bluuebunny/crossref_metadata_2025 huggingface dataset:
Complicated Left-Sided Native Valve Endocarditis in Adults
Authors: Hasbun Rodrigo , Vikram Holenarasipur R. , Barakat Lydia A. , Buenconsejo Joan , Quagliarello Vincent J.
Published: April 2003

Context

Complicated left-sided native valve endocarditis causes significant morbidity and mortality in adults. Lack of valid data regarding estimation of prognosis makes management of this condition difficult.

Objective

To derive and externally validate a prognostic classification system for adults with complicated left-sided native valve endocarditis.

Design, Setting, and Patients

Retrospective observational cohort study conducted from January 1990 to January 2000 at 7 Connecticut hospitals among 513 patients older than 16 years who experienced complicated left-sided native valve endocarditis and who were divided into derivation (n = 259) and validation (n = 254) cohorts.

Main Outcome Measure

All-cause mortality at 6 months after baseline.

Results

In the derivation and validation cohorts, the 6-month mortality rates were 25% and 26%, respectively. Five baseline features were independently associated with 6-month mortality (comorbidity [P = .03], abnormal mental status [P = .02], moderate to severe congestive heart failure [P = .01], bacterial etiology other than viridans streptococci [P<.001 except Staphylococcus aureus, P = .004], and medical therapy without valve surgery [P = .002]) and were used to create a prognostic classification system. In the derivation cohort, patients were classified into 4 groups with increasing risk for 6-month mortality: 5%, 15%, 31%, and 59% (P<.001). In the validation cohort, a similar risk among the 4 groups was observed: 7%, 19%, 32%, and 69% (P<.001).

Conclusions

Adults with complicated left-sided native valve endocarditis can be accurately risk stratified using baseline features into 4 groups of prognostic severity. This prognostic classification system might be useful for facilitating management decisions.
Variability in reproductive success viewed from a life‐history perspective in baboons
Authors: Altmann Jeanne , Alberts Susan C.
Published: April 2003

Nonhuman primates, like humans, mature slowly and have low fertility during a relatively long life. As data have accumulated on life‐history patterns of nonhuman primates, comparative studies have yielded important insights into the evolution of this slow life‐history style of primates. However, in order to understand selection pressures and evolutionary potential within species, it is important to complement comparative studies with detailed studies of life‐history variability within species and to identify sources of this variability. Here we present a summary of how foraging environment, social status, and group size (a measure of population density) contribute to within‐population variance in reproductive success for savannah baboons. We also discuss the extent to which savannah baboons, with their highly flexible and adaptable behavior, change their foraging environments by shifting home ranges and seeking rich food sources and how low‐ranking females, which disproportionately bear the costs of social life, may mitigate those costs. Am. J. Hum. Biol. 15:401–409, 2003. © 2003 Wiley‐Liss, Inc.
Dynamical properties of the new “rubber‐like” irradiated polyethylene
Authors: Rady A. A.
Published: April 2003

Polyethylene irradiated in the B.E.P.O. pile at Harwell has been found to acquire new mechanical properties. At a certain dose, polyethylene was found to behave like rubber.
The effect of solvents on high molecular weight, stable acetal resins
Authors: Alsup R. G. , Punderson J. O. , Leverett G. F.
Published: April 2003

High molecular weight polyoxymethylenes are not soluble at room temperature in any of the hundreds of solvents or solvent systems tested. However, solutions can be obtained at elevated temperatures with a wide variety of solvents. Phenolic compounds are the most effective at temperatures of 50–100°C. At the other extreme of solubility, solvents are absorbed by the acetal polymer in varying amounts, depending on the crystallinity of the polymer and the cohesive energy density of the solvent. The absorption is concentrated entirely in the noncrystalline region of the polymer.
The kinetics of the thermal degradation of the synthetic styrenated polyester, laminac 4116
Authors: Anderson David A. , Freeman Eli S.
Published: April 2003

The kinetics of the thermal decomposition of the polyester, Laminac 4116, were investigated in air and argon at atmospheric pressure by means of a continuous recording thermobalance and by differential thermal analysis. Samples were heated from ambient temperature to 600°C. at rates of 5°/min. and 15°/min. In air and argon, decompostion commences at 200°C. and is complete at 550 and 450°C., respectively. Four modes of degradation in oxygen and two in argon are indicated from derivative plots of the thermogravimetric curves. The kinetics of reaction were evaluated by the method of Freeman and Carroll. In the presence of air, the initial stage of reaction appears to involve formation of an unstable hydroperoxide intermediate which undergoes rearrangement and degradation. The energy of activation was calculated to be 19 kcal./mole. An exotherm corresponding to this first stage of degradation is observed by differential thermal analysis. The second and third stages of reaction in air correspond approximately to the two stages in argon with respect to their endothermal nature and to the temperature regions over which they occur. Mass spectrometric and infrared analysis were employed for identification of gaseous and volatile products. The fourth stage of reaction in air appears to involve the oxidation of carbon to carbon dioxide. Mechanisms of reaction are proposed and discussed.
Effect of spherulites on the mechanical properties of nylon 66
Authors: Starkweather Howard W. , Brooks Richard E.
Published: April 2003

