bluuebunny/crossref_metadata_2025 huggingface dataset:
A global survey of aerosol-liquid water cloud overlap based on four years of CALIPSO-CALIOP data
Authors: Devasthale A. , Thomas M. A.
Published: February 2011

Abstract. Simulating the radiative impacts of aerosols located above liquid water clouds presents a significant challenge. In particular, absorbing aerosols, such as smoke, may have significant impact in such situations and even change the sign of net radiative forcing. It is not possible to reliably obtain information on such overlap events from existing passive satellite sensors. However, the CALIOP instrument onboard NASA's CALIPSO satellite allows us to examine these events with unprecedented accuracy. Using four years of collocated CALIPSO 5 km Aerosol and Cloud Layer Version 3 Products (June 2006–May 2010), we quantify, for the first time, the characteristics of overlapping aerosol and water cloud layers globally. We investigate seasonal variability in these characteristics over six latitude bands to understand the hemispheric differences when all aerosol types are included in the analysis (the AAO case). We also investigate frequency of smoke aerosol-cloud overlap (the SAO case). Globally, the frequency is highest during the JJA months in the AAO case, while for the SAO case, it is highest in the SON months. The seasonal mean overlap frequency can regionally exceed 20% in the AAO case and 10% in the SAO case. In about 5–10% cases the vertical distance between aerosol and cloud layers is less than 100 m, while about in 45–60% cases it less than a kilometer in the annual means for different latitudinal bands. In about 70–80% cases, aerosol layers are less than a kilometer thick, while in about 18–22% cases they are 1–2 km thick. The frequency of aerosol layers 2–3 km thick is about 4–5% in the tropical belts during overlap events. Over the regions where high aerosol loadings are present, the overlap frequency can be up to 50% higher when quality criteria on aerosol/cloud feature detection are relaxed. Over the polar regions, more than 50% of the overlapping aerosol layers have optical thickness less than 0.02, but the contribution from the relatively optically thicker aerosol layers increases towards the equatorial regions in both hemispheres. The results suggest that the frequency of occurrence of overlap events is far from being negligible globally.
Inverse modeling of CO2 sources and sinks using satellite observations of CO2 from TES and surface flask measurements
Authors: Nassar R. , Jones D. B. A. , Kulawik S. S. , Worden J. R. , Bowman K. W. , Andres R. J. , Suntharalingam P. , Chen J. M. , Brenninkmeijer C. A. M. , Schuck T. J. , Conway T. J. , Worthy D. E.
Published: February 2011

Abstract. We infer CO2 surface fluxes using satellite observations of mid-tropospheric CO2 from the Tropospheric Emission Spectrometer (TES) and measurements of CO2 from surface flasks in a time-independent inversion analysis based on the GEOS-Chem model. Using TES CO2 observations over oceans, spanning 40° S–40° N, we find that the horizontal and vertical coverage of the TES and flask data are complementary. This complementarity is demonstrated by combining the datasets in a joint inversion, which provides better constraints than from either dataset alone, when a posteriori CO2 distributions are evaluated against independent ship and aircraft CO2 data. In particular, the joint inversion offers improved constraints in the tropics where surface measurements are sparse, such as the tropical forests of South America, which the joint inversion suggests was a weak sink of −0.17 ± 0.20 Pg C in 2006. Aggregating the annual surface-to-atmosphere fluxes from the joint inversion yields −1.13 ± 0.21 Pg C for the global ocean, −2.77 ± 0.20 Pg C for the global land biosphere and −3.90 ± 0.29 Pg C for the total global natural flux (defined as the sum of all biospheric, oceanic, and biomass burning contributions but excluding CO2 emissions from fossil fuel combustion). These global ocean, global land and total global fluxes are shown to be in the range of other inversion results for 2006. To achieve these results, a latitude dependent bias in TES CO2 in the Southern Hemisphere was assessed and corrected using aircraft flask data, and we demonstrate that our results have low sensitivity to variations in the bias correction approach. Overall, this analysis suggests that future carbon data assimilation systems can benefit by integrating in situ and satellite observations of CO2 and that the vertical information provided by satellite observations of mid-tropospheric CO2 combined with measurements of surface CO2, provides an important additional constraint for flux inversions.
Modeling the Frozen-In Anticyclone in the 2005 Arctic summer stratosphere
Authors: Allen D. R. , Douglass A. R. , Manney G. L. , Strahan S. E. , Krosschell J. C. , Trueblood J. V. , Nielsen J. E. , Pawson S. , Zhu Z.
Published: February 2011

