bluuebunny/crossref_metadata_2025_split huggingface dataset:
Thermal degradation of high nitrile barrier polymers
Authors: Jabarin S. A. , Lofgren E. A. 
Published: December 2004

AbstractEffects of absorbed moisture on degradation behavior of high nitrile barrier polymers were monitored using thermogravimetric analysis techniques. Non‐modified and 10 percent rubber modified samples were heated isothermally at nitrile processing temperatures (200°C to 240°C) in air and nitrogen environments. Degradation was evaluated in terms of weight loss as a function of heating time and sample coloration. It was determined that complete removal of moisture, as well as high moisture concentration, contribute to increased degradation at the temperatures evaluated. Moisture levels in the range of 0.15 to 0.5 percent were found to minimize degradation. Heating environment, time, temperature, and rubber modification were also found to influence thermal stability.
Adhesive processing by electromagnetic irradiation
Authors: Malaczynski Gerard W. 
Published: December 2004

AbstractA mathematical model is presented which describes the degree of cure in a thermosetting adhesive used to bond sheet molding compound (SMC) components. The model allows computer aided optimization of the thermosetting process for any type of electromagnetic heating of the various layers of the structure (e.g. dielectric, microwave or induction), arbitrary material properties and arbitrary layer thickness. Computer simulated results are given for the particular case when the cure of the thermosetting material is initiated by its exposure to a high‐power radio‐frequency electric field (dielectric heating). These results indicate a strong sensitivity of the process to the thickness of the adhesive layer and the degree of coupling with the electromagnetic field. The analysis demonstrates that substantial heat losses from the relatively thin adhesive layer to the structural members of the joint by diffusive heat flow can be counterbalanced by additional electric power dissipated either in the adhesive or the structural members of the joint. Although derived for dielectric heating, those results are general, being independent of the type of electromagnetic heating employed.
Effects of cellulosic fibers on the polymerization of a polyurethane
Authors: De J. Aguilar‐Vega M. , Cruz‐Ramos C. A. 
Published: December 2004

AbstractThe effects that the inclusion of low concentrations (0 to 0.6 percent by Volume) of cellulosic fibers have on the polymerization of a polyurethane was tested by monitoring the viscosity of a reacting diol‐diisocyanate system under isothermal conditions. An increase in viscosity due to the presence of the cellulosic fibers is observed, in addition to the expected rise related to polymer formation. However, a slackening effect appears as more cellulosic fibers are added to the polymerizing medium, in contrast to a system with comparable concentrations of glass fibers. On the basis of reaction kinetics arguments, it is suggested that the hollow nature of the cellulosic fibers and their sorbency play important roles in the effect observed, by reducing the effective concentrations of one of the monomers in the reacting phase, thereby diminishing the overall reaction rate. If similar portions of both monomers are extracted from the bulk of the reacting mass, the reaction is not affected as markedly as when only part of one of the monomers is abstracted. The results found illustrate the type of constraints that arise when certain types of polymerizations are carried out in situ to obtain cellulosic fiber composites.
Interfacial agents for multiphase polymer systems: Recent advances
Authors: Xanthos M. 
Published: December 2004

AbstractThe rapid growth in the use of multiphase polymer systems (blends and composites) is undoubtedly related to the availability of methods of controlling the physical and chemical interactions at the interface. Compounds acting as interfacial agents are commonly known as “compatibilizers” in blends, or “coupling agents” in composites; their function is to promote adhesion and enhance overall properties. This paper is a review of recent advances in the use of these compounds in immiscible polymer blends and thermoplastic composites. Polymeric compatibilizers are classified according to their method of addition (in situformation vs. separate addition) and reactivity. Reactive low molecular weight compounds are also listed and their various coupling mechanisms are discussed. It is demonstrated that common routes to enhanced adhesion exist for some types of blends and composites. For example, reactive graft copolymers and certain crosslinklng agents are equally effective as adhesion promoters in blends and composites containing a polyolefin phase.
Unstable fracture of rubber‐toughened polymers
Authors: Narisawa Ikuo , Takemori Michael T. 
Published: December 2004

