Structural Features of Buna-S. Relation to Physical Properties

1945 ◽  
Vol 18 (1) ◽  
pp. 41-61
Author(s):  
A. R. Kemp ◽  
W. G. Straitiff
Keyword(s):  
Tensile Strength ◽  
Natural Rubber ◽  
Physical Properties ◽  
Structural Features ◽  
Polymer Chains ◽  
Polymerization Reaction ◽  
Gel Structure ◽  
Gutta Percha ◽  
Cross Linkage

Abstract The low tensile strength of Buna-S gum stocks is generally believed to be due to failure to obtain effective cross-linkage as the result of vulcanization with sulfur and accelerators. Combined with this is the complete absence of crystallization of Buna-S on stretching which, in the case of natural rubber, reinforces and strengthens the vulcanized gel structure. The absence of crystallization in Buna-S can be explained on the basis of nonsymmetry along the polymer chains. Strictly speaking, Buna-S is not a true polymer, for ozonolysis shows that the styrene units are not spaced evenly in the chain but are grouped together in some locations. Ozonolysis also has proved the presence of vinyl groups attached to the chain, resulting from the polymerization of butadiene in the 1,2 instead of the 1,4 position. These vinyl groups must be unevenly spaced along the chain, and mixed trans and cis isomers must be present. Figure 1 illustrates the chemical units present in Buna-S, rubber, and gutta-percha hydrocarbons. In a Buna-S copolymer containing 24.5 per cent of styrene, there are six butadiene to one styrene units. It appears that about one butadiene in five polymerizes in the 1,2 position in the chain. It should be emphasized that, in Buna-S, ozonolysis has shown that no regular order exists in the location of A, B, and C units in the polymer. An entire lack of symmetry in the positioning of these units in the chain would be expected in view of the nature of the polymerization reaction.

Graft Polymers Derived from Natural Rubber

1956 ◽  
Vol 29 (1) ◽  
pp. 99-105 ◽  
Author(s):  
G. F. Bloomfield ◽  
F. M. Merrett ◽  
F. J. Popham ◽  
P. Mc L. Swift
Keyword(s):  
Tensile Strength ◽  
Natural Rubber ◽  
Methyl Methacrylate ◽  
Transfer Reaction ◽  
Polymer Chains ◽  
Vinyl Monomers ◽  
Grafted Polymer ◽  
Polymeric Chains ◽  
Graft Polymers ◽  
Direct Growth

Abstract Graft polymers result when vinyl monomers are polymerized in the presence of natural rubber, either in solution or as latex, and some of the polymeric chains become attached to the rubber molecules. The properties of the natural rubber can be widely modified according to the nature and the amount of the grafted polymer. The polymer-modified natural rubber appears to be produced by direct growth of polymer chains on to rubber molecules rather than by a transfer reaction involving the rubber. Graft polymers of styrene and methyl methacrylate with natural rubber can be compounded and cured to give light-colored articles of good tensile strength, and rubber-methyl methacrylate graft polymers have outstanding flex-cracking and fatigue resistance.

Statistical Lengths of Rubberlike Hydrocarbon Molecules

1943 ◽  
Vol 16 (3) ◽  
pp. 479-485
Author(s):  
Frederick T. Wall
Keyword(s):  
Natural Rubber ◽  
Physical Properties ◽  
Chemical Properties ◽  
Hydrocarbon Chain ◽  
Point Of View ◽  
Double Bonds ◽  
Gutta Percha ◽  
Cis And Trans ◽  
Trans Structure ◽  
And Chemical Properties

Abstract It has been known for some time that the pure hydrocarbons of balata (or gutta-percha) and natural rubber have the same chemical composition and chemical properties. Both balata and rubber appear to be polymers of isoprene, (C5H8)n, with the same degree of unsaturation. Their physical properties are sufficiently different, however, to make it clear that their structures must differ in some important respect. Since the molecules contain numerous double bonds, it has been suggested that rubber and balata are geometric isomers. Every fourth bond in a rubber or balata molecule is a double bond, so it follows that the possibilities for geometric isomerism are considerable. It was proposed by Meyer and Mark that natural rubber hydrocarbon has a structure for which the molecular chain is cis with respect to all of the double bonds. Balata (or gutta-percha) is then supposed to have a trans-structure throughout, this view having been verified by Fuller and Bunn. It is the purpose of the present paper to consider, from the point of view of recent theories of rubber elasticity, to what extent these structures explain the differences in physical properties. The method to be employed involves calculation of the root mean square lengths of the cis- and trans-structures, which, when compared to their maximum lengths, should give an indication of their extensibilities. In 1932 Eyring treated the problem of the average square length of a hydrocarbon chain. In the present paper a different derivation of Eyring's equation is given (for illustrative purposes), after which this derivation will be extended to the rubberlike molecules with double bonds.

