Influence Of Vulcanization Research Articles

Preparation and physical properties of fluorosilicone rubber/polypropylene thermoplastic vulcanizates

ABSTRACT A new thermoplastic vulcanizate (TPVs) composed of polypropylene and fluorosilicone rubber was successfully prepared via dynamic vulcanization focusing on undersea cable and automobile applications. Phase morphology confirms the dispersed rubber particles in a continuous thermoplastic phase. The influence of vulcanization and post-curing time on the mechanical and dynamic properties of TPVs was investigated. Notably, the tensile strength decreased, and the compression set increased with an increase in vulcanization time. Overall, the fabricated TPVs possessed good tensile strength, elastic behavior, and thermal stability. The post-curing time effect on TPVs exhibited a good compression set and lower hardness, but tensile properties deteriorated.

Influence of Vulcanization on Adhesion to Non-Vulcanizing Polymers

Abstract According to contemporary ideas the mechanisms of adhesion and co-vulcanization of rubbers have much in common. The phenomenon of co-vulcanization, like that of adhesion of polymers, includes the diffusion of macromolecules and of segments of them, which is particularly intensive in the initial period of vulcanization, when the crosslinks have not yet formed. The difference between covulcanization and adhesion lies solely in the fact that the process of interpenetration of the molecular chains in the former case is sooner or later broken off by the vulcanization process being superimposed upon it, securing the macromolecules or portions of them by strong chemical bonds. This leads to the formation of an adhesion joint considerably superior in strength to a joint in which the molecules diffusing through are attached only by weak intermolecular bonds. It is important to ascertain what is the influence of the vulcanization of elastomers upon their adhesion to polymers not capable of forming chemical bonds with them. This case is of immense practical importance, since unvulcanized rubbers are very often used in combination with vegetable and synthetic fibers which are not capable of vulcanizing. As adhesives we selected elastomers of varying molecular structure, polarity and degree of molecular mobility: butadiene-acrylonitrile rubber (SKN-26), butadiene-styrene rubber (SKS-30A), butadiene-styrene oil-extended rubber (SKS-30ARM-15) and butyl rubber. Using these rubbers we prepared stocks both containing and not containing vulcanizing groups (in the latter case the components of the vulcanizing groups were replaced by an equal quantity of inert filler—whiting). The amount of vulcanizing group was set at the optimum for each rubber. The substrates used were films containing no plasticizers—cellophane (cellulose hydrate) and Perfol' PK-4 (polycaprolactam). The adhesive was applied to the substrate by coating on a calender at the optimum conditions for each elastomer. The specimens produced in this way were plied up and subjected to vulcanization. Vulcanization was carried out in a Berstorff apparatus for continuous vulcanization at 143° C and a specific pressure ≈ 0.85 kg/sq cm. The time of cure was varied between 0 and 88 min.

Influence of Vulcanization on the Oxidizability of Rubber. II. Vulcanizing Agents Other Than Sulfur

Abstract If it is attempted to sum up the important results obtained in the present study, the following points seem to be well established. First of all, with respect to selenium. Whether the oxidizabilities of products vulcanized by selenium alone or of products vulcanized by a mixture of selenium and sulfur are measured, they show the same general behavior as do mixtures vulcanized by sulfur alone. It is the percentage of vulcanizing agent in combined form that governs the oxidizability, for the addition of selenium to sulfur increases this oxidizability. If part of the sulfur is replaced by selenium, there is a decrease in the oxidizability, but this can be explained by the lesser reactivity of the selenium, as a result of which the product is vulcanized to a less extent. It is not true, then, that, for a given state of cure, selenium improves aging. The case of diazoaminobenzene is a more complicated one. This compound decomposes during vulcanization, with liberation of nitrogen and probable formation of antioxygenic substances such as diphenylamine. Diazoaminobenzene itself is a proöxygenic substance, and mixtures containing it which have been heated only a short time have a strong tendency to oxidize. With longer heating, complete decomposition of the diazoaminobenzene inevitably takes place, and the oxidizability becomes established at a relatively small value. In the same way, with chloranil and with dichloroiminoquinone, the reaction leads to the formation of antioxygenic substances, and when vulcanization is carried to a sufficient point, the oxidizability decreases. It should be mentioned that such a prolongation of the time of heating does not have any harmful effect on the mechanical properties of the vulcanizate. Actually all the agents gave a remarkably broad plateau, and no appreciable differences in mechanical properties were found over a wide range of heating times, e.g., 30 minutes to 8 hours. As for the joint use of an amine and an oxidizing agent, such as N, N′-di-β-naphthyl-p-phenylenediamine and lead peroxide, it will be found that, here too, with increase in the time of vulcanization the tendency to oxidize decreases to a minimum, probably as a result of progressive decomposition of the peroxide. if it is attempted to counteract this proöxygenic action directly by the addition of a large amount of the amine, it will be found that, on the contrary, vulcanization becomes less and less effective and the oxidizability increases. However, by adjusting the proportions of amine and of oxidizing agent judiciously, it is possible to obtain products the resistance of which to oxidation is remarkably good. In a special experiment, a direct comparison was made of samples vulcanized with the agents described in the present work and a simple rubber-sulfur vulcanizate, both unprotected and protected by different antioxygenic substances, including diphenylamine, hydroquinone and N, N′-di-β-naphthyl-p-phenylenediamine. By plotting the results, the curves shown in Figure 13 were obtained. These curves make particularly clear the fact that it is possible, by means of certain vulcanizing agents, e.g., diazoaminobenzene or an amine plus an oxidizing agent, to obtain vulcanizates which have as much resistance to oxidation as that of rubber-sulfur vulcanizates containing an antioxygenic substance. This is not true of nitro compounds, with which even ordinary antioxygenic agents have only a relatively slight protective action. A thorough investigation of these vulcanizing agents is then of importance, not only in helping to explain the mechanism of vulcanization itself but also because of the possibilities of its leading to various practical applications.

