bluuebunny/crossref_metadata_2025_split huggingface dataset:
Nucleation of microcellular foam: Theory and practice
Authors: Colton Jonathan S. , Suh Nam P. 
Published: December 2004

AbstractMicrocellular polymer foams exhibit greatly improved mechanical properties as compared to standard foams due to the formers' small bubble size. Microcellular foams have bubbles with diameters on the order of 10 microns, volume reductions of 30 to 40 percent, and six or seven times the impact strength of solid parts. They are produced through the use of thermodynamic instabilities without the use of foaming agents. This method leads to a very uniform cell size throughout a part's cross section. A theoretical model for the nucleation of microcellular foams in thermoplastic polymers has been developed and experimentally confirmed. This model explains the effect of various additives and processing conditions on the number of bubbles nucleated. At levels of secondary constituents below their solubility limits, an increase in the concentration of the additive or the concentration of gas in solution with the polymer increases the number of bubbles nucleated. Nucleation in this region is homogeneous. Above the solubility limit of additives, nucleation is heterogeneous and takes place at the interface between second phase inclusions and the polymer. The number of bubbles nucleated is dependent on the concentration of heterogeneous nucleation sites and their relative effect on the activation energy barrier to nucleation. In the vicinity of the solubility limit, the two mechanisms compete.
Ionic impurities in water contained in plastic and pyrex bottles
Authors: Crine Jean‐Pierre 
Published: December 2004

AbstractIt is shown that most of the impurities in plastic bottles are not extracted by the water contained In these bottles. However, in the presence of water ions can easily be generated at 22 and 75°C in polyethylene, polypropylene, Teflon‐FEP, and Pyrex bottles. Surprisingly, relatively large amounts of fluoride ions are extracted from Teflon‐FEP bottles which contain very few contaminants. These ions greatly affect the electrical conductivity of the water which is linearly related to the ionic content. The plastic bottles containing the lowest ionic contents are those made in polypropylene and polyethylene. Sodium ions are also measured in the water contained in Pyrex bottles. It is also shown that acid rinsing of plastic containers is not a recommended cleaning technique.
Diffuse shear banded zones of blends of polystyrene and poly(2,6‐dimethyl‐1,4‐phenylene oxide)
Authors: McCarthy Stephen P. , Rogers C. E. 
Published: December 2004

AbstractThe formation, mechanical properties, thermal characteristics, and density of diffuse shear banded zones of polystyrene, poly(2,6‐dimethyl‐1,4‐phenylene oxide) (PPO), and their miscible blends were studied. A significant increase in density of 0.2 to 0.3 percent was found for the diffuse shear banded zones. Differential scanning calorimetry results revealed a volume recovery process that occurs below Tg for the diffuse shear banded zones. The post‐yield‐stress drop, anelastic shear strain within the zone, and anelastic tensile strain were all found to decrease with increasing PPO content in an identical manner. The sharp shear band to diffuse shear banded zone transition was related to chain mobility, molecular packing, and free energy as manifested in the post‐yield‐stress drop. The decrease in anelastic shear strain with increasing PPO content for the blends is possibly related to the beta transition and length between entanglements.
The morphology and rheology of polymer blends containing a liquid crystalline copolyester
Authors: Blizard Kent G. , Baird Donald G. 
Published: December 2004

AbstractThe morphology of blends of polycarbonate and nylon 6,6 with a copolyester of 60 mole percent p‐hydroxybenzoic acid/40 mole percent poly(ethylene terephthalate) was characterized under different processing conditions. In particular, single‐screw extrusion, steady simple shear flow, and flow through a capillary were studied to determine what conditions were necessary for the development of a fibrillar morphology of the liquid crystalline polymer (LCP). Results indicate that some extensional flow is required for the coalescence and extension of the particulate LCP phase. The viscosity of the blends was determined both in a cone‐and‐plate geometry of a Rheometrics Mechanical Spectrometer at low shear rates and in the Instron Capillary Rheometer at higher rates. In general, only a small (10 or 30 percent) weight fraction of LCP was required to reduce the viscosity of the thermoplastics to that of the polymeric liquid crystal. An attempt was made to correlate the structure of the blends seen under the scanning electron microscope with the observed rheology. Not all aspects of the morphology were possible to explain in terms of the viscous properties of the blends.
Novel reinforced polymers based on blends of polystyrene and a thermotropic liquid crystalline polymer
Authors: Weiss R. A. , Huh Wansoo , Nicolais L. 
Published: December 2004

