bluuebunny/crossref_metadata_2025 huggingface dataset:
Measurement and calculation of parison dimensions and bottle thickness distribution during blow molding
Authors: Kamal Musa R. , Tan Victor , Kalyon Dilhan
Published: December 2004

Experimental data are reported regarding the dynamics of the blow molding process, including parison formation, growth, and inflation. These data have been obtained with the aid of high speed cinematography and pinch mold experiments, in conjunction with two commercial blow molding polyethylene resins. It is shown that pinch mold experiments alone do not yield accurate data regarding thickness and diameter swell. Furthermore, the inflation process involves decreasing rates of inflation with time, as a result of the rise in viscosity due to the cooling of the parison during inflation. Mathematical procedures are proposed for a first‐order estimation of parison length and swell as a function of time and the inflation behavior after clamping. In the absence of more dependable basic procedures, the proposed treatment is employed to estimate the effective transient swell functions for the parison using experimental data obtained under the specified conditions. The mathematical treatment is extended to determine the thickness distribution of the bottle. Good agreement is obtained between experimental and calculated results.
The melting performance of single screw extruders
Authors: Housz J. F. Ingen , Meijer H. E. H.
Published: December 2004

A number of recent screw designs is analyzed for melting performance, using a simple analytical approach based on Tadmor's original work. The melting length for a screw with constant depth channel is used as reference. An ideal compression screw will have a melting length of one‐half the melting length of the reference screw. The Maillefer melt separation principle is discussed. The Maillefer screw melts in 2/3 of the length of the reference screw. Screws by Barr, by Dray and Lawrence and by Kim are shown to approach the ideal compression screw. A new design screw, using ideal compression and multiple channels and having a very large screw pitch, is shown to be a considerably more efficient melting device than any of the other, screws discussed.
The viscosity effect on autoacceleration of the rate of free radical polymerization
Authors: Dvornić Petar R. , Jaćović Mihailo S.
Published: December 2004

The reaction kinetics at 70°C were investigated for the suspension polymerization of methyl methacrylate initiated by benzoyl peroxide in the presence of variable amounts of dodecyl mercaptan. A dilatometric method designed to follow a suspension polymerization was used. It showed that the autoacceleration of the rate of polymerization begins at higher conversions and becomes less pronounced as the concentration of chain transfer agent is increased. The investigations focused on the determination of the viscosities of the reaction mixtures at the onset of autoacceleration. It was concluded from the flow curves obtained for different reaction mixtures that there exists a critical solution viscosity at which the autoacceleration begins, which supports the accepted theory about the nature of this phenomenon. Measured at a shear rate of 10,000 s−1 and at 25°C this viscosity was found to equal 0.6 poise regardless of the molecular weight of the growing polymer.
Effect of carriers on the performance of aluminum alloy joints bonded with a structural film adhesive
Authors: Brewis D. M. , Comyn J. , Cope B. C. , Moloney A. C.
Published: December 2004

The effect of polyester and nylon carriers on the durability of metal joints bonded with the modified epoxide adhesive BSL 312 has been examined. Joints have been exposed to air at 50°C and 100 percent RH for periods of up to 10,000 h. Some joints were under tensile stress and this seems to have no effect on durability. Carriers cause a slight lowering of the strength of dry joints, but they appear to have negligible effect on joint durability. An analysis of water distribution in exposed joints implies that the rate of strength loss is dependent upon the rate at which water enters joints by diffusion.
On the drying of glassy polystyrene
Authors: Laria J. C. , Aleman J. V.
Published: December 2004

Many commercial polymers contain water which must be reduced to a lower level for application. The drying behavior of polystyrene (PS), molecular weight 12,000, and flow characteristics suitable for extrusion and injection molding, have been studied. A laboratory tray dryer was used at temperatures below the glass transition temperature of PS (Tg ∼ 373 K). Effects of air flow rate (from 0.5 to 3.5 liters/s), temperature (from 323 to 373K) and relative humidity (from 0.5 to 25 percent) on retained water in PS were measured, and from those effects the effective diffusion coefficients (D) have been deduced as:

.
An analysis of thermal warpage in injection molded flat parts due to unbalanced cooling
Authors: Jacques Michael St.
Published: December 2004

To illustrate the potential effect of unbalanced cooling on warpage of flat parts, a simplified two‐part analysis is presented. First a computational model for amorphous polymers cooling in an injection molding cavity is presented. The simulation is a finite difference solution of the one‐dimensional, transient heat conduction equation with constant material properties. Plastic and mold temperature profiles are calculated through the cooling cycle and the transients from cycle to cycle are included. Temperatures are predicted for both sides of the mold allowing asymmetrical cooling to be analyzed. The model is verified analytically and is in agreement with published data. Secondly, a simplified method of predicting the thermal warpage of a fiat part from calculated temperature profiles is discussed and illustrated. The relative effects on calculated part warpage of asymmetric mold geometry and cooling fluid temperature are predicted with this analysis method. The sensitivity of warpage to these design factors is illustrated for an example part.
Energy conservation in plastics processing: A review
Authors: Dealy J. M.
Published: December 2004

