bluuebunny/crossref_metadata_2025 huggingface dataset:
Solidification behavior and recovery kinetics of liquid crystalline polymers
Authors: Done D. , Baird D. G.
Published: May 2005

The supercooling behavior of three thermotropic liquid crystalline polymers (TLCP's), 60 mole% p‐hydroxybenzoic acid and 40 mole% poly(ethyleneterephthalate), 60/40 PHB/PET, 80 mole% p‐hydroxybenzoic acid and 20 mole% poly(ethyleneterephthalate), 80/20 PHB/PET and a copolyester of 73 mole% p‐hydroxybenzoic acid and 27 mole% of 2‐hydroxy‐6‐naphthoic acid, Vectra A900, was studied by means of both rheological and thermal methods. 60/40 PHB/PET and Vectra A900 exhibited a degree of supercooling as high as 80°C while there was only 20°C of supercooling for 80/20 PHB/PET. The degree of supercooling for the blends of 60/40 PHB/PET and 80/20 PHB/PET also decreased with the increase in 80/20 PHB/PET content. The increase in G′ as the temperature decreased was more gradual for 60/40 PHB/PET and Vectra A900 than that for 80/20 PHB/PET, which was beneficial from a processing point of view. The solidification of the LCP melt was attributed to both the crystallization and the freezing of the mesophase. The degree of crystallinity for all three TLCP's was very small, less than 5%, as measured by the DSC. It was found that both 60/40 PHB/PET and Vectra A900 showed an induction period of a few minutes during solidification while 80/20 PHB/PET solidified continuously at the test temperature. Therefore, 60/40 PHB/PET and Vectra A900 seem to be more suitable for use in processes such as blow molding and film blowing than 80/20 PHB/PET.
Injection molding of polypropylene/polycarbonate blends
Authors: Fisa B. , Favis B. D. , Bourgeois S.
Published: May 2005

This work deals with the effects of material and processing parameters on the mechanical behavior and morphology of noncompatlbilized polypropylene‐polycarbonate (PP‐PC) blends. The blends containing between 0 and 40 vol. percent of polycarbonate were compounded using a twin screw extruder and converted by injection molding using molds with rectangular as well as dogbone shaped cavities. The blends exhibit a complex skin‐core morphology which evolves with the composition. Despite the absence of interfacial adhesion, the low strain modulus increases with PC concentration and follows approximately the Takayanagi model for systems with perfect adhesion. A slight increase of stiffness and strength with increasing PP/PC viscosity ratio is also observed. Weldline strength of these blends is generally poor and decreases with the increasing PC concentration.
The reactive extrusion of polyethylene/polypropylene blends
Authors: Cheung P. , Suwanda D. , Balke S. T.
Published: May 2005

The objective of this work was to investigate the compatibilization of a blend of linear low density polyethylene with polypropylene by Injection of a free radical initiator during extrusion. The reactive extrusion process utilized a single screw extruder equipped with two static mixers. The initiator was injected into the extruder feedport and temperature programming used to cause most reaction to occur within the static mixers. Although elongation at yield was increased by 37 percent, impact strength and yield strength decreased by 17 and 54 percent, respectively. Scanning electron microscopy showed that the maximum size of the dispersed phase decreased from a maximum size of four microns to less than two microns upon addition of initiator. Size exclusion chromatography (SEC), temperature rising elution chromatography (TREF), and differential scanning calorimetry showed that the polypropylene in the blend was degrading while the polyethylene was increasing in molecular size. The combination of SEC and TREF was particularly useful in elucidating this result. No copolymer was discerned by any of the methods used.
Deep drawing self‐reinforced thermoplastic sheet
Authors: Pede Sandro Di , Woodhams Raymond T.
Published: May 2005

The conventional sheet metal forming technique known as Deep Drawing was used to investigate the formability of self‐reinforced thermoplastic sheets. The materials studied included uniaxially roll‐drawn oriented polypropylene (OPP), cross‐rolled biaxially oriented polypropylene (BOPP), and cross‐ply laminated OPP (LOPP). OPP exhibits poor room temperature formability as determined by its Limiting Drawing Ratio (LDR). Its formability is improved at elevated temperatures, but samples suffer from non‐uniform material flow, temperature sensitivity during forming, and a loss of mechanical properties due to the relaxation of orientation caused by the need for forming temperatures above the normal melting point. Although BOPP attains only moderate Improvements in mechanical properties compared to the machine direction of OPP, it exhibits much better room temperature formability. This difference in drawability between uniaxial and biaxial orientation states is a consequence of the difference in planar anisotropy between these two materials. LOPP has the potential of producing a material with superior performance compared to BOPP while still possessing the desirable formability of BOPP. The formed parts, however, undergo cracking in the outer ply parallel to the orientation direction as a consequence of the OPP small elongation to break in the transverse direction. In addition to forming problems, ordered polypropylene exhibits large shrinkage stresses at elevated temperatures. This may preclude its use in applications requiring a high level of dimensional stability. Classical plasticity theory for metals was appropriately modified to model the radial drawing stress for planar isotropic thermoplastic sheet materials.
Constrained optimal batch polymerization reactor control
Authors: Secchi Argimiro R. , Lima Enrique Luis , Pinto José Carlos
Published: May 2005