AbstractThe goal of this investigation has been to obtain a useful criterion for the onset of ductile instability. Notched 3‐point bend samples of 4 impact‐modified plastics were tested under load‐controlled conditions to enhance the instability. Neither plastic collapse of the remaining ligament nor large scale yielding at the crack tip was observed, although significant damage zone development and sub‐critical crack growth were observed prior to crack instability. The stress intensity factor at instability (Kc) was found to be independent of crack length for the plastics tested. More surprisingly, whenKcwas normalized by the corresponding yield stress, this normalized value was found to be experimentally the same for these four impact modified polymers. Calculations based on ductile tearing instability theory were ambiguous and inconclusive. These results suggest that linear fracture mechanics criteria in load controlled tests may still be applicable for engineering purposes under what has normally been considered ductile conditions.
Crosslinking of polycaprolactone in the pre‐gelation region
Authors: Gandhi K. , Kriz D. , Salovey R. , Narkis M. , Wallerstein R. 
Published: December 2004

AbstractPolycaprolactone (PCL) crosslinked below the gel point either with peroxide or by exposure to ionizing radiation was compared by Theological studies. As a result of peroxide crosslinking, PCL increases in viscosity and shear rate dependence and exhibits increased dynamic moduli that converge at higher frequencies. The analysis of gases evolved from γ‐irradiated PCL shows that the yield of hydrogen (G = 0.39) approximates the sum of the yields of carbon monoxide (G = 0.19) and carbon dioxide (G = 0.21). It is inferred that equal amounts of crosslinking and scission result from ionizing irradiation. As a result, PCL is converted by irradiation to a densely branched system. Steady shear viscosities do not depend strongly on dose and overlap at higher shear rates. Similarly, dynamic moduli, especially G″, become less sensitive to dose.
An explanation of the discrepancy in gapwise‐density variation of injection‐molded parts between Kamal's and Greener's data
Authors: Chung T.‐S. 
Published: December 2004

AbstractThe purpose of this short note is to attempt to explain the density variation across the thickness of injection‐molded articles. The effects of a gate frozen process on the fluid motion and density buildup during the packing stage were schematically described, determined, and mathematically simulated. The calculated results are qualitatively consistent with the previous data.
Multiplicities and instabilities in film blowing
Authors: Cain John J. , Denn Morton M. 
Published: December 2004

AbstractThe mechanics of the blown film process are studied for Newtonian and viscoelastic models of the polymer melt. Multiple solutions of the governing equations are possible even for the Newtonian fluid, with the existence of more than one steady‐state bubble profile for a given set of operating parameters; steady axisymmetric solutions vanish suddenly at critical combinations of operating variables. Several types of instabilities exist, including one that is analogous to “draw resonance.” The stability of the bubble to infinitesimal disturbances depends on the set of operating parameters that is controlled; control of the bubble inflation pressure is much less stable than control of the amount of inflating air, for example. Heat transfer is stabilizing.
Memory effects in polymers. III. Processing history vs. crystallization rate of nylon 6—comments on the origin of memory effect
Authors: Khanna Y. P. , Kumar R. , Reimschuessel A. C. 
Published: December 2004

AbstractOur previous publication on this subject has dealt with the processing history effects on the crystallization rate of nylon 6 from the molten state. In this manuscript we present some insights into the molecular origin of the observed effects. Based on the available experimental data, we hypothesize that melt‐extrusion, solution precipitation, or freeze grinding of virgin nylon 6 lead to a more ordered molecular arrangement. This enhanced order persists in the molten state due to H‐bonding and causes a faster crystallization. The virgin material, however, due to its process history, e.g. polycondensation in a viscous melt, is disordered and stays disordered even in the molten state due to H‐bonding. Processing treatments such as melt‐extrusion or freeze‐grinding (high shear stresses) or solution precipitation are required to overcome the H‐bond stabilized disordered environment in virgin nylon 6 and introduce locally ordered regions (nucleation sites), thus accounting for an increase in the crystallization rate.
Recent advances in molecular weight determination
Authors: Cooper Anthony R. 
Published: December 2004

