bluuebunny/crossref_metadata_2025_split huggingface dataset:
Anisotropy in mechanical and dynamic properties of composites based on carbon fiber filled thermoplastic elastomeric blends of natural rubber and high density polyethylene
Authors: Roy D. , Bhowmick Anil K. , De S. K. 
Published: December 2004

AbstractThe effects of short carbon fibers on static and dynamic properties of thermoplastic elastomeric blends of natural rubber (NR) and high density polyethylene (HDPE) have been studied. Both mechanical and dynamic properties are dependent on fiber concentration. The fiber aspect ratio ranges from 20 to 30. Adhesion between fiber and matrix is evident from the SEM photomicrographs of the failed composites and from variation of relative damping properties. Fiber orientation occurring during processing causes anisotropy in the physical properties. In composites with longitudinally oriented fibers, tensile failure occurs by both fiber pullout and breakage, while in composites with transversely oriented fibers, matrix failure dominates. The incorporation of fibers into the matrix lowers the tan δmax value, but no change in glass transition temperature is observed.
An investigation of brittle failure in ductile, notch‐sensitive thermoplastics
Authors: Nimmer Ronald P. , Woods Joseph T. 
Published: December 2004

AbstractBrittle failure, a significant design issue for plastic components subject to impact loads, is especially catastrophic when the material is normally ductile. Such behavior is not adequately understood relative to the micromechanisms, controlling parameters, and design consequences in plastics. Previous work has identified the process of crazing as being relevant to these failures in thermoplastics. The relationship between crazes generated through mechanical loading and subsequent brittle failure of amorphous thermoplastics is discussed and the hypothesis that the craze event is a necessary but insufficient condition for brittle failure is employed. Emphasis is focused upon the engineering prediction of craze formation and its use as a conservative brittle failure criteria for defining geometric details to prevent brittle failure. First, a series of experiments using one geometry is applied to study the concept of crazing as a precursor to brittle fracture in the two amorphous polymers polycarbonate and polyetherimide. Second, three‐dimensional finite element analyses are used to assess the effects of changes in geometric detail upon the continuum stress state and eventual failure of the specimen for these two materials.
Scanning tunneling microscopy studies of single‐molecule single‐crystals
Authors: Bu Haishan , Chen Erqiang , Yao Junen , Xu Shengyong , Kuang Yalei 
Published: December 2004

AbstractThe study of single‐molecule single‐crystals of isotactic polystyrene was carried out by scanning tunneling microscopy (STM) and transmission electron microscopy (TEM). It was shown that STM provided more information than TEM. By means of STM, the single‐molecule single‐crystals were found even in the case of aggregation. Regular strips were also found on the top surface of single‐molecule single‐crystals. This seems to imply regular adjacent folding.
Thermal properties of poly(vinyl cyclohexane)
Authors: Grebowicz J. S. 
Published: December 2004

AbstractIsotactic poly(vinyl cyclohexane) (PVCH) was studied by thermal analysis. The deduced equilibrium melting point, T, is 405°C (678 K). The heat of fusion, Δ H was found to be 50.82 J/g (5.60 kJ/mol) and Δ Cp at Tg, is 0.273 J/(gK) [30.1 J/(molK)]. The glass transition temperature, Tg, of the amorphous PVCH is 80°C (353 K). In semicrystalline samples, Tg increases up to 165°C (438 K) for crystallinities > 40%. Beside crystalline and flexible amorphous, a rigid amorphous phase is postulated in the semicrystalline polymer.
Thermal characterization of high performance PBI and 6F polymers and their alloys
Authors: Jaffe Michael , Haider M. Ishaq , Menczel Joseph , Rafalko Joseph 
Published: December 2004

AbstractThe effectiveness of thermal analysis as a technique for screening polymeric candidates for high temperature composite application is described. DSC, DMA, and TGA were employed to measure glass transition temperature, characterize blend phase morphology, and assess thermo‐oxidative stability. The materials studied were polybenzimidazole (PBI), polyimide copolymer (6FCoPI), and blends of PBI with Ultem 1000™ and 6FCoPI. The potential of misinterpretation of thermal analysis as the primary screening tool was also demonstrated. It was shown that if thermal analysis was used with insufficient understanding of the chemistry and physics of the materials under investigation, highly misleading conclusions may be derived.
Crystallite elastic constants and macroscopic moduli of isotropic semicrystalline polyethylenes
Authors: Janzen Jay 
Published: December 2004