The presence of spherulites in nylon 66 increases the yield point and reduces the effects of variations in per cent crystallinity. Decreasing the size of the spherulites through increased nucleation results in a higher flexural modulus and yield point, a lower ultimate elongation, and a loss of ductility. These effects are markedly reduced by raising the temperature or water content. The effects of spherulite size in nylon and grain size in metals such as mild steel are compared.
The mechanism of polyethylene oxidation
Authors: Baum B.
Published: April 2003

As evidenced by formation of peroxides and carbonyl, reaction occurs during the oxidation induction period of polyethylene. The meaning of the term oxidation induction period is revealed by the tremendous change in melt index, carbonyl, density, color, tensile, and elongation occurring towards the end of this time period. Hydroperoxide forms long before the end of the oxidation induction period even in the presence of an antioxidant. At any temperature both chain scission and crosslinking occur simultaneously. The rate of oxidation is accelerated by increasing temperature, unsaturation, and branching. Molecular weight seems to have no effect.
Photosensitive polymers. II. Sensitization of poly(vinyl cinnamate)
Authors: Robertson E. M. , van Deusen W. P. , Minsk L. M.
Published: April 2003

It was reported in Part I of this series that coatings of various polymers containing cinnamic ester groups are rendered insoluble by exposure to ultraviolet radiation, and that the rate of insolubilization may be increased by the inclusion of certain organic compounds. A continued systematic examination of the behavior of several hundred organic compounds has revealed that the ability to sensitize to some degree is quite general, provided that no complicating factors are present. The sensitivity of poly(vinyl cinnamate) is decreased by the presence of reducing groups in the addend, and sensitizing activity is lowered by interaction between adjacent groups. It is enhanced by the introduction of increasing conjugation and of ketone, nitro, or amino groups. Spectrograms of polymer‐sensitizer combinations indicate that, with increasing sensitivity value, the sensitivity shifts towards, and, in some cases, into, the visible portion of the spectrum.
Mechanism of lubricant‐extrusion of teflon tfe‐tetrafluoroethylene resins
Authors: Snelling G. R. , Lontz J. F.
Published: April 2003

For an understanding of the phenomenon of lubricant extrusion of Teflon tetrafluoroethylene resin under nonmelt conditions, a mechanism is proposed based on observed extrusion‐hardening and dependence of flow rate on extrusion pressure. These factors can be derived from expressions in which the maximum shearing stress is equated as the sum of two components, one proportional to the maximum shearing strain (strain‐hardening component) and another proportional to the strain rate. Thus, in turn, permits the derivation of an expression for the die pressure drop which is in agreement with the experimental data related to flow rate, die dimensions, lubricant concentrations, and time of extrusion. The analysis provides some insight into aspects of commercial extrusion, particularly in wire coating, with practical consideration of the critical nature of guide tip positioning and the effect of wire coating speed on die pressure.
Interaction of cellulose with small molecules. Glycerol and ethylene carbonate
Authors: Wellisch Eric , Hagan Lamont , Marker Leon , Sweeting Orville J.
Published: April 2003

The equilibrium moisture content of films softened with hygroscopic glycerol or nonhygroscopic ethylene carbonate was determined as a function of softener concentration at 15, 35, 65, 81, and 93% R.H. and compared to the hygroscopicity of unsoftened film and of the pure softeners at the same concentrations. The difference in water content assumed to be caused by interaction between softener and cellulose was calculated in moles of water per mole of softener and per mole of cellulose. A quantitative measure of softener‐cellulose interaction at low and high relative humidities is thus obtained. Ethylene carbonate shows a negative interaction and seems to function only as an inert cushion between cellulose chains, while glycerol interacts with cellulose. This interaction increases with decreasing moisture content (at lower relative humidities) and with increased softener concentration. The softener‐cellulose interaction is a necessary condition for proper softening.
The crosslinking of plasticized poly(methyl methacrylate) by ionizing radiation
Authors: Pinner S. H. , Wycherley V.
Published: April 2003

Poly(methyl methacrylate) (PMMA) normally undergoes random main‐chain fracture when exposed to ionizing radiation. In the presence of radical traps, partial protection against degradation may occur, but no crosslinking reactions have hitherto been observed. In this work, diallyl sebacate has been incorporated into PMMA prior to exposure to ionizing radiation (2 m.e.v. electrons). The plasticized PMMA had a low softening point, which was increased by irradiation due to polymerization of the diallyl ester. At the same time, the PMMA was rendered insoluble. With methylene chloride as solvent, the gel fraction greatly exceeded the fraction of diallyl ester present, proving that the PMMA had become crosslinked or incorporated into the allyl network. Beyond a certain dose, however, which varied with the diallyl sebacate weight fraction, continued irradiation led to increased sol fractions and reduced transition temperatures. Spectroscopic measurements showed the disappearance of allyl unsaturation per unit radiation dose to be identical, within experimental error, in the presence of PMMA as in the pure diallyl sebacate. A semiquantitative examination of the gel/dose curve and dynamic energy absorption curves for a sample containing 16% diallyl sebacate has pointed to radicals produced by radiation on the PMMA chains to be the principal initiating species, these becoming junction points to the allyl network. When the gel is depleted of allyl monomer, further radiation causes degradation of the PMMA segments.
Recrystallization of polyethylene during annealing
Authors: Statton W. O. , Geil P. H.
Published: April 2003

