The Role of Free Radicals in Low Temperature Vulcanization of Butadiene Rubber

1960 ◽  
Vol 33 (1) ◽  
pp. 199-207
Author(s):  
B. A. Dogadkin ◽  
E. N. Belyaeva
Keyword(s):  
Hydrogen Sulfide ◽  
Low Temperature ◽  
Benzoyl Peroxide ◽  
Spectroscopic Analysis ◽  
Elementary Sulfur ◽  
Butadiene Rubber ◽  
Radical Chain ◽  
Considerable Loss ◽  
Chain Interaction

Abstract 1. Elementary sulfur, liberated in the nascent state at room temperature in the reactions of MBTS with H2S, of benzoyl peroxide with H2S and SO2 with H2S, does not bring about vulcanization of butadiene rubber. In the case of the system MBTS/H2S we observe combination of sulfur in amounts 1.2 to 1.6% to a small portion of the rubber, which does not lead to structurization. The main part of the rubber (about 90% by weight) does not, according to spectroscopic analysis, alter. The combination of sulfur with rubber observed in this case takes place, apparently, according to an ionic mechanism. 2. Low-temperature vulcanization (structurization) of rubber by the system MBTS/H2S becomes apparent with prior irradiation of solutions of rubber containing disulfide with diffuse or ultraviolet light. The rate of structurization depends upon the duration of irradiation and is governed by the interaction with the H2S of the polymeric rubber radicals which are formed as a result of the dehydrogenation of the rubber by the benzothiazolyl radicals which are formed in the photodissociation of the disulfide. 3. Structurization of rubber by the system benzoyl peroxide/hydrogen sulfide is observed in the presence of an amine, in particular PBNA, necessary for the formation of free benzoate radicals as a result of the reaction of the peroxide with the amine. The peroxide in the present case acts similarly to the benzothiazolyl radicals in the case of the system MBTS/H2S. 4. Peachey type low-temperature vulcanization (SO2/H2S) proceeds in the presence of the peroxides of the rubber itself. Prior heating of the solutions of rubber upsets structurization. 5. In the vulcanization of rubber by the systems MBTS/H2S and benzoyl peroxide/hydrogen sulfide we observe combination of sulfur with the rubber in amounts of 0.6 to 0.7% and a considerable loss of double bonds, reaching 60% for 1:4 type bonds and 75% for 1:2 type bonds. 6. Radical chain interaction schemes are put forward for the processes of low-temperature structurization (vulcanization) of rubber under the action of the systems MBTS/H2S, benzoyl peroxide/hydrogen sulfide and SO2/H2S. 7. The reaction of benzoyl peroxide with PBNA is studied. A new compound, O-benzoyl-N-phenyl-N-2-naphthylhydroxylamine, is obtained, which is a powerful inhibitor of rubber oxidation.

The Mechanism of Vulcanization and the Action of Accelerators

1959 ◽  
Vol 32 (1) ◽  
pp. 174-183
Author(s):  
B. A. Dogadkin
Keyword(s):  
Hydrogen Sulfide ◽  
Spatial Structure ◽  
Room Temperature ◽  
Nitrogen Atmosphere ◽  
Elementary Sulfur ◽  
Butadiene Rubber ◽  
Complex Character ◽  
Hydrocarbon Medium ◽  
Kinetics Of ◽  
Radical Character

Abstract Vulcanization of rubber is due to the formation of chemical interlinks between molecular chains of rubber. A number of investigators maintain that formation of these bonds is due to reactions of radical character. In the present paper data are presented which were obtained during the study of reactions in which elementary sulfur is liberated at room temperature. As a prototype of such reaction is the interaction of hydrogen sulfide and SO2 which in rubber causes the socalled Peachey vulcanization. The usual views on the mechanism of this process are that the activity of sulfur liberated in statu nascendi is high enough to enable it to react with rubber and to create the spatial structure of the vulcanizate. However, this is an error. We have shown that pure sodium-butadiene rubber, heated to 80° in nitrogen atmosphere, does not vulcanize by the Peachey procedure, e.g., it does not become insoluble and its modulus of elasticity does not reach finite values. Consequently, the reaction causing the vulcanizing effect has a more complex character. To elucidate the mechanism of vulcanization we have studied the reaction of benzothiazolyl disulfide (MBTS) with hydrogen sulfide. In a hydrocarbon medium these compounds react at room temperature forming quantitatively elementary sulfur and mercaptobenzothiazole (MBT). Kinetics of this reaction are shown in Figure 1. If this reaction is carried out in a 10% solution of sodium-butadiene rubber, then the sulfur adds to the rubber, but vulcanization as characterized by formation of a spatial structure does not occur. The rubber solution is not gelatinized. An analogous phenomenon is observed during interaction of benzoyl peroxide with hydrogen sulfide. Sulfur liberated in this reaction also does not cause crosslinking (vulcanization of rubber).

