bluuebunny/crossref_metadata_2025 huggingface dataset:
Buildup and relaxation of molecular orientation in injection molding. Part I: Formulation
Authors: Flaman A. A. M.
Published: May 2005

A numerical simulation model for the analysis of the buildup and, the relaxation of molecular orientation in injection‐molded products has been developed. The constitutive equations of the material are described using an extended version of the viscoelastic material model developed by Leonov. The volumetric responses are described using two different equations of state, the Tait equation and an equation developed by Spencer and Gilmore. A WLF‐type of equation is used for the temperature and pressure dependence. Stresses calculated with the model are coupled to birefringence by means of the stress‐optical rule. Birefringence, in turn, is used to characterize the molecular orientation. The model is used to investigate the influence of the processing conditions, the mold elasticity, and the pressure dependence of the material functions on the pressure and birefringence profiles. The material data used are for polystyrene, PS 678E, and are determined experimentally.
Plane strain and plane stress analysis of fatigue crack propagation in medium density polyethylene pipe materials
Authors: Strebel J. J. , Moet A.
Published: May 2005

Using the Crack Layer Theory, differences in damage formation under different stress states during fatigue crack propagation in an ethylene‐butene copolymer were quantified and compared. Despite having vastly different stress states and crack propagation behaviors, arc specimens (28 mm thick) and single edge notched (SEN) specimens (2 mm thick) were shown to have the same specific enthalpy of damage, ∼300 J/g, a parameter in the Crack Layer Theory that is a measure of the material's intrinsic toughness. Damage in the SEN specimen consisted of crazing the significant material yielding; the latter damage type is associated with plane stress conditions. In the predominantly plane strain arc specimen, material yielding was minimal compared to crazing, the dominant damage form. After measuring these damage forms and applying the Crack Layer Theory, the constancy of the specific enthalpy of damage was established. Also the dissipation coefficient, β, a second parameter of the Crack Layer Theory, was shown to be a process‐dependent parameter, which was inversely proportional to the lifetime of the specimen: βSEN = 4.6 × 10−5, βarc = 1.1 × 10−4, which corresponds to lifetimes of 140,000 and 30,000 cycles to failure, respectively.
Development of high performance, waterborne coatings. Part I: Emulsification of epoxy resin
Authors: Kojima Shunji , Watanabe Yoshiki
Published: May 2005

A new manufacturing process of high performance, waterborne coatings for can coating applications is developed, which includes emulsification of an epoxy resin with or without its hardener by incorporation of an acrylic resin. It becomes possible by this new process to emulsify a variety of resins with minimum effects of the surfactant acrylic resin. Thus, latitude to design formulations is widened and the performance of epoxy resin and its hardener can be fully developed.
Computer modeling of polymeric materials: Single chains and multiple‐chain systems
Authors: Galiatsatos Vassilios
Published: May 2005

Applications of molecular modeling techniques to the prediction of the properties of polymers are presented. First, a brief overview of the various polymer modeling techniques is presented with a focus on which technique is suitable for which properties. Recent results from current research are shown. The first set of results is from work on the statistical correlation of two physical properties (end‐to‐end distance and dipole moment) of single polymer chains with independent rotational potentials. It is shown that the correlation depends on the orientation of the dipole moment vector. The second set of results reviews work on computer simulation of the irradiation cure of polyethylene. Structural information regarding the crosslinks formed is presented.
Analysis of the coupling between the apparent time scale of thermal degradation and sample size
Authors: Cohen Arie , Carriere Craig J. , Pasztor Andrew J.
Published: May 2005

Sample size sensitivity of thermal gravimetric analysis (TGA) presents a serious handicap in the obtaining of reliable thermal stability data for high‐temperature applications. For example, predictions of the apparent time for degradation during an isothermal experiment based on the results obtained using a 10 μm thick specimen can be off by an order of magnitude when applied to a product with a thickness of 10 cm. To address this effect, TGA experiments studying the thermal degradation of poly(methyl methacrylate) were conducted. Analysis of the experimental data resulted in the development of a relationship between the apparent time scale of the thermal degradation and the specimen thickness. Origins of the new dependence were traced to the change of the diffusivity resulting from material volatilization. Implications of the coupling between these two events for the analysis of thermal stability for new polymeric materials are discussed, and required changes in the current methodology are outlined.
Percolation in electrical conductive polymer / filler systems. I: Density/ filler curves according to a new thermodynamic percolation model
Authors: Lux F.
Published: May 2005

This work deals with the conductivity of polymer/filler‐mixtures, with the conductive filler particles of colloid size. For the interpretation of the conductivity course in such systems Wessling recently proposed a new thermodynamical percolation model, the so‐called “dynamic boundary model.” A consequence of the dynamic boundary model is a fixed picture for some properties of the mixtures, i.e., the density should vary in a defined manner according to the theoretical assumptions of the model. The current paper first gives a short description of the percolation process according to the dynamic boundary model. Second, the derivation of the density/filler concentration curves according to the assumption of this model is given. Third, a comparison is made between calculated and experimentally determined density/filler concentration curves. It is shown that the dynamic boundary model cannot account for the experimentally observed density curves.
Filling of a complex‐shaped mold with a viscoelastic polymer. Part I: The mathematical model
Authors: Papathanasiou Thanasis D. , Kamal M. R.
Published: May 2005

