bluuebunny/crossref_metadata_2025_split huggingface dataset:
In situ composite fibers: Blends of liquid crystalline polymer and poly (ethylene terephthalate)
Authors: Mithal Ashish K. , Tayebi Amad , Lin C. H. 
Published: May 2005

AbstractTo augment the concept of in situ composites as alternatives to fiber‐reinforced composites, polyblends of a thermotropic liquid crystalline polymer (LCP) and poly(ethylene terephthalate) (PET) were prepared. Fiber‐spinning of the blends was performed on a piston‐driven plastorneter. Blends of LCP and a low‐intrinsic‐viscosity PET resin showed poor mechanical performance, which was attributed to their processing behavior. Blends of LCP and a high intrinsicviscosity PET manifested an almost additive behavior with regard to tensile modulus and strength. Elongation of the blends, however, displayed a radical decline, which is reminiscent of fiber‐reinforced composites. Heat treatment of the blend fibers modestly increased the tensile properties of the LCP‐rich compositions. Blend fibers from PET‐rich compositions exhibit a moderate decline in tensile properties owing to thermal relaxation of PET. The data demonstrate that in situ composites or blends of thermotropic LCPs and isotropic polymers present challenging alternatives to fiber‐reinforced composite systems because of their ease of processing.
Melt rheology of electron‐beam‐irradiated blends, of polypropylene and ethylene‐propylene‐diene monomer (EPDM) rubber
Authors: Van Gisbergen J. G. M. , Hoeben W. F. L. M. , Meijer H. E. H. 
Published: May 2005

AbstractA detailed rheologicai analysis over large shear rate intervals has been performed for electron‐beam‐irradiated blends of polypropylene (PP) and ethylenepropylene‐diene monomer (EPDM) rubber. At high frequencies, a lower viscosity results from irradiation compared with unirradiated blends, which implies that the irradiated blends are easily processable via injection molding. At low shear rates, however, the irradiated blends behave like a network, and the viscosity may even exceed the viscosity of the unirradiated blends. This particular behavior can result in the formation of weak weld lines. Aggregation of the dispersed, cross‐linked EPDM particles into a skeletal structure is the most probable explanation. In a first attempt, it was tried to correlate the network behavior to the average (shortest) interparticle distance (ID) between two rubber particles, which takes into account both volume fractions and particle size of the dispersed phase. Provided that the EPDM rubber is sufficiently cross‐linked, the network behavior becomes more pronounced; i.e., increase in viscosity with decreasing interparticle distance. Above a critical value of the ID, the viscosity does not change and is determined by the PP matrix. As a vast amount of literature indicates, the rheology of blends proves to be difficult to understand. Because of the more stable morphology, compared with usual blends, induced by irradiation, a more valuable interpretation of the rheological behavior is possible.
Photoinitiated crosslinking of low density polyethylene: II. Morphology and properties
Authors: Qing Yan , Wenying Xu , Rånby Bengt 
Published: May 2005

AbstractThe crystalline morphology and physical properties of photocrosslinked polyethylene in a low density polyethylene (LDPE)‐benzophenone (BP)‐triallyl isocyanurate (TAIC) system have been studied. The results of X‐ray diffraction and DSC thermal analysis indicate that the effect of crosslinking on the degree of crystallinity of the material is quite limited, but the presence of crosslinks can affect the regularity of the crystal regions. This is proposed to be responsible for the slight variation in properties of the crosslinked material at room temperature, such as the decrease of modulus and the changes of yield behavior. The main improvements in properties of the photocrosslinked polyethylene are found at high temperatures, especially above the melting point. The strength is increased, and the heat distortion temperature is enhanced significantly, as previously reported in the literature.
Influence of chain flexibility and crosslink density on mechanical properties of epoxy/amine networks
Authors: Urbaczewski‐Espuche Eliane , Galy Jocelyne , Gerard Jean‐Francois , Pascault Jean‐Pierre , Sautereau Henry 
Published: May 2005

