bluuebunny/crossref_metadata_2025 huggingface dataset:
The modulus of the amorphous component in polyethylenes
Authors: Boyd Richard H.
Published: December 2004

Various approaches to representing the modulus of a semicrystalline polymer as a composite crystal‐amorphous material are applied to the extensive data of Illers on the shear modulus of linear and branched polyethylenes as a function of crystallinity and temperature. It is found that the modulus of linear polyethylene is fit very well over the range of 47‐96 percent crystallinity from − 180 to 100°C by the Tsai‐Halpin equation with a single value of the contiguity factor, ζ, and crystallinityindependent phase moduli. A value of ζ ≃ 1(near lower bound behavior) is found. In branched polyethylene the behavior below the β relaxation (T < Tβ) is similar to linear polyethylene, but above Tβ, the behavior indicates that the amorphous modulus is crystallinity dependent. The amorphous component modulus as a function of temperature for linear polyethylene extracted from the fitting process is discussed in terms of various interpretations of the relaxations (α, β, γ) in polyethylene.
An overview of amorphous chains in block and segmented copolymers: Their influence on bulk structure and material properties
Authors: Wilkes G. L. , Mody P. C. , Tant M. R.
Published: December 2004

The influence of amorphous chains on bulk structure and material properties is examined in block and segmented copolymer systems whose components are in a variety of morphological states including: rubber‐rubber; rubber‐glass; glass‐glass; rubber‐crystalline glass‐crystalline; and, crystalline‐crystalline. The effects of external variables, such as temperature, time, and internal variables, such as molecular weight and composition ratio on the magnitude of the role played by the amorphous chains in these systems are discussed.
Effects of lubricants on the second fusion behavior of rigid polyvinyl chloride
Authors: Logan Mark S. , Chung Chan I.
Published: December 2004

Rigid polyvinyl chloride (RPVC) is thermally unstable and difficult to process. The processibility of RPVC compounds markedly depends on the type and level of lubricants present. Lubricants are compounded into RPVC powder and the resulting dry blend is either directly converted into the final product requiring the resin to fuse only once, or pelletized first followed by conversion into the final product in a subsequent operation requiring the resin to fuse twice. The effects of lubricants on the first fusion have been well studied but little is known about the second fusion. We studied the effects of eleven common lubricants on the second fusion of a RPVC master, batch at three levels of concentration at several temperatures., The lubricants were compunded with the RPVC powder, the dry blends molded into one‐inch cube samples, and the molded samples fused under shearing conditions comparable to the actual processing. We found that the effects of the lubricants on the second fusion were generally the same as those on the first fusion. Apparently, the properties of the lubricants and their interactions with the RPVC resin are not altered by the first fusion history.
Polymer flow in the clearance between closely spaced candle filter elements
Authors: Trentacosta J. D.
Published: December 2004

A mathematical model for polymer flow in the clearance between high‐resistance filter elements is developed. An analytical solution is obtained for pressure and velocity profiles for Newtonian fluids. A numerical solution is obtained for elastic fluids displaying power‐law behavior in viscosity and entrance pressure loss. Elasticity of the polymer melt or solution is shown to be a significant factor in, determining these profiles. An example of the model's application, using rheological data for a commercial polyethylene, is given, and the impact of clearance flow pressure losses on the mechanical side loading of the filter elements is discussed.
How the morphology of poly (vinyl chloride) compounds affects toughness and weatherability
Authors: Summers James W. , Isner James D. , Rabinovitch Elvira B.
Published: December 2004

Suspension polymerized poly (vinyl chloride) (PVC) is made up of 150 μm grains. Within these grains are 2 μm primary particles which apparently become the flow units under low melt temperature (175°C) extrusion conditions. The 2 μm particles are visible by light transmission microscopy by shearing the extruded product between glass slides after swelling in acetone or by electron transmission microscopy of ultrathin microtomed samples. This product, made up of 2 μm flow units, is brittle and has poor toughness retention upon weathering. At higher melt temperatures (185–190°C), agglomeration of the 2 μm particles occurs, giving a rough surface but tougher product. At higher melt temperatures, a continuous melt occurs, leading to a smooth surface and tough product with excellent toughness retention upon weathering.
Dissolution dynamics of some polymers: Solvent‐polymer boundaries
Authors: Ouano A. C. , Carothers J. A.
Published: December 2004

A critical angle illumination microscopy technique was used to study the in situ dissolution dynamics of polystyrene, poly (α‐methylstyrene) and the two tactic forms of poly (methyl methacrylate), (PMMA), in several solvents. The dissolution characteristics; of polymers were found to be greatly influenced by several factors: type of polymer, processing condition of the sample, type of solvent, and tacticity, Polystyrene was found to exhibit extensive swelling in several solvents while atactic PMMA exhibited extensive cracking on dissolution. Isotactic PMMA, which has a glass temperature of about 70°C lower than the atactic PMMA, showed swelling behavior similar to atactic polystyrene, while the α‐methylstyrene showed the cracking phenomena exhibited by atactic PMMA.
Preparation and properties of high modulus–tensile strength polymeric materials
Authors: Peiffer Dennis G.
Published: December 2004