AbstractA thermotropic liquid crystalline polymer (LCP), when added to polystyrene (PS), can function as both a processing aid and a reinforcing filler. Thermal, rheological, and mechanical properties of the pure components and blends containing up to 10 percent LCP are reported. The LCP used is immiscible with PS, and when an extensional component of flow is present during processing, the LCP forms an elongated fibrous phase oriented in the flow direction. This oriented phase lubricates the melt, substantially lowering the viscosity. When the processed blend is cooled, the dispersed fibrous LCP phase is preserved in the solidified material. The LCP microfibers behave like short reinforcing fibers to improve the mechanical properties of the blend; for example, at an LCP concentration of 4.5 percent, the modulus is increased about 40 percent vs. pure PS.
The essential work of plane stress ductile fracture of linear polyethylenes
Authors: Mai Y.‐W. , Cotterell B. , Horlyck R. , Vigna G. 
Published: December 2004

AbstractThe specific essential works of plane stress ductile tearing of several high‐ and ultrahigh‐molecular‐weight polyethylenes were obtained from deeply edge‐notched tension specimens, with either single or double notches, by extrapolating the straight line relationship between the total specific fracture work and ligament length to zero ligament. Provided the fracture morphologies of the torn ligament are not widely different, the specific essential work (we) is a material property dependent on thickness but independent of specimen geometry. The specific essential fracture work also can be identified with Jc the critical value of the J‐integral along a contour immediately bordering the fracture process zone at the crack tip. There is good agreement between the experimental we values and theoretical Jc estimates for these polyethylene materials.
Surface modifications of polymers with fluorine‐containing plasmas: Deposition versus replacement reactions
Authors: Loh I. H. , Klausner M. , Baddour R. F. , Cohen R. E. 
Published: December 2004

AbstractSurfaces of polyethylene; poly(vinyl fluoride), poly(vinylidene fluoride), poly(tetrafluoroethylene), cellulose acetate butyrate, and polyoxymethylene were modified in various cold plasma reactions; feed gases to the plasma reactor were trifluoromethane, hexafluoroethane, and tetrafluoromethane. Using X‐ray photoelectron spectroscopy (ESCA) to characterize the surfaces, it was established that the plasma reactions lead to fluorinated surfaces containing CF3, CF2, and CF groups, All of these fluorinated surfaces exhibit advancing contact angles (with water) larger than 900. However, differences in the ESCA spectra, weight‐gain/‐loss measurements and scanning‐electron‐microscopy (SEM) photographs reveal that the mechanisms of fluorination in the various plasma environments are markedly different. The CF3H gas polymerizes in the gas phase of the plasma and deposits a smooth, fluorinated film on polymers and other substrates. The C2F6 plasma simultaneously etches polymers and polymerizes onto polymer surfaces. The CF4 plasma etches and reacts with the polymer surface but does not polymerize. For polyoxymethylene, the combined roughening (by etching) and fluorination of the surfaces lead to completely non‐wettable surfaces (water contact angle approximately 180°). The highly non‐wettable surfaces of these two polymers are believed to result from the physical etching and roughening at a very fine scale (approximately five micrometers) while the outermost surfaces are reacting to become highly fluorinated.
Thermal diffusivity in polymers oriented uniaxially in the solid and in the molten state
Authors: Sterzyński Tomasz , Linster Jean‐Jacques 
Published: December 2004