The theory of optimal control is used to analyze the performance of a batch PMMA (poly(methylmethacrylate)) polymerization reactor. Optimal dynamic profiles of temperature, initiator feed rate, and initiator concentration in the reactor are generated in order for specified conversion of monomer, number molecular weight, and polydispersity of the final product to be obtained. Based on tae physical limitations of the system, some restrictions are imposed to the control variable variations. The application of Pontryagin's Minimum Principle leads to a mixed initial/final value problem, which is solved by discretizing the control law in the state‐space, with the usage of a first order holder. A gradient method is used to minimize the Hamiltonian. The simulation results show that the gel‐effect equation and restrictions imposed on the system are of primary importance to the analysis of the reactor performance.
Biaxially oriented polypropylene blown films. I: Morphological analysis of orientation in the machine direction
Authors: Savolainen Antti
Published: May 2005

In biaxial blown film technology of isotactic polypropylene, PP, the film tube drawn over the mandrel contains considerable morphological disorder. This disorder changes on further treatment to greater order i.e. the para‐crystallinity and the metastable crystal forms diminish as the monoclinic crystal form increases. The morphology change in PP was stimulated by further treatment of the drawn film tube over a mandrel corresponding to conditions of biaxial bubble forming. Analyses were by SEM, Wide‐angle X‐ray diffraction (reflection), DSC, and IR Dichroic measurements. A condenser quality PP, Mw/Mn = 7 and MFI = 3.7, shows a tensile yield at 110°C of 11.4 MPa. A tensile stress of 17.7 MPa was obtained at a blow up ratio of 7; the morphology of PP corresponds to deforming spherulites. The fraction of “perfectly” oriented molecules is 0.53.
Yielding, anisotropy, and deformation processing of polymers
Authors: Batterman S. D. , Bassani J. L.
Published: May 2005

Constitutive equations that characterize the deformation induced anisotropy in polymers at large strains are developed for both flow and deformation (nonlinear elastic) theories of plasticity. These equations are used first to predict the evolution of yield surfaces for anisotropies that develop under simple plane strain deformations. Then, non‐uniform deformations are considered including neck propagation and extrusion. Finite element solutions are based on the flow theory version of the constitutive models. Neck propagation loads and draw ratios are found to be sensitive to the degree of anisotropy and pressure sensitivity, while extrusion forces are less so. The results are compared to solutions for an isotropic material with the same effective stress‐strain behavior.
An experimental and anaiytical investigation of the large strain compressive and tensile response of glassy polymers
Authors: Boyce M. C. , Arruda E. M.
Published: May 2005

In this investigation, the plastic flow of polycarbonate (PC) was examined by obtaining true stress‐strain data over a range of strain rates at room temperature through homogeneous, uniaxial, constant strain rate compression testing to strains as high as 125 percent. Uniaxial compressive loading conditions give rise to a planar molecular orientation process which results in the observed strain hardening in compression. Uniaxial tensile tests on PC were also conducted. The necked region of the tensile specimen is being cold drawn resulting in a uniaxial state of orientation. Therefore, the observed macroscopic strain hardening in uniaxial tension distinctly differs from that obtained In uniaxial compression, giving different stress‐strain curves. The major differences experimentally obtained between the large strain response in compression and tension indicate a need for an orientation‐based model of the strain hardening process. The experimental program also acts to uncouple the effects of strain softening and strain rate providing more accurate data for future modeling of the true strain softening process. A constitutive law which directly relates the strain hardening response to the state of molecular network stretch in the polymer is used to model and analyze the experiments. The model is found to simulate the observed rate dependent yield and post yield strain softening and hardening of the compressive data over the entire range of strain rates very well. The model is then utilized in a finite element analysis of the tensile tests on PC. Numerical results compared favorably with the experimental data including: load vs, contraction curves, natural draw ratio, and the axial stress‐strain response of the cold drawing region.
Effect of damage on fatigue crack propagation in polystyrene
Authors: Chudnovsky A. , Huang W.‐L. , Kunin B.
Published: May 2005

In this paper we examine a conventional approach to correlate the fatigue crack growth rate with fracture mechanics parameters such as stress intensity factor or elastic energy release rate. To simulate a complex loading history we grow a fatigue crack in a vicinity of a hole in a single edge notched specimen under tension‐tension. It is found that the correlation between the crack speed and stress intensity factor, etc. may exist only for limited experimental conditions. In general, fatigue crack growth is inseparable from the evolution of the damage zone preceding the crack, and damage evolution parameters should enter constitutive equations of fatigue crack growth. The essential role of the damage zone in determining the crack trajectory and speed is demonstrated.
Three‐dimensional finite element simulation of thermoforming
Authors: Nied H. F. , Taylor C. A. , Delorenzi H. G.
Published: May 2005

