Nature of Chemisorptive Mechanisms in Rubber Reinforcement

1957 ◽  
Vol 30 (2) ◽  
pp. 596-609 ◽  
Author(s):  
V. A. Garten ◽  
G. K. Sutherland
Keyword(s):  
Free Radicals ◽  
Free Radical ◽  
Active Sites ◽  
Rubber Matrix ◽  
Excess Oxygen ◽  
Radical Intermediates ◽  
Chemical Bond Formation ◽  
Crosslinked Networks ◽  
Carbon Gel ◽  
State Of Research

Abstract The present state of research in the field of reinforcing rubber fillers is reviewed and it is pointed out that although a strong school of thought still maintains that the strength of bonding depends on particle size, there are many observations indicating the presence of reactive sites and suggesting the possibility of strong bonds of a chemical nature between filler and rubber matrix. The phenomenon of carbon-gel formation as foremost among these, is discussed as lending fresh support to the idea of chemical bond formation. This effect, known to be most pronounced in the presence of an unsaturated matrix is correlated with the mechanism of vulcanization as proceeding via free radical intermediates. It is suggested that the formation of chemical bonds between pigment and rubber constitutes an integral part of the chemical crosslink formation commenced on the rubber mill and completed by vulcanization. This hypothesis is corroborated by results obtained during studies on the reactivity of pigment surfaces towards simple inorganic and organic free radicals. It is shown that active pigments react with free radicals with the formation of nonionic bonds. Hydrophilic blacks have been prepared by treatment with persulfate. Similarly, electrochemically produced stearate free radicals have been reacted with the surface to form hydrophobic carbons. The “benzidine ”blue free radical, being the monooxidation product of benzidine, reacted easily with less active pigments and thus provided a useful measure of activity. From the experiments with free radicals, the number of active sites for various fillers has been calculated and shown to cover a range of 0.01–3.1 per 100 sq. A˚. Multifunctional polystyrene radicals, obtained in the presence of excess oxygen, yielded crosslinked networks with carbon blacks which resisted solvent extraction. These are considered to be complete analogues to carbon gel. The statistical mechanics of the rubber network has been developed to include crosslink formation as caused by rubber-filler interaction. It is shown that the mechanical properties of a rubber compound that are controlled solely by the network structure are directly proportional to σ/r, the ratio between the number of active sites per unit area and the particle radius. Abrasion does not appear to be only a mechanical phenomenon.

Mechanochemical Reactions Leading to Reinforcement in Rubbers

1960 ◽  
Vol 33 (4) ◽  
pp. 929-939
Author(s):  
R. J. Ceresa
Keyword(s):  
Free Radicals ◽  
Free Radical ◽  
Covalent Bond ◽  
Vinyl Monomers ◽  
Research Association ◽  
Block Copolymerization ◽  
Wide Range ◽  
Carbon Gel ◽  
Internal Mixer ◽  
Mechanochemical Reactions

Abstract The development of the single rotor internal mixer (at the British Rubber Producers' Research Association) has facilitated the research into mechanochemical reactions of a wide range of high polymers. The term “mechanochemical” has been applied to reactions such as mastication, the mechanism of which involves the primary step of mechanical scission of a polymer chain into polymeric free radicals at a carbon to carbon or other covalent bond. The processes which have been studied previously include the cold mastication of rubberlike polymers, the formation of carbon gel, the interpolymerization of two elastomers during blending, and block copolymerization by the cold mastication of polymers plasticized by vinyl monomers. The evidence for the polymeric free radical nature of these reactions has recently been reviewed.

Glutathione Peroxidase-Like Activity of Simple Selenium Compounds. Peroxides and the Heterocyclic N-Oxide Resazurin Acting as O-Atom Donors

1995 ◽  
Vol 50 (3-4) ◽  
pp. 209-219 ◽  
Author(s):  
Walter A. Prtitz
Keyword(s):  
Free Radicals ◽  
Free Radical ◽  
Glutathione Peroxidase ◽  
Crystal Violet ◽  
The Other ◽  
Atom Transfer ◽  
Selenium Compounds ◽  
Radical Intermediates ◽  
Leuco Crystal Violet ◽  
Acid Pathway

