bluuebunny/crossref_metadata_2025 huggingface dataset:
Rural Development Policy, Agricultural Producer Services and Wage Disparities in the Context of Developing Economies
Authors: Run Yuan , Sun Yangshunzi , Wang Dianshuang
Published: January 2024

In developing countries, due to the predominance of marginal and small farmers leads to agriculture practices on small and fragmented plots of land where access and usage to modern farm equipment and implements is hampered. Agricultural producer service sector that acts as an intermediate sector facilitates this process. We build three-sector general equilibrium models to delineate this process: parts of manufacturing goods are utilized by the service sector, the outputs of which are intermediate inputs that could substitute labor in agriculture. We explore the impact of labour market distortion mitigation and input subsidies on rural development policies on pay disparity using this framework. Growing subsidies result in widening wage inequality. Reduction of labor market distortion will raise wage rate of skilled labor, and its impact on wage rate of unskilled labor is ambiguous, depending on elasticity between skilled and unskilled labor. In order for the agricultural development policy to fall short of its broad objectives and may impact on agricultural output.
Softener absorption by regenerated cellulose. Uptake from 10% aqueous glycerol
Authors: Sweeting Orville J. , Mykolajewycz Roman , Wellisch Eric , Lewis Richard N.
Published: April 2003

The softener content of regenerated cellulose film (gel film) in equilibrium with aqueous glycerol solution was found to be determined primarily by only two factors: the softener concentration of the solution and the volume of free space within the gel film. Volume changes of film in contact with 10% glycerol solutions are negligible. Preferential uptake of glycerol as the solution passes into the film is, at most, slight, amounting to no more than 0.04% at the concentration used. No evidence was found for a large enrichment within the gel film, as has been postulated, or for adsorption of glycerol on cellulose chains. The system, cellulose‐glycerol‐water, appears to be a polymer‐liquid mixture brought to equilibrium principally by diffusion. It appears that at 10% concentration, glycerol and probably other organic compounds are taken in by gel film by a diffusion process in which the free water in the film is replaced by solution without appreciable enrichment or change in volume. Water contained in the interchain spaces of cellulose is simply exchanged for softener solution. The free volume of the film as determined by the cellulose structure and the degree of crystallinity remains essentially unchanged on softener uptake at the softener concentration studied.
Stabilization of viscose rayon by heat treatment by means of ammoniacal preswelling bath
Authors: Kanamaru Kisou
Published: April 2003

In continuation of a previously reported experimental study on stabilizing viscose rayon by heat treatment, in which acid baths were used as the preswelling agents for heat treatment of regenerated cellulose further experiments were performed in which ammonium hydroxide solutions served as the preswelling agent. From the effects of heat treatment of the fibers preswollen in ammonium hydroxide bath, as exhibited by dynamic modulus, breaking strength, degree of crystallinity (estimated from x‐ray data), etc., it was confirmed again that, when viscose rayon preswollen in an ammonium hydroxide bath of the concentration or the pH range optimal for it maximal hydration (pH = 9.0) is heat treated at the temperature just above the glass transition temperature of regenerated cellulose (ca. 70–90°C.), the effects of the heat treatment in stabilizing viscose rayon are most marked. Moreover the effects of heat treatment, as exhibited by these properties of rayon at the optimal condition are much larger in this case than when the heat‐treated fibers are preswollen in an acid bath. This effect is also clearly indicated by the results of infrared spectroscopy studies according to the deuteration method. With the use of a series of fiber samples preswollen in acetic acid as well as ammonium hydroxide bath and dried at various degrees of desiccation results were obtained which indicate that there is an optimal degree of desiccation for effecting maximal stabilization.
Chemical and physical nature of insolubles: Acetone solutions of cellulose acetate
Authors: Sperling L. H. , Easterwood Marie
Published: April 2003

An examination of the chemical and physical properties of gels in wood and linters cellulose acetates was carried out with special emphasis on light‐scattering and electron microscopy. Gels were fractionated by filtration, centrifugation, and dialysis techniques to produce gels over and under 15 microns in size. The predominant phenomena observed in the small gels are nearly monodisperse spherical or potato‐shaped gels of about 0.3 micron in dispersion (light‐scattering) and 0.1 micron dry (electron microscopy). Chemical analysis shows these gels much enriched in xylan. The large gels were examined also and were found to consist of fibers (cellulose I) and plates (cellulose triacetate).
Infrared spectroscopic studies of ultrathin microtomed sections of polymers. Part I. Characterization and structure determinations of cured, black‐loaded rubbers
Authors: Corish P. J.
Published: April 2003

Previous time‐consuming, destructive methods for examination of infrared spectra of cured, black‐loaded rubbers have been replaced almost entirely by a rapid new technique which examines the rubber in its original form. By use of ultrathin microtomed sections (ca. 2 μ thick) of the rubber and electrical amplification of the absorptions on a recorder quite good infrared spectra of the rubber may be obtained. Characterization and structure determination of the rubber can then be carried out. Many different polymers, copolymers, and mixtures of polymers which have been loaded with up to 60 parts phr of carbon black and cured have been characterized in this way. Typical applications to determinations of polymers in tires, etc. are described. The effect of variation in particle size of carbon black is considered.
A proposed method for estimating polymer molecular weight distribution without fractionation
Authors: Rehner John
Published: April 2003