AbstractThe aging and lifetimes of polymeric materials depend on the reaction of these materials to the particular stresses which are applied. In many cases the molecular weight of the polymer is changed and this affords a way to follow aging phenomena. In the simplest case a homopolymer is subjected to a stress which increases or decreases its molecular weight without any chemical changes. As the situation becomes more complicated, changes in chemical composition occur and different sized molecular species are generated. These new species may be of extremely low molecular weight or they may be in the form of crosslinked gel. This paper reviews methods which are available for the determination of molecular weight and molecular weight distribution of polymeric materials. Recently developed or modified techniques are treated in more detail. Techniques which may be used to characterize the oligomer region or analyze for the presence of crosslinked gel are included.
Polymer aging insights available from modulus profiling data
Authors: Gillen Kenneth T. , Clough Roger L. 
Published: December 2004

AbstractA recently developed analytical technique, modulus profiling, conveniently allows the mechanical properties of elastomers to be mapped with spatial resclutions approaching 0.05 mm. Thus, spatial heterogeneities in modulus caused by processing and aging phenomena can be easily monitored. This paper describes some typical results from polymer aging studies, which Indicate the insights available from this technique. These include application of modulus profiling to understanding (1) mechanical property deterioration of Viton in an elevated temperature, gamma‐radiation environment, (2) recent continuous stress‐relaxation results, and (3) the role of ozone for non mechanically‐stressed materials in high energy radiation environments.
Shear, tack, and peel of polyisobutylene: Effect of molecular weight and molecular weight distribution
Authors: Krenceski Mary A. , Johnson Julian F. 
Published: December 2004

AbstractThe effect of polymeric molecular weight and molecular weight distribution on pressure‐sensitive adhesive performance was studied in a model system of commercial polyisobutylenes. Molecular weight was characterized by size exclusion chromatography and membrane osmometry. Pressure sensitive adhesive performance was assessed by shear, peel, and probe tack testing based on standardized test methods. Lower molecular weight polyisobutylenes (Mw < 600,000) are successful in peel and probe tack testing due to their ability to flow quickly and wet the substrate test surface. They do not function as well in shear, however, where the polymer must resist flow under a load. High molecular weight species, by contrast, perform well in shear resistance tests and less successfully in peel and probe tack testing. Where high and low molecular weight polyisobutylenes are blended to broaden the molecular weight distribution while maintaining constant weight average molecular weight, adhesive performance in shear, peel, and probe tack are improved. All of the adhesive properties tested were found to have their foundation in some fundamental rheological properties of the polymers (e.g., shear viscosity and tensile creep compliance). This suggests the use of fundamental rheological characterization for screening of adhesive formulations over more empirical adhesive testing methods.
Substituted propyne polymers—part II. Effects of aging on the gas permeability properties of poly[1‐(trimethylsilyl)propyne] for gas separation membranes
Authors: Langsam Michael , Robeson Lloyd M. 
Published: December 2004

AbstractPoly[1‐(trimethylsilyl)propyne] (PTMSP) is an unusual polyyne material which is optically clear, exhibits high solubility in nonpolar organic solvents, and good oxygen compatibility. By contrast, polyacetylene is black, insoluble, and is unstable in oxygen. The long term stability of PTMSP has been determined by a combination of thermal gravimetric analysis (TGA) and permeability test procedures under a number of different isothermal aging conditions. The use of commercial antioxidants at up to 2 weight percent improves the long term stability of PTMSP. The presence of the antioxidant has no effect on the surface fluorination of PTMSP. Testing of PTMSP films for over eight months shows no change in either permeability or selectivity in contrast to previously reported data.
Hydrodynamic analysis of a Banbury mixer
Authors: Cheng Jing‐Jy , Manas‐Zloczower Ica 
Published: December 2004

