Studies in the Vulcanization of Rubber. VII. Unsaturation of Rubber Vulcanized with Nitro Compounds and Benzoyl Peroxide

1937 ◽  
Vol 10 (4) ◽  
pp. 735-742
Author(s):  
John T. Blake ◽  
Phillip L. Bruce
Keyword(s):  
Benzoyl Peroxide ◽  
Chemical Reaction ◽  
Nitro Compounds ◽  
Unsaturated Hydrocarbon ◽  
Secondary Reaction ◽  
Double Bonds ◽  
Decomposition Products ◽  
Vulcanized Rubber ◽  
Chemical Theory

Abstract RUBBER is primarily an unsaturated hydrocarbon. Sulfur adds to its double bonds during vulcanization to form soft and hard vulcanizates. In the formation of soft vulcanized rubber, unsaturation is reduced several per cent by the chemical addition of sulfur. Spence and Scott (10) showed that the proportion of combined sulfur corresponds exactly to the decrease in unsaturation, and therefore that sulfur combination consists entirely of addition to the double bonds of rubber. The studies of one of the authors (1) on the vulcanization of rubber with nitro compounds indicate that these substances or their decomposition products combine with rubber. Van Rossem (8) also showed that vulcanization with benzoyl peroxide is accompanied by a decrease in extractable material, indicating that either the reagent or its decomposition products combine chemically with the rubber. The natural expectation would be that addition to the double bonds occurs and that the unsaturation decreases correspondingly. Van Rossem's proposed mechanism for the vulcanization with benzoyl peroxide would involve no change in unsaturation. Fisher and Gray (2) applied Kemp's method (4) in determining the iodine numbers of a single vulcanizate of each of four compounds. The vulcanizing agents involved were m-dinitrobenzene, trinitrotoluene, and benzoyl peroxide. Their unsaturation values agreed closely with calculated values for the unvulcanized compounds. They concluded from their results that “Ordinary vulcanization is an unknown or undetermined type of change in the hydrocarbon involving no change in the unsaturation and that chemical union of sulfur is a secondary reaction.” If true, this evidence is a serious blow to the chemical theory of vulcanization which postulates that a chemical reaction is essential for the process. The present paper offers evidence that the vulcanization of rubber with these reagents does involve change in its unsaturation.

The Vulcanization of Rubber with m-Dinitrobenzene

1938 ◽  
Vol 11 (1) ◽  
pp. 131-141
Author(s):  
J. M. Wright
Keyword(s):  
Chemical Reaction ◽  
Nitro Compound ◽  
Nitro Compounds ◽  
The Other ◽  
Vulcanized Rubber ◽  
Other Hand ◽  
Aging Properties ◽  
Original Report ◽  
Favorable Conditions ◽  
Better Than

Abstract The literature referring to the vulcanization of rubber with m-dinitrobenzene indicates the present undeveloped state of knowledge of the reaction and of the most favorable conditions for its employment. Much is vague and even contradictory. Ostromislensky (J. Russ. Phys.-Chem. Soc., 47, 1462 (1915)) stated that certain nitro compounds are capable of vulcanizing rubber in the absence of auxiliary substances, and that the products of vulcanization are superior in some respects to sulfur vulcanizates; tensile strengths obtained were comparable with those of sulfur vulcanizates; aging properties were found to be good; color and finish were better than those of sulfur vulcanizates. On the other hand, Porritt (J. Soc. Chem. Ind., 35, 986 (1916)), and Stevens (J. Soc. Chem. Ind., 36, 107 (1917)) failed to confirm these statements, but agreed that the presence of litharge is beneficial. Again in 1929, Ostromislensky (India Rubber World, 80, 55 (1929)) confirmed his original report, stating that he believed that this form of vulcanization is due to an action between rubber and the oxygen of the nitro compound. Blake (Ind. Eng. Chem., 22, 7 (1930)) stated that vulcanization of rubber with dinitrobenzene involves a monomolecular chemical reaction between rubber and dinitrobenzene, in which, of the 6 per cent dinitrobenzene, practically all of the nitrogen combined with the rubber. The end-product of the reaction appears to be a soft vulcanized rubber; no one has claimed to be able to produce an ebonite by the use of this reagent.