A method is proposed for estimating rather simply and with relatively little experimental data the molecular weight distribution characteristics of any crosslinkable polymer which follows the Tung distribution function. This function is combined with a fundamental relationship from the statistical theory of sol–gel ratios in randomly crosslinked polymers, to yield a result which relates explicitly the sol‐gel ratio, the crosslink density, and the molecular weight distribution parameters. These parameters give the various average molecular weights and the polydispersity by simple computation. The method has been tested with meager data available for a peroxide‐cured SBR and a divinylbenzene‐crosslinked polystyrene. Reasonably satisfactory results were obtained. A critical test of the absolute accuracy of the method requires experimental data not now available, and some refinements may eventually have to be made. However, the method should be useful, in its present state, for estimating distribution characteristics and, especially, for comparative studies within a given polymer system.
The oxidative aging in ultraviolet light of dicumyl peroxide vulcanizates of natural rubber in presence of various antioxidants
Authors: Dunn J. R.
Published: April 2003

The oxidative degradation of peroxide vulcanized natural rubber at wavelengths of 300 mμ and above has been studied by the technique of stress relaxation. Substituted naphthylamines and p‐phenylenediamines, particularly the former, initially photosensitize the degradation of the vulcanizate but subsequently give rise to colored products which act as antioxidants. The protective action of these amines is not due to network formation. Completely hindered phenols have been shown to be powerful antioxidants of long life, but nonhindered phenols are not good antioxidants against light. The combination of an ultraviolet absorber with a hindered phenol gives excellent protection which is only fully developed when a little of the phenol has been oxidized to a colored compound. Many dithiocarbamates, dithiophosphates, and xanthates protect against light, but their effect is short‐lived except in the case of nickel and chromium isopropylxanthates. The peculiar stability of these materials is attributed to their acting as both ultraviolet absorbers and antioxidants. Since the addition of ultraviolet absorber to the nickel and chromium xanthates does not further increase their effectiveness, the combination of a hindered phenol and an ultraviolet absorber is the most potent protective agent against light for incorporation into translucent rubber vulcanizates.
X‐ray diffraction by hairs and feathers. Part I
Authors: Venkateswarlu K. , Pillai S. Padmanabha
Published: April 2003

A study of the x‐ray diffraction of tail hairs of mammals, both domestic and wild, and feathers of birds has been made. The pattern due to buffalo hair is unique in the sense that about six Debye‐Scherrer rings have also been recorded in addition to the usual pattern of α‐keratin. The rings have been explained as due to crystallites in the fiber arranged at random about the fiber axis. The chromatographic record in the case of buffalo hair revealed the presence of a new amino acid. The d values have been calculated. The feather pattern resembles more that of β‐keratin. A comparison of the study of the hairs and the feathers has been attempted.
Light‐scattering measurements on solutions of natural and synthetic polyisoprenes
Authors: Allen P. W. , Bristow G. M.
Published: April 2003

The light‐scattering behavior of solutions of natural and synthetic cis‐1,4 polyisoprene is described. For milled natural rubber values of M̄w increase as the solvent power of the solvent is increased and, at the same time, the second virial coefficient tends to zero. These effects may be due to compact (e. g., branched) structures. With unmilled natural rubber there is evidence for the existence of microgel. Synthetic polyisoprene shows the behavior expected of a linear polymer.
Critical comparison of moving bar impact with gas expansion machines for dynamic loading of metals
Authors: Krafft J. M.
Published: April 2003

Achievement of high head speed in a testing machine requires that two conditions be met: (1) a high velocity input to the machine, and (2) a reasonably high stiffness. The machines discussed here, while excelling in requirement (1) are characterized by a rather deficient stiffness. Because of this softness, the strain rate during a test will vary markedly with the amplitude and shape of the stress strain curve; indeed, so much so that it must be considered as a variable in the data. This paper gives an analysis of the motional characteristics of a typical gas‐pressurized testing machine. This machine is driven by a pressure source obtained from a chambered burning of gunpowder; head speeds up to 100 in./sec. are reached by a restricted expansion against a piston. It is found that observed strain rate vs. strain behavior can be predicted from the analysis by taking into account the decrease in driving pressure due to gas cooling and to its expansion, and the decrease in stiffness with strain in the specimen or stroke of the piston. Comparison of this type of machine with impact bar loaders previously developed at NRL shows a comparable degree of strain‐rate variation for both machines. However, with mild steel, the stress–strain data from the two machines can be correlated by considering instant strain rate as a variable.
The determination of surface properties of polymers from liquid drop stability on an inclined plane
Authors: Baer Eric , McLaughlin Thomas F.
Published: April 2003