AbstractAvailable literature data, augmented with a few mild and plausible assumptions, have been used to derive an estimated empirical compliance matrix for orthorhombic crystalline polyethylene at ambient conditions. Compared with this representation of experimental observations, reported theoretical compliance surfaces, derived from molecular mechanics, are shown to be in quantitative disagreement, although qualitatively their shapes are not dissimilar.It is further shown that if an accurate theoretical determination were to be available, it would yield an ability to translate (in surprisingly few, and rather simple, theoretical steps) directly from interatomic forces, acting over nanometer lengths, into realistic, crystallinity‐dependent, estimates of macroscopic moduli of isotropic semicrystalline polyethylenes.
Thermal analysis of poly(phenylene sulfide). II: Non‐isothermal crystallization
Authors: Collins George L. , Menczel Joseph D. 
Published: December 2004

AbstractThe non‐isothermal crystallization of Fortron poly(phenylene sulfide), PPS, was examined to better understand its behavior during injection molding. The nonisothermal Avrami formalism was applied to this system, but this method was found to be questionable because of the sometimes severe curvature that appears in the plots of the transformed data. A method of ranking crystallization rates at low cooling rates by plotting the peak in the crystallization exotherm versus the cube root of cooling rate has been considered and shown to have limitations at the higher cooling rates of interest. The growth rate expression developed by J. D. Hoffman for polymer crystallization of chain folded lamella in three dimensions has been used to simulate crystallization exotherms. It was found that this could only fit the data at low cooling rates. At high cooling rates it was necessary to use a growth rate expression developed by Calvert and Ulhmann for polymer crystallization without chain folding. When this is used to describe a two dimensional growth geometry, close agreement in the positions of high cooling rate exotherms could be obtained. The implication is that a change in crystallization mechanism is possible as the conditions go from low to high cooling rates.
Thermogravimetric kinetics of polymer degradation: Science or fiction?
Authors: Schneider Hans Adam 
Published: December 2004

AbstractWeight changes in thermogravimetry are dependent on the volatility of the degradation products. Thus, molecular weight determinations (or related studies) must fist be undertaken to prove whether or not nonvolatile chain fragments will be removed only at high temperatures. In this case both thermal stability and kinetic studies by thermogravimetry are senseless. But even if volatile products are formed, the kinetic parameters will depend on the conversion degrees because of the kinetic chain character of the polymer degradation. Changes in reaction mechanism aggravate the situation; it is thus problematic to define in such conditions reliable kinetic parameters. Values calculated from a single TG curve are valid for specific conditions only, but of no sense from the general kinetic view.
Thermal properties, phase transitions, and morphology of a conjugated polymer
Authors: Cheng Stephen Z. D. , Wu Xiao Xin , Zhang Anqiu , Meador Michael A. 
Published: December 2004

AbstractA highly conjugated polymer was synthesized from α,α′‐dibromo‐p‐xylene, 1,4‐bis(2‐hydroxy‐benzoyl)benzene, and benzyl bromide via a modified Williamson ether synthesis under phase transfer conditions. Based on thermal analysis, polarized light microscopy, electron diffraction, and wide angle X‐ray diffraction experiments, the heat capacities in the solid and liquid states have been determined. The glass transition temperature is at 358 K with a heat capacity increase of 164 J/(K mol). Two different ordered crystal forms with different crystal unit cells were observed. The more ordered crystal shows a low transition temperature and the less ordered one a high transition temperature. This is mainly due to the effect of entropy change. These crystals exhibit various crystal morphologies with different birefringences. Transition kinetics are expressed by an Avrami equation. Two crystals show different Avrami exponents with crystallization temperature, which corrspond to the morphological change. Competition between crystal growths is also discussed.
NMR spectroscopy, polymer motion, and “Tack” of model printing inks
Authors: Aspler Joseph S. 
Published: December 2004