Abstract. Immediately following the breakup of the 2005 Arctic spring stratospheric vortex, a tropical air mass, characterized by low potential vorticity (PV) and high nitrous oxide (N2O), was advected poleward and became trapped in the easterly summer polar vortex. This feature, known as a "Frozen-In Anticyclone (FrIAC)", was observed in Earth Observing System (EOS) Aura Microwave Limb Sounder (MLS) data to span the potential temperature range from ~580 to 1100 K (~25 to 40 km altitude) and to persist from late March to late August 2005. This study compares MLS N2O observations with simulations from the Global Modeling Initiative (GMI) chemistry and transport model, the GEOS-5/MERRA Replay model, and the Van Leer Icosahedral Triangular Advection (VITA) isentropic transport model to elucidate the processes involved in the lifecycle of the FrIAC, which is here divided into three distinct phases. During the "spin-up phase" (March to early April), strong poleward flow resulted in a tight isolated anticyclonic vortex at ~70–90° N, marked with elevated N2O. GMI, Replay, and VITA all reliably simulated the spin-up of the FrIAC, although the GMI and Replay peak N2O values were too low. The FrIAC became trapped in the developing summer easterly flow and circulated around the polar region during the "anticyclonic phase" (early April to the end of May). During this phase, the FrIAC crossed directly over the pole between the 7 and 14 April. The VITA and Replay simulations transported the N2O anomaly intact during this crossing, in agreement with MLS, but unrealistic dispersion of the anomaly occurred in the GMI simulation due to excessive numerical mixing of the polar cap. The vortex associated with the FrIAC was apparently resistant to the weak vertical shear during the anticyclonic phase, and it thereby protected the embedded N2O anomaly from stretching. The vortex decayed in late May due to diabatic processes, leaving the N2O anomaly exposed to horizontal and vertical wind shears during the "shearing phase" (June to August). The observed lifetime of the FrIAC during this phase is consistent with timescales calculated from the ambient horizontal and vertical wind shear. Replay maintained the horizontal structure of the N2O anomaly similar to MLS well into August. The VITA simulation also captured the horizontal structure of the FrIAC during this phase, but VITA eventually developed fine-scale N2O structure not observed in MLS data.
A five year record of high-frequency in situ measurements of non-methane hydrocarbons at Mace Head, Ireland
Authors: Grant A. , Yates E. L. , Simmonds P. G. , Derwent R. G. , Manning A. J. , Young D. , Shallcross D. E. , O'Doherty S.
Published: February 2011

Abstract. Continuous high-frequency in situ measurements of a range of non-methane hydrocarbons have been made at Mace Head since January 2005. Mace Head is a background Northern Hemispheric site situated on the eastern edge of the Atlantic. Five year measurements (2005–2009) of eleven non-methane hydrocarbons, namely C2–C5 alkanes, benzene, toluene, ethyl-benzene and the xylenes, have been separated into baseline Northern Hemispheric and European polluted air masses, among other sectors. Seasonal cycles in baseline Northern Hemispheric air masses and European polluted air masses arriving at Mace Head have been studied. Baseline air masses show a broad summer minima between June and September for shorter lived species, longer lived species show summer minima in July/August. All species displayed a winter maxima in February. European air masses showed baseline elevated mole fractions for all non-methane hydrocarbons, largest elevations (of up to 360 ppt for ethane maxima) from baseline data were observed in winter maxima, with smaller elevations observed during the summer. Analysis of temporal trends using the Mann-Kendall test showed small (<6%/year) but statistically significant decreases in the butanes, i-pentane and o-xylene between 2005 and 2009 in European air. Toluene was found to have an increasing trend of 34%/year in European air. No significant trends were found for any species in baseline air.
Flow cytometric assessment of specific leucine incorporation in the open Mediterranean
Authors: Talarmin A. , Van Wambeke F. , Catala P. , Courties C. , Lebaron P.
Published: February 2011

Abstract. The surface of the Mediterranean Sea is a low-phosphate-low-chlorophyll marine area where marine heterotrophic prokaryotes significantly contribute to the biogeochemical cycles of all biogenic elements such as carbon, notably through the mineralization of dissolved organic compounds. Cell-specific leucine incorporation rates were determined in early summer in the open stratified Mediterranean Sea. The bulk leucine incorporation rate was on average 5 ± 4 pmol leu l−1 h−1 (n=30). Cell-specific 3H-leucine incorporation rates were assayed using flow cytometry coupled to cell sorting. Heterotrophic prokaryotes (Hprok) were divided into cytometric groups according to their side scatter and green fluorescence properties: high nucleic acid containing cells (HNA) with high scatter (HNA-hs) and low scatter (HNA-ls) and low nucleic acid containing cells (LNA). Cell-specific leucine incorporation rates of these cytometric groups ranged from 2 to 54, 0.9 to 11, and 1 to 12 × 10-21 mol cell−1 h−1, respectively. LNA cells represented 45 to 63% of the Hprok abundance, and significantly contributed to the bulk leucine incorporation rates, from 12 to 43%. HNA/LNA ratios of cell-specific leucine incorporation were on average 2.0 ± 0.7 (n=30). In surface layers (from 0 m down to the deep chlorophyll depth, DCM), cell-specific rates of HNA-hs were elevated (7 and 13 times greater than LNA and HNA-ls, respectively). Nevertheless, on average HNA-hs (26%) and LNA (27%) equally contributed to the bulk leucine incorporation in these layers. Prochlorococcus cells were easily sorted near the DCM and displayed cell-specific leucine incorporation rates ranging from 3 to 55 × 10-21 mol leu cell−1 h−1, i.e. as high as HNA-hs'. These sorted groups could therefore be defined as key-players in the process of leucine incorporation into proteins. The mixotrophic features of certain photosynthetic prokaryotes and the high contribution of LNA cells to leucine incorporation within the microbial communities of the Mediterranean could be reinforced.
Thermal adaptation of net ecosystem exchange
Authors: Yuan W. , Luo Y. , Liang S. , Yu G. , Niu S. , Stoy P. , Chen J. , Desai A. R. , Lindroth A. , Gough C. M. , Ceulemans R. , Arain A. , Bernhofer C. , Cook B. , Cook D. R. , Dragoni D. , Gielen B. , Janssens I. , Longdoz B. , Liu H. , Lund M. , Matteucci G. , Moors E. , Scott R. L. , Seufert G. , Varner R.
Published: February 2011