A method for studying the surfaces of solid polymers is described. Drops of various sizes were deposited on a horizontal surface; then the plane was tilted and the angles of inclination at which the drops begin to slide were recorded. A theory was developed which indicated that a plot of sin αs against V2/3− on linear graph paper should give a straight line. From the slope of the line, a constant K was obtained which characterized the surface. This constant is a function of the interfacial forces and the density of the drop. The critical surface tension for wetting Teflon (TFE) resin was found to be 20.5 dynes/cm. This is in close agreement with the critical surface tension determined by contact angle measurements. Alathon 23A polyethylene film which had been treated by electric corona discharge was studied. It was shown that K is related to the printability level, and that treated and untreated surfaces may readily be distinguished from one another by their K values.
The dry casting of viscose film
Authors: Price C. R. , Haskell V. C.
Published: April 2003

Regenerated cellulose film prepared by a dry‐cast method has demonstrated outstanding superiority over similar film produced by the conventional wet‐cast process. Factors contributing to the superior quality of film prepared by the dry cast process are: (1) physical properties several times greater than for wet‐cast film of corresponding thickness; (2) high durability at conditions of low temperature and low humidity even without the addition of softening agents, and (3) outstanding dimensional stability when exposed to conditions of varying temperature and humidity. The dry‐cast cellophane differs structurally from the commercial product in having a lower degree of order, a lower degree of swelling in the gel form, and minor differences in molecular orientation. A commercial process for producing dry cast cellophane may be envisioned as a heated, polished support for drying the viscose film; a regenerating system of alcoholic hydrochloric acid, hot glycerine, or a hot, oxygenfree gas; a water both for purifying the film; and a conventional cellophane dryer. The ideal viscose composition for producing dry‐cast cellophane is high cellulose content, moderately high DP, sufficient degree of substitution on the cellulose to yield a high degree of dispersion, and low caustic content.
The effect of softeners on the elastic modulus of regenerated cellulose sheet
Authors: Hansen Orin C. , Marker Leon , Sweeting Orville J.
Published: April 2003

The dynamic elastic modulus of cellophanes has been measured by use of the resonant frequency of a 2 × 60‐mm. strip of film in longitudinal vibration. The niodulus was computed from the resonant frequency length of specinieii, and the cross‐sectional area determined from its resonant frequency in transverse vibration. The apparatus is described briefly. Unsoftened film and glycerol‐softened films containing 7.3, 13.7, and 21.3% glycerol prepared from the same roll of never‐dried regenerated cellulose were conditioned a t 75°F. and 15, 35, and 81% R. H., and the elastic moduli were measured in both directions. Moisture and softerier contents were determined. The reciprocals of the geometric means of the moduli in the machine and transverse directions were plotted as a function of the volume of film containing 1 g. of cellulose. The displacement of the curve obtained for each softened film from the curve for the unsoftened film measures the effect of the softener, since the curves would coincide if the effect of softener were from swelling only. This permits construction of an empirical equation for the modulus of these glycerol‐softened films as a function of moisture and softener content. It was found further that the logarithms of the corrected compliance (1/EV2/2c), where E is the geometric mean modulus and Vc is the volunie of film containing 1 g. of cellulose, gave a straight line when plotted as a function of the number of moles of water plus twice the number of glycerol present in 100 g. of cellulose. This indicates that the effect of a mole of glycerol in breaking up the hydrogen‐bonded structure of the cellulose is twice as great as that of a mole of water. These results have been compared with similar results obtained on films containing ethylene carbonate and ethylenediamine. With the exception of ethylenediamine‐treated films studied a t high humidities, these fdms gave points falling approvimately on the corrected compliance curve obtained for the glycerol‐softened and unsoftened films. For these films, however, the simple sums of moles of water plus moles of ethylene carbonate or ethylenediamine monohydrate present in 100 g. of cellulose were used rather than the weighted sum used for the glycerolsoftened films.
Adhesives in printed circuit applications
Authors: Rider D. K.
Published: April 2003

This paper discusses the technology of adhesives employed in printed circuitry. The chemical types of adhesives are described and their general characteristics are given. Typical printed circuit processes are used to spotlight the demands placed on the adhesives. Test methods and requirements peculiar to printed circuitry are discussed in detail, and particular emphasis is placed on those properties which will not be too obvious to the adhesives technologist unfamiliar with circuitry. Secondary applications of adhesives in printed circuitry are touched on briefly, and mention is made of bonding methods in use or under development which do not employ adhesives. Numerous literature references are given.
Progress report, task group on high speed testing, ASTM committee D‐20 on plastics
Authors: Patterson Gordon D. , Smith W. Reed
Published: April 2003

Interlaboratory comparisons on several materials are being conducted among a half‐dozen laboratories having high speed tensile testers of widely different mechanical design and instrumentation. This progress report gives results from the first two round robins, the first on two plastic films and the second on copper wire. These materials were tested a t several speeds in the range of 1.3 to 130 m./min. (50 to 5000 in./min.). Preliminary conclusions and plans for future work are offered.
Estimating isothermal life from thermogravimetric data
Authors: Doyle C. D.
Published: April 2003

Equations are given for estimating equivalent isothermal life from thermogravimetric data and for estimating the apparent activation energy for volatilization even though the nature of the kinetic process is unknown. Illustrative data for polytetrafluoroethylene are presented. The importance of using sample temperatures, rather than furnace temperatures, is noted.
Sign reversal of permselective membranes: A possible mechanism for neural conduction
Authors: De Kőrösy Francis
Published: April 2003