Polybutadienes of Controlled Cis, Trans and Vinyl Structures

1959 ◽  
Vol 32 (2) ◽  
pp. 614-627 ◽  
Author(s):  
J. N. Short ◽  
G. Kraus ◽  
R. P. Zelinski ◽  
F. E. Naylor
Keyword(s):  
Tensile Strength ◽  
Low Temperature ◽  
Natural Rubber ◽  
Physical Properties ◽  
Abrasion Resistance ◽  
High Hardness ◽  
High Modulus ◽  
High Tensile Strength ◽  
Truck Tires ◽  
Wide Range

Abstract The physical properties of polybutadiene vulcanizates have been measured as a function of polymer microstructure. Although the over-all properties of any one polybutadiene are determined by the relative ratio of cis, trans and vinyl units in the polymer chain, marked changes in physical properties do not occur until a relatively pure configuration is approached or unless the raw polymer displays crystallinity. Thus, polybutadienes containing more than 85 per cent cis, trans or vinyl units are characteristically different from each other and the differences are accentuated as the isomeric forms approach 100 per cent of a given configuration. Polybutadiene of 95 per cent cis configuration displays very low heat generation and high resilience (equaling natural rubber in these properties) and excellent abrasion resistance. trans-Polybutadiene (90 per cent), a crystalline plastic in the raw state, becomes rubbery after vulcanization. Gum vulcanizates possess high tensile strength, and tread stocks display high modulus and tensile strength, high hardness and fair hysteresis properties. Vulcanizates of amorphous 94 per cent vinyl polybutadiene are characterized by fair tensile properties, low hysteresis, and poor low temperature properties. Crystalline syndiotactic polybutadiene, 70 per cent vinly, displays much higher gum and tread tensile strengths than its amorphous counterpart. Amorphous polybutadienes containing less than 70–80 per cent of any one configuration are generally similar in most properties, and resemble emulsion polybutadiene in many respects. The wide range of properties of the various polybutadienes makes them suitable for many applications. cis-Polybutadiene is an excellent tire rubber, which has given as much as 40 per cent greater abrasion resistance than natural rubber in passenger tire tests. Heavy duty 10:00 × 20 truck tires fabricated with a 1:1 blend of cis-polybutadiene and natural rubber in the treads have given slightly better abrasion ratings and lower running temperatures than control tires fabricated entirely from natural rubber. Amorphous 80 per cent cis-polybutadiene has been found to possess exceptionally good low temperature properties, far superior to present arctic-type unsaturated elastomers, trans-Polybutadienes by virtue of their high modulus, high tensile strength, and high hardness could be utilized in the preparation of hard rubber goods, floor tiles, and shoe soles. While none of these polybutadienes is yet available commercially, their unusual properties and potential applicability in many areas should lead to their manufacture in the future.

Effect of Carbon Black on Curing Behavior, Mechanical Properties and Viscoelastic Behavior of Natural Sponge Rubber-Based Nano-Composites

2012 ◽  
Vol 510-511 ◽  
pp. 532-539 ◽  
Author(s):  
M.A. Bashir ◽  
M. Shahid ◽  
R.A. Alvi ◽  
A.G. Yahya
Keyword(s):  
Mechanical Properties ◽  
Tensile Strength ◽  
Carbon Black ◽  
Natural Rubber ◽  
Physical Properties ◽  
Viscoelastic Behavior ◽  
Nano Composites ◽  
Curing Behavior ◽  
Auxetic Materials ◽  
Viscosity Variation

Natural rubber (polymer designation cis-1-4 polyisoprene, is obtained from the sap ("latex") of several rubber-yielding plants (e.g.,HeveaBrasiliensisandPartheniaargentatum) by coagulation with chemicals, drying, electrical coagulation, and other processes. Foamy or sponge structure of natural rubber (NR) is very useful in aerospace and as auxetic materials (exhibiting negative poisons ratio) for use in application of homeland security.The main aim of this research to estimate the influence of carbon black on mechanical properties, curing and viscosity variation behaviors of the natural rubber based composites. Different amounts of carbon black were used along with other fillers. The influence of carbon black on curing behavior and mechanicalproperties of natural rubber foams was investigated at different feedingratios of the carbon black. The physical properties of the foamed NRs were then measured as a function of carbon blacks content. The mechanical properties of the foamed NRs such as tensile strength,strength at break and modulus,were gradually increased with increasingcarbon black content whereas elongation decreasedat break.

