bluuebunny/crossref_metadata_2025_split huggingface dataset:
Sur la déagradation thermique du chlorure de polyvinyle. II. Etudes cinéatiques sous atmosphéare inerte
Authors: Guyot Alain , Benevise Jean‐Paul , Trambouze Yves 
Published: April 2003

AbstractFor a commercial polyvinyl chloride (PVC), polymerized in suspension, decomposition kinetics were studied in a nitrogen atmosphere and isothermal conditions, from 150 to 250°C., by measuring simultaneously loss of hydrochloric acid and loss of weight. Below 200°C., hydrochloric acid is the only volatile product freed; reaction is zero order and activation energy is 20 kcal./mole HCl. Active centers are mainly end chains of unsaturated structures. The reaction is terminated by mutual destruction of radicals, creating crosslinks. Above 200°C., when the degree of dehydrochlorination is high enough, a minor difference is observed between loss of weight and hydrochloric acid loss. The reaction is autoaccelerated and can be classified as a degenerated branching chain reaction. It is suggested that activation of irregular structures, initially present or created during the course of the reaction, and thus responsible for autocatalysis, provides active centers for chain dehydrochlorination. Some of these structures are active at temperatures lower than that of their formation. Each kind of structure is believed to be at the origin of a radical zero‐order chain reaction; its activation energy depends on its type. The reaction chains are terminated by inactivate irregular structures.
Studies on the orientation phenomena by fiber formation from polymer melts. III. Effect of structure on orientation. Condensation polymers
Authors: Ziabicki Andrzej , Kȩdzierska Krystyna 
Published: April 2003

AbstractThe principal regularities of molecular orientation occurring by fiber formation from polymer melts have been proved for several polyamides, copolyamides, polyurethane, and polyester. It has been found for these polymers, as for the formerly investigated polycapronamide, that fiber birefringence (used as a comparative measure of the mean degree of macromolecular orientation) practically does not depend on the deformation ratio S = VE/V0, and monotonically increases with velocity difference (VE − V0) and reciprocal fiber diameter ϕE−1 (measure of cooling rate). Hence the general character of the postulated mechanism of orientation, simultaneous action of velocity field and thermal relaxation, seems to be proved for the typical fiberforming polymers. The differences between the shapes of characteristics birefringence–velocity difference, birefringence–spinning stress, and between the x‐ray patterns of polyamides and polyester have been interpreted in terms of molecular structure and occurrence of H bonds.
Special adhesives for rubber bonding
Authors: Peterson Charles H. 
Published: April 2003

AbstractSpecial adhesives for bonding of unvulcanized and vulcanized elastomers are discussed. Major emphasis is placed on adhesives and conditions for bonding of vulcanized elastomers. The decline of brass plating is reviewed. Various methods of adhesion testing are discussed and illustrated. Available organic polymer based adhesives will produce high strength bonds to a wide variety of unvulcanized olefinic elastomers. A single coat adhesive has been developed which provides “maximum performance adhesive bonds” to a variety of unvulcanized elastomers. Factors affecting bonding and “bondability index” for the common elastomers are described. The bonding of vulcanized elastomers is a more difficult task. Present adhesives require mechanical or chemical modification of the surface of the elastomer. Brute force tactics used in conjunction with epoxy‐polyamide, phenolic‐polyvinyl formal, or nitrilephenolic systems have performed well in some applications. The quality of these bonds, however, does not equal those produced to unvulcanized elastomers. With cooperation of the users, the adhesive suppliers are developing newer, more effective products to meet the challenge of the advanced polymers and increasingly severe environments in which they are used.
Recent developments in high‐temperature adhesives
Authors: Levine Harold H. 
Published: April 2003

Abstract(1) The prognosis for adhesives uieful up to an hour at 1000°F., in air, is good. (2) Organic adhesives based on phenolic and silicone‐phenolic resins are more capable than expected of usefulness at 1000°F. (3) Preparation of semiinorganic adhesives by reaction of heat stable organic polymers with inorganic reagents is feasible. (4) The prospect appears excellent for the achievement of adhesives to be used for 1000 hr. at 500°F., in air, on steel. (5) Despite research on 2000°F. adhesives, effort is still urgently needed on materials for use at lower temperatures. (6) Perhaps the area with the most serious shortage of information and research is the development and testing of adhesives for use at 180–500°F. for periods of three to five years. Both military and civilian agencies are planning the construction of supersonic transports which need such structural adhesives.
Infrared spectra and crystallization of poly‐3,3‐bis(chloromethyl)oxacyclobutane
Authors: Hatano Masahiro , Kambara Shu 
Published: April 2003

