Unusual stress-strain properties of natural rubber vulcanizates with high primary molecular weight

1985 ◽  
Vol 13 (1) ◽  
Author(s):  
K. Ono ◽  
A. Kato ◽  
K. Murakami
Keyword(s):  
Molecular Weight ◽  
Natural Rubber ◽  
Stress Strain ◽  
Natural Rubber Vulcanizates ◽  
Unusual Stress

Determination of Degree of Crosslinking in Natural Rubber Vulcanizates. Part III

1961 ◽  
Vol 34 (1) ◽  
pp. 279-289 ◽  
Author(s):  
L. Mullins
Keyword(s):  
Molecular Weight ◽  
Natural Rubber ◽  
Physical Properties ◽  
Intrinsic Viscosity ◽  
Stress Strain ◽  
Strain Behavior ◽  
Equilibrium Volume ◽  
Volume Swelling ◽  
Natural Rubber Vulcanizates

Abstract The two previous parts of this series described an attempt to relate the physical properties of natural rubber vulcanizates to their network structure. The first established an empirical relationship between the stress-strain behavior of highly swollen natural rubbers in simple extension, and their equilibrium volume swelling in n-decane. It also examined the effect of changes in initial molecular weight of the unvulcanized masticated rubber on these properties, and an empirical correction making allowance for network flaws due to chain-segments terminated by a crosslink at only one end was obtained. The second part gave measurements of the equilibrium volume swelling and the intrinsic viscosity before vulcanization for each of a range of natural rubber vulcanizates which had been prepared by a method which enabled the number of crosslinks to be determined by chemical analysis. These measurements permitted a comparison to be made between (i) the chemical estimate of the actual number of crosslinks introduced and (ii) the number derived from the data on equilibrium volume swelling, by means of the empirical relations derived in Part I. For this purpose, an assumption was made that the stress-strain behavior of highly swollen rubbers was in accord with the predictions of the statistical theory. Recent studies of both the stress-strain properties of highly swollen rubbers and the method of determining number-averaged molecular weight from intrinsic viscosity measurements have provided an improved basis for the quantitative determination of the degree of crosslinking from measurements of physical properties. The results described in Parts I and II of this series are reinterpreted here to take account of both of these developments ; in addition, the effect of the introduction of a correction for a network defect equivalent to chain entanglements is examined.

Influence of Crosslink Characteristics Induced by Aromatic-Based Antioxidants on the Swelling and Stress-Strain Behavior of Natural Rubber Vulcanizates

2003 ◽  
Vol 76 (2) ◽  
pp. 334-347 ◽  
Author(s):  
Tarek M. Madkour ◽  
Rasha A. Azzam
Keyword(s):  
Natural Rubber ◽  
Crosslinking Agent ◽  
Oxidative Degradation ◽  
Thermal Oxidative Degradation ◽  
Stress Strain ◽  
Strain Behavior ◽  
Strain Induced Crystallization ◽  
Elastomeric Chains ◽  
Natural Rubber Vulcanizates ◽  
Induced Crystallization

Abstract Stress-strain measurements were performed on dry and swollen natural rubber vulcanizates prepared using both sulfur as the crosslinking agent and aromatic-based bound antioxidants acting as a second crosslinking agent. The aromatic-based antioxidants were synthesized and analyzed spectroscopically in order to relate the final behavior of the vulcanizates to the nature of the crosslink characteristics. The anomalous upturn in the modulus values of these networks in response to the imposed stress was shown to persist in the dry as well as the swollen state. Since the swollen elastomeric chains cannot undergo a strain-induced crystallization, the abnormal upturns in the modulus values in an absence of a filler were explained on the basis of the limited extensibility of the short chains of networks prepared using two different crosslinking agents in line with earlier modeling predictions. Remarkably, the swelling experiments revealed the increase in the crosslink density of the networks in the early stages of the thermal oxidative degradation procedure indicating a post-cure of the chemically bound antioxidants to the elastomeric chains, which incidentally corresponds to a maximum in the modulus values of the networks. The rheological and other mechanical properties such as the hardness were shown not to have been affected as a result of the incorporation of the chemically bound antioxidants.

Extraction of Admixed Polymers from Natural Rubber Vulcanizates

1967 ◽  
Vol 40 (5) ◽  
pp. 1553-1559 ◽  
Author(s):  
W. Cooper ◽  
R. K. Smith
Keyword(s):  
Molecular Weight ◽  
Natural Rubber ◽  
Methyl Methacrylate ◽  
Continuous Extraction ◽  
High Molecular Weight Polymer ◽  
Molecular Weight Polymer ◽  
Considerable Uncertainty ◽  
Consequence Analysis ◽  
Natural Rubber Vulcanizates ◽  
Rate Of Extraction

Abstract Extraction by solvent of admixed poly(methyl methacrylate) or polystyrene from natural rubber vulcanizates is dependent on the crosslink density, the solvent, the molecular weight of the polymer, and the size of sample extracted. High molecular weight polymer is extracted very slowly, and in some cases several weeks of continuous extraction have been found necessary. The rate of extraction is increased, as would be expected, by solvents which swell the rubber strongly, and by increase in temperature of extraction. In some cases the vulcanization procedure degrades the polymer, while in others there is a possibility of cocrosslinking the rubber and polymer. Graft copolymers from rubber and methyl methacrylate or styrene possess similar characteristics when vulcanized. In consequence, analysis of the content of free homopolymer is subject to considerable uncertainty. In the analysis of these rubber and polystyrene mixtures by ozonolysis, polystyrene was found to be very susceptible to attack by ozone.