AbstractBlends of a bisphenol A diglycidyl ether prepolymer and an aliphatic diepoxy diluent crosslinked with a cycloaliphatic diamine were studied. These model networks have the characteristic that the crosslink density and the chain flexibility increase with the amount of diluent. These combined effects were studied by observing their mechanical properties. The decreases in the Young's modulus and the ultrasonic modulus were associated with the secondary thermomechanical relaxations that have been recorded and identified. Pre‐plastic and plastic behaviors were discussed in terms of flexibility and crosslink density. A linear relationship was established between pre‐plastic activation volume and crosslink density at temperatures lower than the activation of molecular chain motions responsible for the sub‐Tg relaxations. At 0°C, a temperature above these secondary transitions, the higher the flexibility, the more defect nucleation and propagation increased. The work hardening rate and the upper yield stress decreased as the amount of diluent was increased. Fracture toughness was improved as the amount of diluent was increased. Crack propagation was related to the ability of the networks to deform plastically.
Analysis of the curing behavior of cyanate ester resin systems
Authors: Osei‐Owusu A. , Martin G. C. , Gotro J. T. 
Published: May 2005

AbstractThe role of metal catalysts on the curing characteristics of bisphenol A‐based cyanate ester resin systems was investigated using Fourier transform infrared spectroscopy, differential scanning calorimetry, and rheological measurements. Bisphenol A dicyanate was cured with the octoates and naphthenates of zinc and manganese and with cobalt acetylacetonate at concentrations ranging from 0 to 750 ppm metal. Nonylphenol at concentrations between 0 and 8 phr was used as the cocatalyst. The results show that at metal catalyst concentrations less than 100 ppm and nonylphenol concentrations less than 4 phr, a maximum glass transition temperature of 250 to 260°C is obtained, irrespective of the type of catalyst used. For samples cured without nonylphenol, the maximum Tg was 298 to 302°C. At high catalyst concentrations, the Tg decreases with increasing catalyst concentration for the zinc catalysts, whereas no concentration effect was observed for samples cured with either manganese or cobalt. Nonylphenol was effective as a cocatalyst in achieving high conversions; however, the Tg at full conversion was found to decrease with increasing nonylphenol levels.
The influence of continuous stabilization on the properties of stabilized fibers and the final activated carbon fibers. Part I
Authors: Ko Tse‐Hao , Chiranairadul P. , Lin Chung‐Hua 
Published: May 2005

AbstractThis study found that, during continuous stabilization and carbonization, the shrinkage behavior of polyacrylonitrile (PAN) fibers affects the morphology and properties of the stabilized fibers, the carbon fibers, and the final activated carbon fibers. In the stabilized fibers, a higher shrinkage of the PAN fibers during the stabilization process increased the oxygen content and the core proportion and decreased the formation of ladder polymers. The effect of the shrinkage behavior of the PAN fibers on the fracture surfaces of the stabilized fibers is discussed. A microstructure model of stabilized fibers is presented, depicting fine radial structure at the fiber center. When stabilized fibers were carbonized during a continuous carbonization process, a hole structure was found in the fiber center at the temperature of 800°C, and a hollow core was found at the temperature of 1300°C. The shrinkage behaviors during the stabilization stage and the formation of the hole and the hollow core in the fiber's center during the carbonization stage are discussed. The carbon fibers developed from shrunk stabilized fibers have a lower density and lower preferred orientation than fibers developed from unshrunk stabilized fibers. But the fibers developed in this new process have greater nitrogen and oxygen content, and have a greater porosity than the traditionally‐produced fibers. The mechanical properties df the new and the traditional fibers are comparable. These characteristics are very valuable in the production of activated carbon fibers, which will be described in our next paper.
Electrically conductive polymer composites and blends
Authors: Lee Biing‐Lin 
Published: May 2005