Elucidation of block boundaries as the dissolution channels in hydrated cement

1978 ◽  
Vol 36 (1) ◽  
pp. 484-485
Author(s):  
N.V. Belov ◽  
U.I. Papiashwili ◽  
B.E. Yudovich
Keyword(s):  
Liquid Phase ◽  
Grain Boundaries ◽  
Benzoyl Peroxide ◽  
Phase Contrast ◽  
Active Role ◽  
Point Of View ◽  
Hardened Cement ◽  
Hydrated Cement ◽  
Hardened Cement Paste

It has been almost universally adopted that dissolution of solids proceeds with development of uniform, continuous frontiers of reaction.However this point of view is doubtful / 1 /. E.g. we have proved the active role of the block (grain) boundaries in the main phases of cement, these boundaries being the areas of hydrate phases' nucleation / 2 /. It has brought to the supposition that the dissolution frontier of cement particles in water is discrete. It seems also probable that the dissolution proceeds through the channels, which serve both for the liquid phase movement and for the drainage of the incongruant solution products. These channels can be appeared along the block boundaries.In order to demonsrate it, we have offered the method of phase-contrast impregnation of the hardened cement paste with the solution of methyl metacrylahe and benzoyl peroxide. The viscosity of this solution is equal to that of water.

The Role of Reactive Oxygen Species, Kinases, Hydrogen Sulfide, and Nitric Oxide in the Regulation of Autophagy and Their Impact on Ischemia and Reperfusion Injury in the Heart

2020 ◽  
Vol 16 ◽  
Author(s):  
Andrey Krylatov ◽  
Leonid Maslov ◽  
Sergey Y. Tsibulnikov ◽  
Nikita Voronkov ◽  
Alla Boshchenko ◽  
...  
Keyword(s):  
Nitric Oxide ◽  
Reactive Oxygen Species ◽  
Hydrogen Sulfide ◽  
Ischemia Reperfusion ◽  
Reactive Oxygen ◽  
Ischemia And Reperfusion ◽  
Oxygen Species ◽  
Ischemia And Reperfusion Injury ◽  
Adaptive Process

: There is considerable evidence in the heart that autophagy in cardiomyocytes is activated by hypoxia/reoxygenation (H/R) or in hearts by ischemia/reperfusion (I/R). Depending upon the experimental model and duration of ischemia, increases in autophagy in this setting maybe beneficial (cardioprotective) or deleterious (exacerbate I/R injury). Aside from the conundrum as to whether or not autophagy is an adaptive process, it is clearly regulated by a number of diverse molecules including reactive oxygen species (ROS), various kinases, hydrogen sulfide (H2S) and nitric oxide (NO). The purpose this review is to address briefly the controversy regarding the role of autophagy in this setting and to examine a variety of disparate molecules that are involved in its regulation.

Taurine treatment reverses protein malnutrition-induced endothelial dysfunction of the pancreatic vasculature: the role of hydrogen sulfide

Metabolism ◽  
2021 ◽  
pp. 154701
Author(s):  
Daniele M. Guizoni ◽  
Israelle N. Freitas ◽  
Jamaira A. Victorio ◽  
Isabela R. Possebom ◽  
Thiago R. Araujo ◽  
...  
Keyword(s):  
Hydrogen Sulfide ◽  
Endothelial Dysfunction ◽  
Protein Malnutrition ◽  
Taurine Treatment

scholarly journals Dissecting the Roles of Cuticular Wax in Plant Resistance to Shoot Dehydration and Low-Temperature Stress in Arabidopsis

2021 ◽  
Vol 22 (4) ◽  
pp. 1554
Author(s):  
Tawhidur Rahman ◽  
Mingxuan Shao ◽  
Shankar Pahari ◽  
Prakash Venglat ◽  
Raju Soolanayakanahally ◽  
...  
Keyword(s):  
Fatty Acids ◽  
Low Temperature ◽  
Cold Acclimation ◽  
Water Loss ◽  
Cuticular Wax ◽  
Dehydration Stress ◽  
Wax Deposition ◽  
Cuticular Waxes ◽  
Gas Chromatography Mass Spectroscopy

Cuticular waxes are a mixture of hydrophobic very-long-chain fatty acids and their derivatives accumulated in the plant cuticle. Most studies define the role of cuticular wax largely based on reducing nonstomatal water loss. The present study investigated the role of cuticular wax in reducing both low-temperature and dehydration stress in plants using Arabidopsis thaliana mutants and transgenic genotypes altered in the formation of cuticular wax. cer3-6, a known Arabidopsis wax-deficient mutant (with distinct reduction in aldehydes, n-alkanes, secondary n-alcohols, and ketones compared to wild type (WT)), was most sensitive to water loss, while dewax, a known wax overproducer (greater alkanes and ketones compared to WT), was more resistant to dehydration compared to WT. Furthermore, cold-acclimated cer3-6 froze at warmer temperatures, while cold-acclimated dewax displayed freezing exotherms at colder temperatures compared to WT. Gas Chromatography-Mass Spectroscopy (GC-MS) analysis identified a characteristic decrease in the accumulation of certain waxes (e.g., alkanes, alcohols) in Arabidopsis cuticles under cold acclimation, which was additionally reduced in cer3-6. Conversely, the dewax mutant showed a greater ability to accumulate waxes under cold acclimation. Fourier Transform Infrared Spectroscopy (FTIR) also supported observations in cuticular wax deposition under cold acclimation. Our data indicate cuticular alkane waxes along with alcohols and fatty acids can facilitate avoidance of both ice formation and leaf water loss under dehydration stress and are promising genetic targets of interest.

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