The rapid recent growth in the relative importance of energy costs has directed the attention of machine manufacturers and processors to more energy‐efficient designs and methods of operation. This paper reviews reports of advances in this field. The energy flows associated with the principal processes used in the plastics industry are enumerated, and the problem of defining a meaningful efficiency is addressed. Specific attention is given to recent advances in the areas of extrusion, injection‐molding, and heat recovery. A method for energy analysis based on the second, law of thermodynamics is described.
Fracture surface features of polyethylene pipe samples
Authors: Lee C. S. , Epstein M. M.
Published: December 2004

Slow crack growth behavior of medium‐density polyethylene pipe samples has been investigated by applying standard and nonstandard fracture mechanics test methods. Slow crack growth rate varied by several orders of magnitude among the PE2306 materials from different manufacturers. Slow crack generated surfaces exhibit fibrous textures of varying degrees of coarseness when examined under the scanning electron microscope. When the measured fiber heights, δ/2, of these samples were plotted against the applied stress intensity factor, KI, they showed a simple power law relationship (of exponent 2). Assuming that the pulled‐out fibers transmit almost uniform tensile stresses across the crazed zone at the crack front, the Dugdale‐Barenblatt model was introduced to predict the fiber height. Although the model needs further modification, it provides a general power law relationship between the fiber height and the applied stress intensity factor.
The dynamics of parison free inflation in extrusion blow molding
Authors: Ryan M. E. , Dutta A.
Published: December 2004

Parison free inflation behavior, associated with the extrusion blow molding process, is considered both experimentally and theoretically. Experimental observations indicate1 that the parison assumes a rather complex shape under conditions of unrestricted inflation. In particular, the time‐dependent shape is markedly ellipsoidal rather than cylindrical in nature. This nonuniform behavior, however, becomes more prominent in relation to the entire length as the parison‐length‐to‐diameter ratio is decreased. Based on the experimental observations, a simplified analytical treatment of the free inflation of a viscoelastic parison is presented. The theoretical results illuminate the influence of material properties and process conditions on the inflation process. Expectedly, inflation is enhanced by an increase in the pressure driving force as well as by a decrease in viscosity. However, melt elasticity is also found to exert a significant influence on the inflation behavior. Moreover, the theoretical analysis suggests that the initial parison dimensions play a central role in controlling the inflation process.
On the law of fatigue crack layer propagation in polymers
Authors: Chudnovsky A. , Moet A.
Published: December 2004

A generalized theory of fatigue crack propagation in polymers is presented. The theory accounts for crack propagation through root craze extension accompanied by the dissemination of micro defects around the main crack thereby describing a crack layer (CL) system. In addition to the conventional crack length(l), the CL width(w) is introduced as another kinematic parameter. Applying the principle of minimum thermodynamic forces, evolution of l and w is formulated in terms of reciprocal thermodynamic forces. Accordingly the law of Fatigue Crack Layer Propagation (FCLP) is derived in the following dimensionless form

where N is the number of cycles, λ ≈ l(N)/l*; l* being the critical CL length, ω = w(l)/w*; w* being the value of w corresponding to l*, β′ and Q′ are energy dissipation and heat evolution functions, respectively. A version of this law provides good description of growth rates from published data.
Studies of epoxy resin systems: Part A: A study of the origins of the secondary relaxations of epoxy resins by thermally stimulated depolarization
Authors: Chang T. D. , Carr S. H. , Brittain J. O.
Published: December 2004

The relaxation behavior of several epoxy resin systems, which have systematic structural differences, has been studied by the thermally stimulated discharge (TSD) technique. Two TSD peaks centered at about 115°K (β peak) and 185°K (β peak) were found for epoxy resins cured with a diamine. Structural change, either in the epoxy resin molecule or the amine molecule, did not seem to affect those two peaks. The TSD thermogram of the DGEBA (diglycidyl ether of disphenol A) epoxy resin part only showed a small new peak at 160°K instead of the ft peak at 185°K. This result, together with the fact that postcuring increased β peak height, leads to the conclusion that the ft peak is most likely due to the newly‐created molecular segment during the curing reaction. The peak at 160°K was assigned to the epoxy group. This assignment was based on the fact that the 160°K peak of an epoxy homopolymer, which has fewer epoxy groups, was smaller than that of the parent DGEBA. The β and γ peaks were found to be of distributed characteristics, and the distribution of activation energy was studied by the partial heating method.
Studies of epoxy resin systems: Part D: Fracture toughness of an epoxy resin: A study of the effect of crosslinking and sub‐Tg aging
Authors: Chang T. D. , Brittain J. O.
Published: December 2004

