Rabin Datta

Activators in Accelerated Sulfur Vulcanization

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 syst...

Flocculation in Silica Reinforced Rubber Compounds

Abstract Flocculation plays an important role in reinforcement of silica filled rubber compounds, even if coupling agents are applied. It is well known that silica tends to flocculate during the early stages of vulcanization, when no dense rubber network has been formed yet. In the present study, flocculation was monitored by following the change in storage modulus at low strain, the so-called Payne effect, using a RPA2000 dynamic mechanical tester. The kinetic parameters: the rate constant and the activation energy of the silica flocculation were calculated according to the well-known Arrhenius equation. On basis of the value of the activation energy obtained for flocculation, it can be concluded that the silica flocculation is a purely physical phenomenon. Bound rubber measurements were also done in order to estimate the interfacial interaction layer between silica and polymer resulting from the coupling agent. The silica flocculation rate decreases with increasing interfacial interaction layer on the s...

Effect of zinc complexes as activator for sulfur vulcanization in various rubbers

Abstract Because of environmental concerns, the zinc content in rubber compounds has come under scrutiny; therefore it is necessary to explore possibilities to reduce this zinc content. In this article the application of several zinc complexes as activator for sulfur vulcanization are discussed, in order to find alternatives for the conventionally used ZnO and fatty acid activator system. The effects of different zinc complexes on the cure and physical properties of two widely different rubbers, viz. EPDM and s-SBR, are studied. It can be concluded that zinc-m-glycerolate is a good substitute for ZnO as activator for sulfur vulcanization, in EPDM as well as in s-SBR rubber, without detrimental effects on the cure and physical properties. Furthermore, the results indicate that, dependent on the intended applications, zinc-2-ethylhexanoate represents a substitute for the commonly used ZnO. Zinc stearate is considerably less active as activator in sulfur vulcanization.

Rubber vulcanizates degradation and stabilization

Abstract Degradation of rubber vulcanizates in the presence and absence of air as well as in presence of ozone is reviewed in this paper. The paper also outlines the means to overcome this undesira...

Fiber Adhesion to Rubber Compounds

Abstract The present paper provides an overview of literature published on fiber-rubber composites. A brief history of Fibers used in rubber applications is given. The emphasis is on the adhesion b...

Zinc loaded clay as activator in sulfur vulcanization: A new route for zinc oxide reduction in rubber compounds

Abstract Concern about the release of eco-toxic zinc species from rubbers into the environment leads to an increasing interest in potential substitutes. Although alternative metal oxides and zinc compounds as activators for sulfur vulcanization have been studied thoroughly, at present no viable alternative has been found to eliminate ZnO completely from rubber compounds, without significantly jeopardizing processing as well as performance characteristics. In this paper, the application of a new activator for sulfur vulcanization will be discussed. This activator is developed based on the assumption that an increase in the availability of Zn2+-ions could lead to a considerable reduction of ZnO in rubber compounds. Montmorillonite clay was used as carrier material and loaded with Zn2+-ions via an ion-exchange process. Application in a wide range of natural and synthetic rubbers has been explored. Results clearly demonstrate that this Zn-Clay can substitute conventional ZnO, retaining the curing and physical...

New concept of co-agents for scorch delay and property improvement in peroxide vulcanization

Abstract Peroxide cure is an important and widely used cure system for rubber. Several properties obtained via peroxide vulcanization are superior and not achievable with sulfur vulcanization, e.g.: aging resistance, no reversion and low compression set. However, other properties such as tensile strength and dynamic properties, are inferior to those of sulfur vulcanizates. The use of co-agents in peroxide cure leads to a certain extent to improvement in mechanical properties such as tensile strength. Nevertheless the properties are still inferior with respect to mechanical/dynamical properties of sulfur-cured articles. If these properties can be improved, the range of applications of peroxide cure in the rubber industry can be significantly broadened. Scorch is a common problem in peroxide cure, especially for injection molding and extrusion applications. Several additives can help to improve scorch safety, however, they always result in a lower peroxide efficiency, thus inferior vulcanizate properties. I...

Multifunctional Additives as Zinc-Free Curatives for Sulfur Vulcanization

Abstract Concern about the release of eco-toxic zinc species from rubbers into the environment leads to an increasing interest in potential substitutes. This investigation reports on the applicatio...

Understanding the chemistry of the rubber/silane reaction for silica reinforcement, using model olefins

Abstract Although bifunctional organosilanes, particularly bis-(triethoxy-silyl-propyl) tetrasulfide (TESPT), are very efficient silica-rubber coupling agents, a high level is required to realize a...

Chemistry of various accelerators in an e-SBR model compound

Abstract Sulfur vulcanization was carried out with 5-phenyl hex-2-ene serving as a model of e-SBR. Various accelerators have been used to study and compare the reactivity in a system containing sulfur and activators. Both HPLC and GC-MS analytical tools were used to identify the reaction products. It has been observed that the vulcanization in the presence of N-cyclohexyl-2-benzothiazole sulfenamide (CBS) generates a large amount of 2-marcaptobenzothiazole (MBT), which continuously increases and finally decreases suggesting further participation in vulcanization generating new crosslinks. The sulfenamide, N-cyclohexyl-4,6 dimethyl-2-pyrimidine sulfenamide (CDMPS) behaves different. Although it generates considerable amount of corresponding thiol, (4,6-dimethyl pyrimidine-2-thiol, DMMP) at the beginning of the reaction, no decrease has been observed during the course of further reaction suggesting that the accelerator, DMMP, somehow remains deactivated and therefore no changes in network is feasible. Ident...