Study of Cure Synergism of the Thiocarbamylsulfenamide-Dibenzothiazyl Disulfide Accelerator System in the Vulcanization of Natural Rubber

1983 ◽  
Vol 56 (4) ◽  
pp. 827-837 ◽  
Author(s):  
D. Pal ◽  
B. Adhikari ◽  
D. K. Basu ◽  
A. K. Chaudhuri
Keyword(s):  
Tensile Strength ◽  
Natural Rubber ◽  
Physical Properties ◽  
Structural Characterization ◽  
Crosslink Density ◽  
Synergistic Activity ◽  
Elongation At Break ◽  
Equimolar Concentration ◽  
Accelerator System

Abstract N-cyclopentamethylenethiocarbamyl-N′-cyclopentamethylenesulfenamide (CPTCS) and dibenzothiazyldisulfide (MBTS), as binary accelerators in a mixture have been found to provide significant mutual enhanced activity with regard to modulus, tensile strength, hardness, and elongation at break in the vulcanization of NR gum stocks. The synergistic activity of the CPTCS-MBTS system is very much dependent upon the accelerator ratios, concentration of sulfur and accelerator, as well as the temperature of vulcanization. Investigations carried out with the Monsanto rheometer also corroborate the above results. It is suggested that the synergism arises out of the interaction between CPTCS and MBTS which produces intermediate accelerators. N,N-Diethylthiocarbamyl-N′-cyclohexylsulfenamide (DETCS) in conjunction with MBTS, produces similar results in the vulcanization of NR. Structural characterization of the vulcanizates obtained at 140 and 160°C reveals that predominantly monosulfidic linkages are obtained with CPTCS or DETCS and MBTS combinations. The intermediate combinations, at near equimolar concentration of the two accelerators, exhibit maximum crosslink density. An attempt has been made to correlate physical properties with crosslink density as well as various types of crosslinks.

Effect of Degree of Elongation on Ozone Cracking of Rubbers

1959 ◽  
Vol 32 (1) ◽  
pp. 278-283
Author(s):  
Yu S. Zuev ◽  
S. I. Pravednikova
Keyword(s):  
Tensile Strength ◽  
Zinc Oxide ◽  
Natural Rubber ◽  
Butyl Rubber ◽  
Objective Method ◽  
Rubber Sample ◽  
Rate Of Growth ◽  
Gutta Percha ◽  
Effective Depth

Abstract It is known from the literature that there exists a socalled critical elongation at which disruption of the structure of rubbers under the influence of ozone is most severe. However, the available data concerning this problem are fairly contradictory. According to a number of statements the critical elongation is observed in the case of vulcanizates of natural rubber, but its estimation by different authors varies from 5 to 50%. Some authors consider that a critical elongation exists in the case of synthetic rubbers susceptible to attack by ozone, while others consider that no such characteristic exists. It is said that polychloroprene and butyl rubber do not possess this characteristic. However, none of these data can be regarded as reliable since in most cases ozone cracking of the rubbers was characterized by arbitrary methods, as a rule by the “degree of cracking” expressed by the number of marks. We have carried out a detailed investigation of the effect of the degree of elongation on ozone cracking of rubbers, the rate of growth of cracks being determined by an objective method based on the effective depth of the cracks calculated from the decrease of stress in the relaxed rubber sample when exposed to the action of ozone. The following rubbers—NK, SKS, neurite, SKN, and SKB were investigated in standard formulas, at optimum true tensile strength. Gutta-percha (elastic vulcanizate) and butyl rubber compositions in phr were: gutta-percha 100, MBT 0.8, sulfur 5; butyl rubber 100, stearine 3, MBT 0.65, thiuram disulfide 1.3, zinc oxide 5, sulfur 2.

Rupture of Rubber. IV. Tear Properties of Vulcanizates Containing Carbon Black

1957 ◽  
Vol 30 (2) ◽  
pp. 584-595
Author(s):  
H. W. Greensmith
Keyword(s):  
Tensile Strength ◽  
Carbon Black ◽  
Natural Rubber ◽  
Physical Properties ◽  
Different Types ◽  
Tear Properties

Abstract A method of studying tear behavior has been described in a previous paper (Part III, subsequently referred to as III), and was illustrated by results obtained with natural rubber and GR-S gum vulcanizates, i.e., vulcanizates containing no added ingredients apart from those necessary for vulcanization. In the present paper the method is applied to vulcanizates containing different types of carbon black. Vulcanizates of this type are of considerable interest, since the carbon black can appreciably modify physical properties such as stiffness and tensile strength and can induce pronounced anisotropy in tearing, referred to by Buist as knotty tearing.