AbstractMeasurements of thermal diffusivity were carried out with semicrystalline and amorphous polymers stretched in the solid and in the molten state to different elongations. For semi‐crystalline materials two regions in the curves of the diffusivity versus the elongation can be detected. The change occurs at an elongation of 1.4 for the polymers stretched in the solid state and at an elongation of 3 for the polymers stretched in the molten state. For amorphous polystyrene the shape of the curves of thermal diffusivity versus elongation also depends on the mode of stretching. Along with thermal diffusivity measurements, wide angle X‐ray scattering investigations were also performed and give explanations for the differences in thermal behavior.
A technique for determination of stress fields in the contact loading of highly deformable polymeric materials
Authors: Reddy Narender P. , Kesavan Sunil K. , Van B. Cochran George , Brunski John B. 
Published: December 2004

AbstractSoft, deformable padding materials are widely used for the fabrication of cushions and pads used to reduce contact loading stresses in several industrial and biomedical applications. This paper, presents an indentation technique that can be used to evaluate cushioning materials. The technique uses a soft‐headed indenter made of poly(vinyl chloride) gel that is impressed upon the polymer cushion to be tested. The strain fields and the high stress regimes that develop in the head are then mapped using a grid technique and finite strain theory. Results of indentation tests carried out on a number of cushions of varying stiffness are presented and analyzed.
Scale‐up of single screw extruders
Authors: Rauwendaal Chris 
Published: December 2004

AbstractScale‐up from small laboratory size extruders to large production size extruders is a procedure of great practical importance. Many scale‐up rules and theories have been proposed in the past, however it is not always clear how the different scale‐up methods will affect extruder performance. A basic analysis of scale‐up in plasticating single screw extruders is developed from which the effect of a certain scale‐up strategy on extrusion performance can be evaluated in terms of solids conveying, melting, melt conveying, mixing, residence time, heat transfer, power consumption, and specific energy consumption. Various existing scale‐up theories are evaluated and compared using the basic analysis. A number of existing scale‐up theories have some significant drawbacks, in particular with non‐constant specific energy consumption and imbalance between melting rate and pumping rate. Conditions that are desirable to achieve in scale‐up are enumerated and ranked in terms of importance. This leads to two new scale‐up methods that result in constant mechanical specific energy consumption and high throughput rates. The first scale‐up method keeps the specific surface area constant. This scale‐up should work well for high values of the Brinkman number. However, at low values of the Brinkman number, the melting rate may be insufficient. The second scale‐up method keeps the melting rate at low Brinkman number equal to the pumping rate and, thus, should be useful in cases where the first scale‐up method cannot be used.
Residual stresses in injection‐molded amorphous polymers
Authors: Siegmann A. , Kenig S. , Buchman A. 
Published: December 2004

AbstractNonisothermal flow of a polymer melt into a cold cavity and its rapid cooling give rise to the buildup of flow and thermal stresses in the molded article. In the present investigation the resultant residual stresses (RS) induced by these two sources were studied in two stages. First, the flow‐induced stresses were relaxed by proper heat treatment followed by quenching, resulting in only thermal stresses. The experimentally determined RS profiles in polysulfone and amorphous polyamide showed a parabolic shape and were correlated with the initial and final quenching temperatures, the glass transition temperature, and Biot Number. In the second stage, the combined effect of thermal‐ and flow‐induced stresses was studied using injection‐molded specimens prepared under a wide speptrum of molding conditions including melt and mold temperatures and injection rate and pressure. Results here indicated that the basic thermal‐induced parabolic RS profiles are altered by the flow‐induced stresses resulting in complicated profiles including local maxima and unbalanced RS. Finally, the tensile mechanical properties obatained for plaques molded under the various injection‐molding conditions were studied and correlated in part with the previously determined RS profiles. Results have shown that a property gradient exists as a function of distance from both the gate and surface of the molded plaque.
Structure‐property relationships in blends of linear low‐ and conventional low‐density polyethylene as blown films
Authors: Siegmann A. , Nir Y. 
Published: December 2004