Abstract. Thermal adaptation of gross primary production and ecosystem respiration has been well documented over broad thermal gradients. However, no study has examined their interaction as a function of temperature, i.e. the thermal responses of net ecosystem exchange of carbon (NEE). In this study, we constructed temperature response curves of NEE against temperature using 380 site-years of eddy covariance data at 72 forest, grassland and shrubland ecosystems located at latitudes ranging from ~29° N to 64° N. The response curves were used to define two critical temperatures: transition temperature (Tb) at which ecosystem transferring from carbon source to sink and optimal temperature (To) at which carbon uptake is maximized. Tb was strongly correlated with annual mean air temperature. To was strongly correlated with mean temperature during the net carbon uptake period across the study ecosystems. Our results suggested that ecosystem CO2 flux switched from source to sink when air temperature reached annual mean temperature in spring and reached maximum uptake at mean temperature of the net carbon uptake period. Our results imply that the net ecosystem exchange of carbon adapt to the temperature across the geographical range due to intrinsic connections between vegetation primary production and ecosystem respiration.
In-situ multispectral and bathymetric measurements over a supraglacial lake in western Greenland using a remotely controlled watercraft
Authors: Tedesco M. , Steiner N.
Published: February 2011

Abstract. We report concurrent in-situ multi-spectral and depth measurements over a supraglacial lake in West Greenland, collected by means of a remotely controlled boat equipped with a GPS, a sonar and a spectrometer. We focus our attention on the analysis of some of the key parameters widely used for multispectral spaceborne bathymetry, namely the lake bottom albedo and the water attenuation coefficient. The analysis of in-situ data highlights the exponential trend of the water-leaving reflectance with lake depth. The values of the attenuation factor are obtained from in-situ data and compared with those computed using approaches proposed in the literature. Also, the values of the lake bottom albedo from in-situ measurements are compared with those obtained from the analysis of reflectance of shallow-waters. Finally, we quantify the error between in-situ measured and satellite-estimated lake depth values for the lake under study.
Form and Figure: Paul Ricoeur and the Rehabilitation of Human Work
Authors: Mei Todd S.
Published: February 2011

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The Scholar and the Pub Crawler: Revisiting the Debate between Ricoeur and Gadamer
Authors: Arthos John
Published: February 2011

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Piercing the Horizon
Authors: Gasché Rodolphe
Published: February 2011

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Anarchist Readings of Spinoza
Authors: Colson Daniel
Published: February 2011

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Foucault and Social Measure
Authors: Mader Mary Beth
Published: February 2011

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Breve philosophie des jardins
Authors: Forthomme Bernard
Published: February 2011

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Derrida and Wittgenstein: Points of Opposition
Authors: Shain Ralph
Published: February 2011

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Pedagogy of the Written Image
Authors: Dronsfield Jonathan Lahey
Published: February 2011

"Text, it is Jean-Luc Godard’s “ennemi royal, principal." Text, it is on the side of death, “les images c’est la vie et les textes, c’est la mort”. Twenty years later and the war is not over: “Une image est paisible. Une image de la Vierge avec son petit enfant sur son âne n'amène pas la guerre, c'est son interprétation par un texte qui amènera la guerre et qui fera que les soldats de Luther iront déchirer les toiles de Raphaël.” Godard’s story is not just of the history of cinema, it is one in which text has won out to the extent that TV and the computer too make of the image something subservient to text. “Since Gutenberg” the text has triumphed in this way. “There was a long struggle, marriage or liaison between painting and text. Then the text carried the day. Film is the last art in the pictorial tradition... Take away the text and you’ll see what’s left. In TV nothing is left.” It is obvious from these lines of demarcation, lines which divide the art of the image from what would declare war on its most sacred icons and defeat its technologies, a conflict in which there is just the one aggressor, a division which makes of the relation between image and text nothing less than a matter of life and death, that for Godard text is indeed the enemy..."
Notes on Contributors
Authors: Bios Author
Published: February 2011

Author Bios
PREVULCANIZATION OF NATURAL RUBBER LATEX BY UV TECHNIQUES: A PROCESS TOWARDS REDUCING TYPE IV CHEMICAL SENSITIVITY OF LATEX ARTICLES
Authors: Schlögl S. , Temel A. , Schaller R. , Holzner A. , Kern W.
Published: February 2011