The thickness of single crystal lamellae of polyethylene, crystallized from solution, is found to increase greatly during annealing at temperatures above 110°C. The change is observed with small‐angle x‐ray diffraction and electron microscopy. The increase in thickness of the lamellae takes place at the expense of their lateral perfection; holes develop within the lamellae. All evidence indicates that a major refolding of the molecules occurs; this emphasizes the need for a new concept of the amount of motion and freedom that polymer molecules can have in the solid state. A similar process apparently occurs during the annealing of bulk samples crystallized from the melt.
Catalysis of the reaction of urea–formaldehyde precondensates on cellulose
Authors: Steele Richard
Published: April 2003

The reaction of dimethylol urea on cotton cellulose at 150°C. has been studied with NH4Cl and Na2CO3 as catalysts. With the ammonium salt, 0.2 mmole/g. precondensate was required to attain the maximum level of fixed resin, while maximum resistance to hydrolysis by dilute acid required 0.3–0.4 mmole/g. The acid resistance is attributed to the crosslinking of the fiber, which is primarily responsible for the changes produced in resilience and other physical properties. The application of monomethylol urea with NH4Cl does not lead to changes in acid resistance or physical properties such as are attributed to crosslinking. Catalysis with Na2CO3 does not appear to lead to crosslinking with dimethylol urea, since the treated cellulose remains soluble in cuprammonium hydroxide. There is very little difference in the effectiveness of monomethyl and dimethylol ureas for changing physical properties when they are applied with the alkaline catalyst. It is suggested that the curing step with Na2CO3 leads to further condensation through methylene ether linkages rather than to reaction with the cellulose substrate.
Studies on chlorinated polyethylenes. I. Infrared spectra of chlorinated polyethylenes
Authors: Nambu Keiichi
Published: April 2003

The infrared absorption spectra of chlorinated polyethylenes with various amounts of combined chlorine have been investigated, and some data on the mechanism of addition of chlorine to the polyethylene molecule has been studied. When polyethylene is chlorinated in carbon tetrachloride solution at 70°C. by chlorine gas, CH2CHCl and the CHClCHCl units are formed in the main carbon chain, but formation of the CCl2 units could not be detected by the present infrared spectral study.
An apparatus for the determination of the minimum film temperature of polymer emulsions
Authors: Protzman Thomas F. , Brown George L.
Published: April 2003

An apparatus has been constructed for measurement of the minimum filming temperature (MFT) of a polymer emulsion. The apparatus consists of a metal bar along which a temperature gradient may be maintained. Recessed channels are provided in which emulsion samples are spread and allowed to dry. Eight thermocouple stations along the bar are connected to a continuous recorder. Following drying of the film, the minimum temperature at which a continuous film is formed is determined. Testing of the apparatus on one emulsion examined under a variety of conditions and on samples of varying composition has demonstrated the reliability, versatility, and utility of the apparatus.
Mechanical degradation of high polymers
Authors: Bueche F.
Published: April 2003

A theory for the shear degradation of high polymers is presented. It assumes the molecules to exist in the rubbery or liquid state and does not include the effects of chemical reactions which might occur subsequent to chain rupture. The computation shows that the entanglements along the chains play a major part in the rupture process. Expressions for the rate of chain rupture are obtained in terms of the melt viscosity, shear rate, and molecular weight. Other factors enter also, but the sensitive variables are those listed. The variation of molecular weight distribution with shear degradation is considered. It is pointed out why oxidative scission during shear is not a random process. In general, the theoretical result agrees with the limited experimental data available.
Molecular basis for the mullins effect
Authors: Bueche F.
Published: April 2003

A molecular theory for the softening of filled rubbers which is caused by prestressing is presented. It is based upon the assumption that the centers of the filler particles are displaced in an affine manner during deformation of the rubber. Those network chains which are fastened at both ends to filler particles will break when the filler particles have separated enough to stretch the chains to near full elongation. The loss of these chains causes a prestressed rubber to exhibit a much lower modulus than did the original rubber. Equations are derived to describe this phenomena and are tested by comparing with data for black filled synthetic rubber. Good agreement is found if the filler surface area per chain attachment is taken as 44 A.2 and if the strength of the chain is 2 × 10−4 dynes. It is shown that the chains break loose from the filler particle rather than breaking at C C bonds along the chain. The theory appears to offer a convenient tool for systematic studies of rubber–filler interactions.
The determination of the relative isotactic content of polypropylene by extraction
Authors: Russell Charles A.
Published: April 2003