AbstractThe process of crystallization and the characteristics of crystalline poly‐3,3‐bis(chloromethyl)oxacyclobutane were investigated by infrared spectroscopy. A comparison of the spectra obtained when the electric vector was vibrating parallel to and perpendicular to the extended direction of specimens of this polymer showed significant dichroism in the majority of absorption bands; also, intensity changes as crystallization of the polymer proceeded were observed in both types of spectra. The crystallization process was examined by noting changes in the spectra with increase in the temperature of the polymer; many crystallization‐sensitive bands were found. The dichroism was particularly marked in the absorption bands which may be due to the wagging‐mode, twisting‐mode, and rocking‐mode vibrations of the methylene groups in this polymer. Optical densities of the bands a t 1027 cm−1, an amorphous band, and 897 cm−1, a crystalline band, were observed a t various temperatures during cooling of the polymer. By use of a plot of the optical densities of both bands against the temperature of the polymer, the degree of crystallinity of the polymer could be estimated as a function of the polymer temperature. The results are in good agreement with the dilatometric results for the crystallization rate. Also, the polymorphism of the polymer, which had been detected by x‐ray analysis, was investigated by the use of infrared spectroanalysis. On the basis of deductions derived from these experimental results, we hypothesized a macromolecular structure for this polyether.
Apparatus for studying the effects of rapid thermal cycles and high strain rates on the elevated temperature behavior of materials
Authors: Savage Warren F. 
Published: April 2003

AbstractA new research tool is described which permits determination of short‐time elevated temperature properties of metals and alloys. Test specimens are heated by their own resistance to the flow of a large magnitude heating current, and a rapid‐acting electronic‐proportioning rate‐control action permits achieving programmed heating of the specimen under test at rates up to and exceeding 3000°F./sec. with negligible thermal overshoot. Complete thermal cycles involving complex programs of alternate heating and cooling may be automatically programmed by means of a special electronic reference generator with a dynamic accuracy of ±15°F. for peak temperatures up to the working limit of existing thermocouple materials. The electronic programming device also initiates testing of the specimen in tension with any desired rate of crosshead motion up to 4.5 in./sec. with loads up to 10,000 lbs. Specimen temperature, load, and crosshead position as a function of time are automatically recorded by a direct—developing recording oscillograph. Examples of recent applications of the apparatus to some metallurgical problems are described briefly, and suggested areas of future application are summarized.
The dynamic properties of carbon black loaded natural rubber vulcanizates. Part II
Authors: Payne A. R. 
Published: April 2003

AbstractThe dynamic shear modulus at very high strains, (G∞), of carbon black filler loaded vulcanizates is regarded as due to the product of two factors: (a) a hydrodynamic interaction due to filler particles, and (b) a second factor for which evidence is given suggesting that it arises from a few strong linkages which are known to link filler particles to the matrix. Experimentally a measure of (a) has been obtained from model vulcanizates using glass spheres as the filler, and of (b) from equilibrium swelling measurements on rubber vulcanizates containing carbon black. Quantitatively, the difference between the shear modulus of the pure gum vulcanizate, Gpure gum, and G∞ can be explained by these measurements.
Electromechanical hysteresis measurements: A new tool for investigation of the properties of plastics
Authors: Kern Edward L. , Skinner Selby M. 
Published: April 2003