The development of a finite element program specifically designed to simulate thermoforming in complex three‐dimensional geometries is described. The large strain finite element model developed for simulating thermoforming processes is based on a total Lagrangian formulation which results in a nonlinear system of equations that must be solved iteratively. The nonlinear material behavior and contact between the polymer and mold surf aces ieads to additional complications in the numerical solution of the thermoforming simulation problem. In an effort to verify the accuracy of the finite element model developed in this study, analyses are compared with measurements obtained from three‐dimensional three‐formed parts.
A numerical study of bubble growth during low pressure structural foam molding process
Authors: Arefmanesh A. , Advani S. G. , Michaelides E. E.
Published: May 2005

The bubble size distribution created by the expanding foam plays a key role in controlling the load‐bearing and other mechanical properties of the manufactured structural foam part. A numerical method to study the bubble growth and predict the bubble size distribution in polymeric foams is presented. On the microscopic scale, a cell model has been used. A cell is a system composed of a hypothetical spherical gas bubble and an envelope of polymer with constant mass surrounding the bubble. On the macroscopic scale, the foam has been modeled as a compressible medium consisting of a number of cells growing in close proximity to each other. The coupled system of the bubble growth equations for a cell and the field equations for the polymeric fluid are solved numerically to predict the spatial bubble size distribution and the flow front movement during the expansion process. The influence of different dimensionless parameters on the growth of spatially distributed bubbles and on the relative reduction in the transient bulk foam density, under isothermal condition; has been predicted. The existence of an axial pressure gradient in the mold due to the spatial variation of bubble growth is demonstrated through numerical experiments.
Flow induced polymer‐filler interactions: Bound polymer properties and bound polymer‐free polymer phase separation and subsequent phase inversion during mixing
Authors: Akay G.
Published: May 2005

The irreversible absorption of macromolecules on to solid filler particles during mixing in the melt is investigated. The molecular weight and concentration dependence of the absorbed layer thickness are evaluated and the chemical and morphological nature of the irreversibly absorbed polymer (bound polymer) are determined. It is found that the thickness of the bound polymer is not only dependent on the filler concentration but also dependent on polymer molecular weight. Bound polymer in high density polyethylene/colloidal silica systems is more amorphous and contains higher concentration of oxidation products (which are induced by a mechanochemical reaction during mixing) when compared with free polymer. As a result of bound polymer formation, flow induced crystallization and polymer entrapment during mixing, a phase separation between bound polymer and free polymer takes place which eventually leads to a liquid to solid phase inversion when the phase volume of the solids exceed a critical value under isothermal conditions. If the mixing is continued after phase inversion, the particle size of the newly formed powder is reduced and particle size distribution, is narrowed. This process of phase inversion and subsequent size reductions are termed as crumbling which can take place at filler concentrations well below the expected maximum packing fraction of solids, if the filler particle size is small and/or the molecular weight of the polymer is high. Crumbling phenomena are utilized in the agglomeration of fine powders and microencapsulation of solids and/or liquids.
Numerical and experimental studies of the flow in the nip region of a partially intermeshing co‐rotating twin‐screw extruder
Authors: Sastrohartono T. , Esseghir M. , Kwon T. H. , Sernas V.
Published: May 2005

The flow pattern within a partially intermeshing co‐rotating twin‐screw extruder is three dimensional and extremely complex. In order to simplify the problem, a slice perpendicular to the axis of the twin‐screw extruder has been considered for flow analysis as a two‐dimensional or a quasi‐three‐dimensional problem. The flow in this slice may be considered to consist of a nip region (located between the two screws) and a translation region in which the movement of the material is very similar to the one found in single‐screw extruders. The flow in these two regions have been studied separately. This paper presents the numerical and experimental results of the nip region study. The flow division in the nip region has been quantified and results are presented in terms of a flow division ratio Xf. The flow field patterns have also been obtained. Newtonian as well as non‐Newtonian behavior has been investigated. The influences of such factors as (i) the geometry (the radius of the barrel, radius of the screw, distance between the two screws), (ii) the material properties (the power‐law index for shear rate dependent viscosity), and (iii) processing conditions (the screw speed), have also been studied.
Mechanical property and residual stress development during cure of a graphite/BMI composite
Authors: White S. R. , Hahn H. T.
Published: May 2005

Residual stresses in composites are developed during processing due to chemical shrinkage of the resin and the thermal mismatch between the constituent materials. How these residual stresses develop during cure is not fully understood. Furthermore, to model their development during cure the effect of cure on composite mechanical properties must be understood. This study addresses such concerns. Warpage of [04/904];T cross‐ply specimens was measured to monitor residual stress build‐up. Fiber‐dominated properties were found to increase moderately with cure extent. Matrix‐dominated properties increased significantly and were highly dependent on degree of cure. The curvature development was found to be elastic and could be predicted by laminated plate theory while neglecting chemical shrinkage. Thermal strains were found to remain essentially constant with cure time.
Scale‐up of counter‐rotating closely intermeshing twin screw extruders without and with reactions
Authors: Ganzeveld K. J. , Janssen L. P. B. M.
Published: May 2005

