Smearing of Vulcanized Rubber

1955 ◽  
Vol 28 (2) ◽  
pp. 508-518 ◽  
Author(s):  
S. D. Gehman ◽  
C. S. Wilkinson ◽  
R. D. Daniels
Keyword(s):  
Melting Point ◽  
Thermal Degradation ◽  
Natural Rubber ◽  
Sulfur Compound ◽  
Important Variable ◽  
Cross Linking ◽  
Curing Agent ◽  
Point Bar ◽  
Tetramethylthiuram Disulfide ◽  
Vulcanized Rubber

Abstract The surface heating which occurs at the interface of rubber sliding under a load may be part of the mechanism of abrasion, especially under severe conditions. Removal of rubber by thermal degradation and a smearing process occurs if the rubber attains sufficiently high localized temperatures. A procedure, using a melting point bar, was developed for measuring the temperature at which smearing occurred for rubber vulcanizates. Smear points reproducible to about ±2° F were measured. The effect of compounding variables on the smear point was investigated. The most important variable in this category was the vulcanization system, probably inasmuch as it determined the type of cross-linking. The presence of free sulfur within the rubber also tended to increase the smear temperature. Highest smear points were obtained with mercaptobenzothiazole-tetramethylthiuram disulfide mixtures, and for a non-sulfur compound using p-quinone-dioxime as the curing agent. The highest smear point observed for natural rubber was 475° F, obtained with this system. GR-S tread compounds showed no smearing even at 560° F, which was as high as could be obtained with the apparatus used. The resistance to smearing of GR-S may be an important factor in explaining its superiority in road wear under severe conditions. Laboratory abrasion experiments were performed to illustrate the effect of smearing on the relative abrasion loss of GR-S and natural-rubber tread compounds.

The Crystallization of Weakly Vulcanized Rubber by Pressure

1940 ◽  
Vol 13 (1) ◽  
pp. 48-48 ◽  
Author(s):  
P. A. Thiessen ◽  
W. Kirch
Keyword(s):  
Melting Point ◽  
Natural Rubber ◽  
Crystalline Phase ◽  
Normal Pressure ◽  
Latex Film ◽  
X Rays ◽  
Amorphous Substance ◽  
Temperature Range ◽  
Vulcanized Rubber

Abstract Crystallization can be brought about in weakly vulcanized rubber by the method described by Thiessen and Kirsch for natural rubber. When samples of this type of vulcanized rubber were exposed to x-rays below + 6° C, but not under pressure, then Debye-Scherrer diagrams corresponding to those of a crystallized latex film were obtained. To determine the influence of pressure on these vulcanizates, samples were subjected to pressure on all sides in the chambers of the pressure apparatus described in the earlier work. After having been exposed for 100 days the sample which had been kept at + 6° C under 30 atmospheres' pressure showed a very marked Debye-Scherrer diagram, whereas samples kept at the same temperature but at normal pressure showed only the halo of an amorphous substance. Consequently pressure has an influence on the crystallization of vulcanized rubber as well as of raw rubber. The melting point of the crystalline phase lies between + 11° C. and +13° C. Obviously then an increase in pressure raises the temperature range of supercooling.

Contribution to the Mechanism of Devulcanization

1957 ◽  
Vol 30 (1) ◽  
pp. 87-92 ◽  
Author(s):  
W. E. Stafford ◽  
R. A. Wright ◽  
D. Sargent
Keyword(s):  
Thermal Stability ◽  
Thermal Degradation ◽  
Natural Rubber ◽  
Zinc Sulfide ◽  
Thermal Conditions ◽  
Chloroform Extract ◽  
Similar Type ◽  
Tetramethylthiuram Disulfide ◽  
Natural Rubber Vulcanizates ◽  
Free Sulfur

