bluuebunny/crossref_metadata_2025_split huggingface dataset:
Long term thromboresistance of heparinized surfaces
Authors: Ehrlich Julian 
Published: December 2004

AbstractIt has long been known that interaction of blood with artificial surfaces results in thrombogenic effects. With the increased use of prosthetic cardiovascular appliances, it is becoming more evident that surfaces which are thromboresistant are of utmost importance. A review is presented of the recent research on binding of heparin by ionic, covalent and thermal means, to different polymer surfaces, with the results of in vitro and in vivo tests. Additionally, a survey of theories on the role of heparin surfaces in thromboresistance is given.
Polyphosphazenes: Synthesis—properties—applications
Authors: Singler Robert E. , Schneider Nathaniel S. , Hagnauer Gary L. 
Published: December 2004

AbstractVarious aspects of polyphosphazene chemistry are reviewed. Stable poly (organophosphazenes) can be prepared from an inorganic precursor, poly(dichlorophosphazene), by careful control of polymerization and substitution reaction conditions. The bulk structure and properties of polyphosphazenes are discussed, and attention is given to those polymers which have promise as useful engineering materials. The successful preparation of stable poly(organophosphazenes) appears to have resulted in a new class of polymers for both specialty and large scale commercial development.
Polyurethane—polystyrene interpenetrating polymer networks
Authors: Kim S. C. , Klempner D. , Frisch K. C. , Frisch H. L. , Ghiradella H. 
Published: December 2004

AbstractTwo component interpenetrating polymer networks (IPN) of the SIN type (simultaneous interpenetrating networks), composed of a polystyrene network (crosslinked with divinyl benzene) and a polyester‐polyurethane network (crosslinked with trimethylolpropane), were made. Electron microscopy and glass‐transition measurements showed that phase separation had resulted with some interpenetration, presumably occurring at the boundaries. At a composition of about 75 percent polyurethane, a phase inversion occurred, the continuous phase being polystyrene at polyurethane compositions of less than 75 percent. The stress‐strain properties and hardness measurements agreed with these results. Enhanced tensile strength was observed in the IPN's in a concentration range where modulus reinforcement was not evident. A small enhancement in tear strength and thermal stability was also noted.
Molecular orientation effects on thermal conductivity of polydimethylsiloxane under shearing strain
Authors: Picot J. J. C. , Debeauvais F. 
Published: December 2004

AbstractExperimental results for thermal conductivity and flow birefringence on liquid poly (dimethyl siloxane), PDMS, under a shearing strain are discussed. An increase in thermal conductivity with increasing shear rate is attributed to an increased degree of orientation in a direction at 45° to the flow direction for simple shear. A mathematical model is set up. It is based on the assumption that the macromolecules do not change their time‐average shape and otherwise behave as rigid, thin cylinders which can be influenced by convection and external fields and are endowed with rotational Brownian motion. The model predicts that thermal conductivity will reach a maximum value at moderate rates of strain and begin to decrease eventually reaching a minimum value (the transverse thermal conductivity of the basic element) at very high rates of strain when the molecules are completely aligned in the flow direction. Liquids studied were a 12,500 centipoise PDMS in the pure state and in solution in methyl ethyl ketone, MEK, as well as a 65,000 centipoise solution in MEK.
Certain aspects of film blowing of low‐density polyethylene
Authors: Menges G. , Predöhl W. O. 
Published: December 2004

AbstractThis article considers two topics: (1) Cooling of the film bubble and (2) Production of shrinkable film. Heat is transported by conduction, convection, and radiation, but only convection and radiation are relevant for the cooling results. Heat radiation can be calculated with known surface area, temperatures, and emission coefficient. Here we learn that the emission coefficient depends on the film thickness. Heat transfer by radiation amounts to about 15 percent of the total heat transfer. Heat transfer by convection normally can be calculated by known methods assuming ideal flow conditions. Because the flow conditions of the cooling air differ considerably from ideal conditions, known heat‐transfer laws give incorrect results. Therefore, a new formula was set‐up by determining the heat transfer conditions in real experiments.Each blown film is shrinkable, but in most cases the influence of the die on the shrinkage is disregarded. The die causes an important anisotropy in the elastic behavior of the film. Further on, shrinkage is influenced by the degree of bubble deformation, the temperature profile, and the deformation velocity between die exit and freeze line. This is discussed qualitatively. A calculations is not yet possible because of the unknown relaxation behavior of the melt. The shrinkage of an LDPE blown film depends on time and temperature. Time and temperature are exchangeable variables.
Predicting the effect of screw wear on the performance of plasticating extruders
Authors: Klein Imrich 
Published: December 2004