The fracture toughness of an epoxy resin system, diglycidyl ether of butanediol, DGEB, cured with 4‐4′ diaminodiphenyl sulphone, DDS, has been studied by varying the crosslinking density and state of aging. A stable, but rough, crack propagation was observed with specimens that were 99 percent cured and quenched. When the extent of curing was less than 99 percent or the material was aged for more than 20 min at 62°C, crack propagation was of the unstable stick‐slip nature. Aging was found to decrease the initiation fracture toughness dramatically, but the arrest fracture toughness was almost unchanged. This result was associated with a change of relaxation strength of the primary, a, transition with aging. An increase of crosslinking density was found initially to reduce the fracture toughness of this epoxy resin, but the fracture toughness increased after 87 percent of curing. The initial decrease of the fracture toughness was attributed to a decrease of relaxation strength of the primary transition (i.e., the area under the α‐relaxation peak), while the increase of the fracture toughness after 87 percent curing was explained by the onset of the stablerough crack propagation, Micrographs taken by scanning electron microscopy‐showed possible existence of blunting during crack propagation and a decrease of blunting with the extent of aging.
Residence time distribution of polymer melts in the linearly tapered coat‐hanger die
Authors: Matsubara Yutaka
Published: December 2004

This article analyzes the average residence time distribution of polymer melt across the die width in a common linearly tapered coat‐hanger die, which excells the T die but is a little inferior to the curvilinearly tapered coat‐hanger die in residence time uniformity according to the approximated calculation of ten used. From another point of view, a linearly tapered coat‐hanger die may be designed so that a desired ratio of the residence time through the die far end to that along the die center line may be imposed as one of the design constraints.
Mathematical modeling of melting of polymers in barrier‐screw extruders
Authors: Elbirli B. , Lindt J. T. , Gottgetreu S. R. , Baba S. M.
Published: December 2004

Some of today's modern screws contain melt‐separating secondary (barrier) flights in the transition zone. With increasing utilization of barrier screws, the availability of proper and accurate design methods for the melting zone remains of paramount importance. A modified version of a mathematical model developed by the authors previously is applied to two most common types of barrier screws, viz.

—The Mailefer screw (varying pitch and constant depth);

—The Barr screw (constant pitch and varying depth). The present analysis provides valuable insight into the operating principles of these screws. A comparative study is presented demonstrating the possible advantages and disadvantages of the Maillefer and Barr screws in relation to conventional compression screws.
Some mechanical properties of rigid polyurethane structural foam
Authors: Lifshitz J. M.
Published: December 2004

The mechanical response of integral‐skin rigid polyurethane foam, with an average density of 300 to 700 kg/m3, to constant rate and creep loading was determined. Sandwich specimens were modeled by layers of a core material and two skins, whose secant moduli had been determined experimentally by separate tests and approximated by linear functions of the density. The effective rigidities of the sandwich in tension and flexure were calculated and compared favorably to experimental measurements. The sandwich structure improved the flexural rigidity of homogeneous foam by a factor of more than 2.20. Tensile creep tests of sandwich specimens at relatively low stress levels (up to about 38 percent of their strength) showed that the creep was nonlinear, but a single creep curve could represent creep of specimens of various densities, provided the relative load on them was the same. A limited number of flexural creep tests led to similar conclusions, but the creep rate was smaller than in tension. Results from torsion tests of core material, compressive tests of sandwich specimens, and tension and compression tests of nonskin rigid foam are included in this article.
Laminar mixing of polymeric liquids; a brief review and recent theoretical developments
Authors: Ottino J. M. , Chella R.
Published: December 2004

This work concerns itself with laminar mixing of viscous liquids. The primary focus is on mechanical mixing of immiscible fluids but mixing of diffusing and reacting fluids is also briefly considered. Operations such as thermal homogenization and reactive mixing usually not treated in the context of laminar mixing are also included here. The emphasis is on mixing of polymeric liquids and on basic experimentation and theory. Dispersion of solids, mechanisms of demixing (such as gradient coagulation), properties of mixtures, and the description of mixing equipment are not considered. There are no substantial reviews covering developments of theory and applications in laminar mixing in terms of a fundamental unifying theory and analyses relating operating variables to mixing quality. This review, although an attempt in this direction, is not self sufficient and cannot stand alone without recourse to the indicated references. The reader is assumed to have some familiarity with the literature on mixing. Thus, basic concepts are not explained but merely reviewed. Emphasis is given to recent theoretical developments; application examples are provided. The objective here is to condense results from several diverse sources, to present and extend recent developments, to point out the relation of the subject to seemingly unrelated work, and to suggest areas for further research.
Dynamic mechanical studies of thermal aging in poly(vinyl chloride)
Authors: Roche E. J.
Published: December 2004

The effects of thermal aging on the dynamic mechanical properties of rigid poly(vinyl chloride) (PVC) and chlorinated poly(vinyl chloride) (CPVC) are examined in the glass transition (Tg) and β transition (Tβ) regions. PVC, when quenched through Tg and then annealed at 40°C, exhibits a sub‐Tg peak in the loss modulus function. The position of the peak moves to higher temperatures with increasing annealing time. The effect is analogous to sub‐Tg endothermic peaks previously observed by differential scanning calorimetry (DSC). A sub‐Tβ peak in the tan δ or the loss modulus functions can be produced by quenching through Tβ. The effect of heating rate on the sub‐Tβ peak is explored.
Chemiluminescence studies of the degradation and stabilization of polymers
Authors: George G. A. , Egglestone G. T. , Riddell S. Z.
Published: December 2004

