 2005

AbstractBlends of γ‐irradiated and unirradiated low density polyethylene with polyamide 6 were made in order to study possible modifications induced by this irradiation. Blends with γ‐irradiated polyethylene show structure and properties significantly different with respect to blends made with the unirradiated polyethylene. In this paper data on mechanical properties (tensile and impact) of these blends are presented. Results are related to the different morphologies in the blends.
Stress relaxation behavior after cyclic preloading in polypropylene
Authors: Ariyama Takashi 
Published: May 2005

AbstractThe viscoelastic behavior of polypropylene before and after cyclic preloading was investigated by stress relaxation tests. The relaxation tests were performed after a simple uniaxial tension (number of cycles N = 0) and after the cyclic preloading (N = 50) by use of a closed loop, electrohydraulic, servocontrolled testing machine. The tests were conducted under different sets of strain rate, number of cycles, and strain amplitude. The experimental data were compared with theoretical results analyzed by use of a linear viscoelastic model. The three‐element model consists of a Maxwell unit and a Hookean spring in parallel. The calculated results agree well with the experimental ones; in particular, in the relaxation tests after the cyclic preloading (N = 50), the calculated results agree very well with the experimental ones at both the predetermined strain rates of 1,000 μ/s and 10,000 μ/s, at a strain amplitude of ±5%. It can be seen that the linear viscoelastic model explains the viscoelastic characteristics of polypropylene despite the solution of the constitutive equation constructed by the simple three‐element model.
Flow defects in linear low density polyethylene processing: Instrumental detection and molecular weight dependence
Authors: Ajji A. , Varennes S. , Schreiber H. P. , Duchesne D. 
Published: May 2005

AbstractAn elongational rheometer coupled with a primary extrusion device has been used for the detection of flow limitations in the extrusion of linear low density polyethylenes (LLDPE). The shear rate for the onset of flow defects (fd) was found to decrease with increasing branch length in the LLDPE copolymer, but the severity of fd was greater in butene‐ than in hexene‐ and octene‐copolymers. Studies of partially fractionated LLDPE showed that the critical shear rate for the onset of fd was closely related to the minimum molecular weight in the distribution of molecular weights. In addition, evaluations of bond strengths in LLDPE/metal joints showed that the same molecular weight parameter significantly affected that performance criterion. In combination, the experimental findings provided confirmation of sporadic adhesive failure (slip/stick effect) as the mechanism responsible for the occurrence of observed flow defects. Its manifestation is attributable to the thermodynamic drive that promotes the preferential localization of low molecular weight moieties at surfaces and at interfaces of polyolefins such as LLDPE.
Phase separation kinetics of rigid‐rod polymers during coagulation
Authors: Nelson Donald S. , Soane David S. 
Published: May 2005

AbstractKinetics of phase separation of poly(p‐phenylenebenzobisoxazole) (PBO) in methanesulfonic acid are examined by the time‐resolved small angle light scattering and turbidity measurements. Thin films of polymer solutions are spin‐coated on microscope slides and observed in a controlled environment light scattering cell. These solutions appear to undergo a spinodal decomposition‐like phase separation, following Cahn‐Hilliard type phase separation kinetics upon exposure to water vapor. An exponential increase in the scattered light intensity at short times is found. Transmittance measurements are used to determine the effects of molecular weight and coagulation medium on the rate of coagulation.
Polyspirodilactam: A new family of high temperature polymers
Authors: Wang Pen‐Chung , Asbell William J. , Chuah Hoe H. , Gergen William P. 
Published: May 2005

AbstractA new class of materials based on a spirodilactam structure has been recently synthesized as part of research into new polymeric materials. Not only is the spirodilactam structure novel, but it was not even the intended product in the synthesis as originally designed. The polymerization process discovered by the reaction of 4‐ketopimelic acid or its corresponding spirodilactone with primary amines opened a new field of polysprodilactam chemistry. This paper describes the chemistry leading to the discovery of spirodilactam‐based polymers and initial applications in the area of thermoplastics and thermosets. Most recent developments to be covered include aromatic spirodilactams and isomeric spirodilactams.
Characterization of ternary blends containing polycarbonate, tetramethyl polycarbonate, and poly (ϵ‐caprolactone)
Authors: Kim C. K. , Paul D. R. 
Published: May 2005

AbstractThe phase behavior of ternary blends of bisphenol‐A polycarbonate (PC), tetramethyl bisphenol‐A polycarbonate (TMPC), and poly (ϵ‐caprolactone) (PCL), where each binary pair forms completely miscible blends, was investigated. The ternary blends were found to be miscible for all compositions and do not phase separate prior to thermal decomposition. The melting point depression method based on both the Flory‐Huggins theory and the equation of state theory of Sanchez‐Lacombe was used to evaluate interaction parameters for each pair.
Radiation pyrometry on semitransparent sheets. I: Gray media
Authors: Hajji N. , Spruiell J. E. 
Published: May 2005

