bluuebunny/crossref_metadata_2025_split huggingface dataset:
Load‐compression behavior of brittle foams
Authors: Rusch K. C. 
Published: April 2003

AbstractQuantitative relationships between the load‐compression behavior and the physical characteristics of the foam matrix, previously reported for flexible systems, have now been extended to brittle foams. The shape of the compression curve is expressed in terms of ψ(ε), a dimensionless function of the compressive strain, while the stiffness, or load‐bearing capacity, is defined by Ef, the apparent Young's modulus. Because the brittle matrix breaks–rather than flexes–when compressed, a brittle foam exhibits a flatter and wider plateau in the load‐compression curve than a rigid (but ductile) foam of equivalent density, cell geometry, and Ef. These differences are expressed quantitatively by ψ(ε). It is important to distinguish between brittle foams and rigid, but ductile, foams. Since both types may exhibit the same stiffness, this distinction, particularly significant in energy absorbing applications, often is not considered in designing foam structures. Using the relationships established in this report, it is now possible to delineate precisely the characteristics a brittle foam must possess to meet a given load‐compression specification.
A comparison of inlet‐ and exit‐region flow of viscoelastic fluids in capillary tubes
Authors: Oliver D. R. , Macsporran W. , Hiorns B. M. 
Published: April 2003

AbstractIt is shown, in confirmation of earlier work, that when a viscoelastic liquid flows into a capillary tube, a definite fraction of the inlet pressure drop is required to overcome effects of elastic origin. This pressure drop, ΔPE, is proportional to the same power of shear rate as the steady‐state first normal stress difference measured by means of the jet thrust method. The values of ΔPE are some 1.6–8.6 times higher than the values of the first normal stress difference, the amount depending on the fluid in use but not on the elastic power‐law exponent m. The importance of the extensional mode of deformation in entry region flow is discussed. It is shown by examining dilute polymer solutions after varying periods of degradation that changes in ΔPE are closely related to changes in the turbulence suppression characteristics of the solutions. The extensional mode of deformation is presumably important in both types of experiment. Both n‐pentanol and a mineral oil, tested in the same small‐diameter capillary tubes as the polymeric solutions, give well‐defined values of ΔPE, which are compared with previously published normal stress figures. The mineral oil is shown to develop particularly high stresses in elongational flow, though the viscous stresses were also higher than for the polymeric solutions used. Previous evidence of the existence of shear elasticity in organic liquids is listed and the potential importance of the case of mineral oil is emphasized.
Thermogravimetric and differential thermal analysis of cellulose, hemicellulose, and lignin
Authors: Ramiah M. V. 
Published: April 2003

AbstractThe thermal degradation of samples of cellulose, hemicellulose, and lignin have been investigated using the techniques of thermogravimetric analysis (TGA) and differential thermal analysis (DTA) between room temperature and 600°C. The results calculated from static and dynamic TGA indicated that the activation energyEfor thermal degradation for different cellulosic, hemicellulose, and lignin samples is in the range 36–60, 15–26, and 13–19 kcal/mole, respectively. DTA of all the wood components studied showed an endothermic tendency around 100°C in an atmosphere of flowing nitrogen and stationary air. However, in the presence of flowing oxygen this endothermic effect was absent. In the active pyrolysis temperature range in flowing nitrogen and stationary air atmospheres, thermal degradation of Avicel cellulose occurred via a sharp endothermic and a sharp exothermic process, the endothermic nadir and exothermic peak being at 320° and 360°C, respectively. In the presence of oxygen, combustion of Avicel cellulose occurred via two sharp exothermic processes. DTA studies of different cellulose samples in the presence of air showed that the shape of the curve depends on the sources from which the samples were prepared as well as on the presence of noncellulosic impurities. Potassium xylan recorded a sharp exothermic peak at 290°C in a nitrogen atmosphere, and in a stationary air atmosphere it yielded an additional peak at 410°C, while in the presence of oxygen the curve showed two sharp exothermic peaks. DTA traces of periodate lignin in flowing nitrogen and air were the same and showed two exothermic peaks at 320° and 410°C, while in the presence of oxygen there were two exothermic peaks in the temperature range 200°–500°C.
The effect of high energy radiation on the electrical characteristics of pyrrone polymers
Authors: Reucroft P. J. , Scott H. , Kronick P. L. , Serafin F. L. 
Published: April 2003