In order to predict the safe service life of a polymer from its rate of oxidation, a detailed understanding of degradation and stabilization reactions in the induction period is required. The mechanism by which an oxidizing polymer emits weak visible light (chemiluminescence) is reviewed and the use of the technique to study the early stages of the oxidation of nylon 66 and polypropylene is considered. Steady‐state chemiluminescence experiments are described to measure the activation energy of initiation of nylon 66 oxidation and to study the mechanism of the dark reaction of a hindered amine light stabilizer (and its nitroxyl radical) with polypropylene hydroperoxide. Non‐stationary experiments, in which the steady state is perturbed by UV irradiation and gas switching, demonstrate the reactions of long lived alkyl radicals in the induction period. The observation of stress‐induced chemiluminescence from nylon 66 shows the effect of even a low fiber load is to greatly increase the rate of oxidation.
Influence of mineral oils on polystyrene fracture
Authors: Paredes Edgar , Bustamante Armando , Rivas Luciano
Published: December 2004

Polystyrene specimens coated with mineral oils of different viscosities were tested in tension. It was found that craze initiation and tensile fracture stresses, and also the breaking energy decreased with decreasing oil viscosity, all being lower than for specimens tested in air. Crazes formed in oil showed a lower fibril volume fraction and thicker fibrils than air crazes. The most striking difference in the fracture patterns was found in the initiation regions, where a globular morphology appears as a result of fibrils breakage at the stages of slow propagation, these globules becoming bigger with decreasing viscosity of the oil environment. Since the polymer‐oil interfacial tensions are similar for the different oils, the trends in mechanical properties and craze and fracture morphologies cannot be attributed to a surface energy effect, but to plasticization because the deterioration in the polymer properties and the increasing craze fibrils thickness go along with the plasticizing ability of the oils.
Annealing of ultra‐oriented high density polyethylene extrudates
Authors: Tsuruta Akeharu , Kanamoto Tetsuo , Tanaka Koji , Porter Roger S.
Published: December 2004

The annealing characteristics of highly‐oriented, high density polyethylene (HDPE) fibers extruded at 90°C to constant extrusion draw ratios (EDR) of 5.8 to 30 have been studied using small‐(SAXS) and wide‐angle (WAXD) x‐ray diffraction, differential scanning calorimetry (DSC), thermal shrinkage and tensile tests. The thermal stability in macroscopic properties, such as transparency, sample dimension, and tensile modulus, remarkably increases with the sample EDR. However, the folded chain crystals within microfibrils sensitively reorganize on annealing at ≥ 110°C, even when the macroscopic properties exhibit no significant changes at high EDR's. Although the EDR has a minor effect on the reorganizability of the fold chain crystals, it has a major influence on the SAXS intensity and the extended chain crystalline component detected by WAXD for both unannealed and annealed extrudates. This specific crystalline component has an improved thermal stability and enhances the thermal stability of macroscopic properties at higher EDR. The fibers extruded at 90°C in this study and those prepared at 134°C in a prior study, exhibit significantly different melting behavior after annealing and for long period vs. EDR relationships. These facts combined with the independent observations of the effect of annealing and extrusion temperatures on the consequent long period strongly suggest that annealing during extrusion plays an important role in determining the microstructure of extrudates, especially for extrusion near the ambient melting point of the polymer.
Melt flow of polymer blends
Authors: Utracki L. A.
Published: December 2004

The production of polymer blends increases at a rate of about 13 percent/y. Most of the commercial blends are multiphase systems of complex morphology, determined by the thermodynamic properties of the components and the rheology. Since the diffusion rates are relatively low, the blends are seldom at equilibrium. In most cases, the blend products have properties imposed by the morphology, created by a particular combination of the thermal and deformational history. There are three main reasons for studying the melt flow of blends: optimization of the processing conditions, search for the appropriate means to generate the desired morphology, and the interest in the basic study of the rheology of these complex systems.

In this paper the results published during the last five years are reviewed. The data for polymer blends are compared with those obtained for simpler model systems: liquid mixtures, emulsions, and polymer blends. From the rheological point of view, the blends are divided into three groups: those where viscosity shows positive deviation from the log‐additivity rule, PDB, those where the opposite effect is observed, NDB, and the remaining mixed‐behavior systems, PNDB. To PDB belong the miscible blends and those with strong inter‐domain interactions. To NDB belong those where the interactions are weak. To PNDB belong the blends in which there is a concentration‐dependent transition of structure. The shear dependent properties of blends are also discussed.
Sandwich injection molding of thermotropic copolyesters and filled polyester
Authors: Baird D. G. , Wilkes G. L.
Published: December 2004