AbstractRadiation pyrometry is often used in the measurement of temperature during polymer processing operations such as film blowing. Since polymers are semitransparent in the infrared, the temperature measured by the pyrometer will correspond to some average of the internal temperature distribution. In the present study, an expression is derived for this average when a sheet with a thermal gradient across its thickness is considered. This expression is used to study the effect of the absorption characteristics of the sheet on this average when the material is a gray medium.
Thermoplastic polyheterocycles. I: Polyalkylene‐benzoxazoles
Authors: Preston J. , Tropsha Y. , Trexler J. W. 
Published: May 2005

AbstractPolyalkylenebenzoxazoles of high molecular weight (inherent viscosity values from 0.76 to 2.95) were prepared from 4,6‐diaminoresorcinol dihydrochloride and aliphatic diacids in polyphosphoric acid by heating at 180 to 200°C for 3–5 h. Melting points of the polymers ranged from 148 to 423°C, depending on the length of the alkylene chain. Glass transition temperatures were relatively low, ranging from 50 to 100°C and did not show the pronounced odd/even effect noted for melting points. In all cases, rapid weight loss occurred above 400°C. No evidence for the formation of a molecular composite was observed in an attempt to prepare in situ a rod‐like polybenzoxazole in a polyalkylenebenzoxazole.
Thermodynamics of processing synthetic fibers
Authors: Mukhopadhyay S. K. 
Published: May 2005

AbstractThis paper deals with a new approach to nonlinear and nonequilibrium thermodynamics. The new concept, developed by P. H. Lindenmeyer, states that in a heat‐setting process, with the same average processing temperature, the addition of a sinusoidal fluctuation (approximately) can produce two opposite changes depending upon the frequency and amplitude of the temperature fluctuation. Preliminary experimental results obtained on nylon 6 monofilaments using a flexible thermomechanical analyzer have clearly shown that the physical properties (in this case torque‐twist modulus) depend not only upon the average temperature but also upon its time rate of change.
Spin coating of very thin polymer films
Authors: Extrand Charles W. 
Published: May 2005

AbstractVery thin films of natural rubber, polystyrene, and poly(methylmethacrylate) have been spun‐cast on silicon wafers from dilute solutions of toluene and cyclohexane. Layers were uniform across the wafers, ranging from 0.5 to 170 nm, as measured by ellipsometry. Their average thickness e increased with solution concentration and decreased with rotational rate w. Changing the volume of the solution pipetted onto the wafers did not affect the final thickness, whereas changing the solvent did. The previously reported empirical relation for much thicker films, e α ω−1/2, held over the range investigated here.
The effect of lithium chloride on polybenzimidazole and polysulfone blend fibers
Authors: Chung Tai‐Shung 
Published: May 2005

AbstractPolybenzimidazole (PBI) and polysulfone (PS) do not form miscible blends; however, the tensile properties of the polymer blend in fibers, and the fiber process window, are strongly dependent on the presence of LiCl. The addition of LiCl opens the molecular chains and reduces dope viscosity. As a result, LiCl increases the stiffness of PBI/PS fibers while making them brittle. The process window for fabricating useful fibers seems to be narrowed by the presence of LiCl. PBI/PS fibers spun from a dope that does not contain LiCl have a broad process window and their overall fiber performance is superior. LiCl also reduced the degree of sulfonation during the stabilization process.
Photoinitiated crosslinking of low density polyethylene. III: Degradation and stabilization of photocrosslinked polyethylene
Authors: Qing Yan , Wenying Xu , Rånby Bengt 
Published: May 2005

AbstractElectron spectroscopy (ESCA) and reflectance infrared spectroscopy (ATR) were used to measure surface oxidation of photocrosslinked polyethylene. The deterioration of bulk properties during an artificial weathering test was also measured. It was found that the UV‐irradiation during crosslinking process decreases the stability of the material considerably. Three kinds of antioxidants and photostabilizers (hindered phenols, hindered amines, and organic sulfides) which have no absorption in the UV region of 300 to 400 nm were added before crosslinking to improve the stability of the crosslinked material. Neither the rate nor the degree of photocrosslinking at different depths of the sample were affected significantly by these additives. It was found possible to prevent the decrease in stability due to the photocrosslinking by using small amounts of a stabilizer, e.g. 0.05% Tinuvin 770 (hindered amine).
Spherulitic crystallization: An analysis of inverse stefan problems in cartesian, cylindrical, and spherical coordinate systems
Authors: Wang Yu F. , Lloyd Douglas R. 
Published: May 2005