Studies in the Vulcanization of Rubber. IV—A Theory of Vulcanization of Rubber

1930 ◽  
Vol 3 (4) ◽  
pp. 659-667
Author(s):  
G. R. Boggs ◽  
J. T. Blake
Keyword(s):  
Electrical Properties ◽  
Joule Effect ◽  
Vulcanized Rubber ◽  
Chemical Theory ◽  
Rubber Compounds ◽  
Kinetics Of ◽  
Kinetics Of Vulcanization

Abstract A new theory has been advanced which, it is believed, explains completely the various phenomena connected with the vulcanization of rubber. It is entirely a chemical theory based on the existence of two separate and distinct rubber compounds, soft vulcanized rubber and ebonite. The theory explains satisfactorily the aging of rubber, the variation in combined sulfur at optimum cure caused by acceleration, the kinetics of vulcanization, the characteristics of various vulcanizing agents, the thermochemistry of vulcanization, the electrical properties of rubber, the reclaiming of rubber, and the Joule effect. A brief review and discussion of the phenomena and past theories of vulcanization have also been given.

Sulfur Linkage in Vulcanized Rubber. Reaction of Methyl Iodide with Sulfur Compounds

1949 ◽  
Vol 22 (1) ◽  
pp. 1-7
Author(s):  
M. L. Selker
Keyword(s):  
Methyl Iodide ◽  
Room Temperature ◽  
Sulfur Compounds ◽  
Point Of View ◽  
Secondary Reaction ◽  
Reaction Products ◽  
Sulfide Sulfur ◽  
Vulcanized Rubber ◽  
Allyl Sulfide

Abstract The work described here is an extension of the study of the reaction of methyl iodide with sulfur compounds originally begun with the purpose of using such data in determining the sulfur linkage in vulcanized rubber. A previous paper dealt with the reactions of methyl iodide with propanethiol, propyl sulfide, propyl disulfide, allyl sulfide, and thiophene. This article adds to the list, n-butyl methallyl sulfide, allyl disulfide, allyl tetrasulfide, n-propyl tetrasulfide, and trithiane. The removal of combined sulfur from vulcanized rubber as trimethylsulfonium iodide on treatment with methyl iodide at room temperature was persuasive evidence of the presence of sulfide sulfur linked to allylic type residues. The evidence offered, however, did not constitute exclusive proof because it was not known whether still other types of sulfur linkage would also yield trimethylsulfonium iodide. To shed more light on this question, the sulfur linkages most likely to occur in vulcanizates—the allyl-alkyl monosulfide, diallyl and dialkyl di- and polysulfide—were investigated. The trithiane reaction is of interest mostly from the point of view of the reaction of overcured stocks or secondary reaction products stemming from the original polysulfides. The reactions were carried out using the method described in a previous paper.

Mechanism of Rubber Vulcanization with Sulfur

1938 ◽  
Vol 11 (1) ◽  
pp. 107-130
Author(s):  
W. K. Lewis ◽  
Lombard Squires ◽  
Robert D. Nutting
Keyword(s):  
Natural Rubber ◽  
Temperature Coefficient ◽  
Chemical Reactions ◽  
Chemical Reaction ◽  
Reaction Rate ◽  
Complex Behavior ◽  
Double Bonds ◽  
Irreversible Reaction ◽  
Sulfur Addition