An electrochemical mechanism is sought for to explain the sudden transient change of potential across a nerve membrane during neural conduction. Ion‐permselective membranes change the sign of their permselectivity if the charge of their fixed ions is overcompensated for by highly charged counterions which become strongly bound to these fixed sites by electrostatic forces. Imagine a membrane with its sign thus reversed beyond a given borderline: cations could traverse on one side in the vicinity of this line and anions on the other, while no ions would traverse pure membrane faces themselves. Thus concentrations would be equalized at the borderline by passive diffusion, while the sign of membrane potential would change from one side to the other of the border. A mechanism for automatic propagation of the border along the membrane is suggested. Sign reversal of membranes can also be caused by covalent bonding of oppositely charged groups to a charged membrane site, for instance by esterification of a carboxyl group or of a phosphoric acid group of a lipoproteid nerve membrane with the amino alcohol choline. Hydrolysis of such an ester would cause the sign of the membrane to revert to its original direction. Such acetic sites and choline abound on nerve membranes, together with enzymes, which are known to split and synthesize choline esters. Their electrochemical function in neutral conduction might well be this changing of sign of membrane permselectivity.
A recording apparatus for the measurement of longitudinal creep
Authors: Scherr Henry J. , Palm William E.
Published: April 2003

A recording apparatus for measuring longitudinal creep was developed to study viscoelastic properties of polymeric films. The heart of the apparatus is a photoelectric transducer that converts specimen extension and contraction into a voltage which is then applied to a millivolt recorder through a d.c. low‐drift amplifier. As used in this apparatus, the phototube detects the variable by having its photocathode surface shadowed by a movable mask. Supplementing the recording part of the apparatus is a mechanism for controlling specimen temperature. A polymer of plasticized polyvinyl chloride was studied, to demonstrate the applicability of the apparatus. The results obtained compared favorably with the method of visually observing the displacement with a cathetometer.
Temperature dependence of dynamic mechanical properties of mixed polymer systems. II
Authors: McIntyre A. D.
Published: April 2003

The temperature dependence at constant frequency of the viscous component E2(1/T) of the dynamic modulus has been determined for a homologous series of butadiene–acrylonitrile copolymers supported in a matrix of styrene homopolymer. The results, which agree with those reported earlier for a homologous series of butadiene–styrene copolymers, indicate that the transition temperature of a given plastic homopolymer, as measured from dynamic mechanical properties at essentially constant frequency in the range 200–300 cycles/sec., is depressed by the presence of a copolymerized rubbery diluent as the melting point of crystalline polymers is depressed by the presence of noncrystallizing comonomers. In addition, it has been found that the transition temperature is depressed by the presence of monomeric diluents much as the melting point of crystalline polymers is depressed by the presence of monomeric diluents. Two earlier assumptions, that the dynamic properties in the frequency range of interest should be independent of both the molecular weight of the rubbery copolymer and the degree of dispersion of the copolymer in the thermoplastic matrix, have been subjected to experimental scrutiny. The assumption regarding the dependence on molecular weight has been substantiated, at least for DP's in excess of 100. The assumption regarding the dependence on the degree of dispersion has been negated; the area under the E2(1/T) peak was found to be considerably greater for a coarse dispersion than for a fine one.
Raman and infrared spectra of 3‐methylbutene‐1
Authors: Ziomek Joseph S. , Forrette John E.
Published: April 2003

Infrared and near‐infrared spectra of 3‐methylbutene‐1 were observed for the vapor phase at room temperature. Also, Raman displacements and depolarization factors of 3‐methylbutene‐1 in methanol and carbon tetrachloride were obtained at the same temperature. Tentative assignments of the observed Raman and infrared bands were made, and a classification of bands on the basis of group frequencies is given.
One‐step polyallylation of phenols
Authors: Aelony David
Published: April 2003

A process for one‐step polyallylation of phenols was developed. Phenol is polyallylated in xylene in the presence of 3 moles of finely divided sodium hydroxide. Three moles of allyl chloride are added at such a rate as to maintain the reflux temperature at 110 to 120°C. Water is continuously azeotropically removed. The product contains allyl ethers of mono‐, di‐, and triallyl phenol. The bulk of the material is allyl ether of dially phenol which can be subjected to Claisen rearrangement followed by glycidyl ether formation and epoxidation of the glycidyl ether of triallyl phenol.
Properties of polyformals of alicyclic diols
Authors: Jackson W. J. , Caldwell J. R.
Published: April 2003

The properties of the polyformals of several alicyclic diols were determined. Particularly unusual were the properties of the polyformal of 2,2,4,4‐tetramethyl‐1,3‐cyclobutanediol. The polymer of the 1 : 1 cis/trans diol mixture had a reversible transition in crystalline phase at about 177°C. and a crystalline melting point of 262°C. The polymer was soluble in chloroform and in hot toluene. It was resistant to hydrolysis, particularly alkaline hydrolysis. Physical properties were determined on molded specimens obtained by injection‐molding, on films obtained by casting and pressing, and on fibers obtained by melt‐spinning.
Color formation in polyurethanes
Authors: Beachell Harold C. , Son C. P. Ngoc
Published: April 2003