Many scale‐up rules and theories have been presented in the area of extrusion. Until now all the theories concerned the single screw extruder. As the use of counter‐rotating twin screw extruders is increasing, it becomes important to propose scale‐up rules for this kind of extruder. Therefore a basic analysis of scale‐up in a twin screw extruder has been developed. It can be concluded that important factors scaling up a twin screw extruder are the fully filled length and the leakage flows of the extruder. So hydrodynamic similarity has to be assured in the scale‐up of most processes. However no serious constraints are put on the throughput of the extruder by this consideration. When the extruder is scaled up on the basis of thermal similarity the Brinkmann number is of importance. At low Brinkmann numbers the throughput is unfavorably affected by scale‐up. If the Brinkmann number is high the throughput is proportional to the diameter cubed. If the extruder is used as a chemical reactor for polymerization, an increasing area of research, the scale‐up rules are dependent on the Damköhler IV number. For low Damköhler IV numbers no consistent scale rules are found. However if the Damköhler IV number is high, useful rules for the scale‐up can be derived.
Extrudate swell and drawdown effects on extruded profile dimensions and shape
Authors: Huneault Michel A. , Lafleur Pierre G. , Carreau Pierre J.
Published: May 2005

Plastic profile die design is a complex task because of cross section area and shape changes occurring after die exit. Dimensions of the profile are increased by the extrudate swell phenomenon and decreased by drawdown and shrinkage. An experimental study on the effect of processing conditions on extrudate swell and on the shape of a rectangular profile was done for rigid poly(vinyl chloride), PVC, and high density polyethylene, HDPE, resins. Extrudate swell was found to be a strong decreasing function of residence time in the die and also, for short dies, of entrance geometry. For PVC, equilibrium swell increased with melt temperature. The differences in swelling for the two polymers are explained with the help of creep/recovery data obtained on a stress rheometer. Drawdown, die land length, and melt temperature were shown to have an important effect on the shape of a rectangular profile. Decreasing the die land and increasing the melt temperature had the effect of increasing preferably the thickness while drawdown, by inhibiting the swelling, decreased the thickness.
371°C (700°F) properties of celion 6000/N‐phenylnadimide modified pmr polyimide composites
Authors: Pater Ruth H.
Published: May 2005

The 371°C (700°F) properties of Celion 6000/N‐phenylnadimide modified PMR‐15 polyimide composites were investigated to determine the feasibility of using these materials at a 371°C (700°F) service temperature. The processing characteristics and physical and mechanical properties of the composite systems are presented. The results of the 371°C thermooxidative stability study suggest that the composite materials can be considered for short‐term (at least 100 hours) application at 371°C.
Phase morphology of injection‐molded blends of nylon‐6 and polyethylene and comparison with compression molding
Authors: Ghiam Farid , White James L.
Published: May 2005

An experimental study is presented of the development of phase morphology in injection and compression molding of 80/20 and 60/40 nylon‐6/polyethylene blends and its evolution during annealing. The phase morphology of the compression‐molded part is isotropic, while that of both screw and ram injection‐molded parts is both heterogeneous and anisotropic through the cross section. In the injection‐molded parts, the morphology exhibits its greatest level of isotropy in the core and becomes increasingly anisotropic approaching the mold wall (through the thinnest cross section); i.e., the 2 direction. There is an intermediate position of maximum anisotropy. Sections made in various directions indicate that the dispersed phase forms platelets oriented in the plane of the machine and width directions. The position of maximum anisotropy seems to represent a frozen layer thickness that increases with decreasing mold temperature and with decreasing injection rate into the mold. Annealing studies show coalescence in both compression‐ and injection‐molded bars. The greatest coalescence occurs in the injection‐molded parts near the positions of greatest anisotropy of morphology. This suggests that coalescence is associated with collisions between dispersed phase globules as their sphericity increases.
Characteristics of binary and ternary blends of poly (p‐phenylene sulfide) with poly(bis phenol A) sulfone and polyetherimide
Authors: Akhtar Sania , White James L.
Published: May 2005

An experimental study of the phase morphology and mechanical properties of binary blends of poly(p‐phenylene sulfide) (PPS) with both polyetherimide (PEI) and poly(bis phenol A) sulfone (PSF) is described. We also study the ternary system PPS‐PEI‐PSF. Differential scanning calirometry indicated the blends are immiscible; these findings were confirmed by scanning electron microscopy. Both PEI and PSF were found capable of improving the impact strength and elongation‐to‐break characteristics of PPS in binary blends and ternary systems.
A unified simulation of the filling and postfilling stages in injection molding. Part I: Formulation
Authors: Chiang H. H. , Hieber C. A. , Wang K. K.
Published: May 2005

This study employs a unified theoretical model to simulate the filling and postfilling stages of the injection‐molding process. Implementation of such a model is based on a hybrid finite‐element/finite‐difference numerical solution of the generalized Hele‐Shaw flow of a compressible viscous fluid under nonisothermal conditions. The shear viscosity of the polymeric material is represented by a Cross model for the shear‐rate dependence and a WLF‐type functional form for the temperature and pressure dependence, whereas the specific volume is modeled in terms of a double‐domain Tait equation. The analysis also handles variable specific heat and thermal conductivity of the polymer as a function of temperature. Complex thin parts of variable thickness can be modeled and discretized by flat, triangular finite elements which may have arbitrary orientation in three‐dimensional space, whereas runners and possible round pins or bosses in the part are represented as one‐dimensional circular‐tube elements. A control‐volume scheme is employed that leads to automatic melt‐front advancement during the cavity‐filling stage.
The effects of physical aging on the thermal and mechanical properties of an epoxy polymer
Authors: Jo Won Ho , Ko Kyoung Jin
Published: May 2005