Abstract THAT vulcanization of rubber with sulfur always involves a chemical reaction consisting in the addition of sulfur to the double bonds of the rubber molecule has been conclusively established (18, 28). The facts indicate that this addition of sulfur to rubber is an irreversible reaction (31). The temperature coefficient of the reaction is high, increasing about 2.65 fold per 10° C. at ordinary curing temperatures (31). Furthermore, the reaction is apparently exothermic (4, 24). It is noteworthy that catalysts are apparently necessary, since synthetic rubbers prepared from pure materials add sulfur slowly, if at all. The proteins and perhaps the resins in natural rubber undoubtedly serve as accelerators. The curves for combined sulfur vs. time of cure for typical mixes are shown in Figures 1 and 2. Figure 1 is taken from the data of Kratz and Flower (16); the composition and temperature of cure for this mix are shown in Cranor's Table I (9). Figure 2, curve 1, is from Table I of Eaton and Day (10), and curve 2 from data obtained in this laboratory (27, Table I). Superficial inspection of these curves shows extraordinary divergence of type. Figure 1 is a typical fadeaway curve, characteristic of most chemical reactions, where the reaction rate decreases with decreasing concentration of the reacting materials. Curve 1, Figure 2, is an entirely different type, where the rate of sulfur addition is constant until nearly 70 per cent of the initial sulfur has reacted. Curve 2, Figure 2, shows even more complex behavior. Again the rate is constant in the initial portions of the cure. However, following this period, the rate increases markedly but later falls off, approaching zero, to give an S-shaped eurve.

Vulcanization of Rubber. By Organic Peroxides or by Ammonium Persulphate

1930 ◽  
Vol 3 (2) ◽  
pp. 195-200 ◽  
Author(s):  
Iwan Ostromislensky
Keyword(s):  
Benzoyl Peroxide ◽  
Organic Peroxides ◽  
Ammonium Persulphate ◽  
Aluminium Powder ◽  
Metallic Oxides ◽  
Vulcanized Rubber ◽  
Viscous Mass ◽  
Metallic Aluminium ◽  
Short Time ◽  
Rubber Product

Abstract 1. Organic peroxides vulcanize rubber not only in the absence of sulphur but likewise without any foreign substances such as metallic oxides or accelerators of any kind. 2. Rubber vulcanized by means of an adequate amount of benzoyl peroxide (10 to 30 per cent.) gives a soft rubber product which does not differ in point of physical properties from products cured with sulphur, or rather with sulphur chloride. 3. The process of vulcanizing rubber with benzoyl Superoxide is completed in a relatively short time even at a fairly low temperature, sometimes even in two minutes at 119° C., corresponding to 13 pounds pressure. 4. Vulcanization of rubber by means of peroxides may lead to the formation of a soft, transparent and elastic product, which is almost entirely colorless. 5. The products in question vulcanized by means of various peroxides are gradually converted to a very sticky and viscous mass. 6. Sulphur protects the vulcanizates in question from such decomposition or oxidation. However, the products obtained in vulcanization of rubber with organic peroxides in the presence of sulphur are opaque. 7. As distinguished from sulphur, selenium, tellurium, their sulphides, metal oxides (in particular, lead oxide) as well as amines (aniline), tannic acid, and metallic aluminium powder not only do not protect the peroxide vulcanized rubber products from decomposition or oxidation but, on the contrary, they accelerate such processes quite considerably. 8. Benzoyl peroxide is the active vulcanizing agent in the process of heating rubber with a mixture of sulphur and benzoyl peroxide. 9. When rubber is subjected to the action of a mixture of some nitrobenzenes and benzoyl peroxides, vulcanization is effected exclusively by the nitrobenzenes, and the benzoyl peroxide remains altogether passive. 10. Ammonium persulphate vulcanizes rubber completely, resulting in a porous product which, generally speaking, is of small practical value.

Strain Test for Evaluation of Rubber Compounds

1949 ◽  
Vol 22 (1) ◽  
pp. 201-211 ◽  
Author(s):  
Frank L. Roth ◽  
Robert D. Stiehler
Keyword(s):  
High Precision ◽  
Chemical Reaction ◽  
Strain Measurements ◽  
Vulcanized Rubber ◽  
Rubber Compounds ◽  
Order Chemical Reaction ◽  
Strain Testing ◽  
Order Of Magnitude ◽  
Single Sheet ◽  
Uniform Treatment