The pyrolysis of a polyurethane obtained from tolylene 2,4‐diisocyanate and ethylene glycol was studied in nitrogen, air, and oxygen from the double aspect of structural change and color formation. The dissociation of the polymer into its components followed by further reactions liberates diisocyanate, the corresponding diamine, and the polypseudourea ether, as well as other degradation products. The color is attributed to the yellowing of TDI, the oxidation of the diamine, and the presence of the polypseudourea ether.
Stress relaxation and hysteresis at various strain rates
Authors: Chang Franklin S. C.
Published: April 2003

Applying the Boltzmann superposition principle on a generalized Maxwell model, an analysis of the relations between extension, relaxation, and hysteresis is presented, which shows that any one of these three can be calculated from the other two. It is shown that the relaxation modulus does not vary with strain rate when time is measured from the start of extension, except in the early period of relaxation. It is demonstrated that the first derivative of the ratio of extension stress‐strain rate with respect to time is the limiting value of the relaxation modulus. The short‐time end of relaxation modulustime curve can be readily extended for several decades of logarithm of time without resorting to the temperature effect. The results obtained from the treatment of experimental data on polyisobutylene verify the theoretical deductions, which may also be considered as an additional explicit proof of the Boltzmann superposition principle.
Geometry effects and high speed tensile behavior in styrene polyblend systems
Authors: Lund J. Kenneth
Published: April 2003

Critical specimen geometry parameters are varied to determine their effect on tensile behavior as a function of rate of testing. Their influence on elongation and energy absorption is pronounced, particularly at low values of specimen cross sectional area and thickness. These effects are attributed to surface imperfections resulting from specimen preparation, and to changes occurring in the combined stress pattern in the specimen. High speed photography and microscope analysis techniques have been developed to determine strain, strain distribution, and strain rate in the specimen gage section during deformation. Elongation measured outside the gage section can be a significant portion of overall specimen deformation; actual strain rate is a fraction of that obtained by assuming all deformation takes place in the gage section. Experimentation is statistically designed and the data statistically analyzed by sequential factorial analysis. Tensile stress response surfaces are accurately predicted by this technique.
Fire‐retardant polyesters based upon 2,3‐dicarboxy‐5,8‐endomethylene‐5,6,7,8,9,9‐hexachloro‐1,2,3,4,4a,5,8,8a‐octahydronaphthalene anhydride
Authors: Roberts Carleton W. , Haigh D. H. , Rathsack R. J.
Published: April 2003

The Diels‐Alder adduct of cis‐4‐cyclohexene‐1,2‐dicarboxylic anhydride (II) with hexachlorocyclopentadiene, 2,3‐dicarboxy‐5,8‐endomethylene‐5,6,7,8,9,9‐hexachloro‐1,‐2,3,4,4a,5,8,8a‐octahydronaphthalene anhydride (compound III), has been incorporated as the fire‐retardant component in polyester compositions. The structure of compound III possesses inherent properties which are exhibited as improved thermal and light stability in the derived polyesters; these improvements are based upon comparisons with polyesters prepared from the chlorendic anhydride, the fire‐retardant moiety in some commercial self‐extinguishing polyesters.
Structural characterization of vulcanizates. Part III. The cis‐1,4‐polyisoprene tetramethylthiuram disulfide–zinc oxide system
Authors: Moore C. G. , Watson A. A.
Published: April 2003

The vulcanization of a purified synthetic cis‐1,4‐polyisoprene (100 parts) with tetramethylthiuram disulfide (TMTD; 4 parts) and zinc oxide (4 parts) at 140°C. yields a network which at short cure time (15 min.) is structurally complex, containing 13.5 atoms of sulfur and 4.3 atoms of nitrogen per chemical crosslink present. The network becomes progressively simpler in structure as crosslinking proceeds, and at full cure (10 hr.) contains 3.2 atoms of sulfur and 0.7 atoms of nitrogen per chemical crosslink present. The initial network complexity is due mainly to the presence of rubber‐bound intermediate compounds, R·SxC(:S)N(CH3)2 (R = polyisoprenyl; x ≥ 2), which yield sulfidic crosslinks and zinc dimethyldithiocarbamate (ZDMC) on heating with zinc oxide or zinc sulfide as revealed by the efficient crosslinking on further heating at 140°C. of extracted undercured vulcanizates. Evidence is presented that the intermediate compounds result from interaction of the polyisoprene with a sulfurating species formed by a prior reaction of TMTD with zinc oxide, and not, as previously supposed by others, by direct reaction of the polyisoprene with TMTD. Our knowledge of the detailed structure of the network obtained at full cure is presented, together with estimates of the principal extra‐network compounds (ZDMC, tetramethylthiourea, and zinc sulfide) formed at full cure; these compounds together with the sulfur and nitrogen combined in the network account for ca. 90% of sulfur and nitrogen originally present as TMTD.
Stress relaxation of unaccelerated natural rubber–sulfur vulcanizates before and after treatment with triphenylphosphine
Authors: Dunn J. R. , Moore C. G. , Trego B. R.
Published: April 2003

