Method for Estimating the Chemical Crosslink Densities of Cured Natural Rubber and Styrene-Butadiene Rubber

Abstract

Chemical crosslink densities of gum and carbon black-filled natural rubber (NR) and styrene-butadiene rubber (SBR) were estimated by using a newly developed rheometer. The rheometer is the Rubber Process Analyzer (RPA 2000) which is designed specifically to measure dynamic properties such as shear storage modulus G′ and shear loss modulus G″ in cured and uncured rubber. It was found that the differences between the G′ values of dicumyl peroxide-cured NR and those of uncured samples yielded estimates of the crosslink densities which were nearly the same as the values inferred by chemical analysis. For TMTD-cured SBR, the same procedure yielded estimates of chemical crosslinks very close to those estimated by a tensile stress-strain method and by NMR. In addition, accelerated sulfur-cured natural rubber was also investigated. The agreement between the crosslink densities of these stocks determined from G′ values and from a solvent-swelling method was very good.

Epoxidized natural rubber and hydrotalcite compounds: rheological and thermal characterization

“…Through this method it is possible to measure the physical crosslink density (X initial ) relative to entanglements and the total crosslink density (X total ), relative to entanglements plus chemical crosslinks. The values of X initial and X total can be obtained using Equations 3 and 4, respectively [9] . ( )…”

“…To measure crosslink density by rheological properties, the elastic modulus (G') was determined for uncured and cured compounds at 100°C, 0.25° of strain, 5 Hz and 0.5 Hz, respectively, using a RPA 2000 Analyser [9] . Through this method it is possible to measure the physical crosslink density (X initial ) relative to entanglements and the total crosslink density (X total ), relative to entanglements plus chemical crosslinks.…”

“…The elastic modulus (G') values were corrected using the Guth-Gold Equation to determine the equivalent rubber modulus without any filler [9] . It was calculated through Equation 5.…”

“…One of then was the method based on swelling resulting from contact with an organic solvent as reported in Flory studies [8] and the other one was based on the rheological property of elastic modulus (G'), obtained by the RPA 2000 Analyser [9] .…”

Influence of Layered Silicate on the Self‐Crosslinking of Polychloroprene and Carboxylated Nitrile Rubber

“…[10] This method is based on the assumption of Langley [11] that the total modulus G of a polymer network equals to the sum of the modulus G chem arising due to the chemical crosslinks and the modulus G phys arising due to the entanglements (physical constraints)…”