The effects of free volume on the thermal and mechanical properties of epoxies from diglycidyl ether of bisphenol A (DGEBA) and ethylene diamine (EDA) were investigated. The degree of free volume was controlled by the different thermal history. For fully cured expoxy systems, the density and modulus of both aged and quenched specimens decreased with increasing EDA concentration. However the yield stress of quenched specimens showed a maximum at about equal stoichiometric formulation, while that of aged ones decreased with increasing EDA concentration.
Polymer‐polymer interdiffusion during coextrusion
Authors: Kim Jin Kon , Han Chang Dae
Published: May 2005

Polymer‐polymer interdiffusion during coextrusion is considered theoretically from the point of view of interdiffusion between two melt streams flowing side by side in a film or sheet coextrusion die. It has been found that three factors, namely, molecular weight, the interaction parameter, and polydispersity have a profound influence on the interfacial layer thickness and adhesive bond strength of coextruded films and sheets. It is pointed out that when interdiffusion between two chemically dissimilar polymers takes place In stratified two‐phase flow, the chain orientation in the flow channel greatly influences the rate of interdiffusion, and consequently the interfacial layer thickness and adhesive bond strength. Orientation factors for macromolecular chains in a steady shear flow field are expressed in terms of shear stress at the interface and the plateau modulus of each of the respective polymers being coextruded. As an illustration, we have used information on the self‐diffusion coefficients for poly(vinylidene fluoride) and poly(methyl methacrylate) in the molten state, to estimate the interfacial layer thickness and adhesive bond strength of coextruded two‐layer sheets, as affected by processing variables.
Ultrasonic velocity and attenuation of polymeric solids under oscillatory deformation. II: High density and linear low density polyethylene and their blends
Authors: Tanaka Akira , Nitta Koh‐Hei
Published: May 2005

In order to understand the viscoelastic non‐linearities in polyethylene, dynamic ultrasonic properties of high density polyethylene (HDPE), linear low density polyethylene (LLDPE) and their blends were studied. In the case of HDPE and HDPE‐rich films, for which the nonlinearity is high, the dynamic attenuation coefficient increased with the dynamic strain amplitude. The increase in the attenuation coefficient can be ascribed to plastic deformations such as defect‐ and/or void‐formation in the spherulites. On the other hand, in LLDPE and LLDPE‐rich blends for which the nonlinearity is low, the attenuation coefficient decreased with strain. The decrease in the attenuation coefficient can be ascribed to the orientation of lamellae. Thus, it was concluded that the viscoelastic nonlinearity of polyethylene is caused by plastic deformation. This conclusion was also deduced from other dynamic ultrasonic quantities such as the dynamic viscosity and dynamic density.
Effect of annealing on the properties of poly(ether ether ketone)
Authors: Arzak A. , Eguiazábal J. I. , Nazábal J.
Published: May 2005

The effect of annealing on the properties of poly(ether ether ketone) has been studied by changing annealing temperature and time. Crystallinity increases with annealing temperature, but is little affected by annealing time. Annealing time results suggest an improved crystalline perfection as annealing time increases. Higher crystallinity levels cause an increase in stress‐related properties and a decrease in strain‐related properties. Crystalline perfection, however, seems to produce an increase in stress‐related properties, but it does not affect strain‐related properties. Consideration has also been given to the effect of other possible parameters different from crystalline structure, such as crosslinking, on the variation of properties.
Anisotropic thermal expansion of densely cross‐linked oriented polymer networks
Authors: Broer Dirk J. , Mol Grietje N.
Published: May 2005

Densely cross‐linked oriented polymer networks are made by in‐situ photopolymerization of oriented liquid‐crystalline diacrylates. Freestanding films that exhibited highly, anisotropic thermal expansion were prepared. The influence of the molecular structure and type and degree of orientation on the anisotrpic thermal expansion is described. The expansion coefficient of uniaxially oriented networks in the direction of the molecular orientation is slightly positive at temperatures below the glass transition of the networks and becomes negative as soon as this transition sets in the result is an effectively zero expansion over a wide temperature range. By introducing a molecular helix in, the network perpendicular to the film surface, a low thermal expansion is established in two directions in the plane of the film or coating.
Solvent penetration in cured epoxy networks
Authors: Kaplan Martin L.
Published: May 2005