Attention is called to the variables effecting the extraction of polypropylene. Under controlled conditions, the extraction of polypropylene with first diethyl ether and then n‐heptane will give reproducible results. It is necessary to extract with heptane in an atmosphere of nitrogen. The values obtained by the extraction procedure described are regarded as relative measures of the amounts of isotactic, stereoblock and atactic material present in a sample. Extraction with n‐heptane alone by this procedure also gives the same value of relative isotacticity. Infrared studies showed that the ether soluble fractions were essentially atactic, while the n‐heptane‐soluble or stereoblock material possessed a degree of order corresponding to 20–40% isotactic polypropylene.
A study of polymer film brittleness
Authors: Amborski L. E. , Mecca T. D.
Published: April 2003

The inability of polymer chains to deform the required amount within the time allowed by a stress‐to‐failure event results in brittle failure. Factors related to brittle behavior of films were investigated. By both conventional and novel testing techniques, stress–time–temperature relationships were studied to determine the brittle point. From high‐speed tensile tests at strain rates up to 106%/min., the critical strain rate (incipient brittleness as indicated by failure accompanied by a marked decrease in ductility) was determined for representative films. High‐speed motion pictures (6,000 frames/sec.) of film failure in rice bag drop tests, were used to ascertain the time of deformation to be related to brittleness. Deformation rates were calculated to be of the order of 130 to 230 × 103%/min.
Viscous flow of molten polyethylene resins
Authors: Schott Hans , Kaghan W. S.
Published: April 2003

A screw extruder and capillary dies of different length radius ratios were used to measure melt flow and end effects for three commercial polyethylene resins, two of low density and one of high density. The apparent melt viscosities of the low density resins decreased faster with increasing shear and temperature than that of the high density resin. Zero shear activation energies for viscous flow were 11.6 and 12.7 kcal./mole for the low density resins and 7.0 for the high density resin. Apparent activation energies at fixed shear stresses were independent of shear stress while apparent activation energies at fixed shear rates decreased with increasing shear rate. End effects and recoverable shear strain were smallest for the high density resin. The differences between the melt flow characteristics of the two types of polyethylene are tentatively correlated with structure.
The estimation of catalytic parameters of metal acetylacetonates in isocyanate polymerization reactions
Authors: Weisfeld L. B.
Published: April 2003

The polyaddition process involving a hydroxy‐terminated linear polyester and an organic diisocyanate in the presence of a series of metal acetylacetonates has been investigated. The method involved kinetic analysis of plasticity build‐up in a Brabender Plastograph. Catalytic orders and relative catalytic constants (kc/k0) were determined for Mn(Aa)3, VO(Aa)2, V(Aa)3, Fe(Aa)3, Cu(Aa)2, Co(Aa)3, and Cr(Aa)3; the constants decrease in that order. Catalytic orders are unity for all complexes save manganese, which is 1.75. No correlation between dissociation potential and catalytic coefficient has been found, and it is believed that catalysis may be associated with the paramagnetic properties of the metal.
Viscoelastic factors in the strength of elastomers under complex stress by a puncture method
Authors: Livingston D. I. , Yeh G. S. , Rohall P. , Gehman S. D.
Published: April 2003

Investigations of the viscoelastic aspects of the mechanical behavior of polymers have been limited almost exclusively to relatively simple conditions of homogeneous stress, that is, to tension or shear loadings. In the present work a study has been made from the viscoelastic standpoint of the response of several elastomers to a much more complex type of stress distribution arising from penetration up to failure by a cylindrical indentor for a range of temperatures and rates of penetration. The failure or “puncture point” was determined by a dip in the recorded curve of load versus depth of penetration. The puncture strength values were reduced to 25°C. by applying the ratio of absolute temperatures and plotted against the logarithm of the reciprocal of the rate of penetration. These curves were then shifted on the time scale to give a master curve after the manner of Tobolsky and of Ferry. The logarithms of the shift factors thus obtained were related to the reciprocal of the absolute temperature over the range studied. The results indicate a broader generality for the viscoelastic principle of time–temperature equivalence than has usually been supposed.
Activated carbon‐loaded rayon monofilaments
Authors: McDowell Robert L.
Published: April 2003

Rayon monofilaments containing 80% activated carbon were prepared. They are an effective medium for adsorbing noxious odors. High grade gas‐adsorbing carbons are intimately bound in a cellulose matrix by niising the carbon in viscose ‘sodium cellulose xanthate solution’ and extruding the mixture through a special conjugate jet as iiioiiofilaments into a rayon coagulating bath. The special jet permits a backbone of plain viscose to be spun as a spine support for the carbon‐loaded portion of the monofilament to give it added strength. The diameters of the dry, nondusting monofils can be varied greatly. For air cleaning purposes the nonfilanients range from 1/64 to 3/64 in. in diameter. Although imbedded in cellulose, the carbon's capxity to remove malodors remains high. In addition, when made into a filter unit, the resistance to air flow through the unit is low. The novel use of regenerated cellulose as a carrier for large quantities of activated carbon indicatcs that other materials (catalysts, ion exchange resins, etc.) can be similarly bound in cellulose and still retain a high level of their original performance.
The dynamic properties of carbon black‐loaded natural rubber vulcanizates. Part I
Authors: Payne A. R.
Published: April 2003