AbstractGamma radiation‐induced conductivity and permanent conductivity effects produced by high doses of 2 MeV electrons have been measured in two polyimidazopyrrolone polymers. Radiation‐induced conductivity levels are small compared to those found in many common insulating polymers. Permanent increases in dark conductivity produced by accumulated doses of 5×109 rad at temperatures up to 300°C are not sufficient to inhibit ultraviolet‐visible photoconductivity. High doses of 2 MeV electrons (5×109 rad) under the same temperature conditions produce no discernible effect on dielectric properties. Both radiation‐induced conductivity and permanent dark conductivity increases were much smaller in one polymer (BTDA–DAB), suggesting the possibility of optimizing radiation resistance in this class of polymers by means of chemical structure variation. The radiolytic and thermal stability reported previously for this class of polymers has been generally confirmed, with particular reference to electrical properties.
Slow crack growth in cellulose film
Authors: Hilyard N. C. , Crum J. L. 
Published: April 2003

AbstractA simple photographic method for measuring the slow crack growth in transparent polymer film is described. Framing speeds up to 100 per second have been achieved. Experimental data for a cellulose film with centrally located initial cuts indicate that for 0 < t < 0.8tb, the crack length c increases with time t according to

where c0 is the initial cut size, K a constant, and tb the time to fracture.
Solution‐polymerized rubbers with superior breakdown properties
Authors: Uraneck C. A. , Short J. N. 
Published: April 2003

AbstractNatural rubber breaks down readily during mechanical mixing, and rubber processors have traditionally made good use of this property. Emulsion SBR rubber breaks down with greater difficulty and some polybutadiene rubbers, not at all. This paper describes a new class of solution elastomers, both polybutadiene and butadiene–styrene copolymers, designed to undergo controlled breakdown during processing. They can be made by reacting active polymer lithium molecules with tin compounds to produce star‐shaped molecules containing a central tin atom connected by tin–carbon bonds. When such a product is mixed with an organic (stearic) acid, some of the tin bonds are ruptured and the desired breakdown occurs. The extent of breakdown can be controlled by the mixing conditions and the amount of organic acid employed. There are numerous applications in which these rubbers process more easily and display better properties than conventional rubbers. Data on breakdown under various conditions and physical properties of the compounds are presented in this paper.In addition to the superior processing characteristics, these products introduce a new concept of elastomer breakdown. The breaking of a polymer chain at a carbon–tin bond by a chemical agent eliminates the need for breaking carbon–carbon bonds by mechanical energy or oxidative degradation. Accomplishing polymer breakdown by a controlled reaction, rather than by conventional means, has long been an unsolved problem of the rubber industry.
Energy‐absorbing characteristics of foamed polymers
Authors: Rusch K. C. 
Published: April 2003

AbstractThe energy‐absorbing characteristics of a foam are determined by its load–compression response, and hence reflect the geometric structure and physical properties of the matrix material. In this report, the energy‐absorbing characteristics are expressed in terms of three dimensionless quantities: (1) K, the energy‐absorbing efficiency, (2) I, the impact energy per unit volume divided by Ef, and (3) I/K, the maximum decelerating force per unit area divided by Ef, where Ef is the apparent Young's modulus. Using the calculation procedures described in this report, it is now possible to delineate the geometric structure and physical properties a foam matrix must possess to meet a given energy absorption specification. This approach shows that: (1) the energy‐absorbing characteristics of a brittle foam are superior to those of a ductile foam, (2) the optimum energy‐absorbing foam has a large cell size, a narrow cell size distribution, and a minimum number of reinforcing membranes between the cells, (3) foam composites offer no significant advantage over a single foam, and (4) the optimum energy‐absorbing region obtains over a tenfold change in impact velocity and can be extended in a given system only if the foam stiffness increases while the impact velocity is increased, as in a fluidfilled foam.
Inorganic polymers. IV. Reactions of poly(P‐phenylphosphonic imide). The replacement polymerization of poly(P‐phenylphosphonic imide) with piperazine
Authors: Shaw R. A. , Ogawa Takeshi 
Published: April 2003

