Determination of degree of crosslinking in natural rubber vulcanizates. Part I

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.