A model for the filling stage of injection molding of viscoelastic thermoplastics in cavities of complex shape is presented. The model considers two‐dimensional melt flow, with converging and diverging flow patterns induced by complex boundary shape and by the presence of an obstacle. The model is non‐isothermal (with the melt loosing heat to the mold walls as it travels into the cavity) and handles a viscoelastic (following the White‐Metzner model) material with properties that vary with temperature, shear rate, and pressure. The numerical method is based on finite differences, with boundary fitted curvilinear coordinates used in the mapping of the flow field (which has an arbitrary shape that evolves with time) into a time invariant rectangle. The numerical results reveal geometry‐induced asymmetries in the flow and thermal fields as well as the effect of various process parameters on the pressure and temperature profiles in the cavity. The model admits variable cavity thickness, thus allowing for a treatment of the cavity thickness as a process parameter in the simulations.
Free radical degradation of polypropylene: Random chain scission
Authors: Triacca V. J. , Gloor P. E. , Zhu S. , Hrymak A. N. , Hamielec A. E.
Published: May 2005

Free‐radical reactions, which are relevant in the chemical modification of polymeric materials, are discussed in relationship to their influence on random chain scission. A mathematical model is developed to calculate the entire molecular weight distribution (MWD) with the degree of chain scission as the sole parameter. This expression is identical to the one derived by Saito for the case of scission initiated by irradiation. An expression for the variation of molecular weight averages with the degree of chain scission is derived and compared with those calculated with the methods of moments found in the literature. The validity of empirical closure conditions used with moment methods is discussed. Experimental data for polypropylene (PP), degraded with organic peroxides in a single screw extruder, are compared with predictions when fitting the degree of chain scission. For a specific degradation process, the degree of chain scission is found to be proportional to the initiator level.
Investigation of polymeric materials using the cone calorimeter
Authors: Goff Leslie J.
Published: May 2005

The use of polymeric materials in building or construction applications is steadily increasing. Therefore, the potential for these materials to be exposed to fire is also increased. The understanding of the pyrolysis characteristics of these materials is thus a necessity. There are many standard tests used to evaluate materials. Unfortunately, the correlation between these tests and large scale fire is less than desirable. A new bench scale rate of heat release apparatus, the Cone Calorimeter, is now being used more frequently in pyrolysis testing of polymeric materials. This apparatus has been shown to correlate much better between room scale testing and large scale fire testing. The cone Calorimeter provides a pyrolysis profile of a material under ambient oxygen conditions. Characteristics such as ignition time, total heat release, maximum rate of heat release, mass loss during pyrolysis, CO2, CO, and smoke production are determined. In this work several almost neat polymers are examined and the general pyrolysis characteristics of these polymers are discussed. The objective of this work is to provide information of basic polymeric pyrolysis properties of these materials. Variations in the material, i.e., molecular weight, polydispersity, and residual catalysis, along with changes in testing procedures, can have dramatic effects on results. Obviously the addition of flame retardant and flame retardant packages to any of these materials will have dramatic effects on results.
The origin of β relaxations in segmented rigid‐rod polyimide and copolyimide films
Authors: Arnold Fred E. , Bruno Katie R. , Shen Dexing , Eashoo Mark , Lee Chul Joo , Harris Frank W. , Cheng Stephen Z. D.
Published: May 2005

Most aromatic polyimides and copolyimides show a β relaxation process below their α relaxation processes in dynamic mechanical and dielectric measurements. The origin of this β relaxation has been under active discussion. In order to gain a better understanding of the origin of the β relaxation process, the dynamic mechanical behavior of a series of segmented rigid‐rod polyimide and copolyimide films with different dianhydrides and diamines has been systematically studied. For some of the polymers, crystallinity and orientation effects on the β relaxation process were also investigated. It is found that the β relaxation process in the unoriented films can mainly be attributed to a relatively noncooperative motion in uncrystallized diamines. However, this noncooperative nature may be gradually lost by increasing the crystallinity and orientation. Molecular modeling and computation have led to a discussion of possible diamine motion in the β relaxation process.
Creep‐based characterization of nonlinear relaxation behavior of plastics
Authors: Brueller O. S. , Steiner H.
Published: May 2005