The UV induced prevulcanization of natural rubber (NR) latex provides an innovative technology for an efficient cross-linking. In the photochemical process, a selected photoinitiator and a poly-functional thiol are added to the NR latex. Free radicals (bond cleavage of the photoinitiator) are generated due to UV irradiation and cross-linking of the latex particles is then achieved by a thiol-ene addition reaction. The thiol-ene addition reaction in NR films is characterized with Fourier transform infrared and Raman spectroscopy. To achieve the prevulcanization of latex, both a thin film photoreactor and a falling film photoreactor are applied. Solid latex films are then produced by conventional dipping of the precured NR latex. The NR latex films are distinguished by good skin compatibility due to the absence of sensitizing or irritating processing agents which are used in conventional sulfur vulcanization. Moreover UV cross-linked films display excellent physical properties as well as high aging stabilities. Further advantages of the new technology compared to conventional sulfur vulcanization are low energy consumption together with short vulcanization times.
MOBILITY OF ADSORBED POLYMER CHAINS
Authors: Goeritz D. , Hofmann R. W. P. , Bissem H. H.
Published: February 2011

The behavior of thin polymer films adsorbed on a graphite surface was investigated by means of atomic force microscopy. Via force–distance curves, which were recorded for layers of polyisoprene adsorbed on graphite [highly ordered pyrolytic graphite (HOPG)], a two-layer system was found. The upper layer proved to be soft and not in the glass state. No indications supporting the supposition of an additional glasslike polyisoprene layer underneath this soft layer could be found. Thus, if such a glass layer exists on the HOPG surface, the upper limit of its thickness is set to 3 nm. On the other hand, polystyrene adsorbed on graphite is in the glass state independent of thickness.
CURING CYCLE OPTIMIZATION OF A THICK-SECTION RUBBER PART
Authors: El Labban Abdulrahman , Mousseau P. , Deterre R. , Bailleul J. L.
Published: February 2011

The curing cycle optimization is a first order concern for the rubber industry both to control part quality and to reduce curing times. The curing control of thick parts is very delicate due to low thermal diffusivity of rubber compounds. We present a numerical method for the optimization of the cure cycle of molded parts. The heat equation and vulcanization kinetic equation are solved considering the induction, curing, and reversion phases. We build a conjugate gradient optimization method that estimates an optimum temperature–time couple applied as boundary conditions necessary to obtain a desired homogeneous state of cure. We describe the experimental device including a thermally controlled mold. We also describe the thermal regulation and instrumentation including an original measuring device recording temperatures directly within the molded part while minimizing thermal disturbances during measurement. Then, we present the model validation by comparing the numerical simulation results with those obtained experimentally. We propose a curing cycle optimization method based on the calculation of the sensitivity of the state of cure with boundary condition variations. It is an iterative procedure that allows converging to the boundary conditions necessary to obtain the best compromise between the state of cure homogeneity within the part thickness and the curing time. We define a productivity criterion inversely proportional to the curing time and a quality criterion proportional to the homogeneity of the state of cure. Based on these two criteria, we define a performance index that qualifies the process considering the compromise between quality and productivity.
THE EFFECT OF MIXED FILLER SIZES ON THE FIBER DIAMETER OF ELECTROSPUN BUTYL RUBBER FORMULATIONS
Authors: Murphy Dan , Barry Carol , Mead Joey , Zukas Walter
Published: February 2011

Electrospinning of thermosetting elastomers is a method for developing nonwoven membranes with a microporous structure for use in dynamic applications (i.e., stretchable). These membranes have potential for chemical protective clothing applications. The most challenging concerns are the ability to control pore sizes, fiber diameter, permeability, and physical properties. We investigated the effect on fiber diameters as a ratio of two different carbon black particulate sizes. Carbon black N110 and N990 were incorporated at various percentages of total carbon black loading in a butyl rubber formulation. Higher levels of small particulates were found to give smaller and more consistent fiber diameters. Understanding of the effects of filler size and concentration on the electrospinning process will lead to the successful tailoring of nonwoven membranes with desired fiber diameter and pore size.
MULTIPLE GLASS TRANSITION TERPOLYMERS OF ISOPRENE, BUTADIENE, AND STYRENE
Authors: Halasa Adel F. , Gross Bill B. , Hsu Wen-Liang
Published: February 2011

Novel polymers that will contribute to a better combination of traction and tread wear in tire applications, which is historically difficult to achieve, have been developed. In this work, multiple viscoelastic polymers possessing multiple glass transition temperatures terpolymers of isoprene/butadiene/styrene were synthesized containing 45/45/10, 40/40/20, and 35/35/30 polymer ratios in 5-gallon laboratory reactors using tetramethylethylenediamine or bis(dipiperdino) ethane as a modifier. These polymers show two glass transition temperatures (Tg's); the one that occurs at higher temperatures (–25 to –10 °C) is known to contribute to good wet traction properties, while the lower Tg is known to contribute to better tread wear properties. These terpolymers were characterized by the fact that their multiviscoelastic loss modulus has narrow molecular distribution for better rolling resistance. In a standard ASTM D31912 carbon-black-filled tread compound recipe, the polymers having all three terpolymers of isoprene/butadiene/styrene polymerized showed excellent values of loss tangent at 0 and 60 ºC, which is a laboratory predictor for both wet traction and rolling resistance. These terpolymers when evaluated in the same ASTM D3191 delivered better properties in a tread compound recipe than either solution or emulsion styrene-butadiene rubber in a formulation that has natural rubber or polybutadiene.
PLASMA POLYMERIZATION OF MONOMERS ONTO FILLERS, TO TAILOR THEIR SURFACE PROPERTIES IN TIRE COMPOUNDS
Authors: Dierkes W. K. , Tiwari M. , Datta R. N. , Talma A. G. , Noordermeer J. W. M. , van Ooij W. J.
Published: February 2011

