bluuebunny/crossref_metadata_2025 huggingface dataset:
Impact response of composite laminates with a hemispherical indenter
Authors: Pang S. S. , Zhao Y. , Yang C. , Griffin S. A.
Published: May 2005

A model for predicting the contact duration, force, indentation, and displacement under impact has been developed for impact of a composite laminated plate with a hemispherical indenter. The governing equations were first proposed and then solved with the initial conditions along with the peak force condition. An expression forr each parameter has been obtained in a simple expression through straightforward derivation. Both static and dynamic tests have been conducted. Ten impact tests were conducted using a weight drop tower tester. Comparison between the, model predictions and the experimental data on the impact duration and impulse are provided, and were found to be within 14% for all tests involved. Comparison of the impact force‐history also shows good accord.
Styrene maleic anhydride and styrene glycidyl methacrylate copolymers as in situ reactive compatibilizers of polystyrene/nylon 6,6 blends
Authors: Chang Feng‐Chih , Hwu Yih‐Chyun
Published: May 2005

The reactive type copolymers styrene maleic, anhydride (SMA) and styrene glycidyl methacrylate (SG) are used as in situ compatibilizers in polyblends of polystyrene (PS) and nylon 6, 6 (N66). Both copolymers can react with N66 to form copolymers as effective compatibilizers to reduce interfacial tension and increase phase adhesion. However, the toughness of the compatibilized blends is significantly lower than of the corresponding noncompatibilized blends. Only a small fraction of SMA is actually reacted in a typical melt blending, and SG copolymer seems to be more reactive than SMA. The unreacted copolymers are expected to be distributed mostly in the PS phase because of their structural similarity. The reacted copolymers are not exclusively distributed along the interface; some may distribute in both matrices. SMA is known as a very brittle polymer, and the way it is distributed can greatly influence the toughness of the resulting blends. PS is also very brittle relative to N66, and moreover a high amount of SMA in the N66 phase is detrimental since N66 is responsible for the toughness of PS/N66 blends. The better compatibilized blends have the tendency to bring more SMA and reacted SMA into the N66 phase. The relative detrimental effect on the inherent toughness of N66 is much more severe than in case of PS, if they contain the same amount of SMA. This study demonstrates that polyblends with good compatibilizers do not guarantee toughness improvement. The way the compatibilizers affect the inherent properties of the matrix needs also to be taken into consideration.
Application of the Flory‐Huggins theory to the system chloroform‐polystyrene‐butadiene rubber
Authors: Geveke D. J. , Danner R. P.
Published: May 2005

According to the Flory‐Huggins theory for polymer blends, the polymerpolymer interaction parameter, χ23, must be positive for incompatible polymers. Previous studies of the incompatible ternary system chloroform‐polystyrerne‐butadiene rubber yielded negative values of χ23 using a solution method based on the Flory‐Huggins theory with the chloroform‐butadiene rubber interaction parameter used as input. An alternate solution method using the chloroform‐polystyrene interaction parameter as input has been used to obtain positive values of χ23 for this incompatible system. This variation in results indicates that the interaction parameters obtained using the Flory‐Huggins theory are not physically meaningful. They are, however, useful as correlating parameters. Both sets of results, although quite different, are shown to correlate the experimental data identically well. In addition, the appropriate equations are presented for the case where one of the solvent‐polymer interaction parameters is concentration dependent.
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

To 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

A 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

The 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

Blends 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

The 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

This 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

Increasing 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

Blends 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

The 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

Two 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

The 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

The 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

In 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

Carboxyl‐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

In 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

A 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

A 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

The 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

A 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

A 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.
Molecular structure, morphology, and antioxidant‐ consumption in polybutene‐1 pipes in hot‐water applications
Authors: Karlsson K. , Eriksson P‐A. , Hedenqvist M. , Ifwarson M. , Smith G. D. , Gedde U W.
Published: May 2005