It is a matter of fact that creep experiments can be conducted more easily and accurately than stress relaxation experiments, since it is easier to maintain a stress constant (for instance by a “dead weight”) than a strain constant. Nevertheless, in practice, structural parts made of plastics (which are nonlinear viscoelastic materials) are very often loaded under stress‐relaxation conditions. The present paper presents an approach to predict the behavior of a nonlinear viscoelastic material under stress‐relaxation‐type loading, based on data obtained from creep‐type experiments. The nonlinear creep compliance is described mathematically by an exponential series with a limited number of terms and a single nonlinearity function depicting the transient behavior. The nonlinear behavior of the material under constant strain (i.e., stress relaxation) is then obtained by dividing the considered time range into very short time intervals in which constant stresses are acting, while the different values of the applied stresses are chosen in a manner that guarantees the same stain at the end of each interval. In this way, one performs a numerical nonlinear superposition of the effects of the loadings in the various intervals, leading to the desired results under stress relaxation. A comparison of theoretical results with experiments conducted on some thermoplastic materials shows good agreement.
The anisotropy of slow crack growth in polyethylene pipes
Authors: Lu Xici , Zhou Zhiqiang , Brown Norman
Published: May 2005

Slow crack growth was measured in the perpendicular and parallel directions relative to the extrusion direction of the pipe. For five pipes from different manufacturers, the anisotropy factor, the lifetime to fracture in the perpendicular direction divided by lifetime in the parallel direction, varied from 1.2 to 4.7 for complete fracture and 1.4 to 4.0 for crack initiation. The degree of molecular orientation was determined by measuring the shrinkage that occured when a pipe specimen was heated near its melting point. The amount of shrinkage correlated with the anisotropy factor for slow crack growth. The shape change after shrinkage was related to the flow pattern of the resin during extrusion and the cooling rate after extrusion.
Analysis of the temperature rise in the projectile and extended chain polyethylene fiber composite armor during ballistic impact and penetration
Authors: Prevorsek Dusan C. , Kwon Young D. , Chin Hong B.
Published: May 2005

The ultra‐high strength/modulus, extended chain polyethylene fiber (Spectra® fiber) composite has shown great potential as a lightweight armor material with its extraordinary capability of absorbing the kinetic energy of projectiles. But the relatively low melting point of this fiber (∼ 145°C) has caused concerns regarding the effect of temperature rise during the impact/penetration process on the performance as armor material. In this article, an analysis of temperature rise in projectile and the fiber composite during the impact/penetration process is described. Combining the simulation of impact deformation by finite element analysis and the simulation of temperature rise by a finite difference approximation of the related dynamic equations, the temperature rise caused by the projectile/composite interaction was estimated. Results show that there is a significant temperature rise at the projectile/composite interface due to the friction but that the short length of time involved in the process and the low thermal conductivity of Spectra fiber composite keep the temperature rise in a very small region (in the order of 0.001 cm) around the interface during the impact/penetration process. Consequently, the volume that is affected by the temperature rise is very small, in the order of total 0.001 cm3 around the projectile, and this is too small to generate any detectable effect on the armor performance. After the projectile is stopped, however, substantial heating of fiber composite can occur under specific conditions as the result of heat flow from the hot projectile embedded in the composite. This heating of fibers, however, is a postmortem effect and hence inconsequential to the ballistic performance of the composite armor.
A model for the unfoamed skin on microcellular foams
Authors: Kumar Vipin , Weller John E.
Published: May 2005

In microcellular plastics, an unfoamed skin that is integral with the foamed core can be created by allowing the nucleating gas to diffuse from the surfaces of a gas saturated specimen prior to foaming. In this paper, a semi‐empirical model is proposed that predicts the skin thickness variation in microcellular foams as a function of gas desorption time. The model shows good agreement with experimental results on the polycarbonate–carbon dioxide system.
Two‐dimensional multilayer coextrusion flow in a flat coat‐hanger die. Part I: Modeling
Authors: Puissant S. , Demay Y. , Vergnes B. , Agassant J. F.
Published: May 2005

The multilayer stratified flow of several polymers in a flat coat‐hanger die was modeled using a finite element method. The problem was formulated using the lubrication approximation theory. A solution procedure in decoupling pressure and streamlines was developed. This new method is very powerful in comparison with more classical approaches, permitting the solution of flow problems involving a great number of layers in a complex industrial geometry. It allows us to obtain, among other things, pressure field, streamlines, residence times, and the values of the interface positions in the whole die.
Crack propagation in biaxially oriented polypropylene at low temperature
Authors: Snyder J. , Hiltner A. , Baer E.
Published: May 2005

The crack growth behavior of polypropylene biaxially oriented by cross‐rolling was studied at low temperature. Single edge notch testing produced a stable tearing type of crack growth in both 50% and 80% biaxially oriented polypropylene at −40°C, in contrast to the brittle fracture of unoriented polypropylene. The crack growth in the two oriented materials began slowly and accelerated to a constant rate that was higher in the 80% oriented material than in the 50% oriented material. The main difference between the crack growth behavior of the two was the longer period of initial slow growth in the case of 80% orientation. This period of slow growth corresponded to crack growth through the notch tip damage zone. Residual strength diagrams were used to present the crack growth data obtained when the stress state was intermediate between plane stress and plane strain. Fractography revealed large differences among the fracture surfaces of the three materials with the unoriented polypropylene showing a grainy appearance from the brittle fracture. The two oriented materials showed considerable ductility. The 50% oriented material showed many voids in the fracture surface, indicating that voiding during the fracture process contributed significantly to the toughness improvement. The 80% oriented polypropylene showed delamination crazing on the fracture surface with layered material and fibrils bridging the crazes.
The influence of inclusion geometry on the elastic properties of discontinuous fiber composites
Authors: Eduljee R. F. , McCullough R. L. , Gillespie J. W.
Published: May 2005

