Structural Changes in Rubber Brought about by Molecular Oxygen. III. Properties of Disintegrated Vulcanized Natural Rubber

1949 ◽  
Vol 22 (2) ◽  
pp. 310-315
Author(s):  
B. Dogadkin ◽  
Z. Tarasova ◽  
A. Pasynskii
Keyword(s):  
Structural Changes ◽  
Distribution Curve ◽  
Average Molecular Weight ◽  
Axial Ratio ◽  
Linear Functions ◽  
Optical Data ◽  
Vulcanized Rubber ◽  
Disintegration Product ◽  
Light Diffusion ◽  
Coefficient Of Diffusion

Abstract 1. The product of destructive solution of vulcanizate contains 50 mg. of oxygen per gram of substance; of this quantity, 3.77 mg. falls to the share of oxygen contained in free carboxyl groups. 2. The disintegrated vulcanizate is soluble in ordinary rubber solvents, as well as in binary mixtures of associated and unassociated liquids. 3. The viscosity and light diffusion of a broad range (up to 6 per cent) of disintegrated vulcanizate solutions are linear functions of the concentration. 4. The average molecular weight of the disintegration product of a vulcanizate, as determined from the coefficient of diffusion, is 3600; according to the viscometric and optical data, the molecules represent very large, elongated entities with an axial ratio of 1:24. The distribution curve of diffusion coefficients has a sevenfold dispersion. 5. The mechanical strength and elasticity of films prepared from a disintegrated vulcanizate are very much lower than those of films made of vulcanized rubber.

Infrared Study of Some Structural Changes in Natural Rubber during Vulcanization

1958 ◽  
Vol 31 (4) ◽  
pp. 719-736 ◽  
Author(s):  
Frederic J. Linnig ◽  
James E. Stewart
Keyword(s):  
Double Bond ◽  
Gamma Rays ◽  
Structural Changes ◽  
Elemental Sulfur ◽  
Carboxyl Groups ◽  
Double Bonds ◽  
Infrared Study ◽  
Tetramethylthiuram Disulfide ◽  
Vulcanized Rubber ◽  
Double Bond Shift

Abstract A knowledge of the structure of vulcanized rubber is essential to the interpretation of vulcanization and oxidation studies and the physical properties of the material. In the present work an infrared study has been made of structures resulting from a number of different methods of vulcanization. Sulfur vulcanizates show the presence of a shifted double bond, originally observed by Sheppard and Sutherland. The presence of conjugated double bonds is also indicated. Accelerators such as tetramethylthiuram disulfide and zinc dibutyl dithiocarbamate increase the rate of the double-bond shift and reduce the amount of conjugated double bonds. Neither the double-bond shift nor conjugation is observed as a result of vulcanization with tetramethylthiuram disulfide alone, hydrogen sulfide and sulfur dioxide (Peachey process), a peroxide, or gamma rays. These result in a possible decrease in carbonyl structures, and in the case of the last three, possible increased absorption due to OH and ionized carboxyl groups. Apparently, the double-bond shift and conjugation are primarily phenomena related to the use of elemental sulfur. The other vulcanization systems studied evidently involve different mechanisms. An implication of the present work is that there may be a relationship between the reported ease of oxidation of sulfur vulcanizates, accelerated vulcanizates, and sulfurless vulcanizates (tetramethylthiuram disulfide alone), which decreases in the order named, and the probable amount of conjugation in the compound, which decreases in the same order.

scholarly journals Exploring the Potential of C-Band SAR in Contributing to Burn Severity Mapping in Tropical Savanna

2019 ◽  
Vol 12 (1) ◽  
pp. 49 ◽  
Author(s):  
Marius B. Philipp ◽  
Shaun R. Levick
Keyword(s):  
Satellite Imagery ◽  
Laser Scanning ◽  
Structural Changes ◽  
Fire Regime ◽  
Spatial Scales ◽  
Landscape Management ◽  
Carbon Accounting ◽  
Optical Data ◽  
Burn Severity ◽  
Sentinel 2