Pipes of isotactic polybutene‐1 (PB) have been exposed to internal water and external air in pressure tests at 105°C. The pipes exposed to different internal pressures exhibited different failure mechanisms, referred to as stages I, II, and III. Samples taken from these pipes have been analyzed by infrared (IR) spectroscopy, wide‐angle X‐ray scattering (WAXS), size exclusion chromatography (SEC), and differential scanning calorimetry (DSC). IR spectroscopy and WAXS confirmed that thermal oxidation of the amorphous part of the polymer accompanied the onset of stage III. Thermal oxidation led to extensive molar mass reduction and to a significant increase in mass crystallinity and melting peak temperature. Extensive and visible degradation in pipes failing according to stage III was confined to so‐called “oxidation spots.” The latter were first formed at the outer wall and propagated inwards, finally constituting approximately 50% of the wall thickness. The antioxidant concentration profiles obtained by DSC were always symmetrical and were successfully adapted to a previously developed model. It was shown that migration of the antioxidant was the dominant loss mechanism, that the diffusion coefficient was constant through the pipe wall, and that the evaporative loss to the external air was marginally greater than the loss to the internal water phase. Chemical consumption of the antioxidant was found to be negligible.
Mechanical properties of corona‐modified cellulose/polyethylene composites
Authors: Dong S. , Sapieha S. , Schreiber H. P.
Published: May 2005

The effect of corona treating the surfaces of components on tensile properties of wood fiber linear low‐density polyethylene composites has been investigated. Corona treatment results in a significant increase in strength properties of the composites. Yield stress increases after treatment of one or both of the composite components. Pronounced improvement in ductility has been observed for composites containing 15 to 30% of the corona modified fiber. Relevant mechanisms involved are discussed.
Dynamic simulation of propylene polymerization in continuous flow stirred tank reactors
Authors: Sarkar Priyabrata , Gupta Santosh K.
Published: May 2005

The dynamic operation of an ideal continuous‐flow stirred tank slurry reactor for propylene polymerization has been studied. A simple model is developed, which could be used for optimal computer control using advanced strategies. Step increases in input feed rates of propylene, solvent, and catalyst are used as the stimuli or forcing functions. It is assumed that the volume of the slurry in the reactor is maintained constant during the period. Responses of three output variables are studied, namely, monomer concentration in the liquid, volume‐fraction of solids in the exiting slurry, and average mass fraction of catalyst in the exiting macroparticles. It is found that the transients last for about five times the mean residence time of the reactor. Competing effects of changes in the diffusional resistance, number density of catalyst particles, and washout and dilution effects lead to interesting dynamic results.
Numerical and experimental investigation of three‐dimensional flow in extrusion dies
Authors: Gupta Mahesh , Jaluria Yogesh , Sernas Valentinas , Esseghir Mohamed , Kwon Tai H.
Published: May 2005

The univariant element, Q1 P0, and the multivariant elements, QP0 and R P0, are compared for the numerical simulation of the flow in extrusion dies. The pressure distribution obtained by using the Q1 P0 element was found to be afflicted with the checkerboard pressure mode. On the other hand, the multivariant elements, Q P0 and R P0, gave accurate and physically reasonable velocity and pressure distributions. The computed values of the pressure drop across extrusion dies matched well with the pressure drop determined experimentally.
Shear effects on thermoplastic foam nucleation
Authors: Lee Shau‐Tarng
Published: May 2005

Polyethylene foam experiments were conducted on a twin screw foam extruder to study the process effects upon foam nucleation. The results indicate that, other than quantity of nucleators, throughput rate and die opening are important process parameters, underscoring the importance of shear in the die on nucleation. It is also found that shear effects increase as nucleator level increases. A modified cavity model shows at least qualitative agreement with experimental results. Dimensionless Capillary number, ratio of shear force to surface tension force, provides evidence that shear force rather than shear rate alone is the principal parameter affecting foam nucleation.
A macromolecular deformation model to estimate viscoelastic flow effects in polymer melts
Authors: Porter David
Published: May 2005