AbstractThe effect of screw wear on the performance of a 2.5 in. diameter extruder is studied with the aid of computer simulations. The effect of progressively increasing flight clearance on the extrusion of low density polyethylene, polypropylene and nylon 6/6 is presented. The remedial effect of increased screw speed and its side effects on melting behavior, solids content, extrudate temperature and power consumption are also described.
The determination of the fracture parameters for polymers in impact
Authors: Plati E. , Williams J. G. 
Published: December 2004

AbstractA method of analysis is given by which the critical strain energy release rate Gc for impact tests may be deduced for both Charpy and Izod tests from normal energy measurements. Suitable calibration factors are determined and the method is applied to a range of polymers. Very close agreement is achieved between the Charpy and Izod results except for highly ductile materials for which it was necessary to use a fully plastic analysis. The method is extended to blunt notches and it is shown that the use of a strain energy per unit volume to yielding, together with a blunt notch stress analysis, gives a good description of the results.
Environmental effects on deformation, strength, and degradation of unidirectional glass‐fiber reinforced plastics. II. Experimental study
Authors: Ishai Ori 
Published: December 2004

AbstractGlass‐fiber reinforced epoxy (GRP) and unfilled epoxy specimens were exposed to different environmental conditions consisting of hot‐ and cold‐water absorption and subsequent drying. Effects of the environmental history on deformational and strength characteristics of the composite material were investigated.GRP specimens exposed to hot water undergo pronounced degradation, which sets in shortly after exposure and is associated with a significant irrecoverable weight loss. Degraded specimens are characterized by higher void content and lower strength compared with their cold‐water and reference counterparts. The degradation process is attributed to penetration of water into the matrix‐fiber interfaces and is followed by an attack, at high temperatures, on the glass‐fibers surface and coupling agent. As a result, glass constituents are leached out and then removed from the system by diffusion.The degradation effect was also confirmed by micro‐observation of the fractured surfaces and by infra‐red spectroscopy. A simple and effective testing method is recommended, permitting detection of degradation onset and its progress by simultaneous measurement of weight and dimensional changes with time.
Development of computer control strategies for plastic extruders
Authors: Parnaby John , Kochhar Ashok K. , Wood Brian 
Published: December 2004

AbstractThe basic idea of automatic control of extrusion machinery is considered. Dynamic interaction among process variables is discussed and it is suggested that a practical form of control might involve steady‐state control of screw and barrel temperature coupled with dynamic control of screw speed. Several alternative forms of control strategy are examined and it is suggested that for higher forms of control, a computer is required together with an accurate process model relating control and controlled variables. With such a strategy, polymer temperature and pressure at the die would be controlled by continuous variations in screw speed coupled with infrequent control of die resistance to counter long term drift and to facilitate pressure and temperature change matching. Methods for developing process models are considered including those for adaptive/predictive control strategies using time‐series techniques and some experimental results are given. The basic form of a computer control system is outlined and the areas where further research is required are indicated.
Inferences concerning the amorphous regions in polyethylene of different morphologies
Authors: Dole Malcolm 
Published: December 2004

AbstractUsing a liquid nitrogen quenching method for the measurement of the ppm of hydrogen dissolved in polythylene (PE) at atmospheric pressure, solubility data were obtained for the following types of samples of linear PE: bulk, single crystalline and extended chain. For samples of equal amorphous volume fraction, the hydrogen is about 10‐fold more soluble in single crystalline PE than in bulk. The solubility in extended chain samples becomes more abnormal, the higher the crystallinity. No hydrogen dissolves in a perfect C20 H42 crystal. The excessive solubility in the single crystalline samples is interpreted in terms of more sorption sites in the folded part of the chains in the amorphous surface layers than in bulk PE. As the heat of sorption changes from endothermic to slightly exothermic in passing from the bulk to the single crystalline or extended chain samples, the sorption sites must pre‐exist in the latter two types.
The flow of non‐Newtonian solutions through packed beds
Authors: Park H. C. , Hawley M. C. , Blanks R. F. 
Published: December 2004

AbstractThe rheological behavior of aqueous solutions of Separan AP‐30®, polymethylcellulose, and polyvinylpyrrolidone was studied experimentally. These solutions exhibit non‐Newtonian flow behavior in simple shear, and are characterized by one of several 2, 3, or 4 parameter rheological equations. The equations used included the power law, the Ellis model, Spriggs equation, the Herschel‐Bulkley equation, and Meter's model. The power law model fits the data for each of the solutions over a limited range of shear rates, whereas the other models, which include either a lower shear rate limiting Newtonian viscosity, and/or an upper shear rate limiting Newtonian viscosity, or a yield stress, fit the data well over a wide range of shear rates from 0.00675 to 1076 sec−1. The pressure drop‐flow rate data for the same aqueous solutions flowing through packed beds were correlated well by the Ergun equation using the various rheological models applied in this work to evaluate a modified fluid viscosity. In each case it was found that the rheological model which best fit the viscometric data also gave the best packed bed friction factor correlation, and that no one model, such as the powerlaw, or the Ellis model, is the best one to use in all cases for all solutions. For polyvinylpyrrolidone solutions large deviations between experimental values of friction factor and those from the Ergun equation occurred for modified Reynolds numbers greater than one. A pseudo viscoelastic parameter was used to improve the friction factor correlation empirically at high Reynolds numbers.
Strength of polymethylmethacrylate in air and in n‐propanol
Authors: McCammond D. , Ward C. A. 
Published: December 2004