AbstractThe charge‐strain hysteresis curve can be measured by simple apparatus. While fundamental interpretation of the effect may be complex, the use of the curves for practical purposes such as investigation of fatigue, quality control, differentiation between materials or methods of preparation or surface characteristics, is simple. The effect shows indication of being related to the chemical nature of the material, its composition and structure, and particularly the phase or quasi‐phase structure. Chargestrain hysteresis curves have been measured. These are quite reproducible if the samples from which specimens are prepared are uniform. The shape of the hysteresis curve is affected by (1) amplitude of strain, (2) rate of straining, including constant strains, (3) the functional dependence of strain upon time, (4) repeated cycling, (5) incorporation of fillers, (6) incorporation of reinforcing fibers, (7) the mechanical properties of the plastic, (8) detailed composition of the polymers, and (9) temperature. Seven general types of hysteresis curve are observed. The general features of the curve, and the hysteresis area are sensitive methods for detecting slight changes for composition. This method of sample differentiation was illustrated with examples showing the magnitude and sensitivity of the effect. When a sample was held at a given strain, the charge decreased; this suggests that both resistivity, and the initial stages of mechanical plastic flow may be observed indirectly through this phenomenon. Continuously repeated cycling shows a change in charging‐strain response related apparently to the initial stages of flexural fatigue. A regular decrease of hysteresis area is observed with repeated cycling, with the area decrease depending upon the plastic composition. The rate of decline of the area with repeated cycling is a second method for differentiating between materials, particularly when differences are obscured in other methods of testing.
Novel technique for following the rigidity changes accompanying the curing of polymers
Authors: Lewis Armand F. , Gillham John K. 
Published: April 2003

AbstractA method is described for measuring the rigidity of a curing polymer system throughout its complete course of reaction (liquid to solid). In this technique, a braided fiber (nylon), impregnated with the polymer system to be studied, is used as the supporting member for a free, torsionally vibrating mass. From the frequency of the vibration, the apparent rigidity modulus Ḡ of the impregnated braid is calculated. The rigidity of the reacting polymer is thus followed nondestructively during the curing period. In a further development, the term relative rigidity Ḡ/Ḡ0 is introduced to normalize the rigidity parameter to a more experimentally adaptable quantity. The curing behavior of several types of polymer is presented to illustrate the general utility of the method.
The attack of ozone on stretched rubber vulcanizates. III. Action of antiozonants
Authors: Braden M. , Gent A. N. 
Published: April 2003

AbstractThe character and extent of protection by certain additives (antiozonants) have been investigated for a number of vulcanized rubbers over a wide range of ozone concentrations. Two distinct modes of action are found: a reduction in the rate of crack growth and an increase in the critical energy necessary for attack to occur. Neither seems explicable on a simple hypothesis of scavenging. Several materials which act in the first manner have been examined. They were found to be similar in effect, reducing the growth rate to about one fifth of its original value when a sufficient amount of the additive was present. The mechanism is obscure. Certain additives, notably N,N′‐dioctyl‐p‐phenylenediamine, also cause a striking and important increase in the critical energy condition. The circumstances under which this occurs have been studied, and a tentative hypothesis for the mode of action is advanced.
Dynamic rheology of modified starches
Authors: Myers Raymond R. , Knauss Carł J. , Hoffman Ray D. 
Published: April 2003

AbstractViscosities η and rigidities G were determined for 5% pastes of phosphate‐linked white milo starches and acidmodified cornstarches, using a resonance elastometer operating in the frequency range 0.1 to 40 cycles/sec. Most of the starches behaved as ideal Kelvin solids under these conditions, thereby permitting η and G to be evaluated from the height and location of the resonance peak. Sample calculations of η and G are given, followed by a discussion of the trends displayed by these values as the severity of treatment is increased.
Détermination de la viscosité intrinsèque de solutions de polymères par une simple détermination de la viscosité
Authors: Solomon O. F. , Ciutǎ I. Z. 
Published: April 2003

AbstractBy studying the molecular weights of various solutions of cis‐1,4‐polyisoprene the authors arrived at the formula \documentclass{article}\pagestyle{empty}\begin{document}$$\left[ \eta \right] = \sqrt {2/c} \sqrt {\eta _{sp} - {\rm l}n\eta } _{rel} $$\end{document} which allowed the calculation of the intrinsic viscosity of the polymer solutions by a single viscosity determination. The formula was verified for different systems of polymer–solvent and the values are in accord with those obtained by extrapolation. An operating concentration of about 0.2% is recommended.
Shapes of cells in polymer foams
Authors: Gioumousis George 
Published: April 2003

