2-t-Butylbenzothiazole Sulfenamide Accelerated Sulfur Vulcanization of Polyisoprene

1999 ◽  
Vol 72 (1) ◽  
pp. 65-73 ◽  
Author(s):  
M. H. S. Gradwell ◽  
M. J. van der Merwe
Keyword(s):  
Special Reference ◽  
Exchange Reaction ◽  
Differential Scanning Calorimeter ◽  
Reaction Mechanisms ◽  
Sulfur Vulcanization ◽  
Pendent Groups ◽  
Delayed Action

Abstract The mechanism of 2-t-butylbenzothiazole sulfenamide (TBBS) accelerated sulfur vulcanization of polyisoprene was investigated. Samples of compounded rubber were heated in a differential scanning calorimeter to preselected temperatures or degrees of vulcanization, the reaction stopped, and the products analyzed. TBBS polysulfides, formed from the reaction of TBBS with sulfur, react with the rubber chain to form benzothiazole pendent groups and free t-butylamine. The delayed action of TBBS accelerated sulfur vulcanization was shown to be due to an exchange reaction involving benzothiazole terminated pendent groups and TBBS. Crosslinking occurred very rapidly once the TBBS was depleted. Special reference was made to the role of the amine. Reaction mechanisms were proposed to account for the formation of products.

Activators in Accelerated Sulfur Vulcanization

2004 ◽  
Vol 77 (3) ◽  
pp. 512-541 ◽  
Author(s):  
Geert Heideman ◽  
Rabin N. Datta ◽  
Jacques W. M. Noordermeer ◽  
Ben van Baarle
Keyword(s):  
Reaction Mechanisms ◽  
Model Compound ◽  
Background Information ◽  
Zinc Compounds ◽  
Chemical Mechanisms ◽  
Sulfur Vulcanization ◽  
Multifunctional Additives ◽  
Vulcanization Process

Abstract This review provides relevant background information about the vulcanization process, as well as the chemistry of thiuram- and sulfenamide-accelerated sulfur vulcanization with emphasis on the role of activators, to lay a base for further research. It commences with an introduction of sulfur vulcanization and a summary of the reaction mechanisms as described in literature, followed by the role of activators, particularly ZnO. The various possibilities to reduce ZnO levels in rubber compounding, that have been proposed in literature, are reviewed. A totally different approach to reduce ZnO is described in the paragraphs about the various possible roles of multifunctional additives (MFA) in rubber vulcanization. Another paragraph is dedicated to the role of amines in rubber vulcanization, in order to provide some insight in the underlying chemical mechanisms of MFA systems. Furthermore, an overview of Model Compound Vulcanization (MCV) with respect to different models and activator/accelerator systems is given. In the last part of this review, the various functions of ZnO in rubber are summarized. It clearly reveals that the role of ZnO and zinc compounds is very complex and still deserves further clarification.

Coactivation of Delayed-Action Vulcanization. Part I. Polymeric, Nonmigratory Cure Coactivators for Accelerated Sulfur Vulcanization

1989 ◽  
Vol 62 (5) ◽  
pp. 957-972
Author(s):  
A. Y. Coran ◽  
F. Ignatz-Hoover ◽  
L. H. Davis
Keyword(s):  
Molecular Weight ◽  
Minimum Loss ◽  
Synthetic Rubber ◽  
Curing Characteristics ◽  
Sulfur Vulcanization ◽  
Delayed Action ◽  
Very High ◽  
Rubber Article

Abstract Rubbery vinylpyridine-butadiene copolymers, containing 20–65% by weight of vinylpyridine monomer units, are effective coactivators of vulcanization for TBBS-accelerated sulfur-vulcanized SBR. In addition to emulsion SBR, the new co-activator has been evaluated in copositions of solution SBR, BR, NR, and various blends. The co-activator is active in all of the compositions which contain butadiene-derived synthetic rubber. This includes blends such as SBR/BR, solution-SBR/BR, SBR/NR, BR/NR, SBR/BR/NR, etc. There is little or no activity in which NR is the only polymer. The most efficacious copolymers contain between 30 and 60% 2-vinylpyridine. The incorporation of such a copolymer into an unvulcanized butadiene-derived rubber mix can give a substantial increase in the rate of crosslink formation with only a minimum loss of scorch resistance. Since the polymeric coactivators are very high in molecular weight, it can be at least tentatively concluded that they will not migrate from one component stock to another in a built-up multi-stock rubber article, either before or during vulcanization. Since the curing characteristics of a vinylpyridine-copolymer-containing TBBS-accelerated stock can be similar to those of TBBS-accelerated NR, it might be concluded that the new additives will solve some of the problems in balancing the cures of adjacent NR and SBR stocks in a multicomponent cured rubber article.

scholarly journals ‘Environmental Impact Assessment’ in Drylands: Late Knowledge Penetration or a Deliberate Ignorance for Megaprojects?