Rubber reinforcement by fillers is primarily based on filler structure and surface properties. A chemical change of the surface properties while maintaining the structure allows tailoring filler properties for improved filler–polymer compatibility, resulting in improved morphological, dynamic, and mechanical properties of straight rubbers as well as elastomer blends. Plasma polymerization based on acetylene, pyrrole, and thiophene as monomers are applied to silica in order to change surface polarity and chemistry, with untreated and silane-treated silica as references. Generally spoken, the plasma coating results in reduced filler–filler interaction, improved dispersion, and increased bound rubber content in straight SBR as well as in SBR/EPDM blends. In terms of stress-strain properties, the plasma treatment results in higher moduli compared to the untreated filler. The most prominent effect was found in the stress-strain properties of straight SBR: Polythiophene-coated silica results in significantly higher moduli and tensile strength values, even higher than the silane-treated material. In the case of the polymer blend, the plasma treatment results in higher tensile strength and elongation at break values. It is important to note that no unambiguous correlation was found between filler–filler interaction and filler–polymer interaction: A lower Payne-effect does not necessarily result in a higher bound rubber content.
Dynamic Fatigue Life of Rubber
Authors: Cadwell S. M. , Merrill R. A. , Sloman C. M. , Yost F. L.
Published: February 2011

If a rubber member is continuously vibrated it will sooner or later crack and ultimately rupture, owing to the repeated oscillations to which it has been subjected. The gradual deterioration of physical and chemical properties which accompanies such vibration is called dynamic fatigue. The number of such repeated vibrations required to rupture the rubber member is here defined as the dynamic fatigue life of the member for the particular condition of vibration imposed. The authors wish to outline briefly the general nature of the results they have obtained in their studies on the dynamic fatigue life of rubber and, in particular, to show the critical dependence of the life on the imposed oscillation conditions. The dynamic fatigue life of rubber which is being vibrated linearly, that is, back and forth along its own length, between constant strain limits will be discussed first. Figures 1 to 3 facilitate a general statement of the problem and also serve to define certain oscillation limits which are of fundamental importance with reference to dynamic fatigue life. The sketches are conventionalized for the sake of simplicity.
Some Remarks on the Measurement of the Viscosity of Latex by Means of a Capillary Viscometer
Authors: Van Gils G. E.
Published: February 2011

In this article the paper of Jordan, Brass and Roe is criticized. The theoretical basis of viscometry is explained, and it is shown that Poiseuille's law can be derived in the case of a true or Newtonian liquid flowing through a capillary tube. It is not permissible, however, in dealing with a non-Newtonian liquid, to use any equation based on Poiseuille's law, as was done by Jordan, Brass and Roe. The Crude Rubber Committee of the Rubber Division of the American Chemical Society has realized clearly the importance of uniformity in viscometry, but we must warn very strongly against methods based on unsound reasoning. We also find some fundamental objections to the paper by Kendrov.
The Investigation of Synthetic Linear Polymers by X-Rays
Authors: Fuller C. S.
Published: February 2011

The ultimate aim of research on high polymeric substances is to explain the properties of these substances in terms of their inner colloidal and molecular nature. x-Eay and electron diffraction investigations, as we have seen, have furnished considerable data on this inner structure. Nevertheless, it is of the utmost importance that the investigator in this field does not obtain a one-sided view from the past work. Nearly always a given study relates to only one phase of the general problem. For example, it is wrong to assume that, since the “unit cell” for cellulose has been well established, we therefore know its entire structure. In reality we have determined simply that parts of the cellulose have this structure. How these parts fit into the other parts that make up the entire system is still not clear. Here again the synthetic high polymers can be of great help. By employing simple polymeric molecules of known chemical constitution and structure, and by determining how these molecules behave in the aggregate, we may expect to make progress in understanding these complex systems. In this endeavor a closer control of both the specimens under examination and the technique itself will serve to make the diffraction method an even more valuable tool for the study of high molecular compounds.
Swelling Measurements in the Rubber Laboratory
Authors: Proske G.
Published: February 2011

In making swelling measurements, which are carried out with great frequency today in rubber laboratories, the most varied procedures are in general use, some of which do not bear careful and critical examination. The most important sources of error, which occur equally in all the methods, are first discussed, then follows a detailed discussion of commonly used methods, particularly the gravimetric and volumetric methods in their various modifications. Especially useful methods are pointed out. The attempt is made to make the discussion clear by means of representative rubber mixtures chosen from practice. Finally an experimental apparatus developed by the author from apparatus already in technical use and well suited to rubber laboratories is described in detail.
Effect of Strain on the Aging of Vulcanized Rubber
Authors: Dawson T. R. , Scott J. R.
Published: February 2011