Abstract (1) Three types of natural-rubber vulcanizates have been treated under specific reclaiming conditions. The resultant products have been examined particularly for the manner of sulfur combination and for chloroform extract. The normally accepted, non-reverting tetramethylthiuram disulfide type stock was found to be by far the most amenable to plasticization by thermal agencies. This observation is more or less in line with conclusions of van Amerongen, drawn from a recent study of the oxidative and non-oxidative thermal degradation of rubber. A natural pure-gum type, cured with tetramethylthiuram disulfide only, when heated in the absence of oxygen, at temperatures up to 175° C, was found to revert much more than a similar type cured with 1.0 per cent Santocure and 2 per cent sulfur. Swelling in benzene, after heating 3 days at 150° C, increased considerably with the former, whereas with the latter it remained unchanged. This greater “devulcanizing tendency” is explained on the basis of the tetramethylthiuram disulfide type having comparatively few crosslinks and no free sulfur to form additional ones, hence, “… if any links are broken down, a seemingly unvulcanized rubber results. …” The access of air under the reclaiming conditions used in our work would certainly be limited, and the highly plastic stocks obtained are to be expected in the light of the reference cited. Finally, van Amerongen concludes that in the absence of oxygen, it is inadvisable to use tetramethylthiuram disulfide vulcanizates where thermal stability is important. Mercaptobenzothiazole and rubber/sulfur types did not show any very significant differences in plasticization. (2) Considerable increases in zinc sulfide resulted in all cases, even when free sulfur was virtually removed before reclaiming, and in the latter instance there appears to be a reduction in rubber combined sulfur. In general, the changes are in line with those reported elsewhere in the reversion of natural and Butyl vulcanizates. (3) In all reclaims made, the ratio of sulfur in the chloroform-insoluble rubber to that in the soluble portion is very much lower than that previously published elsewhere. The comparison is not necessarily sound since the products tested are not technical reclaims, and generally the chloroform extracts were of a low order. (4) Under the highly reverting thermal conditions employed in this work, plasticization was generally inferior. This perhaps supports the theory that reclaiming is essentially a depolymerization process associated with traces of oxygen. The line of demarcation between reclaiming and reversion is by no means well defined. Since reclaiming treatments are normally much more severe than those needed to induce the characteristics of reversion, it may well be that reversion is only one factor in the mechanism of reclaiming, but it is a factor which cannot be ignored in any comprehensive consideration of devulcanization.

Studies of the Heat Deterioration of Specially Prepared Natural Rubber Vulcanizates

1954 ◽  
Vol 27 (2) ◽  
pp. 459-467
Author(s):  
Donald J. Metz ◽  
Robert B. Mesrobian
Keyword(s):  
Natural Rubber ◽  
Elevated Temperatures ◽  
Experimental Methods ◽  
Oxygen Absorption ◽  
Cross Linking ◽  
Vulcanized Rubber ◽  
Chemical Agents ◽  
Complex Process ◽  
Cross Linkage ◽  
Natural Rubber Vulcanizates

Abstract In 1949, Flory, Rabjohn, and Shaffer presented an article describing the dependence of the elastic properties of vulcanized rubber on the degree of cross-linking. In order to prepare rubber vulcanizates characterized by known degrees of cross-linkage recently developed, disazodicarboxylate vulcanizing reagents were employed. These reagents react quantitatively with rubber, one cross-linkage being introduced for each molecule of the reagent. Whereas the conventional vulcanization of rubber with sulfur and accelerators is a complex process and it does not appear possible at the present time to specify the exact number of cross-linkages present in sulfur vulcanizates, the use of disazodicarboxylate vulcanizing reagents presents an opportunity to investigate the changes that occur in the physical properties of vulcanized rubber, characterized by known degrees of cross-linkage, on exposure to oxygen at elevated temperatures. Furthermore, the effect of heat deterioration of various chemical agents commonly employed in sulfur vulcanization recipes may be investigated in a unique way by incorporating such chemical agents in the free state into natural rubber previously vulcanized by disazodicarboxylate reagents. Recent studies of the deterioration of rubber vulcanizates at elevated temperatures have been reported by several workers. In this article, the experimental methods employed to study heat deterioration involve measurements of oxygen absorption, stress relaxation, and changes of 100 per cent modulus of natural rubber vulcanized to known extents of cross-linkage by decamethylene-dismethyl azodicarboxylate.