World ◽  
2021 ◽  
Vol 2 (3) ◽  
pp. 374-378
Author(s):  
Farshad Amiraslani
Keyword(s):  
Ecosystem Services ◽  
Environmental Impact ◽  
Impact Assessment ◽  
Environmental Impact Assessment ◽  
Ecological Resilience ◽  
Delayed Action ◽  
The Way

Despite the paramount role of drylands in supporting people’s livelihoods and rendering ecosystem services, legislation on Environmental Impact Assessment has been introduced belatedly after several decades. By exemplifying Iran, the author proposes two main reasons for such a delayed action. First, drylands are misleadingly considered as barren lands where biodiversity is relatively low. In one classification, deserts are even categorized along with rocks. Second, the author emphasizes that drylands have been subjected to unprecedented changes due to the expansion of infrastructure and urbanization that started in the 1970s. These growing pressures have been beyond the ecological resilience of drylands and have not been monitored, assessed, and modified correctly. Further scrutiny regarding EIA undertakings in drylands and the way they can be improved is now needed.

THEORETICAL STUDIES ON THE COUPLING INTERACTIONS AND SELF-EXCHANGE REACTION MECHANISMS IN THE COMPLEXES OF NO WITH ONH AND NOH

2008 ◽  
Vol 07 (03) ◽  
pp. 435-446 ◽  
Author(s):  
PING LI ◽  
XIAOYAN XIE ◽  
YUXIANG BU ◽  
WEIHUA WANG ◽  
NANA WANG ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Exchange Reaction ◽  
Reaction Mechanisms ◽  
Natural Bond Orbital ◽  
Theoretical Studies ◽  
Exchange Reactions ◽  
Electron Transfer Mechanism ◽  
Proton Coupled Electron Transfer ◽  
Planar Geometries ◽  
Transfer Mechanisms

The coupling interactions and self-exchange reaction mechanisms between NO and ONH (NOH) have been systematically investigated at the B3LYP/6-311++G** level of theory. All the equilibrium complexes are characterized by the intermolecular H-bonds and co-planar geometries. The cisoid NOH/ON species is the most stable one among all the complexes considered due to the formation of an N – N bond. Moreover, all the cisoid complexes are found to be more stable than the corresponding transoid ones. The origin of the blueshifts occurring in the selected complexes has been explored, employing the natural bond orbital (NBO) calculations. Additionally, the proton transfer mechanisms for the self-exchange reactions have been proposed, i.e. they can proceed via the three-center proton-coupled electron transfer or five-center cyclic proton-coupled electron transfer mechanism.

Anorexia Nervosa in a Black Zimbabwean

1984 ◽  
Vol 145 (3) ◽  
pp. 326-330 ◽  
Author(s):  
T. Buchan ◽  
L. D. Gregory
Keyword(s):  
Anorexia Nervosa ◽  
Special Reference ◽  
Diagnostic Criteria ◽  
Traditional Healer ◽  
Clinical Symptoms ◽  
The Social ◽  
Speculative Hypothesis ◽  
African Patients

SummaryIn spite of the comparative rarity of anorexia nervosa in African patients, the case of a young black Zimbabwean woman which fulfils Feighner's diagnostic criteria is presented. Special reference is made to several unusual features which include the social and psychological conflicts engendered by changes of culture, the clinical symptoms, and the role of a traditional healer in her recovery. A speculative hypothesis concerning aetiology is suggested.

Characterization of soluble, FSF-stabilized fibrin complexes with special reference to the role of fibrinogen

1974 ◽  
Vol 5 (1) ◽  
pp. 21-32 ◽  
Author(s):  
Bernt Ly ◽  
Peter Kierulf ◽  
Erling Jakobsen ◽  
Karl Gravem
Keyword(s):  
Special Reference ◽  
Stabilized Fibrin

scholarly journals Estrogen binding by leukocytes during phagocytosis,.

1977 ◽  
Vol 145 (4) ◽  
pp. 983-998 ◽  
Author(s):  
S J Klebanoff
Keyword(s):  
Chronic Granulomatous Disease ◽  
Reaction Mechanisms ◽  
Dehydrogenase Deficiency ◽  
Cell Types ◽  
Neutrophil Function ◽  
Granulomatous Disease ◽  
Glucose 6 Phosphate Dehydrogenase ◽  
Estrogen Binding ◽  
Two Populations

Estradiol binds covalently to normal leukocytes during phagocytosis. The binding involves three cell types, neutrophils, eosinophils, and monocytes and at least two reaction mechanisms, one involving the peroxidase of neutrophils and monocytes (myeloperoxidase [MPO]) and possibly the eosinophil peroxidase, and the second involving catalase. Binding is markedly reduced when leukocytes from patients with chronic granulomatous disease (CGD), severe leukocytic glucose 6-phosphate dehydrogenase deficiency, and familial lipochrome histiocytosis are employed and two populations of neutrophils, one which binds estradiol and one which does not, can be demonstrated in the blood of a CGD carrier. Leukocytes from patients with hereditary MPO deficiency also bind estradiol poorly although the defect is not as severe as in CGD. These findings are discussed in relation to the inactivation of estrogens during infection and the possible role of estrogens in neutrophil function.

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