Behavior of Different Fractions of Purified Hevea Rubber during Vulcanization

1949 ◽  
Vol 22 (4) ◽  
pp. 994-999
Author(s):  
G. T. Verghese
Keyword(s):  
Molecular Weight ◽  
Natural Rubber ◽  
The Other ◽  
Stress Strain ◽  
Strain Behavior ◽  
Other Hand ◽  
The Difference

Abstract Considerable data on the vulcanization characteristics of molecular fractions of ordinary (unpurified) natural rubber are available. There is, on the other hand, little information of any systematic work on the vulcanization of purified rubber and of its fractions. Pummerer and Pahl vulcanized the sol and gel fractions obtained from purified Hevea rubber, and also the purified whole rubber. But apart from a statement that whole rubber vulcanized much faster than the two fractions obtained from it, no details have been published. Vulcanization of purified whole rubber and of its sol and gel fractions was studied also by Smith and Holt. They concluded that the difference which they observed in the stress-strain behavior of the fractions and whole rubber was due to differences in the rubber which persisted through vulcanization. The present paper deals with a study of the vulcanization characteristics of different fractions of purified rubber prepared by a method described in a previous paper. Also, for comparative purposes a similar study was made of the corresponding fractions of unpurified rubber. As the difference in molecular weight of some of the fractions obtained by the above method was rather small, a grouping of the fractions was made as follows :

scholarly journals RUBBER ELASTICITY AT LARGE DEFORMATION (II) STRESS-STRAIN BEHAVIOR OF NATURAL RUBBER VULCANIZATES

1976 ◽  
Vol 49 (8) ◽  
pp. 620-627 ◽  
Author(s):  
Hiroshi OKAMOTO ◽  
Junji FURUKAWA ◽  
Shinji INAGAKI
Keyword(s):  
Natural Rubber ◽  
Large Deformation ◽  
Rubber Elasticity ◽  
Stress Strain ◽  
Strain Behavior ◽  
Natural Rubber Vulcanizates

Stress Softening in Natural Rubber Vulcanizates. Part II. Stress Softening Effects in Pure Gum and Filler Loaded Rubbers

1966 ◽  
Vol 39 (4) ◽  
pp. 814-822 ◽  
Author(s):  
J. A. C. Harwood ◽  
L. Mullins ◽  
A. R. Payne
Keyword(s):  
Natural Rubber ◽  
Effective Strain ◽  
Hysteresis Loops ◽  
Local Orientation ◽  
Stress Strain ◽  
Stress Softening ◽  
Rubber Phase ◽  
Softening Process ◽  
Natural Rubber Vulcanizates

Abstract Considerable stress softening occurs in both gum and filler-loaded vulcanizates and when compared at the same stress the extent of softening is similar in both gum and filled vulcanizates. It thus appears that the softening process is mainly due to the rubber phase alone. Apparent differences between the stress—strain hysteresis loops of gum and filler-loaded vulcanizates are traced to an increase in the effective strain in the rubber phase resulting from the presence of black. This is discussed in Part I of this series. The mechanism of stress softening in gum vulcanizates is not well understood. Possible sources include (1) breaking and remaking of crosslinks during extension, (2) residual local orientation of network chains persisting after recovery, and (3) breaking of network chains.

The Crystallization of Vulcanized Natural Rubber at Low Temperatures

1952 ◽  
Vol 25 (3) ◽  
pp. 397-411 ◽  
Author(s):  
E. W. Russell
Keyword(s):  
Molecular Weight ◽  
Natural Rubber ◽  
Low Temperatures ◽  
Maximum Rate ◽  
Cross Linking ◽  
Low Molecular Weight ◽  
Cross Links ◽  
Temperature Rate ◽  
Two Stages ◽  
Natural Rubber Vulcanizates

Abstract A series of natural rubber vulcanizates have been crystallized at −36° − 26° −17.5° and −2° C and the changes followed dilatometrically. As for raw rubber there is a maximum rate of crystallization at about −26° C; vulcanization decreases the rate and alters the shape of the temperature-rate curve. The amount of combined sulfur is the chief factor in determining the rate and extent of crystallization of pure-gum vulcanizates. Cross-linking, where it is efficient so that the chains between the cross-links are chemically unaffected, also depresses the rate and extent of crystallization. The use of vulcanizates which crystallize slowly permits melting to be accomplished at much lower rates of heating than was previously possible with raw rubber. Two stages of melting are distinguished the first occurring under the influence of forces between the crystalline and amorphous regions and the second analogous to the melting of low molecular weight crystalline substances.

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