A two stage drawing procedure is described for producing highly oriented polymeric materials. The high orientation of both the crystalline and amorphous phase in the semi‐crystalline materials studied resulted in the materials possessing high mechanical properties. The ability to obtain high amorphous orientation is critical. Tensile strengths of 16 g/denier for polyethylene are determined, for example. The results suggest that the existence of a prominent crystalline dispersion mechanism (as observed in dynamical mechanical studies) is not necessary for the attainment of high mechanical properties. Thus a method was devised for the determination of the optimum drawing temperature.
The effects of thermal history on the density and mechanical properties of poly(methyl methacrylate)
Authors: Hutchinson J. M. , Bucknall C. B.
Published: December 2004

The purpose of this work was to show that physical aging effects in poly(methyl methacrylate) (PMMA) could be correlated with the nonequilibrium state of the glassy polymer, as measured by dilatometry. Specimens were annealed at a series of temperatures within the glass transition region (90, 95 and 100°C) and quenched or slowly cooled to the test temperature (40 or 60°C). Volume recovery was monitored throughout the experiment by accurate dilatometry, and low strain tensile creep compliance measurements were made simultaneously on specimens subjected to identical thermal treatments. At both test temperatures, creep behavior and volume recovery showed a similar dependence on annealing temperature and time. However, the specific volume alone was not sufficient to characterize the aging behavior of glassy PMMA: it was also necessary to define the path by which the state of the glass was reached. This memory effect, which has a direct parallel in volume recovery, is attributed to the presence of a distribution of retardation times, and accounts for, the seemingly paradoxical observation that the creep compliance can initially increase on aging at a temperature below Tg if the specimen has previously been stored for a long period at a lower temperature.
High temperature dielectric study of epoxy resins
Authors: Lawless G. W.
Published: December 2004

Four common 177°C‐curing organic resin formulations were studied dielectrically. Results and discussion are presented on the variation of resin electronic properties during cure. In particular, capacitance and dissipation curves are discussed as a function of time in the cure cycle. Variations in frequency are shown to affect the other electronic properties and a frequency “shift” in dissipation sensitivity is noted.
Stepwise increase of hardness in the curing process of one‐step phenolic folding compounds
Authors: Tonogai S. , Hasegawa K. , Inada M.
Published: December 2004

The curing behavior of one‐step phenolic molding compounds was studied using results of Rockwell hardness measurements at elevated temperatures with a cone indenter. The curing process was found to advance in a stepwise manner to the final stage of cure at a specific temperature. An explanation for this phenomenon has been attempted by suggesting the alternating occurrence of two types of curing reactions—propagation and crosslinking. After proceeding to some extent of cure, only the propagation reaction can occur through the migration of low molecular resin to the reactive sites of polymer chains. The propagation facilitates the subsequent crosslinking which drastically enhances the hardness of the resin. The results of electrical resistivity measurements and acetone extraction tests were also found to support the occurrence of above phenomenon.
Some problems of chemical kinetics in polymer aging and stabilization
Authors: Emanuel N. M.
Published: December 2004

Some problems related to polymer aging and stabilization are discussed. Several experimental and theoretical procedures are outlined and their use demonstrated for a number of polymers. Thermal, photochemical as well as mechanical degradation is considered.
Instrumental methods for the study of the thermal degradation of polymers
Authors: McNeill I. C.
Published: December 2004

After consideration of the objectives of a degradation study, product fractions, and experimental variables, an attempt is made to assess the applicability of various instrumental methods to particular objectives. The technique of thermal volatilization analysis (TVA) is discussed in greater detail. Several examples are discussed from degradation investigations to illustrate important aspects of experimental approach.
Degradation kinetics applied to lifetime predictions of polymers
Authors: Flynn Joseph H.
Published: December 2004

The prediction of the lifetime of a polymer by extrapolation from weight‐loss data requires a thorough analysis of degradation kinetics over a wide temperature range. Techniques are described in which entire kinetic spectra are compared among experiments performed at heating rates from 6 deg/min to 9 deg/day. These comparisons permit diagnosing shifts in reaction mechanism, uncoupling of competing processes and more reliably predicting the rate‐limiting process at service conditions. These techniques and a method for obtaining initial X kinetic parameters are illustrated for several polymers.
Processing stability of polyolefins
Authors: Mitterhofer F.
Published: December 2004

Test methods and means of stabilization to counteract degradation during processing of polypropylene, high density polyethylene, and low density polyethylene are discussed. The work contains studies on radical scavengers and hydroperoxide decomposers and their synergistic combinations.
On modeling the solids conveying zone of a plasticating extruder
Authors: Attalla G. , Podio‐Guidugli P.
Published: December 2004