AbstractPolymer motion in solution and in model printing inks (as measured by NMR spectroscopy) was compared to the “tack” or tensile stress developed in the splitting of thin fluid films. For model inks based on polyisobutene, at constant pigment content, increasing the polymer content caused polymer motion to slow down, and caused the tack to increase. At constant polymer content, increasing the pigment level had much less effect on polymer motion. At 20% pigment content, tack values were little different from those of the corresponding polymer solutions. This suggests that the tensile stress developed in an ink film as it splits is related to the motion of its polymeric ingredients, but is much less dependent on the concentration of dispersed solid pigment.
The yield strength of particulate reinforced thermoplastic composites
Authors: Jancar J. , Dianselmo A. , Dibenedetto A. T. 
Published: December 2004

AbstractThe effects of the filler volume fraction and strength of adhesion on the mode of tensile failure of a particulate reinforced polypropylene (PP) are investigated using finite element simulation (FES). When there is perfect adhesion between constituents, an upper bound for tensile yield strength is found to be 1.33 times the matrix yield strength above a critical volume of particulate concentration. Utilizing Sjoerdsma's model for interacting stress concentration fields, one can determine the concentration dependence of the yield strength below the critical filler volume fraction. When there is no adhesion between constituents, a modified version of an equation by Nicolais and Narkis adequately describes a lower bound for the tensile yield strength. The particulate concentration and the matrix ductility are the prime factors in controlling the brittle failure of the composite. Upper and lower bounds for brittle failure strength are characterized using a strength‐of‐materials approach and stress concentration factors for both “perfect” and “zero” adhesion. The properties of calcium carbonate filled PP homopolymer were measured over a wide range of filler volume fractions. CaCO3 was either treated with stearic acid to prevent adhesion between constituents or used as received. Maleic anhydride grafted PP (MPP) was used to promote adhesion. For filler volume fractions below 0.2, yielding of the composite by combined microcavitation and shear deformation was the principal failure mechanism. At vf above 0.35, a brittle failure mechanism dominated. In the range between 0.2 and 0.35, both failure modes were observed in the populations tested. Good agreement was found between the experimental results and the proposed model.
Phase and crystallization behavior of solution‐blended poly(ether ether ketone) and poly(ether imide)
Authors: Chen Hsin‐Lung , Porter Roger S. 
Published: December 2004

AbstractResults on solution‐blended poly(ether ether ketone) (PEEK) and poly(ether imide) (PEI) blends are reported. Dichloroacetic acid was used as the cosolvent for blending. PEEK and PEI are confirmed to be miscible in the melt. The glass transition,Tg, behavior obeys the simple Fox equation or the Gordon‐Taylor equation with the adjustable coefficientk= 0.86. This agrees with prior data on melt‐blended PEEK/PEI blends. TheTgwidth of the amorphous PEEK/PEI blends was found to be broader than that of the pure components. The maximum broadening is about 10°C. The specific volume of the amorphous PEEK/PEI blends shows a slight negative deviation from linearity, indicating favorable interaction between PEEK and PEI. The spherulitic growth and resultant blend morphology at 270°C were studied by a cross‐polarized optical microscope. The radial growth rate of PEEK spherulites formed from the miscible melt at 270°C decreases from 3.04 μm/min for PEEK/PEI 90/10 blend to 0.77 μm/min for PEEK/PEI 70/30 blend. The decrease in crystalization rate of PEEK from PEEK/PEI blends is attributable to the increase in blendTg. A linear growth was observed for PEEK spherulites formed from miscible melt at 270°C in the early growth stage. The spherulitic growth deviated from linearity in the late stage of growth. PEEK spherulites formed from the miscible PEEK/PEI melt at 270°C are essentially volume‐filling. The branches of the spherulites become more clear for PEEK spherulites formed from the blend than that formed from pure PEEK melt.
Development of crystallinity in NEW‐TPI polyimide
Authors: Friler Jerome B. , Cebe Peggy 
Published: December 2004