Abstract Measurements of elongation of rubber vulcanizates at a fixed stress have been made with a precision much greater than can be obtained in the usual measurements of stress at a specified elongation. Such measurements form the basis of a strain test developed to characterize rubber vulcanizates in control and research testing. Statistical analyses show that the errors introduced in the actual strain measurements are negligible compared to those introduced by variations during compounding and curing, whereas the errors introduced by the usual measurements of stress at a specified elongation are of the same order of magnitude as those for compounding and curing. The high precision of strain testing has been used to detect variations within a single sheet of vulcanized rubber and variations among sheets cured from the same compounded batch. It has been possible also to determine with a single sheet its change in stiffness or modulus with age. The uniform treatment of specimens in the strain test makes them particularly useful for precise measurements of set. Further, it has been found that the decrease in elongation with time of cure apparently follows the laws of a second-order chemical reaction; consequently it is possible to represent the data by an equation involving three vulcanization parameters.

Infrared Study of Some Structural Changes in Natural Rubber during Vulcanization

1958 ◽  
Vol 31 (4) ◽  
pp. 719-736 ◽  
Author(s):  
Frederic J. Linnig ◽  
James E. Stewart
Keyword(s):  
Double Bond ◽  
Gamma Rays ◽  
Structural Changes ◽  
Elemental Sulfur ◽  
Carboxyl Groups ◽  
Double Bonds ◽  
Infrared Study ◽  
Tetramethylthiuram Disulfide ◽  
Vulcanized Rubber ◽  
Double Bond Shift

Abstract A knowledge of the structure of vulcanized rubber is essential to the interpretation of vulcanization and oxidation studies and the physical properties of the material. In the present work an infrared study has been made of structures resulting from a number of different methods of vulcanization. Sulfur vulcanizates show the presence of a shifted double bond, originally observed by Sheppard and Sutherland. The presence of conjugated double bonds is also indicated. Accelerators such as tetramethylthiuram disulfide and zinc dibutyl dithiocarbamate increase the rate of the double-bond shift and reduce the amount of conjugated double bonds. Neither the double-bond shift nor conjugation is observed as a result of vulcanization with tetramethylthiuram disulfide alone, hydrogen sulfide and sulfur dioxide (Peachey process), a peroxide, or gamma rays. These result in a possible decrease in carbonyl structures, and in the case of the last three, possible increased absorption due to OH and ionized carboxyl groups. Apparently, the double-bond shift and conjugation are primarily phenomena related to the use of elemental sulfur. The other vulcanization systems studied evidently involve different mechanisms. An implication of the present work is that there may be a relationship between the reported ease of oxidation of sulfur vulcanizates, accelerated vulcanizates, and sulfurless vulcanizates (tetramethylthiuram disulfide alone), which decreases in the order named, and the probable amount of conjugation in the compound, which decreases in the same order.

scholarly journals THE EFFECT OF EXPOSURE PERIOD AND TEMPERATURE ON THE PHOTOSENSORY PROCESS IN CIONA

1926 ◽  
Vol 8 (3) ◽  
pp. 291-301 ◽  
Author(s):  
Selig Hecht
Keyword(s):  
Latent Period ◽  
Chemical Reaction ◽  
Photochemical Reaction ◽  
Oxidation Reaction ◽  
Arrhenius Equation ◽  
Exposure Period ◽  
Secondary Reaction ◽  
Primary Reaction ◽  
Iron Compounds ◽  
Reaction Proceeds

1. Experiments are presented which show that the latent period in the photosensory response of Ciona is inversely proportional to the duration of the exposure period to light. From this it is found that the velocity of the chemical reaction which determines the latent period is directly proportional to the concentration of photochemical products formed during the exposure period. This is interpreted as showing that the two processes form a coupled photochemical reaction, of which the secondary reaction proceeds only in the presence of products from the primary reaction. This coupling may be a catalysis or a direct chemical relation. 2. Further experiments show that the relation between temperature and the latent period is accurately described by the Arrhenius equation in which µ = 16,200. The precise numerical value of µ tentatively identifies the latent period process as an oxidation reaction which is catalyzed by iron. 3. The photocatalytic properties of certain iron compounds are used as a model for the coupled photochemical reaction suggested for the photosensory mechanism of Ciona and Mya.

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