The ability to map burn severity and to understand how it varies as a function of time of year and return frequency is an important tool for landscape management and carbon accounting in tropical savannas. Different indices based on optical satellite imagery are typically used for mapping fire scars and for estimating burn severity. However, cloud cover is a major limitation for analyses using optical data over tropical landscapes. To address this pitfall, we explored the suitability of C-band Synthetic Aperture Radar (SAR) data for detecting vegetation response to fire, using experimental fires in northern Australia. Pre- and post-fire results from Sentinel-1 C-band backscatter intensity data were compared to those of optical satellite imagery and were corroborated against structural changes on the ground that we documented through terrestrial laser scanning (TLS). Sentinel-1 C-band backscatter (VH) proved sensitive to the structural changes imparted by fire and was correlated with the Normalised Burn Ratio (NBR) derived from Sentinel-2 optical data. Our results suggest that C-band SAR holds potential to inform the mapping of burn severity in savannas, but further research is required over larger spatial scales and across a broader spectrum of fire regime conditions before automated products can be developed. Combining both Sentinel-1 SAR and Sentinel-2 multi-spectral data will likely yield the best results for mapping burn severity under a range of weather conditions.

Structural Changes in Rubber Caused by the Action of Molecular Oxygen. V. Destructive Solution of Vulcanized Synthetic Rubbers

1953 ◽  
Vol 26 (4) ◽  
pp. 787-797
Author(s):  
Z. Tarasova ◽  
B. Dogadkin
Keyword(s):  
Natural Rubber ◽  
Molecular Oxygen ◽  
Structural Changes ◽  
Axial Ratio ◽  
Colloid Solution ◽  
Butadiene Rubber ◽  
Rate Of Absorption ◽  
The Mean ◽  
Kinetics Of ◽  
Butadiene Styrene

Abstract 1. Vulcanized synthetic rubbers, when heated in a hydrocarbon medium containing molecular oxygen, dissolve completely. The kinetics of destructive solution of vulcanized synthetic rubbers follows the pattern established for the destructive solution of vulcanized natural rubber. 2. The rate of destructive solution of a vulcanizate depends on the molecular structure of the rubber. Rubbers are classified in the following order according to the increase of rate of solution of their vulcanizates : Butyl rubber < sodium-butadiene rubber < butadiene-styrene rubber < polychloroprene < natural rubber. The apparent energy of activation of natural rubber is 19 kcal. per mole, for sodium-butadiene rubber 31.2 kcal. per mole, and for butadiene-styrene rubber 27.1 kcal. per mole. 3. The rate of destructive solution of vulcanized butadiene rubbers depends linearly on the extent of 1,4-structure in the rubber molecule. 4. The mechanical properties of vulcanizates do not appreciably influence the rate of their destructive solution. The type of accelerator used, however, is of essential importance; in fact, its influence corresponds to its influence on the rate of absorption of oxygen. 5. The presence of water slows down the dissolution of vulcanizates of natural and sodium-butadiene rubbers, since it retards their absorption of oxygen. 6. The rate of destructive solution of a vulcanizate in various solvents depends linearly on the coefficient of absorption of oxygen in the solvents. 7. The viscosity of a solution of decomposed vulcanized sodium-butadiene rubber depends linearly on the concentration up to 50 per cent. 8. The mean specific molecular weight, measured cryoscopically, of sodium-butadiene rubber was 2400– 3600, and the osmotic weight, 16,000. The axial ratio of the particles was 1:15. 9. The hypothesis is advanced that solutions of decomposed vulcanizates constitute a special type of colloid solution.

Ultrafast Laser Induced Structural Modification of Fused Silica—Part I: Feature Formation Mechanisms

2010 ◽  
Vol 132 (6) ◽  
Author(s):  
Siniša Vukelić ◽  
Panjawat Kongsuwan ◽  
Y. Lawrence Yao
Keyword(s):  
Femtosecond Laser ◽  
Material Properties ◽  
Structural Changes ◽  
Three Dimensional ◽  
Laser Pulses ◽  
Femtosecond Laser Pulses ◽  
Fused Silica ◽  
Optical Data ◽  
Formation Mechanisms ◽  
Force Microscopy

Nonlinear absorption of femtosecond-laser pulses enables the induction of structural changes in the interior of bulk transparent materials without affecting their surface. This property can be exploited for transmission welding of transparent dielectrics, three dimensional optical data storages, and waveguides. In the present study, femtosecond-laser pulses were tightly focused within the interior of bulk fused silica specimen. Localized plasma was formed, initiating rearrangement of the network structure. Features were generated through employment of single pulses as well as pulse trains using various processing conditions. The change in material properties were studied through employment of differential interference contrast optical microscopy and atomic force microscopy. The morphology of the altered material as well as the nature of the physical mechanisms (thermal, explosive plasma expansion, or in-between) responsible for the alteration of material properties as a function of process parameters is discussed.