AbstractA fluid dynamics analysis package—FIDAP—using a finite element method was employed to simulate the flow patterns in a Banbury mixer. The flow simulations were carried out only for the intensive mixing region, and they were limited to a two‐dimensional analysis. A Lagrangean point of view was adopted and 18 different geometries were selected to represent one revolution of the rotor. A power‐law model with time and temperature dependent parameters was used to characterize the rheological behavior of the mixture. Steady‐state, isothermal flow simulations as well as a transient, non‐isothermal flow analysis were performed for a Banbury B mixer. The results of the analysis show good agreement with experimental observations regarding the development of vortices, the pressure, and the temperature profiles.
Finite element modeling of a counter‐rotating, non‐intermeshing twin screw extruder
Authors: Nguyen K. T. , Lindt J. T. 
Published: December 2004

AbstractThis paper is concerned with Newtonian flow in a counter‐rotating non‐intermeshing twin‐screw extruder. Both the matched and the mismatched screw flight configurations are considered. A three‐dimensional analysis of the pressure flow through the complete extruder cross‐section is included. The model predictions agree well with the experimental data. Computed examples are given to illustrate the utility of this work.
Yield behavior of PP/CaC03 and PP/Mg(OH)2 composites. II: Enhanced interfacial adhesion
Authors: Jančář J. , Kučera J. 
Published: December 2004

AbstractEffects of the variation of adhesion strength σA on the tensile yield behavior of particulate filled polypropylene (PP) were investigated. To enhance adhesion of PP toward calcium carbonate (CaCO3) and magnesium hydroxide (Mg(OH)2), maleated PP (MPP) was added to PP in various ratios. σA varied from 10‐46 MPa. σA calculated from the Leidner‐Woodhams model are in good agreement with SEM micrographs of the composite fracture surfaces. Dependences σyc vs. σA, at constant Vf = 0.18, were investigated and analyzed in terms of existing models. Using the Turczanyi, Pukanszky, Tüdös model (TPT) for the PP/CaCO3 composite, an effective interlayer “thickness” (teff) and the yield stress of the immobilized PP (σyi) were calculated. Both teff and σyi increased with enhancing of the adhesion.
Processing characteristics, structure development, and properties of uni and biaxially stretched poly(ethylene 2,6 naphthalate) (PEN) films
Authors: Cakmak M. , Wang Y. D. , Simhambhatla M. 
Published: December 2004

AbstractPoly(ethylene 2,6, naphthalene dicarboxilate), PEN, is very similar to poly(ethylene terephthalate), PET, in its chemical structure and was, therefore, expected to exhibit similar processing characteristics. We, however, observed a few problems during stretching of PEN, the most important of which was necking behavior at 145°C, which is between Tg (117°C) and Tcc (195°C). This is usually observed in PET only when it is stretched close to or below Tg. At temperatures between Tg and Tcc (cold crystallization temperature) PET stretches rather uniformly. The temperature window for film stretching appears to be rather wide, but our results indicate that this is not the case. Films stretched to high stretch ratios become uniform due to propagation and final disappearance of necks as a result of stress hardening. Our attempts at stretching these films at higher temperatures indicated that necking is eliminated, but so is stress induced crystallization, which causes stress hardening (unless high stretching rates are employed). The presence of stress hardening is essential for obtaining high quality, uniform films of these polymers. In addition, at high temperatures thermally activated crystallization which starts dominating the structure development, detrimentally affects the general appearance of the films. In brief, the PEN films we investigated have a narrower processing window than was anticipated based on their thermal behavior alone. At elevated temperatures the films are sensitive to the rate of stretching even more than typical PET processed at comparable conditions. The uniformity of the films depends on the stretch ratio, stretching mode, ratio(s) and rates and temperature. WAXS studies on the films indicate that the macromolecules packed into the low temperature crystal modification. In addition, WAXS pole figure studies suggest that naphthalene planes preferentially orient parallel to the film surface during biaxial stretching. The biaxially stretched films were observed to exhibit a bimodal chain orientation as evidenced by pole figure analysis of the (010) planes.
Phase separation behavior of the epoxy‐CTBN mixture during the curing process
Authors: Kim Do Hyun , Kim Sung Chul 
Published: December 2004