A model for the solids conveying zone of a plasticating extruder is presented. The flow of solid granules is studied in the framework of thermomechanics of media with affine structure, and assimilated to plane steady flow of an incompressible viscous fluid with spherical indeformable structure. Simple constitutive equations are accepted, along with those kinematical assumptions which stem directly from the geometry of the system. The resulting balance equations are given a dimensionless form, and integrated so as to arrive at closed‐form solutions for velocity, spin and temperature of granules. A discussion of the influence of the adimensional parameters relevant to the problem is presented; this discussion is supplemented with some examples. Finally, various developments and refinements of the present model are proposed.
Transparent notch width sensitivity improvers for polycarbonate
Authors: Falk John Carl , Narducy K. W. , Cohen M. S. , Brunner R.
Published: December 2004

Notch width sensitivity, a serious deficiency of polycarbonate, can be improved by addition of 3–10 percent of specially modified methacrylate‐butadiene‐styrene (MBS) graft polymers. Blends of these modifiers with polycarbonate are transparent, in contrast to polycarbonate blends with previously reported notch width sensitivity improvers which are opaque. The synthesis of these modifiers is described together with physical properties of polycarbonate/modifier blends.
The dynamics of parison development in blow molding
Authors: Kalyon Dilhan , Tan Victor , Kamal Musa R.
Published: December 2004

An experimental program was carried out to study the dynamics of parison swell and development in extrusion‐blow molding. Two commercial blow molding grade polyethylene resins were employed in conjunction with an Impco, Model A13‐R12 reciprocating screw blow molding machine equipped with a cylindrical bottle mold. Parison weight swell was measured with the aid of a parison pinch‐off mold. In order to obtain more reliable and useful information regarding diameter and thickness swell of the parison and the dynamics of parison formation and development, high speed cinematography was employed. Data obtained by this technique are more reliable than results obtained with the pinch‐off mold alone. They also give further insight into the phenomena of swell, sag, and parison spring back or recovery.
Simulation of reactive injection molding
Authors: Domine Joseph D. , Gogos Costas G.
Published: December 2004

This paper deals with the computer simulation of those aspects of Reactive Injection Molding (RIM) dealing with the non‐isothermal and transient flow of a chemically reacting mixture into a mold cavity, and the in situ polymerization (“curing”) which follows mold filling. Linear polyurethane systems were considered. The purpose of this simulation work is to investigate the effects of the operating, chemical, and rheological variables on the length and the stability of the RIM process, as well as the quality of the resulting product. Since the flowing fluid mixture is reactive, there is a need to know the thermal history of each of the flowing fluid particles. For this reason the “fountain” flow at the fluid‐air interface is considered in a heuristic fashion.
The behavior of thermosetting compounds in injection molding cavities
Authors: Kamal Musa R. , Ryan M. E.
Published: December 2004

The thermo‐mechanical history of thermosetting compounds in injection molding cavities influences the ultimate properties of molded articles and affects both moldability and the productivity of the process. Mathematical modeling is an attractive approach for obtaining information regarding the thermo‐mechanical history of the compound in the cavity. In order to obtain useful mathematical models of the thermoset injection molding process, it is necessary to have information regarding the kinetics and heats of reaction during cure; the rheological, thermal, and PVT properties of the thermosetting compound; and the variation of these properties with operating variables and the degree of cure. The paper outlines a model of the thermoset injection molding process in simple rectangular or semi‐circular cavities. Methods are described for the experimental determination of the various physical and chemical properties of thermosets, which are required for modeling purposes. The results obtained in conjunction with the characterization of an epoxy system are illustrated. Finally, the paper demonstrates the results of mathematical modeling of the injection molding process for a commercial epoxy molding compound in a semi‐circular cavity, and shows that reasonable agreement is obtained between model predictions and experimental data.
Mixing for reaction injection molding. I. Impingement mixing of liquids
Authors: Tucker Charles L. , Suh Nam P.
Published: December 2004

The performance of confined impinging jet mixers, commonly used in reaction injection molding, was investigated. A theory is presented which assumes that large scale mixing is always adequate, provided the mixer operates in turbulent flow, and argues that the scale of segregation of the final mixture should depend on the size of the smallest eddies of the turbulent motion. The theory predicts that a length scale describing the quality of the mixture will decrease like the nozzle Reynolds number to the −3/4 power. Flow visualization experiments were used to find the point of transition to turbulent mixing flow. This transition occurs at a nozzle Reynolds number of 140 for directly opposed nozzles and at higher Reynolds numbers for nozzles angled downstream. Other geometric factors have little influence on the transition point. Quantitative mixing experiments using model fluids support the theory. Momentum ratio is shown to have no effect on mixing quality.
Rheology in polymerization processes
Authors: Malkin A. Ya.
Published: December 2004