Dependence of Tensile Strength of Vulcanized Rubber on the Degree of Cross-Linking

1950 ◽  
Vol 23 (1) ◽  
pp. 27-43
Author(s):  
Paul J. Flory ◽  
Norman Rabjohn ◽  
Marcia C. Shaffer
Keyword(s):  
Tensile Strength ◽  
Natural Rubber ◽  
Chain Scission ◽  
General Character ◽  
Cross Linking ◽  
Vulcanized Rubber ◽  
Relationship Of ◽  
The Relationship ◽  
Considerable Detail ◽  
Proportionality Relationship

Abstract The suitability of disazodicarboxylates as quantitative cross-linking agents for the preparation of rubber vulcanizates of known degrees of cross-linking has been emphasized previously. In a recent paper we have presented the results of an investigation on the dependence of the equilibrium force of retraction on the elongation and degree of cross-linking of rubber and GR-S vulcanized with these compounds. The present paper reports an extension of these investigations of the relationship of physical properties of rubberlike materials to their network structure. Specifically, the tensile strength of azo vulcanized natural rubber has been explored as a function of the degree of cross-linking and of the extent of modification of the chain units. The tensile strengths of natural rubber specimens vulcanized to various extents using sulfur alone or sulfur in conjunction with various accelerators have been investigated in considerable detail recently by Gee, who has emphasized the critical dependence of the tensile strength on the degree of cross-linking. Values for the latter quantity, however, were deduced indirectly from the equilibrium force of retraction using the simple proportionality relationship between force of retraction and degree of cross-linking afforded by the theory of rubber elasticity. This relationship is known to be only approximately valid. Furthermore, the effects on the force of retraction of chain scission, which doubtless accompanied some of the vulcanizations to a considerable degree, were disregarded. For these reasons, Gee's values for the degrees of cross-linking occurring in his vulcanizates are only approximate estimates, and in a few cases they may be seriously in error. Nevertheless, the general character of the relationship between tensile strength and degree of cross-linking which he obtained is confirmed by our results on rubber samples quantitatively cross-linked with measured proportions of decamethylene-dismethyl azodicarboxylate.

Cross-Linking in Natural-Rubber Vulcanizates

1953 ◽  
Vol 26 (4) ◽  
pp. 741-758 ◽  
Author(s):  
H. E. Adams ◽  
B. L. Johnson
Keyword(s):  
Molecular Weight ◽  
Natural Rubber ◽  
Cross Linking ◽  
Cross Link ◽  
General Validity ◽  
Tetramethylthiuram Disulfide ◽  
Cross Links ◽  
The Cross ◽  
Natural Rubber Vulcanizates ◽  
The Relationship

Abstract Recently, a method for measuring the average number of cross-links per chain of vulcanized polymer has been developed. It is possible to calculate the degree of cross-linking of the vulcanizate from its amount of swelling in a solvent such as benzene. This method was used by Flory to study the effect of primary molecular weight on the cross-linking of Butyl vulcanizates. An evaluation of the general validity of the method was ascertained by using quantitative cross-linking agents (diazodicarboxylates) to prepare vulcanizates of natural rubber and GR-S. Bardwell and Winkler have also used this technique to study the relationship between the degree of cross-linking and the force of retraction at 300 per cent elongation of GR-S latex vulcanized with potassium persulfate. The formation of cross-linking during the vulcanization by sulfur of several polymers has also been investigated. Gee has compared the formation of cross-linking in natural rubber vulcanizates with the amount of combined sulfur. Carbon-to-carbon cross-links were believed to be formed in a nonsulfur tetramethylthiuram disulfide (TMTD) cure. A similar study of Butyl rubber vulcanizates, cured with sulfur-TMTD, indicates that disulfide cross-links are formed. Scott and Magat have estimated that eight sulfur atoms are associated with each cross-link in Russian SK (sodium polybutadiene). This investigation was undertaken to extend Gee's study on the correlation of the cross-linking of natural-rubber vulcanizates with the amount of combined sulfur.