The dynamic properties of a natural vulcanized rubber containing carbon black were studied for dynamic tensions of amplitude varying greatly. It was shown that both the elastic responses and viscosity change with amplitude of oscillation and with concentration and type of carbon black. The effects of thermal treatment on the dynamic modulus were also studied. Beginning with conditions of equilibrium between the hard and soft regions of the vulcanizate for very weak stresses, the values for the formation of hard regions from soft regions were determined by means of the Van't hoff isochore.
Temperature dependence of nuclear magnetic resonance absorption in coal
Authors: Sanada Y. , Honda H. , Nishioka A.
Published: April 2003

The proton magnetic resonance in the vitrain of Yūbari caking coal and its residue of pyridine extraction has been studied over the range 90 to 423°K. At lower temperature the absorption line consists of a broad component. At higher temperature this component begins to decrease rapidly in the line width and resolves into two components. This rapid narrowing of the absorption line width suggests a glass transition attributed to the molecular motion in coal. The variation of the second moment of the absorption line with temperature reflects the line width variation. From these results some information on the molecular motion and arrangement in coal have been obtained.
Adhesives in ordnance applications
Authors: Tanner W. C.
Published: April 2003

The advantages to be derived from the use of structural adhesives are discussed. Specific developments are cited to illustrate the effectiveness of adhesives in ordnance materiel. Problems peculiar to ordnance applications are discussed. The strengths of adhesive bonds as determined by “static” and “dynamic” conditions are compared, and the importance of proper joint geometry is illustrated.
Significance of good process control
Authors: Bair Floyd H.
Published: April 2003

The important place that adhesive bonding of structural and nonstructural parts has reached is largely due to the recognition and the practice of adequate and exacting processes necessary to produce acceptable parts. The procedures necessary for adhesive bonding are not common for all adhesives, adherends, or parts being bonded. During any process many variables occur that must be satisfied by the results of tests before production is started. This must be followed by quality control tests to continuously assure that high quality parts are being produced. Closely connected with processes are the temperament and capabilities of personnel doing the bonding. It is recommended that a detailed procedure be established in order to develop methods for bonding any specific end item. The purpose of this paper is to examine some processes in relation to their effect on the finished item and to recommend a pattern to follow in establishing good bonding processes.
High‐temperature ceramic adhesives
Authors: Whitney John B.
Published: April 2003

This paper describes the preparation, application, maturing, and fired properties of ceramic adhesives. The great majority of ceramic adhesives are based on a glass‐type bond similar to that found in porcelain enamels and ceramic coatings. Using a frit as the basic constituent, the adhesives are applied to clean metal surfaces and fired to produce the bond. The adhesives resulting from this process retain a useful strength at temperatures of 1000°F. or higher. A process for combining ceramic adhesives and brazing alloys is also described. This combination has produced joints superior in strength to straight ceramic adhesives and comparable in strength to standard brazed specimens.
A modified method of reduced variables for stress relaxation
Authors: Chang Franklin S. C.
Published: April 2003

It has recently been shown that stress relaxation data may be conveniently interpreted using multiple box distribution of relaxation times. The multiple box distribution treatment suggested the possibility of modifying the method of reduced variables or time‐temperature superposition principle to avoid the difficulty of shifting curves in the rubbery region. This modification has now been applied to the experimental stress relaxation data for polyisobutylene. The results obtained verify the earlier observations that the logarithms of relaxation times and modulus constant are related to the reciprocal of temperature linearly, that the slope of these semilog linear relations changes when there is a phase transition, and that two types of mechanisms are operating in the relaxation of mechanical stress. The theorized stress‐time curves predicted by both methods fit the experimental data equally well, but the modulus at very short time predicted by the reduced variables method generally is higher than that by the multiple box distribution method. Relaxation data collected under high speed stretching condition are needed for better elucidation of the short time behavior of viscoelastic material.
Behavior of high strength parachute components at impact velocities up to 700 feet per second
Authors: Coskren Robert J. , Morgan Henry M. , Chu Chauncey C.
Published: April 2003

A machine has been designed and constructed which is capable of evaluating high strength parachute components in the laboratory at impact speeds ranging from 200–750 ft./sec. The system consists mainly of a device for propelling various masses with photographic instrumentation for observing the impact. Measurement of missile deceleration gives applied force. Extension is measured for changes in gage marh on the test specimen. Energy absorbed can be calculated from the displacement of two ballistic pendulums. Results reveal that a t impact speeds force and strain waves are generated within the material which cause rapid changes in the forces measured. A theory has been proposed to explain this behavior. Energy measurements indicate a potential change in the stress‐strain curve of nylon webbings and joints during impact. Improvements in energy absorption result.
A comparison of the static and dynamic strengths of several phenolic‐ and epoxy‐impregnated paper and cloth honeycombs in compression
Authors: Lacey R. M. , Smith J. E.
Published: April 2003