AbstractDevelopment of crystallinity in NEW‐TPI semicrystalline polyimide has been studied using differential scanning calorimetry (DSC), wide (WAXS), and small angle X‐ray scattering (SAXS). Crystallinity of the fully imidized powder, pellet, or film processed NEW‐TPI can occur from the melt, and depends upon the holding temperature of the melt. Repetitive exposure to elevated temperatures supresses the development of crystallinity from the melt state. In amorphous pellets and film, crystallinity can also develop by cold crystallization from the rubbery amorphous state. SAXS results show that during cold crystallization, NEW‐TPI develops a periodic structure consistent with formation of alternating crystalamorphous stacks, but with crystals only a few molecular repeat units thick. Kinetics of nonisothermal crystallization were studied as a function of heating rate and could be described using the Ozawa analysis. Non‐isothermal crystallization proceeds at a slower rate in NEW‐TPI than in other high temperature thermoplastics such as PEEK, and with a much narrower processing window. The maximum degree of crystallinity that could develop during heating was 0.34, which occurred at a rate of 5°C/min. Similar degrees of crystallinity could be introduced by heating amorphous NEW‐TPI film in N‐methylpyrrolidone.
Analysis of thermal stability of acrylonitrile‐acrylic elastomer‐styrene terpolymer in injection molding
Authors: Kohkame Hisashi , Asano Hideki , Goto Masao , Miyano Yasushi 
Published: December 2004

AbstractAcrylonitrile‐acrylic elastomer‐styrene terpolymer (AAS resin) was developed to improve weatherability of acrylonitrile‐butadiene‐styrene terpolymer (ABS resin). To compare thermal stability of both resins, test parts of AAS and ABS resins were injection molded at various temperatures and the Izod impact value of the resulting moldings was measured. A study was then made to find the relationship between this value and deterioration of the resins. AAS resin was molded at temperatures from 180°C to 280°C. The impact value of the resulting moldings was almost constant for temperatures up to 260°C, with the first major decrease occurring at 280°C. In contrast, the impact value of conventional ABS resin moldings constantly decreased as the molding temperature was elevated. To explain this phenomenon in both resins, two types of test program steps were undertaken: (1) The cause of the change in characteristics of the AAS resin was determined by obtaining its stress‐strain curve in a high‐speed flexural strength test; measuring its infrared absorption spectrum; and determining its flow properties with a constant‐pressure extrusion type rheometer; (2) the distribution of elastomer in the resin was observed with an electron microscope. It was found that the decrease of impact values of both resins at high temperatures is caused by deterionration of the elastomer. Also, it was found that the different relationships between the impact value and molding temperatures for AAS and ABS resins are due to the difference between the rates of thermal degradation of the acrylic elastomer and butadiene elastomer.
Segmental motion of stereoregular poly(methyl methacrylates) in a homologous series of n‐alkyl acetate solvents by nmr relaxation measurements
Authors: Ryoo Byung‐Kyu , Kim Dong‐Won , Lee Jae‐Hun , Park Jung‐Ki 
Published: December 2004

AbstractThe 13C spin‐lattice relaxation times, T1s, of both stereoregular poly(methyl methacrylates) (PMMA) and homologous series of n‐alkyl acetate solvents in solution have been measured at 40°C. It was observed that the motion of polar side‐chains was highly affected by the degree of interaction with solvent molecules. The stronger polymer‐solvent interactions in predominantly syndiotactic PMMA solutions than in isotactic PMMA solutions were shown from the T1 values for the carbonyl, methoxy, and quaternary carbons in polymer segments and also from the carbonyl T1s of solvent molecules. By relating the solvent dependences of the T1 data in syndiotactic polymer solutions to that of the known dissolution rate data of atactic PMMA, it was found that the solvent dependences of the T1 values of those carbon groups in which the polymer‐solvent interaction is not significant, e.g., methylene and α‐methyl carbon groups, were consistent with the solvent dependence of the dissolution rate of polymer. This result suggested that the dissolution of polymer is mainly governed not by the sorption process related to the polymer‐solvent interaction but by the transport process related to the local motions of polymer segments and solvent molecules.
Rheology and structure of liquid crystalline alkylenearomatic polyesters
Authors: Kulichikhin G. V. , Dreval' V. E. , Kotova E. V. , Antipov E. M. , Godovsky Yu. K. , Zuev V. V. 
Published: December 2004

AbstractThe rheological, thermodynamic and structural properties of two liquid crystalline polyesters—poly(oxyfumaroyloxy‐ 1,4‐phenylene carbonyloxyalkyleneoxycarbonyl‐ 1,4‐phenylene)s with six and ten methylene groups (PES‐6 and PES‐ 10, respectively) and a statistical copolyester (co‐PES) have been investigated. It has been shown that they all form a smectic LC‐phase. The change from homopolyesters to co‐PE S expands the temperature range of the LC‐state. The high sensitivity of the structure to the prehistory in the melt state is typical for such copolymers. Prolonged heating leads to rearrangement of the co‐PES crystalline structure and a drastic increase in viscosity. The orientation of these polymers during flow was investigated. It was shown that a high level of molecular orientation of the smectic layers, perpendicular to the direction of flow, was realized at high shear stresses. In the melt region, the existence of a metastable network with junctions of crystalline nature hinders the flow of the homo‐ and copolyesters. The structure of the unit cell of the crystallites depends on the composition and thermal history.
A method for approximate prediction of extrudate swell
Authors: Bush M. B. 
Published: December 2004

