Mineral Sulfide as Index of Disulfide Cross-Bonding

1947 ◽  
Vol 20 (3) ◽  
pp. 649-663 ◽  
Author(s):  
C. M. Hull ◽  
S. R. Olsen ◽  
Wesley G. France
Keyword(s):  
Natural Rubber ◽  
Cross Linking ◽  
Diallyl Disulfide ◽  
Double Bonds ◽  
Metal Soap ◽  
Sulfide Production ◽  
Sulfur Vulcanization

Abstract 1. The mechanism proposed by Armstrong, Little, and Doak to explain sulfur vulcanization in the presence of metal soap was investigated in polyprene and simpler systems from the viewpoint of the inorganic sulfide produced and, in the case of polyprenes, of the accompanying modulus. 2. Dodecanethiol was found to react with sulfur and zinc soap to produce inorganic sulfide equivalent to the oxidation of 80 to 100 per cent of the thiol to disulfide ; with excess thiol substantially quantitative conversion of sulfur or of zinc soap to inorganic sulfide can be obtained. 3. Several simple olefins were found to react readily with sulfur and zinc soap under vulcanizing conditions. The reaction is promoted by M.B.T. On the basis of the mechanism assumed, the inorganic sulfide formed is sufficient to indicate extensive conversion of the olefin to a substituted diallyl disulfide. 4. Assuming the validity of the proposed mechanism, inorganic sulfide production indicates substantial disulfide cross-linking between α-carbon atoms in conventional cures with natural rubber, and appreciable, though relatively less, cross-bonding of this type in the case of GR-S. The smaller extent of this type of cross-linking with GR-S is believed to result from greater tendency on the part of this elastomer to add the intermediate mercapto compound to double bonds, as proposed in the first paper of this series.

The Diamagnetic Anisotropy of Natural and Synthetic Rubbers

1952 ◽  
Vol 25 (4) ◽  
pp. 759-766
Author(s):  
Elizabeth Weir Toor ◽  
P. W. Selwood
Keyword(s):  
Magnetic Anisotropy ◽  
Natural Rubber ◽  
Degree Of Crystallinity ◽  
Cross Linking ◽  
Double Bonds ◽  
Chain Molecules ◽  
Diamagnetic Anisotropy ◽  
Actual Degree ◽  
Long Chain ◽  
Natural And Synthetic

Abstract The change in anisotropy with elongation has been found for natural rubber and for several synthetic rubbers. Unsaturated rubbers have a large principal susceptibility perpendicular to the direction of stretching, because of the presence of olefinic double bonds. The differences between natural rubber and polybutadiene are attributed to the presence of unsaturated side-groups caused by 1,2-addition in polybutadiene. Probably the magnetic anisotropy of these rubbers depends, not on the actual degree of crystallinity of the rubbers, but on the ability of the long-chain molecules to align themselves parallel to the direction of stretching. Therefore the changes in anisotropy with stretching are large when there is no cross-linking, and small when cross-linking occurs to any large extent. Saturated rubbers have an anisotropy opposite in sign to that of unsaturated rubbers. This must be caused by the broadening of electronic orbits perpendicular to the direction of stretching. Apparently methyl side-groups cause such a broadening of electronic orbits in polyisobutylenes, an effect much greater than the similar effect in polyethylene.

Sulfur Vulcanization and Oxidative Aging of Epoxidized Natural Rubber

1985 ◽  
Vol 58 (2) ◽  
pp. 243-257 ◽  
Author(s):  
I. R. Gelling ◽  
N. J. Morrison
Keyword(s):  
Thermal Decomposition ◽  
Natural Rubber ◽  
Ring Opening ◽  
Double Bonds ◽  
Oxidative Aging ◽  
The Poor ◽  
Ring Opening Reactions ◽  
Sulfur Vulcanization ◽  
Subsequent Effect ◽  
Acid Catalyzed

Abstract 1. Vulcanization by sulfur alone is faster and more efficient for ENR than for NR because isolated double bonds react more rapidly than contiguous double bonds. This vulcanization may be accelerated by sodium carbonate, which also protects the cured rubber against the subsequent effect of oxidative aging, and the scorch time may be increased by the addition of CTP. 2. The CBS-accelerated sulfur vulcanization of ENR is essentially similar to that of NR, although ENR reacts with MBT formed during the process. 3. The poor aging of sulfur vulcanizates of ENR is due to acid-catalyzed ring-opening reactions of the epoxide groups with the formation of ether crosslinks. The acids are produced by the thermal decomposition of oxidized sulfides. 4. The addition of a suitable base confers excellent resistance to oxidative aging upon conventional, semi-efficient, and efficient vulcanizates of ENR.