Mold filling studies have shown that thermotropic liquid crystalline copolyesters of p‐hydroxybenzoicacid (PHB) and polyethyleneterephthalate (PET) fill by an advancing front mechanism similar to flexible chain polymers. The structure and orientation developed during filling as determined on solid specimens by an etching method, X‐ray diffraction, and shrinkage study on thin microtomed samples appear to be most pronounced at the surface. Based on this information copolymers of 60 and 80 mole percent PHB/PET were co‐injection molded with filled PET under various processing conditions. Because of the low viscosity of the copolyesters, they readily coated filled PET under most processing conditions to give a sheath/core structure. The bending modulus of co‐injection molded bars with as little as 35 percent PHB/PET was as high as the sample consisting of 100 percent liquid crystalline copolyester. Electron micrographs of fracture surfaces revealed excellent adhesion between the two polymers.
Bulk copolymerization of styrene‐acrylic esters: Some analysis and design considerations
Authors: Balaraman K. S. , Kulkarni B. D. , Mashelkar R. A.
Published: December 2004

A common framework for the analysis of styrene‐acrylic ester systems has been developed by analyzing the pertinent kinetic information. This is shown to lead to a well defined strategy for the design of copolymerization reactors especially in the industrially relevant high conversion region. The existence of stable steady states and its influence on the system parameters has been illustrated for the case of a continuous stirred tank reactor (CSTR). A novel strategy of a CSTR operated with a recycle is proposed. This is shown to lead to an operation in the unique steady state with the added advantage of a high conversion and uniform copolymer composition. This would seem to be the first such analysis in the high conversion region.
Factors affecting the mechanical properties of mica‐filled polypropylenes
Authors: Busigin C. , Martinez G. M. , Woodhams R. T. , Lahtinen R.
Published: December 2004

Water‐ground Phlogopite mica (Kemira Siilinjarvi phlogopite) has been evaluated as a reinforcing filler in polypropylene. The major factors which influence the composite strength and modulus include the size, aspect ratio, and uniformity of the mica flakes. Aqueous delamination permits the production of very small flakes (less than 44 microns diameter) with aspect ratios near 50. Such small flakes impart greater tensile and modulus values to polypropylene than larger flakes and the former can also be reprocessed many times without any deterioration of properties. Surface treatment is necessary for adequate dispersion and coupling, particularly with the finely divided mica fillers. Other properties such as the heat‐distortion temperature, fracture toughness, and gas permeability are also influenced by the mean size and aspect ratio of the mica filler. Guidelines are presented to indicate the preferred characteristics of mica fillers for optimum performance.
Thermal and rheological properties of blends of polystyrene and thermotropic liquid crystals
Authors: Huh Wansoo , Weiss R. A. , Nicolais L.
Published: December 2004

The rheological and thermal properties of composites of polystyrene (PS) and two liquid crystalline low‐molecular‐weight additives have been studied. Both additives act as plasticizers as evidenced by decreases in the glass transition and the melt viscosity. In addition both are miscible with PS over a broad range of concentrations. Partial phase diagrams of the two systems are presented and discussed.
Hydrogen bonding potential, HBP: A model for predicting resin solubilities in organic solvents
Authors: Rider Paul E.
Published: December 2004

In a previous paper, a two‐parameter model was described that could be used to predict the hydrogen bond enthalpy of formation between two compounds forming a single hydrogen bond. This paper describes the extension of the use of the two parameters for solvents and polymeric resins in another mathematical model that involves four terms that determine the “hydrogen bonding potential” (HBP) interaction between a resin and a given solvent. Each solvent and each resin can be assigned a donating and accepting parameter (relative to hydrogen bond formation) that combine to yield a numeric value for HBP. A negative HBP value is associated with favorable hydrogen bonding between a resin and a solvent which should correspond to a situation in which solution formation is favorable. A positive HBP value indicates unfavorable interaction which discourages solution formation. Thus, HBP becomes a predictive model of solubilities. Numerical data are presented for four resins and 26 solvents that correlate well with observed solubility behavior. Using this model, it is also possible to construct “solubility maps,” and these are also discussed.
Blowing of oriented PET bottles: Predictions of free blown size and shape
Authors: Erwin Lewis , Pollock Mark A. , Gonzalez Henry
Published: December 2004

A model of the blowing process for polyethylene terephthalate stretch blowmolded bottles is presented. This model uses a rubber constitutive relation. The free blown diameter and the stretch balance are derived from stress equilibrium. Free blow experiments show good agreement with the predictions.
Modeling nonlinear viscoelastic response
Authors: Partom Y. , Schanin I.
Published: December 2004

We present a model for calculating nonlinear viscoelastic response which we call the “phases model” (PHM). In terms of a mechanical model representation the PHM is a generalized Maxwell model with nonlinear elements where each Maxwell element is referred to as a phase. The viscous material properties are represented in the model in terms of flow curves of the individual phases. The collection of flow curves form the flow diagram. We show how to calibrate the flow diagram from a family of constant rate test curves by means of a simple straightforward procedure. We give an example of such a calibration for a certain rigid polyurethane. We applied our model to the calculation of nonlinear viscoelastic response to varius loading programs in uniaxial tension, and to the creep of a simply supported beam, and obtained good agreement with experimental data.
Water‐soluble copolymers VIII. Synthesis and dilute solution rheological studies of dextran‐g‐poly(acrylamide‐co‐sodium acrylates)
Authors: McCormick C. L. , Park L. S. , Hester R. D.
Published: December 2004

