bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

AbstractThe 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

AbstractFour 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

AbstractThe 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.
Instrumental methods for the study of the thermal degradation of polymers
Authors: McNeill I. C. 
Published: December 2004

AbstractAfter 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

AbstractThe 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.
On modeling the solids conveying zone of a plasticating extruder
Authors: Attalla G. , Podio‐Guidugli P. 
Published: December 2004

AbstractA 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

AbstractNotch 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

AbstractAn 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

AbstractThis 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

AbstractThe 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

AbstractThe 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

AbstractParameters 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

AbstractAn 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

AbstractA 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

AbstractAn 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

AbstractA 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

AbstractFinite‐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

AbstractThe 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

AbstractThe 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

AbstractA 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

AbstractThe 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

AbstractWeld 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

AbstractA 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

AbstractHexamethyldisiloxane (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

AbstractThe 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.