The kinetics of the sorption characteristics of seven different solvents has been measured at 22°, 40°, and 50°C in several cured epoxies. In addition to water, the organic solvents methanol, acetone, isopropanol, ethyl acetate, 1,2‐dichloroethane, and toluene were examined. The resin, diglycidyl ether of bisphenol A, was cured with four hardeners, each one resulting in a different epoxy material. The curing agents include triethylenetetramine, nadic methylanhydride, dicyandiamide and m‐phenylenediamine, all commonly used substances. Data were analyzed using Fick's diffusion equation. In general, three types of behavior were observed, Fickian diffusion, Case II diffusion, and anomalous diffusion. Fickian or anomalous behavior dominated at all temperatures. Diffusion was both material and solvent dependent. The anomalous nature of isopropanol was noted. Although chemically similar to methanol and about the same size, as acetone, isopropanol is sorbed at a much lower rate. A combination of physical and chemical effects appeared to be responsible for the observations in the epoxies. Diffusion coefficients were estimated for all penetrants and were mostly in the range of 10−9 to 10−11 cm2/s. Where appropriate, apparent activation energies for diffusion were calculated from the kinetic curves.
A fatigue test for controlling the quality of polyethylene copolymers
Authors: Zhou Y. , Lu X. , Brown Norman
Published: May 2005

The lifetimes of 17 commercial ethylene‐hexene copolymers were measured under fatigue and constant load. These LLDPE resins all had about the same melt flow index and density, but their lifetimes under fatigue and constant load varied by factors of 17 to 104, respectively. The lifetimes in fatigue were 1/25 to 1/2000 times the lifetime under constant load, but the ranking of the resins in fatigue with respect to their resistance to slow crack growth correlated with the ranking under a constant load. It is recommended that a tensile fatigue test on a notched specimen is a useful short time test for the quality control of ethylenehexene copolymers that may be used for gas pipes or other critical applications.
Compatibilization of polymer blends by reactive processing
Authors: Xanthos M. , Dagli S. S.
Published: May 2005

This review examines some recent developments in the field of reactive compatibilization of polymer blends by melt processing in extruders and intensive batch mixers. Three routes to reactive compatibilization are considered, namely, the use of suitably functionalized blend constituents, the incorporation of polymeric compatibilizers, and the addition of low molecular weight compounds. Representative systems from the recent patent and open literature are classified according to method and assumed mechanism of compatibilization, and the types of chemical reactions involved. A variety of polymer blends are discussed, including impact modified thermoplastics, polymer modified engineering thermoplastics, dynamically vulcanized thermoplastic elastomers, and co‐crosslinked rubber/rubber blends. Examples of potential opportunities in reactive compatibilization are also presented.
Modeling of mold filling process for powder injection molding
Authors: Najmi Liaquat Ali , Lee Daeyong
Published: May 2005

The mold filling process has been modeled for the injection molding of different polymer‐based binders and powder‐polymer mixtures. It is essentially a two dimensional non‐Newtonian fluid flow analysis in a non‐isothermal environment. A complete analysis is accomplished by combining a finite element method and control volume technique to describe an increment of flow front movement, whereas a finite difference method is used to solve the energy equation to characterize the temperature distribution. Numerical results are compared to exact solutions for a circular ring cavity using a power law fluid model under an isothermal condition. Comparison of computed results against published data for a simple circular disk shows good agreement between the two analysis methods. After making selected comparison studies, it is demonstrated that the filling process in Powder Injection Modeling with different combination of powder‐polymer mixtures is markedly dependent on specific combinations of powder; and polymer based binders. Computed flow front results for a rectangular cavity also compared favorably against the data for a power law fluid model under non‐isothermal conditions.
Nylon/Kevlar composites. I: Mechanical properties
Authors: Yu Z. , Ait‐Kadi A. , Brisson J.
Published: May 2005

This paper deals with the characterization of the mechanical properties of Kevlar/nylon composites. It has been shown that addition of up to 5 % Kevlar to nylon matrices (nylon‐6, nylon‐ 11, and nylon‐6,6) is possible by melt blending, and results in improved mechanical properties as compared to the pure matrix. In order to increase the interfacial adhesion of the fibers and the matrix, various chemical treatments were performed on the fibers: surface hydrolysis, succinyl chloride reactions and suberoyl chloride reactions. These were shown to affect significantly the mechanical properties, and depending on the treatment Of the fiber, improvement or deterioration of the mechanical properties could be observed. The effect of humidity has also been investigated, and it was shown that the addition of Kevlar greatly reduced the susceptibility of the tensile modulus to humidity.
On the mode I delamination test and the importance of laminate lay‐ups
Authors: Benzeggagh M. L. , Gong X. J. , Laksimi A. , Roelandt J. M.
Published: May 2005

The aim of this work has been the study of mode I delamination of multiply double cantilever beam specimens of glass fiber/epoxy. The results show an important influence of laminate lay‐ups on delamination resistance. The value ofGIcat the initiation of delamination varies with laminate curvature couplingKy/KxandKxy/Kx. An empirical model describing this variation has been proposed. In addition, it is seen that the values ofGIcat the initiation of delamination and at stable crack growth will be very different. The delamination resistance can be characterized by two constants:GIccorresponds to the initiation of delamination, andGSIpcorresponds to the plateau of stable crack propagation. The correlation between experimental measurement and analysis of compliance and energy release rate results reveals significant three‐dimensional effects.
Impact and compression response of composite materials containing fortifiers
Authors: Scott R. F. , Lee S. , Poon C. , Gaudert P. C.
Published: May 2005