Five organic crosslinked materials have been studied for compression properties at room temperature. Their static behavior (0.02 in./min.) and dynamic behavior (up to 1300 in./min.) have been measured as a function of the nature of the material or of its apparent density. The materials with‐ stand a higher stress, 30 to 40%, and show a higher modulus of elasticity, about 100%, when subjected to rapid loading. Resistance to fracture is a linear function of the apparent density at two speeds. Equipment as well as methods are described.
Relaxation processes in vulcanized rubber. I. Relation among stress relaxation, creep, recovery, and hysteresis
Authors: Gent A. N.
Published: April 2003

An experimental study is described of stress relaxation, creep, recovery, and hysteresis in vulcanized rubbers under moderate deformations. The measurements indicate that the rate of stress relaxation is substantially independent of the amount or type of deformation for moderate deformations, and is simply related to the hysteresis. The rates of creep and recovery are found to be in good agreement with values calculated from the form of the loaddeformation relationship and the (constant) value of the relaxation rate.
Polymerization of tetrahydrofuran
Authors: Burrows R. C. , Crowe B. F.
Published: April 2003

Tetrahydrofuran has been polymerized in bulk using 5–20 wt.‐% BF3 without the addition of cocatalysts to give a very high molecular weight, crystalline polymer which exhibits cold‐drawability, toughness, and low temperature flexibility. Within the ranges studied a maximum conversion of 74% was reached at 10% BF3 and 10°C. and a maximum intrinsic viscosity of 3.3 at 10% BF3 and −5°C. Equilibrium molecular weights were obtained in about two days but the highest conversions required about an eleven day polymerization period. Structure, crystallinity, mechanical properties, solubility, thermal properties, and effect of irradiation are among the aspects of the polymer discussed.
Crosslinking of vinylsilicone resins initiated by dicumyl peroxide
Authors: Hartung H. A. , Berger S. E.
Published: April 2003

The effects of cure time, temperature, and initiator concentration on the mechanical properties of a vinylsilicone resin cured with dicumyl peroxide were investigated. The resin had a second‐order transition extending from below 25 to about 100°C. The transition region broadened as the degree of crosslinking increased. Measurements of physical properties at room temperature were very sensitive to small temperature changes. Ultimate strength measurements were particularly unreliable indicators of degree of cross linking because of large random variations and because they depended upon other structural factors besides crosslink density. The best test of degree of crosslinking was modulus measurements above the transition temperature of the resin. Such measurements have a sound theoretical basis and the practical advantage of being insensitive to small temperature changes. Modulus measurements have the additional advantages of being a nondestructive test with a high degree of inherent precision compared to other physical tests. A concentration of about 1.5 wt.‐% dicumylperoxide was optimum for crosslinking the vinylsilicone resin studied. Maximum crosslinking was obtained when the peroxide was utilized slowly a t low temperatures for long cure periods. When a 4‐hr. cure was used the optimum temperature range was 125 to 135°C.
Sur la dégradation thermique du chlorure de polyvinyle. III. Etudes cinétiques sous atmosphère d'air
Authors: Guyot Alain , Benevise Jean‐Paul
Published: April 2003

Polyvinyl chloride thermal degradation was carried out under air atmosphere from 150 to 250°C. and the kinetics followed, simultaneously by thermogravimetry and hydrochloric acid evolution measurements. The overall scheme of dehydrochlorination is the same under air and inert atmospheres: it is a chain reaction initiated by thermal instability of irregular structures initially present or created during the course of the reaction. Oxidation plays an important part in the activation of these structures and reduces all activation energies; furthermore, it creates new centers. Oxygen participates alao in propagation and termination of chains of reactions. With an increase in the reaction chains, simultaneously, backbone CC bonds are broken up, and the residue is formed by branched molecules small enough to remain soluble. All kinds of structures, but especially the polyenic ones, are oxidized. When their concentration and degree of oxidation are great enough, a further decomposition of these degraded parts into volatile oxidized products occurs; the velocity of this reaction is then nearly equal to that of macromolecular residue oxidation.
On the colligative nature of the specific refractive increment for statistical copolymers
Authors: Kinsinger J. B. , Bartlett J. S. , Rauscher W. H.
Published: April 2003

The specific refractive increment for statistical copolymers is shown to be colligative in nature for copolymers of styrene–methyl methacrylate thus giving direct evidence to support the assumption of Stockmayer et al. on the theory for light scattering in copolymers. The determination of the mole fraction of mer composition in copolymers by specific refractive increment measurements is shown to be a useful technique and nearly as precise as chemical analysis for carbon. The technique is restricted to soluble systems and is limited by the resolution of the measuring instrument.
Hygrophotographic studies on the permeability to water and moisture of packaging materials
Authors: Sivadjian Joseph , Corral Francisco
Published: April 2003