Selenite and selenocystamine [(CyaSe)2] efficiently activate the decomposition of H2O2 y GSH and by other thiols, as demonstrated using a leuco crystal violet POD-based H2O2 assay which is applicable (unlike other assays) also in presence of thiols. The GPx-like activities were estimated to be 3.6 and 2.7 μmol H2O2/min per μmol SeO32- and (CyaSe)2, respectively. Both selenium compounds also activate reduction of the heterocyclic N-oxide resazurin (RN→O) to resorufin (RN) by GSH; H2O2 competes with reduction of this dye. GSSeH and CyaSeH, formed by interaction of GSH with SeO32- and (CyaSe)2, respectively, are likely to be the active reductants. CyaSeH, generated γ-radiolytically from (CyaSe)2, exhibits an absorption peak at 243 nm and is removed by H2O2 with a rate constant of 9.7x102 ᴍ-1 s-1, and slightly slower by hydroperoxides. We have no evidence for one-electron interactions between GSSeH or CyaSeH and H2O2, with formation of free radical intermediates, as previously proposed in the case of selenium-activated reduction of cytochrome c by GSH (Levander et al., Biochemistry 23, 4591-4595 (1973)). Our results can be explained by O-atom transfer from the substrate to the active selenol group. RSeH + H2O2 (RN→O)→RSeOH + H2O (RN), and recycling of RSeOH to RSeH (+ H2O) by GSH, analogous to the selenenic acid pathway of GPx. The substrate specificity appears to be different, however, in that GPx is unable to catalyse RN→O reduction, and GSSeH hardly catalyses the decomposition of cumene- or t-butyl-hydroperoxide; CyaSeH, on the other hand, is active also with the hydroperoxides. RN→O is reduced to RN also by certain oxidizing free radicals, e.g. by the thiyl CyaS·; O -atom transfer may in this case lead to the generation of reactive oxyl radicals.

Free Radicals Generated in Photocatalytic Oxidation of Some Amines and Diamines

1996 ◽  
Vol 1 (2) ◽  
Author(s):  
Ciping Chen ◽  
Daohui Lu ◽  
Guangzhi Xu
Keyword(s):  
Free Radicals ◽  
Free Radical ◽  
Photocatalytic Oxidation ◽  
Spin Trapping ◽  
Experimental Results ◽  
Epr Spectra ◽  
Radical Species ◽  
Radical Intermediates ◽  
Radical Adduct ◽  
Spin Trapping Technique

AbstractFree radical intermediates produced during photocatalytic oxidation of some typical amines and diamines were investigated by a spin trapping technique. The EPR spectra of N-centered radical adduct and Ccentered radical adduct were observed. Experimental results disclose that these radicals are participants in the initial steps of photodegradation of these compounds. A mechanism which is consistent with the observation of these radical species is discussed.

Free-Radical Activity of Reinforcing Rubber Fillers

1955 ◽  
Vol 28 (2) ◽  
pp. 596-597
Author(s):  
V. A. Garten
Keyword(s):  
Free Radical ◽  
Three Dimensional ◽  
Rubber Matrix ◽  
Radical Mechanism ◽  
Radical Intermediates ◽  
Free Radical Mechanism ◽  
Bound Rubber ◽  
Methylene Groups ◽  
Free Radical Activity ◽  
Vulcanization Process

Abstract In our studies of the mechanism of rubber reinforcement, we were led to assume that primary valency bonds are likely to form between an “active” filler and the rubber-matrix via free-radical intermediates. The hypothesis was based on the following considerations. (1) Although a strong school of thought still maintains that the strength of bonding depends mainly on van der Waals forces, and therefore on particle size, a number of individual observations suggest the presence of “reactive sites” and formation of strong bonds of a chemical nature between filler and rubber. Foremost among these is the phenomenon that the incorporation of active pigments such as carbon blacks, silicas and the like into rubber results in the insolubilization of a part of the rubber. This part is conveniently called “bound rubber” or “carbon-gel”. (2) Farmer and his school have shown that the vulcanization process is based on a free-radical mechanism, wherein a number of the rubber double-bonds and α-methylene groups, sulfur and accelerator are involved, resulting in the formation of three-dimensional giant networks. The mechanism of mastication is also known to consist of the production of free radicals in the presence of suitable ‘radical acceptors’, such as oxygen. (3) There are some common features in both reinforcement and vulcanization, such as crystallization effects. (4) Little or no reinforcing action of otherwise active pigments is observed with saturated polymers, for example, polyisobutylene.