The elastic deformation of polymer macromolecules in a shear field is used as the basis for quantitative predictions of viscoelastic flow effects in a polymer melt. Non‐Newtonian viscosity, capillary end correction factor, maximum die swell, and die swell profile of a polymer melt are predicted by the model. All these effects can be reduced to generic master curves, which are independent of polymer type. Macromolecular deformation also influences the brittle failure strength of a processed polymer glass. The model gives simple and accurate estimates of practically important processing effects, and uses fitting parameters with the clear physical identity of viscoelastic constants, which follow well established trends with respect to changes in polymer composition or processing conditions.
Measurement and correlation of liquid‐liquid equilibria for polystyrene‐cyclopentane and polystyrene‐cyclopentane‐cyclohexane systems
Authors: Iwai Yoshio , Shigematsu Yuji , Furuya Takeshi , Fukuda Hiroyasu , Arai Yasuhiko
Published: May 2005

Liquid‐liquid equilibrium data for the polystyrene‐cyclopentane binary system and the polystyrene‐cyclopentane‐cyclohexane ternary system were measured by observing the cloud points at the temperature range in which the systems showed their lower critical solution temperature. The experimental liquid‐liquid equilibria were correlated successfully by the UNIFAC‐FV model with adjustable parameters.
Study of dielectric relaxation of an epoxide oligomer by a direct current transient method
Authors: Koike Tsuneo
Published: May 2005

Dielectric α‐relaxation of a bisphenol‐A type epoxide oligomer has been investigated in the vicinity of the glass transition temperature (Tg) by the direct current (DC) transient method. The logarithm of the DC transient current for the oligomer was well approximated by the third order function of the logarithm of time. The complex dielectric constant was calculated through the Fourier transformation of that approximation function according to Simpson's integration rule in a frequency range of 10−5 − 1 Hz. At the temperature around the Tg (45°C), the dielectric α‐relaxation process of the oligomer was found to be governed by the Havriliak‐Negami equation. The relationship between the DC conductivity (σ) and the dielectric relaxation time (τ), σ·τm = const, is valid near and above the Tg of the oligomer. The DC transient current method combined with the DC conduction and the dielectric bridge measurements is considered to be a practical tool for analyzing the dielectric α‐relaxation process of the epoxide oligomer over a wide frequency and temperature range.
The leveling of thermosetting waterborne coatings. Part I: Observation of leveling process
Authors: Kojima Shunji , Moriga Toshinori , Takenouchi Ken
Published: May 2005

A modified observation system for the leveling process of a coated fluid is proposed, and the observation results are presented and compared with previous results. For the thermosetting waterborne coatings, the theory of Orchard, et al., and ones based on it are not applicable and fail to give even a qualitative description. The theory of Overdiep was found to be reasonable. However, it was insufficient to predict the leveling performances of coatings without experimentation. Qualitatively, the original theory suggests the possibility of the reappearance of surface ripples, in other words, the occurrence of the negative amplitude in the surface ripples during the course of leveling, although little data were presented regarding the phenomenon. It was found here that added co‐solvent plays an important role on the leveling rate and also the occurrence and the control of the negative amplitude of the surface ripples. These are thought to relate closely to the volatility of the co‐solvent and the composition of the solvent residue in the coated film during the leveling process.
Transport studies in poly(methyl methacryalate‐g‐urethane)
Authors: Sreenivasan K.
Published: May 2005

Transport studies of two organic liquids, toluene and n‐hexane, have been performed in polyurethane and poly (methyl methacrylate‐g‐urethane). A high degree of selectivity in the permeation of these two liquids has been achieved by MMA grafting. A near perfect separation has been realized by grafting of MMA to 28%.
Temperature dependence of the nucleation effect of sorbitol derivatives on polypropylene crystallization
Authors: Kim C. Y. , Kim Y. C. , Kim S. C.
Published: May 2005