AbstractPoly(P‐phenylphosphonic imide) reacts with a variety of compounds containing reactive hydrogen atoms, due to the instability of the PNP linkage to such reagents. Utilization of this property of the polymer may provide convenient routes to prepare various types of P‐phenylphosphonic diamides, Ph(O)P(NH2)(NR′2), phosphonamidates, PhP(O)(NH2)(OR), etc. (R = H, alkyl, aryl, etc.). The reaction of the polyimide with piperazine results in a polymer containing
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structural units. The polymer thus obtained is however only partially soluble in the usual organic solvents, and this insolubility is probably due to crosslinking catalyzed by piperazine. The product polymer was found to be thermoplastic.
Studies on sublimation of disperse dye out of dyed polymers. II. Rate of sublimation and amorphous transition of polypropylene
Authors: Okajima Saburo , Sato Nobuhiko , Tasaka Motowo 
Published: April 2003

AbstractThe diffusion coefficient D of disperse dyes through unmodified polypropylene (dyed at 120° and 137°C) was measured at 50°–160°C in the dry system. The diffusion transition points indicated by the breaks in the log D versus 1/T°K were obtained at about 70°, 90°, and 115°C. The 70° and 115°C transitions are in good accordance with the transition temperature of smectic into monoclinic phase and with the temperature of abrupt change in lattice expansion of monoclinic crystal, respectively. These phenomena were explained on the basis of the intimate correspondence between amorphous and crystalline transitions, as expressed by one of us for poly(ethylene terephthalate). The 115°C transition was confirmed by the same sort of diffusion transition occurring, expectedly, at 83°C in the case of polyethylene, an abrupt increase in lattice expansion of which had been found at about 80°C. The diffusion transitions were also confirmed by dilatometry and shrinkage measurement. The 90°C transition has never been reported and it cannot be explained at present.
The sorption of poly(vinyl acetate) on cellulose. I. The nature and extent of the sorbed layer
Authors: Alince B. , Kuniak L. , Robertson A. A. 
Published: April 2003

AbstractThe sorption of poly(vinyl acetate) from benzene solution onto cellulose fibers has been investigated with particular attention to the nature and extent of the sorbed layer of polymer. The cellulose substrate has been varied by swelling pretreatments with water, ethylenediamine, and 18% sodium hydroxide. The density of the sorbed polymer after drying was found to be similar to that of the bulk polymer (1.19–1.20 g/cm3). Water vapor sorption isotherms were used to evaluate the internal surface of cellulose and the decrease in the surface area accessible to water after sorption of the polymer. This decrease was considered equivalent to the area covered by sorbed polymer. The amount of polymer sorbed per unit area (5.0–5.5 mg PVAc sorbed from benzene per 1 m2 of cellulose surface) was found to be substantially independent of the amount of sorbed polymer and of the swelling pretreatment, indicating that the thickness of the sorbed layer was quite uniform (40–50 Å). A comparison of the thickness of the sorbed layer in the dry state with the thickness of a monolayer with polymer molecules lying flat on the solid surface indicated that the fraction of the polymer segments attached directly to the surface was about 0.10. The amount of polymer sorbed per unit area of cellulose and consequently the thickness of the sorbed layer and the fraction of attachment can be affected by the nature of the solvent from which the polymer is sorbed.
Effects of thermal history on the peel strength of linear polyethylene
Authors: Tordella John P. 
Published: April 2003