The aerobic and anaerobic stress relaxation of unaccelerated natural rubber–sulfur vulcanizate networks has been examined before and after treatment with triphenylphosphine, a reagent which converts polysulfidic crosslinks into di‐ and monosulfide crosslinks. This treatment reduces the rate of anaerobic stress relaxation and makes the network more susceptible to protection by zinc dibutyldithiocarbamate against aerobic stress relaxation. Aerobic stress relaxation of the network after treatment with triphenylphosphine remains nonautocatalytic, indicating that it still contains the precursor of an antioxidant, and crosslinking continues to occur during aging, showing that the presence of polysulfide groups is not a sole prerequisite for such network formation.
Investigations on thermal dehydrochlorination of poly(vinyl chloride)
Authors: Crosato‐Arnaldi A. , Palma G. , Peggion E. , Talamini G.
Published: April 2003

The thermal dehydrochlorination of PVC has been examined on some samples prepared by fractionation of a commercial PVC, and some other samples obtained by polymerization at different temperatures. The results disagree with the concept of a continuous dehydrochlorination from one side to the other of the chain, that necessitates initiating structural anomalies in the macromolecule itself.
The influence of fillers and degree of vulcanization on the mechanical properties of hard rubber polyblends
Authors: Meltzer T. H. , Dermody W. J.
Published: April 2003

Hard rubber polyblends, made from SBR–butyl rubber mixtures vulcanized with sulfur, show several consistent patterns of behavior in response to recipe modifications or changes in degree of vulcanization. Tg increases with degree of vulcanization, reinforcing fillers raise the modulus, and reversion is encountered upon overcure as in SBR hard rubber. The dual or stepwise transition from glassy to rubbery modulus behavior which characterizes polyblends is clearly distinguishable in all of the mixtures. The level of the polyblend modulus plateau between glassy and rubbery behavior is dependent on the proportion of butyl in the blend. The range of temperatures spanned by the polyblend modulus plateau is dependent on the degree of vulcanization of the hard rubber portion of the blend. Hard rubber dust suppresses the characteristic stepwise transition of the polyblend in proportion to the amount of dust added. The changes in the other mechanical properties investigated are consistent with the changes in modulus. The impact resistance of the polyblend appears to be effectively limited by the impact resistance of the hard rubber portion at all degrees of vulcanization.
Factors influencing the properties of pectic acid films
Authors: Masters A. T. , Richards G. N.
Published: April 2003

A pectic acid, extracted in 11% yield from tobacco stems, contains 93% anhydrogalacturonic acid and some galactose. Plasticized films have been cast from water solution and the influences on tensile properties of casting temperature, extent of neutralization, nature of cation, and plasticizer (glycerol) content have been studied. The crystallinity of the pectate films is shown to increase very markedly with neutralization by sodium hydroxide in the range 40–100% neutralization. The ion exchange capacities of sodium hydrogen pectate films for alkaline earth cations are discussed.
Relationships between molecular weight, solution viscosity, and melt index for narrow distribution, high pressure polyethylene whole polymers. Fast M̄n determinations
Authors: Mortimer George A. , Daues Greg W. , Hamner William F.
Published: April 2003

Melt and solution viscosity properties of laboratory‐prepared batch polymerized high pressure polyethylene have been found to correlate well with molecular weight. These polymers have narrow and nearly constant molecular weight distributions and contain essentially no long‐chain branches. Short‐chain branching was found to have little or no effect on the relationships. Polyethylene made in the same reactor having long‐chain branches had melt and solution viscosity properties which deviated seriously from these relationships. The deviations serve as a semiquantitative measure of long‐chain branching. When long‐chain branching is absent, the correlations serve as rapid methods of determining M̄n for narrow‐distribution polymers.
The effect of temperature on polyacrylate‐and CMC‐treated drilling muds
Authors: Williams S. A.
Published: April 2003

Viscometric and filtration properties have been studied at 80°F. and at elevated temperature for a saturated gypsum mud and a 20,000 ppm sodium chloride mud, treated with an acrylate‐acrylamide copolymer (0.62 mole fraction sodium acrylate) and with sodium carboxymethyl cellulose (CMC). In the muds containing CMC and also for the acrylic polymer in the sodium system, the observed plastic viscosity decrease (at 175°F.) and the API filter loss increase (at 200°F.) were about what one would predict from the change in the viscosity of water with temperature. In contrast, the polyacrylate‐treated gypsum mud showed a viscosity increase, rather than a decrease, at the elevated temperature, and the API filter loss increased to a level substantially greater than would have been predicted on the basis of the change in the viscosity of water. This anomalous behavior of the acrylate‐treated system is interpreted as evidence of polymer‐calcium ion‐clay interaction. Data are presented to illustrate the extent of degradation of the acrylic polymer and CMC in a gypsum mud when heated for 16 hr. at 350°F. under a nitrogen atmosphere. The room temperature filter loss of the acrylate‐treated mud was scarcely changed after this treatment, while the filter loss of the CMC‐treated system was comparable to that of the blank mud. These results show that, from an operational point of view, CMC was completely degraded. Despite the apparent stability of the acrylic polymer, its usefulness is severely restricted by the high viscosities and filtration rates observed at elevated temperatures in the presence of calcium ions.
Interfacial polycondensation. I. The formation of surface graft polymers on wool
Authors: Whitfield R. E. , Miller L. A. , Wasley W. L.
Published: April 2003