Vulcanized rubber which is stored in a state of strain deteriorates much more rapidly than similar rubber not under strain. This observation has immediate application to rubber goods of many kinds, such as tire tubes packed in a folded state, tires standing under strains due to their own weight or to that of the vehicle, coiled and bent cable and hose, football bladders and bathing caps packed flat, folding-boat covers, and so on. There has been a moderate amount of investigation devoted to this phenomenon in the last two decades, but, in the main, quantitative studies have been devoted to simply stretched rubber, and data on the effects of folds or creases have not been available. As folds and creases involve compression as well as stretching, it cannot be assumed that conclusions drawn from studies of stretched rubber are applicable without change to rubber articles subjected to folding or creasing. The observations given in the present paper, made on different occasions in connection with other work, bring together several examples of the effect of folds on the aging of rubber.
Rational Processing
Authors: Cotton F. H.
Published: February 2011

The processes to which rubber is subjected before vulcanization depend largely for their success on the raw material being rendered plastic. At ordinary temperatures smoked sheet is an elastic substance having nerve and incapable of being kneaded, extruded or moulded. To facilitate these processes and compounding with fillers, rubber is masticated, either on a two-roll mill or in an internal mixer. Experience has shown that mechanical working reduces the elasticity and nerve of rubber and renders it plastic. Mastication is such a familiar practice in rubber technology that it is taken for granted as the first essential in rubber manufacture. This is unfortunate, because it is costly and has several disadvantages. These will be considered in detail and other means of achieving the same end suggested.
The Kinetics of the Polymerization of Isoprene on Sodium Surfaces
Authors: Bolland J. L.
Published: February 2011

In recent years an increasing amount of study has been devoted to gaining a better understanding of the fundamental nature of polymerization reactions. Perhaps the most successful method of approach so far employed has been the systematic study of the kinetics of a wide variety of polymerizations, thermal, catalytic and photochemical. As yet, however, little attention has been directed toward one very important type of polymerization, viz., the polymerization of conjugated compounds in presence of alkali metals. The kinetic method has therefore been applied to the polymerization of isoprene on sodium as a representative example of this class of reactions.
Mixed Polymers and Vulcanizable Plasticizers. Relation to the Vulcanization of Rubber
Authors: Garvey B. S. , Alexander C. H. , Küng F. E. , Henderson D. E.
Published: February 2011

The vital role played by rubber in modern civilization is due in part to the physical properties displayed by soft vulcanized rubber in service and in part to the characteristics of unvulcanized milled rubber which make it amenable to manufacturing operations. Vulcanization of rubber is a change in condition usually induced by heating it with sulfur, and is best defined by contrasting the difference in physical properties: To illustrate, compare a mill-mixed composition before and after vulcanization. Before vulcanization it is easily pulled apart and, if considerably extended, shows little tendency to retract, although, under impact, the recovery or rebound is considerable. If heated it becomes even softer and more plastic, and can easily be formed into any desired shape. If cooled to 0° C or somewhat lower, it becomes stiff and boardy. It is readily soluble in hydrocarbon solvents. When two fresh surfaces are pressed together, they coalesce and become practically integral. This tack, as it is called, is valuable in manufacturing operations. After vulcanization, rubber is tough and strong and, after even a slow distortion, returns rapidly to its original shape. It has little tendency to flow and is devoid of tack. It swells but does not dissolve in hydrocarbon solvents. These characteristics change very little from −40° to well above 100° C.
Frictional Properties of Rubber
Authors: Roth Frank L. , Driscoll Raymond L. , Holt William L.
Published: February 2011

Laboratory measurements of coefficients of friction of soft rubber compounds were made by towing specimens on horizontal tracks and by allowing them to slide down inclined tracks. The specimens were prepared by attaching the rubber to a metal backing and molding it against glass surfaces having different degrees of roughness. The coefficients increase markedly with speed, ranging from about 1 at 10−4 cm. per sec. to more than 4 at 5 cm. per sec. The occurrence of vibrations prevented observations at higher speeds. Static friction is greater than dynamic friction for speeds appreciably less than 10−3 cm. per sec. and less than dynamic friction for greater speeds. The coefficients decrease slightly with increasing pressures and are independent of the size of the specimen. Except at very low speeds the smoother surfaces yield the higher coefficients. Materials such as talc or bloom on the sliding surfaces cause large decreases in the coefficients. Attention is called to the dependence of the coefficients of friction on the speed, which is shown in several previous investigations on rubber and other materials.
Cryoscopic and Viscosity Studies of Polyisobutylene. Cryoscopic Deviation of Polyisobutylene Solutions from Raoult's Law
Authors: Kemp A. R. , Peters H.
Published: February 2011

1. The cryoscopic method is not satisfactory for polyisobutylenes having chain lengths much over 40 isobutylene units, on account of the failure of their solutions to obey Raoult's law. 2. The present work has led to the selection of a Kcm value of 0.75×104 for n-hexane solutions of polyisobutylene for use in the equation M=(log ηr×Kcm)/C. 3. Extrapolation of cryoscopic data obtained on nonideal solutions to infinite dilution gives inordinately high molecular weight values compared with those based on freezing point measurements of ideal solutions. 4. Of several solvents studied, n-hexane was found to be the best for viscosity—molecular weight measurements of polyisobutylene. 5. Fractionation of polyisobutylene by diffusion into mixtures of n-hexane and acetone resulted in the separation of the lower polymer fractions.
Growing Rubber in North America
Authors: Trumbull H. L.
Published: February 2011