Thermal Degradation of Unvulcanized and Vulcanized Rubber in a Vacuum

1957 ◽  
Vol 30 (1) ◽  
pp. 93-111 ◽  
Author(s):  
Sidney Straus ◽  
S. L. Madorsky
Keyword(s):  
Thermal Degradation ◽  
Natural Rubber ◽  
Atmospheric Pressure ◽  
Average Molecular Weight ◽  
Degradation Process ◽  
Extensive Study ◽  
Vulcanized Rubber ◽  
Volatile Products ◽  
History Of ◽  
Cis And Trans

Abstract The history of distillation of rubber under various conditions of temperature, pressure, and atmosphere goes back more than a century. As far back as 1860, Williams distilled rubber in an iron retort at relatively low temperatures and obtained some 5 per cent of crude isoprene. In 1922, Staudinger and Fritschi distilled rubber at 275° to 320° C at 0.1- to 0.3-mm. pressure and obtained 3.1 per cent of isoprene. In 1926 Staudinger and Geiger distilled rubber below 300° C at ordinary pressure in an atmosphere of carbon dioxide and obtained 4.3 per cent of crude isoprene. Distillation of rubber at higher temperatures and under atmospheric pressure yielded as much as 58 per cent of isoprene. In addition to isoprene, dipentene and higher terpene compounds were also identified in the distillation products of natural rubber. More recently, distillations of pure synthetic polyisoprene (a mixture of cis- and trans-polyisoprene), purified natural rubber (cis-polyisoprene), and purified gutta hydrocarbon (trans-polyisoprene) were carried out by the present authors in a vacuum under conditions of molecular distillation. The volatile products were fractionated and analyzed both qualitatively and quantitatively, using the mass spectrometer for the lighter fractions. The volatiles consisted of about 3 to 4 per cent of isoprene and 13 to 20 per cent of dipentene, the rest being large terpene fragments of average molecular weight of about 600. The present paper describes an investigation of the effects of various additions to natural rubber, with or without subsequent vulcanization, on the degradation process during pyrolysis in a vacuum, with the view that such a study might throw some light on the structure of vulcanized rubber. In addition to pyrolysis, a study was also made with unvulcanized and vulcanized rubber of the rates and activation energies of thermal degradation in a vacuum, using techniques and apparatus that were previously developed by the authors in connection with an extensive study of thermal degradation of a number of polymers.

METHOD TO VULCANIZE NATURAL RUBBER FROM MEDIUM AMMONIA LATEX BY USING GLUTARALDEHYDE

2012 ◽  
Vol 85 (4) ◽  
pp. 565-575 ◽  
Author(s):  
Jobish Johns ◽  
Charoen Nakason ◽  
Anoma Thitithammawong ◽  
Pairote Klinpituksa
Keyword(s):  
Natural Rubber ◽  
Natural Rubber Latex ◽  
Ammonium Hydroxide ◽  
Mechanical Analysis ◽  
Cross Linking ◽  
Mechanical And Thermal Properties ◽  
Rubber Latex ◽  
Vulcanized Rubber ◽  
Link Density ◽  
The Cross

ABSTRACT A novel and inexpensive method for vulcanizing natural rubber by using glutaraldehyde was introduced. The vulcanized rubber samples were prepared by adding various amounts of glutaraldehyde to medium ammonia natural rubber latex. Cross-linking reaction occurred only in the presence of ammonium hydroxide in natural rubber latex upon the addition of glutaraldehyde. Cross-linked rubber has been obtained by reacting natural rubber with pentane-1,5-diylidenediamine formed from the reaction between glutaraldehyde and ammonia. The vulcanized materials were characterized by mechanical analysis and thermogravimetry. The results revealed an improvement in mechanical and thermal properties by vulcanization. Activation energy of degradation has been calculated using the Horowitz-Metzger equation. The cross-link density of the vulcanized rubber was determined from swelling experiments in benzene. Fourier transform infrared spectroscopy has been employed to confirm the cross-linking reaction between rubber molecules. From the overall characterizations, natural rubber vulcanized with 12 mL of 10% glutaraldehyde exhibited better properties.

scholarly journals Blooming of Compounding Ingredients in Natural Rubber Compounds under Different Peroxide Loading

2019 ◽  
Vol 8 (4) ◽  
pp. 7027-7031
Keyword(s):  
Natural Rubber ◽  
Paraffin Wax ◽  
Dicumyl Peroxide ◽  
Curing Agent ◽  
Bending Vibration ◽  
Vulcanized Rubber ◽  
Rubber Compounds ◽  
Powdery Material ◽  
Zinc Diethyldithiocarbamate ◽  
Processing Aids