Dextran‐g‐poly(acrylamide‐co‐sodium acrylates) were prepared by partial hydrolysis of dextran‐g‐poly(acrylamides) with controlled numbers and lengths of grafted chains. This hydrolysis route proved to be more effective than Ce(IV)‐induced cografting of acrylamide and sodium acrylate comonomers onto dextran in producing the desired graft‐copolymer structures. The resulting copolymers were characterized and the effects of composition, temperature, ionic strength, and shear rate on dilute solution rheological properties were studied.
Poly(p‐phenylene terephthalamide) films formed from extrusion and coagulation of liquid crystalline sulphuric acid solutions: Characterization of orientation and void structure, annealing, and upgrading of film mechanical properties
Authors: Bodaghi Hassan , Kitao Toshio , Flood John E. , Fellers John F. , White James L.
Published: December 2004

Poly(p‐phenylene terephthalamide) (PPD‐T) films have been prepared by continuous extrusion of liquid crystalline 17 percent PPD‐T/sulphuric acid solutions through an annular die followed by coagulation, Films extruded without drawdown exhibit some polymer chain orientation in the machine direction. This is increased by uniaxially drawing down films. Films produced with a lubricated conical mandrel sitting between the die and the coagulation bath exhibit an equal biaxial orientation. The uniaxially oriented films exhibit highly anisotropic mechanical properties, while the mandrel‐produced film exhibits balanced properties. Heat treatment at 350°C results in significant enhancement of the tensile strength of the mandrel film. Void structures in the films have been investigated by mass density, scanning electron microscopy (SEM), and small‐angle X‐ray scattering (SAXS). Density measurement indicate a void content decreasing with decreasing film thickness and heat treatment. SEM locates micron‐size voids in the thickest films, apparently caused by rapid coagulation. SAXS indicates much smaller void sixes which are roughly prolate ellipsoids (long axis in machine direction) for uniaxial films and oblate ellipsoids (short axis in thickness direction) for the mandrel produced films. Various techniques are used to estimate mean void size.
A quantitative description for the optical properties of crystalline polymers applied to polyethylene
Authors: Wedgewood Alan R. , Seferis James C.
Published: December 2004

A quantitative model which described the microscopic and macroscopic refractive index properties of uniaxially oriented crystalline polymers has been extended in relation to molecular bond polarizabilities in this work. Application of this extended modeling methodology in analyzing measured refractive index data for a series of unoriented and oriented samples of linear polyethylene provided Δ = 0.0585 and Δ = 0.194 as the most probable crystalline and noncrystalline intrinsic birefringences for samples exhibiting spherulitic morphology. With these intrinsic birefringences, noncrystalline orientation functions were determined from the optical measurements coupled to the model and the results compared to values obtained from infrared measurements. This comparison of noncrystalline orientation functions, as well as from low density polyethylene reported by other investigators, provided experimental justification for our modeling methodology to examine the possibility of changing intrinsic birefringences for polyethylene as a function of orientation and morphology. The results of this examination demonstrated that values for Δ = 0.0585 and Δ = 0.12 should be used for both low and high density polyethylene samples oriented above the spherulitic to fibrillar transition region.
“Living” anionic polymerizations in a continuous stirred‐tank reactor under sustained feed oscillations
Authors: Couso D. A. , Meira G. R.
Published: December 2004

“Living” anionic polymerizations carried out in a continuous stirred‐tank reactor (CSTR) and operated under forced‐feed oscillations are theoretically studied to investigate the effects on time average values of average chain lengths, polydispersity, and reagent conversions. The instantaneous mean residence time is maintained constant. The period of the oscillations is varied between 60 and 0.05 mean residence times, and various amplitudes are considered. Some advantages are observed with the periodic forcing as compared to the steady operation; polymers with average polydispersities above 10 may be produced at low frequencies, with polydispersities below the steady‐state value of 2 at intermediate frequencies, and with polydispersities of 2 but with increased monomer conversion at fast cycling.
Flow analysis of rubber transfer molding
Authors: Lee L. J. , Griffith R. M. , Sommer J. G.
Published: December 2004

An experimental study has been carried out on rubber I transfer molding. It reveals that the filling is frequently limited more by the resistance of flow across the transfer pot than by resistance of flow through the sprue holes into the cavities. A mathematical model has been derived, which predicts semi‐quantitatively the molding behavior observed. The mode1 predicts that fill time is proportional to the ratio of compound viscosity divided by molding pressure raised to about the fourth power. For the common cases where most of the fill time is from the resistance to the transverse flow on the top of the sprue plate, the fill time is proportional to about the fifth power of the ratio of transverse distance divided by the charge thickness. Experimental results showed that preheating and mastication of the compound reduced transfer time substantially. The charge pattern did not seem to have a major influence on transfer time.
Molecular orientation in film extrusion of high‐density polyethylene
Authors: Picot J. J. C.
Published: December 2004