PREVULCANIZATION OF NATURAL RUBBER LATEX BY UV TECHNIQUES: A PROCESS TOWARDS REDUCING TYPE IV CHEMICAL SENSITIVITY OF LATEX ARTICLES

2010 ◽  
Vol 83 (2) ◽  
pp. 133-148 ◽  
Author(s):  
S. Schlögl ◽  
A. Temel ◽  
R. Schaller ◽  
A. Holzner ◽  
W. Kern
Keyword(s):  
Natural Rubber ◽  
Addition Reaction ◽  
Bond Cleavage ◽  
Natural Rubber Latex ◽  
Innovative Technology ◽  
Cross Linking ◽  
Latex Films ◽  
Photochemical Process ◽  
Sulfur Vulcanization ◽  
Ene Addition

Abstract The UV induced prevulcanization of natural rubber (NR) latex provides an innovative technology for an efficient cross-linking. In the photochemical process, a selected photoinitiator and a poly-functional thiol are added to the NR latex. Free radicals (bond cleavage of the photoinitiator) are generated due to UV irradiation and cross-linking of the latex particles is then achieved by a thiol-ene addition reaction. The thiol-ene addition reaction in NR films is characterized with Fourier transform infrared and Raman spectroscopy. To achieve the prevulcanization of latex, both a thin film photoreactor and a falling film photoreactor are applied. Solid latex films are then produced by conventional dipping of the precured NR latex. The NR latex films are distinguished by good skin compatibility due to the absence of sensitizing or irritating processing agents which are used in conventional sulfur vulcanization. Moreover UV cross-linked films display excellent physical properties as well as high aging stabilities. Further advantages of the new technology compared to conventional sulfur vulcanization are low energy consumption together with short vulcanization times.

Chlorination of Natural Rubber in Solution with Gaseous Chlorine

1953 ◽  
Vol 26 (4) ◽  
pp. 902-911 ◽  
Author(s):  
C. S. Ramakrishnan ◽  
D. Raghunath ◽  
J. B. Pande
Keyword(s):  
Double Bond ◽  
Natural Rubber ◽  
Cyclization Reaction ◽  
Double Bonds ◽  
Chlorine Atoms ◽  
Reaction Stage ◽  
Stage 1 ◽  
Additive Reaction

Abstract The chlorination of rubber solutions by gaseous chlorine was followed by isolating the partially chlorinated products and preparing their ozonides. The ozonides were hydrolyzed, and the acids and aldehydes formed on hydrolysis were determined. By a comparison with the amounts of acids and aldehydes obtained from ozonides of unreacted rubber, the amount of residual isoprenic double bonds present was found. The loss of double bonds attending the introduction of chlorine atoms into the molecule of rubber indicates four definite stages in chlorination : (1) initial substitutive attack by chlorine, with concomitant cyclization, resulting in a loss of one double bond between two isoprenic units, (2) substitution, (3) additive reaction, and (4) essentially substitution. Chlorination of aged rubber solutions differs from the above in that the cyclization reaction (stage 1) seems to be absent.

scholarly journals Physicochemical, Thermomechanical, and Swelling Properties of Radiation Vulcanised Natural Rubber Latex Film: Effect of Diospyros peregrina Fruit Extracts

2013 ◽  
Vol 2013 ◽  
pp. 1-8
Author(s):  
Kazi Md Zakir Hossain ◽  
Nashid Sharif ◽  
N. C. Dafader ◽  
M. E. Haque ◽  
A. M. Sarwaruddin Chowdhury
Keyword(s):  
Natural Rubber ◽  
Natural Rubber Latex ◽  
Tensile Modulus ◽  
Decomposition Temperature ◽  
Latex Film ◽  
Cross Linking ◽  
Rubber Latex ◽  
Swelling Properties ◽  
Fruit Extracts ◽  
Control Film

A range of radiation vulcanised natural rubber latex (RVNRL) films were prepared using various concentrations of aqueous extracts of mature Diospyros peregrina fruit, which acted as a cross-linking agent. The surface of the RVNRL films exhibited an aggregated morphology of the rubber hydrocarbon with increasing roughness due to increasing fruit extract contents in the latex. An improvement in tensile strength, tensile modulus, and storage modulus of RVNRL films was observed with the addition of fruit extracts compared to the control film due to their cross-linking effect. The glass transition (Tg) temperature of all the RVNRL films was found to be at around −61.5°C. The films were also observed to be thermally stable up to 325°C, while the maximum decomposition temperature appeared at around 375°C. The incorporation of fruit extracts further revealed a significant influence on increasing the crystallinity, gel content, and physical cross-link density of the RVNRL films.