AbstractThree‐layer coextruded blown (either blend or composite) films, made of low‐density polyethylene and linear lowdensity polyethylene (1:1 ratio) of identical density, were compared. The tensile properties of both systems are nearly as high as those of the linear polyethylene while high strain rate properties including impact strength and tear resistance of the composite film are superior. Some structural insight was obtained by thermal analysis and thermoelastic measurements. Structure property relationships are discussed in light of the unique behavior, structure, and morphology of linear low‐density polyethylene. The two polyethylenes are only compatible to a rather limited extent mainly affecting their blend behavior. However, a strong mutual reinforcement effect was observed.
Polyurethane elastomers containing polybutadiene and aliphatic diols: Structure‐property relationships
Authors: Siegmann A. , Cohen D. , Narkis M. 
Published: December 2004

AbstractThe effect of aliphatic diols on the structure and some mechanical properties of polyurethane elastomers containing hydroxyl‐terminated polybutadiene and three different diisocyanates was studied. Differential scanning calorimetric studies revealed the existence of several thermal transitions, characteristic of structures of multiphased elastomers. Three transition temperatures, a subzero transition and two high temperature transitions, were found in some of the elastomers. The higher‐high temperature transition reflects ordered domains, also supported by X‐ray diffraction, Higher degree of order was achieved with longer diols. The mechanical behavior is affected by the multiphase nature of the elastomers, especially by the morphology of the hard segment domains. The structureproperty relationships for the three component polyurethane elastomers in question thus have been established.
Novel reinforced reaction injection molding (RRIM) processing: Computer‐controlled multiple‐stream RRIM production of interpenetrating polymer networks and polyurethanes
Authors: Coates P. D. , Johnson A. F. , Armitage P. D. , Hynds J. , Leadbitter J. 
Published: December 2004

AbstractA four‐stream computer‐controlled reinforced reaction injection molding (RRIM) machine has been developed that attains high accuracy in dispense ratios throughout the injection period. This machine has been used for novel processing of polyurethanes, offering a route to varying product properties either throughout a shot or on a shotto‐shot basis. It also has been used for what appears to be the first production on commercial scale RRIM equipment of a polyurethane‐acrylic interpenetrating polymer network (IPN) in commercial cycle times of around 2 min.
Heat transfer during polymerization in motionless mixers
Authors: Craig T. O. 
Published: December 2004

AbstractInvestigation of the performance of a large‐diameter conventional motionless mixer used as a continuous reactor for styrene polymerization showed that it behaved adiabatically. Computer simulation (in which the mixer is treated as an ideal plug‐flow reactor having perfect radial mixing) predicts this tendency in terms of axial temperature profile. To avoid adiabatic polymerization, with its attendant problems of plant operability and polymer quality, the use of motionless mixers having internal heat transfer surface is indicated.
Dynamics and control of pressure in the injection molding of thermoplastics
Authors: Kamal M. R. , Patterson W. I. , Conley N. , Fara D. Abu , Lohfink G. 
Published: December 2004

AbstractA detailed study was carried out to understand the dynamics of pressure variations at different points in the injection‐molding system. Thus, hydraulic, nozzle, and cavity pressures were evaluated, in addition to the pressure gradient in the cavity. Both steps and pseudorandom binary sequences (PRBS) were employed to obtain and compare dynamic models describing these variables. Subsequently, these models were employed to evaluate and select optimal controllers for the different variables.
The dynamics of peak cavity pressure in injection molding
Authors: Haber A. , Kamal M. R. 
Published: December 2004

AbstractThe modification of the injection‐molding machine, incorporating additional filters, an accumulator, and a servovalve, was shown to reduce the peak cavity pressure variations, in as much as the variations using the microprocessor system were random in comparison to the variations using the normal mode of operation, which exhibited nonstationarity and autoregressive behavior. If the peak hydraulic pressure could be randomized, then the peak cavity pressure variations also would be random. No closed‐loop control would be needed to control the peak cavity pressure.
Polymers as substrates and media for data storage
Authors: Kaempf G. , Loewer H. , Witman M. W. 
Published: December 2004