AbstractThe shape of the cells in a foam is thought to be determined by the interplay between viscosity and surface tension. In order to assess the relative importance of the two, a simplified model is set up which considers only surface tension. It is assumed that the cells are of uniform cross section in one direction and are based on a regular hexagonal lattice in the other two. The resulting two‐dimensional problem is solved by means of the calculus of variations. For high density foams the voids take the form of circles centered within each hexagonal cell. For low densities (below about 9% solids) the solid part is concentrated at the vertices, between tangential circular areas, connected by straight segments of zero thickness. This illustrates the importance of viscosity, since in real foams the cell walls will break if too thin, while the thinner the walls become, the greater is the effect of viscosity in opposing further thinning.
Iterative calculation of relaxation spectrum from free vibration data
Authors: Hopkins I. L. 
Published: April 2003

AbstractThe complex elastic modulus G*(ω) = iG′(ω) + iG′(ω) is shown to be a function not only of the frequency (ω) but also of the damping factor a if the strain is of the form x = x0 exp {− at} sin ωt. The general equations for G*(ω,a) = G′(ω,a) + iG″ (ω,a) = are derived in terms of the relaxation spectrum. The use of a spring to aid the specimen and reduce the ratio a/ω is discussed, and its desirability demonstrated. If data are thus available in terms of either G″(ω) or G″(ω,a) the iterated second approximation of Ninomiya and Ferry provides a rapid and powerful method of finding the relaxation spectrum. To the accuracy to which the time–temperature reduction factor aT is known or can be predicted by means such, for example, as the WLF equation, the function G″(ω,a) over a temperature range at nearly constant frequency can be translated into terms of G″(ω,a) at constant temperature and varying frequency. In such cases, the relatively simple torsional pendulum, or some analogue of it, can economically provide a characterization of the viscoelastic behavior of the material over an extended time or frequency range.
The surface reaction of ozone with chemically protected rubber
Authors: Andrews E. H. , Braden M. 
Published: April 2003

AbstractReplica electron microscopy has been used to elucidate the physical mechanisms by which various additives afford ozone resistance to natural rubber. There exist two classes of chemical antiozonants, namely, those that enhance the critical energy required for ozone cracking and those that retard the rate of crack growth; representatives of these two classes were used in the investigation. The process involved in the first of these protective mechanisms was found to be the formation at the exposed surface of an inextensible layer some 100 A. thick and inert to further ozone attack. That giving rise to rate retardation also involved the formation of a surface layer, but the layer was susceptible to further ozonolysis and, eventually, complete degradation.
Quantitative characterization of polybutadiene networks
Authors: Kraus Gerard 
Published: April 2003

AbstractUsing a relationship found to be applicable for natural rubber networks in establishing contributions of chemical crosslinking, entanglements, and networks defects to physical crosslinking, a physical versus chemical crosslinking “calibration” is developed for polybutadiene prepared by organolithium initiation. This calibration is then used to determine chemical crosslink yields for sulfur‐sulfenamide, thiuram, and peroxide vulcanization. Crosslink yields for polybutadiene in the sulfur‐sulfenamide and thiuram curing systems are shown to be similar to those of natural rubber. In peroxide vulcanization the crosslink yield is in excess of unity for polybutadiene. Evidence is presented which indicates that this is due to a polymerization type reaction involving vinyl groups resulting from 1,2‐addition during polymerization.
Radical decay and color formation at various temperatures in unplasticized poly(vinyl chloride) irradiated in vacuo at 25°C
Authors: Atchison G. J. 
Published: April 2003