Simplifying assumptions are used to reduce micromechanical treatments to compact expressions which directly reveal the role of the inclusion shape and aspect ratio in establishing the elastic behavior of heterogeneous materials. Attention is directed to the comparison of aligned ellipsoidal and cylindrical inclusions that exhibit transversely isotropic behavior characterized by five independent elastic constants. These comparisons show that the effective transverse in‐plane moduli (E,k* andG) are essentially independent of inclusion shape for aspect ratio greater than ∼ 20; ellipsoidal inclusions provide higher longitudinal reinforcement than cylindrical inclusions of equivalent aspect ratio. Comparison of predictions with measured elastic moduli shows that both the cylindrical and ellipsoidal shape models for isolated inclusions overpredict longitudinal elastic constants for systems which exhibit evidence of inclusion agglomeration. The notion of an effective aspect ratio based on clusters of filaments responding as a coherent unit appears to provide a means for reconciling a wide range of experimental observations.
Start‐up pressure transients in a capillary rheometer
Authors: Hatzikiriakos Savvas G. , Dealy John M.
Published: May 2005

The “rise time” required to achieve a steady pressure reading in a capillary rheometer operated at constant piston speed can be very long, up to several hours under certain circumstances. This phenomenon can pose a serious problem in the measurement of melt viscosity, and it would be useful to be able to estimate the rise time in the planning of experiments. Based on experiments involving several types of polyethylene, we found that the rise time increases with L/D and the amount of polymer initially in the reservoir and decreases with diameter and piston speed. When the rise time is short, melt viscoelasticity contributes to the rise time, but when it is long, melt compressibility is the dominant factor. A model was developed for the latter case, and this was found to give an accurate prediction of the rise time, given the viscosity and compressibility. The model can also be used to determine the power‐law parameters from the start‐up pressure trace, P(t), for a single experiment. Alternatively, if the viscosity is known, the compressibility can be inferred from a single pressure trace.
A unified lubrication approach for the design of a coat‐hanger die
Authors: Liu Ta‐Jo , Liu Li‐Dah , Tsou Jenq‐Der
Published: May 2005

A simple unified lubrication approach has been proposed to design a coat‐hanger die that can deliver wide and uniform liquid sheets. This approach requires that the wall stress in the manifold be constant. With this constraint, any inelastic non‐Newtonian fluid model can be used to describe the liquid motion inside the die. Fluid models that can represent the pseudoplastic or viscoplastic behavior of polymeric liquids have been selected for illustration. A general equation that can be solved to determine the effect of production variations on flow uniformity inside the die has also been derived.
The large strain compression, tension, and simple shear of polycarbonate
Authors: Boyce Mary C. , Arruda Ellen M. , Jayachandran R.
Published: May 2005

Polymeric materials subjected to large strains undergo an evolution in molecular orientation. The developing orientation and corresponding strengthening are highly dependent on the state of strain. In this paper, we examine and compare the very different stress‐strain results of polycarbonate produced from four types of mechanical testing: uniaxial compression, plane strain compression, uniaxial tension, and simple shear. These tests produce different states of orientation within the material and, in the case of simple shear, the principle axes of orientation rotate during the deformation. The ability of the recent constitutive model of Arruda and Boyce (1992) to predict the to predict the observed behavior is evaluated. The model has been incoporated into a finite element code in order to properly simulate the material behavior during the inhomogenous deformations of tension (cold drawing) and simple shear. The material properties of the model are obtained from the uniaxial compression test and the model is then found to be truly predictive of the other states of deformation demonstrating its fully three dimensional capability. The disadvantages of the tensile and simple shear tests for obtaining the data needed to accurately quantify the large strain material behavior of polymers are shown and discussed.
Entrance pressure drop studies of corn meal dough during extrusion cooking
Authors: Bhattacharya M. , Seethamraju K. , Padmanabhan M.
Published: May 2005

The entrance pressure drop during extrusion cooking of corn grits was measured using a cylindrical die viscometer attached to a single screw extruder and compared with results obtained using low‐density polyethylene (LDPE). The cylindrical die viscometer had a length to diameter ratio of 40 with half‐entry angles of 30, 37.5, 45 and 90° with the horizontal. The entrance pressure drop at the die was measured as a function of extrusion temperature, product moisture content and the die entry angle. Results indicate that the flow behavior of corn grits and the entrance pressure drop were affected by product moisture content, process temperature and the shear history in the extruder. Entrance pressure drop also increased with wall shear stress for plastic melt, but for food biopolymer, the increase was observed provided shear history effects were minimized. Entrance correction increased with apparent shear rate for LDPE, but the reverse was true for corn meal. Using Cogswell's analysis, corn grits exhibit severe extension thinning behavior in entry flow.
A theoretical analysis of the strength of composite gels with rigid filler particles
Authors: Gao Y. C. , Lelievre J.
Published: May 2005