Rubber compounds normally shows blooming phenomena whereby a thin layer of powdery material or films and oils formed on the surface. These blooms are usually low molecular weight compounding ingredients such as curing agents, accelerator, processing aids and activators that migrated to the surface. Excessive blooming can degrade the vulcanized rubber and reduced its quality. It is therefore necessary to determine the compounding ingredients that bloomed in an effort to reduce the effect of blooming. This study was aimed at identifying the compounding ingredients that dominate the blooming process. Sulphur, paraffin wax and zinc diethyldithiocarbamate (ZDEC) with specific functions were added as compounding ingredients in natural rubber (SMR L). Dicumyl peroxide were added as the curing agent at several loadings. The rubber compounds were cured at 150oC in the presence of dicumyl peroxide as curing agent at several loadings. They were stored under room temperature for blooming to take place. Blooms were analysed using FTIR and EDX. EDX analysis detected the major element present in the blooms to be carbon at 53.5% abundance. Similarly, FTIR results produced high intensity of C-H band at 2916 cm-1 and 722 cm-1 which are due to stretching and bending vibration of C-H paraffinic. It was concluded that paraffin wax preceded sulphur and ZDEC in blooming of SMR L.

EFFECT OF ZINC DITHIOCARBAMATES AND THIAZOLE-BASED ACCELERATORS ON THE VULCANIZATION OF NATURAL RUBBER

2012 ◽  
Vol 85 (1) ◽  
pp. 120-131 ◽  
Author(s):  
Md. Najib Alam ◽  
Swapan Kumar Mandal ◽  
Subhas Chandra Debnath
Keyword(s):  
Mechanical Properties ◽  
Tensile Strength ◽  
High Performance Liquid Chromatography ◽  
Liquid Chromatography ◽  
Reaction Mechanism ◽  
Natural Rubber ◽  
High Performance ◽  
Binary Systems ◽  
Synergistic Activity ◽  
Tetramethylthiuram Disulfide

Abstract Several zinc dithiocarbamates (ZDCs) as accelerator derived from safe amine has been exclusively studied in the presence of thiazole-based accelerators to introduce safe dithiocarbamate in the vulcanization of natural rubber. Comparison has been made between conventional unsafe zinc dimethyldithiocarbamate (ZDMC) with safe novel ZDC combined with thizole-based accelerators in the light of mechanical properties. The study reveals that thiuram disulfide and 2-mercaptobenzothiazole (MBT) are always formed from the reaction either between ZDC and dibenzothiazyledisulfide (MBTS) or between ZDC and N-cyclohexyl-2-benzothiazole sulfenamide (CBS). It has been conclusively proved that MBT generated from MBTS or CBS reacts with ZDC and produces tetramethylthiuram disulfide. The observed synergistic activity has been discussed based on the cure and physical data and explained through the results based on high-performance liquid chromatography and a reaction mechanism. Synergistic activity is observed in all binary systems studied. The highest tensile strength is observed in the zinc (N-benzyl piperazino) dithiocarbamate-accelerated system at 3:6 mM ratios. In respect of tensile strength and modulus value, unsafe ZDMC can be successfully replaced by safe ZDCs in combination with thiazole group containing accelerator.

Aging of Natural Rubber Vulcanizates in the Presence of Dithiocarbamates

1959 ◽  
Vol 32 (3) ◽  
pp. 739-747 ◽  
Author(s):  
J. R. Dunn ◽  
J. Scanlan
Keyword(s):  
Stress Relaxation ◽  
Natural Rubber ◽  
Protective Action ◽  
Dicumyl Peroxide ◽  
Vulcanized Rubber ◽  
Aging Properties ◽  
Photochemical Aging ◽  
Natural Rubber Vulcanizates

Abstract The thermal and photochemical aging of extracted dicumyl peroxide-, TMTD (sulfurless)- and santocure-vulcanized rubber, in presence of a number of metal and alkylammonium dithiocarbamates, has been investigated by measurements of stress relaxation. The dithiocarbamates have a considerable protective action upon the degradation of peroxide- and TMTD-vulcanizates, but they accelerate stress decay in santocure-accelerated vulcanizates. The reasons for this behavior are discussed. It is suggested that the excellent aging properties of unextracted TMTD vulcanizates are due to the presence of zinc dimethyldithiocarbamate formed during vulcanization.

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