AbstractA series of tests was conducted to measure the failure strengths of notched polymethylmethacrylate tensile specimens in air and n‐propanol. Tests were conducted on specimens which had been subjected to creep stresses of various magnitudes and for different times. The resulting data indicate that two opposing factors contribute to the fracture strength in n‐propanol. The presence of fluid during crack propagation increases the nominal fracture failure stress. Diffusion of the fluid into the polymer produces crazing resulting in the provision of a preferential crack path and consequent lowering of the fracture strength. The former mechanism dominates at small pre‐stresses or at short creep times, resulting in an increase in strength in n‐propanol over that in air. However, the latter mechanism is dominant at higher creep stresses and longer creep times with a resulting decrease in strength in n‐propanol compared to that in air.
The migration of plasticizers from poly(vinyl chloride) into edible oils
Authors: Kampouris Emmanuel M. 
Published: December 2004

AbstractThe migration of phthalate plasticizers from poly (vinyl chloride) into edible oils has been analyzed. The principal method used involved 14C‐labeled dibutyl and dioctyl phthalates with detection by liquid scintillation spectrophotometry. In most cases, the migration of the main plasticizer was accompanied by the migration of the secondary plasticizer, when present, and by diffusion of the oil into the polymer. Comparison of the scintillation results with those obtained by weight loss measurements can give quantitative information on the amount of the liquid medium that diffuses during the migration process. The effect of the following factors on the migration process was examined; (a) the nature and acidity of the edible oil, (b) the composition and amount of phthalate plasticizer, (c) the amount of epoxy plasticizer, and (d) the temperature and time of contact.
Uni‐ and biaxial stretching of chlorinated pvc sheets. A fundamental study of thermoformability
Authors: De Vries A. J. , Bonnebat C. 
Published: December 2004

AbstractChlorinated PVC is superior to unmodified PVC as a thermoplastic for use in thermoforming, especially if improved heat resistance and dimensional stability are required. In the present report, results tire given of a fundamental experimental study on the thermoformability of CPVC sheets obtained by calendering various formulations based on CPVC resins with at least 65 percent chlorine content. Extensibility as well as the relationship between stress and strain in uni‐ and biaxial stretching have been determined as a function of temperature and rate of stretching by means of specially devised, highly instrumented laboratory equipment. Stress‐strain relations under isothermal conditions and at constant strain rate are compared for the two modes of stretching, and the difference in behavior between PVC and CPVC, particularly with regard to the effect of temperature, is emphasized. Internal stresses frozen in during cooling, following rapid stretching at appropriate thermoforming temperatures, have been determined by means of a detailed analysis of retractive force measurements. The relationship between internal stress and molecular orientation is discussed as well as the effect of the latter parameters on various properties of technological interest: dimensional stability, impact resistance, and gas permeability.
A study of chain addition polymerizations with temperature variations: III. Thermal runaway and instability in styrene polymerization—an experimental study
Authors: Sebastian D. H. , Biesenberger J. A. 
Published: December 2004

AbstractThermal runaway arid parametric sensitivity were experimentally demonstrated in styrene polymerizations. Ignition boundaries were established for several initiator concentrations and a dimensionless boundary plotted. Runaway sensitivity was shown to disappear under specific conditions.
Crystallization from a strained melt or solution
Authors: Peterlin A. 
Published: December 2004