The effect of adding fortifiers to an epoxy matrix on the response to impact and compression‐after‐impact properties of carbon fabric/epoxy laminates was investigated. The experimental work included determining laminate compression strength, absorbed energy from impact, damage area and compression‐after‐impact strength for an impact energy level of 21 joules per centimeter of thickness. This paper presents the results from this investigation and discusses the relationship between neat resin properties (with and without fortifiers) and the laminate properties.
Weldline strength in injection molded glass fiber‐reinforced polypropylene
Authors: Fisa B. , Rahmani M.
Published: May 2005

Weldlines are inescapable byproducts of the injection molding process. They represent potentially fatal flaws particularly in multiphase materials. In this work weldlines in injection molded glass fiber‐reinforced polypropylene (0 to 40wt%) were studied as a function of the cavity shapes and depths. It was found that the weldline is a zone between 2 and 8 mm wide extending throughout the thickness in which the fibers are oriented almost perfectly in a plane parallel to the weldline. While the strength of moldings without weldlines depends on the mold shape and on the fiber concentration, the weldline strength is a function of fiber content only. A simple model based on the assumption of complete debonding of the fiber‐matrix interface when failure occurs can be used to predict the strength loss in the weldline.
Crystallization of polymer melts under fast cooling. I: Nucleated polyamide 6
Authors: Brucato V. , Crippa G. , Piccarolo S. , Titomanlio G.
Published: May 2005

Samples of nucleated polyamide 6 were quenched from the melt so as to monitor cooling histories. Their morphology and crystal structures were discussed in relation to sample thermal history; cooling history relevant to quenched sample morphology was recognized as being confined in the interval 110 to 160°C. In particular, samples were essentially amorphous for cooling rates larger than 200°C/s. The γ‐crystalline form was observed for cooling rates in the interval 70 to 200°C/s, whereas α crystalline structure was found dominant for yet lower cooling rates. Crystallinities evaluated from densities of quenched samples were compared with predictions of an isokinetic form of the Avrami model for polymer crystallization kinetics.
Property modifications in poly(p‐phenylene benzobisthiazole) fibers with high‐tension and high‐temperature drying versus postprocessing heat treatment
Authors: Pottick L. A. , Farris R. J.
Published: May 2005

Modifications in the structure and mechanics of poly(p‐phenylene benzobisthiazole) (PBT) fibers have been attempted through high‐tension and hightemperature drying and subsequent postprocessing heat treatment experiments. High‐tension drying results in an enhancement in tensile properties by offsetting compressive shrinkage stresses during the drying process and improving the molecular alignment within the fiber. Elevated temperature drying under tension further improves the extent and perfection of the lateral molecular order. The increased molecular ordering and improved tensile properties are believed to result from the removal of water and residual acid at elevated temperatures. The final fiber properties after subsequent postprocessing heat treatment are independent of the drying conditions. These results suggest that the ultimate fiber properties are a function of the total strain imposed in all the processing operations (dry jet stretch region, coagulation and drying process, postprocessing heat treatment). The attainment of the fiber's theoretical highmodulus/high‐strength properties appears limited by defects such as voids and internal stresses which, in turn, restrict the amount of strain imposed during the fiber process.
Polycarbonate‐polystyrene block copolymers and their application as compatibilzing agents in polymer blends
Authors: Jiang Rishan , Quirk Roderic P. , White James L. , Min Kyonsuku
Published: May 2005

The synthesis of a block copolymer with polystyrene (PS) and polycarbonate (PC) segments is described. It is produced by anionic polymerization of the styrene and endcapping with a hydroxyl group followed by subsequent reaction with phosgene and bisphenol‐A. The polystyrene/polycarbonate block copolymer was used as a compatibilizing agent for blends of poly(ethylene terephthalate) (PET) and poly(p‐ phenylene oxide) (PPO). The block copolymer reduced the dimensions of the dispersed phase. The uniaxial mechanical properties of the compatibilized blends were improved by 5 to 10 wt% loadings of the copolymer.
Flow curve–molecular weight distribution: Is the solution of the inverse problem possible?
Authors: Malkin Alexander Ya. , Teishev Albert E.
Published: May 2005

Several different theoretical models have been developed relating the flow curve of a polymer melt to its molecular weight distribution (MWD). These models allow calculation of the flow curve if MWD is known beforehand. According to one model the non‐Newtonian behavior of a polymer melt is considered as a consequence of the gradual transition of high molecular weight (MW) fractions to the rubbery (non‐fluid) state. This model, which gives realistic predictions of the flow curve, can be transformed into the equation for MWD, which appears to be directly related to the flow curve. The derived equation seems to present the exact solution of this inverse problem. Nevertheless, calculation tests show the instability of such a solution. This means that any inevitable experimental error in the flow curve measurements can lead to an unexpected and arbitrary wide divergence of the calculated MWD from the true one. However, if definite preset forms of MWD are used, the MWD width can be determined from the flow curve. This has been confirmed by experiments on different polymers, such as low‐density polyethylene (LDPE), polyisoprene (PI), butyl rubber (BR), and polystyrene (PS).
Analysis of polymer membrane formation through spinodal decomposition. II: Effect of Flory‐Huggins enthalpic and entropic contributions
Authors: Laxminarayan Anand , Caneba Gerard T.
Published: May 2005