Preparation and Vulcanization of Unsaturated Acrylic Elastomers

1949 ◽  
Vol 22 (4) ◽  
pp. 966-981
Author(s):  
W. C. Mast ◽  
C. H. Fisher
Keyword(s):  
Tensile Strength ◽  
Physical Properties ◽  
Vinyl Ether ◽  
Organic Solvents ◽  
Ethyl Acrylate ◽  
The Other ◽  
Acrylic Copolymers ◽  
Cross Linkage

Abstract Ethyl acrylate was copolymerized with small proportions of eleven dienes, eleven polyolefinic esters, and six polyolefinic ethers in an attempt to prepare olefin-containing acrylic elastomers that would vulcanize readily, yielding products having improved rubbery characteristics. In general, the resulting copolymers were insoluble in organic solvents, presumably because of cross-linkage. Acrylonitrile and dodecanethiol appeared beneficial in the copolymerization of ethyl acrylate with polyolefinic esters, but of questionable value in the diene polymerizations. The best vulcanizates from the standpoint of tensile strength and elongation were obtained from an ethyl acrylate-acrylonitrile-vinyl ether copolymer. Some preparations of this copolymer, however, had a tendency to pit and bubble during vulcanization. Isoprene, piperylene, and 2,3-dimethylbutadiene were more suitable for preparing vulcanizable ethyl acrylate copolymers than the other dienes studied; their vulcanizates had moderately high tensile strengths and elongations. Some of the dimethylbutadiene-ethyl acrylate copolymers were soluble. Crotyl acrylate and geranyl acrylate, when copolymerized with ethyl acrylate, yielded copolymers that gave vulcanizates having moderately high tensile strengths and elongations ranging from 300 to 400 per cent. The physical properties of the vulcanizates prepared from unsaturated acrylic copolymers were not superior to those of the chloropropyl acrylate and chloroethyl vinyl ether products described previously.

Physical Properties of Diene Polymers. Effects of Side Vinyl Groups and Other Structural Features

1948 ◽  
Vol 21 (3) ◽  
pp. 596-604
Author(s):  
James D. D'Ianni
Keyword(s):  
Tensile Strength ◽  
Natural Rubber ◽  
Physical Properties ◽  
Molecular Structures ◽  
Acid Oxidation ◽  
Similar Data ◽  
Molecular Weight Range ◽  
Brittle Point ◽  
Organometallic Catalyst ◽  
Butadiene Styrene

Abstract The detailed molecular structures of natural rubber, emulsion polyisoprene, polyisoprene prepared with an organometallic catalyst, and sodium polyisoprene were studied by comparison of data available from infrared absorption spectra, perbenzoic acid titration, refractive index, density, iodine number, chromic acid oxidation, and hydrochlorination. These polymers showed decreasing amounts of 1,4-addition content in the order listed. Similar data were collected where possible for emulsion polybutadiene, polybutadiene prepared with an organometallic catalyst, and potassium polybutadiene (Buna-85), as well as for GR-S and corresponding butadiene-styrene copolymers prepared with an organometallic catalyst and with sodium. These two groups also showed decreasing 1,4-addition content in the order listed. Correlation of structure inferred from the above data with physical properties of corresponding tread stock vulcanizates indicated that for diene polymers with decreasing amount of 1,4-addition content the brittle point rose, the rebound value decreased, and the tensile strength increased, provided comparison was restricted to polymers of approximately the same molecular weight range made with the same monomer. Natural rubber occupied a unique position because it was substantially a linear high polymer with the cis-configuration around all the double bonds. For the butadiene-styrene 75/25 copolymers the brittle point rose with decreasing amount of 1,4-addition content, but no satisfactory correlation could be obtained for the tensile strength and the rebound value, probably because of the predominant effect of the phenyl side groups.

Oxidation of GR-S and Other Elastomers

1947 ◽  
Vol 20 (3) ◽  
pp. 747-759
Author(s):  
John O. Cole ◽  
James E. Field
Keyword(s):  
Tensile Strength ◽  
Natural Rubber ◽  
Physical Properties ◽  
Experimental Methods ◽  
Chain Scission ◽  
Cross Linking ◽  
Antioxidant Action ◽  
Mechanism Of Oxidation ◽  
Natural Rubber Vulcanizates

Abstract The effect of heat aging on the physical properties of an elastomer is generally considered the result of oxidation, which produces both chain scission and cross-linking in the polymer. Early in the development of GR-S, a marked difference in the aging of GR-S and natural rubber vulcanizates was observed. From the effect of aging on hardness, tensile strength, modulus, and elongation it appeared that cross-linking occurred more rapidly than chain scission with GR-S, but the reverse was true with natural rubber. The work reported here was undertaken to provide a better understanding of the differences in aging of GR-S and natural rubber and to introduce new experimental methods for studying the mechanism of oxidation and antioxidant action in elastomers.

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