Long time stress relaxation of unfilled and filled amorphous networks under uniaxial tension

Abstract

The stress relaxation of amorphous filled and unfilled networks is the main objective of the present study. For this purpose, unfilled and filled samples having different cross-link densities and filler loadings were prepared. Stress relaxation tests were performed on a universal tensile test equipment. Constrained Junction Model, which is the model for the amorphous networks at equilibrium, was extended for the stress relaxation of the amorphous networks. For the unfilled section, it was assumed that the parameter which is the measure of the strength of the constraints in Constrained Junction Model follows the stretched exponential form. Experimental results showed that the new theory called Dynamic Constrained Junction Model can very well capture the isochronous Mooney plots and the relaxation of the stress for the unfilled samples. For the filled samples, the new theory was further extended with the second assumption that the phantom, equilibrium and nonequilibrium forces in the Dynamic Constrained Junction Model follow the Guth and Gold viscosity relation when fillers are added into the matrix. The experimental results showed that the Dynamic Constrained Junction Model can well capture the isochronous Mooney plots and stress relaxation of the networks in filled state.