bluuebunny/crossref_metadata_2025_split huggingface dataset:
On the drying of glassy polystyrene
Authors: Laria J. C. , Aleman J. V. 
Published: December 2004

AbstractMany 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

AbstractTo 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

AbstractThe 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

AbstractSlow 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

AbstractParison 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

AbstractA 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

AbstractThe 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

AbstractThe 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

AbstractThis 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

AbstractSome 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

AbstractThe 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

AbstractThis 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

AbstractThe 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

AbstractIn 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

AbstractPolystyrene 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

AbstractThe 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

AbstractThe 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

AbstractMold 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

AbstractA 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

AbstractWater‐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

AbstractThe 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.