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

1957 ◽  
Vol 30 (1) ◽  
pp. 1-10 ◽  
Author(s):  
L. Mullins
Keyword(s):  
Natural Rubber ◽  
Empirical Relationship ◽  
Interaction Constant ◽  
Empirical Correction ◽  
Equilibrium Volume ◽  
Self Consistent ◽  
Volume Swelling ◽  
Natural Rubber Vulcanizates ◽  
The Relationship

Abstract This paper examines the relationship between the stress-strain properties of highly swollen natural rubber vulcanizates and their equilibrium volume swelling. It is shown that the empirical relationship obtained can be described equally well by either the Flory-Huggins equation or the Flory Modification of this equation, and values of the interaction constant µ for natural rubber in decane are determined. Observed differences in the values of µ obtained for sulfur and peroxide vulcanizates are interpreted in terms of the diluent effect of nonrubber constituents in the former. The effect of the initial molecular weight of the unmasticated rubber on these physical properties is examined and an empirical correction making allowance for chain segments terminated by a crosslink at only one end is obtained. The correction is larger than that derived by previous workers and possible sources of the observed differences are discussed. It is considered that internally self-consistent estimates of the degree of crosslinking of natural rubber vulcanizates may be obtained using the methods developed.

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.

Relation between Stress Strain Behavior and Equilibrium Volume Swelling for Peroxide Vulcanizates of Natural Rubber and cis-1,4-Polyisoprene

1967 ◽  
Vol 40 (2) ◽  
pp. 673-678 ◽  
Author(s):  
G. M. Bristow
Keyword(s):  
Natural Rubber ◽  
Elastic Behavior ◽  
Stress Strain ◽  
Strain Behavior ◽  
Equilibrium Volume ◽  
Equilibrium Swelling ◽  
Tentative Evidence ◽  
Volume Swelling ◽  
Natural Rubber Vulcanizates

Abstract Data are reported for the elastic behavior, as described by the parameters C1 and C2, and the equilibrium swelling in n-decane, νr, for cumyl peroxide vulcanizates of natural rubber and cis-1, 4-polyisoprene. For natural rubber vulcanizates the correlation between C1 and νr can be described in terms of the original Flory Rehner equation with χ= 0.41. Tentative evidence is presented which favors this equation rather than the later modified form in which the term in νr1/3 is replaced by one in (νr1/3− νr/2).

Effect and Detection of Loose Chain Ends in Crosslinked Polyurethane Elastomers

1971 ◽  
Vol 44 (1) ◽  
pp. 152-165 ◽  
Author(s):  
A. E. Oberth
Keyword(s):  
Crosslink Density ◽  
Volume Fraction ◽  
Present Theory ◽  
Swelling Ratio ◽  
Polyurethane Elastomers ◽  
Equilibrium Volume ◽  
Equilibrium Swelling ◽  
Volume Swelling

Abstract The effect of loose chain ends on tensile properties and equilibrium swelling of crosslinked polyurethane rubbers is studied. As in plasticized elastomers, tensile strength and elastic modulus are reduced approximately by a factor (1−νE,P)2, where νE,P is the volume fraction of loose chain ends, plasticizer, or both. This effect is much larger than predicted by present theory. Also the equilibrium volume swelling ratio, V0/V, of rubbers having terminal chains or an equal volume of plasticizer is the same, provided they do not differ in crosslink density. However, the volume fraction of “network rubber” in the equilibrium swollen specimen, ν2, differs owing to the non-extractability of terminal chains. On this basis a method is proposed which allows experimental determination of the volume fraction of loose ends. Elastomers abounding in loose chain ends show markedly less long term stress relaxation. This effect is not clearly understood but is useful to detect the presence of non load-bearing network.

Structural Characterization of Filled Vulcanizates Part 1. Determination of the Concentration of Chemical Crosslinks in Natural Rubber Vulcanizates Containing High Abrasion Furnace Black

1967 ◽  
Vol 40 (3) ◽  
pp. 866-882 ◽  
Author(s):  
M. Porter
Keyword(s):  
Carbon Black ◽  
Natural Rubber ◽  
Volume Fraction ◽  
Exponential Relationship ◽  
Furnace Black ◽  
Simple Linear Relationship ◽  
Chemical Crosslinks ◽  
Natural Rubber Vulcanizates

Abstract The degree to which HAF black restricts the swelling of natural rubber vulcanizates in n-decane has been determined using a vulcanizing system in which the stoichiometry of crosslinking is unaffected by the carbon black. The dependence of the degree of restriction, as measured by the ratio of the volume fractions of rubber in the filled and unfilled vulcanizates swollen to equilibrium, on the concentration of carbon black follows an exponential relationship previously proposed by Lorenz and Parks. This is found to be equivalent to a simple linear relationship between the apparent and actual crosslink concentrations: napparent/nactual=1+Kϕ, where K is a constant characteristic of the filler and φ is its volume fraction in the vulcanizate. The relation has been used to determine actual crosslink concentrations in filled natural rubber vulcanizates. HAF black is found to cause increases of up to 25 per cent in the yield of polymer to polymer crosslinks in conventional sulfur vulcanizing systems, accompanied by changes in rate of cure and of crosslink reversion. All these are small compared with the effect of the filler on many physical properties.

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