The phenomenological analysis of the thermal inversion membrane formation through spinodal decomposition was further developed to include enthalpic and entropic contributions to the Flory‐Huggins interaction parameter. We found that material and processing conditions can be lumped into two parameters. One is the Deborah Number, De, which takes into account the thermal quenching relative to the phase separation induction time. The other one, designated as an ε‐parameter, takes into account the quenching temperature relative to the spinodal temperature and the ratio of the enthalpic to the entropic contributions to the Flory‐Huggins interaction parameter. From the model system, we found that the dimensionless interdomain distance, δ, as a function of 1/De (which is proportional to the cooling rate) falls in a relatively narrow banded region for all practical values of ε. As 1/De approaches infinity, δ is asymptotic up to maximum value of 3.5. This means that membranes made under applicable conditions will have a ratio of pore sizes of no more than 3.5. Other assumptions of the model are: (1) the mobility is temperature‐independent; (2) the mutual diffusivity is a linear function of temperature; and (3) the thermal history (Temperature vs. Time), can be represented as two successive linear functions.
Migration and blooming of stabilizing antioxidants in polypropylene
Authors: Spatafore Rinamarie , Pearson L. Timothy
Published: May 2005

We have studied the migration of the hindered phenol, octadecyl‐3,5‐bis (1,1‐dimethylethyl)‐4‐hydroxybenzenepropanoate, and the phosphite co‐stabilizer tris 2,4‐bis(1,1‐dimethylethyl)phenylphosphite, out of films of polypropylene (nominal melt flow 3.5 g/10 min). Loss of additive from an initial 10% weight‐% level in the polymer was followed by FTIR bands in the appropriate regions. Temperatures of 298 K, 313 K and 333 K were used. An attempt was made to analyze migration data using Fick's law for diffusion by means of a least squares fit. Octadecyl‐3,5‐bis (1.1‐dim ethylethyl)‐4‐hydroxybenzenepropanoate diffused according to Fick's law with a temperature independent diffusion constant (D = 1.27 × 10−15 m2 S−1) to a steady state concentration of 7.2 % + −0.56 weight‐%. The phosphite did not diffuse at all at 298 K and 313 K, but diffused with D = 8.1 × 10−16 m2 S−1 to a steady level at 333 K. Our interpretation of the phosphite migration data assumes that most of the phosphite in the sample is immobilized. A subset of the total phosphite level is free to diffuse to the surface of the polymer.
Compatibilized and dynamically vulcanized thermoplastic elastomer blends of poly(butylene terephthalate) and ethylene propylene diene rubber
Authors: Moffett A. J. , Dekkerrs M. E. J.
Published: May 2005

Compatibilized and dynamically vulcanized thermoplastic elastomer blends of poly(butylene terephthalate) (PBT) and ethylene propylene diene terpolymer (EPDM) can be prepared by using an EPDM rubber that contains reactive epoxy groups. During melt mixing the epoxy groups react with PBT endgroups to form graft copolymer. The compatibilized blends can be dynamically vulcanized by conventional vulcanization agents for EPDM such as peroxides or by vulcanization agents that react with residual epoxy groups on the EPDM such as diamines. This paper describes the effects of compatibilization and dynamic vulcanization on microstructure and mechanical properties.
Dielectric characterization of water sorption in epoxy resin matrices
Authors: Maffezzoli A. M. , Peterson L. , Seferis J. C. , Kenny J. , Nicolais L.
Published: May 2005

Water sorption in epoxy based materials was analyzed by dielectric spectroscopy using remote sensors. A method to determine diffusion coefficients from the changes in permittivity during water absorption is proposed and was verified experimentally by comparison with standard water gain measurements. Although the technique is limited by electrode polarization phenomena, it is sensitive to the presence of water molecules and is capable of detecting different levels of water concentration as a function of frequency. The utilization of remote sensors demonstrated the capability of dielectric analysis to be applied both in the laboratory environment, and on a larger scale, as a nondestructive technique for monitoring environmental changes in actual polymer matrix composite parts.
The use of cryogenically ground rubber tires as a filler in polyolefin blends
Authors: Oliphant K. , Baker W. E.
Published: May 2005

The effects of cryogenically ground rubber tires (CGT) on some of the mechanical properties of blends with linear low density polyethylene (LLDPE) and high density polyethylene (HDPE) are presented. Precoating the CGT particles with an ethylene‐acrylic acid copolymer is shown to overcome most of the deleterious effects of adding CGT to LLDPE, while still retaining composite processability. A blend of 40 wt% EAA coated CGT particles with LLDPE is shown to have impact and tensile strengths that are 90% of those for the pure LLDPE, representing increases of 60 and 20%, respectively, over blends with uncoated particles. Blends of LLDPE with ground tire bladders demonstrate that even better mechanical properties can be obtained with similar large rubber particle size but somewhat better adhesion. For HDPE, however, it is shown that with large rubber particles, moderate adhesion is not sufficient to produce useful composites.