AbstractTechnological developments in the 1990s will be determined by progress in the field of microelectronics, particularly with regard to information processing and data storage. Progress in information storage is directly related to the ability to store large amounts of data in the smallest possible space, preferably in erasable form. Polymers are used as components in the standard storage systems of today: as carrier films for magnetic tapes, as photoresists and electron beam resists, and as substrates for magnetic and optical discs used for music or video replication and data storage. Storage systems with higher packing densities such as magnetooptical and phase change systems or memories based on photopolymers or polymers with liquid crystalline side chains are currently under development. In these systems, polymers will be used both as components and as actual storage materials. The development and the availability of advanced erasable memories with high storage densities could be accelerated by the availability and the system‐related modification of “intelligent” polymer materials. Worldwide activities in this interesting field have barely progressed beyond the initial stages. This progress report describes the current state of the art and compares the various developments in an attempt to forecast the possible significance of polymer memories with high data packaging densities in relation to the established technologies.
Poly(ethylene terephthalate) blends for permeability barrier applications
Authors: Subramanian P. M. 
Published: December 2004

AbstractPoly(ethylene terephthalate) (PET) offers good properties as a material of choice for various packaging, electronic, and other applications. In these applications in general, the PET articles achieve improved toughness and other physical properties through molecular orientation resulting from stretching at temperatures slightly above itsTg. Without such orientation, these articles suffer from poor impact toughness. We have been investigating modifications of PET for improving toughness and retaining the permeability properties. PET having intrinsic viscosities of 0.5 to 0.7 have been modified with low modulus polymers, particularly ethylene copolymers such as ethylene‐methacrylic acid (EMAA) copolymers. The effect of crystallinity on toughness was determined. The crystallinity was established by Differential Scanning Calorimetry (DSC) techniques. Many of these modified PET compositions have good toughness and permeability barrier properties for various packaging and other controlled permeability applications such as containers and films.
Oxygen permeation of blends of copolymers of siloxanes and poly(methylmethacrylate)
Authors: Blahovici T. F. , Brown G. R. 
Published: December 2004

AbstractA series of low molecular weight (≈40000) copolymers of methylmethacrylate (MMA) and 4‐(methacryloyloxy)butylpentamethyldisiloxane (MBPD) have been synthesized by free radical polymerization in dimethylformamide solution. The microstructure, as derived from 13C NMR spectra, indicates that the copolymers are about 80% syndiotactic with an overall random distribution of mers. At room temperature, copolymers rich in MMA are clear, rigid glasses but become liquid at high MBPD content. Blends of these copolymers with PMMA are all heterogeneous with visible phase separation over most of the composition range. Differential scanning calorimetry studies show the presence of two Tg's when the relative concentration of PMMA to copolymer is high. Blends of two co‐polymers of similar siloxane content produce clear films with no indication of phase separation. The permeability to oxygen at 25°C increases from 0.20 for pure PMMA to 3.0 (fmol/m·s·Pa.) for a copolymer of MMA/MBPD of the mole ratio of 3:1. Evaluation of the permeation behaviors of the blends suggests that blends rich in siloxane exist as a layered structure with the PMMA rich component dominating the observed permeability.
Additives for improving the strength, stiffness, and ductility of epoxy resins
Authors: Garton Andrew , McLean Paul D. , Stevenson William T. K. , Clark Jane N. , Daly John H. 
Published: December 2004

AbstractA range of additives at 7 to 20 wt% loading can increase the stiffness and strength of crosslinked epoxy resins by up to 60%, yet the tensile specimens also fail in a ductile fashion. In additive formulations where little chemical bonding occurs between the additive and the epoxy matrix (e.g., the reaction product of 4‐hydroxyacetanilide and 1,2‐epoxy‐3‐phenoxypropane), the increase in modulus is directly related to the decrease in free volume available for segmental mobility. The increase in strength results from a combination of the increased modulus and an increased fracture energy, A ductile mode of failure occurs because the cured plastic exhibits a large increase in free volume on straining (low Poinsson's ratio). The strain‐induced increase in free volume effectively takes the sample through the glass to rubber transition. In more highly reactive formulations (e.g., the reaction product of 4‐hydroxyacetanilide and vinyl cyclohexene dioxide), chemical bonding effects complicate this simple free volume interpretation, but the occurrence of a ductile failure mode is again related to the free volume increase with strain.