AbstractSpherulitic crystallization presents an inverse Stefan problem, which is solved by numerical methods using the DuFort‐Frankel scheme and Lagrangian coordinate systems. The numerical solution shows excellent agreement with the analytical solution in the Cartesian coordinate system. A systematic error in the numerical solution for the spherical and cylindrical coordinate systems is examined by a material balance for the system. The systematic error was found to decrease rapidly as the dimensionless time increased and the grid spacing decreased.
Viscoelastic properties of a 60 mol% para‐hydroxybenzoic acid/40 mol% poly(ethylene terephthalate) liquid crystalline copolyester. II: Effect of shear history
Authors: Driscoll P. , Hayase S. , Masuda T. 
Published: May 2005

AbstractTemperature sweeps of dynamic viscoelastic properties have shown that phydroxybenzoic acid (PHB)‐based liquid crystalline polyesters, specifically in this case those copolymerized with poly(ethylene terephthalate) (PET), can be subjected to considerable supercooling if initial heating curves are compared to subsequent cooling curves, indicating that this type of material can be in quite different states even at the same temperature, depending on thermal history. Utilizing this supercooling behavior, viscoelastic properties of a 60 mol% PHB/40 mol% PET material produced by Unitika were monitored before and, particularly, after large‐scale shear deformation to determine how potential structure changes induced by the shear are reflected in viscoelastic properties immediately, and with time. According to dynamic viscoelastic temperature sweep data four quite different initial states were employed including conditions with, as well as largely free of, crystallites. However, in all cases, post‐shear monitoring showed decreased G′ and G″ values with almost no evidence of return towards initial values within approximately 25 min. These results, in addition to furthering somewhat the fundamental understanding of the flow and relaxation properties of liquid crystalline polymers, may be useful in polymer processing, where large‐scale shear deformations employed in forming processes appear to be capable of changing considerably the subsequent behavior of such materials.
Kinetic model and thermal properties of a thermally cured thermosetting polycarbonate
Authors: Delgado R. , McNeill D. M. , Hawley M. C. , Demeuse Mark 
Published: May 2005

AbstractDiethylene gycol bis(allyl carbonate) is widely used for the production of optical plastic for lenses, safety glasses and guards, watch crystal, and instrument windows. The monomer polymerizes via a free radical mechanism using benzoyl peroxide as an initiator to form a thermosetting polycarbonate. This polymerization process involves a long cure cycle at temperature below 100°C. Differential scanning calorimetry (DSC) and rheometric dynamic testing are used to characterize the thermal and kinetic properties. These properties include the heat of reaction, activation energy, rate constants of polymerization, and time and extent of cure at gelation.
Developing critical extrusion parameters for nylon 6, nylon 66, and nylon 46 polyamide from the rheology data
Authors: Shah Pravin L. 
Published: May 2005

AbstractThis paper describes a new approach to the rheological characterization of engineering plastics such as nylon 6, 66, and 46 polyamides using a capillary rheometer. The melt viscosity data as a function of temperature, shear rate, and residence time were measured and evaluated to demonstrate how to accurately predict critical extrusion parameters, such as barrel temperature profile, stock temperature window, and the screw design requirements, for extruding strip, tubing, and profiles. The results of this work provide a practical and simple quality control tool to select a polyamide resin for optimum processing, and to develop critical processing parameters for extrusion.
Toward a high‐impact isotactic polystyrene
Authors: Cazzaniga Luigi A. , Cohen Robert E. 
Published: May 2005

AbstractBrittle isotactic polystyrene has been toughened by the presence of emulsified rubber particles. Semicrystalline diblock copolymers of isotactic polystyrene and polybutadiene functioned successfully as emulsifying agents, as revealed by the results of scanning and transmission electron microscopy. Semiquantitative measures of the toughness of the various materials were obtained via a home‐built micromechanical testing device. The minimum amount of copolymer required to achieve emulsified morphologies and significant toughness depended on the thermal history of the material being tested.
Strength development in powder processing of poly(tetrafluoroethylene)
Authors: Hambir S. S. , Jog J. P. , Nadkarni V. M. 
Published: May 2005

AbstractPoly(tetrafluoroethylene) (PTFE) is a versatile engineering plastic with excellent chemical and electrical resistance, a wide working temperature range, and a low coefficient of friction. PTFE is processed by the powder processing technique because of its high melt viscosity. The powder processing of polymers involves cold compaction of the polymeric powders, followed by sintering of the preforms at elevated temperatures. Sintering is a critical operation since the mechanical properties of the products are determined by the interparticle coalescence and diffusion of polymer chains across the interface. The results of the studies of the strength development during sintering of PTFE are reported here. The strength was measured in terms of the tensile strength at break, and the dependence of the tensile strength on compaction pressure, particle size, and processing time is discussed. The time dependence of strength development could be described by a diffusion controlled process in which the strength is proportional to the 1/4th power of the processing time.