The Influence of Vulcanization on the Oxidizability of Rubber. Vulcanizing Agents Other Than Sulfur

Abstract In a previous publication the influence of vulcanization by sulfur and sulfur compounds on the oxidizability of rubber was shown. The most important conclusion was that, in principle, the higher the proportion of combined sulfur, the greater is the oxidizability. However, with very high proportions, the activity of the sulfur changes, i.e., above a certain upper limiting range, the oxidizability tends towards a plateau, whereas below a lower limiting range the oxidation curve passes through a minimum. After having obtained these results, it seemed to be of interest to complete the investigation by studying the effects of vulcanization by agents other than sulfur on oxidizability. In the present work we have examined vulcanization by nitro compounds and peroxides, taking as examples m-dinitrobenzene, trinitrobenzene and benzoyl peroxide. This domain of rubber chemistry has been relatively little explored and certain points either have not received final confirmation or have even led to contrary conclusions. Accordingly it seemed useful to review from a purely objective point of view what has been done on this subject.

The Influence of Vulcanization on Oxidizability in Relation to Aging. A Preliminary Study

Abstract Because of its preliminary character, the present investigation does not admit any definite conclusions. Rather, by bringing out clearly the various complications which arise in studying the oxidizability of rubber, especially when the aim is to establish a parallelism between oxidizability and the ill-defined phenomenon of aging, the investigation has shown the many difficulties in general involved in the problem. These complications are to a certain extent attributable to the nature of the phenomenon itself which has been measured, i. e., the oxidizability; but for the most part they owe their origin to the nature of the substance studied, and especially to its heterogeneous character. For these reasons the uncertainty in the results is increased by vulcanization, and the more vigorous the treatment, the greater is this uncertainty. As a result, considerable fluctuation in the measurements occurred. This is the reason why, in the past as well as now, so much emphasis has has been laid on the advisability of considering as significant only relatively large differences in measurements when drawing conclusions from them. With these reservations in mind, the facts which emerge from this opening work may be reviewed briefly. First of all, it may be stated that, as a principle, the higher the percentage of combined sulfur, the greater is the oxidizability of rubber. In other words, it is, in a different guise, the principle accepted by the majority of technologists, and which Martin expressed in a particularly clear fashion, viz., that the lower its state of vulcanization, the more stable is rubber.

Influence of Vulcanization on the Index of Refraction of Rubber

Abstract Only recently McPherson has measured various physical properties of highly purified raw rubber, among them its index of refraction. In this work McPherson obtained essentially the same values as did the present writer. In the work of the latter it was pointed out that the sulfur of vulcanization has an influence on the index of refraction, because the high index of refraction of sulfur has a noticeable effect even at low degrees of vulcanization. As a result of other investigations, the present author has not until the present time carried on any further the work planned at that time. It was therefore a pleasure to find that McPherson had carried out these investigations with rubber purified by the process developed in his earlier experiments. In the present work, the determinations of the index of refraction were made at 25° with an Abbé refractometer, and the method of total reflection was used. The rubber used for preparing the samples was free of protein and so-called rubber resins, and contained 99.5 per cent of pure rubber hydrocarbon. The samples were vulcanized to a stage where practically all of the sulfur added had combined with the rubber.