AbstractMoldings were irradiated at ambient temperature in vacuo with 2 m.e.v. electrons to doses of 5.9–7.3 Mrad. The decay of radicals was followed by EPR spectroscopy at 80, 55, and 30°C. while simultaneous extinction measurements were made at 300–700 mμ with a recording spectrophotometer. The radical decay data indicated the presence of three species at each temperature, decaying exponentially with time, with half‐lives of 20 min., 210 min., and 135 hrs. at 80°C. of 40 min., 400 min., and 141 hrs. at 55°C., and of 54 min., 720 min., and 3200 hrs. at 30°C. G values of 1.6, 2.0, and 1.4 were obtained for radical formation at 25°C. by back‐extrapolation of decay curves from the three temperatures to the end of the irradiation period. The activation energy of radical decay was found to be 4.4, 5.0, and 13.7 kcal./mole for the short‐lived, intermediatelived, and long‐lived radicals, respectively. The optical data has a broad absorption maximum at 500–550 mμ and a series of seven absorption peaks with maxima at 505–510, 483–485, 458–460, 430–435, 400–405, 364–365, and 329–330 mμ. The concentration of the material producing the broad bands was found to be inversely proportional to the long‐lived radical concentration. The fine‐structure peaks are consistent with literature data for a polyene chain of 16–17 conjugated double bonds.
Development of constitutive equations for polymeric melts and solutions
Authors: White J. L. , Metzner A. B. 
Published: April 2003

AbstractThe importance and characteristics of viscoelastic fluid behavior are briefly reviewed, as are theoretical predictions of the relationships between the stresses developed in such a fluid and its deformation rate and history. It is seen that most of the equations available for the prediction of these stresses(variously termed “constitutive equations” or “rheological equations of state”) either do not predict the properties of real materials correctly or, alternately, are of such overriding complexity that they cannot be applied to the solution of any but the simplest real problems. A new constitutive equation in which all the significant parameters may be evaluated from only two sets of experiments is developed. Comparison with available experimental results, while not entirely conclusive, indicates that the equation may predict correctly the behavior of nonpolar solutions and polymeric melts and that it may work well on polar systems in the range of high deformation rates, i.e., the region of primary industrial interest. Several problems of interest to the plastics industry are worked to illustrate the use of this constitutive equation.
Evaluation of light‐scattering and small‐angle x‐ray techniques using dilute dispersions of uniform polystyrene latices
Authors: Sperling L. H. 
Published: April 2003

AbstractSeveral light‐ and x‐ray‐scattering formulations were evaluated using polystyrene spheres having diameters near the wavelength of the employed light. While some error in the dimensions calculated using these equations is both expected and found, it is shown that these methods may still be useful for approximate or relative results. One of the purposes of this paper will be to estimate the applicability of these light‐scattering techniques to colloidal systems having sizes near the wavelength of light when only moderate accuracy is required. It is shown that the better diameter estimations are obtained by using (1) the maxima and minima that appear in the angular light‐scattering pattern, or (2) the Shull and Roess formulation adopted from small‐angle x‐ray theory
Polymerization of dialdehydes by metal alkyls
Authors: Sweeny W. 
Published: April 2003

AbstractA variety of metal alkyls have been found to be catalysts for preparing a polyester from terephthalaldehyde via the Tischenko reaction. The polymer was examined by infrared spectra, x‐ray diffraction patterns, and differential thermal analysis, and is apparently a crystallizable random 50 : 50 copolymer composed of p‐methylenebenzoate and p‐xylyleneterephthalate units. Diphenyl‐4,4,‐dicarboxaldehyde also underwent polymerization with the metal alkyls, but a hindered aldehyde, 4,6‐dimethylisophthalaldehyde, did not and was recovered quantitatively.
Reactions of irradiated polytetrduoroethylene resin
Authors: Bro M. I. , Lovejoy E. R. , McKay G. R. 
Published: April 2003

AbstractPowders and compacted preforms of virgin unmelted polytetrafluoroethylene were subjected to ionizing radiation in high vacuum. The specific gravities, melt Visccmities, and mechanical strengths of the irradiated samples after a standard heating cycle in air or at reduced pressures indicate that degradation is more pronounced in the presence of oxygen than in vacuum. The presence of oxygen in the excessively degraded sample was shown by electron spin resonance and pyrolysis experiments. It is suggested that some branched molecules are also formed on heating the irradiated samples resulting in a broadening of the molecular weight distribution. Primary fluorocarbon radicals of the type . disappear rapidly when heated at 75°C. in vacuum while secondary radicals are stable thermally at 200°C. and disappear only slowly at 400°C. Both typea of radicals react rapidly with oxygen and tetrafluoroethylene at 0°C. The reactions which occur in irradiated polytetrafluoroethylene in various atmospheres and at several temperatures are reviewed in light of the information developed during this research.