The strength, under uniaxial load, of composite gels containing filler particles has been investigated by calculating the stress concentration in the gel matrix. The particles were assumed to be rigid spheres, and the interaction between the particles was taken into account based on a self‐consistent model. The bonding between the particles and matrix was treated for two typical cases, (1) perfectly bonded, (2) smoothly connected. For case 1, the analytical result shows that the stress concentration factors decrease with the increasing of the volume fraction of filler. For case 2, the stress concentration factors are independent of the volume fraction of filler. The structural failure caused by the stress concentration was analyzed.
Merits and limitations of the drop and shock tests in evaluating the dynamic properties of plastic foams
Authors: Ramon O. , Mizrahi S. , Miltz J.
Published: May 2005

Cushioning curves for different plastic foams were determined using drop and shock tests. It was found that at intermediate static stresses the two methods give comparable results. At low and very high static stresses however, different results were obtained. An explanation was given why the shock test is more appropriate and reliable at low and the drop test at very high static stresses.
Water soluble copolymers. 54: N‐isopropylacrylamide‐co‐acrylamide copolymers in drag reduction: Synthesis, characterization, and dilute solution behavior
Authors: Mumick Pavneet S. , McCormick Charles L.
Published: May 2005

Copolymers of N‐isopropylacrylamide (IPAM) and acrylamide (AM) have been synthesized by free radical polymerization in deionized water using potassium persulfate as the initiator. Copolymer compositions were obtained by elemental analysis and 13C NMR. An r1r2 value of 0.99 indicates ideal copolymerization with random incorporation of the comonomers in the copolymers. Weight average molecular weights, second virial coefficients, diffusion coefficients, and average diameters were obtained via classical and quasielastic low angle laser light scattering. The molecular weights for all the copolymers and the homopolymers of IPAM and AM ranged from 2.2 × 106 to 5.2 × 106 g/mol. The second virial coefficients in deionized water increased with increasing acrylamide content in the copolymers. The dilute solution properties of the copolymers were studied by turbidimetry, microcalorimetry and viscometry. All the copolymers, with the exception of IPAM‐40 (the copolymer synthesized with 40 mole% IPAM in the feed), showed lower critical solution temperatures below 100°C. The solution studies were performed in deionized water, 0.514 M NaCl, and 1 M urea. The properties of the IPAM copolymers were influenced by both hydrophobic associations and hydrogen bonding. In 0.2% (∼7mM) sodium dodecyl sulfate, the alkyl chain of the surfactant molecules associates with the IPAM moieties on the copolymer backbone, leading to high intrinsic viscosities and the elevation of the LCST above 100°C.
The onset of wall slip and sharkskin melt fracture in capillary flow
Authors: Hatzikiriakos Savvas G.
Published: May 2005

The capillary die flow of high density and linear low density polyethylenes is simulated under slip conditions to investigate the origin of sharkskin melt fracture. As suggested in the literature, it is shown that sharkskin originates at the exit of the die and is due to the acceleration (high stretching rate) of the melt as it exits the die. It is also shown that both adhesion and slip promoters eliminate surface defects by decreasing the stretching rate of the polymer melt at the exit region of the die. The effect of length‐to‐diameter ratio of the die on the sharkskin melt fracture is also examined. It is found that sharkskin is more pronounced in short dies which is in accord with experimental observations. Finally, it is suggested that applied pressure at the capillary exit suppresses surface defects.
Effect of moisture absorption on the tensile properties of short glass fiber reinforced poly(butylene terephthalate)
Authors: Ishak Z. A. Mohd , Lim N. C.
Published: May 2005

Injection molded short glass fiber reinforced poly(butylene terephthalate) was subjected to hygrothermal aging at two different relative humidities—81.2% and 100% RH. A single free phase model of diffusion has been used to analyze the data obtained from the kinetics of moisture absorption study. The diffusion coefficient and the equilibrium moisture content were found to be dependent on the volume fraction of fibers and relative humidity. Incorporation of short glass fibers into a poly(butylene terephthalate) matrix has led to a significant improvement in the retention and recoverability of the tensile properties. Examination of fracture surfaces using a scanning electron microscope (SEM) has revealed some evidence for the hydrolysis of the polymer matrix. The hydrolysis resulted in the formation of microvoids, the absence of a plastic deformation process, and degradation at the fiber‐matrix interface.
Morphology and properties of an epoxy alloy system containing thermoplastics and a reactive rubber
Authors: Woo E. M. , Bravenec L. D. , Seferis J. C.
Published: May 2005