Radical Mechanisms in Saturated and Olefinic Systems. II. Disubstitutive Carbon-Carbon Cross-Linking by Tertiary Alkoxy Radicals in Isoprenic Olefins and Rubber

1951 ◽  
Vol 24 (4) ◽  
pp. 777-786
Author(s):  
E. H. Farmer ◽  
C. G. Moore
Keyword(s):  
Natural Rubber ◽  
Cross Linking ◽  
Chain Molecules ◽  
Alkoxy Radicals ◽  
Full Extent ◽  
Carbon Chains ◽  
Butyl Peroxide ◽  
High Degree ◽  
Vulcanization Process

Abstract The high degree of dehydrogenation effected by tert.-butoxy radicals at the α-methylenic groups of olefins enables these radicals to be used for the carbon-to-carbon cross-linking of unsaturated carbon chains, and especially of the polyisoprenic chains of natural rubber. Such cross-linking amounts to a vulcanization process in which the connecting links between chain molecules are just C—C bonds, which may be expected to have appropriate attributes. An examination has first been made of the cross-linking produced by tert.- butoxy radicals (from di-tert.-butyl peroxide) at 140° between the short iso-prenic chains in 1-methylcyclohexene, 4-methylhept-3-ene, 2,6-dimethylocta-2, 6-diene, and digeranyl. Cross-linking proceeds efficiently in each case, and the points of union in these isoprene units which become directly joined are not confined to original α-methylenic carbon atoms. Where the reagent radicals are in considerable deficit, e.g., one per two or three of the isoprene units present, those olefin molecules which are attacked become linked together mostly by single unions to form aggregates containing two, three or four molecules; but in the tetraisoprenic olefins the extent to which more than one union is formed between some of the directly linked molecules becomes appreciable. In natural rubber, cross-linking occurs smoothly and to nearly the full extent corresponding to the (in practice restricted) proportion of peroxidic reagent employed. Good vulcanizates can be so obtained in which the tensile stength is found to increase towards a maximum and then to decline rapidly as the degree of cross-linking steadily increases. Thus to obtain vulcanizates of the optimum physical characteristics, the degree of cross-linking must be suitably chosen. The role of the peroxidic reagent is almost entirely non-additive and non-degradative.

scholarly journals Modulus of Natural Rubber Crosslinked by Dicumyl Peroxide. I. Experimental Observations

1972 ◽  
Vol 45 (5) ◽  
pp. 1388-1402 ◽  
Author(s):  
L. A. Wood ◽  
G. W. Bullman ◽  
G. E. Decker
Keyword(s):  
Glass Transition ◽  
Natural Rubber ◽  
General Relation ◽  
Quantitative Measure ◽  
Cross Linking ◽  
Rigid Sphere ◽  
Dicumyl Peroxide ◽  
Shear Creep ◽  
Rubber Sheet ◽  
Creep Modulus

Abstract Natural rubber mixed with varying amounts of dicumyl peroxide are crosslinked by heating 120 min at 149° C. The quantitative measure of cross- linking was taken as the amount fp of decomposed dicumyl peroxide, the product of p, the number of parts added per hundred of rubber and f the fraction decomposed during the time of cure. The shear creep modulus G was calculated from measurements of the indentation of a flat rubber sheet by a rigid sphere. The glass transition temperature Tg, was raised about 1.2° C for each part of decomposed dicumyl peroxide. Above (Tg+12) the modulustemperature relations were linear with a slope that increased with increasing crosslinking. The creep rate was negligible except near the glass transition and at low values of fp. Values of G, read from these plots at seven temperatures, were plotted as a function of fp. The linearity of the two plots permits the derivation of the general relation: G=S(fp+B)T+H(fp+B)+A where A, B, H, and S are constants. The lines representing G as a function of fp at each temperature all intersected near the point, fp=0.45 phr, G=2.70 Mdyn cm−2(0.270 MN  m−2). . The constants were evaluated as A=2.70 Mdyn cm−2,B=−0.45 phr, S=5.925×10−3 Mdyn cm−2(phr)−1 K−1 and H=0.0684(Mdyn cm−2) (phr)−1. This equation represented satisfactorily all the data obtained at temperatures from —50 to +100° C for values of fp from about 1 to 24 phr.

Effect of Sulfur and Dicumyl Peroxide on Vulcanization of Natural Rubber with Tetramethylthiuram Disulfide and Zinc Oxide

1970 ◽  
Vol 43 (6) ◽  
pp. 1294-1310 ◽  
Author(s):  
S. P. Manik ◽  
S. Banerjee
Keyword(s):  
Zinc Oxide ◽  
Stearic Acid ◽  
Natural Rubber ◽  
Reaction Mechanisms ◽  
Elemental Sulfur ◽  
Initial Rate ◽  
Dicumyl Peroxide ◽  
Tetramethylthiuram Disulfide ◽  
Sulfur Vulcanization ◽  
Salient Features

Abstract The salient features of both non-elemental sulfur vulcanization by TMTD and elemental sulfur vulcanization promoted by TMTD both in presence and absence of ZnO and stearic acid have been studied. TMTD increases the rate of DCP decomposition and lowers the crosslinking maxima due to DCP depending on its concentration. However, with higher amounts of TMTD the initial rate of crosslinking is increased with the increased amount of TMTD, while crosslinking maxima are still lowered due to reversion. ZnO or ZnO-stearic acid, however, seems to alter the entire course of the reaction. Both the crosslink formation and TMTD decomposition are much higher in presence of ZnO or ZnO-stearic acid, but stearic acid seems to have no effect. The reaction mechanisms for TMTD accelerated sulfuration in absence and presence of ZnO have also been studied.

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.

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