Parameters are developed for predicting rheological changes during ionic, condensation, and free‐radical polymerization. Polymerization is viewed as changes in molecular weight and concentration for polymer solutions. Polymerization data in the laboratory and in tubular reactors are shown to be consistent with the proposed rheokinetic theory. This approach is based on polymerization kinetics and the corresponding solution rheology and phase diagrams.
Experimental investigation of the influence of molecular weight distribution on the rheological properties of polypropylene melts
Authors: Minoshima Wataru , White James L. , Spruiell Joseph E.
Published: December 2004

An experimental study of steady shear and elongational flow Theological properties of a series of polypropylene melts of varying molecular weight and distribution is reported. Broadening the molecular weight distribution increases the non‐Newtonian character of the shear viscosity function and increases the principal normal stress differences at fixed shear stress. The behavior is compared to earlier rheological property‐molecular weight studies. Correlations are developed for these properties in terms of molecular structure. Elongational flow studies indicate that for commercial and broader molecular weight distribution samples, ready failure by neck development occurs and the elongational viscosity appears to decrease with increasing elongation rate. For narrower molecular weight distribution samples, the elongational viscosity is an increasing function of elongation rate, The implication of these experimental results to viscoelastic fluid constitutive equations and polymer melt processing is developed.
Isothermal flow of viscous liquids in corotating twin screw devices
Authors: Booy M. L.
Published: December 2004

A mathematical model is derived for isothermal flow of a Newtonian liquid through corotating twin screw equipment. Two different flow regimes are studied. In the first, channels of twin screw equipment are completely filled with liquid, generate a pressure gradient, and provide a discharge pressure at the end of the pump. Equations are given for drag flow rate, pressure backflow rate, and flow rate through the nip zone. It is shown how the analysis of single screw pumps can be modified for twin‐screw pumps. In the second regime channels are partly full, which is the case with extraction equipment. Equations show how the degree of fill in the equipment changes with flow rate, speed, and dimensions.
Pressure drop‐flow rate equation for adiabatic capillary flow with a pressure‐ and temperature‐dependent viscosity
Authors: Denn Morton M.
Published: December 2004

An approximate analytical solution is obtained for the flow rate‐pressure drop relation for adiabatic capillary flow of a fluid with a pressure‐ and temperature‐dependent viscosity. Neglect of the pressure dependence can result in large errors in the usual range of injection molding practice. The approximate solution follows from an exact solution of capillary flow with a viscosity that depends only on pressure.
The melting of polymer granules through the use of a fluid medium
Authors: Malguarnera Salvatore C. , Suh Nam P.
Published: December 2004

A process of melting individual polymer granules and then combining them into a homogeneous molten mass is examined. The granules are introduced into a high temperature fluid bath, heated as they move due to the polymer‐fluid density difference and finally coalesce under the action of surface and gravity forces into a uniform polymer melt which can be used for extrusion, injection molding or other melt processing techniques. Theoretical models and analyses are presented to predict the time required to melt a granule in a particular polymer‐fluid system and to have the molten granule coalesce into the developing mass of molten polymer. This latter time includes the time for the continuous phase fluid to drain between the approaching granule and the molten polymer‐fluid interface and the time for the granule, once in contact with the interface, to be deposited to some specified depth in the bulk molten polymer. Design parameters for a particular embodiment of the process are presented. Experimental results obtained with a prototype device using mercury as the heat transfer medium are discussed.
The effect of degree of polymerization on glass‐transition temperatures
Authors: Couchman P. R.
Published: December 2004

Finite‐molecular‐mass homopolymers are modeled as binary random mixtures of high polymers and oligomers or chain ends, in proportions determined by the number‐average degree of polymerization. This leads directly to an entropic equation for the effect of molecular mass on Tq in terms of the glass‐transition temperatures and transition increments of heat capacity of these two components. Predictions of the theory are found to be in satisfactory agreement with calorimetric measurements of Tg over a wide range of molecular mass.
Experimental study on cold press workability of aluminum‐polyethylene sandwich laminates
Authors: Ito Katsuhiko , Ogawa Yoshiteru , Furuya Susuma
Published: December 2004

The cold press workability of aluminum‐polyethylene sandwich laminates is experimentally investigated by a deep drawing process with a conical die. “Planium” of 2 mm thickness, in which the core layer, high density polyethylene, is sandwich‐laminated between two aluminum sheets, is used as a test specimen. Soybean oil is employed as a lubricant. The dimensions of the drawing die set are determined for a circular, blank so that the tensile fracture of the drawn.cup occurs at the top corner of the punch. The limiting draw ratio (LDR) is experimentally explored by using many blanks of various initial diameters. In general the maximum punch load in successful drawing increases linearly with increasing draw ratio. Because of the sandwich structure, the fracture of the drawn cup occurs twice. The initial fracture (LDRs) corresponds to a fine bending fracture at the aluminum surface. The second fracture (LDRB) is the complete fracture of the whole laminate. The effect of punch corner radius, working velocity and thickness fraction of aluminum and polyethylene on LDRS and LDRB are studied. The strain distributions of deep drawn cup in three orthogonal directions are analyzed experimentally.
Effects of composition and polymerization mechanism on the mechanical properties of uv‐cured crosslinked polymers
Authors: Levy N. , Massey P. E.
Published: December 2004