A novel approach for toughening thermosetting epoxy matrices using both thermoplastics and liquid reactive rubbers as modifiers has been investigated. The network structure of the modified epoxy systems was characterized using dynamic mechanical analysis, and the morphology of the multiphase structure was examined using scanning electron microscopy (SEM). To investigate the continuity of the phase domains, the constituents in the phase domains were positively identified using solving etching and RuO4 staining techniques for transmission electron microscopy (TEM). The fracture toughness of the modified and basic epoxy samples was measured using compact tension (CT) specimens. Quite limited toughness improvement was achieved for the epoxy modified with only the PSu thermoplastic, or the liquid rubber by itself. However, the fracture toughness was found to increase dramatically when a proper combination of both the liquid reactive rubber and thermoplastic was simultaneously incorporated into the epoxy. Toughening by using dual modifiers resulted in maximum improvement of fracture toughness with minimal compromises in processability and Tg depression by rubbers.
In‐line monitoring of titanium dioxide content in poly(ethylene terephthalate) extrusion
Authors: Batra Jitender , Khettry Atul , Hansen Marion G.
Published: May 2005

Peak absorbance changes correlated to changes in species concentration have been the norm in applied spectroscopy, while baseline shifts have been more of an inconvenience. Taking the first or second derivative of the spectra eliminates these baseline shifts. However, with multivariate techniques becoming more readily available, repeatable baseline changes may now be monitored and correlated to specific physical changes. This concept has been studied by monitoring the concentration of titanium dioxide (TiO2), a white inorganic filler, in molten poly(ethylene terepthalate) (PET). Various mixtures of filled and unfilled PET resins were run through a single‐screw extruder, and near infrared spectra were collected in‐line by using a flow cell, housing two fiber‐optic probes, and mounted downstream of the extruder. The presence of titanium dioxide caused the scattering of light that resulted in a systematic baseline shift. The baseline shifts were correlated to the TiO2 concentration data. Multivariate techniques involving the use of singular value decomposition (SVD) to perform partial least squares regression (PLS) were applied to quantitatively determine TiO2 content in the PET melt stream. Standard error of prediction (SEP) values of about 1% were obtained for a model based on two factors.
Phase stability of ternary blends
Authors: Kim C. K. , Kim Jae‐Jin , Paul D. R.
Published: May 2005

The phase behavior of ternary blends of tetramethyl polycarbonate (TMPC), polycarbonate (PC), and styrenic polymers has been examined by experiment and analyzed in terms of thermodynamic theories. The phase boundaries were predicted using both the modified Flory‐Huggins theory and the lattice fluid theory. The boundaries predicted using the lattice fluid theory agree best with the experimental results. The experimental phase behavior of ternary blends was compared with binary blends having exactly the same chemical components and compositions except that the TMPC and PC units were present in the form of a copolycarbonate in the binary. The miscible region of these ternary blends is much narrower than that of the corresponding binary blends, even though the entropic and energetic terms of such ternary blends are more favorable than those of the binary blends. It is shown that a negative value of noncombinatorial free energy in multicomponent systems is not a sufficient condition for miscibility, because of asymmetries of mer‐mer interactions. A comparison of the stability conditions for these binary and ternary blends shows that increasing the degrees of freedom tends to destabilize the mixture.
On the significance of the standardized notched impact strength for materials selection and design
Authors: Jancar J. , Dibenedetto A. T.
Published: May 2005

Experimental data on the standard Charpy notched impact strength (CNIS) for a large sampling of particulate‐filled and rubber‐modified polypropylenes were analyzed. To determine the significance of the CNIS for material selection and design, CNIS data were compared with fracture toughness measurements expressed as the critical strain energy release rateG′c, measured under impact loading. A scale factor representing the state of stress at the crack tip was calculated, assuming small scale yielding, Class I linear elastic fracture mechanics (LEFM). Based on the data, three principal groups of materials were identified. In the smallest of the three, CNIS andG′cmeasurements showed the same functional dependence on the material variables studied and were characterized by a scale factor independent of the composition. In these cases, one can justify comparisons of toughness of different compositions using single values of the CNIS, since the materials are probably being compared in equivalent states of stress. In a second group, CNIS andG′calso show the same functional dependence on material variables, but exhibit large variations in the scale factor with composition. One should not compare the toughness of different materials from this group based on single values of CNIS, since it is likely that the comparisons would not be made relative to equivalent states of stress. In these cases, only measurements ofG′ccan separate the effect of specimen geometry from those of the intrinsic properties of the material. The majority of materials studied fell into a third group, in which the CNIS andG′cexhibited substantially different functional dependencies on the material properties, and the scale factors depended also on composition. In these latter cases, a comparison of CNIS values for different compositions is not a reliable indication of the relative toughness and is of little value as a parameter for material selection and design.
Interfacial tension in polymer melts. I: An improved pendant drop apparatus
Authors: Demarquette N. R. , Kamal M. R.
Published: May 2005