AbstractThe elongation and orientation of randomly coiled macromolecules in a strained melt or solution reduces their entropy and thus increases the crystallization or melting temperature of the ideal lattice. At any given temperature of experiment this enhances nucleation and crystal growth rate. As a rule, linear primary nuclei are formed. They contain more or less extended chains. The existence of row nuclei reduces the local gradient in the liquid to such an extent that further crystallization proceeds by epitaxial overgrowth of folded chain lamellae. Densely packed cylindrites are formed with the ribbon‐like lamellae radiating from the central row nucleus. The irregular shish‐kebab structure observed in stirred or sonicated solutions seems to be formed by subsequent exial deformation of cylindrites in the flow field. It displaces the lamellae irregularly and thus produces a great many microfibrillar elements parallel to the original row nuclei. The almost completely extended chains in the shish yield a high elastic modulus and tensile strength for exial loading. The shish‐kebab morphology in fibers as spun does not affect to a great extent the mechanical properties obtainable by subsequent drawing. The lamellae are transformed into microfibrils in very much the same manner as in spherulitic samples. But the highly regular orientation of lamellae seems to result in a more uniform drawing and hence a stronger fiber. In an extremely high temperature and pressure gradient, the melt extrusion produces hard elastomers where the lamellae of the cylindrites seem to be locally stapled. Upon application of tensile load in the extrusion direction, the intervening sections bend like beams, thus forming thin holes extending in the direction perpendicular to the load. The holes enormously enhance the permeability for gases and liquids. The elastic bending of lamellae yields the high recoverable strain and low tensile modulus.
Morphological changes during oriented polymer crystallization
Authors: Gaylord R. J. , Lohse D. J. 
Published: December 2004

AbstractA theory of the stress‐induced crystallization of polymeric networks is presented which takes into account 1) the free energy of fusion, 2) crystal surface energies and 3) entropic changes in the amorphous sections of crystallizing chains. It is assumed that the vector running from one end to the other of the crystallite is oriented in the direction of network extension, irrespective of crystal morphology, thus minimizing the free energy of crystallization. Assuming that the network assumes the crystal morphology which minimizes the free energy of the network at a given degree of crystallinity and that the crystallization proceeds along this lowest free energy path, it is predicted for simple network extension that growth of a perfectly oriented extended‐chain crystal occurs initially, changing to a one‐fold crystal oriented perpendicular to extension at low extension and to a two‐fold crystal having nearly perfect orientation at High extension. The stress is predicted to decay initially and then to rise as the network chains switch from an extended‐to a folded‐chain morphology. Spatial factors which may trap chains in the ex tended‐chain morphology or prematurely stopping the crystallization process can result in a mixed crystal morphology. At high extension, the structure is similar to that of the shish kebab.
Crystallization of networks under stress
Authors: Smith K. J. 
Published: December 2004

AbstractA theory of crystallization under stress is developed about the premise that the direction a chain takes through a crystallite, relative to its end‐to‐end vector, is determined by the first few links of a chain that initially deposit onto the crystallite surface. Since these few links are quickly trapped by subsequently crystallizing chains, their orientational probability prior to deposition governs the chain direction through the crystallite, and the properties of the system depend upon a statistical distribution of all vector orientations. Such a model leads to a relationship between the melting temperature and the degree of network orientation, and relates the retractive force to temperature in the crystallization region. The theory appears to adequately describe some of the published data on rubber and polychloroprene networks.
Unlimited flex life in the molded‐in hinge in polypropylene: A structural hypothesis
Authors: Clark E. S. , Spruiell J. E. 
Published: December 2004

AbstractInjection molded hinges of polypropylene possess uniquely unlimited flex life. Polypropylene when crystallized from the melt under extensional flow (as in injection, molded hinges), shows a unique morphology characterized by a planar row structure of lamellae accompanied by a bimodal distribution of the unit cells having the alpha crystal phase. This bimodal orientation consists of two apparently independent orientations of the unit cells with respect to the flow direction: one with the c‐(chain) axis parallel to and one with the a′‐axis parallel to the flow direction. (The a′‐axis is a vector normal to (100) and thus parallel to a* in reciprocal space.) Experimental data on the morphology of polypropylene crystallized under extensional flow are interpreted in terms of two components. The c‐axis component corresponds to those molecules in the planar row structure. The a′‐component is attributed to secondary crystallization in which small crystallites are finely dispersed between the lamellae of the row structure. These small crystallites act as a “morphological plasticizer” protecting the load‐bearing row structure from destructive stress during flexure.
The effect of molecular weight on the physical and mechanical properties of ultra‐drawn high density polyethylene
Authors: Perkins William G. , Capiati Numa J. , Porter Roger S. 
Published: December 2004

AbstractA study has been made on the effects of molecular weight on the physical and mechanical properties of cold‐extruded high density polyethylene. Prior data indicate that such ultra‐drawn strands contain a significant fraction of extended‐chain crystals. Four samples, spanning the molecular weight range of 59,000 to 147,000, were cold‐extruded under the same conditions and were examined with respect to their melting point, degree of crystallinity, linear expansion coefficient, Young' modulus, strain to break, and tensile strength. The degree of crystallinity, linear expansion coefficient, and modulus did not change significantly with molecular weight. The melting point, strain to break, and tensile strength do increase with increasing molecular weight. This leads to the conclusion that the amount of extended‐chain crystals is invariant with molecular weight. Higher molecular weight polymers are seen as providing a greater number of the chains, thus giving the fiber a higher tensile strength.