Molecular orientation in film extrusion has been studied using an extrusion‐grade commercial polyethylene resin. First quad (take‐up) speed was varied over the range 50 to 120 m/min, Web crystallinities were found to be in the range 0.60 to 0.65 as determined by differential scanning calorimetry. Web crystalline orientation function fc was slightly negative below a takeup speed of 50 m/min and rose to a value of 0.4 at 120 m/min at a quench bath temperature of 37.8°C and a melt temperature of 251°C for one of the resins used. (Perfect orientation along the machine direction implies fc equal to 1.0). Amorphous orientation function fa remained below 0.1 and was almost constant with takeup speed. This behavior was modified in a minor way by changes in quench bath and melt temperature as well as resin lot. A qualitative model was proposed for this without definite proof. The major mechanism at work in the film‐forming process is macromolecular network structure deformation in elongational flow. Die gap variation at uniform extrusion rate has a secondary effect on web orientation. With the present state of knowledge, it is not possible to quantitatively separate the amorphous orientation function into its various conformational contributions. It was also noted that high take up speeds and low air gaps tend to freeze the web at greater widths.
Applications of a reaction‐injection‐molding process model in the analysis of premature gelling, demold time, and maximum temperature rise
Authors: Estevez S. R. , Castro J. M.
Published: December 2004

In this paper, we discuss a way to present results or practical interest for the reaction injection molding (RIM) process, such as guidelines to avoid premature gelling and to control demold time and maximum temperature rise. The results are presented as a set of graphs correlated using the relevant dimensionless groups of the process. Examples of applications of these graphs are given and discussed. The numerical calculations are done using the RIM process model developled by Castro and Macosko, which has been shown to agree with experimental results.
Effects of surface treatment on the mechanical properties of carbon fibers
Authors: Bahl O. P. , Mathur R. B. , Dhami T. L.
Published: December 2004

Surface of the carbon fibers developed from PAN (polyacrylonitrile) has been modified using such methods as air oxidation, nitric acid treatment, and anodic (electrolytic) oxidation. By choosing optimum treatment parameters, the tensile strength of such fibers has been found to increase by about 60 percent over that of the untreated value. A quantitative estimation of the surface groups formed during the treatment shows an increase in number with severity of the treatment. Further, removal of these functional groups from the fiber surface during degassing at 1000°C also influences the mechanical properties of the carbon fibers considerably. Results have been discussed in detail.
Drying of plastics with time‐varying surface concentration: Experiments on slabs and application to equipment analysis
Authors: Belofsky Harold
Published: December 2004

Drying of hygroscopic plastics in preparation for molding or extrusion is characterized by very low moisture levels in the polymers and by very low humidity in the drying air. In these circumstances, diffusivity is essentially independent of moisture concentration but surface concentration will vary with time in the general case. An exponential surface concentration/time function is derived from fundamentals and applied to the solution of the diffusion equations for slabs and spheres. Under ideal drying conditions, the solutions reduce to the elementary case in which cs = cf for θ > 0. For non‐ideal drying, the exponential factor b̃ in the surface concentration function appears in the solutions of the diffusion equations. Experiments on slabs were used to verify the analysis since ideal or non‐ideal drying conditions could readily be set up with molded slab samples. Experimental drying curves are in agreement with theory. To complete the analysis for engineering applications, equations for counter flow heat transfer in the dryer hopper are derived and combined with the diffusion solutions to generate dryer performance data.
Durability and failure analyses of a silane treated α‐Al2O3/polyethylene joint in wet environment
Authors: Kaul A. , Sung N. H. , Chin I. , Sung C. S. P.
Published: December 2004

The durability of the joints, consisting of α‐Al2O3 primed with γ‐aminopropyl triethoxysilane (γ‐APS) and polyethylene (PE), in wet environment is investigated as a function of the γ‐APS thickness, dehydration of γ‐APS prior to joint formation and redrying the joint after a certain exposure. The joint strength measured by 180°s peel is found to decrease with exposure time in wet environment more rapidly in water than in 100 percent RH. With exposure time, the debonded area increases from the edges toward the central area of the joint. Relatively thin γ‐APS treatments on α‐Al2O3 appear to provide a more durable joint than thicker γ‐APS treatments resulting in an optimal thickness in the range of 0.3 ∼ 1 percent γ‐APS concentration level. Dehydration of γ‐APS leads to more durable joints with an optimal condition found between 1 ∼ 2 days of dehydration at 100°C in vacuum. Regardless of the γ‐APS thickness and dehydration history, the failure in the de‐bonded area seems to occur by the hydrolysis of γ‐APS near the α‐Al2O3 side and by the deformation of polyethylene (cohesive failure) in the peeled area, as characterized by SEM and ESCA. The debonded area in the dried joint recovers little strength, but in the central bonded areas, the strength is mostly recovered, characterized by cohesive failure of polyethylene. Diffusion of water in γ‐APS near the α‐Al2O3 side rather than the PE side can explain at least qualitatively most of the observed trends. The effects of γ‐APS thickness and dehydration on the durability in wet environments are compared with those on adhesion promotion in dry environments as well as on their respective failure mode.
Interactions in polymer blends‐relationship between thermodynamic and scattering measurements
Authors: Higgins J. S. , Walsh D. J.
Published: December 2004