AbstractThe extrudate swell problem is modeled as the stratified flow of two Newtonian isothermal fluids with differing viscosities. If the viscosity of the thin outer layer is the greater of the two, then enhanced swelling relative to the case of equal viscosity is observed. By suitable selection of the the viscosity ratio, this model can be used to represent thermal, shear‐thinning, and elastic effects in extrusion. The stratified flow problem is solved using an efficient boundary element method. The model then provides a means of studying and predicting complex geometrical effects in profile extrusion without the burden of a full viscoelastic solution, which may yield a practical aid to the die design process.
The evolution of material properties during physical aging
Authors: McKenna Gregory B. , Leterrier Yves , Schultheisz Carl R. 
Published: December 2004

AbstractAging experiments using the NIST (National Institute of Standards and Technology) torsional dilatometer have been performed in which the temperature of an isothermally equilibrated epoxy glass was abruptly changed to a new temperature T0 and the evolution of the volume and torsional relaxation responses recorded. The results of down‐jump and up‐jump experiments were found to differ dramatically. Not only is the normal asymmetry of volume approach to equilibrium found, but the mechanical responses are found to evolve differently from the volume response, contrary to simple free volume models of the physical aging process. It is found that the torsional modulus changes with increasing time after the T‐jump. In the case of the down‐jump the evolution of the modulus ceases prior to that of the volume of the sample. In the up‐jump experiment, the contrary is true, viz., the modulus continues to evolve after the volume has attained its equilibrium value. The implications of this for the description of material behavior are discussed.
Enhanced polycarbonate toughness. I: Measurement methodology
Authors: Kim S. W. , McGarry F. J. , Riew C. K. 
Published: December 2004

AbstractThe JIC values for core‐shell‐particle‐toughened polycarbonate were determined at different temperatures and at 0, 2.5, 5.0, 7.5, and 10.0 phr particle content by six similar methods, using compact tensile specimens. At the 2.5 phr toughener level, the JIC values ranged from 2878 to 6100 J/m2, and at 7.5 phr, they ranged from 6125 to 10,760 J/m2, dependent only upon how the same JI‐Δ a data were interpreted. This indicates that more work will be required before a reliable method of JIC measurement that can be applied to tough polymers is achieved.
Morphology and mechanical properties of liquid crystalline copolyester and poly(ethylene 2,6‐naphthalate) blends
Authors: Jang Sang Hee , Kim Bong Shik 
Published: December 2004

AbstractBlends of poly(ethylene 2,6‐naphthalate) (PEN) and a liquid crystalline copolyester (LCP), poly(benzoate‐naphthoate), were prepared in a twin‐screw extruder. Specimens for mechanical testing were prepared by injection molding. The morphology and mechanical properties were investigated by scanning electron microscopy (SEM) and an Instron tensile tester. SEM studies revealed that finely dispersed spherical domains of the liquid crystalline polymer (LCP) were formed in the PEN matrix, and the inclusions were deformed into fibrils from the spherical droplets with increasing LCP content. The morphology of the blends was found to be affected by their composition and a distinct skin‐core morphology was found to develop in the injection molded samples of these blends. Mechanical properties were improved with increasing LCP content, and synergistic effects have been observed at 70 wt% LCP content whereas the elongation at break was found to be reduced drastically above 10 wt% of LCP content. This is a characteristic typical of chopped‐fiber‐filled composites. The improvement in mechanical properties is likely due to the reinforcement of the PEN matrix by the fibrous LCP phase as observed by scanning electron microscopy. The tensile and modulus mechanical behavior of the LCP/PEN blends was very similar to those of the polymeric composite, and the tensile strength and flexural modulus of the LCP/PEN 70/30 blend were two times the value of PEN homopolymer and exceeded those of pure LCP, suggesting LCP acts as a reinforcing agent in the blends.