Delignification Mechanism during High-Boiling Solvent Pulping Part 3. Structural Changes in Lignin Analyzed by 13C-NMR Spectroscopy

Holzforschung ◽  
2003 ◽  
Vol 57 (6) ◽  
pp. 602-610 ◽  
Author(s):  
T. Kishimoto ◽  
A. Ueki ◽  
Y. Sano
Keyword(s):  
Structural Changes ◽  
Black Liquor ◽  
Average Molecular Weight ◽  
Acid Catalyst ◽  
Gel Permeation Chromatography ◽  
13C Nmr Spectroscopy ◽  
Hydroxyl Groups ◽  
Nmr Study ◽  
High Boiling Solvent ◽  
C Nmr

Summary Milled wood lignin as well as wood meal from todo fir (Abies sachalinensis MAST) was treated with 70% aqueous 1,4-butanediol solution at 220°C without acid catalyst in order to elucidate the delignification mechanism during high-boiling solvent (HBS) pulping. HBS lignin was recovered from black liquor by precipitation, and was subjected to gel permeation chromatography and quantitative 13C-NMR study. The average molecular weight of MWL decreased. The content of phenolic hydroxyl groups in MWL increased from 0.28 to 0.68/OMe. The decrease in the content of β-O-4 substructures was evident, which may be attributed to the homolytic cleavage of phenolic β-aryl ethers. The changes in the content of β-5 and β-β substructures were rather small. The benzyl ether formation of β-O-4 structures with 1,4-butanediol was also confirmed by 13C-NMR. However, the signals corresponding to Hibbert's ketones were not observed, which suggests that acidolysis was not an important degradation pathway during HBS pulping.

Effects of Fenton oxidation on structural changes of lignin from steam-exploded poplar

BioResources ◽  
2020 ◽  
Vol 15 (3) ◽  
pp. 6181-6191
Author(s):  
Cheng Pan ◽  
Lan Yao ◽  
Haitao Yang ◽  
Lanfeng Hui ◽  
Zhong Liu
Keyword(s):  
Quantum Coherence ◽  
Structural Changes ◽  
Oxidation Process ◽  
Average Molecular Weight ◽  
Fenton Oxidation ◽  
Heteronuclear Single Quantum Coherence ◽  
Structural Units ◽  
Weight Average Molecular Weight ◽  
Fenton Oxidation Process ◽  
Total Lignin

Pretreatment of steam-exploded poplar by Fenton oxidation was used to effectively biodegrade lignin. The structure of lignin samples (LS from steam-exploded poplar and LSF from samples further treated by Fenton oxidation) obtained by enzymatic hydrolysis during pretreatment were characterized and compared. The results showed that the demethoxy reaction occurred in the process of Fenton oxidation. GPC results indicated that the weight average molecular weight (Mw) of LSF did not change significantly, indicating that that there was no significant condensation during Fenton oxidation pretreatment. Heteronuclear single quantum coherence nuclear magnetic resonance (HSQC NMR) results suggested that the proportion of the three-unit basic structural units of poplar (H, G, and S) were significantly changed during Fenton oxidation process, and more lignin S units were removed than lignin G units. The content of β-O-4 linkages was lower in LSF (74.0%, as a fraction of β-O-4 + β-5 + β-β) than in LS (78.2%), which indicated that β-O-4 linkages were destroyed to a certain extent during Fenton oxidation process, and the content of total lignin interunit linkages including β-O-4, β−β, and β-5 linkages over total lignin aromatic subunits (Ar%) in LSF was higher, reaching 49.9%.

scholarly journals NATIVE AND REGENERATED BOVINE ALBUMIN

1943 ◽  
Vol 26 (6) ◽  
pp. 513-531 ◽  
Author(s):  
Frank W. Putnam ◽  
John O. Erickson ◽  
Elliot Volkin ◽  
Hans Neurath
Keyword(s):  
Guanidine Hydrochloride ◽  
Average Molecular Weight ◽  
Free Fraction ◽  
Molecular Size ◽  
Axial Ratio ◽  
Molecular Shape ◽  
Carbohydrate Content ◽  
Isoelectric Precipitation ◽  
Denatured State ◽  
Bovine Albumin