The effect of compositional variables on the mechanical properties of a UV‐cured coating was investigated. The coating contains two monomers, 2‐ethoxyethoxyethylacrylate (EEEA) and N‐vinyl‐pyrrolidone (NVP), and a higher molecular weight resin (MW ∼1000) which is a commercial urethane diacrylate. In addition, a photoinitiator, 2,2‐dimethoxy‐2‐phenylacetophenone, was present at a constant concentration. It was found that the mechanical properties of the cured films depend mainly on the concentration of 2‐ethoxyethoxyethylacrylate (EEEA). Spectroscopic analysis. showed that EEEA undergoes both homopolymerization as well as an addition reaction with the photoinitiator and is thus not incorporated in the crosslinked matrix but rather acts similar to a compatible plasticizer. Kinetic analysis of the reactions of the single components and mixtures showed widely diverging reactivities of the components with homopolymerization of EEEA being a favored reaction path. A speculative conclusion is that, to avoid homopolymerization and monomeric reactions, optimized coating formulations (coatings with mechanical properties that are not affected by small compositional variations) should be based on monomers and oligomers with similar reactivities.
Numerical determination of internal stress and viscoelastic parameters for xerographic papers
Authors: Agbezuge Lawrence K.
Published: December 2004

A computerized method has been developed for determining, from one experimentally obtained loading curve for a paper sample: (a) the viscoelastic parameters for predicting paper deformation, and (b) the internal or residual stress level in the paper. The loading curve comprises a stress‐time curve obtained at a constant straining rate, followed by a stress relaxation curve at a constant strain level. The paper deformation is modeled by the Halsey, White, and Eyring model and a nonlinear viscoelastic model.
Effect of long term humid aging on plastics
Authors: Martin John R. , Gardner Robert J.
Published: December 2004

The warm humidity resistance of more than thirty plastic formulations has been evaluated in a program which aged specimens for periods ranging from 10 months to 3 years. Both thermoset and thermoplastic products were included in this study. All of these materials can be used in high humidity at moderate temperatures for short periods of time except where water absorption lowers the glass transition temperature enough to cause distortion. Several of these commercial products exhibit good long term resistance to humidity at temperatures approaching 100°C. However, some are degraded by long term exposure to warm humidity. This hydrolysis effect can result in useful lifetimes which are considerably shorter than would be expected from projections which are based on conventional dry oven aging tests. This broad data base provides a basis for selecting plastics for use in warm, humid environments.
The effects of processing parameters on the tensile properties of weld lines in injection molded thermoplastics
Authors: Malguarnera S. C. , Manisali A.
Published: December 2004

Weld or knit lines result wherever two or more polymer flow fronts unite. This results in a region of a different level of molecular entanglements than the bulk material. Consequently, weld regions have been observed to have inferior mechanical properties compared to the bulk. Although this phenomenon occurs in almost all the commercially important polymer processes, there has been little systematic investigation. The effects of melt temperature, mold temperature, injection speed and injection pressure on the tensile properties of commercial grades of polystyrene (GPS), high impact polystyrene (HIPS) and polypropylene (PP) are examined. The most important processing parameters seemed to be melt and mold temperature; injection speed and pressure had little effect on the tensile properties of any of the samples. A higher melt temperature increased both the strain and stress at break considerably in GPS. In HIPS increased melt temperature increased only the elongation to break substantially. Increased mold temperature improved the stress and elongation to break in GPS but not as much as melt temperature. Polypropylene showed improved weld yield strength with increased mold temperature. Under the conditions examined, injection pressure and injection speed showed no effect on the tensile properties of any of the materials investigated.
The effects of hydrogen on the plasma polymerization of tetrafluoroethylene
Authors: Salhi A. , Soong D. S. , Bell A. T.
Published: December 2004

A study was made of the effects of hydrogen containing additives on the polymerization of tetrafluoroethylene in a radiofrequency low pressure plasma. The addition of ethylene and molecular hydrogen were found, under certain circumstances, to significantly increase the rate of polymer deposition. This effect is ascribed to the release of hydrogen atoms from the additive, which enhance the formation of fluorocarbon‐free radicals and scavenges fluorine atoms. ESCA (electron spectroscopy for chemical analysis) spectra of the deposited films show that upon addition of hydrogen to the monomer, the F/C ratio of the film decreases and the H/C ratio rises. Hydrogen addition also influences the extent of crosslinking—a decrease being observed at low discharge power and an increase being observed at high discharge power.
Plasma polymerization of hexamethyldisiloxane in the gas phase. I. Polymerization studies
Authors: Akovali G. , Bölük M. Y
Published: December 2004