The permeability to water and humidity of films of plastic materials of different natures and thicknesses was the object of much research achieved by many methods. However, these methods, while relatively simple, are very laborious, demand much time (for example, the gravimetric method), and are often imprecise. The hygrophotographic method is as simple as it is rapid. It requires a minimum of measuring instruments, or, in cases of urgency, no instruments a t all. Special attention was given to the action on the permeability of certain factors such as presence of plasticizers, radioactive rays, temperature, and aging. It was demonstrated that while the presence of plasticizer increases the permeability to water, aging lowers it, precisely because of the departure of this plasticizer during the aging process. It was confirmed that in certain cases (e.g., polyethylene deprived of plasticizers) the law of Q10, according to which in general the permeability of a good film approximately doubles for a 10°C. (18°F.) rise in temperature, is sufficiently verified and that in other cases (e.g., plasticized PVC) the experimental results deviate considerably from ths simple law: the augmentation is at times much greater, especially between 45 and 55°C., than this law indicates, whereas between 55 and 65°C. the law obtains better. On the other hand, the action of the γ‐rays is manifested by an increase, sufficiently visible, of the permeability when the polyethylenic film is irradiated in vacuum, but when irradiated in air the films become too brittle for handling. A series of systematic tests determined the importance of the phenomenon of sorption for the different kinds of plastic films; the degrees of discoloration of the hygrophotographic plates enclosed in plastic bags new or previously heated in an oven at 65°C. during a specified time were compared. It was observed that the thicker the film, the more humidity absorbed. The Manolene films, 200 μ in thickness, had to be heated for 13 hr. at 65°C. for the sorbed water to be completely evaporated.
Internal field emission in carbon black‐loaded natural rubber vulcanizates
Authors: van Beek L. K. H. , van Pul B. I. C. F.
Published: April 2003

The nonohmic behavior of carbon black‐loaded natural rubber viilcanizates was studied. Three samples contained high‐abrasion furnace black (HAF) in good, moderate, and poor dispersion. Another sample contained a good dispersion of medium thermal black (MT). The nonohmic behavior of the poor HAF dispersion and that of the MT dispersion could be interpreted as due to internal field emission acroM insulating gap widths of 2 and 2.5 μ. The existence of such gaps waa confirmed by electron micrographs. No clear evidence of internal field emission could be obtained for the good and moderate HAP dispersions where, according to electron micrographs, the gaps are much narrower. There is some indication that the degree of diapersion can be correlated with field emission characteristics.
Some mechanical changes during sorption of water by dry keratin fibers in atmospheres near saturation
Authors: Feughelman M. , Nordon P.
Published: April 2003

If a wool fiber is held at a small fixed strain in water (∼1%) the stress in the fiber relaxes and reaches a steady value in about 1 hr. If, while the fiber is still held extended, it is dried and subsequently rewetted, the stress in the fiber after rewetting drops rapidly to a minimum and then slowly rises. This rise in stress in the fiber was previously interpreted as a rebuilding of hydrogen bonds under strain in the matrix of the wool fiber. Recent torsional measurements on fibers during the absorption of moisture from dry to a high humidity throw doubt on this conclusion. It appears that the rise in stress after moisture sorption is due to the reformation of the structure of the microfibrils, which have been partially disrupted by the swelling of the keratin structure due to the entrance of moisture. Infrared evidence of increased deuterium oxide penetration of the keratin structure during sorption of deuterium oxide agrees with this interpretation. A mechanism is suggested for this disruption of the microfibrils based on the difference of swelling of matrix and microfibril with the sorption of water into the wool fiber.
Relationship between dynamic modulus of thin films and stiffness, as determined by the Handle‐O‐Meter
Authors: Hansen Orin C. , Marker Leon , Ninnemann Karl W. , Sweeting Orville J.
Published: April 2003

A series of thirteen polyethylene and ten polypropylene packaging films was studied by both the Handle‐O‐Meter and the dynamic tensile modulus apparatus, to discover how the stiffness of polyolefin films determined with the Handle‐O‐Meter depended on the modulus of the material and the thickness of the film. The polyethylene films included low‐, medium‐, and high‐density resins and ranged in thickness from 0.7 to 4 mils. The moduli of these films ranged from 2.5 X 109 to 18 X 109 dynes/cm.2 The polypropylene films were made from several types of resins with moduli varying from 73 x 109 to 54 X 109, and the thicknesses of these films ranged from 0.5 to 4 mils. When the logarithm of the ratio of stiffness to modulus was plotted as a function of the logarithm of the thickness of the film, as determined from unit weights and densities, a straight line was obtained with a slope of 2.5. This means that over a wide range of gauge and modulus the Handle‐O‐Meter stiffness of these materials, S (in grams), is related to the modulus, E (in dynes per square centimeter), and the thickness, t (in mils), by the equation S = 1.41 X 10‐9Et2.5. This result, which shows that the Handle‐O‐Meter stiffness of polyolefin films may be represented as a function of the thickness and the modulus as given by the dynamic tensile modulus apparatus, may be used to calculate a modulus value from any single Handle‐O‐Meter stiffness value or, alternatively, to reduce Handle‐O‐Meter stiffness measurements to a standard thickness. Conversely, this relationship may be used to predict the Handle‐O‐Meter stiffness of a film made from a polymer whose modulus is known.
Rupture of rubber. X. The change in stored energy on making a small cut in a test piece held in simple extension
Authors: Greensmith H. W.
Published: April 2003