AbstractIncreasing utilization of the electrical properties of polymeric blends and composites has prompted our renewed interest in developing a general working relationship which can explain the electrical properties of polymer composites and blends in terms of processing characteristics, morphology, and compositions. Here, we restrict our attention to the following two‐component systems: (1) two component systems with conductive particulate inclusions (e.g. carbon black) embedded in a continuous polymeric matrix, and (2) two component polymer blend systems with one conductive polymer (e.g., polyether copolymer) dispersed in another continuous polymeric matrix. The following processing aspects related to the electrical property of particulate filled composites are discussed: (1) critical concentration of rigid conductive fillers, ϕc, and (2) redistribution of conductive fillers upon processing. An equation based on the crowding factor of concentrated suspension rheology and Janzen's particle contacts percolation is proposed to describe the relationship between ϕc, and the maximum packing fraction of conductive fillers. The relationship is used to explain the influence of particle morphology on conductivity, and the conductivity difference in the high shear and the low shear region of a processed polymer composite part. Furthermore, some qualitative guidelines for blending a low conductivity polyether copolymer to achieve an overall balance of antistatic and mechanical properties of polymer blends are also discussed.
Crystallization behavior of polyphenylene sulfide in blends with a liquid crystalline polymer
Authors: Minkova Lili I. , Paci Massimo , Pracella Mariano , Magagnini Pierluigi 
Published: May 2005

AbstractBlends of polyphenylene sulfide (PPS) with a commercial, wholly aromatic, liquid crystal copolyesteramide (Vectra‐B950) have been prepared by meltblending. The crystallization behavior of neat and blended PPS has been studied by differential scanning calorimetry (DSC), under both non‐isothermal and isothermal conditions. It has been found that blending PPS with Vectra‐B leads to an increase of the temperature of non‐isothermal crystallization and to a pronounced acceleration of the isothermal crystallization, without any reduction of the degree of crystallinity. All these effects have been found to occur independent of the Vectra‐B concentration, within the investigated range (2 to 20%, w/w). The results have been interpreted in terms of an incrased nucleation density of the blends, probably due to heterogeneous substances, initially present in the Vectra‐B bulk, which dissolve to saturation in the PPS phase, during melt‐blending.
Elongation viscosity estimates of linear low‐density polyethylene/ low‐density polyethylene blends
Authors: Tremblay Bernard 
Published: May 2005

AbstractThe elongational viscosity (EV) of two series of linear low‐density polyethylene/low‐density polyethylene blends was estimated using an entry flow analysis. The difference, t − n, between the power law index t of the elongational viscosity and the power law index n of the viscosity, is proportional to the LDPE content for both series of blends investigated. Comparison of the EV of the LLDPE/LDPE blend estimated from the analysis of the flow into an orifice die to the EV value estimated from the analysis of the flow into a capillary die with a flat entry, showed that the difference in geometry had little effect on the EV estimates.
Mechanical properties and morphology of polymer blends of poly(ethylene terephthalate) and semiflexible thermotropic liquid crystalline polyesters
Authors: Shin Boo Young , Jang Sang Hee , Chung In Jae , Kim Bong Shik 
Published: May 2005

AbstractTwo thermotropic liquid crystalline polyesters (TLCPs) with long flexible spacer groups in the main chain were prepared by melt polymerization: one was a homopolymer with only decane groups (LCPHO) and the other was a copolymer with hexane or decane groups (LCPCO) between mesogen units. These polyesters were blended with a matrix polymer of poly(ethylene terephthalate) (PET). Scanning electron microscopy (SEM) revealed the excellent interfacial adhesion between polyester and PET, and the large aspect ratio of polyester microfibrils in the blend fiber made by extruding and drawing the blend through a die. The aspect ratio was estimated by using the modified Halpin‐Tsai equation. The fiber with LCPHO showed more extensive fibril formation than that with LCPCO.
The running‐in and steady‐state coefficient of friction of some engineering thermoplastics
Authors: Benabdallah S. H. 
Published: May 2005