The temperature dependence of the nucleation effect of three sorbitol derivatives on the crystallization of isotactic polypropylene (iPP) was studied by means of isothermal crystallization kinetic analysis. Isothermal crystallization thermograms obtained by differential scanning calorimetry (DSC) were analyzed based on the Avrami equation. The Avrami analysis for the nucleated iPP was carried out with DSC data collected to 35% relative crystallinity, and the rate constants were corrected assuming the heterogeneous nucleation and three dimensional growth of iPP spherulites. A semi‐empirical equation for the radial growth rate of iPP spherulites was given as a function of temperature and was used to determine the number of effective nuclei at different temperatures. The number of effective nuclei in the nucleated samples was estimated to be 3 × 102 ∽ 105 times larger than that in the neat iPP. The logarithmic numbers of the effective nuclei decreased linearly with decreasing degree of supercooling in the range of crystallization temperatures tested. The temperature dependence of the effect of the nucleating agents on iPP crystallization was given quantitatively in terms of the deactivation factor defined as a fraction of the particles that are active at a particular temperature but inert at the temperature one degree higher. The nucleation activity and its temperature dependence are considered to be cooperative effects of many factors, including the dispersion and the physical or chemical nature of the agent as well as the interaction between the agent and the polymer. It is suggested that the temperature dependence of the effect of a nucleating agent should be treated as a characteristic of a given polymer/ nucleating agent mixture.
Manufacture of films displaying liquid‐crystalline structure
Authors: Gul′ V. E. , Sdobnikova O. A. , Peshehonova A. L. , Samoilova L. G. , Khanchech O. A. , Suvorova A. I.
Published: May 2005

Reported is an attempt to attain orientation of macromolecules during extrusion of films of cellulose derivatives that led to the liquid‐crystalline state of a polymer and resulted in enhanced film strength.
Process rheometers for molten plastics: A survey of existing technology
Authors: Dealy John M. , Broadhead Taras O.
Published: May 2005

There are many operations in the plastics industry where it is useful to be able to monitor the rheological properties of a melt as it is being processed. Such operations include polymerization, blending, compounding, and reactive extrusion. The design of such instruments poses major challenges, as there is a conflict between the need for rapid sample renewal and the desire for measurement accuracy. In‐line types, which are installed directly in the process flow, have a rapid response but must operate in an environment where temperature, pressure, and flow rate fluctuate in response to process upsets. On‐line types, which make use of a side stream and gear pump to feed the rheometer, allow for more freedom in the design of the rheometer but have an inherent signal delay due to the time required for melt to reach the rheometer. A variety of rheological sensors have been described in the patent and research literature, each with its unique advantages and disadvantages, and some of these are finding increased use in the plastics industry to improve product quality and process efficiency.
The mechanism of skin‐core morphology formation in extrudates of polycarbonate/liquid crystalline polymer blends
Authors: Beery D. , Kenig S. , Siegmann A. , Narkis M.
Published: May 2005

The mechanism of skin/core morphology development and LCP (liquid crystalline polymer) fibril formation in polycarbonate/LCP blends was studied. A certain minimum concentration of the LCP phase must be present for the formation of continuous LCP fibrils in the extrudates. A skin‐core morphology characterizes the PC/LCP extrudates. Short LCP fibrils are formed in the capillary converging entrance section, through the elongation of LCP domains and their coalescence. Continuous fibrils were formed in the skin of extrudates emerging from cylindrical capillaries, through the coalescence of the short fibrils, provided the shear stresses are high enough and the LCP viscosity is equal or lower than that of PC. Increasing capillary length enhances the LCP lateral migration and fibrils formation. The high interfacial tension stabilizes the LCP fibrils. In the core region the short fibrils recoil or breakup, resulting in spherical or elongated droplets. Long and continuous fibrils cannot be formed in a zero length capillary, even at high flow rates.
Solid state extrusion of vinylidene fluoride (VF2)/vinylidene trifluoride (VF3) copolymers. II: Structure development
Authors: Lee J. S. , Cakmak M.
Published: May 2005