Hexamethyldisiloxane (HMDS) was r.f. plasma polymerized (PP) in the gas phase by use of a tubular reactor with inner electrodes, at 13.56 MHz. The film obtained under all conditions tested was highly crosslinked and did not oxidize in air after aging. Time dependence of p.p. HMDS deposition, overall deposition rate as a function of monomer flow rate at different power levels, as well as interrelation between deposition rate, monomer flow rate and r.f. power were examined and results are discussed. Infrared spectra of the products obtained at different conditions were similar, excepting for the differences due to crosslink densities and background absorptions.
Relaxation of damped debye lattices: Poly(methyl methacrylate)
Authors: Lin Kang Chi , Aklonis J. J.
Published: December 2004

The damped Debye lattice model has been helpful in structuring molecular interpretations of viscoelastic relaxation in the primary transition region. Here, this model has been applied to the viscoelastic behavior of plasticized poly(methyl methacrylate) PMMA samples in the primary transition region. More than 25 samples using 11 different plasticizer systems were studied. The steepness indices of these samples remain experimentally indistinguishable from 1.0 inspite of the fact that substantial changes in characteristic temperatures were observed. These results on diluted PMMA lead to the conclusion that intermolecular interactions are dominant in these systems. If this is true, the model clearly predicts that further plasticization will be accompanied by a very distinctive variation of steepness index with plasticizer concentration.
Release of norethindrone from poly(ortho esters)
Authors: Heller J. , Penhale D. W. H. , Helwing R. F. , Fritzinger B. K.
Published: December 2004

The release of norethindrone from a poly(ortho ester) derived from 3,9‐bis(methylene)2,4,8,10‐tetraoxaspiro[5,5] undecane and 1,6‐hexanediol was studied. Thin circular devices containing incorporated drug and a water soluble salt, such as sodium carbonate, sodium sulfate, or sodium chloride, were placed in water buffered at pH 7.4 at 37°C, and release of drug was followed spectrophotometrically. It was found that rate of drug release was close to zero order for long periods of time and that release of the drug from the hydrophobic matrix occurred as a consequence of osmotic imbibing of water driven by the water soluble salt. Thus, a swelling front moves at a slow and constant rate through the solid device and drug release takes place by rapid diffusion of the drug from the swelling front. Polymer erosion lags behind drug release, and no erosion takes place with basic salts such as sodium carbonate when mechanical properties of the matrix are adequate to accommodate osmotic swelling.
Specification of biaxial orientation in amorphous and crystalline polymers
Authors: White James L. , Spruiell Joseph E.
Published: December 2004

The fundamental concepts for specifying orientation in amorphous and crystalline polymers are reviewed. A new set of orientation factors is proposed to represent the second moments of biaxial orientation. The factors are defined both for the chain axis and for three crystallographic axes of an orthorhombic (or pseudo‐orthorhombic) crystal structure. The orientation factors are defined in terms of the angles between the crystallographic axes and Cartesian coordinate reference axes defining the machine, transverse and thickness directions of films. This makes the orientation factors symmetric with respect to the machine and transverse directions unlike the Stein‐Nomura‐Kawai orientation factors which are defined in terms of Euler's angles. A graphical procedure for representing the state of orientation as a point inside an isoceles triangle is described. Methods of measuring the orientation factors are also reviewed. The paper concludes with examples of the application of these concepts to orientation in amorphous polystyrene films fabricated in our laboratories and to crystalline polyethylene samples discussed in the literature.
Free volume, excess entropy and mechanical behavior of polymeric glasses
Authors: Matsuoka S.
Published: December 2004

Free volume fraction of the Williams‐Landel‐Ferry(WLF)‐Doolittle type has been applied to the analysis of the nonequilibrium state for the glassy polymers. The free volume fraction is a two parameter variable since it depends on the free volume and the occupied volume. The excess entropy is derived from the mixing of vacant and occupied sites, and for polymers a factor is added which corresponds to disordering the molecular segments. A relationship between the excess entropy and enthalpy is derived. For a given level of fractional free volume, there is a unique rate constant associated with changing that level of the fractional free volume. The reciprocal of this rate constant, which depends on the exponential order of the fractional free volume, can be considered as a time constant for changing the molecular conformational probability, and its value is in the order of the average dielectric relaxation time in the corresponding state. When mechanical deformation is. imposed with a rate which is too fast as compared to this time constant, the deformation without a change in the conformational probability, i.e., the reversible elastic deformation, will ensue. In contrast, a sufficiently slow deformation will be accompanied by a change in fractional free volume and the excess entropy, and the above‐mentioned time constant will change with deformation. Since dilation will tend to shorten this time constant, tensile deformation will result in reducing the modulus accompanied by the increase in entropy. Shear deformation is considered as a mixture of compression and tension, where only tension contributes to a change in entropy, and the net result is the strain softening which can be predicted from the tensile behavior. Uniaxial compression is controlled by the shear behavior, and the excess entropy and the fractional free volume increase, while the occupied volume decreases with strain. A constitutive relationship has been proposed which accounts for the effects of temperature, pressure, strain rates and thermal history on nonlinear viscoelastic behavior of polymeric glass.
The glass transition temperature of partially cured polymers as a non‐equilibrium parameter and its effect on observed dynamic mechanical behavior
Authors: Lee C. Y‐C. , Goldfarb I. J.
Published: December 2004