1. Whole bovine albumin, homogeneous in diffusion and sedimentation, and essentially homogeneous in electrophoresis, has been prepared by a method involving ammonium sulfate precipitation of the globulins in the cold and of the albumin at room temperature, isoelectric precipitation of the euglobulins, and reprecipitation of the albumin. 2. The product has been characterized by chemical analysis and by viscosity, diffusion, sedimentation, and electrophoresis measurements. The carbohydrate content is 0.38 per cent, the nitrogen content, 15.2 per cent. The molecular shape approximates that of a prolate ellipsoid with an axial ratio of 3.1, assuming 33 per cent hydration; the average molecular weight is 65,000. 3. Bovine albumin is readily denatured by concentrated solutions of urea or guanidine hydrochloride, gross changes in molecular shape resulting. 4. Regeneration of bovine albumin denatured in solutions of 8 M urea or guanidine hydrochloride yields a material closely resembling the native in carbohydrate content, in molecular size and shape, and in electrophoretic properties. However, the regenerated protein differs from the native in susceptibility to tryptic digestion, and, in this respect, appears to be in a denatured state. 5. In 8 M solutions of guanidine hydrochloride a limiting yield of regenerated albumin equivalent to 95 per cent of the original protein is approached. 6. Bovine crystalbumin, a crystalline carbohydrate-free fraction of the whole albumin, appears to be more susceptible to denaturation than whole bovine albumin.

Small-Angle X-Ray Scattering on Malate Synthase from Baker's Yeast Considerations on the Effects of Bound Ligands

1978 ◽  
Vol 33 (7-8) ◽  
pp. 504-510 ◽  
Author(s):  
Peter Zipper ◽  
Helmut Durchschlag
Keyword(s):  
Binding Sites ◽  
Structural Changes ◽  
Radial Distance ◽  
Axial Ratio ◽  
Malate Synthase ◽  
Radius Of Gyration ◽  
Molecular Parameters ◽  
X Ray ◽  
Enzyme Substrate ◽  
X Ray Scattering

Binding of the substrates to the anisometric enzyme causes slight changes of some molecular parameters (Zipper and Durchschlag, Eur. J. Biochem., 1978). Estimations based on several plausible assumptions allow a separation of the experimentally observed effects into effects caused by the substrates or by the enzyme in the enzyme-substrate complexes or by binding of buffer molecules. The results show that the observed changes of molecular parameters are primarily due to structural changes in the enzyme molecule. From the changes in the radius of gyration upon substrate binding, the binding sites of the substrates may be localized to be at a radial distance of 5.3 nm from the centre of the enzyme particle. Binding of one or both of the substrates induces different structural changes of the enzyme particle. On formation of the [enzyme·acetyl-CoA], [enzyme·glyoxylate], or [enzyme·pyruvate] complexes, an increase of the short axis by 4.5 + 1% occurs, while the formation of the [enzyme·acetyl-CoA·pyruvate] complex does not change this axis significantly. A t the same time, binding of the substrates leads to a decrease of the long axes of the enzyme particle by 2.0 ± 0.2%, independent on the kind of the complex formed. These changes of the axes correspond to an increase of the axial ratio by 6.7 ± 1% on formation of the [enzyme·acetyl-CoA], [enzyme·glyoxylate], or [enzyme-pyruvate] complexes and by 2.7.% on formation of the [enzyme-acetyl·CoA·pyruvate] complex, i. e. in all cases to a decrease of anisometry of the enzyme particle.

Structural Modification of Amorphous Fused Silica Under Femtosecond Laser Irradiation

2008 ◽  
Author(s):  
S. Vukelic ◽  
B. Gao ◽  
S. Ryu ◽  
Y. L. Yao
Keyword(s):  
Femtosecond Laser ◽  
Material Properties ◽  
Structural Changes ◽  
Three Dimensional ◽  
Laser Pulses ◽  
Femtosecond Laser Pulses ◽  
Fused Silica ◽  
Femtosecond Laser Irradiation ◽  
Optical Data ◽  
Linear Absorption

Non-linear absorption of femtosecond laser pulses enables the induction of structural changes in the interior of bulk transparent materials without affecting their surface. This property can be exploited for the transmission welding of transparent dielectrics, three dimensional optical data storages and waveguides. In the present study, femtosecond laser pulses were tightly focused within the interior of bulk fused silica specimen. Localized plasma was formed, initiating rearrangement of the network structure. The change in material properties were studied through employment of spatially resolved Raman spectroscopy, atomic force microscopy and optical microscopy. The nature of the physical mechanisms responsible for the alteration of material properties as a function of process parameters is discussed.

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