AbstractThe dry friction properties of three engineering thermoplastics, ultra high‐molecular‐weight polyethylene (UHMWPE), polyoxymethylene (POW) and polyamide 66 (PA 66), have been investigated using a plane on plane contact. During running‐in, the steady‐state of the friction coincides with stable values for the surface temperature of the slider. The proper trend as well as the correct order of magnitude are observed between the measured surface temperatures and those calculated using the equation of Lancaster. The increase of the run‐in friction as function of the Pv factor could be well correlated by μ(t) = μss − Pexp(− 2 104 t), where μss is the steady‐state value of the coefficient of friction, n is a constant depending on the material tested. A decrease of μss with increasing load for UHMWPE and POM indicates that friction is primarily the result of adhesion. However, for the PA 66, the opposite is valid, assuming that in this case the high Tg of this material may play an important role. Friction increases as the rugosity of specimen diminishes and as speed increases. Finally, the coefficient of friction could be well correlated by μ = kPmexp(βv) where k, m, and β are constants depending on roughness and type of material.
Crystallization kinetics of poly(ethylene terephthalate): Cmemory effect of shear history
Authors: Kim S. P. , Kim S. C. 
Published: May 2005

AbstractThe memory effect of shear history was studied with poly(ethylene terephthalate) (PET) prepared under different shear conditions of 11.7 to 1168 s−1 in a capillary rheometer. The shear history of PET resin led to a memory effect, which in turn affected the crystallization kinetics. The crystallization rate increased with increasing shear rate. Double peaks of heating crystallization exotherms and a low value of Avrami exponent appeared at low shear rates, which was attributed to the existence of crystallization processes with different rates; one was the fast process involving the disentangled molecules that persisted during melting, and the other was the slow process involving the highly entangled molecules. The change of instantanenous Avrami exponent and overall crystallization rate constant was in good agreement with the expected trends assuming coexistence of the two crystallization processes. The crystallization kinetics of PET with shear history could be regarded as a growth rate decrease problem to be interpreted by the modified Avrami equation, 1 − Vc = exp[− K·f(t)n], when the fast process dominated the overall crystallization. The effect of shear history was reduced because of the relaxation process as the holding time in melt state before crystallization was increased.
Kinetic modeling of the epoxidation of natural rubber with in‐situ–formed peracid
Authors: Roy Sanjoy , Namboodri C. S. S. , Maiti B. R. , Gupta B. R. 
Published: May 2005

AbstractIn the presence of excess hydrogen peroxide and formic acid the latex stage epoxidation of natural rubber is pseudo–first order in nature. A kinetic model is developed to predict the maximum extent of epoxidation for the reaction system and its variation with increasing acid concentration. Th dependence of the overall rate constant on acid concentration is also studied.
Deformation and fracture of glass bead/ CTBN‐rubber/epoxy composites
Authors: Zhang H. , Berglund L. A. 
Published: May 2005

AbstractCarboxyl‐terminated butadiene‐acrylonitrile‐rubber decreases modulus and yield stress of the studied epoxy but increases fracture toughness. The addition of glass bead compensates for the loss in modulus but has little effect on yield stress. However, it significantly contributes to the fracture toughness by providing additional mechanisms for toughening of both the unmodified and rubber‐modified epoxy. For the toughened epoxies studied, fracture surfaces gave only limited information on fracture mechanisms since significant energy absorption also occurs in the material below the fracture surface. Suggestions for suitable material compositions for fiber composite matrices are given.
Dynamic melt rheology. II: Re‐examining the relationship of g′ in oscillatory rheometry to the melt elasticity
Authors: Khanna Y. P. , Slusarz K. R. 
Published: May 2005

AbstractIn oscillatory rheometry, since the dynamic storage modulus (G′) represents the elastic component of the viscoelastic melt, it has been a rather common practice to associate it with the melt elasticity. Although this assumption might be valid in many instances, there can be exceptions as well. In the present study, we have chosen polypropylene/talc system to demonstrate an exception. For example, the melt elasticity decreases with increasing talc content as revealed by extrudate die swell, entrance pressure drop, and elastic compliance measurements; the opposite trend being reflected by G′. We can envision similar exceptions when stiffening agents are added to a polymer melt, e.g., rigid rod molecules. We are suggesting that G′ represents the elastic modulus or stiffness of the melt, which in certain situations might not reflect elasticity, i.e., the ability of a melt to recover from a deformation. The implication of the present manuscript is that caution be exercised when relating G′ to the melt elasticity of a polymer.
Finite difference solution for flow from a slit die
Authors: Karidio I. , Picot J. J. C. 
Published: May 2005