By means of interfacial polycondensation, ultrathin coatings of polyamides, polyurethanes, polyureas, polyesters, polycarbonates, and various copolymers can be formed on the surface of a substrate. If the substrate contains reactive groups (such as NH2, OH, NCO, COCl, etc.), graft polymer is formed. The graft polymer is not removed by extensive extraction with good solvents for the polymer. In contrast, if wool is used as a substrate and is acetylated prior to the polymerization (to block the grafting sites), the thin coating of polymer is readily extracted. Digestion of the treated wool with enzymes that react with the wool, but not with the grafted coating, permits a characterization of the grafted polymer; amino acid analysis of the residue from the enzyme digestion provides evidence that the grafting sites on the wool are probably the free amino and hydroxyl groups located in the N‐terminal amino acids or internal amino acids containing these groups in their side chain.
On the characterization of non‐newtonian flow. III
Authors: Sabia Raffaele
Published: April 2003

A method is developed for testing extrapolation procedures of shear stress–shear rate data by using the dependence of the flow activation energy on shear. Three polyethylene types are studied, and it is concluded that the difference in flow activation energy observed between conventional low density polyethylene and high density polyethylene is due mainly to long chain branching.
On establishing mechanisms of radiation‐induced network formation in high polymers
Authors: Spiro J. G. , Winkler C. A.
Published: April 2003

In an effort to develop new techniques for studying the effects of irradiation on high polymers, the influence of molecular weight distribution has been investigated. From general mathematical expressions obtained by Saito, equations have been developed to be used for polymers of Schulz‐Zimm distributions, and their mixtures. According to the computations, it should be possible to distinguish between crosslinking and endlinking as alternative mechanisms of network formation, by comparing gelling doses for samples of different initial distributions. From gelling dose determinations for polystyrene samples of different polydispersities, it was confirmed that network formation in irradiated polystyrene takes place through crosslinking, in agreement with mechanisms suggested by several authors. It is believed that the simple technique described should be useful for studying radiation processes in polymers that form networks, especially since the method is insensitive to the extent of degradation.
Effects of morphology and molecular structure on tensile impact behavior of linear polyethylene
Authors: Pritchard R. , Dunn T. , Kelly P.
Published: April 2003

An instrumented tensile impact test which allows a load time curve to be obtained coincident with the energy to rupture values has been applied to the examination of a series of linear polyethylene homopolymers and copolymers of varying molecular weight and thermal history. The effect of test specimen geometry was also investigated. A morphological examination of these resins indicated a strong dependence of spherulite size on molecular weight, and to a much lesser degree on molding conditions; it appeared to be independent of comonomer. The overall crystallinity, as determined by both x‐ray and density methods, and crystallite perfection was increased by a slower crystallization rate, but was independent of molecular weight. The tensile impact strength (energy to rupture) was found to increase with molecular weight, and decrease on the introduction of comonomer. But the effect of thermal history gave rise to results which bore no clear‐cut relation to molecular and morphological parameters. The value of the instrumented tensile impact test is shown by the fact that these apparent anomalies can now be resolved by separating the elastic and plastic portions of the deformation. An increased level and perfection of crystallinity results in higher load bearing properties accompanied by a reduction in duration of impact. It is primarily the duration, rather than the peak load, which is affected by molecular weight. The main effect produced by changing from a type L (long) tensile impact specimen to a type S (short) was to reduce considerably the duration of the plastic region while simultaneously raising the maximum elastic load; this is thought to be associated with a more localized deformation and therefore a higher rate of strain.
Effects of composition and irradiation on the glass transition temperature of methyl methacrylate–styrene copolymers
Authors: Parker M. S. , Krasnansky V. J. , Achhammer B. G.
Published: April 2003

The glass transition temperatures of polystyrene, poly(methyl methacrylate), and copolymers prepared from their respective monomers were determined by using a volume dilatometer. The glass transition temperatures of polystyrene and poly(methyl methacrylate) were found to be 82 and 104°C., respectively. The glass transition temperatures obtained for the copolymers were between the values determined for each of the homopolymers and were a monotonic function of the polymer composition. The experimental values agree with predictions in the literature based on interpolation formulae. The effects of changes in composition and radiation‐induced crosslinking on the glass transition of the copolymer system are described.
Vulcanization with maleimides
Authors: Tawney P. O. , Wenisch W. J. , Van Der Burg S. , Relyea D. I.
Published: April 2003