AbstractTo improve the impact resistance of cured epoxy resin, a carboxyl‐terminated butadiene‐acrylonitrile rubber (CTBN) was added. The phase separation behavior during the curing reaction was analyzed by a light scattering experiment. The measurement of transmitted light intensity showed the onset and ending of the phase separation. The change of the scattered light intensity at different angles showed the process of the phase separation, such as the formation and growth of the dispersed domain. The morphology of the blend was also observed by scanning electron micrography (SEM) and was compared with the domains measured by the light scattering method. The impact strength and dynamic mechanical properties of epoxy resin of different rubber concentrations and cured at different temperature were compared, and the effect of the domain size on these properties was analyzed.
Curing of unsaturated polyester resins: Viscosity studies and simulations in pre‐gel state
Authors: Yang Yeong‐Show , Suspene Laurent 
Published: December 2004

AbstractThe curing of styrene‐unsaturated polyester (UP) resins was studied until gelation. The viscosity and gel points were measured during curing and were correlated with curing temperature, initiator concentration, and accelerator concentration. A gelation model concerning the formation of intra‐crosslinked polymer coils, called microgels, was proposed. The model describes the gelation mechanism in four stages: induction, microgel formation, transition, and macro‐gelation. The kinetic and gelation parameters of the model were experimentally obtained. The gel points and viscosities in the pre‐gel state were simulated by the gelation model for isothermal and nonisothermal curings. Comparisons of the simulation results with experimental data showed good agreement.
Stereological measurement and error estimates for three‐dimensional fiber orientation
Authors: Bay Randy S. , Tucker Charles L. 
Published: December 2004

AbstractA method is presented for measuring three‐dimensional fiber orientation in fiber‐reinforced polymers and placing confidence limits on the results. The orientations of individual fibers are determined from the elliptical intersections between the cylindrical fibers and a polished section. This can be done using either manual digitization or automated image analysis. Volume averages for the sample are computed using an orientation‐dependent weighting function that corrects for the bias of an area‐based sample. Equations are developed for nonuniform fiber lengths, using both number‐average and weight‐average measures of orientation. Sources of systematic, measurement, and sampling error are discussed and equations for sampling error and the propagation of measurement error are derived. The results use a second‐rank tensor to characterize fiber orientation, but the error analysis can be applied to any type of orientation parameter. We implement the technique using manual digitization of optical micrographs. Our implementation accurately measures samples with known orientation, and produces identical results from two perpendicular sections of a glass fiber/nylon injection‐molded sample.
The volume fraction and temperature dependence of the resistivity in carbon black and graphite polymer composites: An effective media—percolation approach
Authors: Blaszkiewicz Michael , McLachlan David S. , Newnham Robert E. 
Published: December 2004

AbstractA quantitative general effective media (GEM) equation is used to describe a broad range of experimental resistivity‐volume fraction results for graphite‐polymer and carbon black‐polymer composites. The parameters used are the resistivities of each component and the two percolation morphology parameters, a critical volume fraction, ϕc, and an exponent, t. A preliminary model, also based on the GEM equation, is used to describe the temperature variation of the resistivity of the diphasic material near the critical volume fraction.
Mechanical and rheological properties of poly(butadiene‐acrylonitrile) rubber compounds reinforced with cellulosic material
Authors: Jasso‐Gastinel C. F. , Lopez‐Carrillo P. , Mendizabal‐Mijares E. 
Published: December 2004

AbstractThe usefulness of waste (mainly cellulosic) materials as a reinforcement for acrylonitrile‐butadiene rubber (NBR) compounds is shown in this work. The materials tested are: henequen, pine, coconut, sugarcane husks, lignin, and wood sawdust. Their performance is compared with that of commercial reinforcement materials (santocel and solka), using the same copolymer composition without reinforcement as a reference compound. Uniform particle size is achieved by milling and screening. For some of the materials, 6 mm fibers and polymerfiber coupling agent are also tested. Reinforced copolymer formulations are prepared by milling. Optimum curing times are determined with a torsion rheometer. Mechanical and rheological tests (stress‐strain behavior, tear resistance, hardness, interfacial strength, storage modulus, and loss tangent), show promising results for some materials, especially when looking for a reinforced product with low dissipation energy.