Observations of time dependent behaviors of polymeric systems are often made with the assumption that the glass transition temperature will remain constant during the course of the experiment. This assumption may not be valid for partially cured thermosetting system, where additional cure can increase the glass transition temperature. The observed behavior can be expressed as a time derivative function of two independent variables, the experimental temperature and the state of the system. With proper assumptions, these two variables can be reduced to a single parameter (T − Tg), whose time derivative will give terms representing the temperature and curing effect separately. Dynamic mechanical measurements have been made on partially cured systems, and the effects of the additional cure on the observed properties are observed. The seemingly complex experimental observations can be qualitatively interpreted with the change of the parameter (T − Tg).
Laser light scattering studies of bulk polymers in the glass transition regime
Authors: Jamieson A. M. , Simha R. , Lee H. , Tribone J.
Published: December 2004

The application of laser light scattering techniques to characterize the structural and dynamical properties of bulk polymers near the glass transition temperature is reviewed. Preliminary results of a study of poly(n‐butyl methacrylate) are presented. As in an earlier study of atactic polystyrene, the results suggest the coexistence of two relaxation mechanisms near Tg: a fast, single exponential decay; a slow process characterized by a wide distribution of relaxation times. The slow relaxation mechanism is evidently the main‐chain glass transition process; it appears possible that the fast decay is a manifestation of side‐chain motion. However, in contrast to the polystyrene system where the fast mechanism is always of small amplitude in the temperature range amenable to study (Tg < T < Tg + 40°), the fast mechanism in the poly(n‐butyl methacrylate) system exhibits a sudden transition to high amplitude (∼50 percent of the total observable relaxation amplitude) at T ∼ Tg + 30°. At this point therefore, we suggest that a strong resonant coupling of the fast process with the slow relaxation is occurring.
Analysis and experimental evaluation of twin screw extruders
Authors: Rauwendaal Chris J.
Published: December 2004

Twin screw extruders can he classified according to their geometrical configuration. The main distinction is made between intermeshing and nonintermeshing extruders. Another distinguishing characteristic is the sense of rotation. The most important characteristics of the various twin screw extruders are examined, with particular emphasis on the effect of screw geometry on the conveying characteristics. A brief review is given of the state of the art in theoretical analysis of twin screw extruders. Experiments with two lab scale, intermeshing twin screw extruders are described, one co‐ and one counterrotating. Results are presented on power consumption, residence time distribution, and mixing characteristics of the two extruders. The counterrotating extruder exhibits a narrower residence time distribution and better dispersive mixing capability. The corotating extruder showed a better distributive mixing capability. These results can be explained in terms of the conveying and mixing mechanisms in both extruders. The overall extruder performance seems to be dominated by the effect of the intenneshing region. Any realistic, theoretical analysis of twin screw extruders should be centered around the flow behavior and mixing characteristics of the intermeshing region. The corotating extruder appears to be best suited for melt blending operations, while the counterrotating extruder seems to be preferred in operations where solid fillers have to be dispersed in a polymer matrix.
The melting performance of single screw extruders. II
Authors: Housz J. F. Ingen , Meijer H. E. H.
Published: December 2004

In the previous paper (1) the melting performance of a number of recent screw designs was analyzed, using a rather simple theory. A new screw design was proposed. Here the results of more elaborate calculations, are given in which the influence of the flight clearance and of a shear‐thinning temperature dependent viscosity are investigated. The former conclusions are not altered in essence by these effects. Experimental results with a prototype screw are presented, showing that melting capacity is increased. Up to 100 percent increase in throughput is possible in the high RPM range (in comparison with a much longer traditional compression screw), provided that the feed capacity is sufficient. This usually requires the use of a grooved, well‐cooled, feed section; the capacity of such a feed section depends, for a given screw geometry, on channel depth and granule dimensions. The melt leaves the melting section at a relatively low temperature. The melting section only melts the material and does not raise, its temperature unnecessarily. A further step towards separating distinct tasks of the extruder by functional screw design has been made.
A Note on the prediction of polyethylene melt rheological properties from molecular weight distribution data obtained by gel permeation chromatography
Authors: Shah B. H. , Darby Ron
Published: December 2004

In the present study, a modification of the method previously presented by the authors for predicting rheological properties of linear polyethylene melts from gel permeation chromatography (GPC) data is presented. The modification involves independent values of the zero shear viscosities for melts rather than generating these values internally. The comparison between the experimental zero shear viscosity values and those calculated from GPC data is shown to be very good.
Polymer compatibility with and without a solvent
Authors: Patterson Donald
Published: December 2004

