Characterization of the aging behavior of raw epoxidized natural rubber with a rubber processing analyzer

Tests of the strain sweep, frequency sweep, and stress relaxation for raw epoxidized natural rubber were carried out with a rubber processing analyzer. The results showed that the complex viscosity, η*, decreased with the prolongation of the aging time in the region of Newtonian flow, but in the region of non‐Newtonian flow, the decrement of η* with a rising shear rate decreased with the prolongation of the aging time. The torque ( S ′) response from the strain sweep indicated that aging brought about an obvious decrease in the increment of S ′ with rising strain in the linear viscoelastic region and a small increase in the slope of the plateau on the curve of the S ′ response in the nonlinear viscoelastic region. The stress relaxation rate constants k and b , calculated according to the equations S t = S 0 e − kt and S t = S 1 t − b (where S t , S 0 , and S 1 are the stresses at relaxation time t , t = 0, and t = 1, respectively), increased, and the stress relaxation time obtained directly from the rubber processing analyzer shortened with the prolongation of the aging time. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1277–1281, 2006