Series of mono‐ and bismaleimides were evaluated as curing agents to determine the effect of structure on crosslinking ability. The activity of N‐phenylmaleimide derivatives (monomaleimides) as crosslinking agents is highly dependent upon the substituent on the phenyl group. The activity of bismaleimides is likewise affected by the nature of the moiety connecting the maleimide rings. Isomaleimides and itaconimides are less effective curatives. Initiators for the maleimide cures include peroxides and sulfur accelerators of the thiazole type. Saturated and unsaturated hydrocarbon rubbers, except those containing a high percentage of isobutylene units, are vulcanized by a maleimide–initiator system. One of the attractive features of a maleimide curing system is that the physical properties of the cured rubbers are independent of curing temperature. Further, these vulcanizates have the good aging characteristics typical of nonsulfur‐cured vulcanizates. In contrast to sulfur vulcanization, the maleimide curing systems do not markedly affect the ability of elastomers to crystallize when stretched. Therefore, the T50 test cannot be used to assess the state of cure of maleimide–natural rubber vulcanizates. Maleimides containing an appropriate second functional group can be used as self‐accelerating curing agents or as adhesives.
N‐chloro and N‐nitroso compounds as synergists for the self‐extinguishing action of bromine compounds in polystyrene
Authors: Ingram Alvin R.
Published: April 2003

Compounds other than peroxides may be used to enhance the self‐extinguishing action of organic bromine compounds on polystyrene. The addition of certain chloramides or nitrosoamines converts some bromide‐containing polystyrene compositions from flammable to instantly self‐extinguishing. Two effective chloramides were N,N‐dichlorotoluene sulfonamide or N,N′‐dichloro‐N,N′‐diphenyl urea but they were of limited value because of hydrolysis by atmospheric moisture. The more effective nitrosoamines were N‐nitroso‐N‐methylaniline, N‐nitrosocarbazole and N‐nitroso‐diphenylamine. An undesirable characteristic of the three compounds is their inhibition of polymerization of styrene. The interaction of a nitrosoamine and an aliphatic bromine compound is apparent from the evolution of nitrogen, nitric oxide, and nitrous oxide. If the minimum temperature for gas evolution falls in the range of about 145–180°C. in a prescribed simple test, the nitrosoamine and bromine compound may be used for rendering polystyrene self‐extinguishing.
Penetration of water‐soluble polymers into cellulose fibers
Authors: Aggebrandt L. G. , Samuelson O.
Published: April 2003

Polymetaphosphate and polyethylene glycol in aqueous solution are excluded completely from rayon fibers. Determinations of nonsolvent water (δ) with these reference substances give the same value which can be used as a measure of the true swelling. The polymers can, however, penetrate into porous areas present in cotton. The average polymer concentration inside these areas is lower than in the external solution. High speed centrifugation results in decreased δ values, which is explained by a compression of the porous areas. Higher δ values are obtained as the molecular weight of the reference substance is increased. With polymetaphosphate the δ values decrease when the external concentration is increased, whereas with polyglycol the δ value within a wide range is independent of the concentration.
Viscoelastic properties of styrene–acenaphthylene copolymers in the transition region
Authors: Schaffhauser R. J. , Shen M. C. , Tobolsky A. V.
Published: April 2003

A series of styrene–acenaphthylene copolymers was prepared by thermal polymerization. Homogeneous samples were obtained except for those compositions where the initial concentration of styrene monomer was 40–60 mole‐%. Master curves and characteristic viscoelastic parameters were obtained for the homogeneous copolymers. The plot of Tg vs. copolymer composition yielded a linear relationship.
Poly(oxatetramethylene) glycol. II. Molecular weight distribution
Authors: Johnston Peter R.
Published: April 2003

Polymer of 1200 molecular weight was prepared from tetrahydrofuran by using a catalyst mixture of ethylene oxide, BF3, and water. Fractionation was accomplished by washing a cyclohexane‐toluene solution with mixtures of methanol and water. Results, plotted on Poisson probability paper, showed that the distribution is somewhat broader than the Poisson.
Effect of structure on the glass temperature of polyamides
Authors: Temin Samuel C.
Published: April 2003

A penetrometer method, for which validity was demonstrated, was utilized for measuring the glass temperatures of several polyamides. Adipic acid, sebacic acid, and hexamethylenediamine were used as representatives of linear aliphatic components of the nylons. Isophthalic acid, diphenic acid, and m‐xylylenediamine were employed to provide examples with phenyl rings in the polymeric chain. Piperazine was used to assay the effect of a rigid alicyclic ring. To provide bulky side groups, 9,9‐bis(2′‐carboxyethyl)fluorene and 9,9‐bis(3′‐aminopropyl)fluorene were utilized. Several new nylon salts and polyamides were prepared. The results illustrate the contribution of chain stiffness and side chain bulkiness to the glass temperature, Tg. Assuming, as did Rybnikar, a Tg of −65°C. for nylon 66 and other linear aliphatic polyamides, the elevation caused by inclusion of a m‐phenylene group in the chain was shown to be about 165°C. The piperazine ring had an effect at least equivalent to that of the m‐phenylene group. A single bulky side group elevated the glass temperature by about 185°C. over the value for linear aliphatic polyamides, the same increment observed in the cases of polyesters and addition polymers. A second bulky group made a smaller incremental addition to Tg. Thus, a value of Tg well below room temperature for linear aliphatic polyamides was found consistent with the present results.