An apparatus is described to measure interfacial tension for molten polymer pairs. The apparatus is based on the pendant drop method. A CCD color video camera captures the image of a pendant drop profile, which is analyzed on‐line using a microcomputer. These almost continuous measurements permit the detection of possible changes in the behavior of the melt that might affect the interfacial tension through thermal degradation. A special syringe to inject the pendant drop has been designed in order to avoid problems such as the capillary effect of the tube of the syringe and the necking and detachment of the pendant drop. The accuracy of the apparatus was verified using water/n‐hexane and water/n‐octane. Experimental results for polypropylene/polystyrene (PP/PS) are presented. The interfacial tension between the polymer pair decreases as temperature increases and as molecular weight decreases. Interfacial tension is estimated from the drop shape when the drop is at mechanical equilibrium. For polymer systems, mechanical equilibrium normally takes from 1 to 10 h to occur. However, transient values of interfacial tension (apparent interfacial tension values obtained before mechanical equilibrium is reached) may be used to estimate the interfacial tension at equilibrium by extrapolation, thus reducing the required experimental time.
Quiescent nonisothermal crystallization kinetics of isotactic polypropylenes
Authors: Hammami Ahmed , Spruiell Joseph E. , Mehrotra Anil K.
Published: May 2005

Recently, a model was developed for the nonisothermal crystallization of normal alkanes with chain lengths between 30 and 50. The model was derived based on the fundamental equation of Ozawa for nonisothermal crystallization, the surface nucleation theory, and the growth rate theory for extended chain crystals. In this paper, the proposed model is modified and extended to the case of polymer crystallization. Experimental differential scanning calorimetry data for three isotactic polypropylene resins with different molecular weights are presented at five cooling rates from 2 to 40 K/min. Model predictions are in excellent agreement with the experimental data for the three polymers at low and high supercoolings.
Dilatometric study of low profile unsaturated polyester resins
Authors: Kinkelaar Mark , Muzumdar Shailesh , Lee L. James
Published: May 2005

An in‐house‐built and designed dilatometer was applied to the study of low profile unsaturated polyester resins. This article first describes the dilatometer used including its calibration then its application to low profile unsaturated polyester resins. Several series of dilatometry experiments were performed, to study the effect of low profile additive concentration and cure temperature on shrinkage control. Scanning electron micro‐graphs of the samples were also prepared to show the correlation between shrinkage control and polymer morphology.
Fiber structure development in high‐speed melt spinning of copolyesters: Poly(ethylene terephthalate‐co‐ 1,4‐cyclohexylene dimethylene terephthalate)
Authors: Kikutani Takeshi , Morohoshi Katsumi , Yoo Hee Yeoul , Umemoto Susumu , Okui Norimasa
Published: May 2005

High‐speed melt spinning of poly(ethylene terephthalate) (PET), poly(1,4‐cyclohexylene dimethylene terephthalate) (PCT) and ET/CT copolysters were performed and the structure and properties of as‐spun fibers were investigated. Molecular orientation increased with an increase in the take‐up velocity, and orientation‐induced crystallization of PET and PCT started at ∼4.5 and 3.5 km/min. With the addition of CT component to PET, and ET to PCT, the onset of crystallization shifted to higher velocities. In as‐spun fibers of the copolymer of ET/CT = 66/34 mol%, which is known as an amorphous copolyester, the crystallization was not observed even at the attained highest take‐up velocity, 6 km/min. On the other hand, crystallization of these fibers occured on annealing suggesting that although the incorporation of copolymer component suppresses the crystallization, the molecular orientation enhances the crystallization of copolymer systems as in the cases of homopolymers.
An overview of the basic aspects of polymer adhesion. Part I: Fundamentals
Authors: Fourche Georges
Published: May 2005

Adhesion between two substrates is a complex phenomenon which at present is still not well understood. The important existing adhesion models (electrical, diffusion, thermodynamic adsorption, chemical, etc.) are reviewed in order to try to explain their mechanisms. Thermodynamic adsorption is now believed to be one of the most importnat mechanisms by which adhesion is achieved. Difusion and wetting are kinetic means in attaining good adsorption of a polymer at the interface. In the case of this model (thermodynamic adsorption), the notion of surface energy is developed and the importance of this property in the understanding of adhesion phenomena is emphasized. The methods of determining the surface characteristics of low and high energy solids are presented. The role played by acid‐base interactions in adhesion is also mentioned.
Indentification of plastic waste using spectroscopy and neural networks
Authors: Scott D. M. , Waterland R. L.
Published: May 2005

In this paper we investigate a new approach for the automated sorting of post‐consumer plastic waste. We show that rapid and relible identification of polymers can eb achieved using a combination of fixed‐filter near‐infrared spectroscopy and neural network data analysis, and we demonstrate the effectiveness of the proposed method for sorting polyethylene terephthalate, high density polyethylene, and poly(vinyl chloride). Finally, we discuss a proposed compact, rugged instrument based on the new sorting method. Owing to the flexibility gained by incorporating neural networds in our system, thismethod can easily be extended to include additional polymers.
Elongational, hysteresis, and oscillatory flows of complex fluids
Authors: De Kee D. , Fong C. F. Chan Man
Published: May 2005