Copolymers of vinylidene fluoride (VF2) and vinyltrifluoride (VF3) exhibit Curie transition temperatures well below their melting points. Above these endothermic transitions, they soften and this behavior helps in their solid state extrudability. In this paper, the effects of extrusion speed, temperature, and draw ratio on structure development in 60/40 and 72/28 VF2/VF3 copolymer compositions are presented. With the increase of extrusion draw ratio the Curie transition temperature of the extrudates decreased and melting temperature increased. This behavior suggested that the chains in the crystalline regions contain higher levels of conformational defects while overall crystallinity is increased. Unoriented polymers were optically opaque and extrudates were found to be transparent as a result of breakdown on the superstructural level which decreases the scattering effects in the visible wavelength range. The micro beam WAXS studies on the samples taken from the entrance of the dies revealed that the unoriented core is surrounded by alternating unoriented and oriented layers close to the core. The remainder of the skin layers are found to be oriented with local symmetry axes and main chain orientation being parallel to the die wall surface. The regions that are found to be oriented were also found to be optically translucent and unoriented regions were optically opaque. This structure turns uniformly transparent–and thus oriented‒as the polymer enters the die. The existence of layered structure suggests that highly localized yielding occurs during early states of deformation at the converging entrance region of the die. Examination of the radial structural variation in extrudates with micro beam X‐ray diffraction technique revealed that the local symmetry axes are tilted away from the extrusion direction and this tilt angle reduces at the sample macro‐symmetry axis at the core of the samples. This indicated that the tilted structure developed at the converging entrance region is partially preserved through the die. While the orientation of local symmetry axes varies from skin to core in the extrudates, the orientation of chains with respect to these local symmetry axes remains relatively unaffected.
The reactive modification of polyethylene. I: The effect of low initiator concentrations on molecular properties
Authors: Suwanda D. , Balks S. T.
Published: May 2005

Commercial samples of high density, linear low density, and low density polyethylene were modified by injection of low concentrations of free radical initiator during extrusion. Molecular properties monitored included molecular weight distribution, degree of unsaturation, and branching. When the polyethylene teed to this reactive extrusion process had similar values of Mw, but varying polydispersity, degree of branching and degree of unsaturation, the magnitude of the change in molecular weight distribution was found to be in the following order: HDPE 1 > LDPE2 > LLDPE. In general, terminal vinyls enhanced molecular weight increase, and branching promoted degradation. However, for a second high density polyethylene sample with Mw = 154,000 (rather than the previous sample's Mw of 85,600), the change in molecular weight distribution was small and located at the lower molecular weight end. This work provided data for the kinetic model development detailed in Part II.
Processing/performance relationships considering voids in structural reaction injection molding
Authors: McGeehan John A. , Gillespie John W. , Hulway Joseph A.
Published: May 2005

The causes of void content and its resulting effect on the material properties of structural reaction injection molded (SRIM) composites were investigated. Plaques were molded under different combinations of five two‐level factors, and the resulting effect of each factor on void content was determined. The geometry of the glass reinforcement had the largest effect, as woven mats caused double the void content of random mats. Evacuating the mold cavity proved to greatly reduce void content as well. Varying the injection rate and shot size had little effect. Material property testing was conducted on groups of specimens with similar void content. Tension testing revealed no decrease in strength with increasing void content. One million cycles of tension‐tension fatigue at 20% of the ultimate strength caused no decrease in strength at any void content, while fatigue at 30% caused premature failure. Impact testing showed that only very high void contents had a substantial effect on performance. Environmental conditioning showed moisture absorption proportional to void content and furthermore significantly reduced the residual tensile strength after a single thermal cycle to 0°C. These results suggest that void content in conjunction with a weak interface may have been responsible for limiting material properties.
Acrylic acid containing copolymers as reactive compatibilitzers for toughening nylon 6
Authors: Lu M. , Keskkula H. , Paul D. R.
Published: May 2005

Nylon 6 has been toughened by rubber particles that were dispersed within the matrix via additives that physically interact with the elastomer phase but chemically react with the polyamide phase. To disperse a core‐shell impact modifier having a poly(methyl methacrylate) or PMMA shell, most of the work presented is based on the use of a styrene/acrylic acid copolymer containing 8 wt% acrylic acid, SAA8. SAA8 is miscible with PMMA and should located in the PMMA grafted chains of the impact modifier while chemically reacting with the nylon 6 matrix; hence, it should aid in both the dispersal and strenghtening the modifier‐matrix interface. Microscopy and mechnical properties confirm that SAA8 does function in this way but less effectively than styrene/maleic anhydride copolymers, which are also miscible with PMMA but evidently react more effectively with the polyamides. The use of ethylene/acrylic acid copolymer for dispersal of the coreshell impact modifier and a styrene/ethylene‐butene/styrene block copolymer in nylon 6 was also briefly considered. Low‐temperature toughness of the blends proved to be a much more critical test of the effectiveness of such additives than room temperature impact strenght.