scholarly journals Anti-Oxidant effects of Swarnamakshika Bhasma : A Experimental Study

2020 ◽  
Vol 5 (04) ◽  
pp. 92-101
Author(s):  
Shrikanth AS ◽  
P. G. Jadar
Keyword(s):  
Free Radicals ◽  
Free Radical ◽  
Food Habits ◽  
Cellular Level ◽  
Oxidation Reactions ◽  
Chain Reactions ◽  
Herbal Preparations ◽  
Radical Intermediates ◽  
Immune System Dysfunction ◽  
Anti Oxidant

Shodhana of Swarnamakshika carried out by Bharjana in Eranda Tila. Marana of Swarnamakshika by finely powdered Shudda Swarnamakshika was taken in a Khalvayantra. Then equal quantity of Shudda Gandhaka was added and triturated together till they become homogenous. To this mixture 100ml of Jambhira Rasa was added triturated well till it becomes semisolid consistency. The paste were made into shape of Chakrikas weighing 25gm and 8cm uniformly and kept for drying. Subjecting into 5 required number of Varahaputas. The present day lifestyle and food habits have increased the production of free radicals. These cytotoxic free radicals not only raise the oxidative stress but also play an important role in the immune-system dysfunction due to which the mankind is prone to various major ailments and it is now proved that diseases like Prameha, Pandu, Vatavyadhi etc. are free radical mediated ones. To tackle these free radicals our body needs antioxidants. An antioxidant is a molecule which is capable of inhibiting the oxidation of other molecules. Oxidation reactions can produce free radicals which in turn start chain reactions that damage cells. Antioxidants terminate these chain reactions by removing free radical intermediates and inhibit other oxidation reactions. Many herbals drugs and compound herbal preparations have been screened for their antioxidant and immuno-modulatory properties but still there is a need for effective antioxidants. This dearth and also the fact that Swarnamakshika is being used in treating many of the free radical mediated diseases prompted us to take the present study which aims to validate the Antioxident effect of Swarnamakshika Bhasma scientifically and explain its probable mode of action at the cellular level.

The involvement of oxygen-derived free radicals in plant–pathogen interactions

1994 ◽  
Vol 102 ◽  
pp. 479-493
Author(s):  
B. A. Goodman
Keyword(s):  
Free Radicals ◽  
Free Radical ◽  
Atmospheric Oxygen ◽  
Oxygen Species ◽  
Defence Mechanisms ◽  
Paramagnetic Resonance ◽  
Radical Intermediates ◽  
Oxygen Derived Free Radicals ◽  
Plant Pathogen Interactions ◽  
Electron Paramagnetic

SynopsisPlants have evolved a multiplicity of defence mechanisms against pathogen attack. Their modes of action may be to (i) kill the pathogen directly, (ii) block the action of enzymes required for infection, or (iii) erect barriers to pathogen growth. Some of these reactions proceed via free radical intermediates and make use of either atmospheric oxygen or reactive oxygen species. This paper reviews the various types of reaction involving oxygen-derived free radicals that are initiated in plant tissue when it is invaded by pathogenic organisms. Both the production of free radicals by plants in defensive processes and the utilisation of free radicals by pathogens in offensive reactions are considered and particular attention is given to the use of electron paramagnetic resonance (EPR) spectroscopy for the direct observation of such free radical reactions.

Study of antioxidant potential in leaves, stems, nuts of Juglans regia L.