AbstractA finite difference solution for an isothermal viscoelastic liquid flowing through a film forming die is investigated. The fluid is described by a Maxwell model in which the time derivative has been replaced by an Oldroyd's convective derivative and the numerical technique used combines features of the Solution Algorithm (SOLA), Simplified Marker and Cell method (SMAC), and SOLASMAC. The numerical scheme was tested with a Newtonian fluid and high density polyethylene (HDPE). Two slit dies with gap‐to‐length ratios 4 and 16 were used. In the two cases, die swell has occurred: A maximum of 4.5% swell was observed for the Newtonian fluid, while up to 77% swell was attained with HDPE. The simulated flow behavior of HDPE exhibited high amplitude oscillations at dimensionless time greater than 0.18. These oscillations are thought to be related to the nature of sheet flow, which can be unstable. This study shows that with some improvement the finite difference method can be used for studying the extrusion of polymer through slit and capillary dies.
The effect of mixing history on the morphology of immiscible polymer blends
Authors: David B. , Kozlowski M. , Tadmor Z. 
Published: May 2005

AbstractA laboratory prototype tester was used to systematically study the effects of geometrical and operational variables on the mixing of two immiscible polymer melts. Results verify that the number of passages is a dominant variable in dispersive mixing. The development of micromorphology in a controlled fashion was studied extensively and backed up with a finite element simulation of the flow in the tester geometry. Complex deformational fields in the laboratory mixer are evident from the highly deformed dispersed phase morphologies.
Volumetric heating by electromagnetic energy absorption—a potential for the mass production of structural composites
Authors: Malaczynski Gerard W. , Dinatale Claude A. , Cinpinski Gerald J. 
Published: May 2005

AbstractThe problem of excessive heat buildup in a heat diffusion supported thermosetting process may lead, especially in the case of thick composite profiles, to compromised quality or even thermal degradation of the final product. A computer simulation of a real manufacturing process demonstrates this intrinsic weakness of the conventional manufacturing process by showing nonuniformities in the degree of cure development and a temperature inversion at the end of the processing cycle. Those nonuniformities in thermal expansion and contraction may be avoided by heating the composite uniformly throughout the whole cross section. This can be achieved with the help of electromagnetic irradiation. The electric energy absorption and, hence, conversion to heat takes place uniformly in the whole bulk of the material, regardless of the position. In effect, one can expect that the uniformly fast cured composite features superior mechanical properties over that of a composite that is conventionally processed.
A study of degradation of high density polyethylene in a corotating intermeshing twin screw extruder
Authors: Dontula N. , Campbell G. A. , Connelly R. 
Published: May 2005

AbstractA study of the effect of extrusion conditions on the degradation of high density polyethylene was carried out. The extent of degradation was quantified by dynamic viscometry. The effect of barrel temperature profile, screw speed, and feed rate on the degradation of high density polyethylene was determined. The viscosity response of high density polyethylene is complex with respect to extrusion conditions. Residence time studies were carried out to correlate the viscosity data. Simulations of simple theoretical models give an insight into the flow behavior of the polymer in a twin screw extruder.
The origin of chain entanglement: Correlations between entanglement and chain structure
Authors: Wu Souheng 
Published: May 2005

AbstractA pseudotopological theory of chain entanglement has recently been developed, which shows that the entanglement junction is a binary hooking contact between two chains, and explicitly relates the entanglement behavior to chain structure. On the other hand, many empirical correlations between entanglement and chain structure have also been proposed to date, including those of Fox and Allen, Porter and Johnson, Privalko and Lipatov, Boyer and Miller, Graessley and Edwards, Aharoni, Lin, and Zang and Carreau. In this work, we show that the various empirical equations cited are variations of the same function, and can be derived as special cases from the theoretical pseudotopological equation. The various forms of the function nevertheless reveal different essential aspects of the chain entanglement behavior, and show that the traditional hooking view of chain entanglement is correct, and also provides a basis for the recent reptation‐tube model.