Ever since war was forced upon us, with the subsequent capture by the Japanese of the Malay Peninsula and the Dutch East Indies, Americans have been groping for new sources of natural rubber to replace those cut off by our enemies. With startling dispatch, lands which produced 90 per cent of the crude rubber used by this country had been captured, and the supplies from another 7 per cent of the world's producing areas had been endangered by action against lines of communication with these sources. The problem was not entirely new, because many farseeing people, both in government service and private business, had been concerned about our dependence on distant sources for what had become one of our essential materials in peace and war. They had made studies of domestic plants which might produce rubber in quantities sufficient for our necessities. The urgency of the task, however, was not so great then as it is now. Early this year I was assigned by the Goodrich company to give this problem primary attention, and to call on any other resources of the organization for assistance whenever necessary. The purpose was to seek information and propose action which would benefit the nation, suffering under an acute shortage of natural rubber. The principal early parts of this work were the study and evaluation of all domestic plants known to produce rubber, and the discovery, if possible, of new sources of this vital material on our continent.
Distribution of Non-Rubber Substances in Preserved Latex Part II. Acids
Authors: Baker H. C.
Published: February 2011

In a previous paper by the present author, a general method for determining the distribution of the nonrubber substances between the rubber-and-water phases in latex was described and results were given of its application to the study of the distribution of nitrogen and materials extractable with acetone. It was shown that the nitrogen associated with the rubber phase is of two different types, a small amount (about 0.02 per cent) being independent of particle size and consequently distributed throughout the mass of the rubber, whereas the remainder is a function of particle size, replaceable by surface-active materials, such as soaps, and is, consequently, situated at the surface of the particles. The surface nitrogen in ammoniated latex was variable, decreased with age of latex, could be partially desorbed at an alkaline pH by washing the latex, for instance, by dilution or repeated creaming, and is considered to represent the protective protein covering of the latex globules. The total variation experienced in unconcentrated ammoniated latices of varying ages was from 0.11 to 0.18 per cent, but in latex of good quality about six months old, surface nitrogen was 0.15 per cent, corresponding to about 1 per cent protein. Distribution experiments on the acetone extract showed that there is from 2 to 3 per cent of acetone-soluble substances associated with the rubber, of which less than one-half represents ammonium soaps at the surface of the particles. The surface of the rubber particles is, therefore, composed largely of protein and fat acids, and it was thought probable that the ratio between them might change, both during the life of a single latex and from one latex to another.
The Phosphatides of Hevea Brasiliensis
Authors: Tristram G. R.
Published: February 2011

The presence of phosphatide in Hevea latex had long been suspected, but it was not until 1931 that Rhodes and Bishop isolated phosphatidic material containing 0.59 per cent nitrogen and 1.72 per cent phosphorus from the serum of latex which had been coagulated with ethanol. The crude material of these authors represented 0.2 per cent of the latex and, on treatment with acetone, yielded an insoluble fraction containing 0.88 per cent nitrogen and 2.56 per cent phosphorus (40 per cent of the former product). This latter fraction was, according to the accepted analytical composition of phosphatide, still very impure. The work of Rhodes and Bishop was repeated by Altman and Kraay, who isolated in very small amounts a product which gave much the same analyses, and extended the findings of Rhodes and Bishop by showing that the crude phosphatide contained both choline and glycerophosphoric acid. It is very probable that the phosphatide, although present in such small amount, is one of the important nonrubber components of latex. Judging from the ease with which phosphatides emulsify in aqueous media, there seems little doubt that the phosphatidic material assists in the maintenance of latex as a stable emulsion. It has been suggested by Bollman that crude phosphatide preparations act as natural antioxidants in vegetable oils. This suggestion has been disputed by Diemair and Fox and other workers, who state that this property is not possessed by pure phosphatide, although the complex system from which the phosphatide had been separated was an active antioxidant. Diemair, Strohecker and Reuland have advanced the opinion that the active antioxidant is a protein-phosphatide complex. The present work was undertaken as part of an investigation of the non-rubber components of latex. The crude phosphatide was prepared by the method of Rhodes and Bishop, the preliminary treatment being carried out at the Rubber Research Laboratories, Ceylon, under the direction of Mr. O'Brien, to whom the author's thanks are due. The raw material was treated by the method outlined below. The crude phosphatide was fractionated by a method which was essentially that used by Channon and Foster in their work on the phosphatides of wheat germ. The fractionation resulted in the isolation of a fairly pure form of phosphatidic acid (the possible source of which is discussed later) and an impure form of lecithin. The lecithin fraction contained little or no kephalin (only about 5.5 per cent of the nitrogen in this fraction was amino-nitrogen), a finding which was unexpected.
Oxidation of Rubber and Its Colloid-Chemical Results
Authors: Houwink R.
Published: February 2011