Methods of preparation and of determining miscibility limits for partially miscible binary polymer blends are described. An equation‐of‐state, theoretical description of this behavior is introduced and the terms describing interactions within the system discussed, Values of these interaction terms are obtained by fitting the models to measured cloud point curves, heats of mixing data, etc. The use of neutron scattering experiments to obtain molecular conformation and interaction parameters is described and a comparison made with values extracted from the thermodynamic measurements.
Bulk and surface thermodynamics of polymer alloys
Authors: Sanchez Isaac C.
Published: December 2004

This paper presents an overview of the subject of phase separation in polymer blends with an emphasis on the thermodynamic stability criteria for phase stability and the classical thermodynamic and microscopic description of polymer interfaces.
On the scale‐up of plasticating extruder screws
Authors: Chung Chan I.
Published: December 2004

In the most commonly used scale‐up method of plasticating extruder screws, the screw channel depth is increased by the square root of the diameter ratio while the screw RPM is decreased by the square root of the diameter ratio such that the output rate increases proportionally to the square of the diameter ratio. This scale‐up method, largely based on the pumping function of the screw, often leads to a higher melt temperature, a higher screw horsepower consumption per unit output rate and an inferior melt quality from the larger diameter screw. Analysis of the common scale‐up method reveals that, although the shear rate in the melt is kept constant, the average residence time and the peripheral screw speed are increased for the larger diameter screw. Our recent study on the melting mechanism also reveals that the melting capacity increases less than the pumping capacity. A detailed examination of the common scale‐up method in this paper shows that the pumping capacity and the solid conveying capacity increase more than necessary while the melting capacity increases insufficiently.
Modification of surface structure and crystallinity in compression‐molded poly(phenylene sulfide)
Authors: Radhakrishnan S. , Nadkarni V. M.
Published: December 2004

The structural modifications and the changes in crystallinity of poly(phenylenesulfide) (PPS) during high‐pressure molding and curing have been investigated as a function of pressure and temperature using wide‐angle X‐ray scattering (WAXS), infrared absorption (IR) and scanning electron microscopy (SEM). It has been found that the crystalline content of the molds varies with applied pressure as Pα where α is 1.5. Major changes in the IR spectra are found in the range of 800 to 600 cm−1 and attributed to structural modifications which have also been noted in the scanning electron micrographs. These various results have been mainly explained on the basis of plastic deformation and flow during the high‐pressure molding process.
General treatment of polymer crystallization kinetics—Part 1. A new macrokinetic equation and its experimental verification
Authors: Malkin A. Ya. , Beghishev V. P. , Keapin I. A. , Bolgov S. A.
Published: December 2004

A new macrokinetic equation of the autocatalytic type is proposed to describe the polymer crystallization process. The derived equation is compared with the known Avrami equation. It is shown to be consistent with the results of isothermal experiments.
Properties of a transparent polycarbonate copolyester blend
Authors: Avakian Roger W. , Allen Richard B.
Published: December 2004

In recent years only a few totally new plastics have been developed, since suppliers are finding it quicker and less expensive to tailor existing resins to meet the requirements of a specific application by alloying. The properties of an alloy of polycarbonate and a proprietary copolyester have been fully characterized. Thermal analysis shows that the polymers are miscible in all proportions. Transparency, glass transition temperature, barrier properties, tensile, and flexural properties of the alloy all fall between those of the neat components. Certain synergistic properties were observed upon blending the polycarbonate and polyester. The tendency of the blend not to yellow during γ‐sterilization is remarkably better than can be predicted by an additive relationship. Chemical resistance of the blends behaves in a similar manner. The excellent balance of properties exhibited by the blend such as transparency, impact strength, γ‐radiation resistance, and chemical resistance makes it useful in applications such as medical disposables and filter bowls.
Hydrodynamic analysis of a spiral disc extruder
Authors: Krein H. L. , Plumtree A. , Rudin A.
Published: December 2004

The flow of polymer melts in a rotating disc extruder is analyzed with the development of a mathematical model for drag flow in a contoured rotating disc. The model assumes a fully melted material which exhibits Newtonian flow behavior under isothermal conditions. Flow is evaluated in successive sections of the flow path, and the drag flow component is calculated by assuming a zero pressure gradient by analogy to the analysis of single screw extruder performance. The final expression involves a computer‐assisted numerical solution. Results of the drag flow model are presented for three different disc geometries. A mathematical model of negative flow, and a comparison of the results with experimental data will be presented in followup papers.