Application of the tearing energy criterion (Part I of this work) to the problem of the tearing of a rubber strip that contains a small cut or tear of length c in one edge and is stretched in simple extension is based on the relation Wi – W = K(λ)c2hE, where Wi and W are the total stored energies of the strip in the absence and presence of the cut, respectively, h is the thickness λ0 of the strip, E is the stored‐energy density in the central region of simple extension, and K(λ) is a numerical factor that varies with the extension ratio λ in this region. An experimental method is described for measuring (Wi – W), which enables the factor K(λ) to be evaluated. The results indicate that K(λ) decreases from a value of about 3 at low extensions to a value somewhat below 2 at λ = 3. The experiments also provide a more stringent test of the accuracy of the above relation than has been possible hitherto.
Differential thermal analysis of polymers. II. Melting
Authors: Strella Stephen
Published: April 2003

A theory is presented of the way in which the melting of a polymer is manifested in a differential temperature analysis thermogram. An analytical method based on this theory allows a precise determination of both the melting point and the crystalline weight fraction as a function of temperature. Experimental results for linear polyethylene and crystalline polypropylene confirm the theory.
Flexcracking of polymers
Authors: Akkerman F. H. D.
Published: April 2003

Accurate measurement of several types of fatigue failure in polymers was obtained with a flexing machine equipped with an automatic camera. The technique is described at length. Observations made include that an antiozonant interferes with crack initiation, that a crack may well start under the surface, and that in the growth of a crack the elastic force is equivalent to the hysteretic force. Several photographs show aspects of crack initiation.
Grafting of polyacrylonitrile in cotton fabrics
Authors: Kulkarni A. Y. , Chitale A. G. , Vaidya B. K. , Mehta P. C.
Published: April 2003

With a sodium thiosulfate–potassium persulfate redox system, in situ polymerization of acrylonitrile was studied in cellulosic materials. Traces of copper are found to accelerate the rate of polymerization, giving higher yields on the treated materials. Other variables studied were (a) material/liquor ratios, (b) monomer concentrations, and (c) initiator concentrations. It is found that high material/liquor ratios and higher initiator concentrations cause increased polymer yields on cotton fabrics. Fabrics containing polyacrylonitrile (PAN) are resistant to microbial degradation. Acrylonitrile was polymerized in secondary cellulose acetate, mercerized cotton, and cellophane. Studies of the insolubility behavior of the treated cellulose acetate samples in acetone and dimethylformamide, and of mercerized cotton and cellophane in cuprammonium hydroxide, were carried out for the purpose of examining the presence of cellulose‐PAN grafts. In the latter case, a constant ratio of cellulose to PAN was obtained in the cuprammonium hydroxide‐insoluble fraction over a wide range of polymer add‐ons. Alkaline saponification of the nitrile groups in the treated cotton fabrics, followed by a treatment with formaldehyde at pH 9–9.5 and subsequent curing in the presence of an acid catalyst, yield highly crosslinked fabrics which exhibit a considerable improvement in the wet crease recovery with slight loss in tensile and tear strengths. It is believed that these changes are brought about by the formation of a CO · NH · CH2. Ocellulose type of crosslink. These results strongly support the presence of a cellulose‐PAN graft.
High gloss of extruded high impact polystyrene sheet. A microscopical study of sheet morphology
Authors: Giuffria Ruth , Carhart R. O. , Davis D. A.
Published: April 2003

Morphological changes effected in the two‐phase high impact polystyrene system by several methods of securing high surface gloss of extruded sheet were studied microscopically. In the glazing process changes occur in refractive index of the copolymer particles and in the matrix. Excessive glazing may result in oxidative damage. The effects of temperature and oxidation and temperature alone on the copolymer particles have been investigated.
Examination of the oxidative degradation of polyacrylonitrile using infrared spectroscopy
Authors: Conley Robert T. , Bieron Joseph F.
Published: April 2003

The oxidative thermal degradation of polyacrylonitrile has been examined using infrared spectroscopy. It was found that the generally accepted mechanism for the thermal degradation of polyacrylonitrile in air, which involves direct interaction of neighboring nitrile groups, and alternate proposals, involving azomethine crosslinks through reaction of the nitrile group and a neighboring tertiary hydrogen atom, do not satisfactorily represent an initial degradation scheme accounting for the observed infrared spectral changes. Rather, it must be concluded that these reactions take place after the initial degradation, to produce highly complex pyridinoid systems, and are not observable under the experimental conditions employed here. By detailed interpretation of the spectral changes using, in part, a difference spectral examination technique, an alternate route for the oxidative degradation involving the introduction of double bonds in the polymer chain could be formulated. This reaction can best be visualized as occurring via the attack of molecular oxygen at the activated tertiary carbon–hydrogen bond adjacent to the electron‐withdrawing nitrile group. The nitrile group was shown to remain unreacted during the course of the initial oxidation. After the introduction of the double bond, a number of secondary degradative reactions, of which the previously proposed routes of degradation are representative, take place; these include degradation reactions of the nitrile groups to form acid and amide groups. It was observed that the accumulation of oxygenated intermediates on the surface of the polymer film is a rapid reaction and that the initial degradation process is controlled by the concentration of these species.