The simple model proposed earlier to describe te rheological properties of complex fluids is used to calculate (a) the extensional viscosity, (b) the hysteresis loops, and (c) the complex viscosity. It has been found that the rheological properties predicted by the model agree with experimental observations. It is shown that for some viscoelastic fluids the extensional viscosity is always finite and for some other fluids the extensional viscosity tends t infinity at finite extensional rate. In the latter case, steady flow is not attainable. The shape of the hysteresis loops depends on the maximum shear‐rate. It also depends on the material properties. In a small amplitude oscillatory flow, our model reduces t a linear viscoelastic fluid.
Double yield points in poly(tetramethylene terephthalate) and its copolymers under tensile loading
Authors: Muramatsu Shigeru , Lando Jerome B.
Published: May 2005

Double yield points before necking were observed in injection molded specimens of poly(tetramethylene terephthalate) (PTMT) and its copolymers under tensile loading. The first yield is associated with deformation of the amorphous region and the second yield is caused by the alpha to beta transition of PTMT crystallites. The first yield point became less apparent with an increase of crystallinity of the specimens. The second yield point became more apparent with an increase of crystallinity. Annealing of injection molded specimens increased the crystallinity and increased the second yield point on stress‐strain curves. Copolymerization decreased the crystallinity and made the first yield point more prominent. Effects of annealing on mechanical and thermal properties of the specimens were also measured. The specimens changed their properties from ductile to brittle during annealing. Their change during annealing was mainly attributed to the increase of crystallinity and not to thermal degradation and/or crosslinking.
Toughening of unsaturated polyester and vinyl ester resins with liquid rubbers
Authors: Ullett Jill S. , Chartoff Richard P.
Published: May 2005

A comprehensive study of toughening unsaturated polyster and vinyl ester resins by addition of liquid rubbers was carried out by considering the effects of cure temperature and gel time on final resin/rubber morphology. The objective was to produce a dispersed rubber phase consisting of particles less than 15 μm in diameter with the addition of limited amounts of rubber, so as not to seriously reduce the modulus and strength of the base resin. A variety of liquid rubbers was used including those based on poly(butadiene acrylonitrile), poly(epichlorohydrin), and two poly(acrylates). Fracture toughness of unmodified and rubber modified materials was measured using the compact tension (CT) test geometry. Significant improvements in fracture toughness were achieved with little to no change in Young's modulus or glass transition temperature. With modest rubber additions, the fracture toughness increased up to 62% for the polyester resin and up to 116% for the vinyl ester resin. In general, fracture toughness increases with increases in volume fraction of rubbery second‐phase particles. However, results suggest that two‐phase particles may be more effective tougheners than single‐phase particles. The toughening mechanism appears to depend on the type of rubbery particle morphology present.
The double yield in the tensile deformation of the polyethylenes
Authors: Lucas J. C. , Failla M. D. , Smith F. L. , Mandelkern L. , Peacock Andrew J.
Published: May 2005

Double yields, as well as other complex yielding behavior, that are observed during the tensile deformation of the polyethylenes have been studied in a systematic manner. The conditions under which such yielding is observed were established by studying a set of linear polyethylenes and well‐characterized ethylene copolymers of narrow molecular weight and composition distributions. A wide range in crystallinity levels were developed and the rate of deformation and the deformation temperature were varied. These experimental results make clear why such complex yielding processes are not always observed. A qualitative explanation, based on the postulate of a partial melting‐recrystallization process during deformation, is given that encompasses all of the experimental data.
Tesile toughness of microcellular foams of polystyrene, styrene‐acrylonitrile copolymer, and polycarbonate, and the effect of dissolved gas on the tensile toughness of the same polymer matrices and microcellular foams
Authors: Collais Dimitris I. , Baird Donald G.
Published: May 2005

This paper reports on the tensile properties of microcellular foams of three different thermoplastics, since there have been several reports in the literature, but with indefinite conclusions so far, that microbubbles act in a manner similar to rubber particles in toughening thermoplastics. Polystyrene (PS), styreneacrylonitrile copolymer (SAN), and polycarbonate (PC), were selected based on their different intrinsic ductilities. The gas supersaturation technique was used to generate samples with microbubbles. The effect of the presence of microbubbles inside the polymer matrix was separated from the effects of the pressure and thermal history experienced by the samples. Nitrogen gas dissolved into PS, and to a lesser extent into SAN, caused and increase of the tensile toughness, but this increased decayed with time as nitrogen gas diffused out of the samples. Furthermore, microcellularly foamed PS samples showed some limited improvement in terms of tensile toughness after all the nitrogen gas diffused out. SAN and PC showed deterioration of the tensile toughness in the presence of microbubbles.