2012 ◽  
Vol 1 (10) ◽  
pp. 79 ◽  
Author(s):  
G. Raja* ◽  
Ivvala Anand Shaker ◽  
Inampudi Sailaja ◽  
R. Swaminathan ◽  
S. Saleem Basha ◽  
...  
Keyword(s):  
Free Radicals ◽  
Free Radical ◽  
Antioxidant Activities ◽  
Radical Scavenging Activity ◽  
Juglans Regia ◽  
Radical Scavenging ◽  
Antioxidant Compounds ◽  
Free Radical Damage ◽  
Radical Damage

Natural antioxidants can protect the human body from free radicals and retard the progress of many chronic diseases as well as lipid oxidative rancidity in foods. The role of antioxidants has protected effect against free radical damage that may cause many diseases including cancer. Primary sources of naturally occurring antioxidants are known as whole grains, fruits, and vegetables. Several studies suggest that regular consumption of nuts, mostly walnuts, may have beneficial effects against oxidative stress mediated diseases such as cardiovascular disease and cancer. The role of antioxidants has attracted much interest with respect to their protective effect against free radical damage that may cause many diseases including cancer. Juglans regia L. (walnut) contains antioxidant compounds, which are thought to contribute to their biological properties. Polyphenols, flavonoids and flavonols concentrations and antioxidant activity of Leaves, Stems and Nuts extract of Juglans regia L. as evaluated using DPPH, ABTS, Nitric acid, hydroxyl and superoxide radical scavenging activity, lipid peroxidation and total oxidation activity were determined. The antioxidant activities of Leaves, Stems and Nuts extract of Juglans regia L. were concentration dependent in different experimental models and it was observed that free radicals were scavenged by the test compounds in all the models.

THE KINETICS OF THE THERMAL REACTIONS OF ETHYLENE OXIDE

1963 ◽  
Vol 41 (12) ◽  
pp. 2956-2961 ◽  
Author(s):  
M. Lynne Neufeld ◽  
Arthur T. Blades
Keyword(s):  
Free Radicals ◽  
Free Radical ◽  
Ethylene Oxide ◽  
Thermal Reactions ◽  
Kinetics Of

The thermal reactions of ethylene oxide in the presence of an excess of propylene have been studied as a function of pressure and it has been found that there are two sets of products, acetaldehyde and free radicals, presumably methyl and formyl. These products are believed to arise from an excited acetaldehyde intermediate. Some evidence has been obtained for the occurrence of a surface-catalyzed rearrangement to acetaldehyde but the free radical products are uninfluenced by surface.

scholarly journals Mechanistic Insight into Antimicrobial and Antioxidant Potential of Jasminum Species: A Herbal Approach for Disease Management

Plants ◽  
2021 ◽  
Vol 10 (6) ◽  
pp. 1089
Author(s):  
Acharya Balkrishna ◽  
Akansha Rohela ◽  
Abhishek Kumar ◽  
Ashwani Kumar ◽  
Vedpriya Arya ◽  
...  
Keyword(s):  
Oxidative Stress ◽  
Drug Resistance ◽  
Free Radicals ◽  
Free Radical ◽  
Microbial Pathogens ◽  
Free Radical Scavengers ◽  
Bioactive Constituents ◽  
Global Issues ◽  
Iridoid Glucosides ◽  
Insight Into

Drug resistance among microbial pathogens and oxidative stress caused by reactive oxygen species are two of the most challenging global issues. Firstly, drug-resistant pathogens cause several fatalities every year. Secondly aging and a variety of diseases, such as cardiovascular disease and cancer, are associated with free radical generated oxidative stress. The treatments currently available are limited, ineffective, or less efficient, so there is an immediate need to tackle these issues by looking for new therapies to resolve resistance and neutralize the harmful effects of free radicals. In the 21st century, the best way to save humans from them could be by using plants as well as their bioactive constituents. In this specific context, Jasminum is a major plant genus that is used in the Ayurvedic system of medicine to treat a variety of ailments. The information in this review was gathered from a variety of sources, including books, websites, and databases such as Science Direct, PubMed, and Google Scholar. In this review, a total of 14 species of Jasminum have been found to be efficient and effective against a wide variety of microbial pathogens. In addition, 14 species were found to be active free radical scavengers. The review is also focused on the disorders related to oxidative stress, and it was concluded that Jasminum grandiflorum and J. sambac normalized various parameters that were elevated by free radical generation. Alkaloids, flavonoids (rutoside), terpenes, phenols, and iridoid glucosides are among the main phytoconstituents found in various Jasminum species. Furthermore, this review also provides insight into the mechanistic basis of drug resistance, the generation of free radicals, and the role of Jasminum plants in combating resistance and neutralizing free radicals.

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