AbstractPeel strength of linear polyethylene–aluminum bonds is strongly affected by thermal history. Slow cooling from the melt resulted in 10 lb/in. peel strength; quenching, in 50–90 lb/in.; annealing of quenched bonds reduced the peel strength to 30 lb/in. Adhesion to aluminum was obtained by treating the substrates in a solution of vinyl triethoxysilane. Cohesive failure occurred regardless of thermal treatment. The changes in peel strength were not due to changes in strength of the bulk polymer. Rather, the volume of polymer deformed in peeling seemed to correlate with strength. No correlation was found between peel strength and degree of crystallinity or of transcrystalline orientation. Segregation resulting in a weak boundary layer seems to be the probable cause of the dependence of peel strength on cooling rate, and changes in the tie molecule configuration, the cause of loss of strength on annealing.
Time‐dependent flow of quasi‐linear viscoelastic fluids
Authors: Chong J. S. , Franks R. G. E. 
Published: April 2003

AbstractTransient flow behavior of an incompressible quasi‐linear viscoelastic fluid under suddenly applied constant pressure as well as under a periodic pressure gradient was investigated using a three‐parameter relaxation function. In the light of these solutions, the roll of viscoelastic relaxation in the overshooting of volumetric flow rate and the effect of viscoelastic parameters on the mean square velocity profile are discussed.
Some studies on the swelling behavior of polyethylene
Authors: Rogers Morris G. 
Published: April 2003

AbstractWhen polymers are extruded from a capillary, the amount of extrudate swelling is generally found to be a function of shear rate and capillary dimensions. Experiments with polyethylene now show that when shear rate is replaced by an average transit time in the capillary, postextrusion swell becomes a function of transit time only. Plots of swell versus transit time are independent of the applied stress and reduce to a single line for capillaries of different dimensions. The swell was found to be dependent upon the average molecular weight and the molecular weight distribution. Little correlation, however, was found with the amount of high molecular weight fractions.
Crosslinking cotton cellulose with ethyleneurea derivatives having varying hydrogen‐bonding capabilities. II. Accessibility determinations
Authors: Stevens C. V. , Smith B. F. 
Published: April 2003

AbstractIn a continuation of previously reported work of the effect on cotton cellulose of ethyleneurea crosslinking agents modified with ring substituents of varying hydrogen‐bonding capabilities, accessibilities of the cellulosic hydroxylic protons to exchange with deuterium oxide vapor were determined by means of infrared spectroscopy. In analyzing these values with respect to previously reported data on physical properties of the treated fabrics, it was found that accessibility to deuterium oxide did not correlate with moisture regain of the resin‐treated samples as has been reported for physically modified celluloses. It appears that the different resins did have some effect on the structure of water adsorbed by the fiber and also that the solvent affected the manner in which the resins attached themselves to the cellulose and eliminated water from the structure. Values of accessibility were not found to correlate well with crease recovery, although a weak trend was indicated. Accessibility was found to decrease as the infrared band for ring stretching decreased.
Some thermodynamic aspects of polymer adhesion
Authors: Owens D. K. 
Published: April 2003

AbstractRecently developed techniques permit the estimation of the surface free energy of polymers and the separation of this free energy into dispersion and hydrogen‐bonding components. These techniques have been used to calculate the thermodynamic reversible work of adhesion of a vinylidene chloride copolymer coating to propylene film. The changes in work of adhesion upon immersion of the coated polypropylene in water and surfactant solutions were calculated. When the calculated work of adhesion was negative, spontaneous separation of the coating from the polypropylene occurred upon immersion in all cases. When the calculated work of adhesion was positive, no separation was observed in agreement with theory.
The radiation‐initiated solution polymerization of vinylidene fluoride
Authors: Doll W. W. , Lando J. B. 
Published: April 2003

AbstractThe radiation‐initiated solution polymerization of vinylidene fluoride was examined in an effort to determine the effect of polymerization conditions on the head‐to‐head content of the resulting poly(vinylidene fluoride). No appreciable change was observed in the head‐to‐head content when this new type of polymerization was utilized. However, the polymers which resulted had melting points 10–15°C higher than those of the suspension‐polymerized poly(vinylidene fluoride), higher crystallinity, and, when trifluoroacetic acid was used as a solvent, a higher molecular weight.
On the rheological interpretation of die swell in molten polymers
Authors: Han Chang Dae 
Published: April 2003