After the structure of raw and vulcanized rubber is discussed, the reactions which probably take place between the rubber molecule, oxygen and sulfur, in presence and absence of light, are indicated. Depending on circumstances, a severance of the molecule or net formation may be expected (dehydrogenation, formation of oxygen and sulfur bridges, cyclization) ; see Table 1. The accompanying changes in solubility, viscosity in solution, tensile strength, hardness and tackiness, are described. Special attention is drawn to the great effect that traces of oxygen, so slight that they cannot be shown analytically, may have because of the highly polymerized structure of rubber. Working hypotheses are established to explain the effect of the external factors mentioned, and these hypotheses are tested against extensive observation material. One of the most important conclusions is that it must probably be assumed that net-formed (chiefly cyclized) aggregates are present in unvulcanized rubber instead of, or in addition to, ehain molecules (Figure 3). How this affects the value of the method of determining molecular weight from viscosity measurements is discussed, and it is suggested that Kuhn's viscosity formula (4), probably with modification of the value of the exponent, will have to be applied instead of the Staudinger formula (1). It is also attempted to explain the drop in tensile strength to about 50 kg. per sq. cm. (see Figure 6) which occurs after optimum vulcanization is exceeded. It is attempted to place the responsibility for this on the oxidation which takes place during vulcanization. But it is shown by calculation that the conditions for this are in all probability not fulfilled. The rate of oxidation is high enough to reduce the tensile strength to 50 kg. per sq. cm. during normal curing conditions, but the amount of oxygen required for this purpose, about 1.5 per cent, is probably not present in rubber in a suitable form. A conclusive explanation of this decrease in tensile cannot as yet be given.
The Role of Zinc Oxide in Compounding Government Synthetic Rubber
Authors: Havenhill R. S. , Rankin J. J.
Published: February 2011

A comparative analysis of some of the factors involved in road tests on tires and laboratory flexometer tests indicates that not enough attention has been paid to heat dissipation and the role of the thermal conductivity of stocks in increasing heat dissipation. Flexometer tests currently used, in which samples are flexed between insulated plates, measure mainly heat generation. A modified St. Joe flexometer test is described, using metal-faced plates, which takes into account not only heat generation but heat dissipation, and should more nearly simulate road tests on tires when comparing GR-S (Buna-S) synthetic rubber stocks having different thermal conductivities. Using the new type test, mixtures of easy-processing channel black and zinc oxide are shown to have higher tensile strength and lower heat generation than soft blacks or mixtures of soft blacks and easy-processing channel blacks. The data given in this report indicate the need of further work along this line in the way of road tests on actual GR-S (Buna-S) tires containing zinc oxide in both tread and carcass.
Properties of Some Synthetic Rubbers
Authors: Sebrell L. B. , Dinsmore R. P.
Published: February 2011

X-RAY STRUCTURE OF SYNTHETIC RUBBER In presenting a series of x-ray diagrams of various types of synthetic rubber in comparison with natural rubber, in both the stretched and the unstretched condition, it is our purpose to bring out the fact that the molecular structure of synthetic rubbers is entirely different from that of natural rubber. It is proposed also to review briefly the theories which have been advanced, based on the x-ray analysis of rubber, to account for the elasticity of natural rubber, and to advance the possible reason for the difference shown by the x-ray diagrams of synthetic rubber. At the present time, from the most general point of view, the molecular structure of a rubberlike material is envisaged as a sort of brush-heap structure of entangled long chain molecules. x-Ray diffraction patterns show that, for some rubberlike materials, notable regularities of structure sometimes occur in the tangle of long-chain molecules. It is now realized that these regularities are not essential for rubberlike behavior. Nevertheless their observation and study is important because they afford a unique opportunity for studying the molecular structure of the chains and the molecular rearrangements which occur with the application of stress.
Statistical Thermodynamics of Rubber
Authors: Wall Frederick T.
Published: February 2011

The entropy change for the stretching of rubber is calculated by statistical methods, neglecting intermolecular attractions and deformation of bonds and bond angles. The calculation involves the probability of finding the system with a given distribution of molecular configurations. An equation of state relating the tension, length, and temperature of a rubber band is then derived. Following this a discussion of the applicability and the limitations of the theory is presented.
Solvents and Plasticizers for Chlorinated Rubber. Critical Data
Authors: Raynolds J. W. , Radcliffe M. R. , Vogel M. R.
Published: February 2011

1. No particular solvent may be classified as the best for use with chlorinated rubber. On the contrary, the solvent must be chosen with a view to its general properties and, where other ingredients are to be compounded with chlorinated rubber, the solvent strength as measured by the dilution ratio is of considerable importance. 2. The compatibility of blown castor oil with chlorinated rubber, some other blown oils, and some alkyds, depends on the strength of the solvent used. Strong solvents as measured by their dilution ratio enhance compatibility. 3. No particular plasticizer is best for use with chlorinated rubber. Different plasticizers impart totally different results at different loading percentages. The choice of plasticizers is dictated by the ultimate properties desired. More frequently than not, the use of two or more plasticizers will be necessary to obtain the optimum properties for any given application. 4. Consideration of the fundamental principles and trends presented in this paper will be helpful in the formulation of chlorinated rubber finishes for a wider variety of uses, and products of an improved nature will be the result.