A qualitative review of the thermodynamics of polymer systems will be given in terms of three contributions: positional (or combinatorial) entropy, an “international” term and a free volume term. From this one finds that a simple polymer‐solvent system phase separates on lowering T to an Upper Critical Solution Temperature (UCST) or raising it to Lower Critical Solution Temperature (LCST), To achieve miscibility of two polymers of high molecular weight, one requires a “specific” interaction, usually a weak charge‐transfer complex or a hydrogen bond. Phase separation takes place on raising the temperature to an LCST. These various UCST and LCST are predicted semi‐quantitative by the Prigogine‐Flory theory. When a solvent is added to two miscible polymers, a new type of phase separation appears since there is an effect of any difference in the strengths of the two polymer‐solvent interactions. Phase separation may easily occur in the ternary system where there is none in the three binary systems, and examples will be given. In the case of two highly‐attractive polymers in a solvent, a quite different phase separation occurs, sometimes called complex coacervation. A simple Flory‐Huggins type theory predicts these phenomena in ternary systems.
Modeling of polymeric film‐blowing processes
Authors: Gupta R. K. , Metzner A. B. , Wissbrun K. F.
Published: December 2004

Industrial film‐blowing processes are characterized by large deformation rates, rapid changes of temperature and high stress levels. A pilot scale process was set up to simulate these variables. The pivotal element in modeling the process is a rheological constitutive equation which describes the fluid properties accurately over the entire range of conditions encountered; it was found that contributions to the stress in the material which arise out of the changing thermal history of a fluid element were a significant fraction of the total. When the deforming film is subjected to stretching but to little or no blowing, the axial stresses in the film are predicted excellently by the model under both isothermal and non‐isothermal processing conditions. With rapid blowing and major deviations from uniaxial extension, the axial stresses are predicted less well, but still satisfactorily, under the conditions used. In no case are the circumferential stresses predicted accurately: i.e. unequal biaxial extensional deformations represent complications which have not been resolved.
Poly(n‐butyl acrylate)/polystyrene interpenetrating polymer networks and related materials I. Dynamic mechanical spectroscopy and morphology
Authors: Yeo J. K. , Sperling L. H. , Thomas D. A.
Published: December 2004

A series of interpenetrating polymer networks, IPN's, and semi‐1 IPN's of poly(n‐butyl acrylate) and polystyrene were prepared. The glass transition behavior via dynamic mechanical spectroscopy (DMS) and the morphology via transmission electron microscopy (TEM) were studied as a function of composition ratio and crosslink density. Transition‐broadening was observed at low crosslink concentrations, while a single broad glass transition peak at an intermediate position was attained at high crosslink density levels. A cellular domain structure was the morphological characteristic of those IPN's and semi‐1 IPN's possessing a low cross‐link density and mid‐range composition ratio. At higher levels of crosslink density, irregular shapes of the domain morphology prevailed. Phase connectivity was also observed at high polymer II compositions. Theoretical phase domain sizes of polymer II were calculated using both the theories developed by the present authors and that published earlier by Donatelli, et al., and were found to agree with the experimental domain sizes. While the theory was developed for uniform spheres, some of the domain structures observed experimentally for high polymer II contents had connectivity and/or a cylindrical shape.
Methods for study of thermal aging and stabilization of grafted acrylonitrile‐butadiene‐styrene (ABS) terpolymers
Authors: Chang D. M.
Published: December 2004

Acrylonitrile‐butadiene‐styrene (ABS) grafted terpolymers are apt to oxidize at an elevated temperature and its stabilization by an antioxidant is critical to processing and performance. The differential thermal analysis was used to study the effect of the AgeRite® Geltrol, a modified high molecular weight hindered phenol antioxidant, on the ABS thermal oxidation. The Kissinger equation was found to be accurate enough to determine the activation energy of oxidation. The induction time was also measured and these results were compared with the activation energies. The polybutadiene component of ABS was oxidized rapidly around 200°C under an oxygen atmosphere while the styrene‐acrylonitrile (SAN) component was oxidized at a higher temperature. Air oven aging at 130°C affected the Izod impact (notched), ultimate elongation, but not the ultimate tensile, melt index and morphology. It further confirmed that the polybutadiene component was oxidized and the SAN component was fairly stable at 130°C in air.
Low temperature thermal aging of ethylene vinyl alcohol copolymers
Authors: Apicella A. , Hopfenberg H. B. , Piccarolo S.
Published: December 2004

The crystallites of semicrystalline polymers formed at low temperatures are subject to partial partial melting and recrystallization resulting in a systematic increase in the size and perfection of the nascent crystallites. Differential scanning calorimetry (DSC) and x‐ray studies suggest that ethylene‐vinyl alcohol copolymers (EVOH), in particular, may undergo these secondary crystallization processes upon storage at temperatures far below Tm. DSC scans have been run on “as received” and quenched samples; the mole percent of vinyl alcohol in the copolymers studied was 0, 62, 70, 72, 82 and 100 percent. Tests on secondary crystallization kinetics, performed at different temperatures, further confirm the hypothesis of an increased degree of perfection (lamellar thickening) of the bulk crystallites achieved upon long term storage at temperature between Tg and Tm.