AbstractThe reasons are given for the failure of the momentum method due to Metzner et al. to predict correct orders of magnitude in normal stress difference of polymer melts in simple shearing flow, and an expression is given for calculating the normal stress difference of polymer melts in steady fully‐developed flow from “exit pressure” measurements.
Dynamic mechanical properties, structure, and composition of impact polystyrene
Authors: Cigna G. 
Published: April 2003

AbstractTwo series of impact polystyrene were studied; they had been obtained by grafting and by mechanical mixing, at two different known polybutadiene levels. Their biphasic structure had been characterized by optical microscopy and physicochemical separation. The following factors were investigated: morphology and content of the dispersed phase and continuous phase, composition of the dispersed phase, and molecular weight of the continuous phase. The elastic shear modulus and mechanical damping were measured. It was found that the elastic shear modulus of the two series of materials does not depend on the total polybutadiene content, as is often suggested in the literature, but on the rubbery dispersed phase content. The polybutadiene concentration of this phase, although varying between 100% for the mechanical mixes and 34% for one of the grafted polymers, does not influence the mentioned correlation. The particle size of the dispersed phase and the molecular weight the continuous phase have very little or no influence. The found correlation agrees with the theories for the moduli of models consisting of dispersions of spheres or particles in a matrix, like those of Kerner,13 Hashin,14,15 and Mackenzie.18
Influence of diphenyl ether and water on the polymerization of isoprene with triisobutylaluminium and titanium tetrachloride
Authors: Gippin Morris 
Published: April 2003

AbstractIn the polymerization of isoprene with the i‐Bu3Al/TiCl4 catalyst at the mole ratio of 1.0 the diphenyl ether adduct of the i‐Bu3Al showed no effect on the catalyst efficiency. The ether did not improve the low efficiency of the catalyst at ratios slightly above 1.0, but below 1.0 it brought the catalyst activity up to optimum. The ether compensated for the deleterious effects upon the catalyst of low amounts of water present in the isoprene solution in hexane. At the Al/Ti mole ratio slightly above 1.0, water and diphenyl ether were found to act synergistically in raising catalyst efficiency. In addition, at or close to optimal operating Al/Ti mole ratios the diphenyl ether had a very marked effect in improving the polymerization rate. Polymer properties were generally unaffected by use of the ether‐coordinated catalyst.
Mechanism and kinetics of polyethylene crosslinking by α,α′‐bis(tert‐butylperoxy)‐p‐diisopropylbenzene
Authors: Šimúnková D. , Rado R. , Mlejnek O. 
Published: April 2003

AbstractThe study of the mechanism of polyethylene crosslinking is realized by a kinetic analysis of the α,α‐bis(tert‐butylperoxy)‐p‐diisopropylbenzene decomposition, as well as by the determination of its decomposition products and crosslink formation in the polymer. The experiments were carried out in a temperature range of 118°–148°C in both polyethylene and its low‐molecular model, n‐octane. From the results obtained it follows that the peroxide decomposition in both hydrocarbon media is kinetically a unimolecular reaction with an activation energy of 36 ± 2 kcal/mole and with an equivalent participation of both peroxidic groups, whereby a biradical formation is improbable. Macroradicals arise by a dehydrogenization reaction in which mainly primary oxyradicals of various types take part and methyl radicals are also formed by a transformation process of the former. Both types of radicals decay exclusively in a substitution reaction with polymer chains. The whole process is terminated by macroradical recombination so leading to crosslink formation in polyethylene.
Nitric acid attack on polypropylene. Weight and density changes and blister formation during the initial stages
Authors: Armond V. J. , Atkinson J. R. 
Published: April 2003

AbstractWeight loss and density change results are presented to indicate the manner in which fuming nitric acid at 70°C attacks three grades of polypropylene of different crystallinity. The phenomenon of surface blistering is discussed in relation to the spherulitic structure at the surface of the bulk specimen.